Three-phase single-stage isolation circuit and rectifier

Abstract

The utility model provides a three-phase single-stage isolation circuit and a rectifier. The three-phase single-stage isolation circuit comprises a low-pass filtering unit, a low-frequency sector selection unit and an isolation DC / DC unit which are connected in sequence, wherein the low-pass filtering unit is connected with a three-phase alternating current, and the isolation DC / DC unit is connected with a direct current load; the low-frequency sector selection unit converts three-phase alternating current into three paths of direct current and adjusts the sequence of the three paths of direct current, and the isolation DC / DC unit converts direct current voltage into output voltage needed by a direct current load and comprises a first isolation unit, a second isolation unit and a third isolation unit. The switching circuit and a switching element in the isolation DC / DC unit adjust the input current of the isolation DC / DC unit, so that the input of the isolation DC / DC unit is resistive. According to the utility model, the problems of low conversion efficiency and high cost of the isolation rectifier can be solved.

Description

Technical Field

[0001] The utility model relates to the technical field of switching power supplies, in particular to a three-phase single-stage isolation circuit and a rectifier. Background Art

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

[0003] Currently, the existing technologies mainly use two-stage high-frequency power conversion. First, through a first-stage non-isolated power factor correction, three-phase alternating current is converted into basically stable direct current, and then through a second-stage isolated DC / DC conversion, the direct current is converted into the voltage and current required by the electrical equipment.

[0004] Such as Figure 1 、 Figure 2 , in the two-stage scheme of the current mainstream three-phase isolated converter rectifier, the front stage is a power factor correction (PFC) circuit composed of a Vienna or full-bridge PWM rectifier, and the rear stage is an isolated DC / DC conversion circuit. In the power range of ten kilowatts to dozens of kilowatts, the mainstream scheme for the rear stage is a phase-shifted full-bridge or LLC. A capacitor with a relatively large capacity is usually required for the DC bus between the front and rear stages to achieve decoupling between the front and rear stages, and they basically work independently (there may be a very slow coordination adjustment of the bus voltage and the output voltage, but there is no coordination relationship of high-frequency switches).

[0005] In the two-stage high-frequency power conversion structure, due to the need for decoupling between the front and rear stages, electrolytic capacitors with relatively large capacities are usually designed for the DC bus between the front and rear stages. In order to avoid a large inrush voltage brought about by the input AC power-on instantaneously, an input pre-charge circuit usually needs to be added to the input part. The three-phase mains are disconnected through a relay, and the bus capacitor is charged with a bypass resistor. After the voltage of the bus capacitor reaches the expected value, the input relay is then closed. This part of the circuit is connected in series in the input loop, and the current is extremely large, which not only brings relatively large losses, increases efficiency losses and heat generation, but also brings additional costs. Summary of the Utility Model

[0006] Embodiments of the utility model provide a three-phase single-stage isolation circuit and a rectifier to solve the problems of low conversion efficiency and high cost of the isolation rectifier.

[0007] In a first aspect, embodiments of the utility model provide a three-phase single-stage isolation circuit, including:

[0008] It includes a low-pass filter unit, a low-frequency sector selection unit, and an isolated DC / DC unit connected in sequence; wherein, the low-pass filter unit is connected to three-phase alternating current, and the isolated DC / DC unit is connected to a DC load;

[0009] The low-frequency sector selection unit converts three-phase alternating current into three paths of direct current and adjusts the order of the three paths of direct current. It includes a first bridge circuit and a switching circuit. The positive terminal of the first bridge circuit is connected to a first terminal P, the first terminal P outputs a high voltage, the negative terminal of the first bridge circuit is connected to a second terminal N, the second terminal N outputs a low voltage, one end of the switching circuit is connected to the first bridge circuit, and the other end of the switching circuit is connected to a third terminal Y, and the third terminal Y outputs a medium voltage;

[0010] The isolated DC / DC unit converts the DC voltage into the output voltage required by the DC load. It includes a first isolation unit, a second isolation unit, and a third isolation unit. The input end of the first isolation unit is respectively connected to the first terminal P and the third terminal Y, and the output end of the first isolation unit is connected to the output voltage; the input end of the second isolation unit is respectively connected to the third terminal Y and the second terminal N, and the output end of the second isolation unit is connected to the output voltage; the input end of the third isolation unit is respectively connected to the first terminal P and the second terminal N, and the output end of the third isolation unit is connected to the output voltage;

[0011] The switching elements in the switching circuit and the isolated DC / DC unit adjust the input current of the isolated DC / DC unit to make the input of the isolated DC / DC unit resistive.

[0012] In a second aspect, an embodiment of the present invention provides a three-phase single-stage isolated rectifier, including:

[0013] The above-mentioned three-phase single-stage isolation circuit.

[0014] The embodiment of the present utility model provides a three-phase single-stage isolation circuit and a rectifier. The low-frequency sector selection circuit converts three-phase alternating current into three paths of direct current, and sorts the three voltages. The three voltages are respectively used as the input voltages of the first isolation unit, the second isolation unit, and the third isolation unit. The first isolation unit, the second isolation unit, and the third isolation unit process the three paths of direct current and output the output voltage required by the DC load. Through the cooperative setting of the low-frequency sector selection circuit and the first isolation unit, the second isolation unit, and the third isolation unit in the isolation unit, the low-frequency sector selection circuit performs power frequency switching, and can select switching tubes and diodes with slower switching speed but lower on-state voltage drop, and there is almost no switching loss, so that the conversion efficiency of the three-phase single-stage isolation rectifier is high. Most of the power of the present utility model is processed by the LLC circuit in the third isolation unit. Since the LLC circuit is connected between the first terminal P and the second terminal N, therefore, the input voltage of the LLC circuit of the present utility model has only one working condition of the voltage between PN. After rectification by the low-frequency sector selection unit, the voltage on PN fluctuates less than the voltages between PY and YN, and the working condition is good. The zero-voltage switching of the primary side switch and the zero-current switching of the secondary side diode can be realized in the full range, so that the conversion efficiency of the three-phase single-stage isolation rectifier is high. Compared with the traditional two-stage scheme, elements such as the bus capacitor and the input pre-charge circuit are omitted, and the cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 is a schematic structural diagram of a two-stage rectification circuit of the prior art;

[0017] Figure 2 is a schematic structural diagram of the circuit of the Vienna rectifier of the prior art

[0018] Figure 3 is a schematic structural diagram of the three-phase single-stage isolation circuit provided by the embodiment of the present utility model;

[0019] Figure 4 is a schematic structural diagram of the first isolation unit provided by the embodiment of the present utility model;

[0020] Figure 5 is a schematic diagram of the control loop of the first isolation unit provided by the embodiment of the present utility model;

[0021] Figure 6a is a schematic diagram of the PY voltage waveform provided by the embodiment of the present utility model;

[0022] Figure 6b It is a schematic diagram of the input current waveform of the first isolation unit provided by an embodiment of the present utility model;

[0023] Figure 6c It is a schematic diagram of the driving waveform of the first switching tube provided by an embodiment of the present utility model;

[0024] Figure 6d It is a schematic diagram of the details of several high-frequency cycles of the PY voltage waveform provided by an embodiment of the present utility model;

[0025] Figure 6e It is a schematic diagram of the details of several high-frequency cycles of the input current waveform of the first isolation unit provided by an embodiment of the present utility model;

[0026] Figure 6f It is a schematic diagram of the details of several high-frequency cycles of the driving waveform of the first switching tube of the first isolation unit provided by an embodiment of the present utility model;

[0027] Figure 7 It is a schematic diagram of the derivative circuit structure of the first isolation unit provided by an embodiment of the present utility model;

[0028] Figure 8 It is a schematic diagram of the circuit structure of the second isolation unit provided by an embodiment of the present utility model;

[0029] Figure 9 It is a schematic diagram of the circuit structure of the third isolation unit provided by an embodiment of the present utility model;

[0030] Figure 10 It is a schematic diagram of the control loop of the third isolation unit provided by an embodiment of the present utility model;

[0031] Figure 11a It is a schematic diagram of the waveform of the PN voltage provided by an embodiment of the present utility model;

[0032] Figure 11b It is a schematic diagram of the waveform of the input current of the third isolation unit provided by an embodiment of the present utility model;

[0033] Figure 11c It is a schematic diagram of the driving waveforms of the third and fourth switching tubes of the third isolation unit provided by an embodiment of the present utility model;

[0034] Figure 11d It is a schematic diagram of the driving waveforms of the fifth and sixth switching tubes of the third isolation unit provided by an embodiment of the present utility model;

[0035] Figure 11e It is a schematic diagram of the details of several high-frequency cycles of the waveform of the PN voltage provided by an embodiment of the present utility model;

[0036] Figure 11f It is a schematic diagram of the details of several high-frequency cycles of the input current of the third isolation unit provided by the embodiment of the present utility model;

[0037] Figure 11g It is a schematic diagram of the details of several high-frequency cycles of the driving waveforms of the third switching tube and the fourth switching tube provided by the embodiment of the present utility model;

[0038] Figure 11h It is a schematic diagram of the details of several high-frequency cycles of the driving waveforms of the fifth switching tube and the sixth switching tube provided by the embodiment of the present utility model;

[0039] Figure 12 It is a schematic diagram of the derivative circuit of the third isolation unit provided by another embodiment of the present utility model;

[0040] Figure 13 It is a schematic diagram of the derivative circuit of the third isolation unit provided by another embodiment of the present utility model;

[0041] Figure 14 It is a schematic diagram of the circuit structure of the low-pass filtering unit provided by the embodiment of the present utility model;

[0042] Figure 15 It is a schematic diagram of the circuit structure of the low-frequency sector selection unit provided by the embodiment of the present utility model;

[0043] Figure 16a It is the waveform diagram after the low-frequency sector selection unit provided by the embodiment of the present utility model rectifies the mains electricity;

[0044] Figure 16b It is a schematic diagram of three-phase alternating current of the mains electricity;

[0045] Figure 16c It is a schematic diagram of the waveforms of the three groups of switches driven by the low-frequency sector selection unit provided by the embodiment of the present utility model;

[0046] Figure 17 It is a schematic diagram of the derivative circuit structure of the low-frequency sector selection unit provided by the embodiment of the present utility model;

[0047] Figure 18a It is a schematic diagram of the waveform of the final input voltage provided by the embodiment of the present utility model;

[0048] Figure 18b It is a schematic diagram of the waveform of the final input current provided by the embodiment of the present utility model. Detailed implementation manners

[0049] To enable those skilled in the art to better understand this solution, the following will clearly describe the technical solution in the embodiments of this solution in conjunction with the accompanying drawings in the embodiments of this solution. Obviously, the described embodiments are part of the embodiments of this solution, rather than all of the embodiments. Based on the embodiments in this solution, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this solution.

[0050] The terms "including" and any other variations in the specification and claims of this solution, as well as in the above-mentioned accompanying drawings, mean "including but not limited to", and are intended to cover non-exclusive inclusion, not limited to the examples listed in the text. In addition, terms such as "first" and "second" are used to distinguish different objects, rather than to describe a specific order.

[0051] The following will describe in detail the implementation of the present invention in conjunction with specific accompanying drawings:

[0052] Figure 3 It is a schematic diagram of a three-phase single-stage isolation circuit structure provided for an embodiment of the present invention. Refer to Figure 3 and this three-phase single-stage isolation circuit includes:

[0053] A low-pass filter unit, a low-frequency sector selection unit, and an isolation DC / DC unit connected in sequence; wherein, the low-pass filter unit is connected to three-phase alternating current, and the isolation DC / DC unit is connected to a DC load;

[0054] The low-frequency sector selection unit converts three-phase alternating current into three paths of direct current and adjusts the order of the three paths of direct current, including a first bridge circuit and a switching circuit. The positive end of the first bridge circuit is connected to a first terminal P, the first terminal P outputs a high voltage, the negative end of the first bridge circuit is connected to a second terminal N, the second terminal N outputs a low voltage, one end of the switching circuit is connected to the first bridge circuit, and the other end of the switching circuit is connected to a third terminal Y, and the third terminal Y outputs a medium voltage;

[0055] The isolation DC / DC unit converts the DC voltage into the output voltage required by the DC load, including a first isolation unit, a second isolation unit, and a third isolation unit. The input end of the first isolation unit is respectively connected to the first terminal P and the third terminal Y, and the output end of the first isolation unit is connected to the output voltage; the input end of the second isolation unit is respectively connected to the third terminal Y and the second terminal N, and the output end of the second isolation unit is connected to the output voltage; the input end of the third isolation unit is respectively connected to the first terminal P and the second terminal N, and the output end of the third isolation unit is connected to the output voltage;

[0056] The switching elements in the switching circuit and the isolation DC / DC unit adjust the input current of the isolation DC / DC unit to make the input of the isolation DC / DC unit resistive.

[0057] The low-pass filter is mainly used to filter out the ripple current caused by the high-frequency switching of the isolated DC / DC 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 fundamental wave of the power-frequency current.

[0058] The first bridge circuit in the low-frequency sector selection unit converts the filtered three-phase alternating current into three-way pulsating direct current, determines the magnitudes of the three-way voltages, identifies the highest voltage, the intermediate voltage, and the lowest voltage, turns on the switch tube of the switch branch corresponding to the intermediate voltage, selects the intermediate voltage from the three-way direct current, makes the voltage at the first terminal P the highest voltage, the voltage at the third terminal Y the intermediate voltage, and the voltage at the second terminal N the lowest voltage, and rectifies the three-phase alternating current into three-way direct current that are all positive.

[0059] The isolated DC / DC unit converts the three-way direct current into the voltage required by the DC load. The output voltage of the isolated DC / DC unit is connected in parallel to the DC load for the DC load to use.

[0060] The first isolation unit in the isolated DC / DC unit is a buck-boost circuit. Its input terminal is connected between the first terminal P and the third terminal Y. After processing the energy between PY, it converts the voltage of this part into the output voltage required by the DC load. By adjusting the switching element in the first isolation unit, the input current of the PY part is adjusted so that the envelope of the input current is the same as the envelope of the voltage between PY, thereby making the input impedance of the first isolation unit resistive.

[0061] The buck-boost circuit of the second isolation unit has the same structure and operating principle as that of the first isolation unit. The input terminal of the second isolation unit is connected between the third terminal Y and the second terminal N, processes the energy between YN, and converts the voltage of this part into the output voltage required by the DC load. By adjusting the switching element in the second isolation unit, the envelope of the input current of the YN part is adjusted to be the same as the envelope of the voltage between YN, thereby making the input impedance of the second isolation unit resistive. The buck-boost circuits of the first isolation unit and the second isolation unit achieve hard switching.

[0062] The third isolation unit is a full-bridge LLC circuit. Its input terminal is connected between the first terminal P and the second terminal N, processes the energy between PN, and its output terminal is connected in parallel to both ends of the DC load and achieves soft switching. By adjusting the driving frequency of each switching element in the third isolation unit, the impedance of the LLC circuit is adjusted so that the envelope of the input current of the third isolation unit is the same as the envelope of the voltage between PN, thereby making the input impedance of the third isolation unit resistive.

[0063] By making the inputs of the first isolation unit, the second isolation unit, and the third isolation unit all resistive, the unity power factor of the entire system is ensured.

[0064] An embodiment of the present utility model provides a three-phase single-stage isolation circuit and a rectifier. The low-frequency sector selection circuit converts three-phase alternating current into three paths of direct current and sorts the three voltages. The three voltages are respectively used as the input voltages of the first isolation unit, the second isolation unit, and the third isolation unit. The first isolation unit, the second isolation unit, and the third isolation unit process the three paths of direct current and output the output voltage required by the DC load. Through the cooperative setting of the low-frequency sector selection circuit and the first isolation unit, the second isolation unit, and the third isolation unit in the isolation unit, the low-frequency sector selection circuit switches at power frequency, and switches and diodes with slower switching speed but lower conduction voltage drop can be selected, with almost no switching loss, making the conversion efficiency of this three-phase single-stage isolation rectifier high. Most of the power of the present utility model is processed by the LLC circuit in the third isolation unit. Since the LLC circuit is connected between the first terminal P and the second terminal N, therefore, the input voltage of the LLC circuit of the present utility model has only one working condition, which is the voltage between PN. After rectification by the low-frequency sector selection unit, the voltage on PN fluctuates less relative to the voltages between PY and YN, and the working condition is good, and zero-voltage switching of the primary side switch and zero-current switching of the secondary side diode can be achieved in the full range, making the conversion efficiency of this three-phase single-stage isolation rectifier high. Compared with the traditional two-stage scheme, components such as bus capacitors and input pre-charge circuits are omitted, reducing costs.

[0065] Generally, the switching dynamic characteristics and conduction characteristics of power semiconductors are a pair of contradictions. When it is desired that the power semiconductor works in a hard-switching scenario, diodes are required to have better reverse recovery characteristics and switches are required to have smaller parasitic capacitances. Taking the products of Infineon as an example, generally, diodes and IGBTs with better high-frequency characteristics will have higher conduction voltage drops.

[0066] The present utility model uses the LLC part to process most of the power. The LLC input voltage has only one working condition, which is PN, and the voltage fluctuation on PN is small, and the LLC working condition is good. Therefore, the conduction loss of the field effect transistor of the LLC in the present utility model will be lower. The low-frequency switching devices and drive circuits selected by the low-frequency sector selection circuit are usually cheaper than high-frequency ones. Since the pre-charge circuit is omitted and there is no need to pre-charge the bus, the startup response speed is greatly improved.

[0067] The above is a summary of the overall solution. The following will detail the specific implementation manners of each part of the three-phase single-stage rectification circuit.

[0068] In a possible implementation manner, both the first isolation unit and the second isolation unit are buck-boost circuits; the third isolation unit is an LLC phase-shifted full-bridge circuit or a multi-phase interleaved circuit of an LLC phase-shifted full-bridge.

[0069] In a possible implementation, the first isolation unit includes a first inductor L1, a first switch tube S1, a first capacitor C1, a first transformer T1, and a first diode D1. One end of the first inductor L1 is connected to the first terminal P, and the other end of the first inductor L1 is connected to one end of the first capacitor C1. The other end of the first capacitor C1 is connected to the first end of the primary winding of the first transformer T1. The other end of the first inductor L1 is connected to one end of the first switch tube S1. The other end of the first switch tube S1 is respectively connected to the third terminal Y and the second end of the primary winding of the first transformer T1. The two ends of the secondary winding of the first transformer T1 are connected to the output voltage. A second capacitor C2 is connected between the two ends of the secondary winding of the first transformer T1, and the two ends of the second capacitor C2 are connected to the output voltage. A first diode D1 is connected between one end of the secondary winding of the first transformer T1 and one end of the second capacitor C2, as Figure 4 shown.

[0070] By controlling the conduction and turn-off of the first switch tube S1 to control the current on the first inductor L1, the envelope of the current on the first inductor L1 is made the same as the envelope shape of the PY voltage, so that the average current of the input current is proportional to the voltage of PY, and the input impedance of the first isolation unit is resistive. The control method is as Figure 5 shown:

[0071] The output voltage Vo is subtracted from the expected value of the output voltage VoRef, and the result is input to the PI regulator to output the amplitude of the expected current value. The voltage Vpy between PY is normalized by multiplying by k, and the normalized result is multiplied by the amplitude of the expected current value to output the expected current value of the current on the first inductor L1. The sampled current (i.e., the actual value of the current) 1L1Sense of the current on the first inductor L1 is filtered by a low-pass filter to remove high-frequency switching noise, and then subtracted from the expected current value of the current on the first inductor L1. The result of the subtraction is input to the PI regulator to obtain the duty cycle of the first switch tube S1, which is compared with the carrier wave to obtain the PWM wave.

[0072] That is, the required power-frequency average current is obtained from the output voltage loop, the current reference loop is obtained from the required power-frequency average current of the PY voltage, and then the gate drive is obtained through the current loop.

[0073] In another possible implementation, the circuit operates in the critical conduction mode. At this time, the input impedance of the circuit shows resistive, and the average value of the input current is naturally proportional to the input voltage. The output voltage is controlled by controlling the conduction time, and the turn-off time is determined according to the time when the current of the first inductor L1 drops to near zero.

[0074] Finally, when the first isolation unit operates stably, the PY voltage, the input current of the first isolation unit, and the drive waveform of the first switch tube S1 are respectively asFigures 6a - 6c as shown Figures 6d - 6f are respectively the expanded details of several high-frequency cycles corresponding to the PY voltage, the input current of the first isolation unit, and the driving waveform of the first switching transistor S1

[0075] In another possible implementation, the first isolation unit can adopt a multi-phase interleaved parallel connection method to further reduce the input current ripple. That is, two or more completely identical structures are connected in parallel, and the switching frequency and control method of each path are the same as the original method, but the driving phase difference is 180° (the phase difference of three-phase interleaving is 120°), as Figure 7 as shown

[0076] In a possible implementation, the second isolation unit includes a second inductor L2, a second switching transistor S2, a third capacitor C3, a second transformer T2, and a second diode D2. One end of the second inductor L2 is connected to the third terminal Y, the other end of the second inductor L2 is connected to the third capacitor C3, the other end of the third capacitor C3 is connected to the first end of the primary winding of the second transformer T2, the other end of the second inductor L2 is connected to one end of the second switching transistor S2, the other end of the second switching transistor S2 is respectively connected to the third terminal Y and the second end of the primary winding of the second transformer T2, both ends of the secondary winding of the second transformer T2 are connected to the second capacitor C2, and a second diode D2 is connected between one end of the secondary winding of the second transformer T2 and the second capacitor C2, as Figure 8 as shown

[0077] The structure and operating principle of the second isolation unit are the same as those of the first isolation unit. The input end of the second isolation unit is connected between the third terminal Y and the second terminal N. So that the envelope of the current on the second inductor L2 has the same shape as the envelope of the YN voltage, making the current on the second inductor L2 proportional to the YN voltage, thereby making the input impedance of the second isolation unit resistive

[0078] The structure of the second isolation unit is the same as that of the first isolation unit, and the derivative circuit is exactly the same as that of the first isolation unit

[0079] In a possible implementation, the third isolation unit includes a second bridge circuit, an LLC circuit, a third transformer T3, and a third bridge circuit 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

[0080] The LLC circuit includes a third inductor L3 and a fourth capacitor C4. One end of the third inductor L3 is connected to the midpoint of the first bridge arm, the other end of the third inductor L3 is connected to one end of the fourth capacitor C4, and the other end of the fourth capacitor C4 is connected to the first end of the primary winding of the third transformer T3; 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 third transformer T3;

[0081] 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 both ends of the second capacitor C2, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the third transformer T3, the positive end and the negative end of the fourth bridge arm are respectively connected to both ends of the second capacitor C2, and the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the third transformer T3;

[0082] The first bridge arm includes a third switch tube S3 and a fourth switch tube S4, and the second bridge arm includes a fifth switch tube S5 and a sixth switch tube S6;

[0083] The third bridge arm includes a third diode D3 and a fourth diode D4, and the fourth bridge arm includes a fifth diode D5 and a sixth diode D6, as Figure 9 shown.

[0084] By adjusting the driving frequencies of the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6, the impedance of the LLC circuit is adjusted, so as to adjust the waveform and amplitude of the circuit input current of the third isolation unit, make the envelope of the circuit input current of the third isolation unit the same as the envelope of the PN voltage, make the circuit input current of the third isolation unit proportional to the PN voltage, so that the input impedance of the third isolation unit is resistive, and the control method is as follows:

[0085] The output voltage Vo is subtracted from the expected output voltage VoRef, and the result is input to the PI regulator to output the amplitude of the expected output current; the voltage Vpn between PN is normalized by multiplying by k, and the normalized result is multiplied by the amplitude of the expected output current to output the expected current of the third isolation unit; the current sampling (i.e., the actual value of the current) linPN of the input current of the third isolation unit is filtered by a low-pass filter to remove high-frequency switching noise, and then subtracted from the expected current of the third isolation unit, and the result of the subtraction is input to the control unit to obtain the PWM waves of the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6, as Figure 10 shown.

[0086] The driving waveforms of the third switch tube S3 and the fourth switch tube S4 in the third isolation unit are complementary, and the driving waveforms of the fifth switch tube S5 and the sixth switch tube S6 are complementary. In the main operating conditions, the duty cycle of each switch tube is 50%. The driving of the third switch tube S3 and the sixth switch tube S6 is in the same phase, and the driving of the fourth switch tube S4 and the fifth switch tube S5 is in the same phase.

[0087] Due to the non-linear loop characteristics of the LLC circuit, the control unit usually requires a non-linear controller to make the input current of the LLC better track the voltage waveform of the PN.

[0088] Finally, when this part is in steady-state operation, the PN voltage waveform is as Figure 11a shown, and the input current waveform of the third isolation unit is as Figure 11b shown. Among them, the a waveform represents the instantaneous value of the input current, and the b waveform represents the average value of the high-frequency period. The driving waveforms of the third switch tube S3 and the fourth switch tube S4 are as Figure 11c shown, and the driving waveforms of the fifth switch tube S5 and the sixth switch tube S6 are as Figure 11d shown. Figures 11e - 11h is a detailed diagram of a high-frequency period of the third isolation unit. Among them, Figure 11f in the a waveform in is a detailed diagram of a high-frequency period of the instantaneous value of the input current, and the b waveform is a detailed diagram of a high-frequency period of the average value of the high-frequency period. Figure 11g is a detailed diagram of a high-frequency period of the driving waveforms of the third switch tube S3 (solid line waveform) and the fourth switch tube S4 (dashed line waveform). Figure 11h is a detailed diagram of a high-frequency period of the driving waveforms of the fifth switch tube S5 (solid line waveform) and the sixth switch tube S6 (dashed line waveform).

[0089] In another possible implementation, a current-mode or charge-mode control method is used to achieve the closed-loop control of the LLC, so as to control the average current flowing into the LLC circuit, make its waveform track the PN voltage waveform, and the amplitude is controlled by the output voltage loop.

[0090] The first switch tube S1 - the sixth switch tube S6 in the first isolation unit, the second isolation unit, and the third isolation unit are high-frequency switch tubes.

[0091] In another possible implementation, the third isolation unit can adopt a three-phase interleaved LLC circuit, as Figure 12 shown.

[0092] In another possible implementation, ways such as the series-parallel connection of multiple transformers or the double-wire parallel winding of the secondary side of a single transformer followed by series-parallel rectification all belong to one of the important implementation methods of this application, as Figure 13 shown.

[0093] In a possible implementation, the low-pass filtering unit includes a fourth inductor L4, a fifth inductor L5, and a sixth inductor L6. One end of the fourth inductor L4 is connected to one phase of the three-phase alternating current, and the other end of the fourth inductor L4 is connected to the first bridge circuit. A fifth capacitor C5 is connected to the other end of the fourth inductor L4;

[0094] One end of the fifth inductor L5 is connected to another phase of the three-phase alternating current, and the other end of the fifth inductor L5 is connected to the first bridge circuit. A sixth capacitor C6 is connected to the other end of the fifth inductor L5;

[0095] One end of the sixth inductor L6 is connected to the third phase of the three-phase alternating current, and the other end of the sixth inductor L6 is connected to the first bridge circuit. A seventh capacitor C7 is connected to the other end of the sixth inductor L6;

[0096] The other ends of the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 are connected to each other, as Figure 14 shown.

[0097] The low-pass filtering unit is not necessary. If the ripple currents of the first isolation unit, the second isolation unit, and the third isolation unit are not large, the filter of this low-pass filtering unit can be greatly reduced, or even the fourth inductor L4, the fifth inductor L5, and the sixth inductor L6 can be removed, and only the three capacitors, namely the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7, are retained.

[0098] In a 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 fourth inductor L4. The positive end of the fifth bridge arm is connected to the first terminal P, and 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 fifth inductor L5. The positive end of the sixth bridge arm is connected to the first terminal P, and 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 sixth inductor L6. 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;

[0099] The switching circuit includes a first switching branch, a second switching branch, and a third switching branch. One end of the first switching branch is connected to the midpoint of the fifth bridge arm, and the other end of the first switching branch is connected to the third terminal Y. One end of the second switching branch is connected to the midpoint of the sixth bridge arm, and the other end of the second switching branch is connected to the third terminal Y. One end of the third switching branch is connected to the midpoint of the seventh bridge arm, and the other end of the third switching branch is connected to the third terminal Y.

[0100] In a possible implementation, the fifth bridge arm includes a seventh diode D7 and an eighth diode D8. The sixth bridge arm includes a ninth diode D9 and a tenth diode D10. The seventh bridge arm includes an eleventh diode D11 and a twelfth diode D12;

[0101] The first switching branch includes a seventh switching transistor S7 and an eighth switching transistor S8, the second switching branch includes a ninth switching transistor S9 and a tenth switching transistor S10, and the third switching branch includes an eleventh switching transistor S11 and a twelfth switching transistor S12, as Figure 15 shown.

[0102] In the low-frequency sector selection circuit, the seventh switching transistor S7 and the eighth switching transistor S8, the ninth switching transistor S9 and the tenth switching transistor S10, and the eleventh switching transistor S11 and the twelfth switching transistor S12 respectively form three groups of power-frequency bidirectional switches. By judging the current three-phase voltage, the conduction states of the three switching branches are controlled. The switching branches corresponding to the highest voltage and the lowest voltage remain cut off, and the switching branch corresponding to the intermediate voltage is turned on. Then each power-frequency cycle is divided into 6 sectors. For example:

[0103] As Figure 16b , Figure 16c , all starting from the vertical line on the left. When Figure 16b in the three-phase alternating current, the Vc voltage is between the Va voltage and the Vb voltage, the Vc voltage is the intermediate voltage. At this time, the eleventh switching transistor S11 and the twelfth switching transistor S12 in the switching branch corresponding to the Vc voltage (represented by VGDC) are turned on, and the seventh diode D7 and the twelfth diode D10 are turned on.

[0104] When the Vb voltage in the three-phase alternating current is between the Va voltage and the Vc voltage, the Vb voltage is the intermediate voltage. At this time, the ninth switching transistor S9 and the tenth switching transistor S10 in the switching branch corresponding to the Vb voltage (represented by VGDB) are turned on, and the seventh diode D7 and the twelfth diode D12 are turned on.

[0105] When the Va voltage in the three-phase alternating current is between the Vb voltage and the Vc voltage, the Va voltage is the intermediate voltage. At this time, the seventh switching transistor S7 and the eighth switching transistor S8 in the switching branch corresponding to the Va voltage (represented by VGDA) are turned on, and the ninth diode D9 and the twelfth diode D12 are turned on.

[0106] The three-phase alternating current is rectified into pulsating three-way direct current. The rectified waveform is as Figure 16a shown. The waveform of the fan shape at the top is the waveform of the voltage Vpn between p and n, and the waveforms of the voltage Vyn between y and n and the voltage Vpy between p and y below cross each other.

[0107] In another possible implementation, since the low-frequency sector selection unit is actually equivalent to a triangular connection formed at three points P, Y, and N after three-phase mains power passes through diodes in each sector transiently, the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 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 points P, Y, and N, the fifth capacitor C5, the sixth capacitor C6, and the seventh capacitor C7 are closer to the high-frequency switching devices such as the first switch tube S1 - the sixth switch tube S6. In an actual product, the lead inductance is smaller, and the operating conditions of the switching devices will be better. The specific circuit is as Figure 17 shown.

[0108] In a possible implementation, the switch tubes in the first isolation unit, the second isolation unit, the third isolation unit, and the switch circuit are bidirectional controllable switch devices formed by two single-phase controllable switch devices connected in series.

[0109] In a possible implementation, the switching device in the switch circuit is a low-frequency switching device.

[0110] The first switch tube S1 - the twelfth switch tube S12 in this three-phase single-stage isolation circuit can adopt power semiconductor devices such as silicon-based or SiC-based field effect transistors, IGBTs, and GaN HEMTs. The first diode D1 - the twelfth diode D12 can adopt diodes made of semiconductor materials such as silicon, SiC, and GaN.

[0111] A three-phase single-stage isolation rectifier includes the above-mentioned three-phase single-stage isolation circuit.

[0112] In the present utility model, the low-frequency sector selection unit converts three-phase alternating current into pulsating three-way direct current PY, YN, and PN. The first isolation unit and the second isolation unit, two isolation buck-boost circuits, respectively process the energy of the PY and YN parts, and the third isolation unit, an LLC circuit, processes the energy of the PN part. The three outputs are connected in parallel, and the output of the output voltage loop controls the amplitude of the input current waveform. By reasonably controlling the input current waveforms of PN, YN, and PY, the input characteristics of the converters of these three isolation units all exhibit resistive, so as to ensure that the entire system achieves a unity power factor. Finally, the input voltage and input current waveforms are as Figure 18a 、 Figure 18b shown.

[0113] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase single-stage isolation circuit, characterized in that, It includes a low-pass filter unit, a low-frequency sector selection unit, and an isolated DC / DC unit connected in sequence; among them, the low-pass filter unit is connected to three-phase alternating current, and the isolated DC / DC unit is connected to a DC load; The low-frequency sector selection unit converts three-phase alternating current into three paths of direct current and adjusts the order of the three paths of direct current. It includes a first bridge circuit and a switching circuit. 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 switching circuit is connected to the first bridge circuit, and the other end of the switching circuit is connected to a third terminal Y, and the third terminal Y outputs a medium voltage; The isolated DC / DC unit converts the DC voltage into the output voltage required by the DC load. It includes a first isolation unit, a second isolation unit, and a third isolation unit. The input end of the first isolation unit is respectively connected to the first terminal P and the third terminal Y, and the output end of the first isolation unit is connected to the output voltage; the input end of the second isolation unit is respectively connected to the third terminal Y and the second terminal N, and the output end of the second isolation unit is connected to the output voltage; the input end of the third isolation unit is respectively connected to the first terminal P and the second terminal N, and the output end of the third isolation unit is connected to the output voltage; The switching element in the switching circuit and the isolated DC / DC unit adjusts the input current of the isolated DC / DC unit to make the input of the isolated DC / DC unit resistive.

2. The three-phase single-stage isolation circuit according to claim 1, wherein Both the first isolation unit and the second isolation unit are buck-boost circuits; the third isolation unit is an LLC phase-shifted full-bridge circuit or a multi-phase interleaved circuit of an LLC phase-shifted full-bridge.

3. The three-phase single-stage isolation circuit according to claim 2, wherein The first isolation unit includes a first inductor, a first switching tube, a first capacitor, a first transformer, and a first diode. One end of the first inductor is connected to the first terminal P, the other end of the first inductor is connected to one end of the first capacitor, the other end of the first capacitor is connected to the first end of the primary winding of the first transformer, the other end of the first inductor is connected to one end of the first switching tube, the other end of the first switching tube is respectively connected to the third terminal Y and the second end of the primary winding of the first transformer, the two ends of the secondary winding of the first transformer are connected to the output voltage, a second capacitor is connected between the two ends of the secondary winding of the first transformer, the two ends of the second capacitor are connected to the output voltage, and the first diode is connected between one end of the secondary winding of the first transformer and one end of the second capacitor.

4. The three-phase single-stage isolation circuit according to claim 3, characterized in that, The third isolation unit includes a second bridge circuit, an LLC circuit, a third transformer, and a third bridge circuit 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 includes a third inductor and a fourth capacitor. One end of the third inductor is connected to the midpoint of the first bridge arm, the other end of the third inductor is connected to one end of the fourth capacitor, and the other end of the fourth capacitor is connected to the first end of the primary winding of the third 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 third 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 both ends of the second capacitor. The midpoint of the third bridge arm is connected to the first end of the secondary winding of the third transformer. The positive end and the negative end of the fourth bridge arm are respectively connected to both ends of the second capacitor. The midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the third transformer; The first bridge arm includes a third switch tube and a fourth switch tube, and the second bridge arm includes a fifth switch tube and a sixth switch tube; The third bridge arm includes a third diode and a fourth diode, and the fourth bridge arm includes a fifth diode and a sixth diode.

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

6. The three-phase single-stage isolation circuit according to claim 5, 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 fourth inductor. The positive end of the fifth bridge arm is connected to the first terminal P, and 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 fifth inductor. The positive end of the sixth bridge arm is connected to the first terminal P, and 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 sixth 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 switch circuit includes a first switch branch, a second switch branch and a third switch branch. One end of the first switch branch is connected to the midpoint of the fifth bridge arm, the other end of the first switch branch is connected to the third terminal Y. One end of the second switch branch is connected to the midpoint of the sixth bridge arm, the other end of the second switch branch is connected to the third terminal Y. One end of the third switch branch is connected to the midpoint of the seventh bridge arm, and the other end of the third switch branch is connected to the third terminal Y.

7. The three-phase single-stage isolation circuit according to claim 6, characterized in that, The fifth bridge arm includes a seventh diode and an eighth diode, the sixth bridge arm includes a ninth diode and a twelfth diode, and the seventh bridge arm includes an eleventh diode and a twelfth diode; The first switch branch includes a seventh switch tube and an eighth switch tube, the second switch branch includes a ninth switch tube and a tenth switch tube, and the third switch branch includes an eleventh switch tube and a twelfth switch tube.

8. The three-phase single-stage isolation circuit according to claim 4 or 7, characterized in that The switch tubes in the first isolation unit, the second isolation unit, the third isolation unit, and the switch circuit are bidirectional controllable switch devices formed by connecting two single-phase controllable switch devices in series.

9. The three-phase single-stage isolation circuit according to claim 8, wherein The switch device in the switch circuit is a low-frequency switch device.

10. A three-phase single-stage isolated rectifier, characterized in that, It includes the three-phase single-stage isolation circuit according to any one of claims 1 to 9.

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