Variable frequency resonant three-phase power factor correction converter

Abstract

The present application provides a variable frequency resonant three-phase power factor correction converter, including: an input filter, including three inductors and three capacitors, for filtering the three-phase input voltage; three input inductors, respectively receiving the filtered three-phase input voltage; a three-phase rectifier bridge, respectively receiving the output of the three input inductors; a switch component, including a first switch and a second switch coupled to both ends of the three-phase rectifier bridge and connected in series; an output capacitor, which is connected in parallel to both ends of the three-phase rectifier bridge; a resonant capacitor, one end of which is connected to a node between the first switch and the second switch, and the other end is connected to a neutral line; a variable frequency control circuit, which is connected to both ends of the output capacitor, detects the differential voltage at both ends of the output capacitor and controls the conduction and disconnection of the first switch and the second switch according to the differential voltage. The present application can eliminate the third harmonic current and reduce the THD to below 3%.

Description

Technical Field

[0001] The invention belongs to the technical field of three-phase power factor correction converters, and more specifically relates to a variable frequency resonant three-phase power factor correction converter. Background Art

[0002] A power factor correction converter (PFC) is a power conversion device that converts single-phase or three-phase AC voltage into DC voltage while achieving an ideal power factor close to 1 (PF=1) to reduce the reactive current and total harmonic current (THD) of the power grid and achieve friendly intervention of electrical equipment in the power grid.

[0003] For three-phase power factor correction converters, there are many circuit topologies for active power factor converters characterized by high-frequency switching. The three-phase current and the corresponding three-phase voltage are strictly proportional to each other through precise control of the three-phase input current, that is, a purely resistive input characteristic is achieved, and the power factor is close to 1. According to the waveform characteristics of the input current, the three-phase power factor correction can be divided into continuous current type and discontinuous current type. The continuous current topology includes a three-phase six-switch bridge circuit, a three-phase Vienna rectifier circuit, etc. The characteristic of this type of circuit is that the three-phase current is regulated as three independent variables. Usually, a dedicated analog chip or a high-speed numerical processor (DSP) is used for multi-variable PWM control, which can achieve a power factor of >0.99 and a THD index of <5%. The control algorithm of this type of circuit is often complex, the circuit cost is relatively high, and it is generally hard-switched, so the operating frequency of the converter cannot be too high, and it is only suitable for high-power applications. Especially for three-phase AC above 400Hz, the processing speed of DSP often cannot meet the requirements, and it is difficult to achieve a low THD index; the discontinuous current type topology has single switch or double switch circuit types, generally using the characteristic that the peak current of the inductor is proportional to the voltage, so that the input current is naturally proportional to the input voltage. No complex algorithm is required, only appropriate frequency conversion control is needed to obtain a power factor of 0.95 to 0.98, but the THD of this type of circuit is relatively high, usually reaching 10 to 20%. The main reason is that this type of circuit cannot solve the problem of third current harmonics. The third current harmonics are the main component of the THD index. Reducing the third current harmonics can reduce the THD value. The limit values ​​of each current harmonic are clearly specified in the test standard of GJB-151B CE101. Therefore, we expect a circuit topology with a simple circuit structure and simple control logic, but can obtain a high power factor and low THD.

[0004] Another problem with three-phase power factor correction converters is efficiency and power density. The continuous current three-phase power factor correction circuit is a hard switching working mode. The existence of switching loss hinders the increase of the converter switching frequency. Generally, it can only work in the frequency range of <100KHz. The volume of magnetic components is large, which hinders the improvement of the power density of the power supply system. With the development of wide bandgap semiconductor devices, such as the maturity of SiC and GaN switch components, the demand for high-frequency converters is becoming more and more urgent. The circuit topology of soft switching can eliminate switching losses and the operating frequency can be increased to hundreds of KHz. Variable frequency resonant circuits can usually realize soft switching working conditions, reduce the loss of switch components, and reduce the volume and weight of magnetic components. Summary of the invention

[0005] The object of the present invention is to provide a variable frequency resonant three-phase power factor correction converter, which eliminates the third harmonic current and reduces the THD to below 3%.

[0006] The present application discloses a variable frequency resonant three-phase power factor correction converter, comprising:

[0007] An input filter, wherein the input filter comprises three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase four-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the zero line of the three-phase input voltage is connected to the other ends of the three capacitors, and the input filter filters the three-phase input voltage;

[0008] Three input inductors, the three input inductors respectively receiving filtered three-phase input voltages;

[0009] A three-phase rectifier bridge, wherein the three-phase rectifier bridge receives outputs of the three input inductors respectively;

[0010] A switch assembly, the switch assembly comprising a first switch and a second switch coupled to both ends of the three-phase rectifier bridge and connected in series;

[0011] An output capacitor, the output capacitor is connected in parallel to two ends of the three-phase rectifier bridge and connected to two ends of the load;

[0012] a resonant capacitor, one end of which is connected to a node between the first switch and the second switch, and the other end of which is connected to the neutral line; and

[0013] A frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch and the second switch according to the differential voltage, wherein the first switch and the second switch are alternately turned on.

[0014] Optionally, the three-phase rectifier bridge includes first to sixth diodes, the first diode and the fourth diode are connected in series at both ends of the switch component, the second diode and the fifth diode are connected in series at both ends of the switch component, the third diode and the sixth diode are connected in series at both ends of the switch component, and the outputs of the three input inductors are respectively connected to the node between the first diode and the fourth diode, the node between the second diode and the fifth diode, and the node between the third diode and the sixth diode.

[0015] Optionally, fs_min is the lowest operating frequency of the correction converter, and fo is the resonant frequency of one of the three input inductors connected in series with the resonant capacitor, wherein fs_min=(1.5-5)*fo.

[0016] Optionally, the frequency conversion control circuit includes a differential amplifier, a proportional integration circuit, a voltage-controlled oscillator and a dead zone setting circuit connected in series in sequence, the differential amplifier is respectively connected to the two ends of the load and generates a differential voltage, the proportional integration circuit compares the differential voltage with a reference voltage and generates a feedback control voltage, the voltage-controlled oscillator generates an oscillation frequency according to the feedback control voltage, and the dead zone setting circuit outputs a first control signal to the first switch and a second control signal to the second switch according to the oscillation frequency.

[0017] The present application also discloses a variable frequency resonant three-phase power factor correction converter comprising:

[0018] An input filter, the input filter comprising three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase three-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the other ends of the three capacitors provide a virtual midpoint, and the input filter filters the three-phase input voltage;

[0019] Three input inductors, the three input inductors respectively receiving filtered three-phase input voltages;

[0020] A three-phase rectifier bridge, wherein the three-phase rectifier bridge receives outputs of the three input inductors respectively;

[0021] A switch assembly, the switch assembly comprising a first switch and a second switch connected in series at two ends of the three-phase rectifier bridge;

[0022] An output capacitor, the output capacitor is connected in series to two ends of the three-phase rectifier bridge and connected to two ends of a load;

[0023] a resonant capacitor, one end of which is connected between the first switch and the second switch, and the other end of which is connected to the virtual midpoint; and

[0024] A frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch and the second switch according to the differential voltage, wherein the first switch and the second switch are alternately turned on.

[0025] Optionally, fs_min is the minimum operating frequency of the correction converter, and fo is the resonant frequency of a capacitor in which one of the three-phase input inductors is connected in parallel with the three capacitors of the input filter and then in series with the resonant capacitor, wherein fs_min=(1.5~5)*fo.

[0026] Optionally, it also includes: a common-mode inductor and two common-mode capacitors connected in series, wherein the two input ends of the common-mode inductor are connected to the two ends of the three-phase rectifier bridge, the two output ends are connected to the two ends of the load, the two common-mode capacitors are connected to the two ends of the load, and the node between the two common-mode capacitors is connected to the virtual midpoint.

[0027] The present application also discloses a variable frequency resonant three-phase power factor correction converter comprising:

[0028] An input filter, the input filter comprising three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase three-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the other ends of the three capacitors provide a virtual midpoint, and the input filter filters the three-phase input voltage;

[0029] Three first input inductors and three second input inductors, the three first input inductors respectively receiving filtered three-phase input voltages, and the three second input inductors respectively receiving filtered three-phase input voltages;

[0030] A first three-phase rectifier bridge and a second three-phase rectifier bridge, wherein the first three-phase rectifier bridge receives outputs of the three first input inductors respectively, and the second three-phase rectifier bridge receives outputs of the three second input inductors respectively;

[0031] A first switch assembly and a second switch assembly, wherein the first switch assembly includes a first switch and a second switch connected in series at both ends of the first three-phase rectifier bridge, and the second switch assembly includes a third switch and a fourth switch connected in series at both ends of the second three-phase rectifier bridge;

[0032] a first output capacitor and a second output capacitor, wherein the first output capacitor is connected in series to two ends of the first three-phase rectifier bridge and connected to two ends of a load, and the second output capacitor is connected in series to two ends of the second three-phase rectifier bridge and connected to two ends of the load;

[0033] a first resonant capacitor and a second resonant capacitor, wherein one end of the first resonant capacitor is connected between the first switch and the second switch, and the other end is connected to the virtual midpoint; one end of the second resonant capacitor is connected between the third switch and the fourth switch, and the other end is connected to the virtual midpoint; and

[0034] A frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch, the second switch, the third switch and the fourth switch according to the differential voltage.

[0035] Optionally, it also includes: a first common-mode inductor, a second common-mode inductor, two first common-mode capacitors connected in series, and two second common-mode capacitors connected in series; the two input ends of the first common-mode inductor are connected to the two ends of the first three-phase rectifier bridge, and the two output ends are connected to the two ends of the load; the two input ends of the second common-mode inductor are connected to the two ends of the second three-phase rectifier bridge, and the two output ends are connected to the two ends of the load; the two first common-mode capacitors are connected to the two ends of the load, and the node between the two first common-mode capacitors is connected to the virtual midpoint; the two second common-mode capacitors are connected to the two ends of the load, and the node between the two second common-mode capacitors is connected to the virtual midpoint.

[0036] Optionally, the first switch and the second switch are alternately turned on, the first switch and the third switch are alternately turned on, the second switch and the fourth switch are alternately turned on, and the third switch and the fourth switch are alternately turned on, or: the first switch and the second switch are alternately turned on, and the third switch and the fourth switch are turned off, or: the first switch and the second switch are turned off, and the third switch and the fourth switch are alternately turned on.

[0037] Compared with the prior art, the method of the present application has the following beneficial effects:

[0038] The variable frequency resonant three-phase power factor correction converter of this application introduces a resonant circuit based on the dual-switch discontinuous current topology, realizes power regulation by frequency conversion, eliminates the third harmonic current, reduces THD to below 3%, and can achieve zero voltage soft switching conditions within the range of frequency conversion operation. The operating frequency can reach 200kHz-800kHz, and can achieve a conversion efficiency of >97% under the condition of 380V AC input. Further combined with the two-way staggered parallel layout, the high-frequency ripple current at the input and output ends is offset, the pressure on the front-stage EMI filter and the rear-stage high-frequency filter capacitor is reduced, and the purpose of high frequency and high power density of the power supply system is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. 4 is a circuit diagram of a three-phase four-wire input in the first embodiment of the present invention.

[0040] Figure 2 1 is an equivalent circuit diagram of two working modes of the first embodiment of the present invention.

[0041] Figure 3 FIG. 1 is a working waveform diagram of a high frequency switch according to the first embodiment of the present invention.

[0042] Figure 4 1 is a waveform diagram of the power frequency voltage and current of the first embodiment of the present invention.

[0043] Figure 5 4 is a circuit diagram of a three-phase three-wire input in the second embodiment of the present invention.

[0044] Figure 6 is a circuit diagram with an output common-mode inductor in the third embodiment of the present invention.

[0045] Figure 7 FIG. 4 is a circuit diagram of two paths connected in parallel in a fourth embodiment of the present invention.

[0046] Figure 8 This is a frequency conversion control circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0048] Please refer to Figure 1 The variable frequency resonant three-phase power factor correction converter of the first embodiment of the present invention includes: an input filter, a group of input inductors, a three-phase rectifier bridge, a switch component, an output capacitor, a resonant capacitor and a variable frequency control circuit.

[0049] The input filter is composed of three inductors Lin and three capacitors Cin, which filter the three-phase input voltages VA, VB, and VC respectively. The three-phase AC input voltages VA, VB, and VC adopt a three-phase four-wire system. The three-phase input voltages VA, VB, and VC are connected to the three inductors Lin respectively, and the other ends of the three inductors Lin are connected to one end of the three capacitors Cin and the three input inductors LA, LB, and LC respectively, and the neutral line N is connected to the other end of the three capacitors Cin (or called the midpoint N).

[0050] The three input inductors LA, LB, and LC are connected to the filtered three-phase input voltage. In general, the three-phase voltage is balanced, that is:

[0051] |VA|=|VB|=|VC|

[0052] The three input inductors should also have the same value, namely:

[0053] LA=LB=LC

[0054] The three-phase rectifier bridge is composed of a group of first to sixth rectifier diodes D1, D2, D3, D4, D5, and D6. The first diode D1 and the fourth diode D4 are connected in series at both ends of the switch component, the second diode D2 and the fifth diode D5 are connected in series at both ends of the switch component, and the third diode D3 and the sixth diode D6 are connected in series at both ends of the switch component. The outputs of the three input inductors LA, LB, and LC are respectively connected to the node between the first diode D1 and the fourth diode D3, the node between the second diode D2 and the fourth diode D4, and the node between the third diode D3 and the sixth diode D6. The output of the three-phase rectifier bridge is connected to the output capacitor Co, providing the first output port Vo+ and the second output Vo- for the load.

[0055] A set of switch components includes a first switch S1 and a second switch S2, which are connected in series to the output ends of the three-phase rectifier bridge and are respectively controlled by a first control signal G1 and a second control signal G2, so that the first switch S1 and the second switch S2 are alternately turned on. In this embodiment, the switches S1 and S2 are implemented by switch MOS transistors, the first control signal G1 controls the gate of the switch S1, and the second control signal G2 controls the gate of the switch S2.

[0056] One end of the resonant capacitor Cp is connected to the midpoint of the first switch S1 and the second switch S2 connected in series, and the other end is connected to the midpoint N of the output capacitor Cin.

[0057] The frequency conversion control circuit is connected to both ends of the output capacitor Co, detects the differential signal of the output voltage Vo+ and Vo-, and provides a set of control signals G1 and G2 to control the alternating on and off of the switch components S1 and S2. The frequency of G1 and G2 changes with different working states to achieve the function of stabilizing the output voltage and adjusting the output power.

[0058] In order to explain the working principle of the first embodiment in detail, a working cycle of the switch component is divided into two working modes: the upper half cycle MODE 1 and the lower half cycle MODE 2. Figure 2 The waveforms of the current and voltage of the key parts of the correction converter are expressed in the form of an equivalent circuit. Figure 3 be expressed in.

[0059] Please refer to Figure 2 and Figure 3 , control signals G1 and G2 are complementary square wave signals with a fixed duty cycle close to 50%. Control signals G1 and G2 are set with a certain dead zone to avoid switches S1 and S2 being turned on at the same time. In a balanced state, the instantaneous values ​​of the three-phase alternating current are balanced with each other, and there is the following relationship:

[0060] VA+VB+VC=0

[0061] In order to analyze the working waveform conveniently, one of the moments is selected, VA>0, VB<0, VC<0, and because the switching cycle is much longer than the power frequency cycle, the voltage amplitudes of VA, VB, and VC remain basically unchanged within a switching cycle. Figure 3 In other time periods of the power frequency cycle, the current and voltage waveforms have similar analysis results.

[0062] In the first half cycle of the switching frequency, MODE 1, G1 is high, G2 is low, S1 is on, S2 is off, and the forward voltage of the VA phase is applied to LA, forming a loop through S1 and Cp. At this time, the voltage applied to both ends of LA is VA-Vcp, and the current Ia in LA increases at a nearly linear slope and reaches the maximum value before S1 is turned off.

[0063] In the second half cycle MODE 2 of the switching frequency, G1 is low, G2 is high, S1 is off, S2 is on, and the current Ia in LA continues to flow to Co and the load, and returns to S2 through Vo-, and returns to the resonant capacitor Cp through the body diode of S2. At this time, the voltage applied to both ends of LA is VA-Vcp-Vo (where Vo is the difference between Vo+ and Vo-, representing the absolute value of the output voltage). The current in LA decreases linearly, and the appropriate value of LA is selected so that the current returns to zero in the second half cycle, that is, it works in the discontinuous mode state. After S1 is turned off, G2 becomes high after a dead time. Since the body diode of S2 is turned on at this time, S2 is in a zero voltage turn-on state and there is no turn-on loss.

[0064] Since the circuit is symmetrical about the polarity of input and output, the working state of VA in the first half cycle is equivalent to the working state of VB and VC in the second half cycle, and the working state of VA in the second half cycle is equivalent to the working state of VB and VC in the first half cycle. Figure 3 As shown, in the second half cycle MODE 2, S1 is turned off, S2 is turned on, and the voltages of VB and VC are applied to LB and LC, causing Ib and Ic to increase in the negative direction and reach the maximum negative value before S2 is turned off, and the amplitude is proportional to the amplitude of VB and VC. In the first half cycle MODE 1, S1 is turned on, S2 is turned off, the output voltage Vo intervenes in the current loop, and the amplitude of Ib and Ic gradually decreases to zero.

[0065] From the above analysis, it can be seen that the three-phase current Ia, Ib, Ic only depends on the voltage of the phase, and has nothing to do with the other two phases. The working process of the three phases is almost independent, except that the current will pass through the resonant capacitor Cp, forming a resonant voltage Vcp on Cp, which will affect the working process of the three phases. If Cp does not exist or Cp is very large, Vcp can be ignored, and the three-phase work is completely decoupled. If Cp intervenes and Vcp has a certain value, Vcp will affect the three-phase current, and the influence of Vcp can be used to eliminate the third harmonic in the three-phase current.

[0066] Please refer to Figure 4, since the three-phase operation is decoupled, we only consider the case of VA and Ia. In a power frequency cycle, Ia reaches a maximum value in each switching cycle, and then returns to zero. Its maximum value is proportional to Va-Vcp. If Vcp is very small, the peak value of Ia is almost proportional to the amplitude of VA, and the average value of Ia is also almost proportional to the amplitude of VA. At this time, the power factor of phase A is close to 1, but there will be a third harmonic component in the Ia current. In some simple three-phase power factor correction topologies, there is a similar working process, but without the existence of Cp, there will be a relatively high third harmonic component in the input current, making it difficult to achieve THD below 10%. Cp is added to our topology, and the three-phase current will flow through Cp. The three-phase current forms a superposition relationship on Cp, and Vcp will contain the third voltage harmonic component, that is, the waveform of Vcp is the superposition of the switching cycle waveform and the third harmonic of the power frequency. Appropriately reduce the value of Cp and make the amplitude of the switching frequency voltage component larger than the amplitude of the third harmonic component of the power frequency. Then the third current harmonic component in Ia will be offset. At this time, Ia will be close to a standard sine wave and THD can be below 3%.

[0067] Another function of capacitor Cp is its resonance. From the above analysis, it can be seen that the position of Cp is in the current loop of Ia, that is, Cp and LA are in a series resonant relationship. The resonant frequency of Cp-LA is selected to be slightly lower than the lowest operating frequency of the converter. When the input voltage is low, the feedback loop will lower the operating frequency to increase the output power. At this time, the operating frequency is close to the resonant frequency of Cp-LA, and the series resonant loop resonates, the current of Ia is increased, and the output power increases. In fact, due to the existence of this resonant relationship, the operating frequency does not need to be reduced too low to achieve the effect of increasing the output power, that is, the existence of Cp reduces the variation range of the converter operating frequency, making the design of the inductor and switch components in the circuit easier, and the working state of the circuit is in a better state. In actual cases, the frequency variation range is reduced by 30-40%, the volume of LA, LB, and LC can be reduced by 20-30%, and the conduction loss of S1 and S2 can be reduced by 10-20%. The size of Cp can be adjusted in the actual circuit to achieve the best working state.

[0068] The selection of Cp is a key factor in the circuit topology. In fact, since the three-phase currents all flow through Cp, the resonant relationship between Cp and LA is actually the resonant relationship after the three input inductors are connected in parallel, that is:

[0069]

[0070] Among them, fs_min is the minimum frequency of the converter, and fo is the resonant frequency of LA-Cp. Considering the error of circuit parameters and the need to avoid the circuit working in a resonant state and generating too high voltage stress, fs_min = (1.5 ~ 5) * fo is generally a more realistic choice.

[0071] Figure 5 This is a variable frequency resonant three-phase power factor correction converter of the second embodiment of the present invention, which is different from the first embodiment in that: the three-phase input voltage of this embodiment adopts a three-phase three-wire AC input, and the access of the neutral line is not required. Only a virtual midpoint VN needs to be provided by the output capacitor Cin. Specifically, the three voltage lines of the three-phase input voltages VA, VB, and VC are respectively connected to three inductors LA, LB, and LC, and the other ends of the three inductors LA, LB, and LC are respectively connected to three capacitors Cin, and the other ends of the three capacitors Cin provide a virtual midpoint VN. One end of the resonant capacitor Cp is connected to this virtual midpoint VN, which can achieve the same effect of eliminating the third harmonic current as in the first embodiment. The difference is that not only Cp participates in the resonance relationship of LA-Cp, but the capacitance value of the three Cin connected in parallel and then in series with Cp participates in the resonance. The selection of Cin first satisfies the effect of input filtering, that is, reducing the high-frequency switching current at the input end. Generally, Cp should take a larger value to meet the following conditions after Cin is added:

[0072]

[0073] Among them, fs_min is the minimum operating frequency of the converter, fo is the resonant frequency of the capacitance (LA-Cp||3Cin) of LA in parallel with three Cin and in series with Cp, 3Cin||Cp represents the capacitance value of 3 Cin in parallel and in series with Cp, generally fs_min=(1.5~5)*fo.

[0074] Figure 6 The third embodiment of the present invention is a variable frequency resonant three-phase power factor correction converter. Figure 5 The improvement of the embodiment shown, wherein a first-stage common-mode filter circuit is added on the output side, including a common-mode inductor Lm and two common-mode capacitors Cm connected in series, the two input ends of the common-mode inductor Lm are connected to the two ends of the three-phase rectifier bridge, the two output ends are connected to the two ends of the load, and the output voltages Vo+ and Vo- are provided, the two common-mode capacitors Cm are connected to the two ends of the load, and the common node between the two common-mode capacitors Cm is connected to the virtual midpoint VN. The purpose of this circuit is to reduce the common-mode voltage of the output terminals Vo+ and Vo- relative to the AC input terminal, so that the potentials of Vo+ and Vo- relative to the input neutral line and the protective ground line PE are relatively stable, and the common-mode current of the system is reduced.

[0075] Figure 7The variable frequency resonant three-phase power factor correction converter of the fourth embodiment of the present invention comprises: an input filter, three first input inductors LA, LB, LC, three second input inductors LA1, LB1, LC1, a first three-phase rectifier bridge, a second three-phase rectifier bridge, a first switch component, a second switch component, a first output capacitor Co, a second output capacitor Co1, a first resonant capacitor Cp, a second resonant capacitor Cp1, and a variable frequency control circuit. The input filter comprises three inductors (not shown in the figure) and three capacitors Cin. The three-phase input voltages VA, VB, and VC adopt a three-phase three-wire system, and the three capacitors Cin provide a virtual midpoint VN. The three first input inductors LA, LB, and LC respectively receive the filtered three-phase input voltages, and the three second input inductors LA1, LB1, and LC1 respectively receive the filtered three-phase input voltages. The first three-phase rectifier bridge receives the outputs of the three first input inductors LA, LB, and LC respectively, and the second three-phase rectifier bridge receives the outputs of the three second input inductors LA1, LB1, and LC1 respectively. The first three-phase rectifier bridge includes six diodes D1-D6, and the second three-phase rectifier bridge includes six diodes D11-D61. Figure 1 Similarly, no further description is given here. The first switch assembly includes a first switch S1 and a second switch S2 connected in series at both ends of the first three-phase rectifier bridge, and the second switch assembly includes a third switch S11 and a fourth switch S21 connected in series at both ends of the second three-phase rectifier bridge. The first output capacitor Co is connected in series at both ends of the first three-phase rectifier bridge and connected to both ends of the load, and the second output capacitor Co1 is connected in series at both ends of the second three-phase rectifier bridge and connected to both ends of the load. One end of the first resonant capacitor Cp is connected between the first switch S1 and the second switch S2, and the other end is connected to the virtual midpoint VN. One end of the second resonant capacitor Cp1 is connected between the third switch S11 and the fourth switch S12, and the other end is connected to the virtual midpoint VN. The frequency conversion control circuit is connected to both ends of the load, detects the differential voltage of the load and provides control signals G1, G2, G11, G21 according to the differential voltage, and controls the conduction and disconnection of the first switch S1, the second switch S2, the third switch S11 and the fourth switch S12 respectively. The first switch S1 and the second switch S2 are turned on alternately, the first switch S1 and the third switch S11 are turned on alternately, and the second switch S2 and the fourth switch S21 are turned on alternately.

[0076] The correction converter of this embodiment also includes: a first common-mode inductor Lm, a second common-mode inductor Lm1, two first common-mode capacitors Cm connected in series, and two second common-mode capacitors Cm1 connected in series. The two input ends of the first common-mode inductor Lm are connected to the two ends of the first three-phase rectifier bridge, and the two output ends are connected to the two ends of the load. The two input ends of the second common-mode inductor Lm1 are connected to the two ends of the second three-phase rectifier bridge, and the two output ends are connected to the two ends of the load. The two first common-mode capacitors Cm are connected to the two ends of the load, and the node between the two first common-mode capacitors Cm is connected to the virtual midpoint VN. The two second common-mode capacitors Cm1 are connected to the two ends of the load, and the node between the two second common-mode capacitors Cm is connected to the virtual midpoint VN.

[0077] In order to reduce the high-frequency switching current at the input and output sides, the present embodiment can use two basic converters in parallel and make the switching frequency phase difference 180°, so that the high-frequency ripple current at the input and output will be greatly reduced, thereby reducing the pressure on the input and output filters and obtaining a better electromagnetic compatibility effect. Figure 7 As shown, in the case of three-phase three-wire input, a group of input capacitors Cin can be shared to provide a virtual midpoint VN for two groups of converters. At the same time, since the control signals of each group of converters are complementary signals with a 50% duty cycle, it is only necessary to exchange the control signals G1 and G2 of the first group to provide control signals for the second group of converters. Figure 7 The markings of G1 and G2 only represent the logical relationship of the control signal. Since the two sets of switches S1, S2 and S11, S12 have potential differences, the actual circuit should consider using appropriate drive circuits, such as half-bridge bootstrap drive or isolation drive, to ensure the normal operation of the circuit. The frequency conversion control circuit can also be completed with only one set of circuits.

[0078] exist Figure 7 In the embodiment, a control method can also be introduced to turn off one of the switches when the load is relatively light, so as to improve the power loss and frequency variation range under light load conditions, and make the THD index better. Of course, this control should also have a certain hysteresis, and restore the two switches to work simultaneously when the load becomes larger, and cannot switch repeatedly at a certain load point. Specifically, the control signals G1 and G2 make the first switch S1 and the second switch S2 turn on alternately, and the control signals G11 and G21 are always at a low level so that the third switch S11 and the fourth switch S21 are turned off, or: the control signals G1 and G2 are always at a low level so that the first switch S1 and the second switch S2 are turned off, and the control signals G11 and G21 make the third switch S11 and the fourth switch S21 turn on alternately.

[0079] Figure 8It is an embodiment of the frequency conversion control circuit in the present invention, and the circuit is composed of U1, U2, U3, and U4. Among them, U1 is a differential amplifier, which is used to detect the size of the output voltage Vo and proportionally reduce the amplitude to a value suitable for the control circuit. U2 is a proportional integral circuit, which compares the detected Vo signal with the reference signal Vref to realize feedback control without static error. The output voltage of U2 is applied to the input end of the voltage-controlled oscillator composed of U3. The output frequency of U3 is controlled by the input voltage, and satisfies the regulation relationship that the higher the input voltage, the lower the output frequency. At the same time, U3 also has the function of setting the maximum frequency and the minimum frequency to ensure that the converter works within the normal range. U4 processes the frequency signal generated by U3 to obtain two sets of complementary signals. The two sets of complementary signals are then passed through the dead zone setting circuit to obtain control signals G1 and G2. The above circuit functions can also be realized by an ordinary MCU. The controller needs a complementary signal with a fixed duty cycle. The only variable to be adjusted is the switching frequency, which can be adjusted in several power frequency cycles. Therefore, a high-speed MCU is not required. Almost all MCUs with general functions can realize the above functions. Moreover, the above adjustment process has nothing to do with the frequency of three-phase AC power. The hardware circuit does not require sampling of three-phase voltage and three-phase current. It is essentially a very low-cost control circuit.

[0080] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A variable frequency resonant three-phase power factor correction converter, characterized in that: include: An input filter, wherein the input filter comprises three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase four-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the zero line of the three-phase input voltage is connected to the other ends of the three capacitors, and the input filter filters the three-phase input voltage; Three input inductors, the three input inductors respectively receiving filtered three-phase input voltages; A three-phase rectifier bridge, wherein the three-phase rectifier bridge receives outputs of the three input inductors respectively; A switch assembly, the switch assembly comprising a first switch and a second switch coupled to both ends of the three-phase rectifier bridge and connected in series; An output capacitor, the output capacitor is connected in parallel to two ends of the three-phase rectifier bridge and connected to two ends of the load; a resonant capacitor, one end of which is connected to a node between the first switch and the second switch, and the other end of which is connected to the neutral line; and A frequency conversion control circuit, the frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch and the second switch according to the differential voltage, wherein the first switch and the second switch are alternately turned on; fs_min is the lowest frequency at which the correction converter operates, and fo is the resonant frequency of one of the three input inductors connected in series with the resonant capacitor, wherein fs_min = (1.5~5)*fo; The frequency conversion control circuit includes a differential amplifier, a proportional integration circuit, a voltage-controlled oscillator and a dead zone setting circuit connected in series in sequence, the differential amplifier is respectively connected to the two ends of the load and generates a differential voltage, the proportional integration circuit compares the differential voltage with a reference voltage and generates a feedback control voltage, the voltage-controlled oscillator generates an oscillation frequency according to the feedback control voltage, and the dead zone setting circuit outputs a first control signal to the first switch and a second control signal to the second switch according to the oscillation frequency.

2. The three-phase power factor correction converter according to claim 1, characterized in that: The three-phase rectifier bridge includes first to sixth diodes, the first diode and the fourth diode are connected in series at both ends of the switch component, the second diode and the fifth diode are connected in series at both ends of the switch component, the third diode and the sixth diode are connected in series at both ends of the switch component, and the outputs of the three input inductors are respectively connected to the node between the first diode and the fourth diode, the node between the second diode and the fifth diode, and the node between the third diode and the sixth diode.

3. A variable frequency resonant three-phase power factor correction converter, characterized in that: include: An input filter, the input filter comprising three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase three-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the other ends of the three capacitors provide a virtual midpoint, and the input filter filters the three-phase input voltage; Three input inductors, the three input inductors respectively receiving filtered three-phase input voltages; A three-phase rectifier bridge, wherein the three-phase rectifier bridge receives outputs of the three input inductors respectively; A switch assembly, the switch assembly comprising a first switch and a second switch connected in series at two ends of the three-phase rectifier bridge; An output capacitor, the output capacitor is connected in series to two ends of the three-phase rectifier bridge and connected to two ends of a load; a resonant capacitor, one end of which is connected between the first switch and the second switch, and the other end of which is connected to the virtual midpoint; and A frequency conversion control circuit, the frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch and the second switch according to the differential voltage, wherein the first switch and the second switch are alternately turned on; fs_min is the lowest frequency at which the correction converter operates, and fo is the resonant frequency of a capacitor in which one of the three input inductors is connected in parallel with the three capacitors of the input filter and then in series with the resonant capacitor, wherein fs_min = (1.5-5) * fo; A common-mode inductor and two common-mode capacitors connected in series, wherein two input ends of the common-mode inductor are connected to two ends of the three-phase rectifier bridge, two output ends are connected to two ends of the load, the two common-mode capacitors are connected to two ends of the load, and a node between the two common-mode capacitors is connected to the virtual midpoint.

4. A variable frequency resonant three-phase power factor correction converter, characterized in that: include: An input filter, the input filter comprising three inductors and three capacitors, wherein the three-phase input voltage adopts a three-phase three-wire system, the three voltage lines of the three-phase input voltage are respectively connected to the three inductors, the other ends of the three inductors are respectively connected to the three capacitors, the other ends of the three capacitors provide a virtual midpoint, and the input filter filters the three-phase input voltage; Three first input inductors and three second input inductors, the three first input inductors respectively receiving filtered three-phase input voltages, and the three second input inductors respectively receiving filtered three-phase input voltages; A first three-phase rectifier bridge and a second three-phase rectifier bridge, wherein the first three-phase rectifier bridge receives outputs of the three first input inductors respectively, and the second three-phase rectifier bridge receives outputs of the three second input inductors respectively; A first switch assembly and a second switch assembly, wherein the first switch assembly includes a first switch and a second switch connected in series at both ends of the first three-phase rectifier bridge, and the second switch assembly includes a third switch and a fourth switch connected in series at both ends of the second three-phase rectifier bridge; a first output capacitor and a second output capacitor, wherein the first output capacitor is connected in series to two ends of the first three-phase rectifier bridge and connected to two ends of a load, and the second output capacitor is connected in series to two ends of the second three-phase rectifier bridge and connected to two ends of the load; a first resonant capacitor and a second resonant capacitor, wherein one end of the first resonant capacitor is connected between the first switch and the second switch, and the other end is connected to the virtual midpoint; one end of the second resonant capacitor is connected between the third switch and the fourth switch, and the other end is connected to the virtual midpoint; and A frequency conversion control circuit, the frequency conversion control circuit is connected to both ends of the load, detects a differential voltage of the load and controls the on and off of the first switch, the second switch, the third switch and the fourth switch according to the differential voltage; A first common-mode inductor, a second common-mode inductor, two first common-mode capacitors connected in series, and two second common-mode capacitors connected in series; two input ends of the first common-mode inductor are connected to two ends of the first three-phase rectifier bridge, and two output ends are connected to two ends of the load; two input ends of the second common-mode inductor are connected to two ends of the second three-phase rectifier bridge, and two output ends are connected to two ends of the load; the two first common-mode capacitors are connected to two ends of the load, and the node between the two first common-mode capacitors is connected to the virtual midpoint; the two second common-mode capacitors are connected to two ends of the load, and the node between the two second common-mode capacitors is connected to the virtual midpoint; The first switch and the second switch are alternately turned on, the first switch and the third switch are alternately turned on, the second switch and the fourth switch are alternately turned on, and the third switch and the fourth switch are alternately turned on, or: the first switch and the second switch are alternately turned on, and the third switch and the fourth switch are turned off, or: the first switch and the second switch are turned off, and the third switch and the fourth switch are alternately turned on.

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