CN116232037A

CN116232037A - Method and system for starting power electronic converter

Info

Publication number: CN116232037A
Application number: CN202310082518.3A
Authority: CN
Inventors: 张雪垠; 赵彪; 白睿航; 屈鲁; 余占清; 曾嵘
Original assignee: Tsinghua University; Sichuan Energy Internet Research Institute EIRI Tsinghua University
Current assignee: Tsinghua University; Sichuan Energy Internet Research Institute EIRI Tsinghua University
Priority date: 2023-01-20
Filing date: 2023-01-20
Publication date: 2023-06-06

Abstract

The invention provides a method and a system for starting a power electronic converter, wherein the method comprises the following steps: starting the converter from the direct current side when the direct current side of the converter is connected with the active system; starting the converter from the ac side of the converter when the ac side is connected to the active system; when both the ac side and the dc side of the converter are connected to the active system, the converter is started from either the dc side or the ac side. The invention can realize stable pre-charge when the power electronic converter is started.

Description

Method and system for starting power electronic converter

Technical Field

The invention belongs to the technical field of direct-current transmission systems, and particularly relates to a method and a system for starting a power electronic converter.

Background

Power electronics is a major feature of the new power system, and power electronic converters are the core equipment of the new power system. High voltage high capacity is a direction of development of power electronic converters. The existing high-voltage high-capacity power electronic converters are mainly based on Modular Multilevel Converters (MMC). MMC was proposed in 2001 and has been in much practice to date. A plurality of projects at home and abroad are developed based on MMC topology and put into operation, and the feasibility of the MMC is proved. However, MMCs have not been widely used in the market to date, and for this reason, they are still costly. MMCs are made up of a large number of modules containing expensive components such as power semiconductor switching devices, capacitors, etc., resulting in a much higher cost than the various devices in conventional power systems. Therefore, the popularization and application of the novel power system are also directly affected.

The existing precharge technical scheme can only be used for an MMC converter topology, and for a novel power electronic converter topology, the topology structure of the novel power electronic converter topology is different from that of an MMC, and the existing precharge technical scheme for the MMC converter cannot be applied.

Therefore, a method and a system for starting a power electronic converter are needed to solve the above technical problems.

Disclosure of Invention

The invention provides a starting method of a power electronic converter, aiming at the technical problems, wherein the method comprises the following steps:

starting the converter from the direct current side when the direct current side of the converter is connected with the active system;

starting the converter from the ac side of the converter when the ac side is connected to the active system;

when both the ac side and the dc side of the converter are connected to the active system, the converter is started from either the dc side or the ac side.

Further, a pre-charging circuit is arranged on the direct current side of the converter, and a switch S3 is arranged on the alternating current side of the converter; or alternatively, the first and second heat exchangers may be,

the alternating current side of the converter is provided with a pre-charging circuit, and the direct current side of the converter is provided with a switch S3; or alternatively, the first and second heat exchangers may be,

the direct current side and the alternating current side of the converter are provided with a pre-charging circuit, and the direct current side and the alternating current side of the converter are provided with a switch S3;

wherein,,

the precharge circuit comprises a switch S1, a switch S2 and a precharge resistor R, wherein one end of the switch S1 is connected with one end of the precharge resistor R, one end of the switch S2 is connected with the other end of the switch S1, and the other end of the switch S2 is connected with the other end of the precharge resistor R.

Further, the converter comprises a switch capacitor valve and a novel switch valve which are connected in parallel, and the novel switch valve is used for realizing conversion between alternating current and direct current; the switched capacitor valve is used for realizing soft switching of an inverter, wherein,

the switch capacitance valve comprises a plurality of switch capacitance modules connected in series;

the novel switch valve comprises two parallel bridge arms, and each phase of bridge arm comprises a plurality of power switch device modules which are connected in series.

Further, the power switch device module comprises a power switch device T1, a diode D1 voltage-sharing capacitor C1 and an energy dissipation element H1, wherein an anode of the diode D1 is connected with an anode of the power switch device T1, one end of the voltage-sharing capacitor C1 is connected with a cathode of the diode D1, the other end of the voltage-sharing capacitor C1 is connected with a cathode of the power switch device T1, one end of the energy dissipation element H1 is connected with one end of the voltage-sharing capacitor C1, the other end of the energy dissipation element H1 is connected with the other end of the voltage-sharing capacitor C1, and a diode D2 is connected in anti-parallel on the power switch device T1.

Further, starting the converter from the dc side, comprising:

the converter is locked, the switch S2 and the switch S3 are opened, and the switch S1 is closed;

controlling the voltages of all the switch capacitor modules to reach a precharge target value Usmr2;

controlling the voltages of all power switch device modules to reach a precharge target value Usmr4;

the whole converter is blocked, switch S1 is opened, and switches S2 and S3 are closed to achieve completion of starting.

Further, controlling all switched capacitor module voltages to reach a precharge target value Usmr2 includes:

starting to put into sequencing voltage equalizing control until the voltages of all the switch capacitor modules reach a precharge target value Usmr1, bypassing N0 switch capacitor modules, and bypassing N0 switch capacitor modules after the voltages of the switch capacitor modules reach k x Udc/(N1-NA);

the above process is repeated until all switched capacitor module voltages reach a precharge target value Usmr2, wherein,

Usmr l＝k*Udc/N1；

wherein Udc is direct current bus voltage, N1 is the number of switch capacitor modules, k is more than 0 and less than or equal to 100 percent

NA denotes the number of switched capacitor modules that have been bypassed.

Further, controlling all power switching device module voltages to reach a precharge target value Usmr4 includes:

starting to input sequencing equalizing control until the voltage of all power switch device modules reaches a precharge target value Usmr3, bypassing dN2 power switch device modules, and bypassing dN2 power switch device modules after the voltage of the power switch device modules reaches k times Udc/(N2-NB);

repeating the process until all power switch device module voltages reach a precharge target value Usmr4;

wherein Usmr3 = k x Udc/N2;

wherein Udc is direct current bus voltage, N2 is the number of power switch device modules of a phase bridge arm, k is more than 0 and less than or equal to 100%, and NB represents the number of bypassed switch capacitor modules.

Further, starting the inverter from the ac side, comprising:

the converter is locked, the switch S2 is opened, and the switch S1 is closed;

starting to put into sequencing voltage equalizing control until the voltages of all the switch capacitor modules reach a precharge target value Usmr1, bypassing N0 switch capacitor modules, and bypassing N0 switch capacitor modules after the voltages of the switch capacitor modules reach k Uac/N1;

the above process is repeated until all switched capacitor module voltages reach the precharge target value Usmr2.

Wherein Usmr1 = k Uac/N1;

wherein Uac is an alternating-current side phase voltage peak value, N1 is the number of switch capacitor modules, and k is more than 0 and less than or equal to 100%.

starting to input sequencing equalizing control until the voltage of all power switch device modules reaches a precharge target value Usmr3, bypassing dN2 power switch device modules, and bypassing dN2 power switch device modules after the voltage of the power switch device modules reaches 2 x k x Uac/N2;

wherein Usmr3 = 2 x k x uac/N2;

wherein Uac is an alternating-current side phase voltage peak value, N2 is the number of power switch device modules of a phase bridge arm, and k is more than 0 and less than or equal to 100%.

Further, the energy dissipation element H1 is any one or a combination of an energy taking power supply, a first energy dissipation resistor and a switchable energy dissipation resistor, wherein the switchable energy dissipation resistor comprises a second energy dissipation resistor and a switch connected in series with the second energy dissipation resistor.

In another aspect, the present invention further provides a system for starting a power electronic converter, where the system includes:

the first starting module is used for starting the converter from the direct current side when the direct current side of the converter is connected with the active system;

the first starting module is used for starting the converter from the alternating current side when the alternating current side of the converter is connected with the active system;

and the first starting module is used for starting the converter from the direct current side or the alternating current side when the alternating current side and the direct current side of the converter are connected with the active system.

Further, the method comprises the steps of,

the direct current side of the converter is provided with a pre-charging circuit, and the alternating current side of the converter is provided with a switch S3; or alternatively, the first and second heat exchangers may be,

the alternating current side of the converter is provided with a pre-charging circuit, and the direct current side of the converter is provided with a switch S3; wherein,,

The invention provides a method and a system for starting a power electronic converter, which can realize stable pre-charging during the starting of the power electronic converter, avoid component damage caused by the generation of impact current, and avoid overvoltage damage of partial power switching device modules caused by unbalance of module voltages (voltages of voltage-sharing capacitors in the power switching device modules) of bridge arms.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, a brief description will be given below of the drawings required for the embodiments or the prior art descriptions, and it is obvious that the drawings in the following description are some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 shows a flow chart of a method of starting a power electronic converter according to an embodiment of the invention

Fig. 2 shows a topology of a power electronic converter according to an embodiment of the invention.

Fig. 3 shows a topology of a power switching device module according to an embodiment of the invention.

Fig. 4 shows a topology of a switched capacitor valve when the switched capacitor module is a half-bridge module according to an embodiment of the invention.

Fig. 5 shows a topology of the energy consuming element H1 when the energy consuming element H1 is an energy taking power source according to an embodiment of the present invention.

Fig. 6 shows a topology of the dissipative element H1 when the dissipative element H1 is the first dissipative resistor according to an embodiment of the invention.

Fig. 7 shows a topology of the energy dissipating element H1 when the energy dissipating element H1 is a switchable energy dissipating resistor according to an embodiment of the present invention.

Fig. 8 shows a topology of a combination of one according to an embodiment of the invention.

Fig. 9 shows a topology of a combination two according to an embodiment of the invention.

Fig. 10 shows a topology of a combination form three according to an embodiment of the present invention.

Fig. 11 shows a topology of an inverter when a precharge circuit is provided on the ac side according to an embodiment of the present invention.

Fig. 12 shows a topology of a combined converter according to an embodiment of the invention transformed on the basis of 3 converters according to fig. 2, with a precharge circuit arranged on the dc positive bus.

Fig. 13 shows a topology of a combined converter according to an embodiment of the invention, transformed on the basis of 3 converters according to fig. 2, with switch S3 arranged on the direct current positive bus.

Fig. 14 shows a topology diagram of a converter according to an embodiment of the invention.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

As shown in fig. 1, the present invention provides a method for starting a power electronic converter, wherein the method includes:

The following is a detailed description.

In one embodiment of the invention, as shown in fig. 2, the converter comprises a switched capacitor valve in parallel and a novel switching valve for realizing the conversion between alternating current and direct current or the conversion between alternating current and pulsating direct current; the switched capacitor valve is used for realizing the conversion between the stable direct voltage of the converter and the pulsating direct voltage, wherein,

In one embodiment of the present invention, as shown in fig. 3, the power switching device module includes a power switching device T1, a diode D1, a voltage-sharing capacitor C1, and an energy-consuming element H1, where an anode of the diode D1 is connected to an anode of the power switching device T1, one end of the voltage-sharing capacitor C1 is connected to a cathode of the diode D1, the other end of the voltage-sharing capacitor C1 is connected to a cathode of the power switching device T1, one end of the energy-consuming element H1 is connected to one end of the voltage-sharing capacitor C1, the other end of the energy-consuming element H1 is connected to the other end of the voltage-sharing capacitor C1, and a diode is connected to the power switching device T1 in anti-parallel.

In one embodiment of the invention, the power switching device T1 may be an insulated Gate bipolar transistor (I nsu l ated Gate B I po l ar Trans I stor, I GBT), an integrated Gate commutated thyristor (I etched Gate-Commutated Thyr I stor, I GCT), a field effect transistor (Fie l d-Effect Trans I stor, FET), or the like.

In one embodiment of the present invention, for each phase leg, the anode of the latter power switching device T1 is connected to the cathode of the former power switching device T1, wherein the power switching device module further comprises a bypass element K1, one end of the bypass element K1 is connected to the anode of the power switching device T1, and the other end of the bypass element K1 is connected to the cathode of the power switching device T1.

The bypass element K1 has two functions, namely, a bypass fault power switch device module is arranged, and normal operation of other power switch device modules in a bridge arm is ensured; secondly, the bypass corresponds to the black module (namely, some power switch device modules cannot be electrified because of some reasons, such as the damage of an energy taking power supply), the black module does not work normally because the energy taking power supply does not work normally, the traditional controllable bypass switch does not have electric control to bypass the module, and the automatic bypass of the module is realized by adopting the overvoltage breakdown characteristic of a thyristor or a diode.

Bypass element K1 the bypass element K1 is any one or a combination of a plurality of mechanical switches, semiconductor switches and thyristors (for example, a parallel combination thereof), or K1 may not be provided. In particular, when T1 is an I GCT, K1 does not need to employ a thyristor, since I GCT has overvoltage breakdown and long-term current-passing characteristics of a thyristor, and can realize bypass of the black module.

In one embodiment of the present invention, the converter further includes a transformer, wherein one end of a winding on one side of the transformer is connected to a midpoint of one phase leg of the novel switching valve through a connection inductance L1, and the other end of the winding on one side of the transformer is connected to a midpoint of the other phase leg of the novel switching valve.

In one embodiment of the invention, the switched capacitor module may be any one or a combination of a half-bridge module, a full-bridge module and a hybrid module (e.g. a series combination of a half-bridge module and a full-bridge module), wherein the energy consuming element H2 is connected in parallel on the corresponding capacitive part, irrespective of the half-bridge module or the full-bridge module.

In this embodiment, T2 may be GBT, I GCT, FET, or the like. In addition, in this embodiment, the switch capacitor module is connected with a bypass switch K2, and the bypass element K2 has two functions, namely, a bypass fault switch capacitor module, so as to ensure the normal operation of other switch capacitor modules; and secondly, the bypass corresponds to the black module.

In this embodiment, the bypass switch K2 is any one or a combination of a plurality of mechanical switches, semiconductor switches, and thyristors (for example, a parallel combination thereof), or in this embodiment, the bypass switch K2 may not be disposed.

In one embodiment of the present invention, as shown in fig. 4, a switched capacitor module is taken as a half-bridge module for illustration, when the switched capacitor module is a half-bridge module, there are a capacitor C2 and two power switches T2 in the half-bridge module, where the cathode of one power switch T2 is connected to the anode of the other power switch T2, one end of the capacitor C2 is connected to the anode of one power switch T2, and the other end of the capacitor C2 is connected to the cathode of the other power switch T2, where the above-mentioned energy dissipation element H2 is connected in parallel to the corresponding capacitor portion, that is, the energy dissipation element H2 is connected in parallel to the capacitor C2.

The anode of one power switching device T2 in the first half-bridge module is connected to the anode of the first power switching device T1 of the one-phase bridge arm (the one-phase bridge arm of the novel switching valve), and the cathode of the other power switching device T2 in the last half-bridge module is connected to the cathode of the first power switching device T1 of the one-phase bridge arm (the one-phase bridge arm of the novel switching valve). In the rest of the half-bridge modules, the anode of one power switching device T2 in the latter half-bridge module is connected with the cathode of the other power switching device T2 in the former half-bridge module.

In an embodiment of the present invention, the energy dissipation element H is any one or a combination of an energy dissipation power source V, a first energy dissipation precharge resistor R1, and a switchable energy dissipation resistor, where the energy dissipation power source V is configured to obtain energy from the equalizing capacitor C1.

As shown in fig. 5, when the energy dissipation element H is the energy taking power V, the positive electrode+ of the energy taking power V is connected to the positive electrode of the voltage equalizing capacitor C1, and the negative electrode-is connected to the negative electrode of the voltage equalizing capacitor C1.

As shown in fig. 6, when the energy dissipation element H is the first energy dissipation precharge resistor R1, one end of the first energy dissipation precharge resistor R1 is connected to the positive electrode of the voltage-sharing capacitor C1, and the other end is connected to the negative electrode of the voltage-sharing capacitor C1.

As shown in fig. 7, when the energy dissipation element H is a switchable energy dissipation resistor, the switchable energy dissipation resistor includes a second energy dissipation precharge resistor R2 and a switch S (for example, the switch S may be a switch with a current that can be disconnected by a relay, a contactor, a circuit breaker, a semiconductor switch, etc.), one end of the switch S is connected to one end of the second energy dissipation precharge resistor R2, the other end of the switch S is connected to the positive electrode of the voltage-sharing capacitor C1, the other end of the second energy dissipation precharge resistor R2 is connected to the negative electrode of the voltage-sharing capacitor C1, and the switching control of the second energy dissipation precharge resistor R2 can be implemented through the set switch S.

When the energy dissipation element H is a combination of the energy dissipation power source V, the first energy dissipation precharge resistor R1, and the switchable energy dissipation resistor, the combination structure includes, but is not limited to, the following combinations:

first combination form: as shown in fig. 8, the energy-saving device comprises a switchable energy-consuming resistor and an energy-taking power supply V, wherein one end of a switch S in the switchable energy-consuming resistor is connected to one end of a second energy-consuming precharge resistor R2, and the other end is connected to the positive electrode +; the other end of the second energy-consuming precharge resistor R2 is connected with the negative electrode of the energy-taking power supply V; the positive electrode of the energy-taking power supply V is + connected to the positive electrode of the voltage-sharing capacitor C1, and the negative electrode is-connected to the negative electrode of the voltage-sharing capacitor C1, and in this combination, the following changes may be made to the switch S:

one end of a switch S in the switchable energy dissipation resistor is connected to the other end of the second energy dissipation precharge resistor R2, and the other end of the switch S in the switchable energy dissipation resistor is connected to the negative electrode of the energy taking power supply V; one end of the second energy-consuming precharge resistor R2 is connected to the positive electrode+ of the energy-taking power supply V.

Second combination form: as shown in fig. 9, the capacitor comprises a first energy consumption pre-charging resistor R1 and an energy taking power supply V, wherein one end of the first energy consumption pre-charging resistor R1 is connected with the positive electrode+ of the energy taking power supply V, the other end of the first energy consumption pre-charging resistor R1 is connected with the negative electrode of the energy taking power supply V-, the positive electrode+ of the energy taking power supply V is connected with the positive electrode of the voltage equalizing capacitor C1, and the negative electrode of the first energy consumption pre-charging resistor R1 is connected with the negative electrode of the voltage equalizing capacitor C1.

Third combination form: as shown in fig. 10, the capacitor comprises a first energy-consuming precharge resistor R1, an energy-taking power supply V and a switchable energy-consuming resistor, wherein one end of the first energy-consuming precharge resistor R1 is connected with the positive electrode+ of the energy-taking power supply V, the other end of the first energy-consuming precharge resistor R1 is connected with the negative electrode of the energy-taking power supply V, the positive electrode+ of the energy-taking power supply V is connected with the positive electrode of the voltage-sharing capacitor C1, and the negative electrode of the first energy-consuming precharge resistor R1 is connected with the negative electrode of the voltage-sharing capacitor C1; one end of the switch S is connected to one end of the second energy-consuming precharge resistor R2, the other end is connected to one end of the first energy-consuming precharge resistor R1, and the other end of the second energy-consuming precharge resistor R2 is connected to the other end of the first energy-consuming precharge resistor R1, and in addition, in this combination, the following changes may be provided:

one end of the switch S is connected to the other end of the second energy consumption pre-charging resistor R2, the other end of the switch S is connected to the other end of the first energy consumption pre-charging resistor R1, and one end of the second energy consumption pre-charging resistor R2 is connected to one end of the first energy consumption pre-charging resistor R1.

In one embodiment of the present invention, as shown in fig. 2, a pre-charging circuit is disposed on the dc side of the inverter, and the pre-charging circuit includes a switch S1, a switch S2, and a pre-charging resistor R, where one end of the switch S1 is connected to one end of the pre-charging resistor R, one end of the switch S2 is connected to the other end of the switch S1, and the other end of the switch S2 is connected to the other end of the pre-charging resistor R.

In this embodiment, the function of the precharge resistor R is to limit the charging current, so as to avoid damage to components caused by excessive current during charging; the switch S1 is used for switching the precharge resistor R; the switch S2 functions to bypass the precharge resistor R and the switch S1 after the completion of the charging.

In one embodiment of the present invention, the precharge circuit is disposed on a dc positive bus (the embodiment of the present invention is exemplified by the precharge circuit disposed on the dc positive bus) or a dc negative bus, and the dc negative bus is connected to the anode of the first power switching device T1 of one phase leg (one phase leg of the novel switching valve) and the cathode of the last power switching device T1 of one phase leg (one phase leg of the novel switching valve). In this embodiment, both the dc positive bus and the dc negative bus are further provided with a smoothing reactance L2.

In this embodiment, the ac side of the converter is provided with a switch S3, i.e. the switch S3 is connected to one end of the winding on the other side of the transformer; in this case, one end of the switch S2 is further connected to the corresponding smoothing reactance L2, and the other end of the switch S2 is further connected to the anode of the first power switching device T1 of the one-phase bridge arm (one-phase bridge arm of the novel switching valve).

In this embodiment, the switch S3 is used to disconnect the output end of the converter before the precharge is completed, so as to avoid the occurrence of non-design conditions, such as over-current damage to circuit components, caused by charging the power supply on the output side to the converter.

In one embodiment of the present invention, as shown in fig. 11, the ac side of the inverter is provided with a precharge circuit, and the dc side of the inverter is provided with a switch S3; that is, at this time, one end of the switch S2 is further connected to one end of the winding on the other side of the transformer, the switch S3 is provided on the dc positive bus (in the embodiment of the present invention, the switch S3 is provided on the dc positive bus for example) or the dc negative bus, one end of the switch S3 is further connected to the corresponding smoothing reactor L2, and the other end of the switch S3 is further connected to the anode of the first power switching device T1 of the one-phase bridge arm (one-phase bridge arm of the novel switching valve).

In one embodiment of the invention, the dc side and the ac side of the converter are provided with pre-charge circuits, and the switch S3 is arranged on both the dc side and the ac side of the converter in such a way that the switch S3 is arranged between the corresponding pre-charge circuit and the corresponding grid (e.g. the dc grid or the ac grid).

In one embodiment of the present invention, the transformer may not be configured in a single-phase structure.

In an embodiment of the present invention, in the above-described method for starting a power electronic converter, starting the converter from the dc side includes:

step 1: the inverter is blocked, switch S2 and switch S3 are opened, and switch S1 is closed.

Step 2: controlling the voltages of all the switch capacitor modules to reach a precharge target value Usmr2; all power switching device module voltages are controlled to reach a precharge target value Usmr4.

Step 3: the whole converter is blocked, switch S1 is opened, and switches S2 and S3 are closed to achieve completion of starting.

In step 2, controlling all the switched capacitor module voltages to reach the precharge target value Usmr2 includes:

when the voltage of the switch capacitor module rises above the working voltage of the energy dissipation element of the corresponding energy-taking power supply, the energy-taking power supply is electrified (it is needed to know that if no energy-taking power supply is configured in the switch capacitor module, namely external energy taking is adopted, the step is ignored, the sequence voltage-sharing control is directly started), the sequence voltage-sharing control is started, the consistency of the voltages of all the switch capacitor modules is ensured, after all the switch capacitor module voltages reach the precharge target value Usmr1 (the DC bus voltage is set to be Udc, the number of the switch capacitor modules is N1, usmr=k×udc/N1, wherein 0 < k is less than or equal to 100%, and is usually 95%), the bypass N0 (the larger the charging speed is, the more difficult the switch capacitor modules are), therefore, N0 is selected according to the actual circuit parameters, the consistency of the module voltages in the charging process is ensured), after the voltages of all the switch capacitor modules reach k×udc/(N1-the number NA of the bypassed switch capacitor modules, the process is repeated until all the switch capacitor module voltages reach the precharge target value of 95% of the switch capacitor module voltage.

In step 2 of the present embodiment, controlling all power switch device module voltages to reach the precharge target value Usmr4 includes:

after the voltage of the power switch device module of the novel switch valve rises to the rated value of the corresponding energy-taking power supply, the energy-taking power supply energy consumption element is electrified (it is needed to know that if no energy-taking power supply is configured in the power switch device module, namely, external energy taking is adopted, the step is ignored, direct start of input sequencing voltage-sharing control is performed), input sequencing voltage-sharing control is performed, consistency of all power switch device module voltages is ensured, after all power switch device module voltages reach a precharge target value Usm 3 (set DC bus voltage as Udc, the number of power switch device modules of a phase bridge arm is N2, usm 3=k×udc/N2, wherein k is usually 95%), by-pass dN2 (the larger the charging speed is, but the more difficult is performed for the switch capacitor module voltage sharing, therefore, dN2 is selected according to actual circuit parameters, consistency of module voltages in the charging process is ensured), dN2 power switch device modules are by-passed after the power switch device module voltages reach k×udc/(N2-the number of bypassed power switch device modules), and all the power switch device modules reach the rated value of 95% in general, and the precharge target value of the power switch device module voltage reaches 95%.

In an embodiment of the present invention, in the above-described method for starting a power electronic converter, starting the converter from the ac side includes:

step 1: the inverter is blocked, switch S2 is opened, and switch S1 is closed.

In step 2 of the present embodiment, controlling all the switch capacitor module voltages to reach the precharge target value Usmr2 includes:

when the voltage of the switch capacitor module rises above the working voltage of the corresponding energy-taking power supply, the energy-taking power supply is electrified, the sequencing voltage-sharing control is started, the consistency of the voltages of all the switch capacitor modules is ensured, until all the switch capacitor module voltages reach a precharge target value Usr 1 (the peak value of the phase voltage of an alternating current side is Uac, the number of the switch capacitor modules is N1, usr l is k×Uac/N1, wherein k is usually 95%), N0 (the larger N0 is, the faster the charging speed is, but the more difficult the module voltage-sharing is, therefore, N0 is selected according to the actual test, the consistency of the voltages of the switch capacitor modules in the charging process is ensured), after the voltages of all the switch capacitor modules reach k×Uac/(N1-the number NA of the bypassed switch capacitor modules), the above-mentioned processes are repeated until all the switch capacitor module voltages reach the precharge target value Usr 2, usually 95% (95% of the switch capacitor module voltages is only exemplary rated value, and can be 0-100%);

after the voltage of the power switch device module of the novel switch valve rises to the rated value, the energy-taking power supply is electrified, the sequence voltage-sharing control is started to ensure the consistency of the voltage of all the power switch device module until the voltage of all the power switch device module reaches a precharge target value Umr 3 (when the peak value of the alternating-current side phase voltage is Uac and the number of the power switch device module of a phase bridge arm is N2, umr 3=2 x k x Uac/N2, wherein k is usually 95%), dN2 bypasses (the larger dN2 is, the faster the charging speed is, the more difficult the module voltage-sharing is, therefore dN2 is selected according to actual circuit parameters, the consistency of the voltage of the charging process module is ensured), after the voltage of all the power switch device module reaches 2 x k x Uac/(N2-bypassed power switch device module number NB), the process is repeated until the voltage of all the power switch device module reaches the precharge target value Umr 4, and is usually 95% of the rated value of the power switch device module voltage.

The sorting and equalizing control method of the novel switch valve comprises the following steps:

step 1: sequencing the voltage equalizing capacitor voltage of all power switching devices in the novel switching valve;

step 2: as known from the starting strategy (i.e. by-pass dN2 power switch device modules), a part of power switch devices in the novel switch valve bridge arm are by-passed, and the other part is put into operation, then: after the voltage sequencing, selecting a bypass of the power switch device corresponding to the higher voltage (namely, the power switch device is conducted), and selecting the rest power switch devices to put into operation (namely, the power switch device is turned off).

Step 3: and (3) repeatedly executing the steps 1-2, and ensuring long-term consistency of the voltage of the equalizing capacitor of the power switch device.

In one embodiment of the present invention, the converters may also be a combination converter of a multiphase structure, for example, the combination converter shown in fig. 12 and the converter shown in fig. 13 are converted based on 3 converters shown in fig. 2, that is, 3 converters shown in fig. 2 are connected in series, and an exemplary manner is illustrated in fig. 12 as a series:

the cathode of the last power switching device T1 of a first phase bridge arm of the first converter is connected with the anode of the first power switching device T1 of a first phase bridge arm of the middle converter in the 3 converters; the cathode of the last power switching device T1 of the one-phase bridge arm of the middle converter is connected with the anode of the first power switching device T1 of the one-phase bridge arm of the third converter. The direct current positive bus is connected with the anode of the first power switching device T1 of the first converter, and the direct current negative bus is connected with the cathode of the last power switching device T1 of the one-phase bridge arm of the third converter.

Among the 3 converters, the following may be set:

as shown in fig. 12, a pre-charging circuit is arranged on the direct current positive bus or the direct current negative bus, one end of the other side winding of the 3 transformers is provided with a switch S3, and the other ends of the other side windings of the 3 transformers are connected with each other.

Or as shown in fig. 13, in the 3 converters, a switch S3 is arranged on a direct current positive bus or a direct current negative bus, one end of the winding on the other side of the 3 transformers is provided with a precharge circuit, and the other ends of the windings on the other side of the 3 transformers are connected with each other.

In the following, an exemplary method for starting a power electronic converter according to the invention will be described.

Analysis is performed by taking the application of the single-phase inverter corresponding to fig. 2 as an example, and as shown in fig. 14, the dc side is connected to a dc power grid, and the ac side may be connected to an ac power grid or directly connected to an ac load. The pre-charging circuit is arranged on the direct current positive bus.

The switch capacitor module only needs to bear the voltage peak value of the direct current bus, the upper bridge arm and the lower bridge arm (each phase of bridge arm comprises the upper bridge arm and the lower bridge arm) of the novel switch valve bear the voltage peak value of the direct current bus which is 1 time in total, and the power switch device module only comprises 1 fully-controlled power switch device, so that the number of the power switch devices shown in fig. 14 is reduced by more than 25% compared with that of an MMC.

According to the bridge arm of the novel switch valve, as the bridge arm does not have bridge arm reactance, no follow current exists after the bridge arm is closed, no larger charge and discharge power exists in the power switch device module, and the capacitance of the power switch device is smaller. The current of the switch capacitor valve is the doubling current obtained by rectification of the novel switch valve, so that the fluctuation frequency of the capacitor voltage in the switch capacitor module is doubled compared with that of the MMC. In addition, the current of the direct current port (the direct current port is formed between two L2 ends), the fluctuation power of the switch capacitor module is 1/8 of the MMC, and the module capacitance (capacitance in the switch capacitor module) is 1/8 of the MMC.

MMCs are still costly due to their inability to market widespread use. MMCs are made up of a large number of modules containing expensive components such as power semiconductor switching devices, capacitors, etc., resulting in a much higher cost than the various devices in conventional power systems. Therefore, the popularization and the application of the novel power system are directly affected, and the power electronic converter can greatly reduce the number of power switching devices and the number of module capacitors, so that the cost and the volume are greatly optimized, and the power electronic converter is suitable for wide application in marketization.

In the aspect of precharging, the reason why the precharging can be safely completed is as follows:

the precharge resistor R is put into, so that the charging current is limited, and the damage of components caused by the generation of impact current is avoided;

the number of the switch capacitor modules and the power switch device modules of each bypass is limited, the charging speed of the bridge arm is reduced under the condition that the bypass/exit states of the modules are inconsistent, time is provided for module voltage equalizing control, and the consistency of module voltage is ensured.

In the present invention, there is also provided a start-up system for a power electronic converter, wherein the system comprises:

The present invention is not limited to the above-mentioned embodiments, but is not limited to the above-mentioned embodiments, and any simple modification, equivalent changes and modification made to the above-mentioned embodiments according to the technical matters of the present invention can be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A method of starting a power electronic converter, wherein the method comprises:

2. A method of starting a power electronic converter according to claim 1, wherein the dc side of the converter is provided with a pre-charge circuit and the ac side of the converter is provided with a switch S3; or alternatively, the first and second heat exchangers may be,

wherein,,

3. A method of starting a power electronic converter according to claim 2, wherein the converter comprises a switched capacitor valve in parallel and a novel switching valve for effecting a change between ac and dc; the switched capacitor valve is used for realizing soft switching of an inverter, wherein,

4. A method of starting a power electronic converter according to claim 3, wherein the power switching device module comprises a power switching device T1, a diode D1 voltage-sharing capacitor C1 and an energy dissipation element H1, wherein the anode of the diode D1 is connected to the anode of the power switching device T1, one end of the voltage-sharing capacitor C1 is connected to the cathode of the diode D1, the other end of the voltage-sharing capacitor C1 is connected to the cathode of the power switching device T1, one end of the energy dissipation element H1 is connected to one end of the voltage-sharing capacitor C1, the other end of the energy dissipation element H1 is connected to the other end of the voltage-sharing capacitor C1, and a diode D2 is connected in anti-parallel to the power switching device T1.

5. A method of starting a power electronic converter according to claim 4 wherein starting the converter from the dc side comprises:

6. A method of starting a power electronic converter according to claim 5 wherein controlling all switched capacitor module voltages to reach a precharge target value Usmr2 comprises:

Usmrl＝k*Udc/N1；

wherein Udc is direct current bus voltage, N1 is the number of switch capacitor modules, k is more than 0 and less than or equal to 100%, and NA represents the number of bypassed switch capacitor modules.

7. A method of starting a power electronic converter according to claim 5 wherein controlling all power switching device module voltages to reach a precharge target value Usmr4 comprises:

wherein Usmr3 = k x Udc/N2;

8. A method of starting a power electronic converter according to claim 4 wherein starting the converter from the ac side comprises:

the converter is locked, the switch S2 is opened, and the switch S1 is closed;

9. A method of starting a power electronic converter according to claim 8 wherein controlling all switched capacitor module voltages to reach a precharge target value Usmr2 comprises:

repeating the above process until all switched capacitor module voltages reach a precharge target value Usmr2;

wherein Usmr1 = k Uac/N1;

10. A method of starting a power electronic converter according to claim 8 wherein controlling all power switching device module voltages to reach a precharge target value Usmr4 comprises:

wherein Usmr3 = 2 x k x uac/N2;

11. A method of starting a power electronic converter according to any of claims 4-10, wherein the energy dissipating element H1 is any one or a combination of an energy capturing power source, a first energy dissipating resistor and a switchable energy dissipating resistor, wherein the switchable energy dissipating resistor comprises a second energy dissipating resistor and a switch connected in series with the second energy dissipating resistor.

12. A start-up system for a power electronic converter, wherein the system comprises:

13. A power electronic converter start-up system according to claim 12, wherein,