High-power high-voltage direct-current converter and control method thereof

Abstract

The invention discloses a high-power high-voltage direct-current converter and a control method thereof. The high-power high-voltage direct-current converter comprises a three-phase bridge type inverter circuit, a three-phase resonance circuit, a three-phase transformer and a three-phase voltage doubling rectifying circuit. The control method corresponds to the high-power high-voltage direct-current converter. According to the three-phase voltage-multiplying rectifying circuit, the two positively and negatively symmetrical three-phase voltage-multiplying modules are adopted for parallel input and series output, the three-phase staggered input characteristic is combined, the output ripple frequency can reach 6 times of the switching frequency, the output ripple is greatly reduced, and the requirement of an industrial microwave device for the output quality of a high-voltage power supply is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current converters, in particular to a high-power high-voltage direct current converter and a control method thereof. BACKGROUND

[0002] Microwave heating technology is widely used in high-quality material preparation, food processing and other industries. The core equipment of industrial microwave devices relies on high-voltage electric field power supply, and different types of magnetrons have large differences in rated voltage requirements of the power supply. At the same time, the power supply requires low output ripple and high power, so a wide range of low-ripple output high-power high-voltage direct current converters are essential.

[0003] In the research of the prior art, the following obvious deficiencies are found: the traditional high-voltage electric field power supply adopts a power frequency step-up transformer, which is large in size, uncontrollable in output voltage and large in ripple; although the switching LCC resonant converter can reduce the size of the magnetic element and realize soft switching by increasing the switching frequency, it is mainly used in small and medium power occasions, and in high-power scenarios, modules need to be connected in parallel, which faces the problems of current sharing difficulty, high cost and complex control; in the commonly used voltage doubling rectifier circuit, the Dickson voltage doubling rectifier circuit has strong load capacity but the voltage of the last stage capacitor is high, which is not suitable for high-voltage output, and the CW voltage doubling rectifier circuit has low device voltage stress but high output ripple, neither of which can balance low device stress and low ripple.

[0004] The Chinese utility model patent with the authorized announcement number CN201893698U discloses a high-voltage wide-output direct current conversion device, which meets the wide-range output requirement to some extent, but it performs poorly in low-ripple output and other aspects.

[0005] In summary, the current conventional high-voltage direct current converter cannot realize low-ripple, low-device voltage and current stress high-power high-voltage direct current energy conversion, and cannot meet the application requirements of industrial microwave devices, so related technical breakthroughs have become an industry difficulty. SUMMARY

[0006] The main purpose of the present application is to provide a high-power high-voltage direct current converter and a control method thereof, which aims to solve the technical problems that the prior art cannot realize low-ripple, low-device voltage and current stress high-power high-voltage direct current energy conversion, and cannot meet the high-power application requirements of industrial microwave devices.

[0007] To achieve the above-mentioned purpose, the present application provides a high-power high-voltage direct current converter, which comprises a three-phase bridge inverter circuit, a three-phase resonant circuit, a three-phase transformer and a three-phase voltage doubling rectifier circuit. The input end of the three-phase bridge inverter circuit is connected with an external DC power supply, the output end of the three-phase bridge inverter circuit is connected with the input end of the three-phase resonant circuit, the output end of the three-phase resonant circuit is connected with the input end of the three-phase transformer, the output end of the three-phase transformer is connected with the input end of the three-phase voltage doubling rectifier circuit, the three-phase voltage doubling rectifier circuit is provided with two three-phase voltage doubling modules which are structurally positive and negative symmetrical, and the output end of the three-phase voltage doubling rectifier circuit is connected with an external load.

[0008] Preferably, the three-phase voltage doubling rectifier circuit is provided with two three-phase voltage doubling modules which are structurally positive and negative symmetrical, specifically: The three-phase voltage doubling rectifier circuit is provided with a first three-phase voltage doubling module and a second three-phase voltage doubling module, and the first three-phase voltage doubling module and the second three-phase voltage doubling module are structurally positive and negative symmetrical. The input end of the first three-phase voltage doubling module and the input end of the second three-phase voltage doubling module are connected in parallel to form the input end of the three-phase voltage doubling rectifier circuit, the input end of the first three-phase voltage doubling module is formed by the first end of a first support capacitor, the first end of a second support capacitor, the first end of a third support capacitor and the first end of a first bus capacitor, and the input end of the second three-phase voltage doubling module is formed by the first end of a fourth support capacitor, the first end of a fifth support capacitor, the first end of a sixth support capacitor and the first end of a second bus capacitor. The output end of the first three-phase voltage doubling module and the output end of the second three-phase voltage doubling module are connected in series to form the output end of the three-phase voltage doubling rectifier circuit, the output end of the first three-phase voltage doubling module is formed by the cathode of a fourth diode, the cathode of a fifth diode, the cathode of a sixth diode and the second end of the first bus capacitor, and the output end of the second three-phase voltage doubling module is formed by the anode of a twelfth diode, the anode of an eleventh diode, the anode of a tenth diode and the second end of the second bus capacitor.

[0009] Preferably, the first three-phase voltage doubling module is provided with at least one first three-phase voltage doubling unit, and the first three-phase voltage doubling unit comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a first support capacitor, a second support capacitor, a third support capacitor and a first bus capacitor. The first end of the first support capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the first support capacitor is connected with the cathode of the first diode, the anode of the first diode is connected with the first end of the first bus capacitor, the second end of the first support capacitor is also connected with the anode of the fourth diode, the cathode of the fourth diode is connected with the second end of the first bus capacitor. The first end of the second support capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the second support capacitor is connected with the cathode of the second diode, the anode of the second diode is connected with the first end of the first bus capacitor, the second end of the second support capacitor is also connected with the anode of the fifth diode, and the cathode of the fifth diode is connected with the second end of the first bus capacitor; The first end of the third support capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the third support capacitor is connected with the cathode of the third diode, the anode of the third diode is connected with the first end of the first bus capacitor, the second end of the third support capacitor is also connected with the anode of the sixth diode, and the cathode of the sixth diode is connected with the second end of the first bus capacitor; The anode of the first diode, the anode of the second diode, the anode of the third diode and the first end of the first bus capacitor are all connected with the neutral output end of the three-phase transformer; The second three-phase voltage doubling module is provided with at least one second three-phase voltage doubling unit, and the second three-phase voltage doubling unit comprises a seventh diode, an eighth diode, a ninth diode, a twelfth diode, an eleventh diode, a tenth diode, a fourth support capacitor, a fifth support capacitor, a sixth support capacitor and a second bus capacitor; The first end of the fourth support capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the fourth support capacitor is connected with the anode of the seventh diode, the cathode of the seventh diode is connected with the first end of the second bus capacitor, the second end of the fourth support capacitor is also connected with the cathode of the twelfth diode, and the anode of the twelfth diode is connected with the second end of the second bus capacitor; The first end of the fifth support capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the fifth support capacitor is connected with the anode of the eighth diode, the cathode of the eighth diode is connected with the first end of the second bus capacitor, the second end of the fifth support capacitor is also connected with the cathode of the eleventh diode, and the anode of the eleventh diode is connected with the second end of the second bus capacitor; The first end of the sixth support capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the sixth support capacitor is connected with the anode of the ninth diode, the cathode of the ninth diode is connected with the first end of the second bus capacitor, the second end of the sixth support capacitor is also connected with the cathode of the tenth diode, and the anode of the tenth diode is connected with the second end of the second bus capacitor; The cathode of the seventh diode, the cathode of the eighth diode, the cathode of the ninth diode and the first end of the second bus capacitor are all connected with the neutral output end of the three-phase transformer.

[0010] As preferred, the number of the three-phase voltage doubling units set by the first three-phase voltage doubling module is determined based on actual output voltage demand.

[0011] As preferred, when the number of the three-phase voltage doubling units set by the first three-phase voltage doubling module is more than one, the connection relationship between the multiple three-phase voltage doubling units is: the first end of the first support capacitor of the next three-phase voltage doubling unit is connected with the second end of the first support capacitor of the previous three-phase voltage doubling unit, the cathode of the first diode and the anode of the fourth diode; the first end of the second support capacitor of the next three-phase voltage doubling unit is connected with the second end of the second support capacitor of the previous three-phase voltage doubling unit, the cathode of the second diode and the anode of the fifth diode; the first end of the third support capacitor of the next three-phase voltage doubling unit is connected with the second end of the third support capacitor of the previous three-phase voltage doubling unit, the cathode of the third diode and the anode of the sixth diode; the first end of the first bus capacitor of the next three-phase voltage doubling unit is connected with the second end of the first bus capacitor of the previous three-phase voltage doubling unit, the cathode of the fourth diode, the cathode of the fifth diode and the cathode of the sixth diode; As preferred, when the number of the three-phase voltage doubling units set by the second three-phase voltage doubling module is more than one, the connection relationship between the multiple three-phase voltage doubling units is: the first end of the fourth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the fourth support capacitor of the previous three-phase voltage doubling unit, the anode of the seventh diode and the cathode of the twelfth diode; the first end of the fifth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the fifth support capacitor of the previous three-phase voltage doubling unit, the anode of the eighth diode and the cathode of the eleventh diode; the first end of the sixth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the sixth support capacitor of the previous three-phase voltage doubling unit, the anode of the ninth diode and the cathode of the tenth diode; the first end of the second bus capacitor of the next three-phase voltage doubling unit is connected with the second end of the second bus capacitor of the previous three-phase voltage doubling unit, the cathode of the twelfth diode, the cathode of the eleventh diode and the anode of the tenth diode.

[0012] As preferred, in the no-load state: The voltage stress of all capacitors in the three-phase voltage doubling rectifier circuit is less than or equal to 1 / (2n) of the total output voltage, and the voltage stress of all diodes is less than or equal to 1 / (2n) of the total output voltage. The primary winding voltage of the three-phase transformer is less than or equal to 1 / (4n) of the total output voltage, and the secondary winding voltage of the three-phase transformer is less than or equal to 1 / (4n) of the total output voltage. Wherein, n is the number of the three-phase voltage doubling units in a single three-phase voltage doubling module.

[0013] To achieve the above-mentioned purpose, the application further discloses a control method of a high-power high-voltage DC converter, which is applied to the high-power high-voltage DC converter as mentioned above, and the control method comprises the following steps: S1: setting the switching frequency operating range of the three-phase bridge inverter circuit as the maximum switching frequency to the minimum switching frequency, and setting the switching phase difference adjustment range between the three bridge arms of the three-phase bridge inverter circuit as 0°~120°; S2: when the actual output voltage demand is greater than the critical voltage value, it is determined as a high-voltage output working condition, and S3 is executed; when the actual output voltage demand is less than or equal to the critical voltage value, it is determined as a low-voltage output working condition, and S4 is executed; S3: fixing the switching phase difference between the three bridge arms as 120°, and adjusting the switching frequency in the range of the maximum switching frequency to the minimum switching frequency to match the actual output voltage demand; S4: fixing the switching frequency as the maximum switching frequency, and adjusting the switching phase difference between the three bridge arms in the range of 0°~120° to match the actual output voltage demand.

[0014] Preferably, the critical voltage value is the output voltage when the three-phase bridge inverter circuit operates at the maximum switching frequency and the switching phase difference between the three bridge arms is 120°.

[0015] Preferably, the minimum switching frequency is greater than the series resonance frequency of the three-phase resonant circuit, and the series resonance frequency is composed of the series resonant inductance and the series resonant capacitance of the three-phase resonant circuit.

[0016] Preferably, after S3 or S4 is executed, the control method further comprises the following steps: A1: after power-on starting, the switching frequency is initially set as the maximum switching frequency, and the switching phase difference between the three bridge arms is initially set as the minimum phase difference, and the minimum phase difference belongs to (0°, 120°]; A2: giving an output reference voltage, and detecting the current actual output voltage in real time; A3: If the current is a high-voltage output condition, the variable frequency PI control strategy is adopted to adjust the switching frequency, so that the actual output voltage approaches the output reference voltage; if the current is a low-voltage output condition, the three-phase phase-shift PI control strategy is adopted to adjust the switching phase difference, so that the actual output voltage approaches the output reference voltage; A4: Repeat A2 to A3 until the actual output voltage and the output reference voltage are equal.

[0017] Beneficial effects: firstly, the three-phase voltage doubling rectifier circuit adopts two positive and negative symmetric three-phase voltage doubling modules in parallel input and series output, combined with the three-phase interleaved input characteristics, the output ripple frequency can reach 6 times of the switching frequency, greatly reducing the output ripple, meeting the requirements of industrial microwave devices on high-voltage power output quality; secondly, through the mixed control strategy of variable frequency and three-phase phase shift, the critical voltage corresponding to the maximum switching frequency and 120° phase difference is used to divide the high-voltage and low-voltage conditions, the high-voltage section is fixed phase difference variable frequency regulation, and the low-voltage section is fixed maximum frequency phase shift regulation, realizing wide range output voltage regulation and adapting to the rated voltage demand of different types of magnetrons; thirdly, in the no-load state, the voltage stress of the capacitor and the diode is less than or equal to 1 / (2n) of the total output voltage, and the voltage of the transformer primary and secondary winding is less than or equal to 1 / (4n) of the total output voltage (n is the number of three-phase voltage doubling units), which significantly reduces the voltage stress of the device and adapts to the large power energy transmission scene; fourthly, a single three-phase transformer is used to replace multiple single-phase transformers, reducing the use of magnetic elements and bus capacitance, reducing hardware cost and control complexity, and facilitating engineering application. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor.

[0019] Figure 1 The basic working principle diagram of the high-power high-voltage DC converter provided by the embodiment of the present application; Figure 2 The circuit principle diagrams of the three-phase bridge inverter circuit, the three-phase resonant circuit and the three-phase transformer provided by the embodiment of the present application; Figure 3 The circuit principle diagram of the three-phase voltage doubling rectifier circuit provided by the embodiment of the present application; Figure 4 The control principle diagram of the control method of the high-power high-voltage DC converter provided by the embodiment of the present application; Figure 5 A typical waveform diagram of the high-power high-voltage DC converter provided by the embodiment of the present application; Figure 6The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 7 The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 8 The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 9 The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 10 The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 11 The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period The three-phase voltage doubling rectifier circuit provided by the embodiment of the present application is in a typical working mode diagram in a time period Figure 12 The voltage stress diagram of each device of the three-phase voltage doubling module provided by the embodiment of the present application.

[0020] In the figure: 10, three-phase bridge inverter circuit; 20, three-phase resonant circuit and three-phase transformer; 30, low-ripple three-phase voltage doubling rectifier circuit; 101, first bridge arm; 102, second bridge arm; 103, third bridge arm; 301, first three-phase voltage doubling module; 3011, first three-phase voltage doubling unit; 3012, second three-phase voltage doubling unit; 302, second three-phase voltage doubling module; 3021, third three-phase voltage doubling unit; 3022, fourth three-phase voltage doubling unit.

[0021] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0022] It should be understood that the specific embodiments described herein are intended to be illustrative only and not limiting of the present application.

[0023] To solve the technical problem that it is difficult to realize a large-power high-voltage direct-current converter with low ripple and low device voltage and current stress, and it is unable to meet the large-power application requirement of industrial microwave devices, the embodiment discloses a large-power high-voltage direct-current converter as shown in Figure 1 Figure 1 ​​​​​​​The basic working principle diagram of the high-power high-voltage DC converter is provided for the embodiment. The high-power high-voltage DC converter comprises a three-phase bridge inverter circuit, a three-phase resonant circuit, a three-phase transformer and a three-phase voltage doubling rectifier circuit; The input end of the three-phase bridge inverter circuit is connected with an external DC power supply, the output end of the three-phase bridge inverter circuit is connected with the input end of the three-phase resonant circuit, the output end of the three-phase resonant circuit is connected with the input end of the three-phase transformer, the output end of the three-phase transformer is connected with the input end of the three-phase voltage doubling rectifier circuit, the three-phase voltage doubling rectifier circuit is provided with two three-phase voltage doubling modules which are structurally positive and negative symmetrical, and the output end of the three-phase voltage doubling rectifier circuit is connected with an external load.

[0024] Referring to Figure 1 , the three-phase bridge inverter circuit corresponds to the three-phase bridge inverter circuit 10 in the figure, the three-phase resonant circuit and the three-phase transformer correspond to the three-phase resonant circuit and the three-phase transformer 20 in the figure, and the three-phase voltage doubling rectifier circuit corresponds to the low-ripple three-phase voltage doubling rectifier circuit 30 in the figure, DC is a preset external DC power supply, is a preset external load. Further, the two three-phase voltage doubling modules which are structurally positive and negative symmetrical and which are provided in the three-phase voltage doubling rectifier circuit correspond to the first three-phase voltage doubling module 301 and the second three-phase voltage doubling module 302 in the figure.

[0025] In the embodiment, the three-phase bridge inverter circuit comprises three bridge arms, namely a first bridge arm 101, a second bridge arm 102 and a third bridge arm 103, each bridge arm is connected by two switching tubes, and three lines are led out from the middle points of the three bridge arms and connected to the input end of the three-phase transformer; any phase of the three-phase resonant circuit comprises a resonant inductor in series, a resonant capacitor in series and a parallel resonant capacitor which is equivalent to being connected in parallel across the secondary winding of the transformer, and the equivalent parallel resonant capacitor comprises the parasitic capacitance of the three-phase transformer, the three-phase voltage doubling rectifier circuit diode and the external parallel resonant capacitor. Referring to Figure 2 , Figure 2 The circuit principle diagram of the three-phase bridge inverter circuit, the three-phase resonant circuit and the three-phase transformer is provided for the embodiment. In a specific application, DC is an input DC source, is an input DC source voltage, and is a DC bus capacitor, and the connection middle point thereof is a potential reference point. A metal-oxide-semiconductor field effect transistor (MOSFET) ~ constitutes the three-phase bridge inverter circuit 10; the three-phase resonant circuit and the three-phase transformer 20 are composed of an A-phase resonant capacitor , a resonant inductor , a parallel resonant capacitor , a B-phase resonant capacitor , a resonant inductor Parallel resonant capacitor C-phase resonant capacitor Resonant inductor Parallel resonant capacitor and three-phase transformers Connection configuration, three-phase transformer Both the primary and secondary sides adopt a star connection, with the parallel connection in the three-phase transformer. Secondary winding three-phase output terminal , , of , , Includes three-phase transformers The parasitic capacitance of the winding, the equivalent parasitic capacitance of the diodes in the three-phase voltage doubler rectifier circuit, and the externally connected resonant capacitor. , , Connect to the input terminal of the low-ripple three-phase voltage doubler rectifier circuit 30.

[0026] Reference Figure 3 , Figure 3 The circuit diagram of the three-phase voltage doubler rectifier circuit provided in this embodiment is shown.

[0027] Specifically, such as Figure 3 As shown, the three-phase voltage multiplier rectifier circuit has two three-phase voltage multiplier modules with symmetrical structures, specifically: The three-phase voltage multiplier rectifier circuit is equipped with a first three-phase voltage multiplier module and a second three-phase voltage multiplier module, which are structurally symmetrical. The input terminals of the first three-phase voltage multiplier module and the second three-phase voltage multiplier module are connected in parallel to form the input terminals of the three-phase voltage multiplier rectifier circuit; the input terminal of the first three-phase voltage multiplier module is composed of the first terminal of the first supporting capacitor, the first terminal of the second supporting capacitor, the first terminal of the third supporting capacitor, and the first terminal of the first bus capacitor; the input terminal of the second three-phase voltage multiplier module is composed of the first terminal of the fourth supporting capacitor, the first terminal of the fifth supporting capacitor, the first terminal of the sixth supporting capacitor, and the first terminal of the second bus capacitor. The output terminals of the first three-phase voltage multiplier module and the second three-phase voltage multiplier module are connected in series to form the output terminals of the three-phase voltage multiplier rectifier circuit. The output terminal of the first three-phase voltage multiplier module is composed of the cathodes of the fourth, fifth, and sixth diodes and the second terminal of the first bus capacitor. The output terminal of the second three-phase voltage multiplier module is composed of the anodes of the tenth, eleventh, and twelfth diodes and the second terminal of the second bus capacitor.

[0028] Specifically, the first three-phase voltage doubling module is provided with at least one first three-phase voltage doubling unit, and the first three-phase voltage doubling unit comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a first supporting capacitor, a second supporting capacitor, a third supporting capacitor and a first bus capacitor; The first end of the first supporting capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the first supporting capacitor is connected with the cathode of the first diode, the anode of the first diode is connected with the first end of the first bus capacitor, the second end of the first supporting capacitor is also connected with the anode of the fourth diode, and the cathode of the fourth diode is connected with the second end of the first bus capacitor; The first end of the second supporting capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the second supporting capacitor is connected with the cathode of the second diode, the anode of the second diode is connected with the first end of the first bus capacitor, the second end of the second supporting capacitor is also connected with the anode of the fifth diode, and the cathode of the fifth diode is connected with the second end of the first bus capacitor; The first end of the third supporting capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the third supporting capacitor is connected with the cathode of the third diode, the anode of the third diode is connected with the first end of the first bus capacitor, the second end of the third supporting capacitor is also connected with the anode of the sixth diode, and the cathode of the sixth diode is connected with the second end of the first bus capacitor; The anode of the first diode, the anode of the second diode, the anode of the third diode and the first end of the first bus capacitor are all connected with the neutral output end of the three-phase transformer; The second three-phase voltage doubling module is provided with at least one second three-phase voltage doubling unit, and the second three-phase voltage doubling unit comprises a seventh diode, an eighth diode, a ninth diode, a twelfth diode, an eleventh diode, a tenth diode, a fourth supporting capacitor, a fifth supporting capacitor, a sixth supporting capacitor and a second bus capacitor; The first end of the fourth supporting capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the fourth supporting capacitor is connected with the anode of the seventh diode, the cathode of the seventh diode is connected with the first end of the second bus capacitor, the second end of the fourth supporting capacitor is also connected with the cathode of the twelfth diode, and the anode of the twelfth diode is connected with the second end of the second bus capacitor; The first end of the fifth supporting capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the fifth supporting capacitor is connected with the anode of the eighth diode, the cathode of the eighth diode is connected with the first end of the second bus capacitor, the second end of the fifth supporting capacitor is also connected with the cathode of the eleventh diode, and the anode of the eleventh diode is connected with the second end of the second bus capacitor; The first end of the sixth support capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the sixth support capacitor is connected with the anode of the ninth diode, the cathode of the ninth diode is connected with the first end of the second bus capacitor, the second end of the sixth support capacitor is also connected with the cathode of the tenth diode, the anode of the tenth diode is connected with the second end of the second bus capacitor; The cathode of the seventh diode, the cathode of the eighth diode, the cathode of the ninth diode and the first end of the second bus capacitor are all connected with the neutral output end of the three-phase transformer.

[0029] In a specific application, as shown in FIG. Figure 3 , 3011 and 3012 correspond to the first three-phase voltage doubling unit and the second three-phase voltage doubling unit, 3021 and 3022 correspond to the third three-phase voltage doubling unit and the fourth three-phase voltage doubling unit, taking the first three-phase voltage doubling unit 3011 as an example, one three-phase voltage doubling unit is composed of six diodes , , , , and , which respectively correspond to the first diode, the fourth diode, the second diode, the fifth diode, the third diode and the sixth diode, three support capacitors , and , which respectively correspond to the first support capacitor, the second support capacitor and the third support capacitor, and one bus output capacitor , which corresponds to the bus capacitor. , , The cathodes of , , are respectively connected with the anodes of , , , and are respectively connected with the output ends of the three-phase transformer , , . , , The anodes of are commonly connected to one end of the bus output capacitor , , The cathodes of are commonly connected to the other end of the bus output capacitor.

[0030] In a specific application, as shown in FIG. Figure 3The second three-phase voltage doubler module 302 is a three-phase voltage doubler module that is structurally positive and negative symmetric with the first three-phase voltage doubler module 301. The first three-phase voltage doubler module 301 and the second three-phase voltage doubler module 302 are connected in series to a load resistor The relationship between the output voltage and the input voltage of each phase when the three-phase voltage doubler rectifier circuit is in an idle state is wherein is the output voltage when the three-phase voltage doubler rectifier circuit is in an idle state, is the number of three-phase voltage doubling units of the first three-phase voltage doubler module 301 and the second three-phase voltage doubler module 302, is the amplitude of the phase voltage of the three-phase input voltage.

[0031] Specifically, the number of three-phase voltage doubling units of the three-phase voltage doubler module is determined based on the actual output voltage demand.

[0032] Specifically, when the number of three-phase voltage doubling units of the first three-phase voltage doubler module is greater than one, the connection relationship between the multiple three-phase voltage doubling units is as follows: The first end of the first support capacitor of the next three-phase voltage doubling unit is connected to the second end of the first support capacitor of the previous three-phase voltage doubling unit, the cathode of the first diode, and the anode of the fourth diode; The first end of the second support capacitor of the next three-phase voltage doubling unit is connected to the second end of the second support capacitor of the previous three-phase voltage doubling unit, the cathode of the second diode, and the anode of the fifth diode; The first end of the third support capacitor of the next three-phase voltage doubling unit is connected to the second end of the third support capacitor of the previous three-phase voltage doubling unit, the cathode of the third diode, and the anode of the sixth diode; The first end of the first bus capacitor of the next three-phase voltage doubling unit is connected to the second end of the first bus capacitor of the previous three-phase voltage doubling unit, the cathode of the fourth diode, the cathode of the fifth diode, and the cathode of the sixth diode; When the number of three-phase voltage doubling units of the second three-phase voltage doubler module is greater than one, the connection relationship between the multiple three-phase voltage doubling units is as follows: The first end of the fourth support capacitor of the next three-phase voltage doubling unit is connected to the second end of the fourth support capacitor of the previous three-phase voltage doubling unit, the anode of the seventh diode, and the cathode of the twelfth diode; The first end of the fifth support capacitor of the next three-phase voltage doubling unit is connected to the second end of the fifth support capacitor of the previous three-phase voltage doubling unit, the anode of the eighth diode, and the cathode of the eleventh diode; The first end of the sixth support capacitor of the next three-phase voltage doubling unit is connected to the second end of the sixth support capacitor of the previous three-phase voltage doubling unit, the anode of the ninth diode, and the cathode of the tenth diode; The first terminal of the second bus capacitor of the next three-phase voltage multiplier unit is connected to the second terminal of the second bus capacitor of the previous three-phase voltage multiplier unit, the cathode of the tenth diode, the cathode of the eleventh diode, and the anode of the twelfth diode.

[0033] like Figure 3 As shown, in a specific application, n units with the same structure as the first three-phase voltage multiplier unit 3011, such as the second three-phase voltage multiplier unit 3012, are cascaded to form the first three-phase voltage multiplier module 301. All three-phase voltage multiplier units have the same bus output capacitor. ~ Series connection.

[0034] like Figure 3 As shown, in a specific application, n units with the same structure as the third three-phase voltage multiplier unit 3021, such as the fourth three-phase voltage multiplier unit 3022, are cascaded to form the second three-phase voltage multiplier module 302. All three-phase voltage multiplier units have the same bus output capacitor. ~ Series connection.

[0035] Specifically, in the no-load state: In a three-phase voltage doubler rectifier circuit, the voltage stress of all capacitors is less than or equal to 1 / (2n) of the total output voltage, and the voltage stress of all diodes is less than or equal to 1 / (2n) of the total output voltage. The voltage of the primary winding of a three-phase transformer is less than or equal to 1 / (4n) of the total output voltage, and the voltage of the secondary winding of a three-phase transformer is less than or equal to 1 / (4n) of the total output voltage. Where n is the number of three-phase voltage multiplier units in a single three-phase voltage multiplier module.

[0036] To solve the above technical problems, refer to Figure 4 , Figure 4 This embodiment provides a control principle diagram for a high-power high-voltage direct current converter. The control method, applied to the high-power high-voltage direct current converter described above, includes the following steps: S1: Set the operating range of the switching frequency of the three-phase bridge inverter circuit to the maximum switching frequency to the minimum switching frequency, and set the adjustment range of the switching phase difference between the three bridge arms of the three-phase bridge inverter circuit to 0°~120°. S2: When the actual output voltage demand is greater than the critical voltage value, it is determined to be a high voltage output condition and S3 is executed; when the actual output voltage demand is less than or equal to the critical voltage value, it is determined to be a low voltage output condition and S4 is executed. S3: Fix the switching phase difference between the three bridge arms to 120°, and adjust the switching frequency within the range of the maximum switching frequency to the minimum switching frequency to match the actual output voltage requirements. S4: The fixed switching frequency is the maximum switching frequency. The switching phase difference between the three bridge arms is adjusted to vary within the range of 0° to 120° to match the actual output voltage requirements.

[0037] like Figure 2 and Figure 4 As shown, in this embodiment, all switches of the high-power HVDC converter operate between the maximum and minimum switching frequencies. Furthermore, the switch of the third bridge arm 103 in the three-phase inverter circuit lags behind the switch of the second bridge arm 102 by the same phase difference, and the switch of the second bridge arm 102 lags behind the switch of the first bridge arm 101 by the same phase difference. The phase difference range is... ~120°, where 0 < ≤120°. With a reasonable switching frequency and resonant component design, the converter output voltage decreases as the switching frequency increases. When the converter operates at its maximum switching frequency, the phase difference between the three bridge arms is reduced, resulting in asymmetry in the primary-side three-phase voltage. The degree of asymmetry increases as the phase difference between the three bridge arms decreases. Therefore, the output voltage can be further reduced by decreasing the phase difference between the three bridge arms, allowing the converter to achieve a wider voltage output range within a certain switching frequency range. Even when operating at its maximum switching frequency under three-phase asymmetry, the low output power has no additional impact on the hardware circuitry.

[0038] Specifically, the critical voltage value is the output voltage of a three-phase bridge inverter circuit when the switching frequency is the maximum switching frequency and the phase difference between the three bridge arms is 120°.

[0039] Specifically, the minimum switching frequency is greater than the series resonant frequency of the three-phase resonant circuit, which is composed of the series resonant inductance and series resonant capacitor of the three-phase resonant circuit.

[0040] Specifically, after executing S3 or S4, the control method further includes the following steps: A1: After power-on, the initial switching frequency is set to the maximum switching frequency, and the initial switching phase difference between the three bridge arms is set to the minimum phase difference, and this minimum phase difference belongs to (0°, 120°]. A2: Given an output reference voltage, detect the current actual output voltage in real time; A3: If the current operating condition is high voltage output, the switching frequency is adjusted using a frequency conversion PI control strategy to make the actual output voltage approach the output reference voltage; if the current operating condition is low voltage output, the switching phase difference is adjusted using a three-phase phase-shifting PI control strategy to make the actual output voltage approach the output reference voltage. A4: Repeat A2 to A3 until the actual output voltage and the output reference voltage are equal.

[0041] In a specific application, the specific control method of this embodiment is as follows: after the converter is powered on, the switching transistor is set to operate at the maximum switching frequency and minimum phase difference. In this state, then given the output reference voltage, determine the phase difference at this time. If the angle is equal to 120°, then frequency conversion PI control is performed by adjusting the operating frequency of all switching transistors. If the angle is not equal to 120° (i.e., less than 120°), then three-phase phase-shift PI control is performed by adjusting the phase difference between the three-phase bridge arms. Next, the output voltage is compared with the reference voltage. If they are not equal, the process loops back to judging the phase difference. Repeat the above process for the next step.

[0042] Therefore, based on the output voltage value, the high-power HVDC converter in this embodiment can operate in two modes: frequency conversion PI control and three-phase phase-shift PI control. When high voltage is output, it operates in frequency conversion control mode, with the phase difference between the three-phase bridge arms fixed at 120°, and voltage is adjusted by changing the switching frequency. When low voltage is output, it operates in three-phase phase-shift control mode, with the switching transistor operating frequency fixed at the maximum switching frequency, and voltage is adjusted by changing the phase difference between the three bridge arms.

[0043] In one specific application, each three-phase voltage multiplier module contains one three-phase voltage multiplier unit, operating in frequency converter control mode, i.e., n=1. Its typical waveform is as follows: Figure 5 As shown. The positive directions of all electrical quantities are as follows. Figure 2 and Figure 3 As shown. , , The voltage between the output terminal of the three-phase bridge inverter circuit and the potential reference point has an amplitude of The frequency of the square wave voltage in each phase is equal to the switching frequency. Current , , These are the currents in the three-phase resonant circuits A, B, and C, respectively. Under a reasonable switching frequency and resonant element design, the current... , , Lagging behind , , The three-phase bridge inverter circuit can achieve zero-voltage turn-on, greatly reducing the switching losses of the MOSFET switches. , , This refers to the voltage between the three-phase output windings and the transformer neutral line of a three-phase transformer, which is also the terminal voltage of the parallel resonant capacitor. It is also the input voltage of the three-phase voltage multiplier rectifier circuit, and its amplitude is... .Voltage It is the voltage across the output capacitor of the first three-phase voltage multiplier module 301 bus. is the voltage across the bus output capacitor of the second three-phase voltage doubler module 302, and the voltage across the load is .

[0044] The typical working mode of the three-phase voltage doubler rectifier circuit of the embodiment is shown in Figures 6-11 . Since the low-ripple three-phase voltage doubler rectifier circuit 30 is forward and reverse symmetric, the current between the first three-phase voltage doubler module 301 and the second three-phase voltage doubler module 302 and the middle line of the three-phase transformer cancels each other, and the current flowing through the middle line is 0, so the input port of the low-ripple three-phase voltage doubler rectifier circuit 30 can be ignored when analyzing the mode . As shown in Figure 5 , the diodes with common cathodes, the diodes with the highest anode potential are turned on, and the diodes with common anodes, the diodes with the lowest cathode potential are turned on, in ~ period, , so the A phase and the B phase are turned on, and the C phase is not working at this time, and the working mode of the three-phase voltage doubler rectifier circuit at this time is shown in Figure 6 . In ~ period, , the A phase and the C phase are turned on, and the B phase is not working at this time, and the working mode at this time is shown in Figure 7 . In ~ period, , the B phase and the C phase are turned on, and the A phase is not working at this time, and the working mode at this time is shown in Figure 8 . In ~ period, , the B phase and the A phase are turned on, and the C phase is not working at this time, and the working mode at this time is shown in Figure 9 . In ~ period, , the C phase and the A phase are turned on, and the B phase is not working at this time, and the working mode at this time is shown in Figure 10 . In ~ period, , the C phase and the B phase are turned on, and the A phase is not working at this time, and the working mode at this time is shown in​​​​​​​​​​​​​​​​​​Figure 11 as shown.

[0045] According to the above analysis, in one switching cycle, A, B, C three-phase alternating conduction is used to charge the bus output capacitor of the three-phase voltage doubler module, and because the first three-phase voltage doubler module 301 and the second three-phase voltage doubler module 302 are positively and negatively symmetrical, the bus output capacitor of the first three-phase voltage doubler module 301 and the second three-phase voltage doubler module 302 are connected in series to the load resistor After that, the output voltage ripple of the two modules is staggered and superimposed, and the voltage across the load resistor pulses 6 times in each switching cycle, that is, the ripple frequency is 6 times the switching frequency, effectively reducing the output voltage ripple.

[0046] According to the working mode analysis of the low-ripple three-phase voltage doubler rectifier circuit 30, the three-phase voltage doubler rectifier circuit of the embodiment reduces the current and voltage stress of capacitors and diodes compared with the traditional voltage doubler rectifier circuit through the three-phase alternating conduction mode and the parallel input and series output connection mode of the three-phase voltage doubler module. In the low-ripple three-phase voltage doubler rectifier circuit 30, the average current of each diode is 1 / 3 , where is the average load current. When the number n of three-phase voltage doubling units in each three-phase voltage doubler module is greater than 1, the current flowing through the support capacitor and the bus output capacitor increases, the current flowing through the diode remains unchanged, but compared with the traditional voltage doubler rectifier circuit, the current stress of all devices is effectively reduced under the same working condition. In a specific application, when each three-phase voltage doubler module contains n three-phase voltage doubling units, the voltage stress of each device is referred to Figure 12 , where is the input phase voltage amplitude of the three-phase voltage doubler rectifier circuit, and the relationship between the output voltage of the three-phase voltage doubler rectifier circuit and the input voltage of each phase when the three-phase voltage doubler rectifier circuit is in an idle state is .

[0047] In summary, the high-power high-voltage DC converter and the control method thereof of the embodiment achieve the following technical effects: First, the three-phase voltage doubler rectifier circuit uses two positively and negatively symmetrical three-phase voltage doubler modules in parallel input and series output, combined with the three-phase interleaved input characteristic, the output ripple frequency can reach 6 times the switching frequency, greatly reducing the output ripple, meeting the output quality requirements of industrial microwave devices for high-voltage power supplies; Second, by using the frequency conversion and three-phase phase shift hybrid control strategy, the high and low voltage conditions are divided by the critical voltage corresponding to the maximum switching frequency and 120° phase difference, the high voltage section is fixed phase difference variable frequency regulation, and the low voltage section is fixed maximum frequency phase shift regulation, realizing wide range output voltage regulation and adapting to the rated voltage requirements of different types of magnetrons. Thirdly, in the no-load state, the voltage stress of the capacitor and the diode is less than or equal to 1 / (2n) of the total output voltage, and the primary and secondary winding voltages of the transformer are less than or equal to 1 / (4n) of the total output voltage (n is the number of three-phase voltage multiplication units), which significantly reduces the voltage stress of the device and adapts to the large-power energy transmission scene. Fourthly, a single three-phase transformer is used to replace multiple single-phase transformers, which reduces the use amount of magnetic elements and bus capacitors, reduces the hardware cost and control complexity, and is beneficial to engineering application.

[0048] It should be understood that the above is only illustrative, and does not constitute any limitation on the technical solutions of the present application. In specific applications, those skilled in the art can set it up according to the needs, and the present application does not limit this.

[0049] It should be noted that the above-described workflow is only illustrative and does not limit the scope of protection of the present application. In actual application, those skilled in the art can select part or all of them to achieve the purpose of the embodiment scheme according to actual needs, which is not limited here.

[0050] It should be noted that in this paper, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or system including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or system. Without more limitations, the element defined by the sentence "includes a" does not exclude the presence of another identical element in the process, method, article or system including the element.

[0051] From the above description of the embodiments, those skilled in the art can clearly understand that the above embodiment method can be realized by software and necessary general hardware platform, of course, it can also be realized by hardware, but in many cases the former is a better embodiment. Based on such understanding, the technical solutions of the present application can be embodied in the form of software product, which is stored in a storage medium (such as read-only memory / random access memory, magnetic disk, optical disk), including a plurality of instructions for making a terminal device (which can be a mobile phone, computer, server, air conditioner or network device, etc.) execute the method described in each embodiment of the present application.

[0052] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A high-power high-voltage DC converter, characterized in that The three-phase bridge inverter circuit, the three-phase resonance circuit, the three-phase transformer and the three-phase voltage doubling rectifier circuit are connected in series. The input end of the three-phase bridge inverter circuit is connected with an external DC power supply, the output end of the three-phase bridge inverter circuit is connected with the input end of the three-phase resonance circuit, the output end of the three-phase resonance circuit is connected with the input end of the three-phase transformer, the output end of the three-phase transformer is connected with the input end of the three-phase voltage doubling rectifier circuit, the three-phase voltage doubling rectifier circuit is provided with two three-phase voltage doubling modules which are structurally positive and negative symmetrical, and the output end of the three-phase voltage doubling rectifier circuit is connected with an external load.

2. The high power high voltage DC converter of claim 1, wherein, The three-phase voltage doubling rectifier circuit is provided with two three-phase voltage doubling modules which are structurally positive and negative symmetrical, and the two three-phase voltage doubling modules are connected in series. The three-phase voltage doubling rectifier circuit is provided with a first three-phase voltage doubling module and a second three-phase voltage doubling module, and the first three-phase voltage doubling module and the second three-phase voltage doubling module are structurally positive and negative symmetrical. The input end of the first three-phase voltage doubling module and the input end of the second three-phase voltage doubling module are connected in parallel to form the input end of the three-phase voltage doubling rectifier circuit, the input end of the first three-phase voltage doubling module is formed by the first end of a first supporting capacitor, the first end of a second supporting capacitor, the first end of a third supporting capacitor and the first end of a first bus capacitor, and the input end of the second three-phase voltage doubling module is formed by the first end of a fourth supporting capacitor, the first end of a fifth supporting capacitor, the first end of a sixth supporting capacitor and the first end of a second bus capacitor. The output end of the first three-phase voltage doubling module and the output end of the second three-phase voltage doubling module are connected in series to form the output end of the three-phase voltage doubling rectifier circuit, the output end of the first three-phase voltage doubling module is formed by the cathode of a fourth diode, the cathode of a fifth diode, the cathode of a sixth diode and the second end of the first bus capacitor, and the output end of the second three-phase voltage doubling module is formed by the anode of a twelfth diode, the anode of an eleventh diode, the anode of a tenth diode and the second end of the second bus capacitor.

3. The high power high voltage DC converter of claim 2, wherein, The first three-phase voltage doubling module is provided with at least one first three-phase voltage doubling unit, and the first three-phase voltage doubling unit comprises a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a first supporting capacitor, a second supporting capacitor, a third supporting capacitor and a first bus capacitor. The first end of the first supporting capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the first supporting capacitor is connected with the cathode of the first diode, the anode of the first diode is connected with the first end of the first bus capacitor, the second end of the first supporting capacitor is also connected with the anode of the fourth diode, and the cathode of the fourth diode is connected with the second end of the first bus capacitor. The first end of the second supporting capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the second supporting capacitor is connected with the cathode of the second diode, the anode of the second diode is connected with the first end of the first bus capacitor, the second end of the second supporting capacitor is also connected with the anode of the fifth diode, and the cathode of the fifth diode is connected with the second end of the first bus capacitor. The first end of the third supporting capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the third supporting capacitor is connected with the cathode of the third diode, the anode of the third diode is connected with the first end of the first bus capacitor, the second end of the third supporting capacitor is also connected with the anode of the sixth diode, and the cathode of the sixth diode is connected with the second end of the first bus capacitor. The first end of the third support capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the third support capacitor is connected with the cathode of the third diode, the anode of the third diode is connected with the first end of the first bus capacitor, the second end of the third support capacitor is also connected with the anode of the sixth diode, and the cathode of the sixth diode is connected with the second end of the first bus capacitor; The anode of the first diode, the anode of the second diode, the anode of the third diode and the first end of the first bus capacitor are all connected with the neutral output end of the three-phase transformer; The second three-phase voltage doubling module is provided with at least one second three-phase voltage doubling unit, and the second three-phase voltage doubling unit comprises a seventh diode, an eighth diode, a ninth diode, a twelfth diode, an eleventh diode, a tenth diode, a fourth support capacitor, a fifth support capacitor, a sixth support capacitor and a second bus capacitor. The first end of the fourth support capacitor is connected with the A-phase output end of the three-phase transformer, the second end of the fourth support capacitor is connected with the anode of the seventh diode, the cathode of the seventh diode is connected with the first end of the second bus capacitor, the second end of the fourth support capacitor is also connected with the cathode of the twelfth diode, and the anode of the twelfth diode is connected with the second end of the second bus capacitor. The first end of the fifth support capacitor is connected with the B-phase output end of the three-phase transformer, the second end of the fifth support capacitor is connected with the anode of the eighth diode, the cathode of the eighth diode is connected with the first end of the second bus capacitor, the second end of the fifth support capacitor is also connected with the cathode of the eleventh diode, and the anode of the eleventh diode is connected with the second end of the second bus capacitor. The first end of the sixth support capacitor is connected with the C-phase output end of the three-phase transformer, the second end of the sixth support capacitor is connected with the anode of the ninth diode, the cathode of the ninth diode is connected with the first end of the second bus capacitor, the second end of the sixth support capacitor is also connected with the cathode of the tenth diode, and the anode of the tenth diode is connected with the second end of the second bus capacitor. The cathode of the seventh diode, the cathode of the eighth diode, the cathode of the ninth diode and the first end of the second bus capacitor are all connected with the neutral output end of the three-phase transformer.

4. The high power high voltage DC converter of claim 3, wherein, The number of the three-phase voltage doubling units provided by the three-phase voltage doubling module is determined based on actual output voltage demand.

5. The high power high voltage DC converter of claim 4, wherein, When the number of the three-phase voltage doubling units provided by the first three-phase voltage doubling module is greater than one, the connection relationship between the multiple three-phase voltage doubling units is as follows: The first end of the first support capacitor of the next three-phase voltage doubling unit is connected with the second end of the first support capacitor of the previous three-phase voltage doubling unit, the cathode of the first diode and the anode of the fourth diode; The first end of the second support capacitor of the next three-phase voltage doubling unit is connected with the second end of the second support capacitor of the previous three-phase voltage doubling unit, the cathode of the second diode and the anode of the fifth diode; The first end of the second support capacitor of the next three-phase voltage doubling unit is connected with the second end of the second support capacitor of the previous three-phase voltage doubling unit, the cathode of the second diode and the anode of the fifth diode; The first end of the third support capacitor of the next three-phase voltage doubling unit is connected with the second end of the third support capacitor of the previous three-phase voltage doubling unit, the cathode of the third diode and the anode of the sixth diode; The first end of the first bus capacitor of the next three-phase voltage doubling unit is connected with the second end of the first bus capacitor of the previous three-phase voltage doubling unit, the cathode of the fourth diode, the cathode of the fifth diode and the cathode of the sixth diode; When the number of the three-phase voltage doubling units of the second three-phase voltage doubling module is greater than one, the connection relationship between the three-phase voltage doubling units is as follows: The first end of the fourth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the fourth support capacitor of the previous three-phase voltage doubling unit, the anode of the seventh diode and the cathode of the twelfth diode; The first end of the fifth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the fifth support capacitor of the previous three-phase voltage doubling unit, the anode of the eighth diode and the cathode of the eleventh diode; The first end of the sixth support capacitor of the next three-phase voltage doubling unit is connected with the second end of the sixth support capacitor of the previous three-phase voltage doubling unit, the anode of the ninth diode and the cathode of the tenth diode; The first end of the second bus capacitor of the next three-phase voltage doubling unit is connected with the second end of the second bus capacitor of the previous three-phase voltage doubling unit, the cathode of the twelfth diode, the cathode of the eleventh diode and the anode of the tenth diode.

6. The high power high voltage DC converter of claim 4, wherein, In the no-load state: The voltage stress of all capacitors in the three-phase voltage doubling rectifier circuit is less than or equal to 1 / (2n) of the total output voltage, and the voltage stress of all diodes is less than or equal to 1 / (2n) of the total output voltage; The primary winding voltage of the three-phase transformer is less than or equal to 1 / (4n) of the total output voltage, and the secondary winding voltage of the three-phase transformer is less than or equal to 1 / (4n) of the total output voltage; Wherein, n is the number of the three-phase voltage doubling units in a single three-phase voltage doubling module.

7. A control method of a high-power high-voltage DC converter, applied to the high-power high-voltage DC converter according to any one of claims 1-6, characterized in that, The control method comprises the following steps: S1: setting the switching frequency operating range of the three-phase bridge inverter circuit to be the maximum switching frequency to the minimum switching frequency, and setting the switching phase difference adjustment range between the three bridge arms to be 0°~120°; S2: when the actual output voltage demand is greater than the critical voltage value, it is determined to be a high-voltage output working condition, and S3 is executed; when the actual output voltage demand is less than or equal to the critical voltage value, it is determined to be a low-voltage output working condition, and S4 is executed; S3: fixing the switching phase difference between the three bridge arms to be 120°, and adjusting the switching frequency in the range of the maximum switching frequency to the minimum switching frequency to match the actual output voltage demand; S4: fixing the switching frequency to be the maximum switching frequency, and adjusting the switching phase difference between the three bridge arms in the range of 0°~120° to match the actual output voltage demand.

8. The control method of a high-power high-voltage DC converter according to claim 7, characterized by, The critical voltage value is an output voltage of the three-phase bridge inverter circuit when the three-phase bridge inverter circuit works at a switching frequency of the maximum switching frequency and a switching phase difference between three bridge arms is 120°.

9. The control method of a high-power high-voltage DC converter according to claim 7, characterized by, The minimum switching frequency is greater than a series resonance frequency of the three-phase resonance circuit, and the series resonance frequency is composed of a series resonance inductance and a series resonance capacitance of the three-phase resonance circuit.

10. The control method of a high-power high-voltage DC converter according to claim 7, characterized by, After S3 or S4 is executed, the control method further comprises the following steps: A1: after power-on starting, initially setting the switching frequency as the maximum switching frequency, initially setting the switching phase difference between three bridge arms as the minimum phase difference, and the minimum phase difference belongs to (0°, 120°]; A2: given an output reference voltage, detecting a current actual output voltage in real time; A3: if the current is a high-voltage output working condition, a variable-frequency PI control strategy is adopted to adjust the switching frequency, so that the actual output voltage approaches the output reference voltage; if the current is a low-voltage output working condition, a three-phase phase-shift PI control strategy is adopted to adjust the switching phase difference, so that the actual output voltage approaches the output reference voltage; A4: A2 to A3 are repeatedly executed until the actual output voltage is equal to the output reference voltage.

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