High-voltage direct-current converter topology and control method thereof

Abstract

The invention discloses a high-voltage direct-current converter topology and a control method thereof, and belongs to the technical field of power generation, power transformation or power distribution. The topology is composed of a high-voltage side filter inductor, a three-phase MMC inverter circuit, a three-phase leakage inductor, a three-phase transformer, a three-phase diode rectifying circuit, a medium-voltage side filter inductor and a medium-voltage side filter capacitor. High reliability and low cost and size can be realized, reliable commutation of a three-phase rectifier diode is realized by accurately controlling three-phase current to be trapezoidal current with symmetrical positive and negative semi-cycles, smooth direct current is synthesized at a high-voltage side and a medium-voltage side, the operation efficiency of the converter and the electric energy quality of a port are remarkably improved, and the size of a filter is reduced.

Description

Technical Field

[0001] The invention relates to power electronics application technology, and in particular discloses a high-voltage direct current converter topology and a control method thereof, belonging to the technical field of power generation, power transformation or power distribution. Background Art

[0002] With the popularization of renewable energy and the development of DC loads, DC transmission and distribution technology has developed rapidly due to its advantages of flexible power control, convenient access to new energy, and long transmission distance. DC grids rely on DC transformers to achieve voltage conversion and electrical isolation, realize the interconnection of DC grids of different voltage levels, and improve the flexibility of DC transmission and distribution.

[0003] Existing high-voltage DC converters are mostly connected by connecting the AC sides of two modular multilevel converters (MMC) through an isolation transformer, and adopting a sinusoidal modulation control method. In practical applications, there are problems of large size and low power density. In particular, for special occasions such as large-capacity receiving-end DC converters with single-phase power flow, the topology structure can be further optimized to reduce the number of power devices and passive components of the DC converter, the floor space and investment cost, while ensuring the system operation reliability and improving the operation efficiency. In addition, the AC side of the isolated DC transformer is an internal AC link, which can further optimize the topology control method, improve the power quality of the input and output ports, and reduce the converter operation loss. Summary of the invention

[0004] The purpose of the present invention is to provide an isolated modular multi-level DC converter topology structure suitable for medium and high voltage DC grid interconnection and a control method thereof in view of the deficiencies of the above-mentioned background technology. On the basis of the three-phase MMC converter, a three-phase industrial frequency / medium frequency transformer and a three-phase diode rectifier circuit are added. By adding a high-voltage side filter inductor, a three-phase transformer leakage inductance and a medium-voltage side filter inductor in the topology of the high-voltage side modular DC converter structure and the medium-voltage side diode series rectifier circuit, the three-phase current is precisely controlled to be a trapezoidal shape with symmetry between the positive and negative half cycles, so as to realize reliable commutation of the three-phase rectifier diode and improve the operating efficiency. At the same time, a smooth DC current is synthesized on both the high-voltage side and the medium-voltage side, so as to significantly improve the output power quality of the high-voltage side and the medium-voltage side, and reduce the volume of the filter, thereby achieving the purpose of the invention of improving the reliability of the DC converter topology while reducing the volume and cost.

[0005] The present invention adopts the following technical solutions to achieve the above-mentioned invention object:

[0006] A high voltage DC converter topology and control method thereof,

[0007] The high-voltage DC converter topology includes: a high-voltage side filter inductor, a three-phase MMC inverter circuit, a three-phase leakage inductor, a three-phase transformer, a three-phase diode rectifier circuit, a medium-voltage side filter inductor and a medium-voltage side filter capacitor; a high-voltage side filter inductor, one end of which constitutes the positive electrode of the high-voltage DC port; a three-phase MMC inverter circuit, the positive electrode of its DC port is connected to the other end of the high-voltage side filter inductor, and the negative electrode of its DC port constitutes the negative electrode of the high-voltage DC port, each phase bridge arm is connected in series with a bridge arm inductor, a three-phase leakage inductor, one end of each phase leakage inductor is connected to a phase AC port of the three-phase MMC inverter circuit, and a three-phase transformer, the first end of the primary winding of each phase transformer is respectively connected to the other end of a phase leakage inductor, and each The second ends of the primary windings of the phase transformers are connected, the three-phase diode rectifier circuit, each phase AC port is respectively connected to the first end of the secondary winding of a phase transformer, each phase diode rectifier branch is composed of two diodes connected in series, the second ends of the secondary windings of the phase transformers are connected, the first end of the primary winding of each phase transformer and the first end of the secondary winding are the same name ends, the medium voltage side filter inductor, one end of which is connected to the positive electrode of the DC port of the three-phase diode rectifier circuit; the medium voltage side filter capacitor, one pole of which is connected to the other end of the medium voltage side filter inductor to form the positive pole of the medium voltage DC port, and the other pole of which is connected to the negative pole of the DC port of the three-phase diode rectifier circuit to form the negative pole of the medium voltage DC port;

[0008] The control method of the high-voltage DC converter topology modulates the multi-level square wave voltage output by each phase MMC bridge arm, and obtains a trapezoidal AC current with positive and negative half-cycle symmetry at the AC port of the three-phase MMC inverter circuit.

[0009] As a further optimization scheme for the high-voltage DC converter topology and its control method, the specific method for modulating the multi-level square wave voltage output by each phase MMC bridge arm is as follows:

[0010] In each commutation stage, the output voltage of the MMC bridge arm in the current rising phase is increased, and the output voltage of the MMC bridge arm in the current falling phase is reduced, and the amplitude of the increase of the output voltage of the MMC bridge arm in the current rising phase is maintained equal to the amplitude of the decrease of the output voltage of the MMC bridge arm in the current falling phase, and the duration of the increase of the output voltage of the MMC bridge arm in the current rising phase is equal to the duration of the decrease of the output voltage of the MMC bridge arm in the current falling phase;

[0011] In each freewheeling stage, the output voltage of the MMC bridge arm of the current freewheeling phase is adjusted to maintain the current of the current freewheeling phase stable at the set value of the trapezoidal wave AC current amplitude.

[0012] As a further optimization scheme for a high-voltage DC converter topology and its control method, the control method of the high-voltage DC converter topology modulates the multi-level square wave voltage output by each phase MMC bridge arm by adjusting the voltage on the inductance of each phase bridge arm and the voltage on the leakage inductance of each phase in a three-phase MMC inverter circuit.

[0013] As a further optimization scheme for the high-voltage DC converter topology and its control method, in each commutation stage, the amplitude and duration of the increase in the output voltage of the MMC bridge arm in the current rising phase are constrained by the voltage on the inductance and leakage inductance of the MMC bridge arm in the rising phase.

[0014] As a further optimization scheme for the high-voltage DC converter topology and its control method, in each commutation stage, the amplitude of the output voltage of the MMC bridge arm in the current rising phase is constrained by the medium-voltage side voltage and the increase amplitude of the output voltage of the MMC bridge arm in the rising phase, and the amplitude of the output voltage of the MMC bridge arm in the current rising phase is constrained by the maximum value of the MMC bridge arm output voltage.

[0015] As a further optimization scheme for the high-voltage DC converter topology and its control method, the amplitude and duration of the increase in the output voltage of the MMC bridge arm during the current rising phase satisfy the expression: t D,X =D t,X T t , where X phase is the electrical rising phase, X is A or B or C, V t,X is the amplitude of the increase in the output voltage of the X-phase MMC bridge arm, t D,X is the duration of the X-phase MMC bridge arm output voltage increase, L ARM,X is the X-phase bridge arm inductance, L K,X is the leakage inductance of the X-phase transformer, I M is the output current on the medium voltage side, n is the transformation ratio of the three-phase transformer, T t is the AC cycle, D t,X t D,X The AC cycle duty cycle.

[0016] As a further optimization scheme for the high-voltage DC converter topology and its control method, the amplitude of the output voltage of the MMC bridge arm in the current rising phase is Among them, V m,X is the amplitude of the X-phase MMC bridge arm output voltage, V M is the medium voltage side voltage.

[0017] As a further optimization scheme for the high-voltage DC converter topology and its control method, the maximum value of the output voltage of the MMC bridge arm in the current rising phase is the high-voltage DC port voltage.

[0018] As a further optimization solution for a high-voltage DC converter topology and a control method thereof, the three-phase transformer is a centralized three-phase transformer.

[0019] As a further optimization scheme for a high-voltage DC converter topology and a control method thereof, in a three-phase diode rectifier circuit, each phase diode rectifier branch is composed of at least two low-voltage diodes connected in series.

[0020] The present invention adopts the above technical solution and has the following beneficial effects:

[0021] (1) The present invention proposes an isolated modular multi-level DC converter suitable for medium and high voltage DC grid interconnection. The high voltage side adopts a three-phase MMC inverter circuit, and the low voltage side adopts a three-phase diode rectifier circuit. The high voltage side and the medium voltage side are connected through an industrial frequency / medium frequency transformer. The topology structure is simple. With the help of the three-phase MMC inverter circuit, the bridge arm inductance, and the three-phase leakage inductance, the precise control of the stepped three-phase current and the reliable commutation of the three-phase rectifier diode are realized, thereby improving the operating efficiency.

[0022] (2) The present invention controls the three-phase AC current to be a trapezoidal shape with symmetry between the positive and negative half cycles, so as to synthesize smooth DC current on both the high-voltage side and the medium-voltage side, thereby significantly reducing the volume of the filters on the medium-voltage side and the high-voltage side. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 It is a schematic diagram of the topological structure of the high voltage DC converter of the present invention.

[0025] Figure 2 It is a schematic diagram of the principle of the half-bridge module in the DC converter of the present invention.

[0026] Figure 3 It is a schematic diagram of the principle diagram of the centralized three-phase transformer of the present invention.

[0027] Figure 4 It is a schematic diagram of the principle of series-connected diodes in the DC converter of the present invention.

[0028] Figure 5 It is a schematic diagram of the basic working waveform of the high voltage DC converter of the present invention.

[0029] Figure 6 It is a simulation waveform diagram of the high voltage side of the high voltage DC converter of the present invention.

[0030] Figure 7 It is a simulation waveform diagram of the medium voltage side of the high voltage DC converter of the present invention.

[0031] Description of the symbols in the figure: L HV , high-voltage side filter inductor, L MV , medium voltage side filter inductor, C MV , medium voltage side filter capacitor, L KA, A phase leakage inductance, L KB , B phase leakage inductance, L KC , C phase leakage inductance, D1, the first diode, D2, the second diode, D3, the third diode, D4, the fourth diode, D5, the fifth diode, D6, the sixth diode. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0033] The high voltage DC converter topology of the present invention is as follows: Figure 1 As shown, the high-voltage side filter inductor L HV , three-phase MMC inverter circuit, three-phase leakage inductance, three-phase transformer, three-phase diode rectifier circuit, medium voltage side filter inductor L MV And the medium voltage side filter capacitor C MV Composition: three-phase MMC inverter circuit and high-voltage side filter inductor L HV The three-phase diode rectifier circuit and the medium voltage side filter inductor L are connected in series to form a high voltage DC port; MV After connecting in series, with the medium voltage DC capacitor C MV They are connected in parallel to form a medium voltage DC port; in the three-phase transformer, the primary winding is connected in series with the three-phase leakage inductance and then connected to the AC port of the three-phase MMC inverter circuit, and the secondary winding is connected to the AC port of the three-phase diode rectifier circuit.

[0034] In the three-phase MMC inverter circuit, the A-phase upper bridge arm A1 and the A-phase lower bridge arm A2 are connected in series, and the connection point of the A-phase upper bridge arm A1 and the A-phase lower bridge arm A2 constitutes the AC port of the A-phase bridge arm. The A-phase bridge arm AC port passes through the A-phase leakage inductance L KA Connect to A phase transformer T A At the first end of the primary winding, the upper bridge arm B1 of the B phase is connected in series with the lower bridge arm B2 of the B phase. The connection point of the upper bridge arm B1 of the B phase and the lower bridge arm B2 of the B phase constitutes the AC port of the B phase bridge arm. The AC port of the B phase bridge arm passes through the B phase leakage inductance L KB Connect to B phase transformer T B At the first end of the primary winding, the C-phase upper bridge arm C1 and the C-phase lower bridge arm C2 are connected in series, and the connection point of the C-phase upper bridge arm C1 and the C-phase lower bridge arm C2 constitutes the AC port of the C-phase bridge arm. The C-phase bridge arm AC port passes through the C-phase leakage inductance L KC Connect to C phase transformer T CThe first end of the primary winding, the upper end of the A phase upper bridge arm A1, the upper end of the B phase upper bridge arm B1 and the upper end of the C phase upper bridge arm C1 are connected to the high-voltage side filter inductor L HV One end, high voltage side filter inductor L HV The other end forms the positive pole of the high-voltage DC port, and the lower end of the lower bridge arm A2 of phase A, the lower end of the lower bridge arm B2 of phase B, and the lower end of the lower bridge arm C2 of phase C are connected to form the negative pole of the high-voltage DC port. Each bridge arm is composed of several half-bridge modules connected in series, and each bridge arm is connected in series with a bridge arm inductor L ARM .

[0035] In the three-phase diode rectifier circuit, the anode of the first diode D1, the cathode of the fourth diode D4 and the A phase transformer T A The first end of the secondary winding is connected to the anode of the third diode D3 and the cathode of the sixth diode D6 and the B-phase transformer T B The first end of the secondary winding is connected to the anode of the fifth diode D5 and the cathode of the second diode D2 and the C phase transformer T C The first end of the secondary winding is connected, and the cathode of the first diode D1, the cathode of the third diode D3 and the cathode of the fifth diode D5 are connected to the medium voltage side filter inductor L MV One end, medium voltage side filter inductor L MV The other end and the medium voltage side filter capacitor C MV One pole is connected to form the positive pole of the medium voltage DC port, the anode of the fourth diode D4, the anode of the sixth diode D6, the anode of the second diode D2 and the medium voltage side filter capacitor C MV The other pole is connected to form the negative pole of the medium voltage DC port.

[0036] In a three-phase transformer, the A phase transformer T A The second end of the primary winding, B phase transformer T B The second end of the primary winding is connected to the C phase transformer T C The second end of the primary winding is connected to the A phase transformer T A Secondary winding second end, B phase transformer T B The second end of the secondary winding is connected to the C phase transformer T C The second end of the secondary winding is connected to the A phase transformer T A The first end of the primary winding and the first end of the secondary winding are the same end. B The first end of the primary winding and the first end of the secondary winding are the same end. C The first end of the primary winding and the first end of the secondary winding are the same-named ends.

[0037] Each bridge arm of the three-phase MMC inverter circuit is composed of Figure 2 The half-bridge modules shown in the figure are connected in series, and the half-bridge module is composed of an upper switch tube S N1 and the lower switch tube SN2 The upper switch tube S N1 and the lower switch tube S N2 The two ends of the series branch are connected with filter capacitor C N .

[0038] like Figure 3 As shown, the three-phase transformer can adopt a centralized three-phase transformer.

[0039] like Figure 4 As shown, the diodes in the three-phase rectifier circuit are formed by connecting multiple low-voltage diodes in series.

[0040] The three-phase MMC inverter circuit can be replaced by any high-voltage voltage source inverter circuit capable of outputting three-phase AC voltage.

[0041] High voltage side filter inductor L HV , medium voltage side filter inductor L MV And the medium voltage side filter capacitor C MV It can be configured according to actual ripple current and fault protection requirements.

[0042] For the high-voltage DC converter topology proposed in the present invention, by modulating the multi-level square wave voltage generated by the three-phase MMC inverter circuit, a trapezoidal AC current with positive and negative half-cycle symmetry is generated at the AC port of the three-phase MMC inverter circuit. Phase A, phase B, and phase C work with a difference of 1 / 3 AC cycle. The basic working waveform is as follows: Figure 5 As shown:

[0043] At t0, the output voltage of the bridge arm of phase A rises by V t,A , so that the A phase current starts to rise steadily from 0, the first diode D1 is turned on, and the output voltage of the C phase bridge arm drops V t,C , so that the C phase current changes from I M / n steadily decreases, I M is the output current on the medium voltage side, n is the transformation ratio of the three-phase transformer, V t,A =V t,C ;

[0044] At t1, the current of phase A rises to the set value I M / n, the current of phase C drops to 0, the fifth diode D5 is turned off, the converter commutation phase ends, and enters the current freewheeling phase. By adjusting the output voltage of the bridge arm of phase A and phase B, the current of phase A and phase B is maintained at the set value. The output voltage of the bridge arm of phase A and phase B is achieved by adjusting the voltage on the bridge arm inductance of phase A and the leakage inductance of phase A, and the voltage on the bridge arm inductance of phase B and the leakage inductance of phase B;

[0045] At t2, the converter enters the commutation phase again, and increases the AC voltage of phase B by controlling V t,B , the C phase AC voltage decreases V t,C, so that the C phase current increases in the reverse direction, the B phase current amplitude decreases, the second diode D2 is turned on, V t,B =V t,C ;

[0046] At t3, the C phase current increases in the reverse direction to the set value -I M / n, at this time, the amplitude of the negative B-phase current decreases to 0, the sixth diode D6 is turned off, the converter commutation phase ends, and enters the current freewheeling phase, by adjusting the output voltage of the A-phase and C-phase bridge arms, maintaining the A-phase and C-phase currents at the set values, and the output voltage of the A-phase and C-phase bridge arms is achieved by adjusting the voltage on the A-phase bridge arm inductance and the A-phase leakage inductance and the voltage on the C-phase bridge arm inductance and the C-phase leakage inductance;

[0047] At t4, the converter enters the commutation phase again, and the A phase AC voltage is reduced by V t,A , the AC voltage of phase B increases by V t,B , so that the current of phase A decreases and the current of phase B increases, the third diode D3 is turned on, V t,A =V t,B ;

[0048] At t5, the current of phase A decreases to 0, the first diode D1 is turned off, and the current of phase B increases to the set value I M / n, the converter commutation phase ends and enters the current freewheeling phase. By adjusting the output voltage of the B-phase and C-phase bridge arms, the current of the B-phase and C-phase currents are maintained at the set values. The output voltage of the B-phase and C-phase bridge arms is achieved by adjusting the voltage on the B-phase bridge arm inductance and the B-phase leakage inductance, as well as the voltage on the C-phase bridge arm inductance and the C-phase leakage inductance.

[0049] At time t6, the negative half cycle begins, and the working principle is similar to that of the positive half cycle.

[0050] In each commutation stage, by ensuring that the amplitude and duration of the increase in the output voltage of the MMC bridge arm in the current rising phase and the amplitude and duration of the decrease in the output voltage of the MMC bridge arm in the current falling phase are equal, the neutral point voltage is maintained unchanged, ensuring that the current freewheeling phase current remains constant.

[0051] The amplitude of the output voltage increase of the X-phase MMC bridge arm during the commutation phase is V t,X and duration t D,X The X-phase bridge arm inductance L ARM,X , X-phase transformer leakage inductance L K,X , transformer ratio n and medium voltage side output current I M Sure;

[0052]

[0053] t D,X =D t,X T t

[0054] Among them, the X phase is the electrical rising phase in the commutation stage, and the X phase bridge arm inductance L ARM,X It is determined by the values ​​of the upper bridge arm inductance of phase X and the lower bridge arm inductance of phase X. X is A, B or C, T t is the AC cycle, D t,X t D,X The AC cycle duty cycle.

[0055] The amplitude of the output voltage of the X-phase MMC bridge arm during the commutation phase is V m,X The three-phase transformer ratio n, the medium voltage side voltage V M , the amplitude of the increase in the output voltage of the X-phase MMC bridge arm during the commutation stage V t,X Determine, at the same time, the amplitude of the output voltage V of the X-phase MMC bridge arm during the commutation phase m,X It should not be greater than the maximum output voltage V of the MMC bridge arm. H , V H is the high voltage DC port voltage.

[0056]

[0057] Figure 6 and Figure 7 The simulated waveforms of the high voltage side and medium voltage side of the high voltage DC converter of the present invention are as follows: the rated power is 1200MW, the high voltage side voltage is 500kV, the low voltage side voltage is 120kV, and the intermediate AC link frequency is 50Hz. Figure 6 It is the simulation waveform of the high-voltage side. The three-phase current on the high-voltage side is a trapezoidal shape with symmetry between the positive and negative half cycles. The line voltage on the high-voltage side and the phase voltage on the high-voltage side are multi-level square wave voltages. Figure 7 It is the simulation waveform of the medium voltage side, in which the rectifier diode current is synthesized into a smooth DC current, the medium voltage side current is 1kA, and the medium voltage side voltage is 120kV.

[0058] The present invention proposes an isolated DC converter with modular multi-level suitable for medium and high voltage DC grid interconnection. The high voltage side adopts a three-phase MMC inverter circuit, and the low voltage side adopts a three-phase diode rectifier circuit, which are connected through an industrial frequency / medium frequency transformer. The topology structure is simple, and higher reliability, lower cost and volume can be achieved through the relatively mature high voltage side modular structure and medium voltage side diode series connection technology.

[0059] With the help of the three-phase MMC inverter circuit, precise control of the three-phase current and reliable commutation of the three-phase rectifier diodes are achieved, thereby improving operating efficiency.

[0060] The present invention controls the three-phase AC current to be a trapezoid with symmetry between the positive and negative half cycles, so that smooth DC current can be synthesized on both the high voltage side and the medium voltage side, significantly reducing the volume of the filters on the medium voltage side and the high voltage side.

[0061] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A high voltage DC converter topology and control method thereof, characterized in that: The high voltage DC converter topology includes: The high-voltage side filter inductor has one end that forms the positive electrode of the high-voltage DC port. The three-phase MMC inverter circuit has a DC port positive electrode connected to the other end of the high-voltage side filter inductor, a DC port negative electrode forming the negative electrode of the high-voltage DC port, and a bridge arm inductor connected in series in each phase bridge arm. Three-phase leakage inductance, one end of each phase leakage inductance is connected to one phase AC port of the three-phase MMC inverter circuit, In a three-phase transformer, the first end of the primary winding of each phase transformer is connected to the other end of a phase leakage inductance, and the second ends of the primary windings of each phase transformer are connected. In a three-phase diode rectifier circuit, each phase AC port is respectively connected to the first end of the secondary winding of a phase transformer, each phase diode rectifier branch is composed of two diodes connected in series, the second ends of the secondary windings of each phase transformer are connected, and the first end of the primary winding of each phase transformer and the first end of the secondary winding are the same end. A medium voltage side filter inductor, one end of which is connected to the positive electrode of the DC port of the three-phase diode rectifier circuit, and, A medium voltage side filter capacitor, one pole of which is connected to the other end of the medium voltage side filter inductor to form the positive pole of the medium voltage DC port, and the other pole of which is connected to the negative pole of the DC port of the three-phase diode rectifier circuit to form the negative pole of the medium voltage DC port; The control method of the high-voltage direct current converter topology modulates the multi-level square wave voltage output by each phase MMC bridge arm, and obtains a trapezoidal alternating current with positive and negative half-cycle symmetry at the AC port of the three-phase MMC inverter circuit.

2. A high voltage DC converter topology and control method thereof according to claim 1, characterized in that: The specific method of modulating the multi-level square wave voltage output by each phase MMC bridge arm is: In each commutation stage, the output voltage of the MMC bridge arm in the current rising phase is increased, and the output voltage of the MMC bridge arm in the current falling phase is reduced, and the amplitude of the increase of the output voltage of the MMC bridge arm in the current rising phase is maintained equal to the amplitude of the decrease of the output voltage of the MMC bridge arm in the current falling phase, and the duration of the increase of the output voltage of the MMC bridge arm in the current rising phase is equal to the duration of the decrease of the output voltage of the MMC bridge arm in the current falling phase; In each freewheeling stage, the output voltage of the MMC bridge arm of the current freewheeling phase is adjusted to maintain the current of the current freewheeling phase stable at the set value of the trapezoidal wave AC current amplitude.

3. A high voltage DC converter topology and control method thereof according to claim 2, characterized in that: The control method of the high-voltage direct current converter topology modulates the multi-level square wave voltage output by each phase MMC bridge arm by adjusting the voltage on the inductance of each phase bridge arm and the voltage on the leakage inductance of each phase in the three-phase MMC inverter circuit.

4. A high voltage DC converter topology and control method thereof according to claim 3, characterized in that: In each commutation stage, the amplitude and duration of the increase in the output voltage of the MMC bridge arm in the current rising phase are constrained by the voltage on the inductance and leakage inductance of the MMC bridge arm in the current rising phase.

5. A high voltage DC converter topology and control method thereof according to claim 4, characterized in that: In each commutation stage, the amplitude of the output voltage of the MMC bridge arm in the current rising phase is constrained by the medium voltage side voltage and the increase amplitude of the output voltage of the MMC bridge arm in the rising phase, and the amplitude of the output voltage of the MMC bridge arm in the current rising phase is constrained by the maximum value of the MMC bridge arm output voltage.

6. A high voltage DC converter topology and control method thereof according to claim 4, characterized in that: The amplitude and duration of the increase in the output voltage of the MMC bridge arm during the current rising phase satisfy the expression: t D,X =D t,X T t , where X phase is the electrical rising phase, X is A or B or C, V t,X is the amplitude of the increase in the output voltage of the X-phase MMC bridge arm, t D,X is the duration of the X-phase MMC bridge arm output voltage increase, L ARM,X is the X-phase bridge arm inductance, L K,X is the leakage inductance of the X-phase transformer, I M is the output current on the medium voltage side, n is the transformation ratio of the three-phase transformer, T t is the AC cycle, D t,X t D,X The AC cycle duty cycle.

7. A high voltage DC converter topology and control method thereof according to claim 6, characterized in that: The amplitude of the output voltage of the MMC bridge arm during the current rising phase is Among them, V m,X is the amplitude of the X-phase MMC bridge arm output voltage, V M is the medium voltage side voltage.

8. A high voltage DC converter topology and control method thereof according to claim 6, characterized in that: The maximum value of the MMC bridge arm output voltage is the high voltage DC port voltage.

9. A high voltage DC converter topology and control method thereof according to any one of claims 1 to 8, characterized in that: The three-phase transformer is a centralized three-phase transformer.

10. A high voltage DC converter topology and control method thereof according to any one of claims 1 to 9, characterized in that: In the three-phase diode rectifier circuit, each phase diode rectifier branch is composed of at least two low-voltage diodes connected in series.

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