The present invention relates to a power converter assembly comprising a resonant power converter configured for converting a rectified input voltage into a DC output voltage and a ripple compensation circuit. The ripple compensation circuit is configured to estimating and synthesizing a ripple compensation signal at least partly based on a ripple component of the rectified input voltage and superimposing, directly or indirectly, the ripple compensation signal onto the DC output voltage of the assembly to suppress a ripple voltage component of the DC output voltage or onto the DC output current of the assembly to suppress a ripple current component of the DC output current.

BACKGROUND OF THE INVENTION

Ripple is a residual periodic variation of a DC voltage that has been derived from an alternating current source. The ripple is due to incomplete suppression of the alternating waveform after rectification. The DC voltage is said to comprise a ripple component in addition to a DC component, or more specifically a ripple voltage component in addition to a DC voltage component, and the current supplied to a load is said to comprise a ripple component in addition to a DC component, or more specifically a ripple current component in addition to the DC current component.

Power density and conversion efficiency are often key performance metrics of a power converter such as AC-DC, DC-AC and DC-DC power converter assemblies where it is desirable to achieve small physical size and high efficiency for a given output power specification. Resonant power converters are well-known types of DC- DC switched mode power supplies or converters (SMPS). Resonant power converters are particularly useful for high switching frequencies such as above 1 MHz where switching losses of standard SMPS topologies (Buck, Boost etc.) tend to be unacceptable for conversion efficiency reasons. Resonant power converters include a semiconductor switch arrangement, often including one or several

MOSFET(s), GaN(s), SiCor or IGBT switches, relying on the resonances of circuit capacitances and inductances to shape the waveform of either the current or the voltage across the switching element(s) such that, when switching takes place, there is no current through and/or voltage across the switching element(s). Hence switching loss is largely eliminated in at least some of the intrinsic capacitances of the input switching element such that a dramatic increase of the switching frequency becomes feasible for example to values at and above 3 MHz, 5 MHz or 10 MHz. This feature is known in the art under designations like zero voltage and/or current switching (ZVS and/or ZCS) operation. Commonly used switched mode power converters operating under ZVS and/or ZCS are often designated class E, class F or class DE inverters or power converters. Long life time and high reliability are other desirable properties of resonant power converters and these properties may be difficult to achieve in view of the desire to reach the smallest possible physical size. Aluminium electrolytic capacitors(s) are for example ordinarily utilized for smoothing a DC input voltage, often derived from rectified mains voltage, at the input of the power converter assembly. The popularity of the aluminium electrolytic capacitors(s) is due to the high energy density (J/cm ³ ) compared to other types of capacitors with the same capacitance. This means that for a given size aluminium electrolytic capacitors provide superior ripple voltage and ripple current suppression on the rectified input voltage than non-electrolytic capacitors. Unfortunately, aluminium electrolytic capacitors suffer pronounced reliability and ageing problems such that it would be desirable to eliminate aluminium electrolytic capacitors for smoothing the rectified input voltage of the power converter assembly.

Another problem associated with prior art resonant power converters is the lack of an effective low-cost mechanism to suppress ripple voltage and ripple current components of the rectified input voltage from propagating to the DC output voltage. This deficiency is typically caused by the fact that frequency components of the ripple voltage and ripple current typically are situated outside frequency control ranges of relatively slowly responding output voltage regulation loops of the resonant power converters.

It has therefore not been possible to eliminate aluminium electrolytic capacitors in prior art resonant power converters without causing a significant and undesirable increase of a level of ripple voltage and ripple current components of the rectified input voltage of the resonant power converter without introducing a fast responding output voltage regulation loop leading to an increase components costs of the power converter. Consequently, it would be advantageous to provide a mechanism for eliminating aluminium electrolytic capacitors and/or improving ripple voltage and ripple current suppression without leading to size or costs increase of the resonant power converter. SUMMARY OF THE INVENTION

A first aspect of the invention relates to a power converter assembly comprising: a rectification circuit for receipt of an AC voltage and generation of a rectified voltage,

a resonant power converter configured for converting a rectified input voltage into a DC output voltage via a controllable switch arrangement where the rectified input voltage is derived from the rectified voltage and comprises a DC voltage component and a voltage and/or current ripple component.

The power converter assembly additionally comprises a switch control circuit configured to control the DC output voltage or current by controlling switching of the controllable switch arrangement.

The power converter assembly additionally comprises a ripple compensation circuit which comprises a ripple detector configured to estimate, from a voltage or current signal derived from the rectified input voltage, one or more waveform parameters of the ripple voltage component or ripple current component of the rectified input voltage, and a ripple generator configured for estimating and synthesizing a ripple compensation signal based on the one or more waveform parameters of the ripple component; and superimposing, directly or indirectly, the ripple compensation signal onto the DC output voltage to suppress a ripple voltage component of the DC output voltage or onto the DC output current to suppress a ripple current component of the DC output current. The voltage or current signal derived from the rectified input voltage may be a voltage or current signal that is distorted, e.g. severely distorted, relative to the rectified input voltage. Typically, the resonant power converter already provides the voltage or current signal derived from the rectified input voltage, e.g. as an isolated auxiliary supply voltage for power supply of control circuitry of the resonant power converter. In such resonant power converters, the ripple compensation circuit may be provided without adding components to the power converter; or, with addition of only a minimum number of components, and thus with a minimum of cost.

The one or more waveform parameters of the ripple voltage component or ripple current component of the rectified input voltage may include at least one of the frequency, the phase, and the amplitude.

Preferably, the one or more waveform parameters of the ripple voltage component or ripple current component of the rectified input voltage include the frequency and the phase. The ripple compensation signal produced by the ripple compensation circuit allows effective cancellation or suppression of ripple components on the DC output voltage of the converter assembly. These ripple voltage and ripple current components of the DC output voltage may be caused by ripple voltage and ripple current of the rectified input voltage which propagates through the resonant power converter including an optional galvanic isolation barrier. The ripple component on the rectified input voltage is often caused by rectification of a mains voltage for example 50/60 Hz and 1 10/230 V from which the rectified input voltage is derived for example through an optional power factor correction circuit as discussed below in additional detail with reference to appended drawings. Depending on the type of rectification circuit used, the ripple component of the rectified input voltage typically includes a major or dominating frequency component located at twice the frequency of the AC voltage. The ripple voltage and ripple current suppression on the DC output voltage provided by the ripple compensation circuit may be exploited to replace one or more traditional aluminium electrolytic capacitors connected to the rectified input voltage with non-electrolytic capacitor(s) with the same physical dimensions. This type of replacement leads to a substantial increase of the life time and reliability of the power converter assembly. Hence, the input capacitance connected of the rectified input voltage may exclusively include one or more non-electrolytic capacitor(s) such as film-capacitors. The ripple voltage and ripple current suppression provided by the ripple

compensation circuit may of course in the alternative be exploited to reduce the capacitance and therefore size of the traditional aluminium electrolytic capacitor(s) to decease dimensions and costs of the power converter assembly for a given level of performance, in particular for applications where use of traditional aluminium electrolytic capacitors is acceptable.

The controllable switch arrangement may comprise one, two or even more interconnected semiconductor switches controlled by respective switch control signals. Each of the semiconductor switches may comprise a MOSFET, e.g. an NMOS transistor, or a Gallium Nitride (GaN) MOSFET or Silicon Carbide (SiC)

MOSFET or IGBT. The control terminal, e.g. a gate or base, of each of the one, two or more semiconductor switches may be coupled to, and driven by, respective switch control signals to alternatingly force the semiconductor switch in question between on-states and off-states. An output of the controllable switch arrangement may be connected to a resonant network and excite the resonant network at a fundamental resonance frequency of the network as discussed below in additional detail with reference to appended drawings.

The skilled person will understand that various resonant power converter topologies may be utilized in the present power converter assembly such as a converter topology selected from a group of {class E, class F, class DE, class EF, LLC, LCC}.

The resonant power converter may comprise a galvanic isolation barrier to provide electrical insulation between primary side circuitry and secondary side circuitry of the power converter assembly. A galvanically isolated resonant power converter may comprise different types of galvanic isolation barriers for example a pair of magnetically coupled inductors that may be arranged as a transformer. The transformer comprises first and second transformer windings wound around a common magnetic permeable structure. The first transformer winding is electrically connected to a primary side circuit of the resonant power converter and the second transformer winding electrically connected to a secondary side circuit of the resonant power converter. In an alternative embodiment, the galvanic isolation barriers comprises first and second inductors integrated in a printed circuit board or similar carrier board without intervening magnetic material. In yet another embodiment, the galvanic isolation barrier comprises a first capacitor coupled in series with the positive input terminal of the primary side circuit and the first positive electrode of an output capacitor and a second capacitor coupled in series with the negative input terminal of the primary side circuit and the second negative electrode of an output capacitor.

According to one embodiment of the power converter assembly, the ripple compensation circuit is configured to estimating at least an amplitude, a frequency and a phase of the ripple voltage component or ripple current component of the rectified input voltage and synthesizing the ripple compensation signal based at least on the amplitude, frequency and phase of the ripple component.

According to some embodiments of the invention, the frequency and phase of the ripple component is estimated directly from the rectified input voltage or the, typically distorted, voltage or current signal representative thereof, while the corresponding amplitude of the ripple component is estimated by other means e.g. from a ripple current component of a load current supplied at the output of the converter assembly. Hence, the ripple detector may be configured for estimating the frequency and phase of the ripple component from the, typically distorted, voltage or current signal representative of the rectified input voltage and estimating the amplitude of the ripple component by measuring a ripple current component of a load current supplied to a converter load connect to the DC output voltage as discussed below in additional detail with reference to appended drawings. According to alternative embodiments of the invention, the amplitude, frequency and phase are all estimated directly from the rectified input voltage or a corresponding rectified input current as discussed below in additional detail with reference to appended drawings.

The ripple compensation circuit may comprise an analog-to-digital converter configured to receive and convert the rectified input voltage, or the, typically distorted, voltage or current signal representative thereof, into a corresponding digital signal representation and a digital processor configured to analyse the digital signal representation, estimating the one or more waveform parameters from the digital signal representation and synthesizing the ripple compensation signal from the digital signal representation.

The digital processor may further configured to derive the ripple compensation signal by utilizing a priori known voltage or current transfer characteristics of the resonant power converter from the rectified input voltage to the DC output voltage.

The a priori known voltage transfer or current transfer characteristics of the resonant power converter may for example comprise that the fundamental frequency is the same for the ripple component of the rectified input voltage and for the DC output voltage, and at least one of {a propagation delay, an amplitude attenuation or amplification, a phase shift} of the ripple component between the rectified input voltage and the DC output voltage.

The ripple generator may be configured for estimating and synthesizing the ripple compensation signal in various ways. One embodiment of the ripple generator comprises a waveform table storing a plurality of values representative of a waveform of the ripple compensation signal. The digital processor is further configured to reading the plurality of values representative of the waveform of the ripple compensation signal and deriving the ripple compensation signal from the plurality of values representative of the waveform of the ripple compensation signal. The waveform of the ripple compensation signal may comprise one more sine waves since the ripple voltage or ripple current component often can be rather accurately modelled by a sine waveform. For example, the table may comprise values of a 50 Hz sine wave and values of a 60 Hz sine wave for selection by the digital processor in accordance with the mains frequency of the mains supply actually connected to the resonant power converter. The table may further comprise different sets of values of a certain wave form, wherein each set of values of the waveform is used in respective different situations. For example, a burst mode controlled resonant power converter may be controlled with different PWM- frequencies, and a value of the set of values is read out of the waveform table at turn-on of the PWM-signal and therefore a set of values suitable for each PWM- frequency is needed. Thus, the digital processor may be configured for reading the plurality of values representative of the 50 Hz or 60 Hz sine wave and deriving the ripple

compensation signal from the plurality of values representative of the 50 Hz or 60 Hz sine wave in accordance with the determined frequency, typically app. 50 Hz or app. 60 Hz, and phase of the distorted voltage or current signal derived from the rectified input voltage.

The digital processor may further be configured for deriving an amplitude of the ripple compensation signal iteratively based on measurement of the ripple voltage component or ripple current component of the DC output voltage, i.e. upon a measurement, the digital processor may be configured for adjusting the amplitude of the ripple compensation signal and performing a new measurement, and for performing a new adjustment in response to the difference between the

measurements after and before the adjustment. The digital processor may further be configured for continuing performing a new measurement followed by an adjustment in response to the difference between the measurements after and before the adjustment until a minimum of the amplitude of the ripple voltage component of the DC output voltage has been obtained or a or minimum of the amplitude of the ripple current component of the DC output current has been obtained. The optimization may be performed in accordance with any well-known iterative optimization algorithm(s) for finding the minimum of the amplitude of the ripple voltage component or ripple current component, such as gradient descent by which the adjustment of the amplitude is made proportional to the negative of the gradient, or of the approximate gradient, of the last measurements. The determination of the amplitude of the ripple compensation signal may be repeated from time to time, e.g. regularly at certain time intervals, and/or in response to certain events, such as turn- on of the power converter assembly, load change, temperature change, etc.

The digital processor may further be configured for adjusting the phase of the ripple compensation signal iteratively based on measurement of the ripple voltage component or ripple current component of the DC output voltage, i.e. upon a measurement, the digital processor may be configured for adjusting the phase of the ripple compensation signal and performing a new measurement, and for performing a new adjustment in response to the difference between the measurements after and before the adjustment. The digital processor may further be configured for continuing performing a new measurement followed by an adjustment in response to the difference between the measurements after and before the adjustment until a minimum of the amplitude of the ripple voltage component or ripple current component of the DC output voltage has been obtained. The optimization may be performed in accordance with well-known iterative optimization algorithms for finding the minimum of the amplitude of the ripple voltage component or ripple current component of the DC output voltage, such as gradient descent by which the adjustment of the phase is made proportional to the negative of the gradient, or of the approximate gradient, of the last measurements. The determination of the phase of the ripple compensation signal may be repeated from time to time, e.g. regularly at certain time intervals, and/or in response to certain events, such as turn-on of the power converter assembly, load change, temperature change, etc.

The digital processor may further be configured to determine a plurality of values representative of a waveform of the ripple compensation signal and store the determined plurality of values in the waveform table. For example, the digital processor may be configured to determine the frequency of the, typically distorted, voltage or current signal representative of the rectified input voltage, e.g. 50.1 Hz, and determine the plurality of values representative of a 50.1 Hz sine wave and store the determined plurality of values in the waveform table. The determination of the frequency of the, typically distorted, voltage or current signal representative of the rectified input voltage may be repeated from time to time, e.g. regularly at certain time intervals, and/or in response to certain events, such as turn-on of the resonant power converter, etc.

The digital processor may further be configured to determine a plurality of values representative of a waveform of the ripple compensation signal and store the determined plurality of values in the waveform table from sampling of the ripple voltage component of the DC output voltage, or ripple current component of the DC output current, and computing the plurality of values based on the samples, e.g. the plurality of values may include the samples of one period of the ripple voltage component or ripple current component of the DC output voltage or current, respectively. The sampling of the ripple voltage component or ripple current component of the DC output voltage may be repeated from time to time, e.g.

regularly at certain time intervals, and/or in response to certain events, such as turn- on of the resonant power converter, load change, temperature change, etc. The skilled person will understand that the ripple compensation circuit may exploit different mechanism for superposition of the ripple compensation signal onto the DC output voltage or DC output current. One embodiment of the ripple compensation circuit is configured to control a modulation of a control signal of the controllable switch arrangement to generate the ripple compensation signal. This embodiment may be used to adjust a modulation of a modulated control signal for the controllable switch arrangement such that the ripple compensation signal effectively is embedded in the modulated control signal. This modulation adjustment based scheme for superposition of the ripple compensation signal onto the DC output voltage or current is a highly effective implementation because existing hardware and software components of an output voltage regulation loop of the converter assembly can be reused as discussed below in additional detail with reference to appended drawings.

Another embodiment of the ripple compensation circuit utilizes analog summation techniques for superimposing the generated ripple compensation signal onto the DC output voltage or current. Consequently, the ripple compensation circuit may comprise a summing circuit configuring for adding the ripple compensation signal to the DC output voltage as discussed below in additional detail with reference to appended drawings. The resonant power converter may comprise a so-called self-oscillating topology where a feedback loop is extending from an output node of the controllable switch arrangement to a control terminal of at least one of the one or more semiconductor switches of the controllable switch arrangement. The feedback loop is configured to induce self-oscillation in the resonant power converter for example by designing the feedback loop with appropriate loop gain and loop phase characteristics. The previously discussed output voltage regulation loop may be used to turn-off and turn-off the self-oscillating resonant power converter using on/off control to control the DC output voltage as discussed below in additional detail with reference to appended drawings.

Certain embodiments of the power converter assembly may further comprise a power factor correction circuit (PFC) coupled in-between the rectification circuit and an input of the resonant power converter for deriving the rectified input voltage with power factor correction from the rectified voltage. The power factor correction circuit may for example comprise a DC-DC converter, e.g. build around a second resonant power converter. The DC-DC converter may comprise a boost inductor connected in series with the rectified voltage such that the boost inductor is repeatedly charged by a DC component and a ripple current component of the rectified voltage. The ripple detector additionally comprises a sense inductor magnetically coupled to the boost inductor for generating a ripple voltage signal proportional to the ripple current component of the rectified input voltage. Various advantages and features by the connection of the PFC in-front of the resonant power converter is discussed below in additional detail with reference to appended drawings.

A second aspect of the present invention relates to a method of suppressing ripple components of a DC output voltage or DC output current of a resonant power converter. The method comprising:

receiving and rectifying an AC voltage, e.g. a mains voltage, to supply a rectified voltage,

deriving a rectified input voltage comprising a DC voltage component and a ripple component from the rectified voltage,

converting the rectified input voltage into a DC output voltage or DC output current, adjusting the DC output voltage or the DC output current by controlling switching of a controllable switch arrangement of the resonant power converter; and

estimating one or more waveform parameters of the ripple component of the rectified input voltage,

synthesizing a ripple compensation signal based on the estimated one or more waveform parameters of the ripple component, and

utilizing the ripple compensation signal to control the DC output voltage for suppression of a ripple voltage component of the DC output voltage or a ripple current component of the DC output current, e.g. by superimposing the ripple compensation signal onto the DC output voltage or the DC output current to suppress a ripple component of the DC output voltage or output current, e.g.

directly; or, indirectly by utilizing the ripple compensation signal for appropriate modulation of a control signal of the power converter to suppress the ripple voltage component of the DC output voltage or supress a ripple current component of the DC output current.

One embodiment of the methodology of suppressing ripple components of the DC output voltage or DC output current may comprise:

modulating the at least one switch control signal to generate the ripple

compensation signal as discussed above.

The new method of suppressing ripple components of the DC output voltage or DC output current, and the corresponding power converter assembly, provide suppression of ripple current components and ripple voltage components at a minimum of cost and size increase because, all, or almost all, of the components required for proper operation of the new methodology are available in known power converter assemblies. Hence, the functionality of the new methodology can often be added with a minimum of physical changes to existing power converter hardware. Also, there is no need for fast computation since phase and frequency can be determined over many input frequency cycles, because these parameters do not change fast and also the amplitude and, possibly, the phase of the ripple compensation signal can be determined over many input frequency cycles and can be optimized slowly for maximum performance. Preferably, a sine function is stored in the waveform table, and read out by the digital processor based on the determined phase and frequency of the ripple component of the rectified input voltage to synthesize the ripple compensation signal. Thus, there is no need for a fast, power consuming and expensive digital processor. For example, the digital processor may reside in a small, low power and cheap microprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described in more detail in connection with the appended drawings, in which:

FIG. 1 is a simplified electrical block diagram of a power converter assembly comprising a ripple compensation circuit in accordance with a first embodiment of the invention,

FIG. 2 is simplified electrical block diagram of a power converter assembly comprising a ripple compensation circuit in accordance with a second embodiment of the invention,

FIG. 3 is simplified electrical block diagram of a power converter assembly comprising a ripple compensation circuit in accordance with a third embodiment of the invention,

FIGS. 4A) and 4B) show simplified electrical circuit diagrams of first and second exemplary galvanically isolated class E resonant power converters, respectively, for use in any of the power converter assemblies disclosed in connection FIGS.1 , 2 and 3; and

FIG. 5 shows plots of experimentally measured ripple voltage waveforms on the DC output voltage of an exemplary power converter assembly illustrating the effect of the ripple compensation circuit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, various exemplary embodiments of the present power converter assembly are described with reference to the appended drawings. The skilled person will understand that the accompanying drawings are schematic and simplified for clarity and therefore merely show details which are essential to the understanding of the invention, while other details have been left out. Like reference numerals refer to like elements or components throughout. Like elements or components will therefore not necessarily be described in detail with respect to each figure. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required.

FIG. 1 is a simplified electrical circuit diagram of a power converter assembly 100 in accordance with a first embodiment of the invention. The present power converter assembly 100 comprises a galvanically isolated resonant power converter 1 15, 120 configured for converting a rectified input voltage, supplied across positive and negative input terminals, 125a, 125b, respectively, into a DC output voltage V ₀ UT across a schematically illustrated load resistor or impedance RL. The load may generally exhibit inductive, capacitive or resistive impedance. A mains power supply supplies an AC voltage, for example 50/60 Hz and 1 10/230 V, to the input of a rectifier 1 10 of the power converter assembly 100. In response, the mains rectifier or mains rectification circuit 1 10 generates a rectified voltage, e.g. an intermediate rectified input voltage at terminal 1 1 1. The present power converter assembly 100 additionally comprises a power factor circuit (PFC) 1 12 which receives the intermediate rectified input voltage at terminal 1 1 1 and derives the rectified input voltage at positive and negative input terminals, 125a, 125b including a power factor correction. The PFC 1 12 is configured such that input current drawn from the mains voltage, through the mains rectification circuit 1 10, is proportional to the mains voltage and substantially in phase with the mains voltage. The PFC 1 12 may be operative to provide a power factor of the power converter assembly 100 larger than 0.9 or larger than 0.95 where the specific power factor value may be set depending on specific requirements from a relevant regulating body.

Ripple voltage and ripple current components on the intermediate rectified input voltage at terminal 1 1 1 is conveyed through the PFC 1 12 such that the rectified input voltage at the positive and negative input terminals, 125a, 125b comprises a DC component and a ripple component such as a ripple voltage component or ripple current component. The dominating frequency of the ripple component is typically located at twice the frequency of the mains source and may include additional harmonics of the mains frequency, due to frequency doubling carried out by the operation of the rectification circuit 1 10.

The PFC 1 12 preferably includes a boost type DC-DC power converter which includes a boost inductor Lb connected in series with the rectified input voltage supplied at the output of the rectification circuit 1 10. The PFC 1 12 is designed such that current through the boost inductor Lb is proportional to the rectified input voltage across the positive and negative input terminals 125a, 125b. Consequently, a ripple current component of the rectified input voltage can be measured or estimated from the current through the boost inductor Lb. This is utilized by a ripple detector of the power converter assembly 100 as discussed below. An aluminium electrolytic capacitor or film capacitor Cin is connected across the rectified input voltage for smoothing the latter, i.e. reducing amplitude of the ripple voltage component or ripple current component of the rectified input voltage to the extent feasible by practical size constraints of the input capacitor Cin. However, the skilled person will appreciate that a ripple voltage component or ripple current component with substantial amplitude typically will exist on the rectified input voltage, in particular when the resonant power converter 1 15, 120 draws a significant level of input current from Cin.

The skilled person will understand that the PFC 1 12 circuitry may be absent in alternative embodiments the invention and a more direct estimation or measurement of the ripple component carried out as discussed below in additional detail with reference to FIG. 2 and FIG. 3.

The galvanically isolated resonant power converter 1 15, 120 comprises a controllable switch arrangement, schematically illustrated by first and second controllable semiconductor switches S1 , S2, excited or controlled by one or more switch control signal(s) 1 18 generated by a control circuit 137 from a control signal MOD(f(VouT, Vc)). Vc is the determined ripple compensation signal. The control signal MOD(f(V ₀ uT, Vc)) and switch control signal(s) 1 18 derived therefrom are utilised to control the DC output voltage V ₀ UT of the converter assembly 100 by a suitable feedback voltage regulation loop and mechanism as discussed below in additional detail. The controllable switch arrangement S1 , S2 is connected to a resonant network (not shown) for excitation of the latter with resonant voltage and current in accordance with the switch control signal. The galvanic isolation between the primary side circuitry and secondary side circuitry of the galvanically isolated resonant power converter 1 15, 120 may be provided by a transformer, T, as schematically illustrated on the drawing. The skilled person will understand that other types of galvanic isolation components may be utilized in other embodiments of the invention for example a pair of series coupled capacitors, opto-isolators etc. A primary winding of the transformer T may be connected to the output of the resonant network such that the resonant voltage is conveyed to the secondary side circuitry with a predetermined voltage step-up or voltage step-down ratio as the case may be. The resonant voltage and current at the secondary side of the transformer T is applied to an input 1 18 of a secondary side rectification circuit 120 such that the output of the rectification circuit 120 in response supplies the DC output voltage V ₀ UT of the assembly 100 across a pair of positive and negative output terminals, 130a, 130b, respectively. An output smoothing capacitor (not shown) may be connected across the positive and negative output terminals, 130a, 130b to attenuate output voltage ripple to a certain extent.

This DC output voltage V ₀ UT also includes a ripple voltage component or a ripple current component caused by the previously discussed ripple voltage component existing on the rectified input voltage. The ripple voltage component or ripple current component of the rectified input voltage typically alternates at frequency which lies outside a control range of a feedback output voltage regulation loop of the power converter assembly 100 unless fast and expensive components are used in the regulation loop. However, this undesired ripple voltage component or ripple current component on the DC output voltage is eliminated, or at least significantly suppressed, by superimposing, directly or indirectly, a precisely inverted ripple compensation signal onto the DC output voltage V ₀ UT- This ripple voltage or ripple current suppression or cancellation is carried out by a ripple compensation circuit through a feed-forward path extending from the rectified input voltage to the DC output voltage. The skilled person will understand that where the power converter assembly 100 incorporates the previously-discussed galvanic isolation barrier, T, separating the rectified input voltage and the DC output voltage, a precise ripple compensation signal is not readily available on the output side/secondary side of the galvanic isolation barrier T1 , due to inevitable waveform distortion in the galvanic isolation/insulating components (opto-isolators, transformers etc.). However, by utilizing a priori known voltage transfer characteristics of the resonant power converter, possibly including the galvanic isolation barrier T1 , and the secondary side rectification circuit 120, the inevitable waveform distortion can be taken into account in connection with synthesizing a suitable ripple compensation signal for superposition, directly or indirectly, onto the DC output voltage for suppression of the ripple voltage component or ripple current component of V ₀ UT as discussed below.

The ripple compensation circuit of the power converter assembly 100 is configured for estimating and synthesizing the ripple compensation signal and superimposing, directly or indirectly, the ripple compensation signal onto V ₀ UT across the positive and negative output terminals 130a, 130b. The ripple compensation circuit is partly integrated with certain components of the previously-mentioned feedback output voltage regulation loop of the resonant power converter such that the additional number of separate components associated with the implementation of the ripple compensation circuit is minimized. This integration is beneficial in reducing incremental costs associated with the addition of this feature and for limiting any increase of physical dimensions of the power converter assembly 100. The ripple compensation circuit comprises a ripple detector which may be configured to estimate directly from the rectified input voltage one or more waveform parameters of the previously discussed ripple component, e.g. a ripple voltage component or corresponding ripple current component.

However, in the present power converter assembly 100, the ripple detector is configured to estimate the one or more waveform parameters of the ripple component of the rectified input voltage across terminals 125a, 125b in an indirect manner using a, typically distorted, current or voltage signal representative of the ripple voltage component or ripple current component. The ripple detector comprises a pair of magnetically coupled inductors Ls1 , Ls2, e.g. a transformer, that function as a galvanic isolation barrier towards the mains voltage. The first inductor Ls1 may be formed as one or several auxiliary winding(s) of the previously discussed boost inductor Lb of the PFC 1 12 or formed a separate sense inductor magnetically coupled to the boost inductor Lb. In both cases, the first inductor Ls1 senses the ripple current component of the rectified input voltage as mentioned previously. A corresponding ripple current and ripple voltage is induced in the second inductor Lb2 in response to the ripple current component flowing through the first inductor Ls1 . The ripple voltage of the second inductor Lb2 is applied to a rectification circuit 129 which generates the voltage signal Vr representative of the ripple component. The voltage signal Vr may correspond to a down-scaled and phase-shifted replica of the rectified input voltage across terminals 125a, 125b. This voltage signal Vr is transmitted through a DC blocking capacitor C2 coupled in series with a first input IN1 of an A/D-converter 140. Consequently, the A D- converter 140 receives and converts/digitizes the voltage signal Vr to produce a digital representation thereof. An exemplary waveform of the voltage signal Vr is schematically indicated as graph 150. The digital representation of the voltage signal Vr is read by a digital processor 135 for example via a suitable port. The digital processor 135 may comprise a programmable microprocessor programmed to carry out the various functions discussed in the following by a suitably configured set or sets of executable program instructions. The digital processor 135 may alternatively be implemented by appropriately configured digital combinatorial and sequential digital logic circuitry or the digital processor 135 may be implemented by any combination of digital hardware and software comprising executable program instructions. In all instances, the digital processor 135 may be configured for determining at least frequency and phase of the voltage signal Vr by analysing the waveform of the received digital representation of Vr. The skilled person will understand that the voltage signal Vr will typically have a dominating frequency component at 100 Hz or 120 Hz where the rectified input voltage is derived from a typical mains connection. The dominating frequency of the voltage signal Vr corresponds to the dominating frequency of the rectified input voltage. There furthermore exists a substantially fixed phase shift between the measured phase of the voltage signal Vr and the phase of the ripple component on the rectified input voltage caused by known transfer characteristics of the previously discussed components e.g. Ls1 , LS2, 129 and C2 of the ripple detector. This substantially fixed phase shift may be simulated, measured or otherwise determined during the design and/or manufacturing of the power converter assembly 100. Based on the knowledge of the substantially fixed phase shift, the digital processor 135 is capable of, and configured to, determine, estimate or compute the phase of the ripple component on the rectified input voltage. The digital processor 135 is furthermore configured to measure the frequency content, in particular the above-discussed dominating frequency, of the voltage signal Vr.

However, the amplitude of the ripple voltage component or ripple current component of the rectified input voltage varies depending on the capacitance of the input capacitor Cin and an current load current supplied at the output of the resonant converter to the load RL. The digital processor 135 may be configured to estimate or measure the load current for example via a suitable current sensor (not shown), e.g. a small resistance in series with the load, and estimate the amplitude of the ripple voltage component of the rectified input voltage based on the measured load current and a priori knowledge of the capacitance of the input capacitor Cin. The digital processor 135 thereafter utilizes the measured or estimated amplitude, frequency and phase of the ripple voltage component or ripple current component of the rectified input voltage in combination with a priori known voltage or current transfer characteristics of the galvanically isolated resonant power converter 1 15, 120 from rectified input voltage to the DC output voltage. These a priori known voltage or current transfer characteristics of the galvanically isolated resonant power converter preferably comprises at least one of {a propagation delay, an amplitude attenuation or amplification, a phase shift} of the ripple component through the galvanically isolated resonant power converter 1 15, 120. The reliance on such a priori known voltage or current transfer characteristics is possible by noting that properly designed galvanic isolation components, e.g. including opto-isolators, insulation capacitors or transformers, will not alter a frequency or amplitude of the ripple voltage component or ripple current component even though the waveform of the ripple voltage component or ripple current component may be distorted and/or shifted by a constant propagation delay. The digital processor 135 is configured to synthesize the ripple compensation signal by reference to a waveform table 160 which stores a plurality of waveform values across a cycle time or period of the waveform in question and being representative of the waveform of the ripple component on the DC input voltage to the resonant power converter 1 15, 120. The skilled person will appreciate that the ripple component on the rectified input voltage may possess a largely sine shaped waveform at twice the mains frequency of the AC source such that the plurality of waveform values stored in the waveform table 160 are representative of a sine wave. The digital processor 135 furthermore detects the phase of the sine shaped component of the ripple voltage or ripple current and uses this phase to adjust a corresponding phase of the ripple

compensation signal for the known propagation delay of the ripple voltage component or ripple current component through the galvanically isolated resonant power converter 1 15, 120. This phase adjustment may conveniently be achieved by incrementing a table pointer with a certain integer number corresponding to the phase shift caused by the known propagation delay. Likewise, the digital processor 135 uses the estimated amplitude of the ripple component to appropriately adjust an amplitude of the ripple compensation signal by exploiting known amplitude attenuation or amplification of the ripple component through the galvanically isolated resonant power converter 1 15, 120. Additionally, or supplementally, to the adjustment of the amplitude of the ripple compensation signal based on the determination of the amplitude of the ripple voltage component or ripple current component of the signal representative of the rectified input voltage, the digital processor 135 may be configured for deriving the amplitude of the ripple compensation signal iteratively based on measurement of the ripple voltage component or ripple current component of the DC output voltage, i.e. upon a measurement, the digital processor adjusts the amplitude of the ripple compensation and performs a new measurement, and performs a new adjustment in response to the difference between the measurements after and before the adjustment. This continues until a minimum of the amplitude of the ripple voltage component or ripple current component of the DC output voltage has been obtained. The optimization may be performed in accordance with well-known iterative optimization algorithms for finding the minimum of the amplitude of the ripple voltage component or ripple current component of the DC output voltage, such as gradient descent by which the adjustment of the amplitude is made proportional to the negative of the gradient, or of the approximate gradient, of the last measurements. The determination of the amplitude of the ripple compensation signal may be repeated from time to time, e.g. regularly at certain time intervals, and/or in response to certain events, such as turn-on of the resonant power converter, load change, temperature change, etc.

Furthermore, the digital processor 135 may be adapted to additionally take into account a pre-stored phase correction representing the above-discussed fixed phase shift between the measured phase of the voltage signal Vr and the phase of the ripple component on the rectified input voltage in connection with adjustment of the phase of the synthesized ripple compensation signal. This pre-stored phase correction may have been stored within an internal data memory area of the digital processor 135 in connection with manufacturing of the power converter assembly for example using a dedicated calibration procedure. The skilled person will understand that the use of the waveform table 160 minimizes the amount of arithmetic computations required by the digital processor 135 for synthesizing or generating the appropriate waveform sample values/shape of the ripple compensation signal. This is a beneficial feature enabling small, low-power and low-cost microprocessors to carry out the functions discussed above in connection with the ripple

compensation circuit and thereby minimizing the total costs of the power converter assembly 100. However, the skilled person will understand that other embodiments of the assembly 100 may utilize more sophisticated microprocessors or Digital Signal Processors which are configured to carry out a direct computation and synthesis of the waveform shape of the ripple compensation signal based on the estimated and/or measured amplitude, frequency and phase of the ripple

component on the rectified input voltage.

The digital processor 135 is also configured to regulate the DC output voltage or current of the converter assembly in addition to carrying out the above-described synthesis of the ripple compensation signal. The digital processor 135 regulates the DC output voltage by a feedback voltage regulation loop which comprises the sensing of the DC output voltage, at the output terminal 130a, by a second input, IN2, of the A/D-converter 140. The feedback voltage regulation loop comprises a regulation algorithm executed by the digital processor 135 based on received and digitized DC output voltage samples from the A/D-converter 140. The regulation algorithm generates a modulated control signal MODf(V ₀ uT, Vc)). A switch control circuit 137 is configured to convert the modulated control signal MODf(V ₀ uT, Vc)) into one or more appropriate switch control signals 1 18 for respective ones of the one or more semiconductor switches of the resonant converter. The switch control circuit 137 may include various components depending on the specific type of modulation utilized by the regulation algorithm, voltage level and type of

semiconductor switches. The switch control circuit 137 may for example comprise one or more of: level shifters, signal buffers and start-up and shut-down circuitry. The regulation algorithm adjusts the instantaneous modulation of the modulated control signal MODf(V ₀ uT, Vc)) to increase or decrease the output voltage, power or current of the galvanically isolated resonant power converter 1 15, 120 as needed to maintain a target or desired DC output voltage. However, the skilled person will appreciate that the regulation algorithm of certain embodiments of the galvanically isolated resonant power converter 1 15, 120 may utilize on/off modulation or burst- mode modulation of the modulated control signal MODf(V ₀ uT, Vc)). The burst-mode modulation scheme may comprise a switching frequency of 3 MHz or higher and a burst frequency larger than 25 kHz and preferably smaller than 100 kHz. One embodiment of the galvanically isolated resonant power converter 1 15, 120 may comprises a self-oscillating resonant power converter topology where the above- discussed switching frequency is achieved by appropriate tuning of feedback loop characteristics.

While the digital processor 135, A/D-converter 140 and waveform table 160 are illustrated as separate components the skilled person will appreciate that these components may be integrally formed, for example on a common semiconductor substrate or die, in some embodiments of the converter assembly. The waveform table 160 and may for example reside in an internal data memory area, e.g. RAM, ROM, EEPROM etc., of the digital processor 135.

Different embodiments of the ripple compensation circuit may apply different control mechanisms and hardware components for superimposing, directly or indirectly, the ripple compensation signal onto the DC output voltage. The present embodiment of the ripple compensation circuit is configured to adjust the modulation of the modulated control signal MODf(V ₀ uT, Vc)) through utilization of an inverted replica of the determined ripple compensation signal Vc such that the ripple compensation signal effectively gets embedded in the modulated control signal MODf(V ₀ uT, Vc)). This feature is schematically illustrated by the reference to both the DC output voltage and to the ripple compensation signal Vc in the designation MODf(V ₀ uT, Vc)). The skilled person will appreciate that this modulation adjustment scheme for, indirectly, superposition of the ripple compensation signal onto the DC output voltage is a highly effective implementation because existing hardware and software components and functions of the feedback voltage regulation loop, such as the A/D converter 140, digital processor 135, switch control circuit 137 etc., are fully or partly re-used for estimation and synthesis of the ripple compensation signal leading to minimal cost and size increase of the power converter assembly 100.

FIG. 2 is a simplified electrical circuit diagram of a power converter assembly 200 in accordance with a second embodiment of the invention in which the rectified input voltage is applied directly to an input of a resonant power converter 215, 220. Some embodiments of the present power converter assembly 200 comprise a galvanically isolated resonant power converter while alternative embodiments comprise nonisolated resonant power converters. In either case, the resonant power converter is configured for converting a rectified input voltage, supplied across positive and negative input terminals, 225a, 225b, respectively, into a DC output voltage V ₀ UT across a schematically illustrated load resistor or impedance RL. The load may generally exhibit inductive, capacitive or resistive impedance. A mains power supply 205 supplies an AC voltage, for example 50/60 Hz and 1 10/230 V, to the input of a rectifier 210 of the power converter assembly 200. In response, the rectifier or rectification circuit 1 10 generates the rectified input voltage such that the rectified input voltage comprises a DC component and a ripple component. As discussed above, the ripple component typically includes a major or dominating frequency component located at twice the frequency of the mains source 205, and possibly additional harmonics of the mains frequency, due to frequency doubling carried out by the operation of the rectification circuit 210. An aluminium electrolytic capacitor, film capacitor or ceramic capacitor(s) Cin is connected across the rectified input voltage for reducing an amplitude of the ripple voltage component of the rectified input voltage to the extent possible as discussed above. The galvanically isolated resonant power converter 215, 220 comprises a controllable switch arrangement, schematically illustrated by first and second controllable semiconductor switches S1 , S2, excited or controlled by a one or more switch control signal(s) 218 supplied by a switch control circuit 237 for controlling the DC output voltage of the converter via a feedback voltage regulation loop and mechanism using the principles discussed above in connection with the first embodiment of the invention.

The power converter assembly 200 comprises a ripple compensation circuit configured for estimating and synthesizing the ripple compensation signal and superimposing, directly or indirectly, the latter onto the DC output voltage across the positive and negative output terminals 230a, 230b. The ripple compensation circuit comprises a ripple generator which is configured to estimate one or more waveform parameters of the ripple component of the rectified input voltage directly from the rectified input voltage in contrast to the indirect estimation methodology discussed above based on the voltage signal Vr representative of the ripple voltage or ripple current component of the rectified input voltage. The present ripple detector measures the ripple voltage component of the rectified input voltage across terminals 225a, 225b through a galvanic isolation barrier 280 and a DC blocking capacitor C2 coupled in series with a first input IN1 of an A/D-converter 240.

Consequently, the A/D-converter 240 receives and converts/digitizes the inputted ripple voltage component to produce a digital representation of the latter. The digital representation of the ripple voltage component is read by a digital processor 235 for example via a suitable port. The digital processor 235 may thereafter determine amplitude, frequency and phase of the ripple voltage component of the rectified input voltage. In connection with adjustment of the phase and/or amplitude of the synthesized ripple compensation signal, the digital processor 135 may optionally be adapted to take into account pre-stored phase and/or amplitude correction factor(s) representing a priori known signal phase shifts and signal amplitude changes imparted through the ripple detector for example the isolation barrier 280. The digital processor 235 is configured for synthesizing the ripple compensation signal by reference to a waveform table 260 which stores a plurality of waveform values across a cycle time or period of a waveform representative of the waveform of the ripple voltage component. An exemplary waveform of the voltage signal Vr is schematically indicated as graph 250. The digital processor 235 is additionally configured to regulate the DC output voltage V ₀ UT of the converter assembly in addition to carrying out the above-described synthesis of the ripple compensation signal. This output voltage regulation may be carried out by digital processor 235 using a suitable regulation scheme or algorithm in similar manner as the algorithm discussed above in connection with the first embodiment of the converter assembly 100.

FIG. 3 is a simplified electrical circuit diagram of a power converter assembly 300 in accordance with a third embodiment of the invention. The present power converter assembly 300 may be largely identical to the above-disclosed second embodiment of the converter assembly 200 except for the use of a different method and circuit structure for superimposing, directly, the ripple compensation signal Vr onto the DC output voltage V ₀ UT- This third embodiment comprises a digital processor 335 which regulates the DC output voltage by a feedback voltage regulation loop operating in a similar manner as the corresponding feedback regulation loop discussed above in connection with the second embodiment of the power converter assembly. However, the modulated control signal MODf((V ₀ uT)) is only adapted to maintain a mean target of the DC output voltage V ₀ UT by adjusting modulation of the control signal

MODf((VouT))- This is in contrast to the previously discussed embodiments of the power converter assembly where the modulated control signal in both instances is adjusted to cancel the determined ripple voltage component or ripple current component of the DC output voltage V ₀ UT arising from the ripple component on the rectified input voltage, as well as the mean DC output voltage. This difference is illustrated schematically by observing that the modulated control signal

MODf((VouT)) depends on the measured DC output voltage V ₀ UT but is independent of any synthesized ripple compensation signal Vc for controlling the DC output voltage of the assembly 300. The control signal modulation scheme is replaced by analog superposition at the DC output voltage V ₀ UT of the assembly 300 to achieve the desired superposition of the ripple compensation signal onto the DC output voltage. This analog superposition of the ripple compensation signal is carried out by a differential output operational amplifier 365, or similar driver circuit, and transformer 370. A first winding of the transformer 370 is connected between a negative output of an output side rectification circuit 320 and the negative terminal 330b of the DC output voltage and a second winding of the transformer 370 is connected across a differential output of the differential output operational amplifier 365 supplying the determined ripple compensation signal Vr. The ripple

compensation signal Vc is synthesized or generated by the digital processor 335 by reference to a priori known voltage transfer characteristics of the galvanically isolated resonant power converter and a waveform table 360 in a similar manner as the one discussed above in connection with the first embodiment of the converter assembly. The digital processor 335 may generate the ripple compensation signal in digital representation and convert the latter into a corresponding analog signal for supplying the ripple compensation signal Vc. The conversion of the digital ripple compensation signal into a corresponding analog ripple compensation signal may be carried by a D/A-converter integrally formed with the digital processor 335 or by a separate D/A-converter - for example inserted between a digital output port of the processor 335 and the input of the differential output operational amplifier 365.

FIG. 4A) shows an electrical circuit diagram of an exemplary galvanically isolated class E resonant power converter 415, 420 for use in any of the previously discussed power converter assemblies 100, 200, 300. The class E resonant power converter 415, 420 comprises a series resonant network including inductor L ₂ and capacitor Ci . The resonant power converter 415, 420 comprises a primary side circuit and a secondary side circuit connected through a galvanic isolation barrier 407. The primary side circuit comprises a positive input terminal 425a and a negative input terminal 325b for receipt of the rectified input voltage V _in from the one of the mains rectification circuit discussed above. An input or smoothing capacitor C _in is electrically connected between the positive and negative input terminals 425a, 425b. The primary side circuit comprises a resonant network which includes first and second series connected inductors U and L ₂ , capacitor C _s and a controllable semiconductor switch arrangement. The controllable semiconductor switch arrangement comprises at least one semiconductor switch S, e.g. a MOSFET or another suitable type of semiconductor switch. The controllable semiconductor switch S has a drain terminal connected to a midpoint node between the resonant inductors L-i and L ₂ . The primary side circuit is arranged in front of the isolation barrier 407 which comprises series coupling capacitors C-i and C ₂ .The secondary side circuit comprises an output capacitor C _ou t having a first electrode electrically connected to the converter output voltage V _ou t at output terminal 430a. A second negative electrode of the output capacitor C _ou t is coupled to a negative terminal 430b of the converter output voltage. A load of the isolated class E resonant DC-DC converter 415, 420 is schematically illustrated by load resistor R _L and coupled between the positive and negative output terminals 430a, 430b. A modulated switch control signal is applied to the control or gate terminal of the semiconductor switch S such that the latter is alternatingly switched between on and off states leading to excitation of the resonant network at, or proximate to, a fundamental resonance frequency of the network. This fundamental resonance frequency may be larger than 3 MHz or larger than 5 MHz. The ripple compensation signal generated by the previously discussed digital processor is preferably embedded in the modulated control signal MODf(V ₀ uT, Vc)) following the principles discussed above such that the modulated control signal performs both DC output voltage regulation/control and ripple voltage or ripple current suppression on the converter output voltage V _out .

FIG. 4B) shows an electrical circuit diagram of yet another exemplary galvanically isolated class E resonant power converter 415, 420 for use in the previously discussed power converter assemblies 100, 200, 300. The class E resonant converter 415, 420 comprises a series resonant network including at least inductors L ₂ , L ₃ and capacitors C _s and Ci. The primary side circuit and a secondary side circuit of the class E resonant power converter 415, 420 are connected through a galvanic isolation barrier 407 provided by an isolation transformer 408. An additional inductor L-i has a first end coupled to the positive input terminal 425a and a second end to a drain terminal of a semiconductor switch S which forms part of a

controllable switch arrangement as discussed above. The secondary side circuit of the power converter comprises an output capacitor C _ou t connected to the converter output voltage V _ou t across the positive and negative output terminals 430a, 430b. A power converter load is schematically illustrated by load resistor R _L and coupled between the positive and negative output terminals 430a, 430b of the DC-DC converter. The secondary side circuit furthermore comprises the third inductor L ₃ connected across a secondary transformer winding of the isolation transformer 408. A secondary transformer winding of the isolation transformer has a first end coupled to a cathode of rectifying circuit comprising merely a single diode D. A second end of the secondary transformer winding is coupled to the positive terminal 430a and a positive electrode of the output capacitor C _ou t- The rectifying diode D rectifies AC current generated by the secondary transformer winding and generates a DC voltage as the converter output voltage between the positive and negative output terminals 430a, 430b. An electrical or power converter load is schematically illustrated by load resistor R _L coupled between the positive and negative output terminals 430a, 430b. FIG. 5 shows an uncompensated ripple voltage waveform on plot 550 and a compensated ripple voltage waveform on plot 560 depicting an experimentally measured ripple voltages on the DC output voltage, i.e. across the output terminals of an experimental DC-DC power converter assembly. The ripple voltage waveform on plot 550 is measured without activation of the present ripple suppression circuit while the voltage waveform on plot 550 is measured with an activated ripple suppression circuit. The experimental DC-DC power converter assembly is identical to the power converter assembly 100 discussed above in accordance with the first embodiment of the invention. The y-axis has a scale of 1 V/division on both plots 550, 560 and the x-axis shows time with 10 ms per division. In both instances, the experimental DC-DC power converter assembly delivers a DC output voltage of 40 V while supplying 60 W of load power to a purely resistive load. As illustrated by plot 550, the output ripple has a dominating frequency component located at 100 Hz as expected since the DC input voltage is derived from the rectified 50 Hz mains voltage. The amplitude of the 100 Hz ripple voltage is approximately 5.73 V. Plot 560 shows a reduction of measured output ripple voltage down to 1 .33 V by activation of the ripple suppression circuit. The waveform plot 560 also reveals that the presence of a 200 Hz ripple voltage component which becomes clearly visible by the large suppression of the 100 Hz ripple voltage component. The origin of this residual 200 Hz ripple voltage component may be a corresponding 200 Hz ripple voltage on the DC input voltage, caused by harmonics of from rectification of the 50 Hz mains voltage, or may be introduced by a slight phase inaccuracy of the synthesised ripple compensation signal relative to the "true" phase of the 100 Hz ripple voltage waveform on the DC output voltage.