CN111181374B - Starting control method of MMC type multi-port solid-state transformer - Google Patents

Starting control method of MMC type multi-port solid-state transformer Download PDF

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CN111181374B
CN111181374B CN202010102373.5A CN202010102373A CN111181374B CN 111181374 B CN111181374 B CN 111181374B CN 202010102373 A CN202010102373 A CN 202010102373A CN 111181374 B CN111181374 B CN 111181374B
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voltage
mmc
bridge arm
module
dab
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CN111181374A (en
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李东野
赵剑锋
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Nanjing Source Automation Control Co ltd
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Nanjing Institute of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a starting control method of an MMC type multi-port solid-state transformer, which provides a corresponding starting control method by respectively taking buses connected with each port of the MMC type multi-port solid-state transformer as a starting power supply, not only realizes the control requirement of the solid-state transformer in the starting process, but also gives full play to the topological structure characteristics of the MMC type multi-port solid-state transformer, avoids the problem of module voltage divergence caused by factors such as inconsistent hardware parameters and the like in the existing pre-charging strategy, and reduces the complexity of starting control.

Description

Starting control method of MMC type multi-port solid-state transformer
Technical Field
The invention relates to a starting control method of a solid-state transformer, in particular to a starting control method of an MMC type multi-port solid-state transformer.
Background
With the rapid development of society, the contradiction between energy supply and energy demand is increasingly obvious, and the large-scale development and utilization of new energy and the efficient utilization of energy are main ways for solving the contradiction. Among them, the solid-state transformer is a key device for energy interconnection and energy conversion. In high voltage applications such as long-distance power transmission, Modular Multilevel Converters (MMC) are widely accepted and used due to the characteristics of modularization, easy expansion, good output waveform and the like. Similarly, the modular multilevel converter is also introduced into the solid-state transformer, which not only can meet the requirement of high-voltage application, but also provides a high-voltage direct-current interface, and provides an effective solution for the access of a direct-current network. The MMC type multi-port solid-state transformer can realize the functions of high voltage, low voltage, electric energy transmission and conversion between direct current and alternating current, electric energy quality control and the like. In high voltage or high power occasions, generally, an MMC type multiport solid-state transformer is composed of a plurality of modules connected in series and a plurality of DC/DC converters connected in parallel, wherein the modules include a floating capacitor, and the capacitors are charged during the start-up phase of the system to establish a required voltage for the normal operation of the system. Although there has been a related research on the start-up control technology of the MMC or the solid-state transformer, there is no targeted technology for the start-up control of the MMC type multi-port solid-state transformer. This is because, on one hand, the MMC type solid-state transformer has a plurality of ports, and the power supply condition for start-up control is complicated, and on the other hand, some limitations are imposed on start-up control due to the topology difference of the MMC type solid-state transformer. Particularly, in practical application, the difference of hardware parameters and the loss of the module auxiliary circuit can affect the voltage unbalance of the module capacitor to different degrees, so that the management difficulty of the voltage balance of the module capacitor in the starting process is increased. In addition, because the DC/DC converter contains a medium-high frequency transformer, it cannot bear large current impact during the starting process, which also adds a limitation to the starting control. In short, although the MMC type multi-port solid-state transformer has more functions, the start control strategy is also more complex, more factors need to be considered, and more requirements need to be coordinated.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the existing MMC type multiport solid-state transformer, the buses connected with all ports of the MMC type multiport solid-state transformer are respectively used as a starting power supply, and a corresponding starting control method is provided, so that the control requirement of the solid-state transformer in the starting process is met, the topological structure characteristics of the MMC type multiport solid-state transformer are fully exerted, and the complexity of starting control is reduced.
The technical scheme is as follows: the invention discloses a starting control method of an MMC type multiport solid-state transformer.A topological structure of the MMC type multiport solid-state transformer comprises an MMC unit, a DC/DC converter unit and a low-voltage converter unit; each of the three phases of the MMC unit consists of an upper bridge arm and a lower bridge arm which are formed by connecting a plurality of modules in series, a one-phase high-voltage alternating current side of the MMC unit is arranged between the two bridge arms, and each module consists of a direct-current capacitor C and a power electronic switch; the DC/DC converter unit is composed of a plurality of DAB circuits, the front stage of each DAB circuit is connected with a DC capacitor C of the MMC unit, the rear stage output ends of all DAB circuits are connected in parallel to form a low-voltage DC port, and the low-voltage DC port is connected with a DC capacitor C in parallelLVDC(ii) a The DC side of the low-voltage converter and the DC capacitor CLVDCParallel connection;
when a bus connected with a high-voltage direct-current port or a high-voltage alternating-current port of the MMC type multi-port solid-state transformer is used as a starting power supply, the starting control method specifically comprises the following steps:
step 1: pre-charging the DC capacitors of the three-phase modules of the MMC unit until the DC capacitor voltage of each module reaches the starting voltage U of the module controllercstThen, step 2 is executed;
step 2: performing bypass control on a lower/upper bridge arm module of the MMC unit, pre-charging the upper/lower bridge arm module group until the voltage of a direct current capacitor of the upper/lower bridge arm module reaches a rated value UcAnd then step 3 is performed, wherein Uc＝UHVDC/N，UHVDCThe direct current voltage is the direct current voltage on the high-voltage direct current side, and N is the rated capacitance quantity contained in one bridge arm of the MMC unit;
and step 3: the upper/lower bridge arm module keeps a charging state, controls the switch of the front stage of the DAB circuit connected with the upper/lower bridge arm module to increase the duty ratio of the control signal of the front stage switch of the DAB circuit from 0 to 0.5, and carries out uncontrolled rectification to form a direct current capacitor C through a diode at the rear stage of the DAB circuitLVDCCharging until the DC capacitor CLVDCIs up to the rated voltage ULVDCThen, executing the next step, wherein the switch of the DAB circuit connected with the lower/upper bridge arm module keeps a blocking state in the process;
and 4, step 4: the upper/lower bridge arm module keeps a charging state to enable the low-voltage direct-current side voltage UcLVDCStabilized at rated voltage ULVDCControlling a DAB circuit rear-stage switch connected with the lower/upper bridge arm module to increase the duty ratio of a DAB circuit rear-stage switch control signal from 0 to 0.5, not controlling a DAB circuit front-stage switch connected with the MMC lower/upper bridge arm, enabling a DAB circuit front stage connected with the lower/upper bridge arm module to work in an uncontrolled rectification state through the characteristic of unidirectional conduction of a diode in the DAB circuit front stage connected with the lower/upper bridge arm module, charging a direct current capacitor of the lower/upper bridge arm module until the voltage of the direct current capacitor of the lower/upper bridge arm module reaches a rated voltage Uc。
Further, in step 3, if the duty ratio of the front stage switch control signal of the DAB circuit does not reach 0.5 and the low-voltage dc side voltage UcLVDCUp to the rated voltage ULVDCThen stopping the DC capacitor CLVDCCharging is carried out if the duty ratio of the preceding stage switch control signal reaches 0.5 and the low-voltage direct-current side voltage UcLVDCNot reaching the rated voltage ULVDCThe duty ratio of the control signal of the front-stage switch is kept at 0.5, and the direct-current capacitor C is continuously connectedLVDCCharging;
in step 4, if the duty ratio of the post-stage switch control signal does not reach 0.5 and the direct current capacitor voltage of each module of the lower bridge arm reaches the rated voltage UcStopping charging if the duty ratio of the rear-stage switch control signal reaches 0.5 and the direct-current capacitor voltage of each module of the lower bridge arm does not reach the rated voltage UcAnd if so, keeping the duty ratio of the post-stage switch control signal at 0.5, and continuing to charge.
The invention also discloses a starting control method of the MMC type multi-port solid-state transformer, when a bus connected with a low-voltage direct-current port or a low-voltage alternating-current port of the MMC type multi-port solid-state transformer is used as a starting power supply, the starting control method specifically comprises the following steps:
step 1: to the capacitor C on the low-voltage DC portLVDCCharging is carried out until the rated voltage U is reachedLVDCEntering the next step;
step 2: blocking and keeping the switches of all modules of the MMC unit unchanged, controlling the switches of the next stage of the DAB circuit connected with each module to charge the direct current capacitors of the corresponding modules until the direct current capacitor voltage of all the modules reaches the rated voltage UcAnd starting control is realized.
Furthermore, in step 1, if the bus connected to the low-voltage dc side is used as the starting power supply and the starting energy is supplied, the bus directly supplies the dc capacitor CLVDCCharging is carried out; if the bus connected to the low-voltage AC side is used as the starting power supply and provides starting energy, the low-voltage converter rectifies the DC capacitor C controllably or uncontrollablyLVDCAnd charging is carried out.
Further, in step 2, the specific steps of controlling the switch at the post stage of the DAB circuit connected to each module to charge the dc capacitor of the corresponding module are as follows:
and controlling the switch of the DAB circuit rear stage connected with each module to increase the duty ratio of the switch control signal of the DAB circuit rear stage from 0 to 0.5, and performing uncontrolled rectification through a diode of the DAB circuit front stage to charge the direct current capacitor of each module.
Further, if the duty ratio of the control signal of the post-stage switch of the DAB circuit does not reach 0.5 and the voltage of the direct current capacitors of all the modules reaches the rated voltage UcIf the duty ratio of the post-stage switch control signal reaches 0.5 and the voltage of the DC capacitor does not reach the rated voltage UcAnd if so, keeping the duty ratio of the post-stage switch control signal at 0.5, and continuing to charge.
Has the advantages that: the invention has the following advantages:
1) the invention fully utilizes the characteristics of the topological structure of the MMC type multiport solid-state transformer, and compared with the existing starting control method which firstly charges the MMC module capacitor and then charges the low-voltage direct-current side capacitor, the steps of the proposed starting control method are reduced;
2) in the starting process, all capacitor voltages are always controlled to be close to respective rated values, so that the problems of capacitor voltage unbalance caused by loss of auxiliary circuits of modules in the MMC, inconsistency of hardware parameters and overlong starting time are solved, and effective guarantee is provided for the operation of the solid-state transformer;
3) the starting control method has low control complexity, is easy to realize and is convenient to popularize;
4) the impact of overlarge starting current on the DAB medium-high frequency transformer can be effectively avoided;
5) a starting control method for starting the power supply of the buses connected with the ports is provided, and the method is suitable for various application occasions.
Drawings
FIG. 1 shows a topological structure diagram of an MMC type multi-port solid-state transformer applied in the start control method of the present invention;
fig. 2 shows a flow chart of the start-up control method of the present invention.
Detailed Description
The technical solution of the present invention will be further explained with reference to the accompanying drawings and examples.
Fig. 1 is a topological structure diagram of an MMC multiport solid-state transformer applied in the start control method of the present invention, which mainly comprises an MMC portion, a DC/DC converter portion and a low-voltage converter portion. Each of the three phases of the MMC part is composed of an upper bridge arm and a lower bridge arm which are formed by connecting a plurality of modules in series, and a one-phase high-voltage alternating current side of the MMC is arranged between the two bridge arms. Each module consists of a direct current capacitor C and power electronic switches, the switches form an AC/DC converter, the topological structure forms are various in order to adapt to different requirements, wherein the most basic topological structure is a half-bridge structure, the DC/DC converter consists of a plurality of bidirectional active bridge (DAB) circuits, the front stage of each DAB circuit is connected with a direct current capacitor of an MMC unit, the rear stage output ends of all DAB circuits are connected in parallel, so that a low-voltage direct current port of a solid-state transformer is formed, and the voltage is UcLVDCA DC capacitor C is connected in parallel to the portLVDCDC side of low-voltage converter and DC capacitor CLVDCAnd (4) connecting in parallel.
Example 1:
as shown in fig. 2, the present embodiment uses the bus connected to the high-voltage dc port of the solid-state transformer as the starting power supply, and includes the following steps:
step 1: carrying out uncontrolled pre-charging on the MMC part, and specifically comprising the following steps: the charging current flows through the MMC three-phase modules from the positive end of the high-voltage direct current side and flows out from the negative end of the high-voltage direct current side, in each MMC module, the current charges the capacitor through the diode capable of being conducted in the forward direction, the capacitor voltage rises, and when the capacitor voltage of each module reaches the starting voltage U of the module controller of the modulecstAnd finally, the step is finished and transferred to the next step, which is necessary under the condition that each module controller is powered by the module direct current capacitor, and if each module controller is powered by other independent power supplies, the step is omitted and the next step is directly transferred.
Step 2: the method comprises the following steps of carrying out controllable pre-charging on an MMC part in a first step: sending control signals for charging the capacitors of all the modules of the MMC three-phase upper bridge arm to MMThe switches of all the modules of the C three-phase lower bridge arm send out control signals which enable the capacitors of the modules to be bypassed, namely, the MMC three-phase upper bridge arm module is only charged, but not the MMC three-phase lower bridge arm module, until the capacitors of the MMC three-phase upper bridge arm module are charged to a rated value UcThen, go to the next step, UcIs equal to UHVDCN, wherein UHVDCThe voltage is the direct current voltage on the high-voltage direct current side, and N is the rated capacitance number contained in one bridge arm of the MMC. The added spare modules in this step for reliable operation need not participate in this step.
And step 3: the method comprises the following steps of carrying out controllable pre-charging on a DC/DC converter part: in MMC type multiport solid state transformer, the electric capacity of every MMC module has all connected a two-way active bridge (DAB) circuit, and all DAB circuit output ends are parallelly connected together to form the low voltage direct current port of solid state transformer, voltage is UcLVDCThe port is connected in parallel with a DC capacitor CLVDCIn the step, the on-off state of the upper bridge arm module of the MMC is kept unchanged, the duty ratio of a DAB front-stage switch control signal is gradually increased from 0 to 0.5 by controlling the switch of the DAB front-stage connected with each module of the upper bridge arm, and the increase time t of the duty ratio of the switch control signalchThe longer, the smaller the impact of the current generated in DAB on the transformer; the switch of the DAB post stage is not controlled, but is rectified into a capacitor C of a low-voltage direct current port by a diode of the post stage without controlLVDCCharging until the capacitor CLVDCUp to the rated voltage ULVDCThen the stage is finished and the next step is carried out; in the step, the DAB front-stage switch connected with each module of the upper bridge arm is controlled to gradually increase the duty ratio of a control signal of the DAB front-stage switch from 0 to 0.5, specifically, T3 and T4 are conducted together to a medium-high frequency transformer T in the DABDABIs provided with a positive voltage, and T5 and T6 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T3 and T4 is the same as the turn-on time of T5 and T6, ranging from 0 to T6c/2, wherein TcIs the rated control period of DAB; in the step, all DAB switches connected with all modules of the MMC lower bridge arm are kept in a blocking state, namely, no switch is carried outAct, not to charge the capacitance in the module; in this step, every DAB control target connected with the bridge arm module on the MMC is to make the low-voltage direct-current side voltage U of the solid-state transformercLVDCUp to the rated voltage ULVDCIn the process, if the duty ratio of the DAB front stage switch control signals does not reach 0.5 and the control target is achieved, the control target is not continued to be carried out on CLVDCCharging, if the duty ratio of the front-stage switch control signal reaches 0.5 and the control target is not achieved yet, keeping the duty ratio of the front-stage switch control signal at 0.5 and continuing to be CLVDCAnd (6) charging.
And 4, step 4: and carrying out controllable pre-charging of a second step on the MMC part, wherein the specific steps are as follows: the on-off state of the MMC upper bridge arm module is still kept unchanged, namely the MMC upper bridge arm module is used for charging the module capacitor, and the DAB control targets connected with the MMC upper bridge arm module are used for keeping the low-voltage direct-current side voltage U of the solid-state transformercLVDCStabilized at rated voltage ULVDCNamely, the MMC upper bridge arm module provides energy to the low-voltage direct current side of the solid-state transformer, the duty ratio of a DAB post-stage switch control signal connected with the MMC lower bridge arm is gradually increased from 0 to 0.5, and specifically, T7 and T8 are conducted together to the medium-high frequency transformer T in DABDABProvides a positive voltage, and T9 and T10 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T7 and T8 is the same as the turn-on time of T9 and T10, ranging from 0 to T10c/2, wherein TcIs the rated control period of the DAB. The DAB preceding stage switch connected with the MMC lower bridge arm is not controlled, the DAB preceding stage connected with the MMC lower bridge arm works in an uncontrolled rectification state by utilizing the characteristic of unidirectional conduction of a diode in the DAB preceding stage connected with the MMC lower bridge arm, and the capacitors of the MMC lower bridge arm modules are charged until the capacitors of the modules reach the rated voltage UcWhen so, this step ends. In this step, every DAB control target connected with the MMC lower bridge arm is to make the capacitance of the MMC module connected with the DAB control target reach the rated voltage UcIn the process, if the duty ratio of the post-stage switch control signal does not reach 0.5, the control target is realized, the corresponding MMC module is not charged continuously, and if the duty ratio of the post-stage switch control signal reaches 0.5, the control target is not realized, the post-stage switch control signal is not charged continuouslyThe duty cycle remains at 0.5 and the corresponding MMC module continues to be charged.
In step 2, the module of the lower bridge arm of the MMC can be selected to be charged, the module of the upper bridge arm is bypassed, the module of the lower bridge arm of the MMC is provided with energy to the low-voltage direct current side of the solid-state transformer in the subsequent step 3, and the charged module of the upper bridge arm of the MMC is the module of the upper bridge arm of the MMC.
Example 2:
in this embodiment, a bus connected to a high-voltage ac port of a solid-state transformer is used as a starting power supply, and the method includes the following steps:
step 1: carrying out uncontrolled pre-charging on the MMC part, and specifically comprising the following steps: charging current is used for carrying out uncontrolled rectifying charging on capacitors of each module of the MMC from a high-voltage alternating current side according to the high-voltage alternating current side line voltage of the solid-state transformer and the single-phase conduction characteristic of a diode in the module in the MMC, the voltage of each capacitor of the module is gradually increased, and when the voltage of each capacitor of the module reaches the starting voltage U of a module controller of the modulecstAfter that, the procedure is ended and goes to the next procedure. The step is necessary under the condition that each module controller is powered by the module direct current capacitor, and if each module controller is powered by other independent power supplies, the step is omitted and the next step is directly carried out.
Step 2: the method comprises the following steps of carrying out controllable pre-charging on an MMC part in a first step: sending control signals for enabling the capacitors of the modules to be charged to the switches of all the modules of the MMC three-phase upper bridge arm, sending control signals for enabling the capacitors of the modules to be bypassed to the switches of all the modules of the MMC three-phase lower bridge arm, namely only charging the MMC three-phase upper bridge arm until the capacitors of the MMC three-phase upper bridge arm modules are charged to a rated value UcThen go to the next step, UcIs equal to UHVDCN, wherein UHVDCThe voltage is the direct current voltage on the high-voltage direct current side, and N is the rated capacitance number contained in one bridge arm of the MMC. The added spare modules in this step for reliable operation need not participate in this step.
And step 3: the method comprises the following steps of carrying out controllable pre-charging on a DC/DC converter part: in the MMC type multi-port solid-state transformer, a capacitor of each MMC module is connected with a bidirectional active bridge (DAB) powerThe output ends of all DAB circuits are connected in parallel to form a low-voltage DC port of the solid-state transformer, and the voltage is UcLVDCThe port is connected in parallel with a DC capacitor CLVDC. In the step, the on-off state of the MMC upper bridge arm module is kept unchanged, the DAB front-stage switch connected with each module of the upper bridge arm is controlled to gradually increase the duty ratio of a DAB front-stage switch control signal from 0 to 0.5, and the increase time t of the duty ratio of the front-stage switch control signalchThe longer the current generated in DAB is, the smaller the impact on the transformer, the switch of the DAB post-stage is not controlled, but is rectified into a low-voltage DC port capacitor C by the diode of the post-stageLVDCCharging until the capacitor CLVDCUp to the rated voltage ULVDCAfter that, the stage is ended and the next step is carried out. The DAB front-stage switch connected with the modules of the upper bridge arm is controlled to gradually increase the duty ratio of a control signal of the DAB front-stage switch from 0 to 0.5, specifically, T3 and T4 are conducted together to a medium-high frequency transformer T in DABDABIs provided with a positive voltage, and T5 and T6 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T3 and T4 is the same as the turn-on time of T5 and T6, ranging from 0 to T6c/2, wherein TcIs the rated control period of the DAB. In the step, all DAB switches connected with the MMC lower bridge arm module are kept in a blocking state, namely, no switching action is carried out, and the capacitor in the module is not charged. In this step, every DAB control target connected with the bridge arm module on the MMC is to make the low-voltage direct-current side voltage U of the solid-state transformercLVDCUp to the rated voltage ULVDCIn the process, if the duty ratio of the DAB front stage switch control signals does not reach 0.5 and the control target is achieved, the control target is not continued to be carried out on CLVDCCharging, if the duty ratio of the front-stage switch control signal reaches 0.5 and the control target is not achieved yet, keeping the duty ratio of the front-stage switch control signal at 0.5 and continuing to be CLVDCAnd (6) charging.
And 4, step 4: and carrying out controllable pre-charging of a second step on the MMC part: the step is charging the capacitance of the MMC lower bridge arm module, specifically, the switching state of the MMC upper bridge arm module is still kept unchanged, namely the charging of the capacitance of the module is carried out, andthe DAB control targets connected with the MMC upper bridge arm module are to maintain the low-voltage DC side voltage U of the solid-state transformercLVDCStabilized at rated voltage ULVDCNamely, the MMC upper bridge arm module supplies energy to the low-voltage direct current side of the solid-state transformer. The duty ratio of a DAB rear-stage switch control signal connected with the MMC lower bridge arm is gradually increased from 0 to 0.5, and the increasing time t of the duty ratiochThe longer the current generated in DAB has less impact on the transformer. Particularly, T7 and T8 are conducted together to the medium-high frequency transformer T in DABDABProvides a positive voltage, and T9 and T10 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T7 and T8 is the same as the turn-on time of T9 and T10, ranging from 0 to T10c/2, wherein TcIs the rated control period of the DAB. The DAB preceding stage switch connected with the MMC lower bridge arm is not controlled, the DAB preceding stage connected with the MMC lower bridge arm works in an uncontrolled rectification state by utilizing the characteristic of unidirectional conduction of a diode in the DAB preceding stage connected with the MMC lower bridge arm, and the capacitors of the MMC lower bridge arm modules are charged until the capacitors of the modules reach the rated voltage UcWhen so, this step ends. In this step, every DAB control target connected with the MMC lower bridge arm is to make the capacitance of the MMC module connected with the DAB control target reach the rated voltage UcIn the process, if the duty ratio of the rear-stage switch control signal does not reach 0.5, the corresponding MMC module is not charged continuously, and if the duty ratio of the rear-stage switch control signal does not reach 0.5, the control target is not realized, the duty ratio of the rear-stage switch control signal is kept at 0.5, and the corresponding MMC module is charged continuously.
In step 2, the module of the lower bridge arm of the MMC can be selected to be charged, the module of the upper bridge arm is bypassed, the module of the lower bridge arm of the MMC is provided with energy to the low-voltage direct current side of the solid-state transformer in the subsequent step 3, and the charged module of the upper bridge arm of the MMC is the module of the upper bridge arm of the MMC.
Example 3:
in this embodiment, a bus connected to a low-voltage dc port of a solid-state transformer is used as a starting power supply, and the method includes the following steps:
step 1: establishing a low voltage DC side of a solid state transformerRated voltage, specifically: when the bus connected with the low-voltage direct current side of the solid-state transformer is used as a starting power supply and provides starting energy, the bus directly couples the capacitor C on the low-voltage direct current port of the solid-state transformerLVDCCharging is carried out until the rated voltage U is reachedLVDCWhen so, this step ends.
Step 2: the method for controllably precharging the MMC part specifically comprises the following steps: the method comprises the steps that the switches of all MMC modules are blocked and kept in an unchanged state, the capacitor of each MMC module is charged by controlling the rear-stage switch of DAB (digital audio broadcasting), specifically, the duty ratio of a DAB rear-stage switch control signal is gradually increased from 0 to 0.5, and the increasing time t of the duty ratiochThe longer the current generated in DAB has less impact on the transformer, in particular T7 and T8 are conducted together to the medium-high frequency transformer T in DABDABProvides a positive voltage, and T9 and T10 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T7 and T8 is the same as the turn-on time of T9 and T10, ranging from 0 to T10c/2, wherein TcIs the rated control period of the DAB. All DAB front-stage switches are blocked and kept unchanged, uncontrolled rectification is carried out by diodes of all DAB front-stage switches to charge capacitors of all modules until all module capacitors reach rated voltage UcAfter which this phase ends. In this step, every DAB control object connected to the MMC module is to make the capacitance of the MMC module connected to it reach the rated voltage UcIn the process, if the duty ratio of the DAB post-stage switch control signal does not reach 0.5, the corresponding MMC module is not charged continuously, and if the duty ratio of the post-stage switch control signal does not reach 0.5, the control target is not achieved, the duty ratio of the post-stage switch control signal is kept at 0.5, and the corresponding MMC module is charged continuously.
Example 4:
in this embodiment, a bus connected to a low-voltage ac port of the solid-state transformer is used as a starting power supply, and the method includes the following steps:
step 1: establishing rated voltage of a low-voltage direct-current side of the solid-state transformer, which specifically comprises the following steps: the bus connected with the low-voltage AC side of the solid-state transformer is used as a starting power supplyWhen starting energy is supplied, the capacitor C on the low-voltage direct-current port of the solid-state transformer is rectified by the low-voltage converter through controllable or uncontrollable rectificationLVDCCharging is carried out until the rated voltage U is reachedLVDCWhen so, this step ends.
Step 2: the method comprises the following steps of carrying out controllable pre-charging on an MMC part: the method comprises the steps that the switches of all MMC modules are blocked and kept in an unchanged state, the capacitor of each MMC module is charged by controlling the rear-stage switch of DAB (digital audio broadcasting), specifically, the duty ratio of a DAB rear-stage switch control signal is gradually increased from 0 to 0.5, and the increasing time t of the duty ratiochThe longer the current generated in DAB has less impact on the transformer, in particular T7 and T8 are conducted together to the medium-high frequency transformer T in DABDABProvides a positive voltage, and T9 and T10 are conducted together to a medium-high frequency transformer T in DABDABThe turn-on time of T7 and T8 is the same as the turn-on time of T9 and T10, ranging from 0 to T10c/2, wherein TcIs the rated control period of the DAB. All DAB front-stage switches are blocked and kept unchanged, uncontrolled rectification is carried out by diodes of all DAB front-stage switches to charge capacitors of all modules until all module capacitors reach rated voltage UcAfter which this phase ends. In this step, every DAB control object connected to the MMC module is to make the capacitance of the MMC module connected to it reach the rated voltage UcIn the process, if the duty ratio of the DAB post-stage switch control signal does not reach 0.5, the corresponding MMC module is not charged continuously, and if the duty ratio of the post-stage switch control signal does not reach 0.5, the control target is not achieved, the duty ratio of the post-stage switch control signal is kept at 0.5, and the corresponding MMC module is charged continuously.
In the existing starting control method, the problem of voltage divergence exists in the pre-charging process, and the starting control disclosed by the embodiment can effectively solve the problem of voltage divergence in the pre-charging process by carrying out voltage balance control.

Claims (6)

1. Starting control method of MMC type multiport solid-state transformer, wherein MMC type multiportThe topological structure of the solid-state transformer comprises an MMC unit, a DC/DC converter unit and a low-voltage converter unit; each phase of the three phases of the MMC unit consists of an upper bridge arm and a lower bridge arm which are formed by connecting a plurality of modules in series, the upper bridge arm and the lower bridge arm are included, one-phase high-voltage alternating current side of the MMC unit is arranged between the two bridge arms, a plurality of one-phase high-voltage alternating current sides are connected in parallel to form a high-voltage alternating current port of the MMC type multi-port solid-state transformer, the input end of the upper bridge arm and the input end of the lower bridge arm form a high-voltage direct current port of the MMC unit, and each module consists of a direct current capacitor; the DC/DC converter unit is composed of a plurality of DAB circuits, the front stage of each DAB circuit is connected with a DC capacitor C of the MMC unit, the rear stage output ends of all DAB circuits are connected in parallel to form a low-voltage DC port, and the low-voltage DC port is connected with a DC capacitor C in parallelLVDC(ii) a DC side of low-voltage converter and DC capacitor CLVDCThe output ends of the low-voltage converter units form a low-voltage alternating-current port of the MMC type multi-port solid-state transformer;
the method is characterized in that: when a bus connected with a high-voltage direct-current port or a high-voltage alternating-current port of the MMC type multi-port solid-state transformer is used as a starting power supply, the starting control method specifically comprises the following steps:
step 1: carrying out uncontrolled pre-charging on the direct current capacitors C of the three-phase modules of the MMC unit until the voltage of the direct current capacitors C of the modules reaches the starting voltage U of the module controllercstThen, step 2 is executed;
step 2: charging the upper/lower bridge arm module group to make the voltage of DC capacitor C of upper/lower bridge arm module reach rated voltage UcAnd then step 3 is performed, wherein Uc=UHVDC/N，UHVDCIs the direct-current voltage at the high-voltage direct-current side,Nthe rated quantity of the direct current capacitors C contained in one bridge arm of the MMC unit is set;
and step 3: inheriting the charging state of the upper/lower bridge arm module group in the step 2, controlling a switch of a front stage of the DAB circuit connected with the upper/lower bridge arm module to increase the duty ratio of a control signal of the front stage switch of the DAB circuit from 0 to 0.5, and performing non-charging through a diode of a rear stage of the DAB circuitCapacitor C for controlling rectification into direct currentLVDCCharging until the DC capacitor CLVDCIs up to the rated voltage ULVDCThen, executing the next step, wherein the switch of the DAB circuit connected with the lower/upper bridge arm module keeps a blocking state in the process;
and 4, step 4: inheriting the charging state of the upper/lower bridge arm module group in the step 3 and inheriting the low-voltage direct-current side voltage U in the step 3cLVDCStabilized at rated voltage ULVDCThe method comprises the steps of controlling a DAB circuit rear-stage switch connected with a lower/upper bridge arm module to enable the duty ratio of a DAB circuit rear-stage switch control signal to be increased to 0.5 from 0, not controlling a switch of a DAB circuit front stage connected with an MMC lower/upper bridge arm, enabling a DAB circuit front stage connected with the lower/upper bridge arm module to work in an uncontrolled rectification state through the characteristic of unidirectional conduction of a diode in the DAB circuit front stage connected with the lower/upper bridge arm module, and charging a direct current capacitor C of the lower/upper bridge arm module until the voltage of the direct current capacitor C of the lower/upper bridge arm module reaches a rated voltage UcAnd starting control is realized.
2. A start-up control method of an MMC-type multiport solid-state transformer as claimed in claim 1, characterized in that: in step 3, if the duty ratio of the front stage switch control signal of the DAB circuit does not reach 0.5 and the low-voltage direct-current side voltage U is not reachedcLVDCUp to the rated voltage ULVDCThen stopping the DC capacitor CLVDCCharging is carried out if the duty ratio of the preceding stage switch control signal reaches 0.5 and the low-voltage direct-current side voltage UcLVDCNot reaching the rated voltage ULVDCThe duty ratio of the control signal of the front-stage switch is kept at 0.5, and the direct-current capacitor C is continuously connectedLVDCCharging;
in step 4, if the duty ratio of the post-stage switch control signal does not reach 0.5 and the voltage of the direct current capacitor C of each module of the lower bridge arm reaches the rated voltage UcStopping charging if the duty ratio of the rear-stage switch control signal reaches 0.5 and the voltage of the direct current capacitor C of each module of the lower bridge arm does not reach the rated voltage UcAnd if so, keeping the duty ratio of the post-stage switch control signal at 0.5, and continuing to charge.
3. A start-up control method of an MMC type multi-port solid state transformer in accordance with claim 1,
the method is characterized in that: when a bus connected with a low-voltage direct current port or a low-voltage alternating current port of the MMC type multi-port solid-state transformer is used as a starting power supply, the starting control method specifically comprises the following steps:
step 1: for DC capacitor C on low-voltage DC portLVDCCharging is carried out until the rated voltage U is reachedLVDCEntering the next step;
step 2: the switches of all modules of the MMC unit are blocked and kept unchanged, and the switches of the DAB circuit rear stage connected with each module are controlled to charge the direct current capacitors C of the corresponding modules until the voltage of the direct current capacitors C of all the modules reaches the rated voltage UcAnd starting control is realized.
4. A start-up control method of an MMC-type multiport solid-state transformer as claimed in claim 3, characterized in that: in step 1, if the bus connected to the low-voltage DC side is used as the starting power supply and provides starting energy, the bus directly couples the DC capacitor CLVDCCharging is carried out; if the bus connected to the low-voltage AC side is used as the starting power supply and provides starting energy, the low-voltage converter rectifies the DC capacitor C controllably or uncontrollablyLVDCAnd charging is carried out.
5. A start-up control method of an MMC-type multiport solid-state transformer as claimed in claim 3, characterized in that: in step 2, the specific steps of controlling the switch at the post stage of the DAB circuit connected to each module to charge the dc capacitor C of the corresponding module are as follows:
and controlling the switch of the DAB circuit rear stage connected with each module to increase the duty ratio of a DAB circuit rear stage switch control signal from 0 to 0.5, and performing uncontrolled rectification through a diode at the front stage of the DAB circuit to charge the direct current capacitor C of each module.
6. A start-up control method of an MMC type multi-port solid state transformer according to claim 5, characterized in that: if the duty ratio of the post-stage switch control signal of the DAB circuit does not reach 0.5 and the voltage of the direct current capacitors C of all the modules reaches the rated voltage UcIf the duty ratio of the post-stage switch control signal reaches 0.5 and the voltage of the DC capacitor C does not reach the rated voltage UcAnd if so, keeping the duty ratio of the post-stage switch control signal at 0.5, and continuing to charge.
CN202010102373.5A 2020-02-19 2020-02-19 Starting control method of MMC type multi-port solid-state transformer Active CN111181374B (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103840478A (en) * 2014-02-27 2014-06-04 国家电网公司 Pre-charging method for modularized multi-level converter direct-current transmission system
EP3032680A1 (en) * 2014-12-12 2016-06-15 ABB Technology AG Standby and charging of modular multilevel converters
CN107124115A (en) * 2017-06-16 2017-09-01 特变电工新疆新能源股份有限公司 A kind of method that solid-state transformer starts
CN107317471A (en) * 2017-06-16 2017-11-03 特变电工新疆新能源股份有限公司 A kind of method started suitable for solid-state transformer
CN107317472A (en) * 2017-06-30 2017-11-03 中国西电电气股份有限公司 A kind of full-bridge starts method with half-bridge mixed type module multilevel converter

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103840478A (en) * 2014-02-27 2014-06-04 国家电网公司 Pre-charging method for modularized multi-level converter direct-current transmission system
EP3032680A1 (en) * 2014-12-12 2016-06-15 ABB Technology AG Standby and charging of modular multilevel converters
CN107124115A (en) * 2017-06-16 2017-09-01 特变电工新疆新能源股份有限公司 A kind of method that solid-state transformer starts
CN107317471A (en) * 2017-06-16 2017-11-03 特变电工新疆新能源股份有限公司 A kind of method started suitable for solid-state transformer
CN107317472A (en) * 2017-06-30 2017-11-03 中国西电电气股份有限公司 A kind of full-bridge starts method with half-bridge mixed type module multilevel converter

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Fast pre-charge strategy of a modified MMC with enhanced DC fault ride-through capability;Li Dongye et al;《IEEE 26th International Symposium on Industrial Electronics (ISIE)》;IEEE;20170808;第717-722页 *
模块化多电平换流器电容电压均衡控制策略研究;马尚，王毅;《现代电力》;华北电力大学;20150430;第32卷(第2期);第50-55页 *

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