FIELD OF THE INVENTION

[0001 ] The present invention provides for systems and methods for modulating power converters, to reduce Electromagnetic Interference (EMI). In particular, there is disclosed a method of modulating the driving circuit of a Z-source power converter to reduce electromagnetic interference.

REFERENCES

[0002] [1] Fang Zheng Peng, "Z-source inverter", IEEE Transactions on Industry Applications, vol.39, no.2, pp. 504-510, Mar/Apr 2003.

[0003] [2] Anderson, J.; Peng, F., "Four quasi-Z-Source inverters", Power Electronics Specialists Conference, 2008. PESC 2008. IEEE, vol., no., pp. 2743-2749, 15-19 June 2008

[0004] [3] Vinnikov, D.; Roasto, I., "Quasi-Z-Source-Based Isolated DC/DC Converters for Distributed Power Generation," in Industrial Electronics, IEEE Transactions on , vol.58, no. l, pp.192-201, Jan. 2011

[0005] [4] Yuan Li; Anderson, J.; Peng, F.Z.; Dichen Liu, "Quasi -Z-Source Inverter for Photovoltaic Power Generation Systems," in Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE , vol., no., pp.918-924, 15-19 Feb. 2009

[0006] [5] http://www.apec-conf.org/wp-content/uploads/IS-14.Lpdf

[0007] [6] http://www.fujitsu.com/global/documents/about/resources/publ i- cations/fstj/archives/vol50-l/paper21.pdf

[0008] [7] https://www.transphormusa.com sites/default/files/public/TPH3-006PS.pdf

[0009] [8] http://eprints.qut.edu.au/31175/2/31175.pdf [001 0] [9] Siwakoti, Y.P.; Town, G., "Improved modulation Technique for voltage fed quasi-Z- source DC/DC converter," in Applied Power Electronics Conference and Exposition (APEC), 2014 Twenty- Ninth Annual IEEE , vol., no., pp.1973-1978, 16-20 March 2014

[001 1 ] [10] Jalakas, T.; Jarkovoi, M.; Roasto, I.; Zakis, J.; Garganeev, A., "Investigation of radiated emissions of a galvanically isolated qZS DC-DC converter," in Power Engineering, Energy and Electrical Drives (POWERENG), 2015 IEEE 5th International Conference on , vol., ηο., ρρ.176-181, 11-13 May 2015

[001 2] [11] Roasto, Indrek, and Dmitri Vinnikov. "Analysis and evaluation of PWM and PSM shoot-through control methods for voltage-fed qZSI based DC/DC converters." Power Electronics and Motion Control Conference (EPE/PEMC), 2010 14th International. IEEE, 2010.

[001 3] [12] Vinnikov, Dmitri, et al. "Four Novel PWM Shoot-Through Control Methods for Impedance Source DC-DC Converters." Journal of Power Electronics 15.2 (2015): 299-308.

[0014] [13] Siwakoti, Yam P., and Graham E. Town. "Design of FPGA- controlled power electronics and drives using MATLAB Simulink." ECCE Asia Downunder (ECCE Asia), 2013 IEEE. IEEE, 2013.

[001 5] [14] http://beehive-electronics.com/datasheets/100SeriesDatasheet Current.pdf

[001 6] [15] Siwakoti, Yam P., et al. "Impedance-source networks for electric power conversion part II: review of control and modulation techniques." Power Electronics, IEEE Transactions on 30.4 (2015): 1887-1906.

BACKGROUND OF THE INVENTION

[001 7] Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.

[001 8] Efficient power converters with the ability to deal with widely varying input voltage, and hence a high voltage gain, are required for many power conversion uses, including the use with renewable energy sources such as photo-voltaic cells, wind generators, etc. Various boost converter topologies have been reported in which the voltage boost is provided by one or more inductive elements - these topologies can be classified as single stage, cascaded or interleaved structures. Efficiency is also important as low-voltage sources are likely to be associated with high currents in the primary part of the power converter, which can lead to high conduction and switching losses.

[001 9] Impedance-source (or Z-source) converters and inverters, first proposed in 2002, are a major breakthrough in DC-DC converters, overcoming the limitations of voltage -source and current source inverters (VCSI), and capable of providing a large voltage boost [1]. There have been many developments and variations of the Z-source circuit topology, all providing various additional advantages, such as the four quasi -Z-source inverters [2].

[0020] The present invention has application to any Z-source inverter having semiconductor devices switching rapidly between states producing high levels of EMI. Unlike the simple Z- source topology, the voltage-fed quasi-Z-Source (qZS) converter, such as shown 10 in Fig. 1, has (in theory) a constant input current due to the line inductance, LI (11). This is a significant advantage for ensuring power quality in the supply circuit, i.e. by reducing electromagnetic interference (EMI) produced by the Z-source converter interfering with equipment connected to it. Nevertheless, the effectiveness of the quasi-Z source network as a low-pass filter may be compromised in practice, especially at very high frequencies, due to leakage through parasitic elements and non-ideal components.

[0021 ] Whilst not limited to the use of gallium nitride (GaN)-on-silicon HEMTs in power converters, the present invention has some advantageous application to GaN HEMTs which are of increasing interest for their potential to reduce switching and conduction losses at reasonable cost, and to realize compact converters by operating at relatively high switching frequencies. However, EMI is a potential concern when using high electron mobility transistors (HEMTs), which can switch between on and off states more rapidly than silicon field-effect transistors (FETs), thereby generating EMI to relatively high frequencies. In such cases, additional care must be taken to limit EMI, which is usually very obvious at harmonics of the switching frequency. The invention is also applicable to other transistor technologies such as Silicon based FETs.

[0022] There is therefore a general need for voltage converters having low EMI or improved efficiencies.

SUMMARY OF THE INVENTION

[0023] It is an object of the invention, in its preferred form to provide a power converter having improved operational efficiencies such as a low EMI. [0024] In accordance with a first aspect of the present invention, there is provided a method of reducing electromagnetic interference in a power converter, the power converter including a series of switches controlling a series of active and shoot through states of the power converter, by means of switch control threshold levels, the method including the step of: (a) driving the switches with an anharmonic modulation of the switch control threshold levels.

[0025] In some embodiments, the sum of the shoot through duty cycle, the active duty ratio and the zero duty ratio of the power converter can be substantially 1. In some embodiments, the power converter can be a quasi-Z-source power converter.

[0026] In some embodiments, the switches are pulse modulated. The timing of the pulse modulation can be generated from a sawtooth waveform with variable width and/or period. The pulse modulation can be generated by a variable width sawtooth driving sequence and the anharmonic modulation can include variation of the period of the sawtooth driving sequence.

[0027] The anharmonic modulation preferably can include aperiodic modulation of the switch control threshold level. The degree of anharmonic modulation can be about 4%.

[0028] In accordance with a further aspect of the present invention, there is provided a method of improving at least one of efficiency of operation, available gain, voltage regulation or electromagnetic interference suppression in a power converter, the power converter including at least one switch or transistor driven in a modulated manner, the method including the step of: (a) driving the switch in an aperiodic or quasi periodic manner.

[0029] In some embodiments the driving can include generating a first sawtooth waveform signal having a variable height or period, generating a second sinusoidal signal with dc offset; and comparing the first sawtooth waveform signal with the second sinusoidal signal to determine a pulse width modulated switch driving signal for driving the switch. Preferably, the period of the second sinusoidal signal is substantially different from the average period of the first sawtooth waveform signal.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0031 ] Fig. 1 illustrates schematically a voltage -fed quasi-Z-Source isolated DC-DC converter; [0032] Fig. 2 illustrates one form of cascode hybrid GaN structure

[0033] Fig. 3 illustrates the switching sequence for the reference modulation scheme;

[0034] Fig. 4 illustrates and example Block diagram implementation of logic to generate switching signals in the reference modulation scheme;

[0035] Fig. 5 illustrates the switching pattern of an embodiment;

[0036] Fig. 6 illustrates a block diagram of the logic used to generate the switch control signals for the aperiodic modulation scheme;

[0037] Fig. 7 illustrates traces of the switching sequence for reference modulation scheme (SI - S4 top to bottom);

[0038] Fig. 8 illustrates traces of the switching sequence for an embodiment (SI - S4 top to bottom);

[0039] Fig. 9 illustrates a Spectrum Plot of the conducted EMI measured in the converter supply line for a Reference modulation scheme at 0 to 6 MHz;

[0040] Fig. 10 illustrates a Spectrum Plot of the conducted EMI measured in the converter supply line for an Aperiodic modulation scheme at 0 to 6 MHz;

[0041 ] Fig. 11 illustrates a Spectrum Plot of the conducted EMI measured in the converter supply line for a Reference modulation scheme at 0 to 30 MHz;

[0042] Fig. 12 illustrates a Spectrum Plot of the conducted EMI measured in the converter supply line for an Aperiodic modulation scheme at 0 to 30 MHz;

[0043] Fig. 13 illustrates a chart of the relative improvements with different driving scenarios for various embodiments; and

[0044] Fig. 14 illustrates one form of simplified pulse width modulation technique. DETAILED DESCRIPTION

[0045] The embodiments provide a new aperiodic pulse modulation method for broadband EMI suppression in qZS and related power converter circuits. The method is relatively simple to implement, i.e. by anharmonic modulation of the switching thresholds (and hence duration) of the active and shoot-through states, whilst ensuring Eq. (2) below remains satisfied.

[0046] In the embodiments, a quasi Z source (qZS) DC-DC converter, such as that shown in Fig. 1, is utilised, incorporating a number of further innovations, including: a novel aperiodic variation of pulse modulation methods which substantially reduces high-frequency EMI.

[0047] Quasi-Z-Source (qZS) DC-DC Converter

[0048] An understanding of the qZS-based DC-DC converter operation, and its advantages, may be obtained from the formulas derived in references [3] and [4]. Like the Z-Source inverter, the qZS converter has two operating states, i.e. non -shoot-through states (active states and zero states, in which one switch on each side of the H-bridge conducts, on the diagonal or parallel arm, respectively), and shoot-through states (i.e. when both switches on one or both sides of the H- bridge conduct simultaneously).

[0049] The qZS impedance network in theory behaves as a low pass filter, blocking high frequency currents in the H-bridge switching section of the circuit from entering the supply circuit, and preventing damage to the switching devices during short shoot -through states. Applying a volt- second balance to the qZS impedance network and switches for the two operating states, the qZS converter voltage gain is given by:

V _out = (l - 2T/T _s )- ¹ - V _in = BV _in , (1) in which B is the voltage boost factor. The voltage gain therefore depends solely on the shoot- through state duty cycle, defined as D _ST = T/Ts, in which T is the shoot-through state duration and T _s is the period of one switching cycle.

[0050] Duty cycles of the other switching states may be defined similarly, such that D _A + D _z + D _ST = 1, (2) in which D _A is the active state duty cycle, and D _z the zero state duty cycle.

[0051 ] According to the derived relations, the factor "B*Vin" is also the voltage across the forward diode. Hence it gives a good idea about the voltage and current rating of the diode to be used in the prototype. The Table 1 in [4] gives a comparison of ZSI and qZSI network which clearly depicts the advantages of qZSI over ZSI by taking into account many of the important parameters such as Voltages across the capacitors, inductors and forward diode. QZSI is both implemented with single phase and three phase VSI topologies according to different applications.

[0052] Complete DC-DC Converter Circuit

[0053] The complete DC-DC converter circuit used in the embodiments is shown schematically 10 in Fig. 1. The complete circuit comprises a voltage -fed quasi-Z-Source impedance network 11, followed by a full H-bridge switching circuit 12 driving a high-frequency (HF) isolation transformer 13, with an output voltage doubler 14. This topology has been shown to have numerous advantages, including: It can realize a buck or boost function in a single stage, requiring less components than multistage converters and providing improved reliability. The qZS topology is not vulnerable to damage during conduction of both top and bottom switches of inverter 12 (such "shoot-through" states are forbidden in VSI circuits). The qZS topology enables the use of components with lower-voltage ratings than in the Z-Source topology. The constant input current makes the qZS topology well-suited for the applications having wider input voltage. The HF transformer 13 provides galvanic isolation of the load from the source, which is advantageous in many applications. The voltage-doubler circuit 14 reduces the turns ratio required of the HF transformer. Depending on the switch modulation scheme, soft-switching of the active devices can occur for at least some switch transitions.

[0054] Gallium Nitride (GaN) HEMT Switches

[0055] Whilst the embodiments are not limited to the use of GaN HEMT switches, the embodiments can include the advantageous incorporation thereof. The concept of using wide bandgap (WBG) material based power semiconductor devices is becoming popular as compared to using ordinary silicon based devices for provision of high power density with high efficiency and robustness against high temperatures. WBG refers to the materials with an energy gap between the valance band and the conduction band being significantly higher than 1 electronvolt (eV). This is the basic reason why a WBG device offers a greater power density and energy efficiency along with high reliability at high temperatures. An overview of the basic parameters associated with Silicon and other WBG materials is given in [5]. It is also believed that Silicon capability is touching its theoretical limits and it might be the last decade of using Silicon based power switches. Gallium Nitride (GaN) compound on the other hand is one of the best WBG materials offering high operating voltages and high temperature robustness. The integration of GaN devices in power converters provides a beneficial use because of the higher efficiency, small size, lighter and cheaper passives and higher power density etc [5].

[0056] The concept of "High Electron Mobility Transistor" (HEMT) is to utilize high density, two dimensional electron gas (2DEG) accumulated in the boundary layer between GaN and AlGaN through their piezoelectric effect and natural polarization effect. This makes it possible to realize a low on- state resistance (R _ON ) [6]. This low R _DS(ON) in addition to high breakdown voltage (because of WBG) makes the GaN HEMT a powerful candidate to be used as a high Power switch.

[0057] GaN based HEMTS are available in both the "Enhancement mode" and "Depletion mode" (alike MOSFETs which allow compatibility with the commercial drivers). The Enhancement mode GaN devices are also called as "eGaN" devices. Though qualified high voltage and high power GaN devices have a great potential to be toughened towards ideal behavior of a power switch (High operating frequency, high reverse voltage blocking capability, very low switching and conduction losses, stability and reliability etc). Fig. 2 illustrates schematically the structure of the cascade hybrid GaN transistor. These are a potential candidate to provide overall better performance as compared to the ordinary Silicon based high frequency MOSFETs. Cascode hybrid GaN HEMTs [7] have been used in the embodiments. The qZS converter used in the prototype embodiments incorporated four hybrid GaN HEMTs (i.e. Transphorm TPH3006PS ) as the power switching devices. The HEMTs were each driven by an Avago ACPL-P349 integrated high-speed optocoupler and gate driver circuit. The gate drive modulation signals were generated by a Xylinx Spartan 6 FPGA development board which was programmed using MatLab/Simulink and the HDL coder toolbox.

[0058] EMI in Power Converter Circuits

[0059] Broadband electromagnetic interference is generated by rapid changes in current and voltage which occur in hard-switched power electronic circuits. This is especially the case with high-speed switching devices, such as GaN HEMTs. Furthermore, when the power devices are switched periodically, the EMI is concentrated at harmonics of the fundamental switching frequency.

[0060] Unless careful precautions are taken, the EMI can be radiated and/or conducted away from the circuit, where it may then interfere with wireless communication systems, reduce power quality in the supply and/or load circuits, etc. Several techniques have been proposed to mitigate the EMI generated in switch-mode power converters and inverters, including: EMI filtering, i.e. adding one or more filters to the circuit to prevent conducted EMI escaping from the circuit; Electromagnetic shielding, i.e. enclosing the source of EMI with shielding material to block radiated EMI from escaping the circuit enclosure, soft switching, i.e. reduction of switching transients, thereby reducing the amount of EMI generated; quasi-periodic switch modulation, in which the periodicity of the power switching waveform is reduced, reducing the peak EMI by spreading the interference to an increased number of harmonics; and aperiodic (e.g. chaotic) switch modulation to spread the EMI over a continuum of frequencies - this substantially reduces the peak EMI, but can be complicated to implement.

[0061 ] The embodiments use a new aperiodic pulse modulation method for broadband EMI suppression in qZS and related power converter circuits. The method is relatively simple to implement, i.e. by anharmonic modulation of the switching thresholds (and hence duration) of the active and shoot-through states, whilst ensuring Eq. (2) remains satisfied.

[0062] qZS converter modulation scheme

[0063] A model of the qZS based DC-DC converter (Fig. 1) was built in the MATLAB- Simulink environment to facilitate rapid prototyping, programming and control of the gate -drive logic.

[0064] Reference Modulation Method

[0065] Numerous modulation schemes have been developed for use with the qZS DC-DC converter circuit. The modulation schemes are mainly differentiated by the relative positions of the different switching states, i.e. the active, zero and shoot-through states, and several have been evaluated with respect to the EMI generated.

[0066] A periodic modulation scheme is used here as the reference, against which other modulation schemes may be compared, e.g. with respect to the EMI generated, etc. The reference modulation scheme, as presented in [9] and, shown schematically 30 in Fig. 3, was chosen as it has a number of attractive features, i.e. independent control of active and shoot-through states; lower number of switching commutations per switching cycle, and only two shoot-through states per switching cycle.

[0067] Fig. 4 illustrates a block diagram 40 of the logic required to generate the modulation signals of Fig. 3. There are four outputs SI to S4, (e.g. 41) which drive the power transistors comprising the H-bridge switching circuit. There are two key functions in the signal generator; i) the sawtooth function generator 42 which, together with a comparator (Comp 1) 43, controls the on-time for the upper two switches SI, S2, in the H-bridge, and ii) the fixed-level threshold and a comparator (Comp 2) 44, which controls the shoot-through signal timing. Delays 45, 46, 47, were used to ensure correct timing of the pulses comprising each switching sequence. The complete control logic is easily implemented by any digital controller - in prototype form by an FPGA development board.

[0068] Aperiodic Modulation Scheme

[0069] An aperiodic modulation scheme was devised to suppress EMI in qZS and related switch-mode power conversion circuits. The principles underlying the design and implementation of this modulation scheme are as follows: 1. The duration of each switching cycle is varied by a small amount (e.g. up to 4%) from it's nominal value, Ts, within each switching cycle the duration of each switching state (active, zero, and shoot-through) varies, but the total remains consistent with Eq. (2). 2. The duty-cycle of the shoot -through state, DST = T/TST, and hence the converter's boost factor, is kept constant, and pairs of switching states are balanced in duration each switching cycle (i.e. to avoid saturation of the isolation transformer). 3. The sum of the three states (active, zero and shoot- through) is always equal to 1 (to make sure that the converter remains stable and there is no ambiguous state). 4. The width of active and zero states keep on varying in every consecutive switching cycle. 5. For one complete waveform (positive and negative cycle which is actually generated by the active states) across the primary transformer winding, the width of positive and negative half should always be same, (to make sure there is no saturation in the transformer). An example switching pattern fulfilling all the above requirements is shown in Fig. 5.

[0070] Implementation of the Aperiodic Modulation Scheme

[0071 ] Fig. 6 illustrates a block diagram 60 of the logic used to generate the switch control signals for the aperiodic modulation scheme. There are two key changes relative to the reference modulation scheme of Fig. 4. The first difference is that the sawtooth waveform generator 61 is programmed to generate variable duration (with variable height) sawtooth pulses. The result is that the width of every consecutive sawtooth pulse, and hence the timing of each switching state, varies randomly within a specified range (e.g. 4%) from the nominal value. The second difference is that a sinusoidal waveform 62 is added to the reference, 'Vp', that is used to trigger transitions between switching states. The peak-peak magnitude 'h' of the sine -wave relative to the reference value determines the range of variation in pulse position and pulse width of the resulting PWM signal. Ideally, the frequency of the sine -wave is not harmonically related to the switching cycle repetition rate, 1/T _S

[0072] The additional delay blocks, labelled Delay4 64 and Delay5 65 in Fig. 5, ensure that each shoot-through state is fixed, ensuring the boost factor, B, and average output voltage to remain constant.

[0073] The essentially random variation in switching pulse position and duration achieved by the above method in each switching cycle prevents the accumulation of energy at harmonics of the fundamental switching frequency. It is notable that the technique is generic, and should be equally applicable with other modulation schemes.

[0074] Experimental Results

[0075] A prototype qZS DC-DC converter was adapted and used to test the aperiodic modulation method and measure the reduction in EMI relative to the reference modulation method. Key design parameters and components were as follows: fundamental switching frequency, f _s = 24 kHz; isolating transformer turns ratio, n = 1 : 1 ; qZS inductors LI = L2 = 1.3 mH; capacitors CI = C4 = 470 uF; and rectifiers Dl - D3 were silicon carbide Scottky diodes, C3D06060G. The H- bridge switches SI - S4 were hybrid GaN HEMTs, TPH3006PS, driven by high-speed optoelectronically isolated gate drivers, ACPL-P349. The supply voltage was set to 48 volts and a programmable electronic load set to 100 watts was connected to the converter's output. The shoot- through duty cycle was set to D _ST = 10% (best practice is to keep D _ST < 33% for low conduction losses and high efficiency). A Xilinx Spartan 6 FPGA development board was programmed to generated the switch modulation signals.

[0076] Measured switch drive signals for the reference and aperiodic modulation schemes are shown in Figs. 7 and 8, respectively. The blurred edges evident, e.g. 81 in Fig. 8, show the extent of the random variation in the switching pulse timing and duration produced by the aperiodic modulation scheme.

[0077] Conducted EMI in the converter's positive supply line was monitored using an inductively coupled near-field probe, "lOOC" from Beehive Electronics, which was positioned and oriented for maximum coupling to the magnetic field produced by the converter's input current. The spectrum of the input current was displayed over a broad bandwidth using a RIGOL DSA815 RF spectrum analyser. The results are illustrated in Fig. 9 to Fig. 12, as follows:

[0078] Fig. 9 and Fig. 11 illustrate the spectrum of measured EMI response in the source circuit for the reference modulation scheme for frequency ranges 0-6 MHz and 0-30 MHz respectively. Fig. 10 and Fig. 12 illustrate the corresponding EMI response for the aperiodic modulation scheme of the embodiment, again for frequency ranges 0-6 MHz and 0-30 MHz respectively. From an examination of the response results, it is evident that the EMI response levels are much lower for the aperiodic modulation.

[0079] On closer examination, it is evident that the quasi-Z-source impedance network prevented EMI from entering the supply line at low frequencies (i.e. < 1 MHz). However, discrete harmonics of the fundamental switching frequency are clearly evident at higher frequencies, especially between 1 and 8 MHz, but also up to 30 MHz.

[0080] The EMI measured under identical conditions as previously, except using the aperiodic modulation method, is shown in Figs. 10 and 12. Comparisons with results obtained using the reference modulation method show that discrete harmonics of the fundamental switching frequency were largely eliminated by using the proposed aperiodic modulation method. As a result EMI was reduced by up to lOdB at most frequencies.

[0081 ] In summary, it can be seen that a quasi-Z-source DC-to-DC converter has been developed and tested, and incorporated high speed hybrid GaN HEMTs driven by integrated high speed optoelectronic couplers and gate-drivers. Conducted electromagnetic interference was monitored in the converter's supply circuit using an inductively-coupled EMI probe. When using standard periodic modulation of the HEMTs, low frequency EMI, i.e. up to approximately 1 MHz (the 40th harmonic of the switching frequency), was blocked by the low-pass quasi-Z-source impedance network. However, a substantial amount of EMI was evident passing through the impedance-source network and into the supply circuit at higher frequencies, i.e. from 1 to 30 MHz, and beyond. [0082] An aperiodic modulation method was developed to reduce the EMI generated by the quasi-Z-source converter. Experimental results showed a marked decrease, by up to 10 dB, in the conducted EMI present in the converter's supply circuit. The aperiodic modulation method described herein is generic, and so applicable with other modulation schemes proposed to date, and is expected to be equally effective in any impedance-source based converter.

[0083] The technique also has applications to other quasi-Z-source (qZS) DC-DC converters which use other PWM schemes.

[0084] Considering the arrangement 60 as outlined in Fig. 6, an aperiodic and quasi-periodic modulation methodology can be implemented for other various modulation schemes for quasi-Z- source (qZS) DC-DC converters. For example, the proposed methodology has been extended to 2 different modulation schemes presented for a qZS DC-DC converter. Turning to Fig. 13, the modulation schemes are briefly illustrated 131, 132.

[0085] There is also shown a guide chart in Fig. 13 explaining the various advantages and disadvantages in terms of efficiency, voltage gain, voltage regulation and EMI suppression. Generally speaking, aperiodic modulation will give more EMI suppression as compared to a quasi- periodic modulation scheme but various other parameters also need to be considered along with various modulation schemes.

[0086] The chart of Fig. 13 is divided into various quadrants. In Quadrant I: Aperiodic modulation gives high EMI suppression along with high efficiency but since the shoot-through states are not independent of the active states, this methodology is not applicable for high shoot- through duty ratios. Additionally, since the shoot -through state is dependent upon the active states and there is no zero- state, hence the scheme lacks the voltage regulation.

[0087] In Quad-II, Aperiodic modulation gives a high EMI suppression and since the active and shoot-through states are independent of each other, the voltage regulation is within bounds. Additionally, since the shoot-through states are independent, the modulation methodology is applicable to high gain applications with high shoot -through duty ratios. The disadvantage in this case is that the additional switching transients may add up to the switching losses and hence decrease the efficiency.

[0088] In Quad-Ill, the quasi-periodic modulation leads to lower switching losses which implies a higher efficiency. Moreover, the EMI suppression is less because of quasi-periodic natured modulation. Additionally, since the shoot-through states are independent of active states, the methodology is applicable to high gain applications along with the capability of voltage regulation.

[0089] In Quad IV, the quasi-periodic modulation gives a low EMI. Additionally, since the shoot-through states are not independent, the modulation methodology is not applicable for high gains. Voltage regulation is not offered due to limitation of the modulation scheme.

[0090] The embodiments therefore can be many and varied, depending on requirements. For example, the methodology can be used on a single switch power converter using simple integrated circuits. Although the technique was originally described using H-bridge (4-switches) based quasi- Z-source DC-DC converters, the EMI suppression technique is also applicable to single switch power converters. For Example, the technique can be implemented in a single switched power converter (SEPIC converter). In the simple case, the implementation doesn't require an FPGA to coordinate switching of 4 active devices.

[0091 ] Fig. 14 illustrates 140 a schematic of how the modulation for the EMI suppression technique is implemented in this case. A sawtooth generator 141 and modulated output are compared 143. The output 144 consists of an aperiodic modulation signal for driving the single switched power converter.

Interpretation

[0092] Reference throughout this specification to "one embodiment", "some embodiments" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment", "in some embodiments" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0093] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner. [0094] In the claims below and the description herein, any one of the terms comprising, comprised of or which comprises is an open term that means including at least the elements/features that follow, but not excluding others. Thus, the term comprising, when used in the claims, should not be interpreted as being limitative to the means or elements or steps listed thereafter. For example, the scope of the expression a device comprising A and B should not be limited to devices consisting only of elements A and B. Any one of the terms including or which includes or that includes as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, including is synonymous with and means comprising.

[0095] As used herein, the term "exemplary" is used in the sense of providing examples, as opposed to indicating quality. That is, an "exemplary embodiment" is an embodiment provided as an example, as opposed to necessarily being an embodiment of exemplary quality.

[0096] It should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, FIG., or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[0097] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0098] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[0099] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00100] Similarly, it is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Coupled" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

[00101 ] Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as falling within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.