CN104900444B - The topological structure and its control method of dc circuit breaker - Google Patents

Abstract

The invention discloses a topological structure and a control method of a DC circuit breaker belonging to the technical field of power electronics. The DC circuit breaker is a "T"-shaped bidirectional symmetrical structure, consisting of a first current path, a second current path and a third current path composition. The lead-out terminal a of the first current path is connected to one end of the equivalent inductance L9 of the DC power transmission and distribution system, the middle lead-out terminal b of the first current path is connected to one end of the parallel connection of the second current path and the third current path, and the first current The lead-out terminal c of the path is connected to the DC transmission and distribution lines; the other end of the parallel connection of the second current path and the third current path is grounded; , Distribution network under different voltages and current levels, current flow, cut-off, withstand voltage, loss and energy absorption requirements, and can significantly reduce equipment costs.

Description

Topology Structure and Control Method of DC Circuit Breaker

technical field

The invention belongs to the technical field of power electronics, and in particular relates to a topology structure of a DC circuit breaker for DC transmission and a control method thereof, in particular to a topology scheme and a control strategy of a DC circuit breaker of a high-performance and low-cost DC transmission and distribution network.

Background technique

DC circuit breaker is a key equipment for carrying rated current, shutting off fault current, and shutting off load current in DC transmission and distribution networks. It can reliably clear fault current and prevent the expansion of fault range. With the rapid development of multi-terminal DC transmission technology, smart grid and DC distribution network technology, distributed power supply and DC micro-grid technology, DC circuit breakers are of great significance to the reliable, high-quality and economical operation of the power grid. However, the arc extinguishing problem caused by the lack of natural zero-crossing point of the DC current, the overvoltage and energy absorption during the breaking process have also become difficulties in the research of DC circuit breakers.

At present, there are mainly four technical routes for DC circuit breakers: DC circuit breakers that use mechanical switches to directly shut off the current, the action speed is slow, and the switch cannot meet the requirements of quick action and economy; The time is longer and the control is more difficult; the all-solid-state DC circuit breaker using power electronic devices has high loss during normal operation, resulting in poor scalability to higher voltage levels; the hybrid type using mechanical switches and power electronic devices DC circuit breaker. Among them, the hybrid DC circuit breaker is more suitable for the application of DC transmission and distribution network. As shown in Figure 1, the schematic diagram of the hybrid DC circuit breaker of ABB’s patent WO2011141054A1 is shown. ABB’s hybrid DC circuit breaker is suitable for various working conditions, but the obvious disadvantage is that in order to achieve bidirectional current flow and bidirectional shutdown, The fully-controlled power electronic devices 6 in the DC circuit breaker are connected in a bidirectional structure, which doubles the number of devices and significantly increases the equipment cost. As shown in Figure 2, the circuit schematic diagram of the hybrid DC circuit breaker of the patent 201310364653.3 of the Smart Grid Research Institute of the State Grid Corporation of China, the full-control power electronic device 6 of the main switch of the patent is a unidirectional structure, thus reducing part of the cost. However, its DC circuit breaker is to realize two-way flow and two-way cut-off, and the two auxiliary transfer switches adopt an anti-parallel structure composed of two fully-controlled power electronic devices 6, and are respectively connected with the series resistance R1 and the isolation switch BRK11, The resistor R2 in series and the isolating switch BRK21 are connected in parallel, so the number of fully-controlled power electronic devices is doubled; in the case of low current and voltage stress such as opening and closing for maintenance, the resistor R1 and the isolating switch BRK11, resistor The soft opening circuit composed of R2 and isolation switch BRK21, and the DC load switch composed of arrester MOV2, AC circuit breaker BRK3, inductor L and capacitor C significantly increase the equipment cost and control complexity.

In order to deal with the high cost of hybrid DC circuit breakers, there is an urgent need for high-performance and low-cost hybrid DC circuit breakers for DC transmission.

Contents of the invention

The object of the present invention proposes a topology structure of a DC circuit breaker and a control method thereof, wherein the topology structure of the DC circuit breaker adopts a "T-shaped" bidirectional symmetrical structure; the DC circuit breaker of the "T-shaped" bidirectional symmetrical structure The device is composed of a first current path 1, a second current path 2 and a third current path 3, and the second current path 2 and the third current path 3 are connected in parallel to the midpoint of the first current path 1 to form a bidirectional symmetrical T-shaped Structure: the lead-out terminal a of the first current path 1 is connected to one end of the equivalent inductance L9 of the DC power transmission and distribution system, and the middle lead-out terminal b of the first current path 1 is connected in parallel with the second current path 2 and the third current path 3 The other terminal c of the first current path 1 is connected to the DC transmission and distribution line; the other end of the second current path 2 and the third current path 3 are connected in parallel to the ground; the equivalent inductance L9 is in the DC In the operating circuit of the circuit breaker, the total equivalent inductance including the bridge arm inductance, smoothing reactor and line inductance of the DC power transmission and distribution system.

The first current path 1 is formed by a first auxiliary circuit breaker 16 and a second auxiliary circuit breaker 17 .

The second current path 2 is composed of at least one third unidirectional full-control power electronic device 63, which has the function of breaking current; each of the third unidirectional full-control power electronic devices 63 is directly connected in series, and the number of series connected is based on the DC transmission 1. The high, medium and low voltage levels of the power distribution line are determined by different voltage levels, and there should be certain redundancy; the fully controlled power electronic device is composed of an IGBT device and a diode D connected in antiparallel.

The third current path 3 is composed of an energy absorbing unit, and the energy absorbing unit includes at least one lightning arrester 15, and each lightning arrester 15 is connected in parallel or in series; The withstand voltage level of the first auxiliary circuit breaker 16 and the second auxiliary circuit breaker 17, and the withstand voltage level of the second current path 2 are determined.

The first auxiliary circuit breaker is composed of the first fast mechanical switch 4 and the first commutation unit 18 in series, and the second auxiliary circuit breaker is composed of the second commutation unit 19 and the second fast mechanical switch 14 in series; the first The auxiliary circuit breaker and the second auxiliary circuit breaker are symmetrical in structure and have the same components.

The first commutation unit 18 is composed of a first unidirectional full-control power electronic device 61 , and the second commutation unit 19 is composed of a second unidirectional full-control power electronic device 62 .

The first fast mechanical switch and the second fast mechanical switch are elements with the same parameters; both adopt fast mechanical switches or adopt a bidirectional anti-parallel structure of high-power power electronic device V; when the current is transferred from the first current path to the second current After the circuit is disconnected, it mainly plays the role of withstand voltage.

The high-power power electronic device includes a thyristor or a half-controlled and full-controlled device whose gate can be turned off.

The fully controlled power electronic device is a crimping type or a welding type IGBT, IGCT, IEGT and BiGT.

The control method of the DC circuit breaker is characterized in that first, the direction of the current is set to flow from the first auxiliary circuit breaker to the second auxiliary circuit breaker, and the control method includes the following steps:

(1) Fault opening control

Before the fault, the first fast mechanical switch, the first commutation unit, the second fast mechanical switch, and the second commutation unit are all turned on, the current interruption unit is turned off, and the current passes through the first current path; after the fault occurs, each part triggers The control sequence is determined by the pre-set current limit;

a. After a fault occurs, when it is detected that the current reaches a certain limit value, the current interruption unit is triggered to make it conduct;

b. triggering the second commutation unit to turn it off, and the current is quickly transferred from the first current path to the second current path;

c. Trigger the second fast mechanical switch to turn it off;

d. After the second fast mechanical switch reliably recovers the withstand voltage capability, trigger the cut-off unit to turn it off, and the energy absorbing unit in the third current path changes from a high-impedance state after the turn-off overvoltage reaches its initial operating voltage In a low resistance state, the current is quickly transferred from the second current path to the third current path;

e. The arrester in the energy absorption unit dissipates the energy during the breaking process and limits the overvoltage, and the second converter unit and the current breaking unit are effectively protected;

f. Trigger the system isolating switch 8 to turn it off, and complete the fault opening;

(2) Inspection and opening control

a. Trigger the cut-off unit to make it conduct;

b. triggering the second commutation unit to shut it down;

c. Trigger the second fast mechanical switch to turn it off;

d. After the second fast mechanical switch reliably recovers its withstand voltage capability, trigger the cut-off unit to shut it off;

e. The arrester in the energy absorbing unit of the third current path dissipates the energy during the breaking process and limits the overvoltage;

f. Trigger the system isolating switch 8 to turn it off, and complete the inspection and isolation.

(3) Closing control

a. Triggering the second commutation unit to conduct it;

b. Trigger the first fast mechanical switch and the second fast mechanical switch to make them conduct;

c. Trigger the system isolating switch 8 to make it conduct, and complete the normal operation of closing.

(4) Fault identification control

a. When the detection current reaches the pre-set limit value, trigger the cut-off unit to make it conduct;

b. If the detection current recovers, trigger the current interruption unit to shut it off; if the detection current continues to rise, trigger the second commutation unit to shut it off, and trigger the second fast mechanical switch to shut it off;

c. If the detection current recovers, trigger the second commutation unit to turn it on, trigger the second fast mechanical switch to turn it on, and trigger the current interruption unit to turn it off; if the detection current continues to rise, trigger the current interruption unit to make it turn on. its off.

The DC circuit breaker control methods all assume that the direction of current flows from the first auxiliary circuit breaker to the second auxiliary circuit breaker. When the current flows in the reverse direction, the first converter unit and the first fast mechanical switch should be operated in the corresponding steps, and other The steps are the same.

The beneficial effect of the present invention is compared with prior art, has following advantage:

1) The new DC circuit breaker circuit topology proposed by the present invention adopts a "T-shaped" bidirectional symmetrical structure, which effectively reduces the number of core full-control power electronic devices used and significantly reduces costs.

2) The new circuit topology of the DC circuit breaker proposed by the present invention has a flexible structure and strong expandability, and can meet the DC breaking requirements under different voltage and current levels.

3) The new DC circuit breaker circuit topology proposed by the present invention has low on-state loss during normal operation, and has good energy absorption and overvoltage suppression effects.

4) The new DC circuit breaker circuit control strategy proposed by the present invention can reliably deal with different working conditions such as fault opening, maintenance opening, and closing. All parts of the equipment can be effectively protected during the breaking process, and fault detection and Identifying control strategies can effectively reduce equipment misoperations.

Therefore, the hybrid DC circuit breaker of the present invention is a DC circuit breaker topology and control scheme with low cost and excellent performance indicators such as on-state loss, cut-off level, withstand voltage level, action speed, and control strategy.

Description of drawings

Fig. 1 is a circuit schematic diagram of a DC circuit breaker provided by ABB's invention patent WO2011141054A1.

Figure 2 is the circuit schematic diagram of the DC circuit breaker provided by the invention patent 201310364653.3 of the Smart Grid Research Institute of the State Grid Corporation of China.

Fig. 3 is a schematic diagram of the topological structure of the DC circuit breaker provided by the present invention.

Fig. 4 is a circuit schematic diagram of a DC circuit breaker provided by the present invention.

Fig. 5 is a schematic circuit diagram of another DC circuit breaker provided by the present invention.

Fig. 6 is a schematic circuit diagram of a configuration example of a DC circuit breaker provided by the present invention.

Fig. 7 is a schematic diagram of the main wiring of DC circuit breaker application case 1 provided by the present invention.

Fig. 8 is a schematic diagram of the main wiring of DC circuit breaker application case 2 provided by the present invention.

Fig. 9 is a time sequence diagram of fault opening of a DC circuit breaker provided by the present invention.

Fig. 10 is a time sequence diagram for maintenance and opening of a DC circuit breaker provided by the present invention.

Fig. 11 is a timing diagram for closing a DC circuit breaker provided by the present invention.

Fig. 12 is a time sequence diagram of DC circuit breaker fault identification control provided by the present invention.

detailed description

The present invention proposes a topology structure of a DC circuit breaker and a control method thereof. The technical content of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 3 is a schematic diagram of the topological structure of the DC circuit breaker provided by the present invention. In Fig. 3, the topological structure of the DC circuit breaker adopts a "T-shaped" bidirectional symmetrical structure; the DC circuit breaker of the "T-shaped" bidirectional symmetrical structure consists of a first current path 1, a second current path 2 and a third current path 3, the second current path 2 and the third current path 3 are connected in parallel to the midpoint of the first current path 1 connected in a bidirectional symmetrical T-shaped structure; the lead-out terminal a of the first current path 1 is connected to the DC power transmission and distribution One end of the equivalent inductance L9 of the system is connected, where the equivalent inductance L9 is in the operating circuit of the DC circuit breaker, including the total inductance of the bridge arm inductance, smoothing reactor and line inductance of the DC power transmission and distribution system. Equivalent inductance, the other end of the equivalent inductance L9 is connected to one end of the system isolating switch 8, the middle lead-out terminal b of the first current path 1 is connected to one end of the parallel connection of the second current path 2 and the third current path 3, the first The other lead-out terminal c of the current path 1 is connected to the DC transmission line; the second current path 2 is composed of at least one third unidirectional full-control power electronic device 63, which has the function of breaking current; the full-control power electronic device consists of IGBT, IGCT, IEGT or BiGT devices and anti-parallel diodes D; each of the third unidirectional fully-controlled power electronic devices 63 is directly connected in series, and the number of connected devices in series depends on the high, medium and high levels of DC transmission and distribution lines. It is determined by different voltage levels, and there should be some redundancy. The third current path 3 is composed of an energy absorbing unit, and the energy absorbing unit includes at least one energy absorbing element, and its energy absorbing element is a lightning arrester 15, and each lightning arrester 15 is connected in parallel or in series; The rated voltage of the DC side of the power grid, the withstand voltage level of the first auxiliary circuit breaker 16 and the second auxiliary circuit breaker 17, and the withstand voltage level of the second current path 2 are determined.

The first auxiliary circuit breaker is composed of the first fast mechanical switch 4 and the first commutation unit 18 in series, and the second auxiliary circuit breaker is composed of the second commutation unit 19 and the second fast mechanical switch 14 in series. The first auxiliary circuit breaker and the second auxiliary circuit breaker are symmetrical in structure and have the same components.

The first commutation unit 18 is composed of a first unidirectional full-control power electronic device 61 , and the second commutation unit 19 is composed of a second unidirectional full-control power electronic device 62 .

Fig. 4 is a circuit schematic diagram of a DC circuit breaker provided by the present invention. The first current path 1 in FIG. 4 consists of the first auxiliary circuit breaker 16 (as shown in FIG. 3 ) composed of the first commutation unit 18 and the first fast mechanical switch 4 connected in series, and the second commutation unit 19 and the second fast mechanical switch 4. The second auxiliary circuit breaker 17 (as shown in FIG. 3 ) composed of mechanical switches 14 connected in series is formed in series; wherein the first auxiliary circuit breaker 16 and the second auxiliary circuit breaker 17 are symmetrical in structure and have the same components. But when the current flows from the first auxiliary circuit breaker 16 to the second auxiliary circuit breaker 17, the current passes through the diode D of the first unidirectional full-control power electronic device 61 and the IGBT device of the second unidirectional full-control power electronic device 62 ; When the current flows from the second auxiliary circuit breaker 17 to the first auxiliary circuit breaker 16, the current passes through the diode D of the second unidirectional full control type power electronic device 62 and the IGBT device of the first unidirectional full control type power electronic device 61 ; The second current path 2 is composed of a plurality of third unidirectional fully-controlled power electronic devices 63 connected in series, which act as a current interruption; the number of the series connection is determined according to the high, medium and low voltage levels of the direct current transmission and distribution lines, And there should be some redundancy; the energy absorbing unit in the third current path 3 includes at least one lightning arrester 15, and the lightning arresters 15 can be connected in parallel or in series, as shown in FIG. 4 . The parameters such as the rated voltage and residual voltage of the arrester are determined by the rated voltage of the DC side of the DC transmission and distribution lines, the withstand voltage level of the first auxiliary circuit breaker 16 and the second auxiliary circuit breaker 17, and the withstand voltage level of the second current path 2 .

The first fast mechanical switch 4 and the second fast mechanical switch 14 are elements with the same parameters; the purpose of using the fast mechanical switch is to disconnect the first current path quickly after the current is transferred from the first current path to the second current path, It is usually disconnected within 1ms and assumes the withstand voltage function after disconnection. The first fast mechanical switch 4 and the second fast mechanical switch 14 may use bidirectional anti-parallel high-power electronic devices, as shown by reference numerals 22 and 23 in FIG. 5 .

The high-power electronic devices include semi-controlled devices such as thyristors, or fully-controlled devices such as thyristors whose gates can be turned off, or fully-controlled devices such as IGBTs.

In Fig. 5, an anti-parallel semi-controlled power electronic device V is adopted, and its labels 22, 23 replace the first fast mechanical switch 4 and the second fast mechanical switch 14 in Fig. 4 respectively. ) in the DC power distribution system application, the semi-controlled power electronic device V (such as a thyristor) has a strong withstand voltage capability, low on-state loss, and can avoid contact wear and service life problems caused by multiple operations of the mechanical switch .

Figure 6 is a schematic diagram of a circuit composed of a DC circuit breaker. The schematic diagram of the circuit composed of the DC circuit breaker represents the equivalent circuit of the DC network. The equivalent circuit consists of the equivalent converter station (or equivalent power supply) of the DC transmission and distribution system 20. System isolating switch 8, equivalent inductance L9, DC circuit breaker and equivalent load R21, wherein equivalent inductance L9 is in the DC circuit breaker operating circuit, including DC power transmission and distribution system converter bridge arm inductance, flat The total equivalent inductance including the surge reactor and line inductance, etc., the DC circuit breaker shown in the figure adopts the topology in Figure 4. As shown in Figure 6, the DC circuit breaker topology provided by the present invention is composed of a first current path 1, a second current path 2 and a third current path 3, and the second current path 2 and the third current path 3 are connected in parallel with the first current path A current path 1 is connected into a bidirectional symmetrical T-shaped structure; the lead-out terminal a of the first current path 1 is connected to one end of the equivalent inductance L9 of the DC power transmission and distribution system, and the other end of the equivalent inductance L9 of the DC power transmission and distribution system It is connected to one end of the system isolating switch 8, and the other end of the system isolating switch 8 is connected to the positive terminal of the equivalent converter station (or equivalent power supply) 20 of the DC transmission and distribution system, and the equivalent converter station or equivalent power supply 20 The negative terminal is grounded; the middle lead-out terminal b of the first current path 1 is connected to one end of the parallel connection of the second current path 2 and the third current path 3; the other end of the parallel connection of the second current path 2 and the third current path 3 is grounded; The other lead-out terminal c of the first current path 1 is connected to one end of the equivalent load R21 of the DC transmission and distribution line, and the other end of the equivalent load R21 is grounded. The rest are identical in structure with Fig. 5;

As shown in Figure 6, the current direction flows from the first auxiliary circuit breaker 16 to the second auxiliary circuit breaker 17. When the DC transmission and distribution lines are in normal operation, the first fast mechanical switch 4, the first The diode D in the one-way full-control power electronic device 61, the IGBT device in the second one-way full-control power electronic device 62 and the second fast mechanical switch 14 are all turned on, and the third unit in the second current path 2 All the IGBTs in the fully-controlled power electronic device 63 are turned off, and the current passes through the first current path 1; when a short-circuit fault occurs at the remote end of the DC line, that is, the short-circuit fault occurs at the equivalent load R21 end, and the line current rises rapidly at this time , when it is detected that the current reaches a certain set limit value, first trigger the IGBT devices in each third unidirectional full-control power electronic device 63 in the second current path 2 to turn on, and then trigger the second auxiliary circuit breaker The IGBT device in the second unidirectional full-control type power electronic device 62 in 17 makes it turn off, and the current is quickly transferred from the first current path 1 to the second current path 2; then turn off the second auxiliary circuit breaker 17. Two fast mechanical switches 14; after the second fast mechanical switch 14 reliably recovers the withstand voltage capability, turn off the IGBT devices in each third unidirectional full-control power electronic device 63 in the second current path 2, and the third current The arrester 15 in the path 3 changes from a high-impedance state to a low-impedance state after the overvoltage reaches its initial operating voltage, and the current quickly transfers from the second current path 2 to the third current path 3; in the third current path 3 The lightning arrester 15 dissipates the energy in the breaking process and limits the overvoltage, and the second auxiliary circuit breaker 17 and the third unidirectional full-control power electronic device 63 in the second current path 2 are effectively protected; finally the shutdown system is isolated Switch 8, completes current shutdown.

As shown in Figure 6, the current direction flows from the second auxiliary circuit breaker 17 to the first auxiliary circuit breaker 16. When the DC transmission and distribution lines are in normal operation, the first fast mechanical switch 4 and the second fast mechanical switch 4 in the first current path 1 The diode D in the unidirectional fully-controlled power electronic device 62, the IGBT device in the first unidirectional fully-controlled power electronic device 61 and the second fast mechanical switch 14 are all turned on, and the third unit in the second current path 2 All the IGBTs in the fully-controlled power electronic device 63 are turned off, and the current passes through the first current path 1; when a short-circuit fault occurs at the near end of the DC line, that is, the short-circuit fault occurs in the equivalent converter station (or equivalent power supply) 20 At this time, the line current rises rapidly. When it is detected that the current reaches a certain set limit value, the IGBTs in the third unidirectional full-control power electronic devices 63 in the second current path 2 are first triggered to turn on. Then trigger the IGBT in the first unidirectional full-control power electronic device 61 in the first auxiliary circuit breaker 16 to turn it off, and the current is quickly transferred from the first current path 1 to the second current path 2; then turn off the first auxiliary The first fast mechanical switch 4 in the circuit breaker 16; after the first fast mechanical switch 4 reliably recovers the withstand voltage capability, turn off the IGBT in each third unidirectional full-control power electronic device 63 in the second current path 2 , the arrester 15 in the third current path 3 turns from a high-impedance state to a low-impedance state after the shutdown overvoltage reaches its initial operating voltage, and the current quickly transfers from the second current path 2 to the third current path 3; the third The lightning arrester 15 in the current path 3 dissipates the energy during the breaking process and limits the overvoltage, and the first auxiliary circuit breaker 16 and the third unidirectional full-control power electronic device 63 in the second current path 2 are effectively protected; finally Turn off the system isolating switch 8 to complete the current shutdown.

Figure 7 shows the DC circuit breaker application case 1. As shown in Figure 7, this is a multi-terminal DC transmission network. The AC systems A, B, C and D are respectively connected to the converter stations E, F, G, and H through the transformer T to form a multi-terminal DC transmission network. DCBs are respectively installed on each port of the DC lines of the converter stations E, F, G, H. When the multi-terminal DC transmission network is in normal operation, each DC circuit breaker DCB is closed. When a fault occurs, taking the most serious DC bipolar fault as an example, when the fault occurs at point f1 _of the near-end exit of converter station F, the DC circuit breaker DCB1 is disconnected, and DCB1 is closed again to resume normal operation after the fault is cleared; When the fault occurs at point f2 of the remote DC transmission line of converter station F, the DC circuit breaker _DCB2 is opened, and after the fault is cleared, DCB2 is closed again to resume normal operation; when the fault occurs at the near or remote end of other converter stations , the DC circuit breaker DCB corresponding to the converter station is disconnected, and the DCB is closed again to resume normal operation after the fault is cleared.

Figure 8 shows DC circuit breaker application case 2. As shown in Figure 8, this is a multi-terminal DC power distribution network. AC system A and AC system B are respectively connected to the DC distribution network through the AC/DC converter, and the DC circuit breaker DCB is installed at the outlet of each part of the converter and on the DC line; the DC distribution network is composed of AC loads, DC Load, photovoltaic power generation, wind power generation, energy storage equipment and low-voltage DC distribution network. Among them, the low-voltage DC distribution network is connected to the DC network through the DC transformer and DC circuit breaker DCB; the AC load and wind power are respectively connected to the DC network through the AC/DC converter and the DC circuit breaker DCB; The equipment is connected to the DC network through the DC/DC converter and the DC circuit breaker DCB; when the DC network is operating normally, each DC circuit breaker DCB is closed, and when the fault occurs at point _f3 of the DC bus, the DC circuit breaker DCB3 is opened After the fault is cleared, DCB3 closes again to resume normal operation; when the fault occurs at point _f4 of the DC line, the DC circuit breaker DCB4 opens, and DCB4 closes again to resume normal operation after the fault is cleared.

FIG. 9 is a time sequence diagram of opening of a DC circuit breaker (the circuit structure shown in FIG. 6 ) when a fault occurs. As shown in Figure 9, the DC circuit breaker fault opening control steps are:

₁ ) In stage 0-t1, the system operates normally, and the current direction flows from the first auxiliary circuit breaker 16 to the second auxiliary circuit breaker 17 . The first fast mechanical switch 4 in the first current path 1, the diode D in the first one-way full-control power electronic device 61, the second fast mechanical switch 14 and the second one-way full-control power electronic device 62 The IGBT devices are all turned on, the IGBTs in the third unidirectional full-control power electronic device 63 in the second current path 2 are all turned off, the voltage at both ends of the arrester 15 in the third current path is lower than its operating voltage, and the arrester 15 Maintain a high-impedance state, only a small current passes through, which is similar to an open circuit. The rated current i _N flows through the first current path 1 ;

2) At time _t1 after the fault, when it is detected that the current reaches the limit value i1, the IGBTs in the third unidirectional full-control power electronic devices 63 in the second current path ₂ are triggered to turn on, and the fault current continue to rise;

3) At time _t2 , when the detection circuit detects that the fault current exceeds the limit value _i2 , it triggers the IGBT in the second unidirectional full-control power electronic device 62 in the second auxiliary circuit breaker 17 to turn it off, and the fault current quickly transfer from the first current flow 1 to the second current path 2;

4) At time _t3 , when the detection circuit detects that the current in the first current flow 1 is zero or a very low value, the second fast mechanical switch 14 in the second auxiliary circuit breaker 17 is turned off. Since the current has been largely transferred from the first current flow 1 to the second current path 2, the second fast mechanical switch 14 can realize arc-free breaking, and its action speed, reliability and service life are significantly improved;

₅ ) At time t4, when the detection circuit detects that the fault current reaches the limit value _ib and the second fast mechanical switch 14 reliably recovers the withstand voltage capability, the third unidirectional full-control power electronic switch in the second current path 2 is turned off. The IGBT in the device 63 generates a higher voltage overshoot when the third unidirectional full-control power electronic device 63 is turned off, and when the voltage overshoot reaches the operating voltage of the arrester 15 in the third current flow 3, the arrester 15 From the high-resistance state to the low-resistance state, the fault current is quickly transferred from the second current flow 2 to the third current path 3;

₆ ) In the stage t4 _- t5, the arrester 15 in the third current flow 3 dissipates the energy in the shutdown process, the voltage across the arrester 15 is maintained at its residual voltage level, and the second unit in the second auxiliary circuit breaker The third unidirectional full-control power electronic device 63 connected in series to the full-control power electronic device 62 and the second current path are reliably protected. The fault current in the third current flow 3 decreases rapidly during the energy dissipation process;

7) _At time t5, the system isolating switch 8 is turned off, the fault residual current is cleared, and the current shutdown is completed.

Fig. 10 is a time sequence diagram of 6 DC circuit breakers (the circuit structure shown in Fig. 6 ) during maintenance and opening. During maintenance and opening, the current that the DC circuit breaker shuts off is the system rated current i _N , and the voltage and current stress during the breaking process are relatively small. As shown in Figure 10, the DC circuit breaker inspection and opening control steps are:

₁ ) Before time t1, the system operates normally, and the current direction flows from the first auxiliary circuit breaker 16 to the second auxiliary circuit breaker 17 . The first fast mechanical switch 4 in the first current path 1, the diode D in the first one-way full-control power electronic device 61, the second fast mechanical switch 14 and the second one-way full-control power electronic device 62 The IGBTs are all turned on, the IGBTs in the third unidirectional full-control power electronic device 63 in the second current path 2 are all turned off, the voltage at both ends of the arrester 15 in the third current flow is lower than its operating voltage, and the arrester 15 Maintain a high-impedance state, only a small current passes through, which is similar to an open circuit. The rated current i _N flows through the first current path 1 ;

2) At time _t1 , perform maintenance and opening operation, trigger the IGBT in the third unidirectional full-control power electronic device 63 in the second current path 2 to make it conduct;

3) At time _t2 , trigger the IGBT in the second unidirectional full-control power electronic device 62 in the second auxiliary circuit breaker 17 to turn it off, and the fault current is quickly transferred from the first current flow 1 to the second current path 2 ;

4) At time _t3 , when the detection circuit detects that the current in the first current flow 1 is zero or a very low value, the second fast mechanical switch 14 in the second auxiliary circuit breaker 17 is turned off. Since the current has been largely transferred from the first current flow 1 to the second current path 2, the second fast mechanical switch 14 can realize arc-free breaking, and its action speed, reliability and service life are significantly improved;

₅ ) At time t4, when the detection circuit detects that the second fast mechanical switch 14 has reliably recovered its withstand voltage capability, it turns off the IGBT in the third unidirectional full-control power electronic device 63 in the second current path 2, and the third single Higher voltage overshoot is generated when the fully-controlled power electronic device 63 is turned off, and the voltage overshoot reaches the operating voltage of the arrester 15 in the third current flow 3, and the arrester 15 changes from a high-resistance state to a low-resistance state. The current is rapidly diverted from the second current flow 2 to the third current path 3;

6) _At time t5, the arrester 15 in the third current flow 3 dissipates the energy in the shutdown process, the voltage across the arrester 15 is maintained at its residual voltage level, and the second one-way full control in the second auxiliary circuit breaker The power electronic device 62 and the third unidirectional full-control power electronic device 63 connected in series in the second current path are reliably protected. The fault current in the third current flow 3 decreases rapidly during the energy dissipation process;

7) _At time t6, the system isolating switch 8 is turned off, the residual current is cleared, and the maintenance isolation is completed.

FIG. 11 is a timing diagram when the DC circuit breaker (the circuit structure shown in FIG. 6 ) is switched on. As shown in Figure 10, the closing control steps of the DC circuit breaker are as follows:

1) Before time t ₁ , the DC circuit breaker is in the off state. The first fast mechanical switch 4 in the first current path 1, the IGBT in the first unidirectional full-control power electronic device 61 and the second unidirectional full-control power electronic device 62, and the second fast mechanical switch 14 are all turned off , the IGBTs in the third unidirectional full-control power electronic device 63 in the second current path 2 are all turned off, the voltage across the arrester 15 in the third current flow is lower than its operating voltage, and the arrester 15 maintains a high-impedance state , only a small current passes through, which is approximately an open circuit;

2) At time _t1 , perform a closing operation to trigger the IGBT in the second unidirectional full-control power electronic device 62 in the second auxiliary circuit breaker 17 to turn on;

3) At time _t2 , trigger the first fast mechanical switch 4 and the second fast mechanical switch 14 to make them conduct;

4) At time _t3 , the system isolating switch 8 is triggered to be turned on, the rated current i _N flows through the first current flow 1, the closing operation is completed, and the system operates normally.

FIG. 12 is a time sequence diagram for fault identification control of a DC circuit breaker (the circuit structure shown in FIG. 6 ) provided by the present invention. In actual operation, considering the working conditions of temporary rise in line current and slow development of faults, the detection circuit needs to continuously detect the current level to perform corresponding operations. As shown in Figure 12, the DC circuit breaker fault identification control steps are:

₁ ) Before time t1, the system operates normally, and the current direction flows from the first auxiliary circuit breaker 16 to the second auxiliary circuit breaker 17 . The first fast mechanical switch 4 in the first current path 1, the diode D in the first one-way full-control power electronic device 61, the second fast mechanical switch 14 and the second one-way full-control power electronic device 62 The IGBTs are all turned on, the IGBTs in the third unidirectional full-control power electronic device 63 in the second current path 2 are all turned off, the voltage at both ends of the arrester 15 in the third current flow is lower than its operating voltage, and the arrester 15 Maintain a high-impedance state, only a small current passes through, which is similar to an open circuit. The rated current i _N flows through the first current path 1 ;

2) At time _t1 , the detection circuit detects that the current rises. When the current reaches the limit value i1 at time _t2 , trigger the IGBT in the third unidirectional full _- control power electronic device 63 in the second current path 2 to turn on;

₃ ) At time t3, when it is detected that the current continues to rise and reaches the limit value _i2 , the IGBT in the second unidirectional full-control power electronic device 62 in the second auxiliary circuit breaker 17 is triggered to turn off, and the current rapidly changes from diversion of the first current flow 1 to the second current path 2;

₄ ) At time t4, when it is detected that the current continues to rise and reaches the limit value _i3 , trigger the second fast mechanical switch 14 in the second current flow 2 to turn it off;

₅ ) At time t5, the current drop is detected, and the IGBT in the second unidirectional full-control power electronic device 62 in the second auxiliary circuit breaker 17 is triggered to turn on;

₆ ) At time t6, it is detected that the current returns to near the rated value, triggering the second fast mechanical switch 14 in the first current path 1 to make it conduct;

₇ ) At time t7, the detection current returns to the rated value i _N , triggering the IGBT in the third unidirectional full-control power electronic device 63 in the second current path 2 to turn off, and the DC circuit breaker resumes normal operation.

During the process of current change, the current level should be detected continuously according to the above steps until the detection circuit judges that a fault occurs and executes the fault opening operation.

It should be noted that the above-mentioned embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and those changes or modified equivalent forms also fall within the appended claims of the application. limited range.

Claims (1)

1. A method for controlling the topological structure of a DC circuit breaker, the topological structure of the DC circuit breaker adopts a "T-type" bidirectional symmetrical structure; the topological structure of the DC circuit breaker consists of a first current path (1), a second current path (2 ) and the third current path (3), the second current path (2) and the third current path (3) are connected in parallel with the midpoint of the first current path (1) to form a bidirectional symmetrical T-shaped structure; the first The terminal b in the middle of the current path (1) is connected to one end of the second current path (2) and the third current path (3) connected in parallel, and the terminal c of the first current path (1) is connected to the DC transmission and distribution line connection; the other end of the second current path (2) and the third current path (3) connected in parallel is grounded; the terminal a of the first current path (1) is connected to one end of the equivalent inductance L9 of the DC power transmission and distribution system, The equivalent inductance L9 is the total equivalent inductance in the operating circuit of the DC circuit breaker, including the bridge arm inductance, smoothing reactor and line inductance of the DC power transmission and distribution system; the first current path (1) It is composed of a first auxiliary circuit breaker (16) and a second auxiliary circuit breaker (17); the first auxiliary circuit breaker is composed of a first fast mechanical switch (4) and a first commutation unit (18) in series, and the second The auxiliary circuit breaker is composed of a second converter unit (19) and a second fast mechanical switch (14) in series; the first auxiliary circuit breaker and the second auxiliary circuit breaker have symmetrical structures and the same components; the first fast mechanical switch and the second fast mechanical switch The two fast mechanical switches are components with the same parameters, both of which adopt fast mechanical switches or bidirectional anti-parallel structures of high-power power electronic devices V, which are disconnected after the current is transferred from the first current path to the second current path, mainly for withstand voltage Function; it is characterized in that, firstly, the current direction of the topological structure of the DC circuit breaker is set to flow from the first auxiliary circuit breaker to the second auxiliary circuit breaker, and the control method includes the following steps: (1) Fault opening control Before the fault, the first fast mechanical switch, the first commutation unit, the second fast mechanical switch, and the second commutation unit are all turned on, the current interruption unit is turned off, and the current passes through the first current path; after the fault occurs, each part triggers The control sequence is determined by the pre-set current limit; a. After a fault occurs, when it is detected that the current reaches a certain limit value, the current interruption unit is triggered to make it conduct; b. triggering the second commutation unit to turn it off, and the current is quickly transferred from the first current path to the second current path; c. Trigger the second fast mechanical switch to turn it off; d. After the second fast mechanical switch reliably recovers the withstand voltage capability, trigger the cut-off unit to turn it off, and the energy absorbing unit in the third current path changes from a high-impedance state after the turn-off overvoltage reaches its initial operating voltage In a low resistance state, the current is quickly transferred from the second current path to the third current path; e. The arrester in the energy absorption unit dissipates the energy during the breaking process and limits the overvoltage, and the second converter unit and the current breaking unit are effectively protected; f. Trigger the system isolating switch (8) to turn it off, and complete the fault opening; (2) Inspection and opening control a. Trigger the cut-off unit to make it conduct; b. Triggering the second commutation unit to shut it down; c. Trigger the second fast mechanical switch to turn it off; d. After the second fast mechanical switch reliably recovers its withstand voltage capability, trigger the cut-off unit to shut it off; e. The arrester in the energy absorbing unit of the third current path dissipates the energy during the breaking process and limits the overvoltage; f. Trigger the system isolating switch (8) to turn it off, and complete the maintenance isolation; (3) Closing control a. Triggering the second commutation unit to conduct it; b. Trigger the first fast mechanical switch and the second fast mechanical switch to make them conduct; c. Trigger the system isolating switch (8) to make it conduct, and complete the normal operation of closing; (4) Fault identification control a. When the detection current reaches the pre-set limit value, trigger the cut-off unit to make it conduct; b. If the detection current recovers, trigger the current interruption unit to shut it off; if the detection current continues to rise, trigger the second commutation unit to shut it off, and trigger the second fast mechanical switch to shut it off; c. If the detection current recovers, trigger the second commutation unit to turn it on, trigger the second fast mechanical switch to turn it on, and trigger the current interruption unit to turn it off; if the detection current continues to rise, trigger the current interruption unit to make it turn on. its shutdown; The control methods of the DC circuit breaker topology all assume that the direction of current flows from the first auxiliary circuit breaker to the second auxiliary circuit breaker. When the current flows in the reverse direction, the first converter unit and the first fast mechanical switch, and the other steps are the same.