A phase shedding power converter

Abstract

A multi-phase bridgeless totem-pole PFC power converter configured to improve switching losses by shedding phases at low power levels. The converter includes at least one fixed phase and at least one operating phase. Fixed phases are turned off during portions of each input power cycle where the input voltage is below a threshold. Operating phases are turned off during portions of each input power cycle where the input current is below a threshold and output power or RMS input current are within predetermined ranges. The phase shedding scheme results in operating phases carrying less effective current than fixed phases thereby allowing boost inductor sizes to be reduced yielding improvements in power density.

Description

[0001] A PHASE SHEDDING POWER CONVERTER

[0002] TECHNICAL FIELD

[0003] The aspects of the disclosed embodiments relate generally to power conversion apparatus and more particularly to multi-phase AC to DC power converters.

[0004] BACKGROUND

[0005] Today’s shift toward renewable energy, is accelerating the need for power supplies with ever growing output power. To satisfy this need, multiphase paralleling is often used to increase the output capacity and peak efficiency of switching regulators, while reducing output ripple. Unfortunately, adding phases increases the number of switching devices leading to increased switching loss and reduced efficiency, especially when operating at light loads.

[0006] Phase shedding, a technique used to turn off one or more phases, may be used to improve overall converter efficiency by reducing switching and magnetic losses at lighter load levels. Conventional phase shedding techniques are based on load power and turn off one or more phases when operating at light output load levels and turn the phases on during higher power conditions. Unfortunately, these conventional solutions switch phases on and off over many cycles of the input power and do not provide finer control of current and switching losses in each phase.

[0007] Thus, there is a need for improved multiphase power converters that employ flexible phase shedding techniques to improve overall power supply efficiency, while also improving power density and maintaining reduced output ripple. Accordingly, it would be desirable to provide apparatus and methods that addresses at least some of the problems described above.

[0008] SUMMARY

[0009] The aspects of the disclosed embodiments are directed to a multiphase totem-pole bridgeless power factor correction power converter apparatus incorporating flexible phase shedding techniques. Turning phases on during a portion of each input cycle based on the output power and magnitude of the input current reduces switching losses and allows reduction in inductor volume leading to improved power density.

[0010] According to a first aspect, the above and further advantages are obtained by a power converter apparatus including: a bridgeless rectifier stage configured to receive an AC input voltage and produce a DC output voltage; a plurality of switching phases configured to receive the AC input voltage and deliver a power factor corrected AC power to the DC output voltage; and a controller configured to operate the plurality of switching phases. The plurality of switching phases includes at least one fixed phase configured to remain on while the converter is producing the DC output voltage, and at least one operating phase configured to be on during a first portion of a line frequency cycle and off during a second portion of the line frequency cycle. The controller is configured to: when a magnitude of the input voltage exceeds a first predetermined voltage threshold and a magnitude of an input current exceeds a first current threshold, turn the first operating phase on; and when the magnitude of the input current falls below the first current threshold or the magnitude of the AC input voltage falls below a second predetermined voltage threshold, turn the operating phase off. Turning phases on during a portion of each input cycle based on the output power and magnitude of the input current reduces switching losses and allows reduction in inductor volume leading to improved power density. In a possible implementation form each switching phase in the plurality of switching phases includes an upper switching device and a lower switch switching device coupled in series across the DC output voltage and forming a midpoint between the upper switching device and the lower switching device, and a boost inductor coupled between the AC input voltage and the midpoint, and wherein the controller is configured to: when the switching phase is on, operate the switching phase to provide power factor correction and transfer power from the AC input voltage to the DC output voltage; and when the switching phase is off, turn both the upper switching device and the lower switching device off. Turning a phase off during portions of the input power cycle eliminates switching losses while the phase is off.

[0011] In a possible implementation form the controller is configured to select the first current threshold from a plurality of predetermined current thresholds based at least in part on one of the output power and an rms input current. In the illustrated converter apparatus 100, the plurality of predetermined current thresholds includes three values 7TI, hi, hi. Optionally, and suitable number of predetermined current thresholds may be advantageously employed. Selecting thresholds based on the converter input enables larger portions of each phase to be shed as input power decreases.

[0012] In a possible implementation form the controller is configured to: when the output power is less than a first predetermined power threshold, select a first predetermined current threshold as the first current threshold, and when the output power is not less than the first predetermined power threshold and is less than a second predetermined power threshold, select a second predetermined current threshold as the first current threshold, and when the output power is not less than the second predetermined power threshold, select a third predetermined current threshold as the first current threshold, wherein the first predetermined current threshold is less than the second predetermined current threshold and the second predetermined current threshold is less than the third predetermined current threshold. The use of multiple thresholds allows larger portions of each input cycle to be shed as the load decreases.

[0013] In a possible implementation form the plurality of switching phases includes a second operating phase, and the controller is configured to: when the output power is less than a first predetermined power threshold, turn the second operating phase off; when the output power is greater than or equal to the first predetermined power threshold and is less than the second predetermined power threshold, select a fourth predetermined current threshold as a second current threshold, when the output power is greater than or equal to the second predetermined power threshold select a fifth predetermined current threshold as the second current threshold, wherein the fourth predetermined current threshold is less than the fifth predetermined current threshold; when the magnitude of the input voltage exceeds the first predetermined voltage threshold, and the magnitude of the input current exceeds the second current threshold, turn the second operating phase ON; and when the magnitude of the input current falls below the second current threshold or the magnitude of the input voltage falls below the second predetermined voltage threshold, turn the second operating phase OFF. Applying the intra-cycle phase shedding techniques to a second phase provides additional light load efficiency.

[0014] In a possible implementation form the first predetermined voltage threshold is greater than the second predetermined voltage threshold. Making the second threshold smaller than the first threshold reduces the effective current in the second phase thereby allowing a smaller inductor to be employed in the second phase.

[0015] In a possible implementation form the first predetermined voltage threshold and the second predetermined voltage threshold are proportional to a rated voltage of the power converter. The disclosed phase shedding techniques are easily tailored to different converters based on their rated power.

[0016] In a possible implementation form the magnitude of the input voltage exceeds the first predetermined voltage threshold, turn the at least one fixed phase on, and when the magnitude of the input voltage falls below the second predetermined voltage threshold, turn the at least one fixed phase off. Shedding phases when input voltage is low further reduces switching losses. In a possible implementation form a boost inductor associated with an operating phase comprises less volume than a boost inductor associated with a fixed phase. The disclosed phase shedding techniques result in reduced effective current in the operating phases allowing reduction in inductor volume which improves power density of the converter.

[0017] According to a second aspect, the above and further advantages are obtained by a method for operating a multi-phase bridgeless totem-pole PFC power converter The power converter includes at least one fixed phase and a first operating phase, and the method includes: when an input voltage is greater than a first predetermined voltage threshold, turn the at least one fixed phase on; when the input voltage is greater than the first predetermined voltage threshold and an output power is less than a first predetermined power threshold and an input current is greater than a first predetermined current threshold, turn the first operating phase on, and when the input current falls below the first predetermined current threshold, turn the first operating phase off; when the input voltage falls below a second predetermined voltage threshold turn the first operating phase off and turn the at least one fixed phase off. Turning phases on during a portion of each input cycle based on the output power and magnitude of the input current reduces switching losses and allows reduction in inductor volume leading to improved power density.

[0018] In a possible implementation form the first predetermined current threshold is determined based at least in part on the first predetermined power threshold. Selecting current thresholds based on converter power simplifies converter design.

[0019] In a possible implementation form the power converter includes a second operating phase and the method further includes: when the input voltage is greater than the first predetermined voltage threshold, the output power is greater than or equal to the first predetermined power threshold and less than a second predetermined power threshold, and the input current is greater than a second predetermined current threshold, turn the first operating phase on, and when the input current falls below the second predetermined current threshold, turn the first operating phase off; when the input voltage is greater than the first predetermined voltage threshold and the output power is greater than or equal to the first predetermined power threshold and less than the second predetermined power threshold, and the input current is greater than a fourth predetermined current threshold, turn the second operating phase on, and when the input current falls below the fourth predetermined current threshold, turn the second operating phase off, when the input voltage is greater than the first predetermined voltage threshold, the output power is greater than or equal to the second predetermined power threshold, and an input current is greater than a third predetermined current threshold, turn the first operating phase on, and when the input current falls below the third predetermined current threshold, turn the first operating phase off ; when the input voltage is greater than the first predetermined voltage threshold and the output power is greater than the second predetermined power threshold and the input current is greater than a fifth predetermined current threshold, turn the second operating phase on, and when the input current falls below the fifth predetermined current threshold turn the second operating phase off ; and when the input voltage falls below the second predetermined voltage threshold turn the first operating phase off, turn the second operating phase off, and turn the at least one fixed phase off. Shedding phases by turning switching off during portions of each cycle significantly improves low power efficiency and also reduces effective current in the operating phases thereby allowing reduction in inductor volume.

[0020] In a possible implementation form the fourth predetermined current threshold is greater than the second predetermined current threshold, and the fifth predetermined current threshold is greater than the third predetermined current threshold. Employing this relationship between the thresholds, the switching time of each operating phase is different in a line frequency cycle and much less than the fixed phases, resulting in successively lower effective current in each inductor allowing improved power density.

[0021] In a possible implementation form the first predetermined voltage threshold is greater than the second predetermined voltage threshold. Including hysteresis avoids chattering in the shedding mechanism. In a possible implementation form the second predetermined current threshold, the third predetermined current threshold, the fourth predetermined current threshold, and the fifth predetermined current threshold are determined based at least in part on the first predetermined power threshold and the second predetermined power threshold. Selecting current thresholds based on power thresholds provides a reliable method of reducing effective current delivered by the operating phases.

[0022] These and other aspects, implementation forms, and advantages of the exemplary embodiments will become apparent from the embodiments described herein considered in conjunction with the accompanying drawings. It is to be understood, however, that the description and drawings are designed solely for purposes of illustration and not as a definition of the limits of the disclosed invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which like references indicate like elements and:

[0025] Figure 1 illustrates a schematic diagram of an exemplary power converter apparatus incorporating aspects of the disclosed embodiments.

[0026] Figure 2 illustrates a flow chart of an exemplary method for operating a multi-phase power converter incorporating aspects of the disclosed embodiments.

[0027] Figure 3 illustrates graphs showing representative operating signals of an exemplary power converter apparatus incorporating aspects of the disclosed embodiments.

[0028] Figure 4 illustrates a pictorial diagram of an exemplary set of boost inductor cores incorporating aspects of the disclosed embodiments.

[0029] Figure 5 illustrates a block diagram of an exemplary control strategy incorporating aspects of the disclosed embodiments.

[0030] Figure 6 illustrates graphs showing efficiency improvements obtained by the exemplary power converter apparatus incorporating aspects of the disclosed embodiments.

[0031] Figure 7 illustrates graphs showing performance of a power converter apparatus incorporating aspects of the disclosed embodiments.

[0032] DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0033] Figure 1 illustrates a diagram of an exemplary power converter apparatus 100 incorporating aspects of the disclosed embodiments. The exemplary power converter 100 incorporates a multi-phase bridgeless totem-pole power factor correction (PFC) converter topology adapted to shed phases when operating at lower power levels. In contrast with conventional phase shedding techniques, the exemplary converter apparatus 100 is configured to reduce switching losses by turning operating phases on and off within each cycle of the AC input power. Phase shedding by cycle allows more flexible control of the effective current in each operating phase and yields reduced switching losses while also allowing improvements in power density.

[0034] As shown in the example of Figure 1, in one embodiment, the power converter apparatus 100 includes a bridgeless rectifier stage 102 configured to receive an AC input voltage (Vin) and produce a DC output voltage (Vo). A plurality of switching phases 104 are configured to receive the AC input voltage (Vin) and deliver a power factor corrected AC power to the DC output voltage (Vo). A controller 106 is configured to operate the plurality of switching phases (104).

[0035] The plurality of switching phases 104 in the embodiment of Figure 1 include at least one fixed phase 104a, 104b that is configured to remain on while the converter 100 is producing the DC output voltage (Vo). At least one operating phase 104c, 104d is configured to be on during a first portion of a line frequency cycle and off during a second portion of the line frequency cycle.

[0036] The controller 106 of Figure 1 is further configured to turn off (118) the first operating phase (104d) when a magnitude (|Vin|) of the input voltage (Vin) exceeds a first predetermined voltage threshold (VT1), a magnitude (|Iin|) of an input current exceeds a first current threshold (IC1), a first operating phase (104d) in the at least one operating phase (104c, 104d) is turned on (114); and when the magnitude (|Iin|) of the input current (lin) falls below the first current threshold (IT1) or the magnitude (|Vin|) of the AC input voltage (Vin) falls below a second predetermined voltage threshold (VT2).

[0037] In the schematic diagram illustrated in Figure 1, crossed circuit lines marked with a dot 130 are electrically connected and crossed circuit lines without a dot 132 are not electrically connected. Lines forming a tee intersection are always connected.

[0038] AC power, such as from a power grid or other suitable AC power source 134, is applied to the exemplary power converter apparatus 100 across a line L and neutral N node, optionally, an input filter 108 may be configured to receive the AC power 134 and produce a conditioned input voltage Fm. and current Im to be consumed by the rectifier stage 102. Any suitable type of input filter configured to condition the AC power 134 and / or prevent EMI created within the converter 100 from leaking back onto the AC power may be advantageously employed as the input filter 108.

[0039] A bridgeless rectifier 102 receives the AC input power Fin, Im and produces a DC power Po. In the illustrated embodiment, a bridgeless rectifier 102, is formed with switches S9 and S10, which are operated to rectify the AC input voltage. Four diodes, Di, D2, Da, D4, are included in the rectifier stage 102 to provide surge protection. While a bridgeless rectifier stage, such as the bridgeless rectifier 102, provides certain advantages, any suitable rectification stage may be included without straying from the spirit and scope of the present disclosure. As will be discussed further below, the plurality of switching phases 104 may also be operated to provide rectification of the AC input voltage Fin.

[0040] A plurality of switching phases 104 are configured to receive the AC input voltage Fin and deliver a power factor corrected AC power to the DC output voltage Vo. The exemplary power converter apparatus 100 includes four switching phases 104a, 104b, 104c, 104d in the plurality of phases 104. Optionally, the plurality of phases 104 may include any number of two or more switching phases. Each switching phase 104a, 104b, 104c, 104d in the plurality of switching phases 104 includes an upper switching device Si, S3, Ss, ST and a lower switch switching device S2, S4, Se, Ss coupled in series across the DC output voltage Vo and forming a midpoint 122, 124, 126, 128 between the upper switching device Si, S3, Ss, ST and the lower switching device S2, S4, Se, Ss. A boost inductor Li, L2, L3, L4 is included in each switching phase 104a, 104b, 104c, 104d coupled to the AC input voltage Fin and configured to deliver electric power to a corresponding one midpoint 122, 124, 126, 128. In the exemplary converter apparatus 100, the switching devices Si, Sa, Sa, S4, Sa, Se, ST, SS, SS, S10 are implemented with metal-oxide-semiconductor field-effect transistors (MOSFET). Alternatively, any suitable type of switching device capable of switching the desired power at the desired frequency may be advantageously employed as the switching devices Si, Sa, Sa, S4, Sa, Se, ST, SS, SS, S10 in the exemplary power converter apparatus 100.

[0041] An output capacitor Co may be coupled across the output voltage Voto provide smoothing and conditioning of the output power Po. When desired, a switching device Ssmay be coupled in series with the output capacitor Co to provide the exemplary power converter 100 with soft start functionality.

[0042] As used herein a phase is referred to as “off’ or “turned off’ when both switching devices are off or not conducting current, and the phase is referred to as “on” or “turned on” when the switching devices, are being operated as a switching regulator, such as in a PFC boost mode, to transfer power from the AC input voltage Fin to the DC output voltage Vo. For example, the first phase 104a is off when both switch Si and S2 are turned off, and the first phase 104a is on when switches Si and S2 are being operated as a switching converter to transfer power from the input Fin to the output Vo.

[0043] As used herein a switching device, such as any of the switching devices Si, S3, S3, S4, Ss, Se, ST, SS, SS, S10, is referred to as “off’ when it is not conducting current and referred to as “on” when it is conducting current.

[0044] The plurality of switching phases 104 are operated by a controller 106, where the controller 106 is configured to receive signals corresponding to the output power Po, input voltage Fin, and input current / in, and produce switching signals 120 configured to turn each switching device Si, S3, S3, S4, Ss, Se, ST, SS, SS, S10 on and off. In the exemplary power converter apparatus 100 the rectifier is operated at a line frequency of the AC input power 134, such as the fifty hertz line frequency (50Hz) used in the European power grid or the sixty hertz (60Hz) line frequency used in the North American power grid. Each switching phase in the plurality of the switching phases 104 is operated at a frequency significantly higher than the line frequency, which in certain embodiments may be in the kilohertz range.

[0045] The exemplary power converter apparatus 100 is illustrated with two fixed phases 104a, 104b, and two operating phases 104c, 104d. However, the exemplary power converter may include any number of fixed and operating phases as desired, but must include at least one fixed phase 104a, 104b and at least one operating phase 104c, 104d.

[0046] As used herein, the term input cycle refers to one full cycle of the AC input voltage Fin or AC input current / in.

[0047] As used herein the term fixed phase refers to a phase that is continuously turned on to provide PFC and current to the output power. A fixed phase may remain on all the time or be turned on during portions of each input power cycle when the input voltage is above a certain voltage threshold. The operation of a fixed phase remains constant and does not vary with changes in output power or RMS input current.

[0048] As used herein an operating phase is a phase that is turned on and off during portions of each input cycle based at least in part on one or more of the output power, the rms input current, the input voltage, and the input current of the converter. An operating phase is turned on during portions of each input cycle when the input current exceeds a current threshold, where the current threshold is selected based on an output power or RMS input current of the converter. When the converter is operating at low power levels, the amount of time an operating phase is turned on may be reduced or the operating phase may be completely turned off thereby reducing switching losses and improving overall efficiency of the converter.

[0049] Generally, the controller 106 turns an operating phase on and off by comparing the input voltage Fin and input current to corresponding thresholds. When a magnitude of the input voltage | Fin| exceeds a first predetermined voltage threshold Fri and a magnitude the input current | / in| exceeds a first current threshold / ci 112 (|Fin|>Fri) A ( / in|> / ci), the first operating phase is turned on 114. When the magnitude of the input current |Zm | falls below the first current threshold / TI or the magnitude of the AC input voltage |J4n| falls below a second predetermined voltage threshold I T2 116 (|Fm|<FT2) V (| Zin|< Zci), the operating phase is turned off 118. Magnitude, also known as absolute value, is used in the above logic to provide the same operational logic during both the positive half cycle and negative half cycle of the AC input power 134.

[0050] In one embodiment the first predetermined voltage threshold Pn and second predetermined voltage threshold I T2 are determined based on the rated voltage of the power converter 100. For example, in one embodiment the first and second predetermined voltage thresholds KTI, V I are proportional to the rated voltage of the converter 100. Selecting the voltage thresholds based on the rated voltage of the converter provides a simple and reliable approach for selecting these values for different applications.

[0051] Including hysteresis when selecting the predetermined voltage thresholds KTI, Vn, such as setting the turn on voltage threshold KTI higher than the turn off threshold 122. may provide operational advantages, in certain embodiments. For example, a converter rated for an input voltage of two hundred twenty volts (220v) may have a first predetermined voltage threshold Pn set to twenty-five volts (25v) and a second predetermined voltage threshold 172 set to fifteen volts (15v). This may be useful when the AC input voltage experiences noise or other undesired voltage variations.

[0052] The exemplary controller 106 is configured to select 112 the first current threshold Ici based on operating conditions of the converter 100 such as converter output power Poor rms input current / in RMS. When desired, multiple predetermined power thresholds PTI, PT? may be employed to select the first current threshold / ci from a plurality of predetermined current thresholds / TI, / T2, TS where each predetermined current threshold in the plurality of predetermined current thresholds hi, hi, hi is selected for different values of converter output power Poor rms input current / in RMS.

[0053] In one embodiment, the controller 106 may be configured to divide converter operation into three regions based on two predetermined output power thresholds PTI, PT2. When the output power Pois less than a first predetermined power threshold PTI, the controller is configured to select 112 a first predetermined current threshold hi as the first current threshold / ci. When the output power Pois not less than the first predetermined power threshold PTI and is less than a second predetermined power threshold PT2, the controller 106 is configured to select 112 a second predetermined current threshold hi as the first current threshold Ici, and when the output power Pois not less than the second predetermined power threshold PT2, the controller 106 is configured to select 112 a third predetermined current threshold hi as the first current threshold Ici. It may be beneficial in certain embodiments to select the predetermined current thresholds hi, hi, hi such that the first predetermined current threshold hi is less than the second predetermined current threshold hi and the second predetermined current threshold hi is less than the third predetermined current threshold hi. Alternatively, any suitable values may or ordering of the predetermined current thresholds may be advantageously employed as the plurality of current thresholds hi, hi, hi. Optionally, any desired ordering of the predetermined current thresholds hi, hi, hi may be advantageously employed.

[0054] When multiple operating phases are included in a power converter apparatus, such as the two operating phases 104c, 104d of the power converter apparatus 100, a second operating phase 104d may be controlled by using the same predetermined power thresholds PTI, PT2 to select a second current threshold Ici from a different set of pre-determined current thresholds / T4, hi. When the output power Pois less than the first predetermined power threshold PTI, turn the second operating phase off. When the output power Pois greater than or equal to the first predetermined power threshold PTI and is less than the second predetermined power threshold PT2 select a fourth predetermined current threshold / T4 as the second current threshold Ici, and when the output power Pois greater than or equal to the second predetermined power threshold PT2 select a fifth predetermined current threshold hi as the second current threshold Ici. In one embodiment, the fourth predetermined current threshold / T4 is less than the fifth predetermined current threshold hi. Alternatively, the fourth predetermined current threshold / T4 may be greater than or equal to the fifth predetermined current threshold hi. When the magnitude of the input voltage |Fin| exceeds the first predetermined voltage threshold Ln, and the magnitude of the input current |Zm| exceeds the second current threshold Ici, the controller 106 is configured to turn the second operating phase ON; and when the magnitude of the input current |Zm | falls below the second current threshold Ici or the magnitude of the input voltage | Km| falls below the second predetermined voltage threshold Vn, the controller 106 is configured to turn the second operating phase OFF.

[0055] Figure 2 illustrates a flow chart of an exemplary method 200 for operating a multi-phase power converter incorporating aspects of the disclosed embodiments. The exemplary method 200 is appropriate for operating a power converter apparatus incorporating a multi-phase bridgeless totem-pole PFC power converter topology, such as the power converter apparatus 100 described above. The exemplary method 200 supports a phase shedding technique, where phases are operated on a per cycle bases to reduce switching losses and improve converter efficiency at lower power levels.

[0056] The exemplary method 200 may be advantageously employed in any appropriate power converter configured to receive an AC power and produce a DC power and incorporating at least one fixed phase and at least one operating phase. In one embodiment, the exemplary method 200 may be used with the exemplary power converter apparatus 100 described above, where phases one and two 104a, 104b are fixed phases and phases three and four 104c, 104d are operating phases.

[0057] The exemplary method 200 includes separate paths 256, 258 to handle the positive portion of the AC input cycle and the negative portion of the AC input cycle. The negative path 256, is the same as the positive path 258 with the signs and logic reversed resulting in symmetric operation during the positive and negative portions of the input power cycle.

[0058] During each cycle of the AC input power the method 200 checks the input voltage 202 and when the input voltage is greater than a first voltage threshold Vri both fixed phases are turned on 254. When the input voltage Fin falls below 214 a second predetermined voltage threshold FT? all of the switching phases are turned off 216. Turning off all of the phases means that all operating phases are turned off and all fixed phases are turned off.

[0059] When operating at low power, such as when the output power Pois less than 204 a first predetermined power threshold PTI, and the input current Ln is greater than 206 a first predetermined current threshold In, the first operating phase, is turned on 208. Later, curing the same cycle of the input power, when the input current Ln falls below the first predetermined current threshold In, the first operating phase is turned off 212.

[0060] When operating at moderate power levels, where the output power is between 218 the first predetermined power threshold Pn and the second predetermined power threshold PTI, and the input current Ln is greater than 220 a second predetermined current threshold IT2 the first operating phase is turned on 222. The second operating phase is turned on 226 when the input current Ln is greater than 224 a fourth predetermined current threshold IT4. When, during the same cycle of the input power, the input current Ln falls below 228 the fourth predetermined current threshold IT4, the second operating phase is turned off 230 and when the input current Ln falls below 232 the second predetermined current threshold IT2, the first operating phase is turned off234.

[0061] When operating at high power, such as when the output power Pois greater than or equal to 236 a first predetermined power threshold PTI, the first operating phase is turned on 240 when the input current Ln is greater than 238 a third predetermined current threshold ITS, and the second operating phase is turned on 244 when the input current Ln is greater than 242 a fifth predetermined current threshold ITS. When the input current Ln falls below 246 the fifth predetermined current threshold ITS, the second operating phase is turned off 248 and when the input current Ln falls below 250 the third predetermined current threshold ITS, the first operating phase is turned off 252. The exemplary method 200 allows effective current flowing in each operating phase to be adjusted based on selection of the current thresholds. With appropriate selection of the predetermined voltage and current thresholds, current in each of the operating phases may be reduced to reduce volume of boost inductors associated with each operating phase to be reduced.

[0062] Figure 3 illustrates graphs 300 showing representative operating signals of the exemplary power converter apparatus 100 incorporating aspects of the disclosed embodiments. Graph 314 illustrates AC input voltage Km with time depicted along the horizontal axis 306 increasing to the right, and voltage depicted along the vertical axis 312 increasing upwards. Graph 316 illustrates input current Im with time depicted along the horizontal axis 304 increasing to the right and current in amperes depicted along a vertical axis 310 increasing upwards. Graphs 318, 320 and 322 show the on and off times of a first operating phase 104c, a second operating phase 104d, and a fixed phase 104a respectively, with time depicted along the horizontal axis 302 increasing to the right and the on and off status of each phase depicted along the vertical axis 308 as shown.

[0063] The first graph 314 represents a rated AC input voltage Vm of two hundred twenty volts (220v) with the first predetermined voltage threshold set to twenty-five volts (25 v) and the second predetermined voltage threshold set to fifteen volts (15v). Graph 316 illustrates the AC input current showing the first current threshold set to ten point five amps (10.5 A) and a second predetermined current threshold of thirteen point five amps (13.5A). Graphs 318 and 320 shows how the on and off times of the first and second operating phases respectively are determined based on the AC input current Im and the current thresholds. Graphs 318 and 320 show how the operating phases are periodically turned on and off during each cycle of the input current. Graph 322 illustrates a fixed phase in an embodiment where the fixed phase is turned off during low voltage portions of the AC input voltage Vm.

[0064] Figure 4 illustrates a pictorial diagram of an exemplary set of boost inductor cores 400 incorporating aspects of the disclosed embodiments. The exemplary boost inductor cores 400 are appropriate for use in a multiphase power converter apparatus, such as the four phase power converter apparatus 100 described above and with reference to Figure 1. As discussed above, effective current flowing through each operating phase 104c, 104d may be reduced through selection of the current thresholds Zci, Zc2 used by the controller 106. Thus, the first two cores 402, 404 are full size cores and correspond to fixed phases 104a, 104b configured to carry a full rated current, and the second two cores 406, 408 are reduced size cores corresponding to operating phases 104c, 104d configured to carry a reduced effective current. Lowering the effective current in each operating phase 104c, 104d allows a smaller boost inductor core to be used in each operating phase, thereby reducing the overall power density of the converter.

[0065] Inductor cores 402, 404 for the two fixed phases are the same size: twenty-four millimetres (24mm) high and twenty point 3 millimetres (20.3mm) wide, and have the same window size 410, 412 of fifteen point two (15.2mm) by four point two five millimetres (4.25mm). The third 406 and fourth 408 inductor core correspond to operating phases configured to carry a reduced effective current. The lower current allows use of smaller inductor cores 406, 408 with smaller window sizes 414, 416 in each operating phase. To maintain the same inductance, the affective core area and number of winding turns remains the same among all four boost inductors 402, 404, 406, 408. However, because the effective current is reduced in the operating phases, the inductor volume of boost inductors corresponding to these operating phases may be reduced by reducing the number of Litz wire strands used in the smaller cores 406, 408. In the example illustrated in Figure 4, inductor volume is reduced by twenty six percent (26%) as compared to conventional phase shedding solutions.

[0066] Figure 5 illustrates a block diagram of an exemplary controller 500 incorporating aspects of the disclosed embodiments. The exemplary controller 500 is appropriate for operating a multiphase totem-pole bridgeless PFC power converter apparatus, such as the power converter apparatus 100 described above and with reference to Figure 1. In the illustrated controller 500 each phase of the power converter, such as phase 104a, 104b, 104c, and 104d is represented as a block 514, 524, 526, and 528 respectively and is driven by a corresponding pulse width modulated (PWM) switching signal generator 512, 522, 546, 548. An error signal 542 is created by comparing 502, or subtracting, a reference signal Vref and the converter output Vo. Loop compensation is provided by applying a control algorithm 504 to the error signal 542. Any suitable control algorithm may be advantageously employed as the loop compensation 504, such as a proportional plus integral (PI) control algorithm. When desired, signal limiting 506 and scaling 508 may be applied to generate the control signal 550. A zero-voltage switching signal 516 may be added 510 to the control signal 550 to generate a switching control signal 544 configured to drive each PWM signal generator 512, 522, 546, 548.

[0067] In low power conditions, only two phases 514 524 are operating and the other two phases 516, 528 are turned off. A phase 1 - 2 ref signal, which is shifted one hundred eighty degrees (180°) from the phase 1 reference signal Vref, is compared 530 with the phase two output 522 to create a phase 2 error signal 554. When desired the phase 2 error signal 554 may be scaled 518 and limited 530 then added 520 to the phase 1 switch control signal 544 to create a phase 2 switch control signal 532.

[0068] As power output of the converter increases, it becomes desirable to use three phases to produce the additional power. When three phases 514, 524, 526 are operating, a control signal to drive the phase 3 PWM is generated in a similar fashion to generation of the phase 2 PWM control signal 532. When three phases 514, 524, 526 are operating, three reference signals spaced one hundred twenty degrees (120°) apart are used and when all four phases 514, 524, 526, 528 are operating four reference signals spaced ninety degrees (90°) apart are used.

[0069] Figure 6 illustrates graphs showing efficiency improvements obtained by the exemplary power converter apparatus incorporating aspects of the disclosed embodiments. Simulations of a four-phase totem-pole bridgeless PFC AC-DC converter, such as the exemplary power converter apparatus 100 described above and with reference to Figure 1, were used to generate graphs of converter efficiency. In the graphs 600 converter output is depicted along the horizontal axis 602 increasing to the right, and converter efficiency is depicted along a vertical axis 604 increasing upwards. The first graph 606 was created using the herein disclosed improved phase shedding techniques, such as the method 200 described above and with reference to Figure 2. For comparison purposes, the second graph 608 illustrates converter efficiency obtained using conventional phase shedding techniques.

[0070] Figure 7 illustrates graphs 700 showing performance of a power converter apparatus incorporating aspects of the disclosed embodiments. Graphs 700 show total harmonic distortion 710 and power factor 708 achieved by a four-phase totem-pole bridgeless PFC AC-DC converter, such as the exemplary power converter apparatus 100 described above, when operated using the herein disclosed phase shedding methodologies described above and with reference to Figure 1 and Figure 2. In the graphs 700 converter output power is depicted along a horizontal axis 702 increasing to the right. Total harmonic distortion (THDi) is depicted along a first vertical axis 704 increasing upwards, and power factor is depicted along a second horizontal axis 706 increasing upwards.

[0071] Thus, while there have been shown, described, and pointed out, fundamental novel features of the invention as applied to the exemplary embodiments thereof, it will be understood that various omissions, substitutions and changes in the form and details of devices and methods illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the presently disclosed invention. Further, it is expressly intended that all combinations of those elements, which perform substantially the same function in substantially the same way to achieve the same results, are within the scope of the invention. Moreover, it should be recognized that structures and / or elements shown and / or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMS1. A power converter apparatus (100) comprising: a bridgeless rectifier stage (102) configured to receive an AC input voltage(Lin) and produce a DC output voltage (Co); a plurality of switching phases (104) configured to receive the AC input voltage (Liii) and deliver a power factor corrected AC power to the DC output voltage (Co); and a controller (106) configured to operate the plurality of switching phases (104), wherein the plurality of switching phases (104) comprises at least one fixed phase (104a, 104b) configured to remain on while the converter (100) is producing the DC output voltage (Co), and at least one operating phase (104c, 104d) configured to be on during a first portion of a line frequency cycle and off during a second portion of the line frequency cycle, wherein the controller (106) is further configured to: when a magnitude (| Cin|) of the input voltage (Cin) exceeds a first predetermined voltage threshold (CTI) and a magnitude (|Zin|) of an input current exceeds a first current threshold (Zci), a first operating phase (104d) in the at least one operating phase (104c, 104d) is turned on (114); and when the magnitude (|Zin|) of the input current (Ln) falls below the first current threshold (ZTI) or the magnitude (| Cin|) of the AC input voltage (Cin) falls below a second predetermined voltage threshold (CTI), the first operating phase (104d) is turned (118) off.

2. The power converter apparatus (100) according to claim 1, wherein each switching phase (104a, 104b, 104c, 104d) in the plurality of switching phases (104) comprises an upper switching device (Si, Sa, Sa, ST) and a lower switch switching device (Sa, ST, Se, Ss) coupled in series across the DC output voltage (Co) and forming a midpoint (122, 124, 126, 128) between the upper switching device (Si, Sa, Sa, ST) and the lower switching device (Sa, ST, Se, Ss), and a boost inductor ( Li, La, La, LT) coupled between the AC input voltage (Cin) and the midpoint (122, 124, 126, 128), and wherein the controller (106) is configured to: when the switching phase is on, operate the switching phase to provide power factor correction and transfer power from the AC input voltage ( in) to the DC output voltage (Co); and when the switching phase is off, turn both the upper switching device and the lower switching device off.

3. The power converter apparatus (100) according to any one of the preceding claims, wherein the controller is configured to select the first current threshold (Zci) from a plurality of predetermined current thresholds (ZTI, ZTI, Zra) based at least in part on one of the output power (Po) and an rms input current (Zin _RMS).

4. The power converter apparatus (100) according to any one of the preceding claims, wherein the controller (106) is configured to: when the output power (Po) is less than a first predetermined power threshold (PTI), select (110) a first predetermined current threshold (ZTI) as the first current threshold (Zci), and when the output power (Po) is not less than the first predetermined power threshold (PTI) and is less than a second predetermined power threshold (PTT), select (110) a second predetermined current threshold (ZTT) as the first current threshold (Zci), and when the output power (Po) is not less than the second predetermined power threshold (PTT), select (110) a third predetermined current threshold (ZTS) as the first current threshold (Zci), wherein the first predetermined current threshold (ZTI) is less than the second predetermined current threshold (ZTT) and the second predetermined current threshold (ZTT) is less than the third predetermined current threshold (ZTS).

5. The power converter apparatus (100) according to any one of the preceding claims, wherein the at least one operating phase(104c, 104d) comprises a second operating phase (104c), and the controller (106) is configured to: when the output power (Po) is less than a first predetermined power threshold (PTI), turn the second operating phase (104c) off;when the output power (Po) is greater than or equal to the first predetermined power threshold (PTI) and is less than the second predetermined power threshold (PT?) select a fourth predetermined current threshold ( / TT) as a second current threshold (la), when the output power (Po) is greater than or equal to the second predetermined power threshold (PT?) select a fifth predetermined current threshold ITS as the second current threshold (7c?), wherein the fourth predetermined current threshold ( / TT) is less than the fifth predetermined current threshold (ITS)', when the magnitude (| J n|) of the input voltage (Pin) exceeds the first predetermined voltage threshold ( TI), and the magnitude (|Zin|) of the input current ( / in) exceeds the second current threshold (la), turn the second operating phase (104c) ON; and when the magnitude (|Zin|) of the input current ( / in) falls below the second current threshold (la) or the magnitude (|Pin|) of the input voltage (Pin) falls below the second predetermined voltage threshold (Pr?), turn the second operating phase (104c) OFF.

6. The power converter apparatus (100) according to any one of the preceding claims, wherein first predetermined voltage threshold (VTI) is greater than the second predetermined voltage threshold (VT?).

7. The power converter apparatus (100) according to any one of the preceding claims, wherein the first predetermined voltage threshold ( TI) and the second predetermined voltage threshold (Pr?) are proportional to a rated voltage of the power converter (100).

8. The power converter apparatus (100) according to any one of the preceding claims, wherein when the magnitude (| Pin|) of the input voltage (Pin) exceeds the first predetermined voltage threshold (PTI), turn the at least one fixed phase on, and when the magnitude (| Pin|) of the input voltage (Pin) falls below the second predetermined voltage threshold (Pr?), turn the at least one fixed phase off.

9. The power converter apparatus (100) according to any one of the preceding claims, wherein a boost inductor (406, 408) associated with an operating phase (104c, 104d) comprises less volume than a boost inductor (402, 404) associated with a fixed phase(104a) in the at least one fixed phase (104a, 104b).

10. A method (200) for operating a multi-phase bridgeless totem-pole PFC power converter, wherein the power converter comprises at least one fixed phase and a first operating phase, the method (200) comprising: turning on (254) the at least one fixed phase when an input voltage (Pin) is greater than (202) a first predetermined voltage threshold (PTI), turning on (208) the first operating phase when the input voltage (Pin) is greater than (202) the first predetermined voltage threshold (VTI), an output power (Po) is less than (204) a first predetermined power threshold (PTI), and an input current (Iin) is greater than (206) a first predetermined current threshold (ITI), and when the input current (Iin) falls below (210) the first predetermined current threshold (ITI), turn the first operating phase off (212); when the input voltage (Pin) falls below (214) a second predetermined voltage threshold (VT?) turn all phases off (216).

11. The method (200) according to claim 10, wherein the first predetermined current threshold (ITI) is determined based at least in part on the first predetermined power threshold (PTI).

12. The method (200) according to claim 10 or 11, wherein the power converter comprises a second operating phase and the method further comprises:

13. The method (200) according to any one of claims 10 through 12, wherein the fourth predetermined current threshold (ITT) is greater than the second predetermined current threshold (ITI), and the fifth predetermined current threshold (ITS) is greater than the third predetermined current threshold (ITS).

14. The method (200) according to any one of claims 10 through 13, wherein the first predetermined voltage threshold (VTI) is greater than the second predetermined voltage threshold (VTI).

15. The method (200) according to any one of claims 10 through 14, wherein the second predetermined current threshold (ITI), the third predetermined current threshold (ITS), the fourth predetermined current threshold (ITT), and the fifth predetermined current threshold (ITS) are determined based at least in part on the first predetermined power threshold (PTI) and the second predetermined power threshold (PTI).

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