Three-phase single-stage isolation rectifier and power factor correction method thereof

Abstract

The present invention provides a three-phase single-stage isolation rectifier and a power factor correction method thereof, belonging to the technical field of switching power supplies. The three-phase single-stage isolation rectifier includes: a low-pass filter unit, a sector selection unit, a DC / DC high-frequency conversion unit, and a compensation conversion unit; wherein the low-pass filter unit is connected to the three-phase alternating current, and the DC / DC high-frequency conversion unit is connected to the DC load; the sector selection unit includes a first bridge circuit and a switch circuit, and the compensation conversion unit includes an industrial frequency switching unit and a high-frequency converter, the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end of the industrial frequency switching unit is connected to the third terminal Y, the third input end of the industrial frequency switching unit is connected to the second terminal N, the output end of the industrial frequency switching unit is connected to the output end of the high-frequency converter, the first input end of the high-frequency converter is connected to the first terminal P, and the second input end of the high-frequency converter is connected to the second terminal N. The present invention can improve the conversion efficiency of the isolation rectifier.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, and in particular to a three-phase single-stage isolation rectifier and a power factor correction method thereof. Background Art

[0002] With the popularization of new energy technologies and the development of energy Internet, AC / DC converters that require input and output electrical isolation are becoming more and more widely used in application scenarios such as electric vehicle charging and power supply, and the requirements for conversion efficiency and power density of related products are also getting higher and higher, such as three-phase isolated single-stage converters.

[0003] At present, the three-phase isolated single-stage converter is usually studied by adopting the sector selection method. The principle of the sector selection method is to convert the three-phase AC power into three power frequency fluctuation points of P, Y, and N through the sector selection unit. The voltage waveforms between PY and YN are similar, both varying from zero to about 0.866 times the voltage peak value; the voltage between PN varies from 0.866 times to 1 times the voltage peak value. Then select a suitable DC / DC converter to convert the pulsating voltage waveform of the three points PYN into a DC output. The advantage is that the switching elements of the sector selection unit are all power frequency action, and low voltage drop power frequency elements can be selected, with less loss, while the PN link with small voltage fluctuation provides most of the power, which is conducive to the soft switching of the subsequent DC / DC converter and can achieve higher power density.

[0004] However, most of the existing three-phase isolated single-stage converters based on sector selection adopt a three-level converter, with P, Y, and N as input voltages, and adjust the action time of PY, YN, and PN levels to achieve power factor correction. In this way, the input voltage range of the DC / DC converter fluctuates greatly, and a wide voltage gain range needs to be considered at the cost of parameter design, resulting in low conversion efficiency of the entire system. A three-phase single-stage isolated rectifier with high conversion efficiency is urgently needed. Summary of the invention

[0005] The embodiment of the present invention provides a three-phase single-stage isolation rectifier and a power factor correction method thereof to solve the problem of low conversion efficiency of the isolation rectifier.

[0006] In a first aspect, an embodiment of the present invention provides a three-phase single-stage isolation rectifier, comprising:

[0007] A low-pass filter unit, a sector selection unit and a DC / DC high-frequency conversion unit are connected in sequence, and a compensation conversion unit is connected in parallel between the sector selection unit and the DC / DC high-frequency conversion unit; wherein the low-pass filter unit is connected to the three-phase alternating current, and the DC / DC high-frequency conversion unit is connected to the DC load;

[0008] The sector selection unit converts the three-phase AC power into three DC power paths and adjusts the order of the three DC power paths, and includes a first bridge circuit and a switch circuit, wherein the positive end of the first bridge circuit is connected to the first terminal P, and the first terminal P outputs a high voltage, the negative end of the first bridge circuit is connected to the second terminal N, and the second terminal N outputs a low voltage, one end of the switch circuit is connected to the first bridge circuit, and the other end of the switch circuit is connected to the third terminal Y, and the third terminal Y outputs a middle voltage;

[0009] The compensating conversion unit obtains energy from between the first terminal P and the second terminal N, and injects the obtained energy between the first terminal P and the third terminal Y or between the third terminal Y and the second terminal N according to different sectors, and includes an industrial frequency switching unit and a high-frequency converter, wherein the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end of the industrial frequency switching unit is connected to the third terminal Y, the third input end of the industrial frequency switching unit is connected to the second terminal N, the output end of the industrial frequency switching unit is connected to the output end of the high-frequency converter, the first input end of the high-frequency converter is connected to the first terminal P, and the second input end of the high-frequency converter is connected to the second terminal N.

[0010] In a second aspect, an embodiment of the present invention provides a power factor correction method for a three-phase single-stage isolated rectifier, which is applied to the above-mentioned three-phase single-stage isolated rectifier, including:

[0011] The sector selection unit converts the input three-phase alternating current into pulsating direct current outputted from the first terminal P, the second terminal N and the third terminal Y through low-frequency switching; wherein the first terminal P is a high voltage, the second terminal N is a low voltage, and the third terminal Y is a middle voltage;

[0012] By controlling the DC / DC high-frequency conversion unit and the compensation conversion unit, the power between the first terminal P and the second terminal N is distributed to the DC / DC high-frequency conversion unit according to a first preset ratio, and the power between the first terminal P and the second terminal N is distributed to the compensation conversion unit for processing according to a second preset ratio; the first preset ratio is greater than the second preset ratio;

[0013] By controlling the compensating transformation unit, the energy processed by the compensating transformation unit is injected between the first terminal P and the third terminal Y, or between the third terminal Y and the second terminal N, so as to compensate the current of the first terminal P or the second terminal N, so that the currents of the first terminal P, the second terminal N and the third terminal Y are all reference values ​​corresponding to the unity power factor.

[0014] The embodiment of the present invention provides a three-phase single-stage isolation rectifier and a power factor correction method thereof, wherein three-phase alternating current is converted into three pulsating direct currents PY, YN, and PN, wherein the first terminal P outputs the highest voltage level among the three phases, the second terminal N outputs the lowest voltage level among the three phases, and the third terminal Y outputs the voltage level in the middle of the three phases, and the energy of the PN part is processed by a DC / DC high-frequency conversion unit and outputted to a load. Since the PN voltage fluctuation is small, the gain range that needs to be taken into account in the parameter design of the DC / DC high-frequency conversion unit is narrow, thereby achieving optimization of conversion efficiency. A small portion of energy is obtained from PN through the compensation conversion unit and the obtained energy is compensated and output to PY or YN according to different sectors. The output power of the DC / DC high-frequency conversion unit and the compensation conversion unit is reasonably controlled to control the input current and output current of the DC / DC high-frequency conversion unit and the compensation conversion unit, thereby controlling the current waveforms of PN, YN and PN, so that the currents of the first terminal P, the second terminal N and the third terminal Y are all reference values ​​corresponding to the unit power factor, and the sum of the currents of the first terminal P, the second terminal N and the third terminal Y is zero, thereby ensuring that the entire system reaches a unit power factor, reducing energy loss, and improving the conversion efficiency of the rectifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0016] Figure 1 is a schematic diagram of a three-phase single-stage isolation rectifier provided by an embodiment of the present invention;

[0017] Figure 2a is a schematic diagram of the circuit structure of a compensation conversion unit provided in an embodiment of the present invention;

[0018] Figure 2b is a schematic diagram of the circuit structure of the power frequency switching unit provided in an embodiment of the present invention;

[0019] Figure 2c is a schematic diagram of the circuit structure of a high-frequency converter provided by an embodiment of the present invention;

[0020] Figure 2d It is a schematic diagram of a high-frequency current waveform outputted from one of the two interlaced parallel paths of the high-frequency converter provided by an embodiment of the present invention;

[0021] Figure 2e It is a schematic diagram of the total high-frequency average value of the high-frequency current outputted by one of the two high-frequency converters connected in parallel in an alternate manner provided by an embodiment of the present invention;

[0022] Figure 2f Schematic diagram of a derivative circuit of a compensation conversion unit provided in an embodiment of the present invention Figure 1 ;

[0023] Figure 2g Schematic diagram 2 of a derivative circuit of a compensation conversion unit provided in an embodiment of the present invention;

[0024] Figure 2h Schematic diagram 3 of a derivative circuit combining a power frequency switching unit and a compensation conversion unit provided in an embodiment of the present invention;

[0025] Figure 3a is a circuit diagram of a DC / DC high-frequency conversion unit provided by an embodiment of the present invention;

[0026] Figure 3b is a control principle diagram of a DC / DC high frequency conversion unit provided by an embodiment of the present invention;

[0027] Figure 3c is the expected average current of the DC / DC high frequency conversion unit provided in the embodiment of the present invention;

[0028] Figure 3d is the voltage between the first terminal P and the second terminal N of the DC / DC high-frequency conversion unit provided in the embodiment of the present invention;

[0029] Figure 3e is a schematic diagram of actual input current of a DC / DC high frequency conversion unit provided by an embodiment of the present invention;

[0030] Figure 3f It is a detailed schematic diagram of several high-frequency cycles of driving the switch tube provided by an embodiment of the present invention;

[0031] Figure 3g It is a detailed schematic diagram of several high-frequency cycles of the voltage between the first terminal P and the second terminal N of the DC / DC high-frequency conversion unit provided by an embodiment of the present invention;

[0032] Figure 3h It is a detailed schematic diagram of several high-frequency cycles of the actual input current of the DC / DC high-frequency conversion unit provided by an embodiment of the present invention;

[0033] Figure 3i It is a detailed schematic diagram of several high-frequency cycles of the current in the resonant cavity of the LLC converter of the DC / DC high-frequency conversion unit provided by an embodiment of the present invention;

[0034] Figure 3j The derived circuit diagram of the DC / DC high frequency conversion unit provided by the embodiment of the present invention is Figure 1 ;

[0035] Figure 3k Schematic diagram 2 of a derivative circuit of a DC / DC high-frequency conversion unit provided in an embodiment of the present invention;

[0036] Figure 4 is a circuit diagram of a low-pass filter unit provided in an embodiment of the present invention;

[0037] Figure 5a is a circuit diagram of a sector selection unit provided by an embodiment of the present invention;

[0038] Figure 5b Schematic diagram of voltage waveforms of PY, YN, and PN after sector selective rectification provided by an embodiment of the present invention;

[0039] Figure 5c The embodiment of the present invention provides a mains voltage;

[0040] Figure 5d It is the driving of three bidirectional switches provided by the embodiment of the present invention;

[0041] Figure 5e is a derivative circuit diagram of a sector selection circuit provided in an embodiment of the present invention;

[0042] Figure 6a : is a reference value waveform of the current at points P, Y and N provided by an embodiment of the present invention;

[0043] Figure 6b It is a schematic diagram of the input current of the DC / DC high-frequency conversion unit and the output current of the compensation conversion unit of the PN link provided by an embodiment of the present invention;

[0044] Figure 6c It is a power schematic diagram of a DC / DC high frequency conversion unit, a PN and a compensation conversion unit provided in an embodiment of the present invention;

[0045] Figure 7a is a schematic diagram of the final input current of the present invention provided by an embodiment of the present invention;

[0046] Figure 7b It is a schematic diagram of the final input voltage waveform of the present invention provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to enable people in the technical field to better understand the present solution, the technical solution in the embodiment of the present solution will be clearly described below in conjunction with the drawings in the embodiment of the present solution. Obviously, the described embodiment is an embodiment of a part of the present solution, not all of the embodiments. Based on the embodiments in the present solution, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present solution.

[0048] The term "including" and any other variations in the specification and claims of this solution and the above drawings mean "including but not limited to", and is intended to cover non-exclusive inclusions and is not limited to the examples listed in the text. In addition, the terms "first" and "second" are used to distinguish different objects, not to describe a specific order.

[0049] The following is a detailed description of the implementation of the present invention in conjunction with the specific drawings:

[0050] Figure 1 A schematic diagram of the structure of a three-phase single-stage isolation rectifier provided by an embodiment of the present invention. Figure 1 , the three-phase single-stage isolated rectifier comprises:

[0051] A low-pass filter unit, a sector selection unit and a DC / DC high-frequency conversion unit are connected in sequence, and a compensation conversion unit is connected in parallel between the sector selection unit and the DC / DC high-frequency conversion unit; wherein the low-pass filter unit is connected to the three-phase alternating current, and the DC / DC high-frequency conversion unit is connected to the DC load;

[0052] The sector selection unit converts the three-phase AC power into three DC power paths and adjusts the order of the three DC power paths, and includes a first bridge circuit and a switch circuit, wherein the positive end of the first bridge circuit is connected to the first terminal P, and the first terminal P outputs a high voltage, the negative end of the first bridge circuit is connected to the second terminal N, and the second terminal N outputs a low voltage, one end of the switch circuit is connected to the first bridge circuit, and the other end of the switch circuit is connected to the third terminal Y, and the third terminal Y outputs a middle voltage;

[0053] The compensating conversion unit obtains energy from between the first terminal P and the second terminal N, and injects the obtained energy between the first terminal P and the third terminal Y or between the third terminal Y and the second terminal N according to different sectors, and includes an industrial frequency switching unit and a high-frequency converter, wherein the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end of the industrial frequency switching unit is connected to the third terminal Y, the third input end of the industrial frequency switching unit is connected to the second terminal N, the output end of the industrial frequency switching unit is connected to the output end of the high-frequency converter, the first input end of the high-frequency converter is connected to the first terminal P, and the second input end of the high-frequency converter is connected to the second terminal N.

[0054] In a possible implementation, the power frequency switching unit includes a first switch tube S1, a second switch tube S2, a first diode D1 and a second diode D2, the first diode D1 is connected between the first input end of the power frequency switching unit and the positive output end of the power frequency switching unit, the first switch tube S1 is connected between the second input end of the power frequency switching unit and the positive output end of the power frequency switching unit, the second switch tube S2 is connected between the second input end of the power frequency switching unit and the negative output end of the power frequency switching unit, and the second diode D2 is connected between the third input end of the power frequency switching unit and the negative output end of the power frequency switching unit, such as Figure 2a , Figure 2b shown.

[0055] The high-frequency converter includes a first transformer T1, a third diode D3, a first capacitor C1, a first inductor L1 and a third switch tube S3. The first end of the primary winding of the first transformer T1 is connected to the third diode D3 and then connected to the positive output end of the high-frequency converter. The second end of the primary winding of the first transformer T1 is connected to the negative output end of the high-frequency converter. The first end of the secondary winding of the first transformer T1 is connected to the first capacitor C1 and the first inductor L1 in sequence and then connected to the first terminal P. The second end of the secondary winding of the first transformer T1 is connected to the second terminal N. The first capacitor C1 is connected to the third switch tube S3 and then connected to the second terminal N. Figure 2a , Figure 2c shown.

[0056] The positive output terminal of the power frequency switching unit is connected to the positive output terminal of the high frequency converter, and the negative output terminal of the power frequency switching unit is connected to the negative output terminal of the high frequency converter. Figure 2a-2c shown.

[0057] In this embodiment, the high-frequency converter mainly realizes the waveform control of the input current and the output current, and the power frequency switching unit mainly connects the output of the high-frequency converter to PY or YN according to the sector.

[0058] The high-frequency converter is an isolated Sepic circuit. In order to achieve power factor correction, the output current of the isolated Sepic circuit should be controlled to a Y-point waveform. Usually, peak current control can achieve the purpose better. If you want to reduce the pressure of the input low-frequency filter, you can choose to connect two Sepic circuits in parallel. The high-frequency current waveform of the output of one of the circuits is as follows: Figure 2d , the total high frequency average value is Figure 2e The control logic of the power frequency switching unit is: Figure 2e When the average value IyAvg of the current at point Y is greater than zero, the first switch tube S1 is turned off and the second switch tube S2 is turned on. When IyAvg is less than zero, the second switch tube S2 is turned off and the first switch tube S1 is turned on.

[0059] The compensation conversion unit obtains about 5% of the energy of the entire converter output power from PN in each power frequency cycle, and injects it into PY or YN according to different sectors to compensate the current at point P or point N to ensure the realization of unity power factor.

[0060] In one possible implementation, multi-phase interleaving can be used to further reduce the input current ripple. That is, two or more identical structures are connected in parallel, and the switching frequency and control method of each circuit are the same as the original method, but the driving phase difference is 180° (120° for three-phase interleaving). When interleaving in parallel, the power frequency link can be reused, such as Figure 2f .

[0061] In one possible implementation, Boost-LLC or other topologies such as dual-switch flyback are used to implement it, such as Figure 2g .

[0062] In a possible implementation, a BuckBoost-like structure can be selected to have the functions of both power frequency switching and compensation conversion unit, such as Figure 2h .

[0063] In a possible implementation, the DC / DC high-frequency conversion unit includes a second bridge circuit, an LLC circuit, a second transformer T2, a third bridge circuit and a third capacitor C3 connected in sequence, the second bridge circuit includes a first bridge arm and a second bridge arm, the positive end of the first bridge arm is connected to the first terminal P, the negative end of the first bridge arm is connected to the second terminal N, and the midpoint of the first bridge arm is connected to the LLC circuit, such as Figure 3a shown.

[0064] The LLC circuit includes a second inductor L2 and a second capacitor C2, one end of the second inductor L2 is connected to the midpoint of the first bridge arm, the other end of the second inductor L2 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the first end of the primary winding of the second transformer T2.

[0065] The positive end of the second bridge arm is connected to the first terminal P, the negative end of the second bridge arm is connected to the second terminal N, and the midpoint of the second bridge arm is connected to the second end of the primary winding of the second transformer T2.

[0066] The third bridge circuit includes a third bridge arm and a fourth bridge arm, the positive end and the negative end of the third bridge arm are respectively connected to the two ends of the third capacitor C3, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the second transformer T2, the positive end and the negative end of the fourth bridge arm are respectively connected to the two ends of the third capacitor C3, the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the second transformer, and the two ends of the third capacitor C3 are connected to the output voltage.

[0067] In a possible implementation, the first bridge arm includes a fourth switch tube S4 and a fifth switch tube S5, and the second bridge arm includes a sixth switch tube S6 and a seventh switch tube S7.

[0068] The third bridge arm includes a fourth diode D4 and a fifth diode D5, and the fourth bridge arm includes a sixth diode D6 and a seventh diode D7.

[0069] The DC / DC high-frequency conversion unit of the present invention is a typical full-bridge LLC, the driving waveforms of the fourth switch tube S4 and the fifth switch tube S5 are complementary, the driving waveforms of the sixth switch tube S6 and the seventh switch tube S7 are complementary, the duty cycle of each switch tube in the main working condition is 50%, the driving phase of the fourth switch tube S4 and the seventh switch tube S7 is the same, and the driving phase of the fifth switch tube S5 and the sixth switch tube S6 is the same.

[0070] The impedance of the resonant circuit is adjusted by adjusting the frequency of each drive, thereby controlling the waveform and amplitude of the input current of this part of the circuit. The control principle block diagram is shown in Figure 3b As shown. IDcDcAvg is the average value of each high-frequency cycle of the actual input current of the DC / DC high-frequency conversion unit, which can be obtained by passing the actual input current through a low-pass filter with a cutoff frequency of about several kHz; IMainRef is the input current reference of the DC / DC high-frequency conversion unit determined by the output voltage loop and the current mains voltage; CntlFunc is the regulator. Since the input reference is not a DC quantity, a simple PI regulator is generally not competent. It is usually necessary to select a double-zero bipolar or a nonlinear regulator with better performance. Its output is the switching frequency, which is converted into two complementary square waves through a square wave generator. Its duty cycle is fixed at 50%, and the dead zone is set according to the switching frequency and the selected hardware circuit, usually at 100ns-1us.

[0071] In addition to the above methods, current-type or charge-type control methods can also be used to implement LLC closed-loop control, thereby controlling the average current flowing into the LLC circuit to IMainRef, so that its product with the PN voltage is a stable DC value.

[0072] When the DC / DC high-frequency conversion unit finally works in steady state, Figure 3c is the expected average current of the DC / DC high-frequency conversion unit, which is obtained by dividing the expected input power determined by the output voltage loop by the PN voltage. Figure 3d is the input voltage of the DC / DC high-frequency conversion unit, that is, the voltage between the first terminal P and the second terminal N. Figure 3e is the actual input current of the DC / DC high-frequency conversion unit, where I-DcDc is the instantaneous value that changes with the high-frequency operation of the converter, and IDcDcAvg is the average value of the current in each high-frequency cycle. Figure 3c-Figure 3e A certain instant of the current waveform is magnified, such as Figure 3f It is the driving of the field effect tube, wherein DRV1 is the driving of the fourth switch tube S4 and the seventh switch tube S7, and DRV2 is the driving of the fifth switch tube S5 and the sixth switch tube S6. Figure 3g It is the input voltage of the DC / DC high frequency conversion unit, that is, the voltage between the first terminal P and the second terminal N. Figure 3h It is the actual input current of the DC / DC high-frequency conversion unit, where I-DcDc is the instantaneous value that changes continuously with the high-frequency action of the converter, and IDcDcAvg is the average current of each high-frequency cycle. Figure 3i It is the current on the primary side of the DC / DC high-frequency conversion unit transformer, that is, the current in the resonant cavity of the LLC converter.

[0073] The DC / DC high-frequency conversion unit obtains energy from PN and outputs it to the load. Its input voltage and input current are both DC quantities with small pulsation. The product of the average values ​​of the input voltage and input current in a single high-frequency cycle, that is, the average power, is a DC quantity.

[0074] In a possible implementation, the DC / DC high-frequency conversion unit is an LLC, a phase-shifted full-bridge circuit, or a multi-phase interleaved circuit of an LLC or a phase-shifted full-bridge. Figure 3j shown.

[0075] In a possible implementation, multiple transformers are connected in series and parallel, or a single transformer secondary side is wound in parallel with two wires and then rectified and connected in series and parallel. Figure 3k .

[0076] In a possible implementation, the low-pass filtering unit includes a third inductor L3, a fourth inductor L4 and a fifth inductor L5, one end of the third inductor L3 is connected to one phase of the three-phase alternating current, the other end of the third inductor L3 is connected to the first bridge circuit, and the other end of the third inductor L3 is connected to the fourth capacitor C4.

[0077] One end of the fourth inductor L4 is connected to another phase of the three-phase alternating current, the other end of the fourth inductor L4 is connected to the first bridge circuit, and the other end of the fourth inductor L4 is connected to the fifth capacitor C5.

[0078] One end of the fifth inductor L5 is connected to the third phase of the three-phase alternating current, the other end of the fifth inductor L5 is connected to the first bridge circuit, and the other end of the fifth inductor L5 is connected to the sixth capacitor C6.

[0079] The other end of the fourth capacitor C4, the other end of the fifth capacitor C5 and the other end of the sixth capacitor C6 are connected to each other. Figure 4 shown.

[0080] The low-pass filter unit is usually an LC low-pass filter or a filter unit composed only of X capacitors, which is mainly used to filter out the high-frequency current ripple generated by the high-frequency converter. The low-pass filter unit is mainly used to filter out the ripple current caused by the high-frequency switch of the compensation conversion unit and the DC / DC high-frequency conversion unit, suppress the harmonics of the input current, and improve the quality of the input current. The cut-off frequency should be between the switching frequency and the mains frequency, which can effectively filter out the high-frequency current ripple without affecting the power frequency current fundamental wave.

[0081] Low-pass filtering is an optional unit. In general product implementations, the differential mode filter added to the AC or the differential mode filter parasitic on the common mode filter can have the function of this part. If the high-frequency conversion of the compensation conversion unit and the DC / DC high-frequency conversion unit adopts a multi-phase interleaved parallel structure, the input high-frequency ripple will be greatly reduced to the point where it can be filtered out only by X capacitors and parasitic inductance.

[0082] In one possible implementation, the first bridge circuit includes a fifth bridge arm, a sixth bridge arm and a seventh bridge arm, the midpoint of the fifth bridge arm is connected to the other end of the third inductor L3, the positive end of the fifth bridge arm is connected to the first terminal P, the negative end of the fifth bridge arm is connected to the second terminal N, the midpoint of the sixth bridge arm is connected to the other end of the fourth inductor L4, the positive end of the sixth bridge arm is connected to the first terminal P, the negative end of the sixth bridge arm is connected to the second terminal N, the midpoint of the seventh bridge arm is connected to the other end of the fifth inductor L5, the positive end of the seventh bridge arm is connected to the first terminal P, and the negative end of the seventh bridge arm is connected to the second terminal N.

[0083] The switching circuit includes a first branch, a second branch and a third branch, one end of the first branch is connected to the midpoint of the fifth bridge arm, the other end of the first branch is connected to the third terminal Y, one end of the second branch is connected to the midpoint of the sixth bridge arm, the other end of the second branch is connected to the third terminal Y, one end of the third branch is connected to the midpoint of the seventh bridge arm, and the other end of the third branch is connected to the third terminal Y.

[0084] In a possible implementation, the fifth bridge arm includes an eighth diode D8 and a ninth diode D9, the sixth bridge arm includes a tenth diode D10 and an eleventh diode D11, and the seventh bridge arm includes a twelfth diode D12 and a thirteenth diode D13.

[0085] The first branch includes a first bidirectional switch S14, the second branch includes a second bidirectional switch S15, and the third branch includes a third bidirectional switch S16.

[0086] like Figure 5aThe first bidirectional switch S14, the second bidirectional switch S15 and the third bidirectional switch S16 are three groups of power frequency bidirectional switches. The conduction state of the three groups of switches is controlled by judging the current three-phase voltage. The two corresponding switches with the highest and lowest voltages are kept off, and the switch with the middle voltage is turned on. In this way, each power frequency cycle is divided into 6 sectors. Figure 5b It is the voltage waveform of PY, YN, and PN after sector selection rectification, where the voltage waveform of PN is above the dotted line and the voltage waveform of the intersection of PY and YN is below the dotted line. Figure 5c is the mains voltage, Figure 5d It is the driving of three bidirectional switches, wherein VGDC is the driving of the third bidirectional switch S16, VGDB is the driving of the second bidirectional switch S15, and VGDA is the driving of the first bidirectional switch S14.

[0087] Since the sector selection unit is actually equivalent to the three-phase mains electricity passing through the diode and the field effect tube in each sector to form a triangle connection at the first terminal P, the third terminal Y and the second terminal N, the fourth capacitor C4, the fifth capacitor C5 and the sixth capacitor C6 can be moved between the three points P, Y and N, which is completely equivalent to the original circuit in principle. After moving to the first terminal P, the third terminal Y and the second terminal N, the capacitor is closer to the high-frequency switching devices such as the first switch tube S1 to the seventh switch tube S7, the lead inductance in the actual product is smaller, and the working condition of the switching device will be better. The specific circuit is as follows Figure 5e shown.

[0088] In a possible implementation, all switch tubes in the topology may be power semiconductor devices such as silicon-based or SiC-based field effect tubes, IGBTs, and GaN HEMTs, and all diodes may be diodes made of semiconductor materials such as silicon, SiC, and GaN.

[0089] A power factor correction method for a three-phase single-stage isolated rectifier is applied to the above-mentioned three-phase single-stage isolated rectifier, comprising:

[0090] The sector selection unit converts the input three-phase alternating current into pulsating direct current outputted from the first terminal P, the second terminal N and the third terminal Y through low-frequency switching; wherein the first terminal P is a high voltage, the second terminal N is a low voltage, and the third terminal Y is a middle voltage;

[0091] By controlling the DC / DC high-frequency conversion unit and the compensation conversion unit, the power between the first terminal P and the second terminal N is distributed to the DC / DC high-frequency conversion unit according to a first preset ratio, and the power between the first terminal P and the second terminal N is distributed to the compensation conversion unit for processing according to a second preset ratio; the first preset ratio is greater than the second preset ratio;

[0092] By controlling the compensating transformation unit, the energy processed by the compensating transformation unit is injected between the first terminal P and the third terminal Y, or between the third terminal Y and the second terminal N, so as to compensate the current of the first terminal P or the second terminal N, so that the currents of the first terminal P, the second terminal N and the third terminal Y are all reference values ​​corresponding to the unity power factor.

[0093] In a possible implementation, the method further includes:

[0094] Determine the power of the compensation conversion unit according to a preset formula;

[0095] The default formula is:

[0096]

[0097] Where T is the period of the input mains power, is the voltage between the first terminal p and the third terminal y, is the current at the third terminal y, It is the voltage between the third terminal y and the second terminal n.

[0098] In a possible implementation, the power of the DC / DC high-frequency conversion unit is:

[0099] In the sector where Iy is greater than or equal to zero, the power of the DC / DC high frequency conversion unit is equal to ABS(In)*Vpn-Iy*Vpy, and in the sector where Iy is less than zero, the power of the DC / DC high frequency conversion unit is equal to Ip*Vpn-Iy*Vyn, where ABS(In) is the absolute value of In.

[0100] The mechanism of the present invention to achieve power factor correction is as follows:

[0101] The total system power is divided into the theoretical value of 100% of the total output power, and- Three parts (taking into account Approximately equal to 5%, hereinafter referred to as approximately 5% ), use the DC / DC high-frequency conversion unit between the PN levels to process 100% of the power, and select a small power converter of about 5% of the total power as a compensation conversion unit to process this part of the power. The compensation conversion unit obtains about 5% of the power from PN and feeds this part of the power back to PY or YN according to different sectors. Figure 6a-6cTake the sector between the two vertical lines as an example, in this sector, Ppn=In*VPN corresponds to about 105% power; compensation power Pcompensate=Iy*VPY corresponds to about -5% power; IyRefABS is the absolute value of the Iy reference value, that is, the current that the compensation conversion unit should inject into PY; IMainRef=(In*VPN-Iy*VPY) / VPN corresponds to the current that the PN link needs to process, that is, 100% output power. Specifically, as Figure 6a-6c It can be seen that in the sector between the two vertical lines, if the DC / DC high-frequency conversion unit connected to the PN link controls its input current to IMainRef, the compensation conversion unit controls its output current to IyRefABS, and connects its output between PY through a low-frequency switching unit, then the unity power factor can be achieved and the input power IMainRef*Vpn of the DC / DC high-frequency conversion unit is a DC quantity, that is, the power factor correction is achieved while achieving stable DC power output. The same is true for other sectors, just connect the compensation conversion unit between PY or YN according to different sectors. By Figure 6a-6c By averaging the waveform shown, it can be obtained that the average output power of the compensation conversion unit is only about 5% of the power of the main converter, and the DC / DC high-frequency conversion unit has no power fluctuation, and the input power is 100% at any time. Figure 6a In the figure, the top of the upper dotted line is the reference value waveform of the current at the first terminal point P, the figure between the two dotted lines is the reference value waveform of the current at the third terminal point Y, and the bottom of the lower dotted line is the reference value waveform of the current at the second terminal point N.

[0102] The present invention achieves extremely small input voltage fluctuation and nearly zero power fluctuation of the DC / DC high-frequency conversion unit at the cost of only 5% power, greatly improves the working conditions of the DC / DC high-frequency conversion unit, and easily realizes full-range soft switching. In high-power scenarios ranging from tens of kilowatts to hundreds of kilowatts, it is only necessary to select a Boost-like structure converter with a power of several kilowatts, such as an isolated Sepic circuit, a BuckBoost circuit, etc., to achieve significant optimization of the efficiency and cost of the main power link, which has great practical value.

[0103] The specific calculation process of the power of the compensation conversion unit is as follows:

[0104] The three-phase mains voltage is known to be Va, Vb, and Vc.

[0105]

[0106] is the peak value of the input voltage, , f is the mains frequency.

[0107] The input current expression is:

[0108]

[0109] Im is the peak value of input current.

[0110] The instantaneous values ​​of Va, Vb, Vc are:

[0111]

[0112]

[0113]

[0114] The peak voltage is:

[0115]

[0116]

[0117] If unity power factor can be achieved, the three-phase current is:

[0118]

[0119]

[0120]

[0121] The total output power of the entire converter is:

[0122] The peak current is:

[0123] I

[0124] After sector selection, Vp, Vn, and Vy are:

[0125] Max(Va(t),Vb(t),Vc(t))

[0126] Min(Va(t),Vb(t),Vc(t))

[0127] Mid(Va(t),Vb(t),Vc(t))

[0128] After sector selection, Vpn, Vyn, and Vpy are:

[0129]

[0130]

[0131]

[0132] After sector selection, Ip, Iy, and In are:

[0133] Max(Ia(t),Ib(t),Ic(t))

[0134] Min(Ia(t),Ib(t),Ic(t))

[0135]

[0136] when When , where T is the input mains cycle, and the power processed by the compensation conversion unit is:

[0137]

[0138]

[0139]

[0140] The proportion of the compensation conversion unit to the total power is:

[0141]

[0142] Therefore, the power of the compensation conversion unit of the present invention accounts for about 5% of the total power.

[0143] Finally, the input current and voltage waveform diagram of the present invention is as follows: Figure 7a , Figure 7b shown.

[0144] The present invention converts three-phase AC power into three power frequency fluctuation points of P, Y, and N through a sector selection unit, thereby reducing the voltage fluctuation that the subsequent DC / DC converter needs to handle, thereby reducing the loss. The compensation conversion unit is added, which only occupies about 5% of the total system power and is used to process the power flow of PY and YN, while most of the power is processed through the PN link. The DC / DC high-frequency conversion unit obtains energy from PN and outputs it to the load. Its input voltage and input current are both DC quantities with small pulsation, which reduces the average power fluctuation in the high-frequency cycle, is easy to achieve full-range soft switching, and improves the conversion efficiency. By selecting mainstream soft-switching high-frequency DC / DC conversion topologies such as LLC / phase-shifted full-bridge, full-range zero voltage switching (ZVS) is achieved, switching losses are reduced, and conversion efficiency is improved. The sector selection circuit switches at power frequency, and switches and diodes with slower switching speeds but lower conduction voltage drops can be selected to reduce conduction losses. The power factor inductor, busbar capacitor, and input pre-charge circuit in the two-stage solution are omitted, the number of circuit components is reduced, and the cost and loss are reduced. By optimizing circuit design and component selection, the power density is increased, the volume and weight are reduced, and the cost performance of the system is improved. The pre-charging circuit is omitted, and there is no need to pre-charge the busbar. The startup response speed is greatly improved, and the energy loss during the startup process is reduced. Through a reasonable control strategy, the input and output currents of the high-frequency isolation DC / DC unit and the auxiliary regulation unit are accurately controlled, and the current waveforms of PN, YN and PY are optimized to ensure that the entire system reaches unity power factor and reduce energy loss.

[0145] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase single-stage isolation rectifier, characterized in that: include: A low-pass filter unit, a sector selection unit and a DC / DC high-frequency conversion unit are connected in sequence, and a compensation conversion unit is connected in parallel between the sector selection unit and the DC / DC high-frequency conversion unit; wherein the low-pass filter unit is connected to a three-phase alternating current, and the DC / DC high-frequency conversion unit is connected to a DC load; The sector selection unit converts three-phase AC power into three DC power paths and adjusts the order of the three DC power paths, and includes a first bridge circuit and a switch circuit, wherein the positive end of the first bridge circuit is connected to a first terminal P, and the first terminal P outputs a high voltage, the negative end of the first bridge circuit is connected to a second terminal N, and the second terminal N outputs a low voltage, one end of the switch circuit is connected to the midpoint of the first bridge circuit, and the other end of the switch circuit is connected to a third terminal Y, and the third terminal Y outputs a middle voltage; The compensating conversion unit obtains energy from between the first terminal P and the second terminal N, and injects the obtained energy between the first terminal P and the third terminal Y or between the third terminal Y and the second terminal N according to different sectors, and includes an industrial frequency switching unit and a high-frequency converter, the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end of the industrial frequency switching unit is connected to the third terminal Y, the third input end of the industrial frequency switching unit is connected to the second terminal N, the output end of the industrial frequency switching unit is connected to the output end of the high-frequency converter, the first input end of the high-frequency converter is connected to the first terminal P, and the second input end of the high-frequency converter is connected to the second terminal N.

2. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The power frequency switching unit includes a first switch tube, a second switch tube, a first diode and a second diode, wherein the first diode is connected between the first input end of the power frequency switching unit and the positive output end of the power frequency switching unit, the first switch tube is connected between the second input end of the power frequency switching unit and the positive output end of the power frequency switching unit, the second switch tube is connected between the second input end of the power frequency switching unit and the negative output end of the power frequency switching unit, and the second diode is connected between the third input end of the power frequency switching unit and the negative output end of the power frequency switching unit; The high-frequency converter includes a first transformer, a third diode, a first capacitor, a first inductor and a third switch tube, wherein a first end of a primary winding of the first transformer is connected to the third diode and then to a positive output end of the high-frequency converter, a second end of a primary winding of the first transformer is connected to a negative output end of the high-frequency converter, a first end of a secondary winding of the first transformer is connected to the first capacitor and the first inductor in sequence and then to the first terminal P, a second end of a secondary winding of the first transformer is connected to the second terminal N, and the first capacitor is connected to the third switch tube and then to the second terminal N; The positive output end of the power frequency switching unit is connected to the positive output end of the high frequency converter, and the negative output end of the power frequency switching unit is connected to the negative output end of the high frequency converter.

3. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The DC / DC high-frequency conversion unit is an LLC, a phase-shifted full-bridge circuit, or a multi-phase interleaved circuit of an LLC or a phase-shifted full-bridge.

4. The three-phase single-stage isolation rectifier according to claim 3, characterized in that: The DC / DC high-frequency conversion unit includes a second bridge circuit, an LLC circuit, a second transformer, a third bridge circuit and a third capacitor connected in sequence, the second bridge circuit includes a first bridge arm and a second bridge arm, the positive end of the first bridge arm is connected to the first terminal P, the negative end of the first bridge arm is connected to the second terminal N, and the midpoint of the first bridge arm is connected to the LLC circuit; The LLC circuit comprises a second inductor and a second capacitor, one end of the second inductor is connected to the midpoint of the first bridge arm, the other end of the second inductor is connected to one end of the second capacitor, and the other end of the second capacitor is connected to the first end of the primary winding of the second transformer; The positive end of the second bridge arm is connected to the first terminal P, the negative end of the second bridge arm is connected to the second terminal N, and the midpoint of the second bridge arm is connected to the second end of the primary winding of the second transformer; The third bridge circuit includes a third bridge arm and a fourth bridge arm, the positive end and the negative end of the third bridge arm are respectively connected to the two ends of the third capacitor, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the second transformer, the positive end and the negative end of the fourth bridge arm are respectively connected to the two ends of the third capacitor, the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the second transformer, and the two ends of the third capacitor are connected to the output voltage.

5. The three-phase single-stage isolation rectifier according to claim 4, characterized in that: The first bridge arm includes a fourth switch tube and a fifth switch tube, and the second bridge arm includes a sixth switch tube and a seventh switch tube; The third bridge arm includes a fourth diode and a fifth diode, and the fourth bridge arm includes a sixth diode and a seventh diode.

6. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The low-pass filter unit includes a third inductor, a fourth inductor and a fifth inductor, one end of the third inductor is connected to one phase of the three-phase alternating current, the other end of the third inductor is connected to the first bridge circuit, and the other end of the third inductor is connected to a fourth capacitor; One end of the fourth inductor is connected to another phase of the three-phase alternating current, the other end of the fourth inductor is connected to the first bridge circuit, and the other end of the fourth inductor is connected to a fifth capacitor; One end of the fifth inductor is connected to the third phase of the three-phase alternating current, the other end of the fifth inductor is connected to the first bridge circuit, and the other end of the fifth inductor is connected to a sixth capacitor; The other end of the fourth capacitor, the other end of the fifth capacitor and the other end of the sixth capacitor are connected to each other.

7. The three-phase single-stage isolation rectifier according to claim 6, characterized in that: The first bridge circuit includes a fifth bridge arm, a sixth bridge arm and a seventh bridge arm, the midpoint of the fifth bridge arm is connected to the other end of the third inductor, the positive end of the fifth bridge arm is connected to the first terminal P, the negative end of the fifth bridge arm is connected to the second terminal N, the midpoint of the sixth bridge arm is connected to the other end of the fourth inductor, the positive end of the sixth bridge arm is connected to the first terminal P, the negative end of the sixth bridge arm is connected to the second terminal N, the midpoint of the seventh bridge arm is connected to the other end of the fifth inductor, the positive end of the seventh bridge arm is connected to the first terminal P, and the negative end of the seventh bridge arm is connected to the second terminal N; The switching circuit includes a first branch, a second branch and a third branch, one end of the first branch is connected to the midpoint of the fifth bridge arm, the other end of the first branch is connected to the third terminal Y, one end of the second branch is connected to the midpoint of the sixth bridge arm, the other end of the second branch is connected to the third terminal Y, one end of the third branch is connected to the midpoint of the seventh bridge arm, and the other end of the third branch is connected to the third terminal Y.

8. The three-phase single-stage isolation rectifier according to claim 7, characterized in that: The fifth bridge arm includes an eighth diode and a ninth diode, the sixth bridge arm includes a tenth diode and an eleventh diode, and the seventh bridge arm includes a twelfth diode and a thirteenth diode; The first branch includes a first bidirectional switch, the second branch includes a second bidirectional switch, and the third branch includes a third bidirectional switch.

9. A power factor correction method for a three-phase single-stage isolated rectifier, applied to the three-phase single-stage isolated rectifier according to any one of claims 1 to 8, characterized in that: include: The sector selection unit converts the input three-phase alternating current into pulsating direct current outputted from the first terminal P, the second terminal N and the third terminal Y through low-frequency switching; wherein the first terminal P is a high voltage, the second terminal N is a low voltage, and the third terminal Y is a middle voltage; By controlling the DC / DC high-frequency conversion unit and the compensating conversion unit, the power between the first terminal P and the second terminal N is distributed to the DC / DC high-frequency conversion unit according to a first preset ratio, and the power between the first terminal P and the second terminal N is distributed to the compensating conversion unit for processing according to a second preset ratio; the first preset ratio is greater than the second preset ratio; By controlling the compensation transformation unit, the energy processed by the compensation transformation unit is injected between the first terminal P and the third terminal Y, or between the third terminal Y and the second terminal N, so as to compensate the current of the first terminal P or the second terminal N, so that the currents of the first terminal P, the second terminal N and the third terminal Y are all reference values ​​corresponding to the unity power factor.

10. The power factor correction method of the three-phase single-stage isolation rectifier according to claim 9, characterized in that: The method further comprises: Determining the power of the compensation conversion unit according to a preset formula; The preset formula is: Where T is the period of the input mains power, is the voltage between the first terminal p and the third terminal y, is the current at the third terminal y, It is the voltage between the third terminal y and the second terminal n.

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