CN115065230B - Three-phase bridgeless SEPIC type PFC converter - Google Patents

Abstract

The utility model provides a three-phase bridgeless SEPIC type PFC converter, has solved the problem of current distortion that current SEPIC type three-phase PFC converter topology components and parts utilization ratio is lower and power switch tube junction capacitance brings, belongs to the bridgeless PFC converter topology field of three-phase. The invention comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of two-way switches, six switches and two output filter capacitors, wherein the six switches are divided into three groups of one-way switches, and each group of two switches; the single-phase conversion circuit in the three-phase conversion is the same, and shares two output filter capacitors; compared with the existing topology, the semiconductor power device, the inductance and the capacitance reach the optimal quantity, and the utilization rate of the components is higher. Meanwhile, critical conduction mode control is adopted, power factor correction of an input side is achieved according to a conduction time control equation, the problem of current distortion is effectively solved, conduction loss of the converter can be further reduced, and the efficiency of the converter is effectively improved.

Description

A three-phase bridgeless SEPIC PFC converter

Technical Field

The invention relates to a novel three-phase bridgeless SEPIC type PFC converter with wide gain based on CRM (critical conduction mode) control, belonging to the field of three-phase bridgeless PFC converter topology.

Background Art

The three-phase PFC converter topology based on SEPIC circuit has the advantages of simple circuit structure, good power factor correction effect, wide output voltage adjustment range, etc. It has been widely used in small and medium power fields such as LED driver power supply and battery charger. The input side of the traditional SEPIC type PFC converter usually introduces a rectifier bridge composed of diodes to rectify the input voltage, so there are always two diodes flowing through the current during circuit operation. In the case of low power and high current, the diode loss of the input rectifier bridge is particularly serious. In order to reduce or even eliminate the loss in the diode rectifier bridge, three-phase bridgeless PFC converter topologies based on SEPIC circuit have been proposed one after another. At present, there are mainly two types of totem pole phase modular SEPIC type three-phase PFC converter and bridgeless Dual SEPIC type three-phase PFC converter.

The totem pole phase module SEPIC three-phase PFC converter topology can be considered as three parallel single-phase totem pole bridgeless SEPIC PFC converters with three independent output ports. Considering the coupling problem of the three-phase non-isolated structure, the three independent output ends cannot be connected together. At the same time, there is an input diode in each single-phase module of the converter that always works, reducing the system efficiency. The bridgeless Dual SEPIC three-phase PFC converter topology uses more semiconductor power devices. For each phase of AC input, two sets of inductors and capacitors are used to work on the positive and negative half axes of the input voltage respectively, which solves the coupling problem caused by the non-isolated structure, but the utilization rate of the device is low and the system power density is low.

In addition, due to the actual existence of the power switch junction capacitance, during the freewheeling period when the switch is turned off, the switch junction capacitance will resonate with the energy storage inductor, causing the input filter inductor current to be unequal to the energy storage inductor current when the next turn-on signal of the switch comes. Therefore, the input current of the three-phase bridgeless PFC converter based on the SEPIC circuit will have current distortion under fixed duty cycle DCM control.

Summary of the invention

Aiming at the problems of low utilization rate of topological components of existing SEPIC type three-phase PFC converter and current distortion caused by junction capacitance of power switch tube, the present invention provides a three-phase bridgeless SEPIC type PFC converter.

A three-phase bridgeless SEPIC type PFC converter of the present invention comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of bidirectional switches, six switches and two output filter capacitors, the six switches are divided into three groups of unidirectional switches, each group has two switches; the single-phase conversion circuits in the three-phase conversion are the same and share two output filter capacitors, the single-phase conversion circuit comprises an input filter inductor, an energy storage capacitor, an energy storage inductor, a group of bidirectional switches, a group of unidirectional switches and two output filter capacitors;

In the single-phase conversion circuit, each phase input power supply is connected in series with an input filter inductor, a group of bidirectional switches, and an energy storage inductor in sequence. An energy storage capacitor is connected in parallel at both ends of the bidirectional switch and the energy storage inductor. The connection point of the bidirectional switch and the energy storage inductor is point M. The connection point of the energy storage inductor and the energy storage capacitor is simultaneously connected to one end of two switches in a group of unidirectional switches. The other ends of a group of unidirectional switches are _X1 and _X2 , respectively. Two output filter capacitors are connected in series between point _X1 and point M and between point _X2 and point M, respectively.

Preferably, the bidirectional switch is two reverse series power switch tubes, and the reverse series power switch tubes include anti-parallel diodes and junction capacitors, and the PFC converter operates in a critical conduction mode;

后，A相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase A and when it crosses zero, the bidirectional switch of phase A is turned on, and the conduction time

After that, the A-phase bidirectional switch is turned off, completing a switching cycle;

后，B相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase B and when it crosses zero, the bidirectional switch of phase B is turned on, and the conduction time

After that, the B-phase bidirectional switch is turned off, completing a switching cycle;

后，C相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase C and when it crosses zero, the bidirectional switch of phase C is turned on, and the conduction time

After that, the C-phase bidirectional switch is turned off, completing a switching cycle;

r_A＝r_B＝r_C，v _A , v _B , v _C represent the instantaneous values of the three-phase input voltage of the input power supply under the industrial frequency, V _dc represents the output voltage of the PFC converter,

_rA ＝ _rB ＝ _rC ，

_rA , _rB , _rC represent the equivalent input resistance of the three-phase A, B, C grid side, and _L2 represents the inductance value of the energy storage inductor.

The present invention also provides a four-wire three-phase bridgeless SEPIC type PFC converter, in which the middle line of the three-phase input power supply is connected to the M point.

Preferably, the bidirectional switch is two reverse-series power switch tubes, and the reverse-series power switch tubes include anti-parallel diodes and junction capacitors, and the PFC converter operates in a critical conduction mode;

后，A相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase A and when it crosses zero, the bidirectional switch of phase A is turned on, and the conduction time

After that, the A-phase bidirectional switch is turned off, completing a switching cycle;

后，B相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase B and when it crosses zero, the bidirectional switch of phase B is turned on, and the conduction time

After that, the B-phase bidirectional switch is turned off, completing a switching cycle;

后，C相双向开关关断，完成一次开关周期；A set of unidirectional switch currents of phase C and when it crosses zero, the bidirectional switch of phase C is turned on, and the conduction time

After that, the C-phase bidirectional switch is turned off, completing a switching cycle;

r_A＝r_B＝r_C，r_A、r_B、r_C表示A、B、C三相网侧等效输入电阻，L₁表示滤波电感的电感值，L₂表示储能电感的电感值。v _A , v _B , v _C represent the instantaneous values of the three-phase input voltage of the input power supply under the industrial frequency, V _dc represents the output voltage of the PFC converter,

r _A = r _B = r _C , r _A , r _B , r _C represent the equivalent input resistance of the three-phase A, B, C grid side, L ₁ represents the inductance value of the filter inductor, and L ₂ represents the inductance value of the energy storage inductor.

As a preference,

α represents the current ripple factor, _{TA_min} represents the minimum switching frequency, _Vrms represents the effective value of the three-phase voltage, and P _o represents the output power of the PFC converter.

The beneficial effect of the present invention is that there is no diode that is always working on the input side in the topology of the present invention. Compared with the existing topology, the number of semiconductor power devices, inductors and capacitors is optimized, and the component utilization rate is high. At the same time, in order to solve the current distortion problem caused by the junction capacitance of the power switch, the critical conduction mode (CRM) control is adopted, and the power factor correction on the input side is realized according to the conduction time control equation, so that the current distortion problem can be effectively solved, the conduction loss of the converter can be further reduced, and the converter efficiency is effectively improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a circuit diagram of a three-wire three-phase bridgeless SEPIC type PFC converter;

FIG2 is a circuit diagram of a four-wire three-phase bridgeless SEPIC type PFC converter;

FIG3 is a diagram showing the division of different working intervals of three-phase input voltage, where the vertical axis v represents the three-phase input voltage and the horizontal axis t represents the working time;

FIG4 is a waveform diagram of the currents of switches S _a1 , S _b2 , and S _c2 , the currents of energy storage inductors L _a2 , L _b2 , and L _c2 , and the currents of switches Q _a1 , Q _b2 , and Q _c2 of a three-wire three-phase bridgeless SEPIC PFC converter in one switching cycle when the input voltage is in the range of [π/3,π/2];

FIG5 is a working modal diagram of a three-wire three-phase bridgeless SEPIC PFC converter with input voltage in the range of [π/3,π/2] under different switching states, wherein FIG5(a) is a working modal diagram of working stage (1), FIG5(b) is a working modal diagram of working stage (2), FIG5(c) is a working modal diagram of working stage (3), FIG5(d) is a working modal diagram of working stage (4), and FIG5(e) is a working modal diagram of working stage (5); FIG5(f) is a working modal diagram of working stage (6); and FIG5(g) is a working modal diagram of working stage (7);

FIG6 is a block diagram of a CRM control algorithm for a three-phase bridgeless SEPIC PFC converter;

FIG7 is a waveform diagram of the A-phase switch S _a1 current, the energy storage inductor L _a2 current, and the switch Q _a1 and Q _a2 currents of the four-wire three-phase bridgeless SEPIC PFC converter in four different working modes within one switching cycle;

FIG8 is a working mode diagram of phase A of a four-wire three-phase bridgeless SEPIC PFC converter under different states, including FIG8(a) is a bidirectional switch conduction mode when v _A >0, FIG8(b) is a bidirectional switch turn-off mode when v _A >0, FIG8(c) is a bidirectional switch conduction mode when v _A <0, and FIG8(d) is a bidirectional switch turn-off mode when v _A <0;

Figure 9 is a three-phase input voltage and current waveform diagram under the conditions of three-phase input 110V/50Hz and output 270V/1500W, wherein Figure 9(a) is the input voltage and current waveform of the three-wire three-phase bridgeless SEPIC type PFC converter of Example 1; Figure 9(b) is the input voltage and current waveform of the four-wire three-phase bridgeless SEPIC type PFC converter of Example 2.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

The three-phase bridgeless SEPIC PFC converter of this embodiment includes three input filter inductors, namely _La1 , _Lb1 , and _Lc1 , three small-capacity energy storage capacitors, namely _Ca1 , _Cb1 , and _Cc1 , three small-inductance energy storage inductors, namely _La2 , _Lb2 , and _Lc2 , two output filter capacitors _Cdc1 and _Cdc2 , three groups of bidirectional switches, namely a first group Sa1 and Sa2; a second group _Sb1 and _Sb2 ; and a third group _Sc1 and _Sc2 , and six switches _Qa1 - _Qc2 . The switches can be selected according to the working mode of the circuit: a diode/synchronous rectifier is used in the boost mode; a _{unidirectional} current-controlled switch with reverse blocking capability is used in the boost-boost mode, such _as a unidirectional current-controlled switch IGBT with reverse blocking capability or a standard IGBT series diode without reverse blocking capability.

Among them, the inductance value of the three input filter inductors is the same, which is L ₁ , the capacitance value of the three small-capacity energy storage capacitors is the same, which is C ₁ , the inductance value of the three small-capacity energy storage inductors is the same, which is L ₂ , and the capacitance value of the two output filter capacitors is the same, which is C _dc . Each group of bidirectional switches is realized by reverse series switch tube switches, with the same action, and can realize bidirectional flow of energy.

The single-phase conversion circuit is the same in the three-phase conversion and shares two output filter capacitors. The single-phase conversion circuit includes an input filter inductor, an energy storage capacitor, an energy storage inductor, a set of bidirectional switches, a set of unidirectional switches and two output filter capacitors.

Depending on whether there is a neutral line in the three-phase AC power supply, the circuit structure of the three-phase bridgeless SEPIC PFC converter can be divided into two types: three-phase three-wire system and three-phase four-wire system.

Embodiment 1: As shown in FIG1 , in the three-phase bridgeless SEPIC PFC converter of the three-wire system of the present embodiment, in the A-phase single-phase conversion circuit, the A-phase input power supply is respectively connected in series with the input filter inductor _La1 , the bidirectional switches _Sa1 , _Sa2 , and the energy storage inductor _{La2 ,} and an energy storage capacitor _Ca1 is connected in parallel at both ends of the bidirectional switches _Sa1 , _Sa2 and the energy storage inductor _La2 after being connected in series, and the connection point of the bidirectional switches _Sa1 , _Sa2 and the energy storage inductor La2 is point M, the connection point of the energy storage inductor _La2 and the energy storage capacitor _Ca1 is simultaneously connected to one end of two switches in a group of unidirectional switches, and the other ends of the group of unidirectional switches are _X1 and _X2 , respectively, and the two output filter capacitors _Cdc1 and _Cdc2 are respectively connected in series between point _X1 and point M and between point _X2 and point M.

The number of semiconductor power devices used in this embodiment is relatively small. Compared with the 18 semiconductor power devices, 6 energy storage capacitors, and 6 energy storage inductors of the three-switch bridgeless Dual SEPIC type three-phase PFC converter, the topology of this embodiment adopts 12 semiconductor power devices, 3 energy storage capacitors, and 3 energy storage inductors. The number of semiconductor power devices is reduced, and the number of inductors and capacitors is halved. The utilization rate of components is effectively improved, and the system efficiency and power density are also improved.

The working condition of the three-phase bridgeless SEPIC PFC converter of this embodiment is related to the waveform change of the three-phase input voltage v _A , v _B , v _C and the control condition of the three-way bidirectional switches. According to the polarity relationship of the three-phase input voltage, a power grid cycle is divided into 12 intervals, and the positive and negative and absolute value relationship of the three-phase voltage in each interval remains unchanged. Taking the interval [π/3,π/2] as an example, the working process of the converter is specifically analyzed.

Before analyzing the working principle of the PFC converter, the following explanations are made:

1) The PFC converter operates in critical conduction mode (CRM);

2) The output filter capacitors C _dc1 and C _dc2 are large enough, and the voltage divided by the two capacitors is equal, that is, v _Cdc1 =v _Cdc2 =V _dc /2;

3) The power switch tube of the bidirectional switch includes an anti-parallel diode and a junction capacitor;

4) The switching frequency is much higher than the input AC power frequency. During the switching period T _S, the three-phase input voltage is considered to be a fixed value of _VA , _VB , and _VC , and the energy storage capacitor voltage is a fixed value of V _a1 , V _b1 , and V _c1 .

In the three-phase input voltage range of [π/3,π/2], the converter has seven operating modes according to the conduction conditions of the three bidirectional switches. The main current waveform of the circuit in a switching cycle in the range of [π/3,π/2] is shown in Figure 4, and the corresponding operating mode is shown in Figure 5.

Mode I: As shown in Figure 5(a), in this stage, all three sets of bidirectional switches are turned on. The input filter inductor _La1 of phase A is charged forward, and the current of inductor _La1 rises linearly in the forward direction; the input filter inductors _Lb1 and _Lc1 of phase _B and C are charged reversely, and the current of inductors _Lb1 and _Lc1 rises linearly in the reverse direction. The voltage across the energy storage inductors _La2 , _Lb2 , and _Lc2 is equal to the voltage across the energy storage capacitors _Ca1 , Cb1, and _Cc1 , that is, v _La2 = _Va1 , v _Lb2 = _Vb1 , and v _Lc2 = _Vc1 . The energy storage capacitors _Ca1 , _Cb1 , and _Cc1 discharge to the energy storage inductors _La2 , _Lb2 , and _Lc2 respectively, and _La2 , _Lb2 , and _Lc2 store energy. At the same time, the output filter capacitors _Cdc1 and _Cdc2 jointly provide energy to the load.

Mode II: As shown in Figure 5(b), the bidirectional switches of phases A and C are turned on, and the bidirectional switch of phase B is turned off. The input filter inductors _La1 and _Lc1 of phases A and C are charged linearly; the voltages across the energy storage inductors _La2 and _Lc2 are still the energy storage capacitor voltages _Va1 and _Vc1 , respectively, and the inductors _La2 and _Lc2 are charged linearly. The bidirectional switch of phase _B is turned off, and the voltage across the bidirectional switch is clamped to _Vb1 - _Vdc /2. The input filter inductor Lb1 discharges to the output side, and the current decreases linearly; the reference direction of the voltage across the energy storage inductor _Lb2 is opposite to the current, and the inductor _Lb2 also releases energy to the output side. At the same time, switch _Qb2 is turned on to provide energy to the filter capacitor _Cdc2 and the load, and its current decreases linearly from the peak value until the current of switch _Qb2 drops to 0, and the bidirectional switch of phase B begins to turn on.

Mode III: As shown in Figure 5(c), the A-phase bidirectional switch is turned on, and the B-phase and C-phase bidirectional switches are turned off. The A-phase input filter inductor _La1 and the energy storage inductor _La2 are linearly charged. The B-phase and C-phase bidirectional switches are turned off, and the voltage across the B-phase bidirectional switch is clamped to _Vb1 - _Vdc /2, and the voltage across the C-phase bidirectional switch is clamped to _Vc1 - _Vdc /2. The input filter inductors _Lb1 and _Lc1 release energy to the output side. The reference direction of the voltage across the energy storage inductors _Lb2 and _Lc2 is opposite to the current, and the inductors _Lb2 and _Lc2 also release energy to the output side. At the same time, switches _Qb2 and _Qc2 are turned on to provide energy to the filter capacitor _Cdc2 and the load until the current of switches _Qb2 and _Qc2 drops to 0, and the B-phase and C-phase bidirectional switches begin to turn on.

Mode IV: As shown in Figure 5(d), the A-phase bidirectional switch is turned off, and the B-phase and C-phase bidirectional switches are turned on. The B-phase and C-phase input filter inductors L _b1 and L _c1 are charged linearly; the voltages across the energy storage inductors L _b2 and L _c2 are the energy storage capacitor voltages V _b1 and V _c1 , respectively, and the inductors L _b2 and L _c2 are charged linearly. The A-phase bidirectional switch is turned off, and the voltage across the bidirectional switch is clamped to V _a1 +V _dc /2. The input filter inductor _La1 discharges to the output side, and the current decreases linearly; the reference direction of the voltage across the energy storage inductor _La2 is opposite to the current, and the inductor _La2 also releases energy to the output side. At the same time, the switch Q _a1 is turned on to provide energy to the filter capacitor C _dc1 and the load, and its current decreases linearly from the peak value until the current of the switch Q _a1 drops to 0, and the A-phase bidirectional switch begins to turn on.

Mode V: As shown in Figure 5(e), the A and C phase bidirectional switches are turned off, and the B phase bidirectional switch is turned on. The voltage across the A phase bidirectional switch is clamped to V _a1 +V _dc /2, and the voltage across the C phase bidirectional switch is clamped to V _c1 -V _dc /2. The A phase input filter inductor _La1 and the energy storage inductor _La2 release energy to the output side, and the switch Q _a1 is turned on to provide energy to the filter capacitor C _dc1 and the load. The B phase input filter inductor L _b1 and the energy storage inductor L _b2 are linearly charged. The C phase input filter inductor L _c1 and the energy storage inductor L _c2 release energy to the output side, and the switch Q _c2 is turned on to provide energy to the filter capacitor C _dc2 and the load.

Mode VI: As shown in Figure 5(f), the A and B phase bidirectional switches are turned off, and the C phase bidirectional switch is turned on. The voltage across the A phase bidirectional switch is clamped to V _a1 +V _dc /2, and the voltage across the B phase bidirectional switch is clamped to V _b1 -V _dc /2. The A phase input filter inductor _La1 and the energy storage inductor _La2 release energy to the output side, and the switch Q _a1 is turned on to provide energy to the filter capacitor C _dc1 and the load. The B phase input filter inductor L _b1 and the energy storage inductor L _b2 release energy to the output side, and the switch Q _b2 is turned on to provide energy to the filter capacitor C _dc2 and the load. The C phase input filter inductor L _c1 and the energy storage inductor L _c2 are linearly charged.

Mode VII: As shown in Figure 5(g), all three sets of bidirectional switches are turned off in this stage. The voltage across the A-phase bidirectional switch is clamped to V _a1 +V _dc /2, the voltage across the B-phase bidirectional switch is clamped to V _b1 -V _dc /2, and the voltage across the C-phase bidirectional switch is clamped to V _c1 -V _dc /2. The three input filter inductors _La1 , L _b1 , L _c1 and the energy storage inductors _La2 , L _b2 , L _c2 release energy to the output side, and at the same time, the switches Q _a1 , Q _b2 , and Q _c2 are all turned on, providing energy to the filter capacitors C _dc1 , C _dc2 , C _dc2 and the load respectively.

Through the analysis of the above 7 working modes, it can be seen that the three phases A, B, and C work relatively independently, and the turn-on signal of each phase bidirectional switch of A, B, and C comes from the zero-crossing detection signal of the current of each switch Q _a1 , Q _b2 , and Q _c2 . When the current of switch Q _a1 drops to 0, the bidirectional switch of phase A is turned on, when the current of switch Q _b1 drops to 0, the bidirectional switch of phase B is turned on, and when the current of switch Q _c1 drops to 0, the bidirectional switch of phase C is turned on.

According to the above analysis of the working mode of the three-phase PFC converter, taking phase A as an example, in order to realize the power factor correction function, it is required that the switch Q _a2 is turned off during the conduction period of the bidirectional switch of phase A. During the conduction period of the bidirectional switch, the voltage across the switch Q _a2 is V _A -V _dc /2. When the converter works in the boost mode, that is, the output voltage is greater than 2 times the peak value of the single-phase input voltage, the voltage across the switch Q _a1 is negative. At this time, the switch Q _a1 can realize the power factor correction function by using a diode/synchronous rectifier. When the converter works in the boost-boost working mode, that is, the output voltage is less than 2 times the peak value of the single-phase input voltage, the switch Q _a2 needs to use a unidirectional current-controlled switch with reverse blocking capability to realize the PFC function of the converter, such as a unidirectional current-controlled switch IGBT with reverse blocking capability or a standard IGBT series diode without reverse blocking capability. When the standard IGBT series diode without reverse blocking capability is used, the operating frequency of the standard IGBT without reverse blocking capability is the frequency of the three-phase input power supply.

The average voltage across the three-phase input filter inductor during the switching cycle is 0, so:

v _A , v _B , v _C are the instantaneous values of the three-phase input voltage of the input power supply under the power frequency, v _AM , v _BM , v _CM are the instantaneous values of the voltage between nodes A, B, C and point M under the power frequency, and v _MN is the instantaneous value of the voltage between the midpoint M of the output capacitor and the midpoint N of the three-phase power supply under the power frequency;

The three-phase AC voltage is balanced, v _A +v _B +v _C = 0, from which we can get:

Substituting formula (2) into formula (1), we can obtain:

From this we can get:

Considering that the average voltage across the energy storage inductors _La2 , _Lb2 , and _Lc2 during the switching cycle is 0, the instantaneous values of the voltage across the energy storage capacitors C _a1 , C _b1 , and C _c1 at the power frequency, v _Ca1 , v _Cb1 , and v _Cc1, can be expressed as:

The voltages across the energy storage capacitors C _a1 , C _b1 , and C _c1 are equal to the three-phase voltages of A, B, and C, respectively. Therefore, during the switching cycle:

Through the analysis of the previous seven working modes, it can be known that the turn-off moment of the bidirectional switch is the peak moment of the current of switches Q _a1 , Q _b2 , and Q _c2 . Considering L ₁ >> L ₂ , ignoring the change of the current on the input filter inductor of each phase, the current peak values i _{Qa_peak} , i _{Qb_peak} , i _{Qc_peak} of switches Q _a1 , Q _b2 , and Q _c2 can be expressed as:

Wherein, d _A and _TA are the duty cycle and switching period of the A-phase bidirectional switch, d _B and _TB are the duty cycle and switching period of the B-phase bidirectional switch, and d _C and _TC are the duty cycle and switching period of the C-phase bidirectional switch.

The voltage switching period across the energy storage inductors _La2 , _Lb2 , and _Lc2 satisfies the volt-second balance, that is:

According to equations (7) and (8), the average current values i _{Qa_avg} , i _{Qb_avg} , i _{Qc_avg} of switches Q _a1 , Q _b2 , Q _c2 in the switching cycle can be obtained:

In other intervals of three-phase AC voltage, the working condition of the converter is similar to that in the interval [π/3,π/2]. According to the ideal input-output power conservation condition, the expression of the three-phase input current under CRM control is obtained:

Wherein, _{TA_ON} , _{TB_ON} and _{TC_ON} are the on-times of the three-phase bidirectional switches A, B and C respectively.

To achieve unity power factor correction on the three-phase input side, the on-time of the bidirectional switch control of each phase needs to meet:

In the formula, r _A , r _B , and r _C are the equivalent input resistances of the three-phase grid side A, B, and C respectively. When the three-phase voltage and power are balanced, r _A ＝r _B ＝r _C .

对式(11)变形可得：make

By transforming formula (11), we can get:

Formula (12) is the CRM control equation of the proposed three-phase bridgeless SEPIC PFC converter. The structural block diagram of the control method is shown in Figure 6, where V _m can be obtained from the voltage closed loop of the output voltage. The CRM control method based on formula (12) is timed turn-on and controlled turn-off. The turn-on signal depends on the zero-crossing detection signal of the current sum of each phase switch, that is, the turn-on time of phase A is the zero-crossing time of the current sum i _Qa1 +i _Qa2 , the turn-on time of phase B is the zero-crossing time of the current sum i _Qb1 +i _Qb2 , and the turn-on time of phase C is the zero-crossing time of the current sum i _Qc1 +i _Qc2 . The current sum is selected because the stage when the input voltage of each phase is positive is the upper switch working and the lower switch is turned off, and the stage when the input voltage is negative is the lower switch working and the upper switch is turned off. Zero-crossing detection of the current sum can omit the judgment of the input voltage. When each phase bidirectional switch is turned on, the integrator is reset and starts to integrate V _m . When the output of each phase integrator satisfies the CRM control equation shown in formula (12), the comparator flips, the bidirectional switch is turned off, and a switching cycle is completed. By adopting the CRM control method based on formula (12), the three-phase PFC converter can operate in the critical conduction state, and the freewheeling stage is effectively avoided. The problem of input current distortion caused by resonance of the junction capacitance of the bidirectional switch in the freewheeling stage is effectively solved.

According to formula (8), the three-phase PFC converter has a wide output gain, which can be expressed as:

When the input voltage of a phase is near zero, the duty cycle of the phase is large; at the peak of the input voltage, the duty cycle of the phase is small. A wide range of output voltage changes can be achieved through closed-loop regulation of the output voltage.

Embodiment 2: As shown in FIG2 , in the four-wire three-phase bridgeless SEPIC PFC converter of this embodiment, in the A-phase single-phase conversion circuit, the A-phase input power supply is respectively connected in series with the input filter inductor _La1 , the bidirectional switches _Sa1 , _Sa2 , and the energy storage inductor _La2 , and an energy storage capacitor _Ca1 is connected in parallel at both ends of the bidirectional switches _Sa1 , _Sa2 and the energy storage inductor _La2 in series, the connection point of the bidirectional switches _Sa1 , _Sa2 and the energy storage inductor _La2 is point M, the connection point of the energy storage inductor _La2 and the energy storage capacitor _Ca1 is simultaneously connected to one end of two switches in a group of unidirectional switches, and the other ends of the group of unidirectional switches are _X1 and _X2 , respectively, the two output filter capacitors _Cdc1 and _Cdc2 are respectively connected in series between point _X1 and point M and between point _X2 and point M, and the neutral line of the three-phase input power supply is connected to point M. At this time, the three-phase bridgeless SEPIC PFC converter is decoupled in the circuit structure, and each phase circuit works completely independently. The three-phase input voltage and power are balanced, and the output current of each phase is I _dc /3. Taking phase A as an example, according to the positive and negative AC voltage of phase A and the switching state of the bidirectional switch, the single-phase model of the three-phase bridgeless SEPIC PFC converter based on CRM control has 4 different working modes. The main current waveform of the circuit in the switching cycle is shown in Figure 7, and the corresponding working mode is shown in Figure 8.

Mode I: As shown in Figure 8(a), in this stage v _A >0, the A-phase bidirectional switch is turned on, the voltage across the input filter inductor _La1 is V _A during the switching cycle, and the inductor current rises linearly in a positive direction. The voltage across the energy storage inductor _La2 is the energy storage capacitor voltage V _a1 , and the energy storage capacitor C _a1 discharges to the energy storage inductor _La2 through the bidirectional switch, and the current of the energy storage inductor _La2 rises linearly. At this time, the load is provided with energy by the output filter capacitors C _dc1 and C _dc2 .

Mode II: As shown in Figure 8(b), in this stage, v _A >0, the A-phase bidirectional switch is turned off, and the voltage across the input filter inductor _La1 is V _A -V _a1 -V _dc /2<0 during the switching cycle, and the inductor current begins to decrease linearly. The voltage across the energy storage inductor _La2 is the voltage of the output filter capacitor C _dc1 , and the reference direction of the voltage is opposite to the current. The energy storage inductor _La2 releases energy to the output side, and the current of the energy storage inductor _La2 decreases linearly. At this time, the switch Q _a1 is turned on and provides energy to the filter capacitor C _dc1 and the load, and its current decreases linearly from the peak value until the current of the switch Q _a1 drops to 0, and the A-phase bidirectional switch is turned on.

Mode III: As shown in Figure 8(c), in this stage v _A <0, the A-phase bidirectional switch is turned on, the voltage across the input filter inductor _La1 is V _A during the switching cycle, and the inductor current rises linearly in the opposite direction. The voltage across the energy storage inductor _La2 is the energy storage capacitor voltage V _a1 , and the energy storage capacitor C _a1 discharges to the energy storage inductor _La2 through the bidirectional switch, and the current of the energy storage inductor _La2 rises linearly. At this time, the load is provided with energy by the output filter capacitors C _dc1 and C _dc2 .

Mode IV: As shown in Figure 8(d), in this stage, v _A <0, the A-phase bidirectional switch is turned off, the voltage across the input filter inductor _La1 is V _A -V _a1 -V _dc /2<0, and the inductor current begins to decrease linearly. The voltage across the energy storage inductor _La2 is the voltage of the output filter capacitor C _dc2 . The reference direction of the voltage is opposite to the current. The energy storage inductor _La2 releases energy to the output side, and the current of the energy storage inductor _La2 decreases linearly. At this time, the switch Q _a2 is turned on and provides energy to the filter capacitor C _dc2 and the load. Its current decreases linearly from the peak value until the current of the switch Q _a2 drops to 0, and the A-phase bidirectional switch is turned on.

From the previous analysis, it can be seen that the working mode of the circuit is basically the same when the input voltage is positive or negative, mainly the two modes of inductor charging and discharging. When _{v A} >0 and the bidirectional switch is turned off, the current of switch Q _a1 reaches the current peak; when v _A <0 and the bidirectional switch is turned off, the current of switch Q _a2 reaches the current peak. The current peak i _{Qa_max} can be expressed as:

Therefore, the average value of the switch current _Qa1 / _Qa2 during the switching cycle under CRM control can be expressed as:

Under power frequency conditions, the input and output power are conserved, and the input current of phase A can be expressed as:

Where _{TA_on} is the on-time of the A-phase bidirectional switch.

Each phase circuit of the three-phase bridgeless SEPIC PFC converter under three-phase four-wire system works completely independently, and the working process is basically the same. Therefore, the three-phase input current wave expression under three-phase four-wire CRM control is obtained:

Wherein, _{TA_on} , _{TB_on} and _{TC_on} are the conduction times of the three-phase bidirectional switches A, B and C respectively.

According to the unity power factor correction requirement on the input side, the CRM control equation of the three-phase four-wire system can be expressed as:

In the formula,

By comparing equation (12) with equation (17), it can be found that the CRM control equation of the three-wire system is basically the same as that of the four-wire system, which shows that the proposed three-phase bridgeless SEPIC PFC converter does not have the problem of current coupling between the three phases, and the converter can be controlled using a single-phase control algorithm.

Combining equation (8) with equation (11), the switching cycle of the three-phase double-open switch can be obtained:

Where, P _o is the output power of the three-phase bridgeless SEPIC PFC converter, and V _rms is the effective value of the three-phase voltage.

Under CRM control, the switching cycle of the three-phase bridgeless SEPIC PFC converter is directly related to the circuit operating index. It can be seen from formula (18) that when the input voltage, output voltage, output power and energy storage inductance are constant, the switching cycle reaches the maximum at the peak of the three-phase input voltage and the minimum near the zero crossing of the three-phase input voltage. When designing the energy storage inductor parameters in Example 1 and Example 2, it is necessary to clarify the range of the switching cycle and design the inductance of the energy storage inductor according to this condition.

The design of the three-phase input filter inductor mainly considers the current ripple of the three-phase input current. From the previous working principle, we can know that taking phase A as an example, the current ripple of the input filter inductor of phase A is:

When the energy storage inductor size and current ripple coefficient α are determined, the filter inductor _La1 can be obtained by formula (20):

From the above formula, we can know that the larger the input filter inductance value, the smaller the input current ripple. Taking the three-phase input voltage of 110V, output 270V constant voltage, and output power of 1500W as an example, the design of circuit parameters is described.

The minimum switching frequency T _{A_min} is designed to be 50kHz. Based on the given working index, the inductance value of the energy storage inductor can be obtained according to formula (18):

Take the input current ripple coefficient α = 0.2, and determine the input filter inductance L according to formula (20):

The power factor correction of the three-phase bridgeless SEPIC PFC converter under the above circuit parameters is shown in Figure 9, where Figure 9(a) is a three-phase three-wire system and Figure 9(b) is a three-phase four-wire system. From the simulation results, it can be seen that the input current of the converter under CRM control is a sine wave and can track the input voltage waveform in real time, with good power factor correction effect.

This application is used in small and medium power fields such as LED drive power supplies and battery chargers.

Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims (5)

1. A three-phase bridgeless SEPIC type PFC converter, is characterized in that, comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of bidirectional switches, six switches and two output filters Capacitor, the six switches are divided into three groups of one-way switches, each with two switches; the single-phase conversion circuit in the three-phase conversion is the same, and shares two output filter capacitors, and the single-phase conversion circuit includes an input filter inductor and an energy storage capacitor , an energy storage inductor, a set of bidirectional switches, a set of unidirectional switches and two output filter capacitors; In a single-phase conversion circuit, each phase of the input power supply is connected in series with an input filter inductor, a group of bidirectional switches, and an energy storage inductor in sequence, and an energy storage capacitor is connected in parallel between the two ends of the bidirectional switch and the energy storage inductor in series, and the bidirectional switch and The connection point of the energy storage inductance is point M, the connection point of the energy storage inductance and the energy storage capacitor is connected to one end of two switches in a group of unidirectional switches at the same time, and the other ends of a group of unidirectional switches are respectively X ₁ and X _2. Two output filter capacitors are connected in series between point X ₁ and point M and between point X ₂ and point M; The bidirectional switch is two reverse-series power switch tubes, and the reverse-series power switch tubes include anti-parallel diodes and junction capacitance, and the PFC converter works in critical conduction mode; When the sum of the currents of a group of unidirectional switches of phase A crosses zero, the bidirectional switches of phase A are turned on, and the turn-on time

After that, the phase A bidirectional switch is turned off to complete a switching cycle; When the sum of the currents of a group of one-way switches of phase B crosses zero, the two-way switch of phase B is turned on, and the on-time

After that, the B-phase bidirectional switch is turned off to complete a switching cycle; When the sum of the currents of a group of unidirectional switches of phase C crosses zero, the bidirectional switches of phase C are turned on, and the turn-on time

After that, the C-phase bidirectional switch is turned off to complete a switching cycle; v _A , v _B , v _C represent the instantaneous value of the three-phase input voltage of the input power supply under industrial frequency, V _dc represents the output voltage of the PFC converter,

r _A =r _B =r _C , r _A , r _B , and r _C represent the equivalent input resistance of the A, B, and C three-phase network sides, and L ₂ represents the inductance value of the energy storage inductor. 2. The three-phase bridgeless SEPIC PFC converter according to claim 1, wherein the switch adopts a unidirectional current controllable switch IGBT or a standard IGBT series diode. 3. The three-phase bridgeless SEPIC PFC converter according to claim 1, wherein the switch adopts a diode or a synchronous rectifier. 4. A three-phase bridgeless SEPIC type PFC converter is characterized in that it comprises three input filter inductors, three energy storage capacitors, three energy storage inductors, three groups of bidirectional switches, six switches and two output filter Capacitor, the six switches are divided into three groups of one-way switches, each with two switches; the single-phase conversion circuit in the three-phase conversion is the same, and shares two output filter capacitors, and the single-phase conversion circuit includes an input filter inductor and an energy storage capacitor , an energy storage inductor, a set of bidirectional switches, a set of unidirectional switches and two output filter capacitors; In a single-phase conversion circuit, each phase of the input power supply is connected in series with an input filter inductor, a group of bidirectional switches, and an energy storage inductor in sequence, and an energy storage capacitor is connected in parallel between the two ends of the bidirectional switch and the energy storage inductor in series, and the bidirectional switch and The connection point of the energy storage inductance is point M, the connection point of the energy storage inductance and the energy storage capacitor is connected to one end of two switches in a group of unidirectional switches at the same time, and the other ends of a group of unidirectional switches are respectively X ₁ and X _2. Two output filter capacitors are connected in series between point X ₁ and point M and between point X ₂ and point M; The neutral line of the three-phase input power supply is connected to point M; The bidirectional switch is two reverse-series power switch tubes, and the reverse-series power switch tubes include anti-parallel diodes and junction capacitance, and the PFC converter works in critical conduction mode; When the sum of the currents of a group of unidirectional switches of phase A crosses zero, the bidirectional switches of phase A are turned on, and the turn-on time

After that, the phase A bidirectional switch is turned off to complete a switching cycle; When the sum of the currents of a group of one-way switches of phase B crosses zero, the two-way switch of phase B is turned on, and the on-time

After that, the B-phase bidirectional switch is turned off to complete a switching cycle; When the sum of the currents of a group of unidirectional switches of phase C crosses zero, the bidirectional switches of phase C are turned on, and the turn-on time

After that, the C-phase bidirectional switch is turned off to complete a switching cycle; v _A , v _B , v _C represent the instantaneous value of the three-phase input voltage of the input power supply under industrial frequency, V _dc represents the output voltage of the PFC converter,

r _A ＝r _B ＝r _C , r _A , r _B , r _C represent the equivalent input resistance of the A, B, C three-phase network side, L ₁ represents the inductance value of the filter inductor, L ₂ represents the inductance value of the energy storage inductor . 5. three-phase bridgeless SEPIC type PFC converter according to claim 4, is characterized in that,

α represents the current ripple coefficient, T _{A_min} represents the minimum switching frequency, V _rms represents the effective value of the three-phase voltage, and P _o represents the output power of the PFC converter.

Images