Three-phase single-stage isolation rectifier and control method

Abstract

The invention provides a three-phase single-stage isolation rectifier and a control method, and relates to the technical field of switching power supplies. The three-phase single-stage isolation rectifier comprises a sector selection unit, an auxiliary conversion unit, a main conversion unit and a total output end, the sector selection unit is connected with three-phase alternating current and is used for converting the three-phase alternating current into three paths of pulsating direct current and outputting the three paths of pulsating direct current through a first terminal P, a second terminal N and a third terminal Y; wherein the first terminal P outputs high voltage, the second terminal N outputs low voltage, and the third terminal Y outputs middle voltage; the input end of the auxiliary conversion unit is connected with the first terminal P, the second terminal N and the third terminal Y, and the output end of the auxiliary conversion unit is connected with the total output end and provides energy of a first preset proportion for the total output end. According to the three-phase single-stage isolation rectifier, the loss can be reduced.

Description

Technical Field

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

[0002] Three-phase single-stage isolated rectifiers are mainly used to convert three-phase AC power into DC power and achieve electrical isolation, and are commonly used in industrial fields and power systems. With the popularization of new energy technologies and the continuous 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 operation power supply, and the requirements for the conversion efficiency and power density of related products are also getting higher and higher.

[0003] At present, the three-phase isolated single-stage converter is mainly studied by using the matrix converter type, sector selection type and the idea of ​​treating three phases as three single phases. The principle of the matrix converter type is that six sets of bidirectional switches are used to realize the current distribution relationship between the three-phase current and the high-frequency DC / DC link, taking into account the three-phase power factor and output voltage regulation, and realizing electrical isolation at the same time. The principle of the sector selection type is to convert the three-phase AC power into three power frequency fluctuation points P, Y, and N through the sector selection unit, where the voltage waveforms between PY and YN are similar, both varying from zero to about 0.866 times the voltage peak; the voltage between PN varies from 0.866 times to 1 times the voltage peak. Then select a suitable DCDC converter to convert the pulsating voltage waveform of the three points PYN into a DC output. The principle of the three single-phase types is to divide the three-phase TV into three single phases AB, BC, and CA, and then use three single-phase DC / DC converters to process them respectively.

[0004] However, all power semiconductors in the matrix converter type operate at high frequencies, the soft switching logic is complex, and all bridge arms cannot be short-circuited or open-circuited, making it difficult to ensure reliability. The converter in the sector selection type has large losses and cannot meet high power requirements. The voltage fluctuations of each phase of the three single-phase types are very large and cannot meet high power requirements. A three-phase single-stage isolated rectifier with low losses is urgently needed. Summary of the invention

[0005] The embodiment of the present invention provides a three-phase single-stage isolation rectifier and a control method to solve the problem that the current three-phase single-stage isolation rectifier is prone to serious damage.

[0006] In a first aspect, an embodiment of the present invention provides a three-phase single-stage isolation rectifier, comprising a sector selection unit, an auxiliary conversion unit, a main conversion unit and a total output terminal; The sector selection unit is connected to the three-phase AC power, and is used to convert the three-phase AC power into three pulsating DC power and output it through the first terminal P, the second terminal N and the third terminal Y; wherein the first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage; The input end of the auxiliary conversion unit is respectively connected to the first terminal P, the second terminal N and the third terminal Y, and the output end of the auxiliary conversion unit is connected to the total output end to provide a first preset proportion of energy to the total output end; The input end of the main conversion unit is connected to the first terminal P and the second terminal N, and the output end thereof is connected to the total output end, and provides a second preset ratio of energy to the total output end; wherein the first preset ratio is less than the second preset ratio, and the sum of the first preset ratio and the second preset ratio is 1; the total output end is used to provide voltage and energy to the DC load; Control the action time of the input level of the auxiliary conversion unit so that the change law of the input current of the auxiliary conversion unit is the same as the first preset reference current; control the action time of the input level of the main conversion unit so that the change law of the input current of the main conversion unit is the same as the second preset reference current; the first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal Y, and the second preset reference current is a reference current flowing from the first terminal P to the second terminal N.

[0007] In one possible implementation, the first preset reference current includes a first standard current and a second standard current, wherein the first standard current is a current greater than zero obtained by decomposing the current waveform at the third terminal point Y, and the second standard current is a current less than zero obtained by decomposing the current waveform at the third terminal point Y.

[0008] In a possible implementation, the auxiliary conversion unit includes a first high-frequency conversion unit and a second high-frequency conversion unit, and the first high-frequency conversion unit and the second high-frequency conversion unit output energy to the total output end alternately based on different sectors; The first input end of the first high-frequency conversion unit is connected to the first terminal P, the second input end thereof is connected to the third terminal Y, and the output end of the first high-frequency conversion unit is connected to the total output end; The first input end of the second high frequency conversion unit is connected to the second terminal N, the second input end is connected to the third terminal Y, the output end of the first high frequency conversion unit is connected to the total output end, and the output end of the second high frequency conversion unit is connected to the total output end.

[0009] In a possible implementation, the first high-frequency conversion unit or the second high-frequency conversion unit includes at least one high-frequency isolation converter; When the first high-frequency conversion unit or the second high-frequency conversion unit includes a plurality of identical high-frequency isolation converters, the plurality of identical high-frequency isolation converters are connected in parallel.

[0010] In a possible implementation, the auxiliary conversion unit includes an industrial frequency switching unit and a high-frequency conversion unit, the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end is connected to the second terminal N, and the third input end is connected to the third terminal Y; the output end of the industrial frequency switching unit is connected to the input end of the high-frequency conversion unit, and the output end of the high-frequency conversion unit is connected to the total output end.

[0011] In a possible implementation, the main conversion unit is an LLC circuit, a phase-shifted full-bridge circuit, a multi-phase interleaved circuit composed of an LLC circuit or a phase-shifted full-bridge circuit, a plurality of transformers connected in series and parallel to a rectifier circuit, or a single transformer secondary-side double-wired rectifier circuit; The three-phase single-stage isolation rectifier further includes a low-pass filtering unit, which includes an LC low-pass filter, an X capacitor or a parasitic inductor.

[0012] In a possible implementation, the first preset ratio is , the second preset ratio is 1- .

[0013] In a second aspect, an embodiment of the present invention provides a control method for a three-phase single-stage isolated rectifier, which is applied to the three-phase single-stage isolated rectifier of any one of the first aspects, including: The sector selection unit converts the input three-phase AC power into three pulsating DC power and outputs them through the first terminal P, the second terminal N and the third terminal Y; wherein the first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage; Based on the positive and negative polarity of the current at the third terminal Y, the current output from the third terminal Y is decomposed into a first standard current and a second standard current, and the input current of the auxiliary conversion unit is controlled to track the first standard current and the second standard current, so that the change rule of the input current of the auxiliary conversion unit is the same as the first preset reference current and the energy of the first preset proportion is output to the total output end; The input current of the main conversion unit is controlled to track the second preset reference current so that the change pattern of the input current of the main conversion unit is the same as the second preset reference current and a second preset proportion of energy is output to the total output end; wherein the second preset reference current is a reference current flowing from the first terminal P to the second terminal N; the first preset proportion is less than the second preset proportion, and the sum of the first preset proportion and the second preset proportion is 1.

[0014] In a possible implementation, controlling the input current of the auxiliary conversion unit to track the first standard current and the second standard current includes: The input current of the auxiliary conversion unit is controlled by using peak current to track the first standard current and the second standard current; Controlling the input current of the main conversion unit to track a second preset reference current includes: The input current of the main conversion unit is controlled by using the peak current to track the second preset reference current.

[0015] In a possible implementation, the first preset ratio is , the second preset ratio is 1- .

[0016] The embodiment of the present invention provides a three-phase single-stage isolation rectifier, including a sector selection unit, an auxiliary conversion unit and a main conversion unit. By controlling the action time of the input level of the main conversion unit, the change law of the input current of the main conversion unit is made the same as the second preset reference current, so that most of the power can be processed by the main conversion unit. In addition, by controlling the action time of the input level of the auxiliary conversion unit, the change law of the input current of the auxiliary conversion unit is made the same as the first preset reference current, and the first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal point Y, so that when the auxiliary conversion unit processes the current at the point Y, it can select the sector with a higher voltage in the PY circuit and the YN circuit as the input voltage, without having to process the working condition where the input voltage in the PY circuit and the YN circuit is close to zero, thereby greatly changing the working conditions of the auxiliary conversion unit, further reducing the loss, and more easily realizing soft switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic diagram of the structure of a three-phase single-stage isolation rectifier provided in an embodiment of the present invention; Figure 2a Schematic diagram of voltage waveforms of PY, YN, and PN after sector selection provided by an embodiment of the present invention; Figure 2b is a schematic diagram of reference waveforms of currents at points P, Y, and N after sector selection provided by an embodiment of the present invention; Figure 2c It is a schematic diagram of decomposing the Y point current waveform into a first standard current IynRef and a second standard current IpyRef after sector selection provided by an embodiment of the present invention; Figure 3a is a circuit structure diagram of an auxiliary conversion unit provided by an embodiment of the present invention; Figure 3b 1 is a schematic diagram of a waveform diagram of an auxiliary converter input voltage Vpy provided in an embodiment of the present invention; Figure 3c 1 is a schematic diagram of a waveform diagram of an auxiliary converter input current Ipy provided in an embodiment of the present invention; Figure 3d is a schematic diagram of a waveform diagram of an isolated Sepic unit provided in an embodiment of the present invention; Figure 4aIt is a circuit diagram of an auxiliary conversion unit including power frequency switching provided by an embodiment of the present invention; Figure 4b It is a circuit diagram of a specific implementation scheme of power frequency switching provided by an embodiment of the present invention; Figure 5a is a schematic diagram of the LLC circuit structure provided by an embodiment of the present invention; Figure 5b is a schematic diagram of a reference current waveform Ipy of a main control unit provided in an embodiment of the present invention; Figure 5c It is a schematic diagram of the instantaneous value of the input current of the main control unit provided by an embodiment of the present invention and the average value of the high-frequency cycle; Figure 5d The embodiment of the present invention provides Figure 5a Schematic diagram of driving waveforms of S9 and S10; Figure 5e The embodiment of the present invention provides Figure 5a Schematic diagram of driving waveforms of S11 and S12; Figure 6a is a schematic diagram of the structure of a three-phase interleaved LLC circuit provided by an embodiment of the present invention; Figure 6b It is a schematic diagram of the structure of a transformer winding series-parallel switching circuit provided by an embodiment of the present invention; Figure 7a is a schematic diagram of voltage waveforms of PY, YN, and PN after sector selection provided by an embodiment of the present invention; Figure 7b is a schematic diagram of current waveforms at points P, Y, and N after sector selection provided by an embodiment of the present invention; Figure 7c is a schematic diagram of a reference current IpnRef flowing from point P to point N provided by an embodiment of the present invention; Figure 8 is a schematic diagram of a circuit structure of a low-pass filter unit provided in an embodiment of the present invention; Fig. 9 is a schematic diagram of a circuit structure of a sector selection unit provided by an embodiment of the present invention; Fig.10a It is a schematic diagram of voltage waveforms of PY, YN, and PN outputted after the three-phase alternating current passes through the sector selection unit provided by an embodiment of the present invention; Fig.10b is a schematic diagram of the mains voltage provided by an embodiment of the present invention; Fig.10c is a schematic diagram of driving three bidirectional switches provided by an embodiment of the present invention; Fig.11ais a waveform diagram of an input voltage of a main conversion unit and an input voltage of an auxiliary conversion unit provided by an embodiment of the present invention; Fig.11b It is a schematic diagram of a current reference IpnRef of a main conversion unit and current references IpyRef and IynRef tracked by an auxiliary conversion unit provided in an embodiment of the present invention; Fig.11c is a power schematic diagram of a main conversion unit and an auxiliary conversion unit provided in an embodiment of the present invention; Fig.12a Schematic diagram of input Va, Vb, Vc AC voltage waveforms provided in an embodiment of the present invention; Figure 12b is a schematic diagram of the voltage waveforms of the Vyn and Vab lines provided in an embodiment of the present invention; Fig.12c 1 is a schematic diagram of an IynRef current waveform and an input current waveform of Ia provided in an embodiment of the present invention; Fig.13a is a schematic diagram of the final input voltage waveform provided by an embodiment of the present invention; Fig.13b It is a schematic diagram of the final input current waveform provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] The following is a detailed description of the implementation of the present invention in conjunction with the specific drawings: At present, although there are also ideas of using sector selection to construct three-phase single-stage isolated rectifiers, after long-term research by the inventors, it is found that in the existing sector selection schemes, a large part of the power actually needs to be processed by PY and YN as the input of the power converter, and the power converter that processes PY and YN still needs to provide a large processing power. In addition, there is another big problem. The inventors found that the switching loss and conduction loss of the current sector selection scheme are large. Since the voltage variation range of PY and YN is relatively wide, the voltage waveforms between PY and YN are similar, both varying from zero to about 0.866 times the voltage peak value. The wide voltage variation range leads to large losses, making it difficult to achieve soft switching, and the range of selection of power component parameters is relatively small, which is not conducive to the development of three-phase single-stage isolated rectifiers.

[0021] In order to solve many existing problems, the present invention provides a three-phase single-stage isolation rectifier.

[0022] 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 includes a sector selection unit 110, an auxiliary conversion unit 120, a main conversion unit 130 and a total output terminal 140.

[0023] The sector selection unit 110 is connected to the three-phase AC power, and is used to convert the three-phase AC power into three pulsating DC power and output it through the first terminal P, the second terminal N and the third terminal Y. The first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage.

[0024] The input end of the auxiliary conversion unit 120 is connected to the first terminal P, the second terminal N and the third terminal Y respectively, and the output end of the auxiliary conversion unit 120 is connected to the total output end 140 to provide the total output end 140 with energy of a first preset ratio and a DC voltage.

[0025] The input end of the main conversion unit 130 is connected to the first terminal P and the second terminal N, and the output end thereof is connected to the total output end 140, and provides energy of a second preset ratio and a DC voltage to the total output end 140. The first preset ratio is smaller than the second preset ratio, and the sum of the first preset ratio and the second preset ratio is 1, and the total output end 140 is used to provide voltage and energy to the DC load.

[0026] During the operation of the three-phase single-stage isolation rectifier, the action time of the input level of the auxiliary conversion unit 120 is controlled so that the change rule of the input current of the auxiliary conversion unit 120 is the same as the first preset reference current. The action time of the input level of the main conversion unit 130 is controlled so that the change rule of the input current of the main conversion unit 130 is the same as the second preset reference current. The first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal Y point, and the second preset reference current is a reference current flowing from the first terminal P to the second terminal N.

[0027] The first preset ratio is , the second preset ratio is 1- .

[0028] In order to reduce the overall loss, the present invention controls the action time of the input level of the main conversion unit 130 so that the change rule of the input current of the main conversion unit 130 is the same as the second preset reference current, so that most of the power can be processed by the main conversion unit 130. Since the voltage between the PN circuits input by the main conversion unit 130 changes from 0.866 times to 1 times of the voltage peak, the PN circuit voltage fluctuation range is small, the DC voltage is high, and the full range of zero voltage switching can be achieved, which can reduce the switching loss. In addition, by controlling the action time of the input level of the auxiliary conversion unit 120, the change rule of the input current of the auxiliary conversion unit 120 is made the same as the first preset reference current, and the first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal Y point, so that when the auxiliary conversion unit 120 processes the current at the Y point, it can select the sector with higher voltage in the PY path and the YN path as the input voltage, without having to process the working condition where the input voltage in the PY path and the YN path is close to zero, thereby greatly changing the working conditions of the auxiliary conversion unit, further reducing the loss, and making it easier to achieve soft switching. When selecting the parameters of the power element, it is not necessary to take into account the situation where the voltage variation range is high, and a small amount of power can be processed by the auxiliary conversion unit. By using the main conversion unit to process most of the power, the power of the auxiliary conversion unit can be greatly reduced, and soft switching can be more easily achieved.

[0029] In some embodiments, in order to more easily realize soft switching, it is necessary to control the input and output currents of the auxiliary conversion unit, thereby controlling the current waveforms of the PY circuit and the YN circuit, ensuring that the entire system reaches a unity power factor, and also ensuring that the main conversion unit can handle more power. The first preset reference current can be divided into a first standard current and a second standard current, the first standard current being a current greater than zero obtained by decomposing the current waveform at the third terminal Y point, and the second standard current being a current less than zero obtained by decomposing the current waveform at the third terminal Y point.

[0030] For example, Figure 2a , 2bAs shown in 2c, Figure 2a The red one is the voltage waveform of PY, the blue one is the voltage waveform of YN, and the green one is the voltage waveform of PN. Figure 2b The red one is the reference waveform of the current at point P, the green one is the reference waveform of the current at point N, and the blue one is the reference waveform of the current at point Y. Figure 2b It can be seen that Ip+Iy+In=0 at any time. Figure 2c In order to decompose the current waveform at point Y into the first standard current IynRef and the second standard current IpyRef, green represents IpyRef and red represents IynRef. The first standard current IynRef and the second standard current IpyRef correspond to the two states of the current at point Y being greater than zero and less than zero, respectively. At this time, as long as the input current of the auxiliary converter is controlled to track IynRef and IpyRef respectively, the power factor tracking of the Iy part can be achieved while transmitting energy to the load end.

[0031] from Figure 2c In the sectors of the two vertical lines 1 and 2 in , IynRef is the part of IyRef that is greater than zero. At this time, the auxiliary converter obtains energy from the corresponding Vyn. By controlling the action time of the auxiliary converter input level, the change law of the auxiliary converter input current meets the requirements of power factor correction. IpyRef is the other part of IyRef that is less than zero, and its working principle is consistent with the above principle.

[0032] In some embodiments, the auxiliary transform unit includes a first high frequency transform unit and a second high frequency transform unit, and the first high frequency transform unit and the second high frequency transform unit output energy to the total output end alternately based on different sectors.

[0033] In this embodiment, the first input end of the first high-frequency conversion unit is connected to the first terminal P, the second input end thereof is connected to the third terminal Y, and the output end of the first high-frequency conversion unit is connected to the total output end. The first input end of the second high-frequency conversion unit is connected to the second terminal N, the second input end thereof is connected to the third terminal Y, the output end of the first high-frequency conversion unit is connected to the total output end, and the output end of the second high-frequency conversion unit is connected to the total output end.

[0034] In this embodiment, the first high-frequency conversion unit or the second high-frequency conversion unit may include at least one high-frequency isolation converter. When the first high-frequency conversion unit or the second high-frequency conversion unit includes multiple identical high-frequency isolation converters, the multiple identical high-frequency isolation converters are connected in parallel.

[0035] For example, Figure 3aAs shown, the high-frequency isolation converter can be an isolated Sepic circuit. In order to achieve power factor correction, the output current of the isolated Sepic unit should be controlled to a Y-point waveform, and peak current control can usually achieve the desired result. Figure 3b , 3c As shown in 3D, Figure 3b This is the waveform of the auxiliary converter input voltage Vpy. Figure 3c This is the waveform of the auxiliary converter input current Ipy. Figure 3d The waveform diagram of the isolated Sepic unit. In addition, when the first high-frequency conversion unit or the second high-frequency conversion unit contains multiple identical isolated Sepic circuits, the multiple identical isolated Sepic circuits can be connected in parallel. The switching frequency and control method of each circuit are the same as the original method, but the phase difference of the drive is 180° if it is three-phase interleaving, which is 120°. The power frequency link can be reused when interleaving in parallel.

[0036] In some embodiments, the auxiliary conversion unit may further include an industrial frequency switching unit and a high-frequency conversion unit, wherein a first input end of the industrial frequency switching unit is connected to a first terminal P, a second input end thereof is connected to a second terminal N, and a third input end thereof is connected to a third terminal Y. An output end of the industrial frequency switching unit is connected to an input end of the high-frequency conversion unit, and an output end of the high-frequency conversion unit is connected to a total output end. By utilizing an industrial frequency switching unit, the input of the high-frequency conversion unit is connected to a PY path or a YN path as required.

[0037] In this embodiment, it can be Figure 4a The power frequency switching unit shown, Figure 4a The DC / DC conversion unit in is the high-frequency conversion unit in this embodiment. Figure 4b As shown, the power frequency switching unit in the present application can also be replaced by a switch tube and a diode. Figure 4a The switch in.

[0038] In some embodiments, the main conversion unit can be an LLC circuit, a phase-shifted full-bridge circuit, a multi-phase interleaved circuit composed of an LLC circuit or a phase-shifted full-bridge circuit, a plurality of transformers in series-parallel rectifier circuits, or a single transformer secondary side double-wired rectifier circuit.

[0039] In this embodiment, if Figure 5a In the LLC circuit shown, the drive waveforms of S9 and S10 are complementary, the drive waveforms of S11 and S12 are complementary, the duty cycle of each switch tube is 50% in the main working condition, the drive of S9 and S12 is in phase, and the drive of S10 and S11 is in phase. The impedance of the resonant circuit is adjusted by adjusting the frequency of each drive, thereby adjusting the waveform and amplitude of the input current of this part of the circuit.

[0040] In addition, in addition to using current-type or charge-type control methods to implement LLC closed-loop control, the average current flowing into the LLC circuit is controlled so that its waveform tracks the PN reference current waveform and its amplitude is controlled by the output voltage loop, such as Figure 5b-5e As shown, 5b is the reference current Ipy of the main control unit, and its value is obtained by subtracting the current value of the PY terminal from the current value of the P terminal Ip. 5c is the instantaneous value (green) of the input current of the main control unit and the average value (red) of the high-frequency cycle.

[0041] In this embodiment, the structure of the main conversion unit can also be as follows Figure 6a The three-phase interleaved LLC circuit structure diagram shown in FIG. Figure 6b This is a schematic diagram of the circuit structure for switching the transformer winding series and parallel.

[0042] In this embodiment, if Figure 7a-7c As shown, after the sector is selected, by controlling the action time of the input level of the main conversion unit, the change law of the input current of the main conversion unit is made the same as the second preset reference current IpnRef. The second preset reference current is the reference current IpnRef flowing from the first terminal P to the second terminal N, which is obtained by subtracting the current flowing from point P to point Y from the current flowing through point P. The main conversion unit obtains energy from Vpn, and by controlling the action time of the input level of the main converter, the change law of the input current of the main conversion unit is made consistent with IpnRef. The main conversion unit and the auxiliary conversion unit work together to make the input current of the entire converter meet the requirements of power factor correction, and at the same time complete the energy transmission to the load end.

[0043] In some embodiments, the three-phase single-stage isolated rectifier may further include a low-pass filter unit, which is mainly used to filter out the ripple current caused by the high-frequency switch in the auxiliary conversion unit and the main 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.

[0044] Of course, the low-pass filter unit can also be a differential mode filter or a common mode filter added by the AC in the product. The differential mode filter can also have this function. If the high-frequency conversion in the auxiliary conversion unit and the main conversion unit adopts a multi-phase interleaved parallel structure, the input high-frequency ripple will be greatly reduced to only require X capacitors and parasitic inductances to filter out. Figure 8 Shown is a schematic diagram of the circuit structure of a low-pass filtering unit.

[0045] In some embodiments, Fig. 9A schematic diagram of a sector selection unit circuit structure is shown, where S14, S15 and S16 respectively constitute three groups of industrial 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 remain off, and the switch with the middle voltage is turned on. In this way, each industrial frequency cycle is divided into 6 sectors.

[0046] The present invention converts three-phase alternating current into three power frequency fluctuation points of P, Y, and N through a sector selection unit, wherein the voltage waveforms between PY and YN are similar, both varying from zero to about 0.866 times the voltage peak value, and the voltage between PN varies from 0.866 times to 1 times the voltage peak value. In order to further reduce power consumption and realize full-range soft switching of almost all power semiconductor components at a low cost, about 78% of the total power is handled by the main conversion unit corresponding to the PN level, and the remaining 22% is handled by the auxiliary conversion unit corresponding to the PY and YN levels, thereby greatly reducing the power processed by the auxiliary conversion unit. Due to the high average PN voltage, the power element of the main conversion unit is easier to realize soft switching than the auxiliary conversion unit. When designing the parameters of the power element, there is no need to take into account the PY and YN working conditions with a wide voltage variation range, and the overall loss is much less than that of the auxiliary conversion unit. In addition, the difficulty of designing the auxiliary converter can be greatly reduced, and the working condition of the whole machine can be improved. In addition, the auxiliary conversion unit does not need to handle the working condition of the input voltage close to zero, and the design difficulty and loss of the auxiliary conversion unit are greatly improved. Thereby, the loss of the entire converter is further reduced and the efficiency is further improved.

[0047] The first preset ratio is , the second preset ratio is 1- , the calculation process of the first preset ratio and the second preset ratio is as follows: The input voltage expression is:

[0048] Vm is the peak value of the input voltage, ω=2πf, f is the mains frequency.

[0049] The input current expression is:

[0050] Im is the peak value of input current.

[0051] The expression of total power is

[0052] by Figure 2c Taking the vertical lines 1 and 2 as an example, the power at the YN end is:

[0053] The YN power of other sectors can also be obtained according to the different voltages and currents corresponding to different sectors, and the energy of YN in the cycle is obtained as follows:

[0054] After simplification, we get:

[0055] The total energy is:

[0056] After simplification, we get:

[0057] Combining 6 and 8, we get the power proportion of the auxiliary conversion unit corresponding to YN:

[0058] The auxiliary conversion unit processes a total power of , about 22.44%.

[0059] The output end of the auxiliary conversion unit in the present invention is connected to the total output end. The auxiliary conversion unit in this application extracts the energy obtained from the PN and YN ends to the total output end, which is completely different from the energy injection from the output end of the auxiliary conversion unit to the input end connected to the main conversion unit.

[0060] In addition, in a second aspect, the present invention further provides a control method for a three-phase single-stage isolated rectifier, which is applied to the three-phase single-stage isolated rectifier described above, comprising: The sector selection unit converts the input three-phase AC power into three pulsating DC power and outputs it through the first terminal P, the second terminal N and the third terminal Y. The first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage. Fig.10a The figure shows the voltage waveforms of PY, YN, and PN output after the three-phase AC passes through the sector selection unit. Fig.10b is the mains voltage, Fig.10c It is the driver of three bidirectional switches.

[0061] Based on the positive and negative polarity of the current at the third terminal Y, the current output from the third terminal Y is decomposed into a first standard current and a second standard current, and the input current of the auxiliary conversion unit is controlled to track the first standard current and the second standard current, so that the change pattern of the input current of the auxiliary conversion unit is the same as the first preset reference current and outputs a first preset proportion of energy to the total output end.

[0062] The input current of the main conversion unit is controlled to track the second preset reference current, so that the change rule of the input current of the main conversion unit is the same as the second preset reference current and the second preset ratio of energy is output to the total output end. The second preset reference current is a reference current flowing from the first terminal P to the second terminal N; the first preset ratio is less than the second preset ratio, and the sum of the first preset ratio and the second preset ratio is 1.

[0063] In some embodiments, in order to make the variation pattern of the input current of the auxiliary conversion unit the same as the first preset reference current, the input current of the auxiliary conversion unit can be controlled by peak current to track the first standard current and the second standard current.

[0064] In this embodiment, in order to more easily realize soft switching, it is necessary to control the input and output currents of the auxiliary conversion unit, thereby controlling the current waveforms of the PY circuit and the YN circuit, ensuring that the entire system reaches a unity power factor, and also ensuring that the main conversion unit can handle more power. The first preset reference current can be divided into a first standard current and a second standard current. The first standard current is a current greater than zero obtained by decomposing the current waveform at the third terminal Y point, and the second standard current is a current less than zero obtained by decomposing the current waveform at the third terminal Y point. Figure 2c shown. Figure 2c In order to decompose the current waveform at point Y into the first standard current IynRef and the second standard current IpyRef, green represents IpyRef and red represents IynRef. The first standard current IynRef and the second standard current IpyRef correspond to the two states of the current at point Y being greater than zero and less than zero, respectively. At this time, as long as the input current of the auxiliary converter is controlled to track IynRef and IpyRef respectively, the power factor tracking of the Iy part can be achieved while transmitting energy to the load end.

[0065] from Figure 2c In the sectors of the two vertical lines 1 and 2 in , IynRef is the part of IyRef that is greater than zero. At this time, the auxiliary converter obtains energy from the corresponding Vyn. By controlling the action time of the auxiliary converter input level, the change law of the auxiliary converter input current meets the requirements of power factor correction. IpyRef is the other part of IyRef that is less than zero, and its working principle is consistent with the above principle.

[0066] In some embodiments, in order to make the variation rule of the input current of the main conversion unit the same as the second preset reference current, the input current of the main conversion unit can be controlled by using peak current to track the second preset reference current.

[0067] In this embodiment, if Figure 7a-7cAs shown, after the sector is selected, by controlling the action time of the input level of the main conversion unit, the change law of the input current of the main conversion unit is made the same as the second preset reference current IpnRef. The second preset reference current is the reference current IpnRef flowing from the first terminal P to the second terminal N, which is obtained by subtracting the current flowing from point P to point Y from the current flowing through point P. The main conversion unit obtains energy from Vpn, and by controlling the action time of the input level of the main converter, the change law of the input current of the main conversion unit is made consistent with IpnRef. The main conversion unit and the auxiliary conversion unit work together to make the input current of the entire converter meet the requirements of power factor correction, and at the same time complete the energy transmission to the load end.

[0068] In this embodiment, if Fig.11a Schematic diagram of the waveform of the input voltage of the main conversion unit and the input voltage of the auxiliary conversion unit shown, Fig.11b The schematic diagram of the current reference IpnRef of the main conversion unit and the current references IpyRef and IynRef tracked by the auxiliary conversion unit is shown, Fig.11c The power schematic diagram of the main conversion unit and the auxiliary conversion unit is shown.

[0069] In addition, for ease of understanding, the following Fig.12a 12a shows the schematic diagram of the input Va, Vb, Vc AC voltage waveforms, 12b shows the schematic diagram of the Vyn and Vab line voltage waveforms, 12c shows the IynRef current waveform and the input current waveform of Ia.

[0070] In some embodiments, the first preset ratio is , the second preset ratio is 1- .

[0071] The calculation process of the first preset ratio and the second preset ratio has been introduced in detail in the first part and will not be repeated here.

[0072] The present invention converts three-phase AC into three pulsating DC - PY, YN, PN - through a sector selection unit. The auxiliary conversion unit obtains energy from PY or YN and outputs it to the load. Another main conversion unit processes the energy of the PN part and outputs it to the load. The amplitude of the input current waveform is determined by the output of the output voltage loop. By reasonably controlling the input and output currents of the main conversion unit and the auxiliary conversion unit, the current waveforms of PN, YN and PN are controlled, thereby ensuring that the entire system reaches unity power factor. The final input voltage and current waveforms are as follows: Fig.13a and Fig.13b shown.

[0073] The embodiment of the present invention provides a control method for a three-phase single-stage isolated rectifier, including a sector selection unit, an auxiliary conversion unit and a main conversion unit. By controlling the action time of the input level of the main conversion unit, the change law of the input current of the main conversion unit is made the same as the second preset reference current, so that most of the power can be processed by the main conversion unit. In addition, by controlling the action time of the input level of the auxiliary conversion unit, the change law of the input current of the auxiliary conversion unit is made the same as the first preset reference current, and the first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal Y point, so that when the auxiliary conversion unit processes the current at the Y point, the sector with a higher voltage in the PY path and the YN path can be selected as the input voltage, without having to process the working condition where the input voltage in the PY path and the YN path is close to zero, thereby greatly changing the working conditions of the auxiliary conversion unit, further reducing the loss, and more easily realizing soft switching. When selecting the parameters of the power element, there is no need to consider the situation where the voltage variation range is high, and a small amount of power can be processed by the auxiliary conversion unit. By using the main conversion unit to process most of the power, the power of the auxiliary conversion unit can be greatly reduced, and soft switching can be more easily realized.

[0074] 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: It includes a sector selection unit, an auxiliary conversion unit, a main conversion unit and a total output terminal; The sector selection unit is connected to the three-phase AC power, and is used to convert the three-phase AC power into three pulsating DC power and output it through the first terminal P, the second terminal N and the third terminal Y; wherein the first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage; The input end of the auxiliary conversion unit is connected to the first terminal P, the second terminal N and the third terminal Y respectively, and the output end of the auxiliary conversion unit is connected to the total output end to provide a first preset proportion of energy to the total output end; The input end of the main conversion unit is connected to the first terminal P and the second terminal N, and the output end is connected to the total output end, providing a second preset ratio of energy to the total output end; wherein the first preset ratio is less than the second preset ratio, and the sum of the first preset ratio and the second preset ratio is 1; the total output end is used to provide voltage and energy to a DC load; Control the action time of the input level of the auxiliary conversion unit so that the change law of the input current of the auxiliary conversion unit is the same as the first preset reference current; control the action time of the input level of the main conversion unit so that the change law of the input current of the main conversion unit is the same as the second preset reference current; the first preset reference current is determined based on the positive and negative polarity separation of the current at the third terminal Y point, and the second preset reference current is a reference current flowing from the first terminal P to the second terminal N.

2. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The first preset reference current includes a first standard current and a second standard current, the first standard current being a current greater than zero obtained by decomposing the current waveform at the third terminal point Y, and the second standard current being a current less than zero obtained by decomposing the current waveform at the third terminal point Y.

3. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The auxiliary conversion unit includes a first high-frequency conversion unit and a second high-frequency conversion unit, wherein the first high-frequency conversion unit and the second high-frequency conversion unit output energy to the total output end alternately based on different sectors; The first input end of the first high-frequency conversion unit is connected to the first terminal P, the second input end thereof is connected to the third terminal Y, and the output end of the first high-frequency conversion unit is connected to the total output end; The first input end of the second high-frequency conversion unit is connected to the second terminal N, the second input end thereof is connected to the third terminal Y, the output end of the first high-frequency conversion unit is connected to the total output end, and the output end of the second high-frequency conversion unit is connected to the total output end.

4. The three-phase single-stage isolation rectifier according to claim 3, characterized in that: The first high-frequency conversion unit or the second high-frequency conversion unit includes at least one high-frequency isolation converter; When the first high-frequency conversion unit or the second high-frequency conversion unit includes a plurality of identical high-frequency isolation converters, the plurality of identical high-frequency isolation converters are connected in parallel.

5. The three-phase single-stage isolation rectifier according to claim 1, characterized in that: The auxiliary conversion unit includes an industrial frequency switching unit and a high-frequency conversion unit, wherein the first input end of the industrial frequency switching unit is connected to the first terminal P, the second input end thereof is connected to the second terminal N, and the third input end thereof is connected to the third terminal Y; the output end of the industrial frequency switching unit is connected to the input end of the high-frequency conversion unit, and the output end of the high-frequency conversion unit is connected to the total output end.

6. The three-phase single-stage isolation rectifier according to any one of claims 1 to 5, characterized in that: The main conversion unit is an LLC circuit, a phase-shifted full-bridge circuit, a multi-phase interleaved circuit composed of an LLC circuit or a phase-shifted full-bridge circuit, a plurality of transformers connected in series and parallel to a rectifier circuit, or a single transformer secondary-side double-wired rectifier circuit; The three-phase single-stage isolation rectifier further includes a low-pass filtering unit, and the low-pass filtering unit includes an LC low-pass filter, an X capacitor or a parasitic inductor.

7. The three-phase single-stage isolation rectifier according to any one of claims 1 to 5, characterized in that: The first preset ratio is , the second preset ratio is 1- .

8. A control 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 7, characterized in that: include: The sector selection unit converts the input three-phase AC power into three pulsating DC power and outputs them through the first terminal P, the second terminal N and the third terminal Y; wherein the first terminal P outputs a high voltage, the second terminal N outputs a low voltage, and the third terminal Y outputs a middle voltage; Based on the positive and negative polarity of the current at the third terminal Y, the current output from the third terminal Y is decomposed into a first standard current and a second standard current, and the input current of the auxiliary conversion unit is controlled to track the first standard current and the second standard current, so that the change rule of the input current of the auxiliary conversion unit is the same as the first preset reference current and the energy of the first preset proportion is output to the total output end; Control the input current of the main conversion unit to track the second preset reference current so that the change pattern of the input current of the main conversion unit is the same as the second preset reference current and outputs a second preset proportion of energy to the total output end; wherein the second preset reference current is a reference current flowing from the first terminal P to the second terminal N; the first preset proportion is less than the second preset proportion, and the sum of the first preset proportion and the second preset proportion is 1.

9. The control method of the three-phase single-stage isolation rectifier according to claim 8, characterized in that: The controlling the input current of the auxiliary conversion unit to track the first standard current and the second standard current comprises: Using peak current to control the input current of the auxiliary conversion unit to track the first standard current and the second standard current; The controlling the input current of the main conversion unit to track the second preset reference current comprises: The input current of the main conversion unit is controlled by using peak current to track the second preset reference current.

10. The control method of the three-phase single-stage isolation rectifier according to claim 8, characterized in that: The first preset ratio is , the second preset ratio is 1- .

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