TECHNICAL FIELD

The invention relates to a power supply for generating a DC output signal from an AC input signal, especially to a power supply with a high efficiency and a low ripple.

BACKGROUND

A paralleling of power converter modules in power supplies is a very attractive approach in power applications. It expands the output power, provides a heightened reliability and ease of maintenance to the whole system. In N-paralleled interleaved power converters, all interleaved legs are operated with a same switching frequency and a displaced phase shift of 2*pi/N to each other, in order to achieve high current ripple cancelation.

A low current ripple of the interleaved converters, the possibility to achieve a higher power density, and a reduced amount of necessary copper and weight make this solution very attractive for UPS applications.

However, the complexity of system design and control increases as well. It introduces new challenges regarding the control concept and realization because of a high number of interleaved legs, a high current dynamic, and the requirement to avoid circulating currents among the interleaved legs. Usually, coupled or non-coupled inductors are used to interface the interleaved legs. The manufacturing procedure of these inductors though cannot guarantee, in general, the equality of their inductances, which leads, without proper control, to circulating currents between the interleaved legs.

Another factor influencing the circulating current, is the voltage imbalance on the outputs of the interleaved legs, where already a slight volt difference at small inductors can cause large circulating currents among the interleaved legs.

Circulating currents in principle mean extra losses, a possible transformer saturation and a possible system failure. To reduce or even eliminate the effect of inductance inequality and to assure input current sharing between the individual inductors, a current sensing procedure and balancing algorithm can be integrated into the current control structure. Using current transducers to sense the individual current signals within a high number of interleaved legs is a quite expensive solution in term of money, hardware resources, and space.

One approach for current sensing and control in interleaved converters is based on sensing the individual currents and using highly dynamic current controllers to keep the individual currents equal to an average current. In this approach, N high resolution current sensors and respectively complex controllers with high bandwidth are required, which means an increased software and hardware resource requirement.

In exemplary approaches, the total switching DC-current of three interleaved legs in a three- phase interleaved bidirectional DC-DC converter is sensed using a single current sensor for each converter. The current is sampled at either the peak or the valley of the PWM carrier signals regularly. A current reconstruction algorithm is then applied, according to the duty reference of the controller output. Locating the correct current position on the total DC-current makes the separation and reconstruction procedure even more complex, because of the overlapping states of the currents. The DC-link current can be represented here by combinations of the switching factions and leg currents. Therefore the current reconstruction procedure requires a knowledge of the modulation signal as well as of the switching states. One of the limitations of this approach is that there exists a minimum duty width for which it can be assured to completely reconstruct the phase currents. This and other limitations are only difficult to overcome.

SUMMARY Accordingly, an object of the present invention is to provide a power supply and a power supply method, which achieve a high efficiency and low circulating currents, while requiring only a low hardware effort.

The object is solved by the features of claim 1 for the apparatus and claim 14 for the method. The dependent claims contain further developments. According to a first aspect of the invention, a power supply for generating a DC output signal from an AC input signal, is provided. The power supply comprises a Vienna rectifier, comprising at least a first converter branch supplied with the AC input signal, the first converter branch comprising a first converter, adapted to selectively switch the AC input signal between a joint midpoint terminal of the first converter branch and a first rectification terminal, and a second converter, adapted to selectively switch the AC input signal between the joint midpoint terminal and a second rectification terminal. The power supply moreover comprises a current sensor, which is adapted to measure a switching current at the joint midpoint terminal, a current reconstructor, adapted to determine a current through the first converter and a current through the second converter, based upon the switching current, and a controller, adapted to adjust duty cycles of the first converter and the second converter of the first converter branch based upon the currents determined by the current reconstructor. It is thereby possible to determine the currents through the converters using only a single current sensor for two separate converters. This allows for a prevention of circulating current with a very low hardware effort. According to a first implementation form of the first aspect, the first converter is adapted to switch the AC input signal between the joint midpoint terminal and the rectification terminal controlled by a first modulation signal. The second converter is adapted to switch the AC input signal between the joint midpoint terminal and the rectification terminal controlled by a second modulation signal. The first modulation signal is generated from a first modulation carrier signal. The second modulation signal is generated from a second modulation carrier signal. The first modulation carrier signal and the second modulation carrier signal are 180° phase shifted. This allows for a very simple determining of the modulation signals and thereby to a very simple control of the converters.

According to a second implementation form of the first aspect, the Vienna rectifier comprises a plurality of N converter branches. Each converter branch is supplied with the same AC input signal. Each converter branch comprises a first converter, which is adapted to selectively switch the AC input signal between a joint midpoint terminal of the converter branch and a rectification terminal of the converter branch, and a second converter, adapted to selectively switch the AC input signal of the converter branch between the joint midpoint terminal of the converter branch and a rectification terminal of the converter branch. The power supply moreover comprises a single current sensor for each converter branch, adapted to measure a switching current at the joint midpoint terminal of the converter branch. The current reconstructor is adapted to determine currents of the first converters and currents of the second converters of the converter branches, based upon the switching currents of the converter branches. The controller is adapted to adjust duty cycles of the first converter and the second converter of the plurality of converter branches based upon the currents determined by the current reconstructor. By allowing more than two converter branches, the maximum output power can be significantly increased while at the same time increasing the achieved efficiency.

According to a first implementation form of the second implementation form of the first aspect, the first converter of each converter branch of the power supply is adapted to switch the AC input signal between the joint midpoint terminal of the converter branch and the rectification terminal of the converter branch controlled by a first modulation signal. The second converter of each converter branch of the power supply is adapted to switch the AC input signal between the joint midpoint terminal of the converter branch and the rectification terminal of the converter branch controlled by a second modulation signal. The first modulation signal of each converter branch is generated from a first modulation carrier signal of the respective converter branch. The second modulation signal of each converter branch is generated from a second modulation carrier signal of the respective converter branch. The first modulation carrier signal of each converter branch and the second modulation carrier signal of each converter branch are 180° phase shifted. The first modulation carrier signals between different converter branches are phase shifted by 360°/N. The second modulation carrier signals between different converter branches are phase shifted by 360°/N. This allows for a further increase in maximum output power and efficiency. According to a third implementation form of the first aspect, the rectification terminal of each converter branch is connected by a first diode to a positive DC output rail, and by a second diode to a negative DC output rail. The first diode and the second diode are reverse polarized. This allows for a very-simple-to-construct rectification.

According to a first implementation form of the third implementation form of the first aspect, the midpoint terminal of each converter branch is connected by the current sensor of the converter branch to a DC-bus midpoint. This further decreases the hardware effort.

According to a fourth implementation form of the first aspect, the current sensors are shunts or transducers. This allows for a high accuracy and low hardware effort.

According to a fifth implementation form of the first aspect, the switching currents at the midpoint terminals are identical to a current through the first converter of the converter branch during a time period at a valley of the first modulation carrier signal. The switching currents at the midpoint terminals are identical to a current through the second converter of the converter branch during a time period at a valley of the second modulation carrier signal. Each current sensor is adapted to successively measure the current through the first converter of the converter branch and the current through the second converter of the converter branch at the midpoint terminal. This allows for having only a single current sensor for each two converters. According to a sixth implementation form of the first aspect, the power supply moreover comprises a single analog-digital-converter, and a multiplexer, which is adapted to successively connect current signals measured by the current sensors to the single analog-digital-converter. The single analog-digital-converter is moreover adapted to successively digitize the current signals measured by the current sensors. This allows for a further reduction of the hardware effort.

According to a first implementation form of the previous implementation form, the current reconstructor is adapted to determine the currents through the converter branches from the switching currents measured by the current sensors. This allows for a very simple determining of the currents through the converter branches.

According to a seventh implementation form of the first aspect, the current reconstructor is adapted to determine the currents through the converter branches as follows:

/,. (?) : 5,. (t) = ON & S _j (t) = OFF

ISN _1J (t) = I ₁ (t).S _{1 +} I _J (t).S _J (t)

I _j (t) : S _j (t) = ON & S. (i) = OFF ' wherein

ISN^t) is the switching current to the joint midpoint terminal of the converter branch ij,

/ _; ( ) is a first current flowing through the first converter of the converter branch ij,

/ - (t) is a second current flowing through the second converter of the converter branch ij, a first switching state applied to the first converter of the converter branch ij,

S _j (t) is a second switching state applied to the second converter of the converter branch ij, wherein the first switching state S _; (t) and the second switching state 5 - (t) are non-overlapped switching states with 180° phase shift, wherein the first switching state and the second switching state S - (t) each have a value of

0 as a switched off state and a value of 1 as a switched on state. This allows for a very simple determining of the currents through the converter branches.

According to an eighth implementation form of the first aspect, the controller is adapted to adjust the duty cycles of the first converter and the second converter of all converter branches based upon the currents determined by the current reconstructor, compensating for circulating currents. This allows for a very low effort circulating current compensation.

According to a second aspect of the invention, a power supply system comprising M power supplies according to the first aspect or any of the implementation forms of the first aspect is provided. Each of the power supplies is supplied with an individual AC input signal. Additionally or alternatively each of the power supplies is supplied with a single phase of a multi-phase AC input signal. Additionally or alternatively, the AC input signals of the M power supplies are phase shifted by 360°/M. Additionally, the DC output signals of the M power supplies are combined to a DC system output signal. This allows for a further increase in achievable system output power. Moreover, the efficiency can thereby be increased. Furthermore, multi-phase input signals can be used. This increases the flexibility of use.

According to a third aspect of the invention, a method for generating a DC output signal from an AC input signal is provided. The method comprises providing the AC input signal to a first converter branch of a Vienna rectifier, selectively switching, by a first converter of the first converter branch, the AC input signal between a joint midpoint terminal and a first rectification terminal, selectively switching, by a second converter of the first converter branch, the AC input signal between a joint midpoint terminal and a second rectification terminal, measuring a switching current at the joint midpoint terminal, by a current sensor, determining a current through the first converter and a current through the second converter, based upon the switching current, and adjusting the duty cycles of the first converter and the second converter of the first converter branch based upon the currents, determined. It is thereby possible to determine the currents through the converters using only a single current sensor for two separate converters. This allows for a prevention of circulating current with a very low hardware effort.

According to a first implementation form of the third aspect, the switching of the AC input signal between the joint midpoint terminal and the rectification terminal is controlled by a first modulation signal, the switching of the AC input signal between the joint midpoint terminal and the rectification terminal is controlled by a second modulation signal. The first modulation signal is generated from a first modulation carrier signal. The second modulation signal is generated from a second modulation carrier signal. The first modulation carrier signal and the second modulation carrier signal are 180° phase shifted. This allows for a very simple determining of the modulation signals and thereby to a very simple control of the converters. According to a second implementation form of the third aspect, a plurality of N converter branches of the Vienna rectifier are supplied with a same AC input signal. A selective switching of the AC input signal between a joint midpoint terminal of the converter branch and a rectification terminal of the converter branch is performed by a first converter of each converter branch. A selective switching of the AC input signal of the converter branch between the joint midpoint terminal of the converter branch and a rectification terminal of the converter branch is performed by a second converter of each converter branch. A switching current is measured at the joint midpoint terminal of each converter branch, by a current sensor of each converter branch. Currents of the first converters and currents of the second converters of the converter branches are determined based upon the switching currents of the converter branches, which have been determined. Duty cycles of the first converter and the second converter of the plurality of converter branches are adjusted based upon the currents determined by the current reconstructor. By allowing more than two converter branches, the maximum output power can be significantly increased while at the same time increasing the achieved efficiency.

According to an implementation form of the previous implementation form, the switching of the AC input signal between the joint midpoint terminal of the converter branch and the rectification terminal of the converter branch is controlled by a first modulation signal. The switching of the AC input signal between the joint midpoint terminal of the converter branch and the rectification terminal of the converter branch is controlled by a second modulation signal. The first modulation signal is generated from a first modulation carrier signal of the respective converter branch. The second modulation signal of each converter branch is generated from a second modulation carrier signal of the respective converter branch. The first modulation carrier signal of each converter branch and the second modulation carrier signal of each converter branch are 180° phase shifted. The first modulation carrier signals between the different converter branches are phase shifted by 360°/N. The second modulation carrier signals between the different converter branches are phase shifted by 360°/N. This allows for a further increase in maximum output power and efficiency.

According to a third implementation form of the third aspect, the switching currents at the midpoint terminals are identical to a current through the first converter of the converter branch during a time period at a valley of the first modulation carrier signal, and the switching currents at the midpoint terminal are identical to a current through the second converter of the converter branch during a time period at a valley of the second modulation carrier signal. The current through the first converter of the converter branch and the current through the second converter of the converter branch are measured successively. This allows for having only a single current sensor for each two converters.

According to a fourth implementation form of the third aspect, current signals measured by the current sensors are connected to a single analog-digital-converter of the power supply by a multiplexer. A digitization of the current signals measured by the current sensors is performed by the analog-digital-converter. This allows for a further reduction of the hardware effort.

According to a first implementation form of the previous implementation form, the currents through the converter branches are determined from the switching currents measured by the current sensors, by the current reconstructor. This allows for a very simple determining of the currents through the converter branches. According to a fifth implementation form of the third aspect, the currents through the converter branches are determined by the current reconstructor as follows:

/,. (?) : 5,. (t) = ON & S _j (t) = OFF

ISN _1J (t) = I ₁ (t).S _{1 +} I _J (t).S _J (t)

I _j (t) : S _j (t) = ON & S. (i) = OFF ' wherein

ΙΞΝ _ϋ (ί) is the switching current to the joint midpoint terminal of the converter branch ij,

/ _; ( ) is a first current flowing through the first converter of the converter branch ij,

/ - (t) is a second current flowing through the second converter of the converter branch ij, a first switching state applied to the first converter of the converter branch ij,

S _j (t) is a second switching state applied to the second converter of the converter branch ij, wherein the first switching state S _; (t) and the second switching state 5 - (t) are non-overlapped switching states with 180° phase shift, wherein the first switching state and the second switching state S - (t) each have a value of

0 as a switched off state and a value of 1 as a switched on state. This allows for a very simple determining of the currents through the converter branches.

According to a sixth implementation form of the third aspect, duty cycles of the first converter and the second converter of all converter branches are adjusted based upon the currents determined by the current reconstructor, compensating for circulating currents. This allows for a very low effort circulating current compensation.

Generally, it has to be noted that all arrangements, devices, elements, units and means and so forth described in the present application could be implemented by software or hardware elements or any kind of combination thereof. Furthermore, the devices may be processors or may comprise processors, wherein the functions of the elements, units and means described in the present applications may be implemented in one or more processors. All steps which are performed by the various entities described in the present application as well as the functionality described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if in the following description or specific embodiments, a specific functionality or step to be performed by a general entity is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respect of software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is in the following explained in detail in relation to embodiments of the invention in reference to the enclosed drawings, in which:

Fig. 1 shows a first embodiment of the power supply according to the first aspect of the invention in a block diagram;

Fig. 2 shows a detailed circuit diagram of parts of a second embodiment of the power supply of the first aspect of the invention;

Fig. 3a shows a number of signals in a third embodiment of the power supply of the first aspect of the invention; Fig. 3b shows a number of signals in the third embodiment of the power supply of the first aspect of the invention;

Fig. 3c shows a number of signals in the third embodiment of the power supply of the first aspect of the invention;

Fig. 3d shows a number of signals in the third embodiment of the power supply of the first aspect of the invention;

Fig. 3e shows a number of signals in the third embodiment of the power supply of the first aspect of the invention;

Fig. 3f shows a number of signals in the third embodiment of the power supply of the first aspect of the invention;

Fig. 4 shows details of a fourth embodiment of the power supply according to the first aspect of the invention in a block diagram;

Fig. 5 shows a number of signals in a fifth embodiment of the power supply according to the first aspect of the invention;

Fig. 6 shows a number of signals in a sixth embodiment of the power supply according to the first aspect of the invention;

Fig. 7 shows results achievable with a seventh embodiment of a power supply according to the first aspect of the invention, and

Fig. 8 shows an embodiment of the method according to the third aspect of the invention in a flow diagram.

DESCRIPTION OF THE EMBODIMENTS

First, we demonstrate the general construction and function of an embodiment of the power supply according to the first aspect of the invention along Fig. 1. With regard to Figs. 2 - 6, the detailed function of different embodiments are explained. With respect to Fig. 7, achievable results are shown. Finally, along Fig. 8 the function of an embodiment of the method according to the third aspect of the invention are shown. Similar entities and reference numbers in different figures have been partially omitted.

In this invention, shunt measurement is introduced as an alternative simple and cheap way to sense the switching currents instead of individual inductor currents. Different proposals are made here, considering different types of current sensors, considering different levels of accuracy, and considering different levels of modularity of the sensing circuit. Current signals needed for total current control and equal current sharing will be reconstructed form these sensed switched currents.

The provided invention helps to reduce the hardware resources required to sample N currents of an N-leg interleaved converter using a single analog-digital-converter ADC, where N is an even integer number. The invention is based on sensing N/2 switching currents of each two coupled legs operated without overlapping in the switching functions or in flowing currents, and then reconstructing the individual currents from the switching current using a single ADC.

Sampling the total switching current to the DC-rails or to the midpoint and trying to reconstruct the individual intercell currents without further assumptions and simplifications is not possible straight forward. In order to determine an accurate reconstruction, the switching currents of each two coupled legs are sensed with non-overlapped switching functions, as shown in the following. Using one current sensor on the switching current for each two converters gives the possibility to reconstruct the individual currents very accurate, if the sampling occurs exactly at the midpoint of the duty cycle of each. This can be here guaranteed if the ADCs are triggered at the valley or peaks of the PWM carrier signals.

In Fig. 1, a first embodiment of the power supply 1 according to the first aspect of the invention is shown. The power supply 1 comprises a Vienna rectifier 10, which has a first converter branch comprising a first converter 101 and a second converter 102. The first converter 101 is connected to a first rectification terminal 2 and a joint midpoint terminal 3 of the first converter branch. The second converter 102 is connected to the joint midpoint terminal 3 and to a second rectification terminal 4. The first converter 101 is adapted to switch an input signal between the first rectification terminal 2 and the joint midpoint terminal 3. The second converter 102 is adapted to switch an input signal between the joint midpoint terminal 3 and the second rectification terminal 4.

Between the converters 101, 102 and the joint midpoint terminal 3, a current sensor 11 is connected. This current sensor 11 measures a switching current at the joint midpoint terminal. This means that the current sensor 11 measures the entire current flowing from both converters 101, 102 in sum towards the joint midpoint terminal 3.

The power supply 1 moreover comprises a current reconstructor 12, which is connected to the current sensor 11. The current reconstructor determines a current through the first converter 101 and a current through the second converter 102 based upon the current measured by the current sensor 11. These resulting currents are handed to a controller 13, which is connected to the current reconstructor 12 and to the converters 101, 102. The controller adjusts duty cycles of the first converter 101 and the second converter 102 based upon the currents determined by the current reconstructor 12. Since the individual currents through the first converter 101 and the second converter 102 are determined by the current reconstructor 12 based upon the switching current measured by the current sensor 11, it is possible to adjust the function of the converters 101, 102, so that circulating currents are minimized. This increases the efficiency of the power supply and at the same time increases the power supply's reliability. Especially, an AC input signal in is provided to the power supply 1. This signal is either directly used by the converters 101, 102 or preprocessed, for example split into a symmetric signal before being handled by the converters 101, 102.

As already explained before, the converters 101, 102 are controlled by the controller 13. Especially, the timing of the switching of the converters 101, 102 is controlled by the controller 13. Especially, the first converter switches the AC input signal between the joint midpoint terminal 3 and the first rectification terminal controlled by a first modulation signal, while the second converter 102 switches the AC input signal between the joint midpoint terminal and the second rectification terminal controlled by a second modulation signal. The first modulation signal is generated from a first modulation carrier signal, while the second modulation signal is generated from a second modulation carrier signal. These carrier signals are 180° phase shifted.

Instead of only comprising a single converter branch, as shown in Fig. 1, the Vienna rectifier 10 can comprise a plurality of N converter branches. Each one of the converter branches is then supplied with the same AC input signal. Each of the converter branches comprises a first converter and a second converter. This is further shown in Fig. 2.

A single power sensor is provided for each converter branch measuring the summed up switching current through the first converter and the second converter of the respective converter branch. These signals are then handed to the current reconstructor, which reconstructs the currents through the individual converters. The controller 13 then sets the duty cycles of the switching by the individual converters of the converter branches.

The current sensor 11 shown in Fig. 1 is either a shunt or a current transducer. By using a shunt, an especially simple implementation is possible. This implementation though results in a slightly reduced accuracy, since using a shunt slightly influences the function of the power supply. In the alternative implementation of using a current transducer, this results in a higher accuracy, but also in a significantly increased cost.

It is possible to determine the current through the first converter 101 and the current through the second converter 102 independently from one another from the summed up switching current through the midpoint terminal 3, since at specific time periods, with regard to the switching of the converters, the switching current through the midpoint terminal 3 is identical to the current through the first converter 101, while at other times, it is identical to the current through the second converter 102. Especially, the switching current at the midpoint terminal is identical to a current through the first converter 101 during a time period at a valley of the first modulation carrier signal, and is identical to a current through the second converter 102 during a period at a valley of the second modulation carrier signal. By successively measuring the switching current at these times, it is possible to determine the independent currents through the converters 101, 102. To put this into more mathematical terms, the currents through the converter branches are as follows:

_/ x S _i (t) = ON & S _j (t) = OFF

,SN, (,) _{S) (f) = 0N &} ' _{i(t) =} ,„.,,

Ι8Ν _ϋ (ί) is the switching current to the joint midpoint terminal of the converter branch ij, is a first current flowing through the first converter of the converter branch ij, I _j (t) is a second current flowing through the second converter of the converter branch ij, is a first switching state applied to the first converter of the converter branch ij, S _j (t) is a second switching state applied to the second converter of the converter branch ij, The first switching state and the second switching state S - (t) are non- overlapped switching states with 180° phase shift. The first switching state and the second switching state S - (t) each have a value of 0 as a switched off state and a value of 1 as a switched on state.

At present, in Fig. 1, only the use of a single AC input signal in is shown. It is also possible to combine a number of according power supplies in order to increase the overall efficiency and the overall power output. Therefore, using only a single AC input signal, a plurality of such power supplies, presented before, may be operated. Also, a plurality of different phase shifted input signals can be used. For example in a three-phase-system, one power supply can be operated by each phase of the system. The output signals may then be summed up. Using such a plurality of power supplies forms a power supply system according to the second aspect of the invention.

In Fig. 2, a more detailed circuit diagram of the power supply 1 according to the first aspect of the invention is shown. Here, the power supply 1 comprises a Vienna rectifier 10 with a plurality of converter branches 26a, 26b, 26c. Each converter branch 26a - 26c comprises a power splitter 23a, 23b, 23c, which splits an AC input signal into a symmetric AC input signal.

Each converter branch 26a - 26c moreover comprises a first converter 101a, 101b, 101c and a second converter 102a, 102b, 102c. The first converters 101a - 101c are adapted to switch a first symmetric AC input signal between a first rectification terminal 2 and a joint midpoint terminal 3. The second converters 102a - 102c are adapted to switch the respective second symmetric AC input signal between the joint midpoint terminal 3 and the second rectification terminal 4.

The converters 101a - 101c, 102a - 102c are each connected to their respective rectification terminal 2, 4 by a diode. The first converters 101a - 101c are connected by diodes 24 in conduction direction to the first rectification terminal 2, while the second converters 102a - 102c are connected by diodes 25, which are reverse polarized to the second rectification terminal 4.

Each first converter 101a - 101c is connected together with the respective second converter 102a - 102c to the joint midpoint terminal 3. The converters 101a - 101c, 102a - 102c each belonging to a single converter branch are therein connected together and then connected to the joint midpoint terminal 3. At this connection, a current sensor 11a, l ib, 11c is located, which measures the summed up current through the two connected converters 101a - 101c, 102a - 102c. In this figure, additional current sensors 27, 28 are depicted. They are though not part of the power supply according to the first aspect of the invention. These additional power sensors only illustrate that by measuring the currents towards a single rectification terminal 2, 4, it is not possible to determine the entire necessary information without using a greater number of current sensors. It is important to note that the power supply according to the first aspect of the invention does not contain or require these current sensors.

The first rectification terminal 2 is moreover connected to the joint midpoint terminal 3 by a number of capacitances 20. Moreover, the joint midpoint terminal 3 is connected to the second rectification terminal 4 by a number of capacitances 21. In this example, the second rectification terminal 4 is moreover connected to mass 22. This is though not necessary. Also a symmetric rectification with mass connected to the joint midpoint terminal 3 or even an inverse rectification with mass connected to the first rectification terminal 2 is possible.

In the exemplary embodiment shown in Fig. 2, all interleaved legs 26a, 26b, 26c are operated with the same switching frequency and a displaced phase shift of 2*pi/N to each other, and with 180 degrees displaced phase shift between each two coupled legs. The total input current ripple frequency is N times the switching frequency. The input current of each two coupled legs (I if) 26a, 26b, 26c is shared in between those legs 26a, 26b, 26c and then flows, according to the switching states, either though the positive/negative flying diodes to the positive/negative DC- rails (ISDUij JSDLij) 2, 4, respectively or through the switches to the joint midpoint terminal (ISNij) 3.

In order to reconstruct the inter-cell currents ( , If), meaning the currents through the individual converters, from the switching currents or from diode currents is possible if the switching currents (ISNij) are sampled exactly at the middle of turn on cycle (carrier' s valley), or if the diode currents (ISDUij JSDLij) are sampled at the middle of turn off cycle (carrier's peak) and holding these values for the rest of cycle, assuming that the currents will continue flowing through the diodes or the switches.

It is actually a valid assumption, that the inter-cell average current in CCM of PFC operation is approximately the same as the switching current at the middle of switch conduction period, or the same as the flying diode current at the middle of diode conduction period. Since the Vienna rectifier is unidirectional converter, it is more reasonable to sense the switching currents to the midpoint of the DC-link and to keep number the current sensors half the interleaved legs. However, for bidirectional converters, it is possible to sense the switching currents to the positive rectification terminal 2 or the negative rectification terminal 4 with half the number of interleaved legs 26a - 26c. In the following, only the option of sensing the currents through the joint midpoint terminals 3 of the converter legs 26a - 26c is considered. Thanks to the 180 degrees carrier phase shift between the coupled legs 26a - 26c, this makes the separation procedure of the individual coupled currents accurate.

According to the switching possibilities of the coupled legs 26a - 26c, the sensed switching currents to the joint midpoint terminal 3 are only either of these two individual coupled currents, if the sampling is done at the valleys of their respective carrier signals. This means that sampling the switching current at the carrier signal zero crossing delivers exactly the midpoint sample of the corresponding leg current.

In Fig. 3a, a switching current ISN12, is shown as curve 30. Moreover, a current II, which is equivalent to the current through the first converter 101a of the first converter branch 26a of Fig. 2 is shown as curve 31. Moreover, a current 12, which corresponds to a current through the second converter 102a of the first converter branch 26a of Fig. 2 is shown as curve 32. The switching current (ISN12) can be split into 3 regions depending on the duty cycle of the converters.

Fig. 3b on the other hand, shows the respective carrier first modulation carrier signal Crrl as curve 33 and a second modulation carrier signal Crr2 as curve 34. These signals Crrl, Crr2 correspond to the modulation carrier signals of the first converter and the second converter of Fig. 2.

Figs. 3a and 3b show that whatever the operated region is, the sampling at the valley of the modulation carrier signals Crrl, Crr2 is always valid for reconstructing the respective current II, 12, and there is no need to select different sampling time instances. In Figs. 3c and 3d alternative values for the modulation carrier signals and the respective switching currents are shown. In Fig. 3c, current II is shown as curve 37 and corresponds to the current through the first converter 101a. Current 12 is shown as curve 36 and corresponds to the current through the second converter 102a. The switching current ISN12 is shown as curve 35. At the same time, in Fig. 3d, the first modulation carrier signal Crrl is shown as curve 38, while the second modulation carrier signal Crr2 is shown as curve 39. Moreover, alternatively, in Figs. 3e and 3f values for different switching currents and modulation carrier signals are shown. In Fig. 3e, the current II, which corresponds to the current through the first converter 101a, is depicted as curve 41, the current 12, which corresponds to the current through the second converter 102a, is depicted as curve 42. Finally, the switching current at the joint midpoint terminal ISN12 is shown as curve 40. At the same time, in Fig. 3f, the first modulation carrier signal Crrl is shown as curve 44, while the second modulation carrier signal Crr2 is shown as curve 43.

As in the elaborations on Fig. 3a and Fig. 3b, it is evident here, that in the regions of the valleys of the respective modulation carrier signals, it is possible to sample the switching current ISN12, in order to determine the value of the respective current II, 12 through the respective converter.

In order to perform this sampling, a plurality of analog-digital-converters (ADCs) can be used - one for each switching current to be sampled. In Fig. 4 an alternative embodiment showing a possible reduction of the amount of analog-digital-converters is depicted.

Instead of using one or two ADCs for each coupled pair 101a, 102a, 101b, 102b, 101c, 102c, it is possible to use only one single analog-digital-converter 402 and one multiplexer 401 for N interleaved converter legs.

A multiplexer 401 is connected to an analog-digital-converter 402, which in turn is connected to a storage 403. The multiplexer 401 is supplied with the switching currents ISN1, ISN2, ISN N/2- 1, ISN N/2. Each of these switching currents corresponds to the joint switching currents of a first converter and a second converter of a single converter branch. The multiplexer 401 successively switches between these different switching currents and simultaneously only hands on a single one of the switching currents to the analog-digital-converter 402. The analog-digital-converter 402 digitizes the respective current value and stores it in the storage 403.

The sampling by the analog-digital-converter 402 as well as the switching by the multiplexer 401 needs to be quick enough so that within a valley region of a modulation carrier signal, it is possible to sample all switching currents of the respective coupled legs.

Using one multiplexer 401 with N/2 inputs and single output makes therefore it possible to use single ADC for sampling. In addition, some logic may be implemented in a logic block for triggering the multiplexer and the analog-digital-converter 402 in a proper way. This logic block may manage the sorting procedure of the samples in the memory bank 403 as well.

The triggering signal mentioned before, is be generated at the valley of the six carrier signals as narrow as possible to sample at the midpoint of the sampled currents, and as wide as necessary to trigger the ADC 402. Chip-select signals CSO, CS1 and the period to pass a signal through the multiplexer should be wide enough to let the associated signal pass through, but not more than the total current harmonic period; otherwise the multiplexer will lose some signals.

The triggering is further shown along Figs. 5 and 6. In Fig. 5, a first modulation carrier signal 50 and a second modulation carrier signal 51 are depicted. Moreover, a first threshold Thl and a second threshold Th2 are shown.

The two threshold signals Thl, Th2 are used to generate the ADC triggering signal and chip select signals for the multiplexer with a proper duty.

Comparing the first carrier modulation signal 50 to the first threshold Thl results in a first triggering signal Trigl shown as curve 52. Comparing the first carrier modulation signal 50 to the second threshold Th2 results in a chip select signal channel 12CS, depicted as curve 53.

Moreover, as curve 54, a memory enable signal Enl is shown. This signal is generated by placing the midpoint of the peaks at the endpoint of the peaks of the first trigger signal Trigl.

Moreover, as curve 55, a second trigger signal Trig2 is generated by comparing the second carrier modulation signal 51 to the first threshold Thl. A channel select signal channel 12CS is shown as curve 56. It is generated by comparing the second carrier modulation signal 51 to the second threshold Th2.

Finally, a second memory enable signal En2 is shown as curve 57. It is generated by placing midpoints of peaks at the endpoints of the peaks of the second trigger signal Trig2.

In Fig. 6, moreover, a plurality of carrier modulation signals 60 for a plurality of carriers 1...N are shown. The resulting trigger signals 61, 62, 63 and 64 are depicted. Moreover, a joint trigger signal Trig is shown as curve 65. It encompasses all individual trigger signals Trigl-TrigN shown in curves 61 - 64. In Fig. 7, results of the current reconstruction are shown. The actual current II is shown as curve 70, while the reconstructed current is shown as curve 71. It is easily discernible that only minimal error occurs.

Finally, in Fig. 8, an embodiment of the method according to the third aspect of the invention is shown. In a first step 80, an AC input signal is supplied to a Vienna rectifier, comprising a first converter branch, which in turn comprises a first converter and a second converter. In a second step 81, the AC input signal is selectively switched between a joint midpoint terminal of the first converter branch and a first rectification terminal by the first converter. In a third step 82, the AC input signal is switched between the joint midpoint terminal and a second rectification terminal by the second converter. The second switch 81 and the third switch 82 are actually performed simultaneously.

In a fourth step 83, a switching current at the joint midpoint terminal of each converter branch is measured by a current sensor for each converter branch. In a fifth step 84, a current through the first converter and a current through the second converter of each converter branch is determined based upon the switching current measured by the current sensor of each converter branch. In a final sixth step 85, the duty cycles of the first converter and the second converter of the first converter branch is adjusted based upon the currents determined by the current reconstructor, so as to minimize circulating currents. In case of more than one converter branch, the duty cycles of all converters are adjusted based upon the reconstructed currents through the respective converters.

Since the power supply according to the first aspect of the invention and the method according to the third aspect of the invention are very closely interrelated, regarding the method, it is also referred to the elaborations regarding Fig. 1 - Fig. 7 with regard to the power supply.

By use of the different embodiments of the inventive power supply, the following benefits can be achieved:

- no limitation on the number of interleaved converter legs

- cheap solution for current sensing using shunt measurements

- locating the shunts to DC-link midpoint reduces the losses on shunts

- shunt or LEM sensor can be used - reduced number of necessary current sensors at half the number of interleaved legs - reduced number ofADCs of only one for all interleaved legs

- current reconstruction can be implemented in ASIC

- no assumptions, simplifications, or complex algorithms for current reconstruction

The invention is not limited to the examples and especially not to a specific number of converter branches or legs. The characteristics of the exemplary embodiments can be used in any advantageous combination.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in usually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless communication systems.