CN105119511B - A kind of MMC submodular circuits with DC side failure blocking ability - Google Patents

Abstract

An MMC sub-module circuit with DC side fault blocking capability. It involves the field of power system protection and control. The short-circuit current can be completely blocked, the structure is simple, the required components are few, and the integration degree is high. Consists of two half-bridge sub-modules, power switch one with anti-parallel diodes and diodes. One of the half-bridge sub-modules is connected to the emitter of the first power switch tube with an antiparallel diode, and the other is connected to the collector of the first power switch tube with an antiparallel diode. The cathode of the diode is connected to the collector of the power switch tube 2 with an anti-parallel diode in the half-bridge sub-module connected to the emitter of the power switch tube 1 with an anti-parallel diode, and the anode is connected to the collector of the power switch tube 1 in the other half-bridge sub-module. The emitter connection of the power switch tube three with an antiparallel diode. The product is small in size and high in stability; the topology is simple, low in cost and easy to implement; flexible in configuration and low in power consumption; it can disconnect the DC side at any time and respond quickly.

Description

A MMC sub-module circuit with DC side fault blocking capability

technical field

The invention relates to the field of power system protection and control, in particular to an MMC sub-module circuit with DC side fault blocking capability.

Background technique

The output voltage level of the traditional power quality comprehensive compensation device with three-phase half bridge as the main circuit is limited and the compensation ability for negative sequence current is limited, so the final compensation result cannot achieve the required effect, and its switching frequency Higher, greater loss. Sometimes in order to improve the withstand voltage of the system, it is necessary to divide the voltage in series with multiple switching devices, but this will bring problems such as the consistency of the switching devices and the voltage equalization.

An invention patent application published by the State Intellectual Property Office on May 13, 2015 (application number: 201410848005X name: improved structure and isolation method of MMC converter with DC fault current limiting capability) discloses a DC fault current limiting capability MMC converter, including current limiting module, controllable switch, resistor and DC circuit breaker. When a fault occurs on the DC side, through fast and comprehensive fault current limiting, the requirements for the action speed and cut-off capacity of the DC circuit breaker are reduced. Its disadvantages are that various components are required, the withstand voltage value is low, the DC circuit breaker takes a long time to respond, the action frequency is high, and the loss of components is large. When the DC side is short-circuited, due to the freewheeling effect of the diode, the DC side cannot completely lock the short-circuit current in time, and it is necessary to cooperate with the circuit breaker to realize the disconnection of the DC side circuit.

Contents of the invention

Aiming at the above problems, the present invention provides an MMC sub-module circuit with DC side fault blocking capability that can timely and completely lock short-circuit current at the DC side, has a simple structure, requires few components, and is highly integrated.

Technical scheme of the present invention is:

Including two half-bridge sub-modules, power switch tube 1 with anti-parallel diodes and diodes, half-bridge sub-modules include power switch tube 2 with anti-parallel diodes, power switch tube 3 with anti-parallel diodes and regulator Capacitor, the power switch tube 2 with anti-parallel diode is connected in series with the power switch tube 3 with anti-parallel diode, the positive terminal of the voltage stabilizing capacitor is connected with the collector of the power switch tube 2 with anti-parallel diode, The negative terminal is connected to the emitter of the power switch tube 3 with an anti-parallel diode, and the sub-module is between the emitter of the power switch tube 2 with an anti-parallel diode and the collector of the power switch tube 3 with an anti-parallel diode Incoming line terminal; the negative terminal of the voltage stabilizing capacitor is the submodule outlet terminal, and it is characterized in that one of the half-bridge submodules is connected to the emitter of the power switch tube one with the antiparallel diode, and the other is connected to the The collector connection of the power switch tube one with the anti-parallel diode;

The cathode of the diode is connected to the collector of the power switch tube 2 with an anti-parallel diode in the half-bridge sub-module connected to the emitter of the power switch tube 1 with an anti-parallel diode, and the positive pole is connected to the other half-bridge sub-module The emitter connection of the power switch tube three with anti-parallel diodes in the module.

Including incoming and outgoing wires;

The incoming line terminal is the same as the submodule incoming line terminal of the half-bridge submodule connected to the emitter of the power switch tube 1 with the antiparallel diode, and the outgoing line terminal is connected to the set of the power switch tube 1 with the antiparallel diode. The outlet terminals of the sub-modules of the half-bridge sub-modules whose electrodes are connected are the same.

It also includes N half-bridge sub-modules for capacity expansion.

When N=1, the submodule inlet terminal of the half-bridge submodule used for increasing capacity is connected to the submodule inlet terminal of the half-bridge submodule connected to the collector of the power switch tube one with an antiparallel diode ;

The negative end of the voltage stabilizing capacitor in the half-bridge sub-module used for capacity expansion is a new outlet end.

When N=2, the incoming line end of the newly added half-bridge sub-module used for capacity expansion is connected to the outgoing line end of the previous half-bridge sub-module used for capacity expansion;

The negative terminal of the voltage stabilizing capacitor in the newly added capacity expansion module is a new outlet terminal.

The voltage stabilizing capacitor is an electrolytic capacitor.

The invention adopts a power switch tube as a switching device, which has high integration, small product volume and high stability; avoids the use of DC circuit breakers, and avoids the problem of large loss of DC circuit breakers; requires few devices, simple topology structure, and difficult control algorithm Reduced; less components required, low cost, easy to implement; modular production can be flexibly configured according to actual needs, reducing power consumption; when the circuit fails, the DC side can be disconnected without configuring a DC circuit breaker, and the response is fast and the disconnection Open the DC side for fault isolation.

Description of drawings

Fig. 1 is a circuit diagram of the present invention,

Figure 2 is a circuit diagram of the half-bridge sub-module,

Fig. 3 is the circuit diagram of the present invention when N=1,

Fig. 4 is the circuit diagram of the present invention when N=2,

Fig. 5 is the simulation waveform figure of the present invention,

Fig. 6 is a schematic diagram of the flow path of the current when the current direction is positive,

Fig. 7 is a schematic diagram of the current flow path when the current direction is negative,

Fig. 8 is a schematic structural diagram of a power switch tube with an antiparallel diode;

1 in the figure is a power switch tube 1 with an antiparallel diode,

2 is a diode,

3 is the half-bridge sub-module,

4 is the incoming terminal,

5 is the outlet terminal,

301 is a power switch tube 2 with an antiparallel diode,

302 is a power switch tube three with an antiparallel diode,

303 is a voltage stabilizing capacitor (C1, C2, C3, C4),

304 is the incoming terminal of the sub-module,

305 is a sub-module outlet.

3011 is a power switch tube (T1, T2, T3, T4, T5, T6, T7, T8, T9),

3012 is diode one (D1, D2, D3, D4, D5, D6, D7, D8, D9).

detailed description

As shown in Figure 1, the present invention includes two half-bridge sub-modules 3, a power switch tube 1 and a diode 2 with an anti-parallel diode, and the half-bridge sub-module 1 includes a power switch tube 2 301 with an anti-parallel diode, Power switch tube 3 302 with anti-parallel diode and voltage stabilizing capacitor 303, power switch tube 2 301 with anti-parallel diode and power switch tube 3 302 with anti-parallel diode connected in series, positive terminal of voltage stabilizing capacitor 303 It is connected to the collector of the power switch tube 2 301 with anti-parallel diodes, the negative end is connected to the emitter of the power switch tube 3 302 with anti-parallel diodes, and the power switch tube 2 301 with anti-parallel diodes Between the emitter and the collector of the power switch tube three 302 with an antiparallel diode is the submodule inlet terminal 304; the negative terminal of the voltage stabilizing capacitor is the submodule outlet terminal 305, and it is characterized in that the half bridge submodule 3. One of them is connected to the emitter of the power switch tube-1 with an anti-parallel diode, and the other is connected to the collector of the power switch tube-1 with an anti-parallel diode;

The cathode of the diode 2 is connected to the collector of the power switch tube 2 301 with an anti-parallel diode in the half-bridge sub-module 3 connected to the emitter of the power switch tube 1 with an anti-parallel diode, and the positive pole is connected to another The emitter of the power switch tube 3 302 with an anti-parallel diode in a half-bridge sub-module is connected.

The present invention has incoming wire end 4 and outgoing wire end 5. The incoming terminal 4 is the same as the submodule incoming terminal 304 of the half-bridge submodule 3 connected to the emitter of the power switch tube-1 with an antiparallel diode, and the outgoing terminal 4 is the same as the power switch tube with an antiparallel diode. The outlet terminals 5 of the submodules of the half-bridge submodules 3 connected to the collectors of -1 are the same.

The present invention uses modularization to manufacture multi-level converters. By connecting the sub-modules in series, the problem of unbalanced voltage division caused by the direct series connection of switching devices is avoided, and the MMC is easy to realize the balance between each sub-module through a corresponding voltage equalization strategy. In addition, the number of MMC output levels can theoretically be increased to a specified number, so that the switching frequency of the device is greatly reduced. Compared with the traditional half-bridge sub-module, it has the ability to block faults on the DC side, which can avoid the problem that the fault current cannot be blocked when a short-circuit fault occurs on the DC side of the MMC, thereby improving the stability of the system.

The present invention can add N half-bridge sub-modules 3 for capacity expansion according to actual usage conditions.

As shown in Figure 3, when N=1, the submodule inlet terminal 304 of the half bridge submodule 3 used for increasing the capacity is connected with the collector of the power switch tube one with an antiparallel diode 3 of the sub-modules are connected to the incoming terminal 304, and the negative terminal of the voltage stabilizing capacitor in the half-bridge sub-module 3 used for capacity expansion is the new outgoing terminal 5.

As shown in FIG. 4 , when N=2, a new half-bridge sub-module 3 for capacity expansion is added on the basis of N=1. The submodule inlet terminal 304 of the new half-bridge submodule 3 is connected to the submodule inlet terminal 304 of the first half-bridge submodule 3 for capacity expansion, and the submodule outlet terminal 305 of the new half-bridge submodule 3 As the new outgoing terminal 3. By analogy, when N is 3, 4, 5..., each time a new half-bridge sub-module 3 for capacity expansion is added, the sub-module of the new half-bridge sub-module 3 for capacity expansion enters the line The terminals 304 are all connected to the incoming terminal 304 of the previous sub-module, and the sub-module outgoing terminal 305 of the new half-bridge sub-module 3 is used as the new outgoing terminal 5 .

In order to timely and completely block the short-circuit current flowing through the half-bridge sub-module, it is only necessary to make the voltage across the diode 2 less than zero. In the present invention, when a short-circuit fault occurs on the DC side of the MCC, the power switch tube 1 with an anti-parallel diode, the power switch tube 2 301 with an anti-parallel diode, and the power switch tube 3 302 with an anti-parallel diode are all in the locked state. In this state, regardless of whether the current is in the positive half cycle or the negative half cycle, according to Kirchhoff's law, the voltage values at both ends of the diode 2 are less than 0, so the present invention can completely block the short circuit current from flowing through the half cycle when the DC side short circuit fault occurs. The bridge sub-module thus protects the circuit and prolongs the service life.

When a short-circuit fault occurs on the DC side of the MMC, all switching tubes are blocked, and the study of the flow path of the fault current in the integrated sub-module at this time is the key to measuring the DC fault ride-through capability.

As shown in Figure 6, when the direction of the current flowing into the integrated sub-module is positive, the current flow path includes five diodes-3012 (D1, D3, D5, D6, D8) and four capacitors (C1, C2, C3, C4).

As shown in Figure 7, when the direction of the current flowing through the sub-module is negative, the current flow path includes 5 diodes (D2, D4, D7, D8, D9) and 2 capacitors (C1, C2).

Taking phase A and C as an example, if a fault occurs on the DC side and the fault current i>0, the fault current flows through 10 diodes (D1, D3, D5, D6, D8), and 8 capacitors (C1, C2, C3, C4) and two reactors L. According to Kirchhoff's voltage law, we have

u _ac ＝10u _D +8U _c +2u _L (1)

Where: u _ac is the instantaneous value of the AC line voltage; u _L is the instantaneous value of the voltage across the reactor; u _D is the instantaneous value of the diode voltage; U _C is the sub-module DC side voltage.

By formula (1) get

Therefore, in order to be able to block the fault current from flowing through the sub-module, it can be realized as long as u _D <0.

According to the basic theory of MMC:

U _dc ＝4U _C u _ac ＜4U _C (3)

Assuming that the influence of the inductor voltage u _L is neglected, the condition of being able to block the fault current (i.e. u _D <0) can be obtained from formula (2):

u _ac <8 U _C (4)

According to formula (3), it can be obtained that u _ac <4U _c <8U _c , so the effectiveness of the above scheme can be proved theoretically.

When the number of traditional half-bridge sub-modules contained in the integrated sub-module is 2 and 3, the purpose of suppressing the DC side fault current can also be achieved, so in order to reduce costs, two or three half-bridge sub-modules can be made into An integrated sub-module is used in conjunction with an integrated sub-module composed of four half-bridge sub-modules. Because when the number of half-bridge sub-modules contained in the integrated sub-module is 2 or 3, it can also meet the requirements of blocking the MMC DC short-circuit fault, but at this time the integrated sub-module must include the first two half-bridge sub-modules, reverse direction switch tube and reverse diode. In addition, when the number of half-bridge sub-modules contained in the integrated sub-module is greater than 4, according to the analysis similar to the number of half-bridge sub-modules of 4, it can be concluded that the integrated sub-module at this time cannot meet the conditions for blocking the DC side fault current .

In the present invention, the power switch tube 1 with anti-parallel diodes, the power switch tube 2 301 with anti-parallel diodes and the power switch tube 3 302 with anti-parallel diodes are fully controlled transistor devices, preferably using insulated gate double pole type transistor (IGBT). The insulated gate bipolar transistor (IGBT) has a short response time and fast on-off speed, which can quickly lock the fault current; the driving power is small, which reduces the power consumption of the entire circuit and saves energy; it has good thermal stability and can be used in high-temperature environments. Can work stably.

Workers can flexibly configure the number of half-bridge sub-modules according to the actual use conditions, reduce the power consumption of the present invention in actual use, and reduce the production cost. Improved control efficiency.

As shown in Figure 5, it is a simulation waveform diagram of the present invention. The simulation parameters of the MMC system model are: the DC side voltage is 20kV, the DC side voltage of the half-bridge sub-module in the integrated sub-module is 1kV, and the DC side capacitance is 15mF. The simulation parameters of the load model are: the resistance is 10Ω, and the inductance is 65mH.

At 0.13s, the two poles of the DC side of the MMC are short-circuited, and the gate signals of all power switch tubes with anti-parallel diodes are turned off; at 0.148s, the short-circuit fault of the two poles of the DC side of the MMC is cleared, and the power grid is used to The capacitor on the DC side of the MMC is charged; at 0.15s, the MMC is started and a trigger signal is sent to the gates of all power switch tubes with anti-parallel diodes.

It can be seen from the simulation waveform diagram that before 0.13s, the MMC outputs a three-phase symmetrical current waveform. Between 0.13s and 0.15s, due to a short-circuit fault on the DC side of the MMC, the integrated sub-module uses its own blocking DC fault The characteristics of the current make the MMC bridge arm circuit and output current drop to 0 rapidly during this period, avoiding the delay of the action of the AC contactor and causing it to fail to cut off the fault current, achieving the purpose of blocking the fault on the DC side, and blocking Works well and responds quickly.

Claims (5)

1. A kind of MMC sub-module circuit with DC side fault blocking ability, comprises two half-bridge sub-modules, a power switch tube 1 and a diode with an anti-parallel diode, and the half-bridge sub-module includes a power switch with an anti-parallel diode Switch tube 2, power switch tube 3 with anti-parallel diode and voltage stabilizing capacitor, power switch tube 2 with anti-parallel diode and power switch tube 3 with anti-parallel diode connected in series, the positive terminal of the voltage stabilizing capacitor is connected with The collector of the power switch tube two with anti-parallel diodes is connected, the negative end is connected with the emitter of the power switch tube three with anti-parallel diodes, and the emitter of the power switch tube two with anti-parallel diodes is connected to the power switch tube two with anti-parallel diodes. Between the collectors of the power switch tube three of the anti-parallel diode is the incoming terminal of the sub-module; the negative terminal of the voltage stabilizing capacitor is the outgoing terminal of the sub-module, It is characterized in that one of the half-bridge sub-modules is connected to the emitter of the power switch tube 1 with an anti-parallel diode, and the other is connected to the collector of the power switch tube 1 with an anti-parallel diode; The cathode of the diode is connected to the collector of the power switch tube 2 with an anti-parallel diode in the half-bridge sub-module connected to the emitter of the power switch tube 1 with an anti-parallel diode, and the positive pole is connected to the other half-bridge sub-module The emitter connection of the power switch tube 3 with anti-parallel diodes in the module also includes N half-bridge sub-modules for capacity increase, and the multi-level converter is made in a modular way to connect the sub-modules in series, avoiding the The problem of unbalanced voltage division caused by the direct series connection of switching devices, and the MMC sub-module circuit realizes the DC side voltage balance between each sub-module through a voltage equalization strategy, and the output level of the MMC sub-module circuit increases to the specified number , which reduces the switching frequency of the device. 2. A kind of MMC sub-module circuit with DC side fault blocking ability according to claim 1, is characterized in that, comprises incoming line end and outgoing line end; The incoming line terminal is the same as the submodule incoming line terminal of the half-bridge submodule connected to the emitter of the power switch tube 1 with the antiparallel diode, and the outgoing line terminal is connected to the set of the power switch tube 1 with the antiparallel diode. The outlet terminals of the sub-modules of the half-bridge sub-modules whose electrodes are connected are the same. 3. A kind of MMC submodule circuit with DC side fault blocking ability according to claim 1, it is characterized in that, when N=1, the submodule inlet terminal of the described half-bridge submodule used for increasing capacity It is connected to the sub-module inlet terminal of the half-bridge sub-module connected to the collector of the power switch tube 1 with an anti-parallel diode; The negative end of the voltage stabilizing capacitor in the half-bridge sub-module used for capacity expansion is a new outlet end. 4. a kind of MMC sub-module circuit with DC side fault blocking ability according to claim 3, is characterized in that, when N=2, add the incoming line end of the described half-bridge sub-module that is used for increasing capacity Connect to the outgoing terminal of the previous half-bridge sub-module for capacity expansion; The negative end of the voltage stabilizing capacitor in the newly added half-bridge sub-module is a new outlet end. 5. A kind of MMC sub-module circuit with DC side fault blocking capability according to claim 1, characterized in that, the voltage stabilizing capacitor is an electrolytic capacitor.