CN107294054A - A kind of topological structure of the quick mixed type dc circuit breaker of both arms framework - Google Patents

Abstract

The invention discloses a topological structure of a fast hybrid DC circuit breaker with a double-arm structure. In the first bridge arm, the main circuit breaker A ₁ branch is composed of a solid-state switch group with unidirectional series connection and anti-parallel diodes. The main current The branch is composed of a fast mechanical switch A3 and a bidirectional load conversion solid _- state switch A2 in series. _The energy freewheeling absorption circuit is composed of a non _- linear bleeder resistor A5 connected in series with the freewheeling diode group A4, and a parallel _circuit is connected at both ends of A4 _. Diode A ₆ and fast mechanical switch A ₇ form a series branch; in the second bridge arm, the main circuit breaker B ₁ branch is composed of a solid-state switch group with one-way series connection with anti-parallel diodes, and the main current branch is composed of fast mechanical switch B ₃ is connected in series with the bidirectional load switching solid-state switch B ₂ . The invention can close, carry and break the current under normal circuit conditions, and can close, carry and break the current under abnormal circuit conditions within a specified time, thereby improving the practical engineering applicability.

Description

Topology of a fast hybrid DC circuit breaker with double-arm structure

technical field

The invention relates to the field of circuits, in particular to a topological structure of a double-arm structure fast hybrid DC circuit breaker.

Background technique

With the gradual development of high-voltage voltage source converters and multi-terminal flexible DC transmission (distribution) technology, fast DC circuit breakers are one of the key equipment for the engineering application of DC transmission (distribution) grids, which need to be loaded and opened within a specified time The normal current and various fault currents of the DC power grid are the basis for the operation, control and protection of the DC transmission (distribution) network construction.

High-voltage DC circuit breakers face major challenges: the DC current has no natural zero-crossing point, and the DC arc is not easy to extinguish; after breaking the DC current, a large overvoltage will be generated, and at the same time, a large amount of energy stored in the DC system needs to be absorbed; the DC system impedance ( In the steady state, only resistance) is much smaller than that of the AC system, and its short-circuit fault current will rise rapidly within a few milliseconds, and it is necessary to accurately judge the fault and break the short-circuit current at the millisecond level.

With the development of power electronic technology and fast mechanical switch technology, there are currently three main solutions for circuit breakers that meet the breaking requirements of DC systems: artificial zero-crossing circuit breakers based on fast mechanical switches, solid-state circuit breakers based on power electronics technology, and power-based The hybrid DC circuit breaker with electronic technology and fast mechanical switching technology compares these four schemes with the traditional mechanical circuit breaker mentioned above, as shown in Table 1 below:

Table 1 Comparison of advantages and disadvantages of four kinds of DC circuit breakers

The hybrid DC circuit breaker topology scheme based on fast mechanical isolating switches and power electronic switches proposed by ABB has made breakthroughs in DC circuit breakers. During normal operation, the main current branch is composed of fast mechanical isolating switches and load transfer switches. When the load transfer switch is turned off, the current is transferred to the bidirectional solid-state switch group branch connected in parallel; when the main current branch current drops to zero, the fast isolation switch is quickly turned off, thereby protecting the load transfer switch and establishing it in the overall circuit Primary voltage isolation; by turning off the bidirectional solid-state switch group, the fault current is transferred to the parallel surge arrester, so as to solve the purpose of overvoltage and energy absorption, so as to realize the DC current shutdown, which has the advantages of fast, reliable and almost zero loss. However, the main problem is that the source and grid are always in the grounding loop during the discharge of the arrester, which increases the rated voltage and energy consumption capacity of the arrester, thereby affecting the cut-off speed of the circuit breaker. As the grid voltage level increases, the cost will also increase significantly.

Contents of the invention

In order to solve the above problems, the present invention provides a dual-arm structure fast hybrid DC circuit breaker topology, while retaining the good static characteristics of the mechanical switch and the good dynamic characteristics of the solid-state switch, the DC arrester is greatly reduced The voltage rating and energy consumption capacity, including fast mechanical isolating switch, bidirectional load transfer switch, unidirectional series solid state switch group with anti-parallel diode, current limiting reactor, freewheeling diode group and nonlinear discharge resistor , It can close, carry and break the current under normal circuit conditions, and can close, carry and break the current under abnormal circuit conditions (including short circuit conditions) within a specified time.

In order to achieve the above object, the technical scheme that the present invention takes is:

A dual-arm structure fast hybrid DC circuit breaker topology, in the first bridge arm, the main circuit breaker A ₁ branch is composed of solid-state switch groups with anti-parallel diodes connected in series in one direction, the main current branch (i.e. load transfer branch) consists of a fast mechanical switch A3 and a bidirectional load switching solid _- state switch A2 in series, and the energy freewheeling absorption circuit is composed of a non _- linear discharge resistor _A5 connected in series with the _freewheeling diode group A4, and between _A4 A series branch composed of diode A ₆ and fast mechanical switch A ₇ is connected in parallel at the terminal; in the second bridge arm, the main circuit breaker B ₁ branch is composed of a solid-state switch group with anti-parallel diodes connected in series in one direction, and the main current branch (that is, the load transfer branch) is composed of a fast mechanical switch _B3 and a bidirectional load conversion solid _- state switch B2 in series, and the energy freewheeling absorption circuit is composed of a non _- linear discharge resistor B5 connected in series with the _freewheeling diode group B4, and at B ₄ Both ends are connected in parallel, a series branch composed of diode B ₆ and fast mechanical switch B ₇ ; the double bridge arm branch is connected to N ₁ and N ₂ through the current-limiting reactor L in the form of back-to-back, and the 1 and 2 ends are respectively connected to DC The positive pole and the negative pole of the grid, and the 3rd and 4th terminals are respectively connected to the positive pole and the negative pole of the DC grid on the other side; in the main circuit breaker branches A ₁ and B ₁ , each solid-state switching tube is connected in parallel with a buffer capacitor C _Q and a resistor R _Q ; Each freewheeling diode in the freewheeling diode groups A ₄ and B ₄ is connected in parallel with a resistor R _D , where R _Q << R _D .

Preferably, in the case of normal conduction, the main current branches on the double bridge arms are used in series as the main current flow branches, and the bidirectional load transfer switches A ₂ and B ₂ on the double bridge arms are turned off at the same time in case of a fault, so as to transfer the fault current One-way series solid-state switch group A ₁ and B ₁ branch with anti-parallel diodes connected in parallel; when the main current branch current drops to zero, the mechanical isolating switch A ₃ and B ₃ are quickly turned off, and the mechanical isolating switch contacts No arc separation of the heads.

Preferably, when the mechanical switch is opened to the rated opening distance, the bidirectional load transfer switches A2 and B2 are protected, and primary voltage isolation is established for them in the overall circuit _; at the same time, the one _- way series solid-state with anti-parallel diodes is quickly turned off The switch group A ₁ and B ₁ , followed by the closure of the mechanical switches A ₇ and B ₇ , transfers the fault current to the non-linear bleeder resistor A ₅ , B ₅ circuit.

Preferably, when the current is transmitted from the left port to the right port, the remaining energy flows from the anti-parallel freewheeling diode of the solid-state switch group of the main circuit breaker B ₁ branch in the second bridge arm, and finally by the nonlinear Resistor A ₅ discharges; on the contrary, the remaining energy flows through the anti-parallel freewheeling diode of the main circuit breaker branch solid-state switch group in the first bridge arm, and finally, it is discharged by the nonlinear resistor B ₅ in the second bridge arm, reaching Solve the purpose of overvoltage and energy absorption, so as to realize the shutdown of DC current.

Preferably, when the circuit breaker needs to resume normal operation, the voltage at both ends of A4 and _B4 is detected by controlling the opening of switches _A7 and _B7 to determine whether the fault _on the DC side has been cleared, due to the fact that the main circuit breaker branch solid-state switch is connected in parallel The equivalent resistance R _Q is much smaller than the equivalent resistance R _D of the freewheeling diode in parallel, so the two ends of the freewheeling diode group bear most of the DC side voltage, which can realize the zero voltage turn-on (Zero Voltage) of the solid state switch group in the branch circuit of the main circuit breaker. Switching, ZVS), if the short-circuit fault is not eliminated, the voltage across the freewheeling diode group will not rise, so that N ₁ and N ₂ are at ground potential: when the DC side fault is cleared and the circuit breaker needs to resume normal operation, turn on in turn On the main circuit breaker, solid-state switch group A ₁ and B ₁ with anti-parallel diode, fast mechanical isolating switch A ₃ and B ₃ , bidirectional load changeover switch A ₂ and B ₂ are connected in series in one direction.

Preferably, the main circuit breakers A ₁ and B ₁ adopt a unidirectional series solid-state switch group with anti-parallel freewheeling diodes, and by turning off A ₁ and B ₁ , the fault current is diverted to the non-linear bleeder resistor A ₅ , B ₅ and the freewheeling diode group A ₄ , B ₄ form an energy discharge circuit, so that the source is not in the ground fault circuit, thereby increasing the breaking speed of the circuit breaker.

Preferably, in the residual energy freewheeling (energy discharge) link, the voltage ratings of the non _- linear resistors A5 and _B5 in the bridge arm are much smaller than the rated voltage level of the overall DC grid, and the energy consumption capacity is only controlled by the current limiting reactor L The main circuit breaker decides to store energy after cutting off the fault current, and the remaining energy absorption and overvoltage protection are mainly completed by the non-linear bleeder resistor.

The present invention has the following beneficial effects:

1. A fast hybrid topology with dual-arm architecture is proposed. The main circuit breakers A ₁ and B ₁ adopt unidirectional series connection of solid-state switch groups with anti-parallel diodes, and turn off the unidirectional series connection of solid-state switch groups with anti-parallel diodes. A ₁ and B ₁ divert the fault current to the discharge circuit composed of the non-linear discharge resistor A ₅ (B ₅ ) and the freewheeling diode group Ax (B ₄ ), so that the source is not in the ground fault circuit, thereby improving The cut-off speed of the circuit breaker;

2. The voltage ratings of nonlinear resistors A ₅ and B ₅ in the bridge arm are much smaller than the rated voltage level of the overall DC grid, and the energy consumption capacity is only determined by the energy stored in the current-limiting reactor L after the main circuit breaker cuts off the fault current;

3. This type of hybrid DC circuit breaker makes full use of the low-loss current-carrying capacity and insulation capacity of mechanical switches, and the breaking capacity of solid-state switches to achieve fast transfer of DC current and fast breaking. Compared with the hybrid type proposed by ABB Although a set of freewheeling diode group A ₄ (B ₄ ) is added to the topological structure of the high-voltage DC circuit breaker, it can prevent the source from being in the ground fault loop after the main circuit breaker is turned off, thereby increasing the breaking speed of the circuit breaker. At the same time, the rated voltage level and energy consumption capacity of the DC arrester are greatly reduced, and the manufacturing cost is significantly reduced. The invention can meet the requirements of the direct current transmission network and the direct current distribution network for the direct current circuit breaker in China.

Description of drawings

Fig. 1 is a schematic diagram of the basic topology of a double-arm structure fast hybrid DC circuit breaker provided by the present invention;

In the figure: (a) is the basic topology of a fast hybrid DC circuit breaker with a double-arm structure; (b) the specific structure of a single IGBT with an anti-parallel diode; (c) a freewheeling diode with a voltage equalizing resistor;

Fig. 2 is a schematic diagram of the topological structure of a double-arm structure fast hybrid DC circuit breaker provided by the present invention;

Fig. 3 is a schematic flow chart of the control strategy of a dual-arm structure fast hybrid DC circuit breaker provided by the present invention;

In the figure: (a) control strategy when opening; (b) control strategy when closing;

Fig. 4 is a schematic diagram of the working state topology of the hybrid DC circuit breaker when the circuit breaker in Fig. 2 is in normal operation;

Fig. 5 is a schematic diagram of the working state (off state) of the hybrid DC circuit breaker when a fault occurs in Fig. 2 at an instant;

Fig. 6 is a schematic diagram of the working state (off state) of the hybrid DC circuit breaker when the bidirectional load transfer switches A ₂ and B ₂ in Fig. 2 are disconnected;

Fig. 7 is a schematic diagram of the working state (off state) shown by the fault current charging the buffer capacitor when the main circuit breakers A ₁ and B ₁ are disconnected in Fig. 2;

Fig. 8 is a schematic diagram of the working state (off state) when the fault current is transferred to the non-linear resistor A ₄ (B ₄ ) branch when the main circuit breakers A ₁ and B ₁ are disconnected in Fig. 2 ;

Fig. 9 is a schematic diagram of the working state (starting state) of the hybrid DC circuit breaker when the main circuit breakers A1 and B1 in _Fig . ₂ are turned on;

Fig. 10 is a schematic diagram of the working state (starting state) of the hybrid DC circuit breaker when the mechanical switches A3 and _B3 of the load transfer branch in Fig. ₂ are closed;

Fig. 11 is a schematic structural diagram of the hybrid DC circuit breaker in the unipolar two-terminal DC power transmission system provided by the present invention;

In the figure: (a) Schematic diagram of the practical application topology of the fast hybrid DC circuit breaker with a double-arm structure, (b) the topology of a fast hybrid DC circuit breaker with a single-arm structure (only suitable for energy transmission from the left port to the right port) case), (c) fast hybrid DC circuit breaker topology with single-arm structure (only applicable to the case where energy is transmitted from the right port to the left port);

Fig. 12 is a schematic diagram of another topology structure of the hybrid DC circuit breaker in the unipolar two-terminal DC transmission system provided by the present invention;

In the figure: (a) Schematic diagram of another topology structure of a fast hybrid DC circuit breaker with a double-arm structure; (b) a topology of a fast hybrid DC circuit breaker with a single-arm structure (only suitable for energy transmission from the left port to the right port case); (c) fast hybrid DC circuit breaker with single-arm structure (only applicable to the case where energy is transmitted from the right port to the left port);

Fig. 13 is a schematic structural diagram of the hybrid DC circuit breaker in the bipolar two-terminal DC power transmission system provided by the present invention;

Fig. 14 is the simulation waveform of the opening process of the double-arm structure fast hybrid DC circuit breaker provided by the present invention; in the figure: (a) current simulation waveform of the opening process; (b) voltage simulation waveform of the opening process;

Fig. 15 is the simulation waveform of the closing process of the double-arm structure fast hybrid DC circuit breaker provided by the present invention; in the figure: (a) the current simulation waveform during the closing process; (b) the voltage simulation waveform during the closing process.

detailed description

In order to make the objects and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, the embodiment of the present invention provides a dual-arm structure fast hybrid DC circuit breaker topology, in the first bridge arm, the main circuit breaker A ₁ branch is unidirectionally connected in series with anti-parallel diodes The main current branch (that is, the load transfer branch) is composed of a fast mechanical switch A3 and a bidirectional load switching solid _- state switch A2 in series, and the energy freewheeling absorption circuit is composed of a non _- linear bleeder resistor _A5 and continuous The flow diode group A ₄ is connected in series, and a series branch composed of a diode A ₆ and a fast mechanical switch _{A 7} is connected in parallel at both ends of A ₄ ; The solid-state switch group of parallel diodes is formed. The main current branch (i.e., the load transfer branch) is composed of a fast mechanical switch B ₃ and a bidirectional load switching solid-state switch B ₂ in series. The energy freewheeling absorption circuit is composed of a non-linear discharge resistor B ₅ It is connected in series with the freewheeling diode group B ₄ , and a series branch composed of diode B ₆ and fast mechanical switch B ₇ is connected in parallel at both ends of B ₄ ; the double bridge arm branch is connected back to back through the current limiting reactor L to N ₁ and N ₂ , terminals 1 and 2 are connected to the positive pole and negative pole of the DC network respectively, and terminals 3 and 4 are respectively connected to the positive pole and negative pole of the DC network on the other side; (4) In the branch circuit A ₁ (B ₁ ) of the main circuit breaker, Each solid-state switch tube is connected in parallel with a buffer capacitor _{C Q} and a resistor R _Q ; in the freewheeling diode groups A ₄ and _{B 4} , each freewheeling diode is connected in parallel with a resistor RD , wherein _RQ <<RD .

Due to the small loss of mechanical switches A ₃ and B ₃ and the large loss of solid-state switch group A ₁ and B ₁ during long-term current flow, we use a mechanical switch A ₃ (B ₃ ) in series with the load transfer switch A ₂ (B ₂ ) structure, when the normal current flows, although the bidirectional load transfer switch A ₂ (B ₂ ) of this type of circuit breaker increases a certain on-state loss, but in terms of reliability, since the transfer process is controlled by the bidirectional load transfer switch A ₂ ( B2 ₎ is realized, and the transfer speed is fast and the reliability is high, so that the practicability of this type of DC circuit breaker is significantly improved. The current-limiting reactor L in Fig. 1 can effectively limit the rising rate of the fault current, thereby reducing the requirement on the quickness of the mechanical switch A ₃ (B ₃ ). During the opening process of the circuit breaker, firstly, the bidirectional load transfer switch A ₂ (B ₂ ) is turned off, and the fault current is forcibly transferred to the branch circuit of the main circuit breaker A ₁ (B ₁ ), at this time, the bidirectional load transfer switch A ₂ ( B ₂ ) bears only the tube pressure drop of the main circuit breaker solid-state switch group A ₁ (B ₁ ), when the main current branch current decreases to zero, the fast mechanical switch acts, at this time, the bidirectional load transfer switch A ₂ (B ₂ ) withstands the voltage quickly transferred to the fast mechanical switch; when the fast mechanical switch reaches a certain opening distance, the voltage at both ends of the fast mechanical switch A ₃ (B ₃ ) is the main circuit breaker solid-state switch group A ₁ (B ₁ ), the solid-state switch group A ₁ (B ₁ ) of the main circuit breaker triggers shutdown, the fault current is cut off by the solid-state switch group A ₁ (B ₁ ), and the voltage across the solid-state switch of the main circuit breaker rises rapidly, so The fault current begins to charge the snubber capacitor C _Q , when the voltage across the snubber capacitor rises to the DC side voltage, the freewheeling diode group _A4 and _B4 are opened (then switches _A7 and _B7 are closed), and the stored in the reactor L The remaining energy is finally discharged by the non-linear bleeder resistor A ₅ (B ₅ ). When the circuit breaker needs to resume normal operation, the voltage at both ends of A ₄ (B ₄ ) is detected by controlling the opening of switches A ₇ and B ₇ to determine whether the fault on the DC side has been cleared. Due to the equivalent The resistance Σ(R _Q ) is much smaller than the equivalent resistance Σ(R _D ) of the freewheeling diode in parallel, so the two ends of the freewheeling diode group bear most of the DC side voltage, and the zero voltage of the solid state switch group of the main circuit breaker branch can be realized Turn on (ZeroVoltage Switching, ZVS), if the short circuit fault is not eliminated, the voltage across the freewheeling diode group will not rise, making N ₁ and N ₂ at ground potential; when the DC side fault is cleared and the circuit breaker needs to resume normal operation , turn on the unidirectional series solid-state switch group A ₁ and B ₁ with anti-parallel diodes on the main circuit breaker, the fast mechanical isolating switch A ₃ and B ₃ , and the bidirectional load transfer switch A ₂ and B ₂ .

In practical engineering applications, in a unipolar two-terminal DC transmission system, as shown in Figure 11, when a fault occurs on one side of the double-arm structure fast hybrid DC circuit breaker or when the line is actively cut off, it is necessary to shut down both directions at the same time. The load transfer switches A ₂ and B ₂ , at this time, the current is transferred from the mechanical switch branch to the main circuit breaker branch, and the main circuit breaker branches on the double bridge arms are connected in series together as the current flow branch. When the one-way series solid-state switch group with anti-parallel diodes on the branch of the main circuit breaker is triggered to shut down (then mechanical switches A ₇ and B ₇ are closed); Reverse diode flow (when the current is transmitted from the left port to the right port, the remaining energy flows from the anti-parallel freewheeling diode of the solid-state switch group of the main circuit breaker B ₁ branch in the second bridge arm, and finally by the first bridge arm The non-linear resistor A ₅ discharges; on the contrary, the remaining energy flows through the anti-parallel freewheeling diode of the main circuit breaker branch solid-state switch group in the first bridge arm, and finally, it is discharged by the non-linear resistor B ₅ in the second bridge arm ).

In a bipolar two-terminal DC transmission system, as shown in Figure 13, when a fault occurs at one pole or the line is actively cut off, both bidirectional load transfer switches A ₂ and B ₂ (C ₂ and D ₂ ) need to be turned off at the same time , at this time, the current is transferred from the mechanical switch branch to the main circuit breaker branch, and the main circuit breaker A ₁ and B ₁ (C ₁ and D ₁ ) branches on the double bridge arm are connected in series as the current flow branch. When the solid-state switch group with anti-parallel diodes connected in series on the branch of the main circuit breaker triggers shutdown (then the mechanical switches A ₇ and B ₇ (C ₇ and D ₇ ) are closed); the remaining energy can be connected in series along the main circuit breaker in one direction The reverse diodes connected in parallel at both ends of the solid-state switch group flow (when energy is transmitted from the left port to the right port, the remaining energy flows through the reverse diode connected in parallel with the solid-state switch group of the second bridge arm; when the energy is transmitted from the right port to the left port , the remaining energy flows from the reverse diode connected in parallel with the solid-state switch group of the first bridge arm); finally, the remaining energy is released by the non-linear resistor A ₅ or B ₅ (C ₅ or D ₅ ).

The following is an example of the action of the hybrid DC circuit breaker when the energy flows in one direction, and specifically describes the breaking process and closing process of the hybrid DC circuit breaker, as shown in Figure 2:

1. The opening process of the hybrid DC circuit breaker:

(1) In the normal operation of the system, the mechanical switches A ₃ and B ₃ are both in the closed state, the bidirectional load transfer switches A ₂ and B ₂ are in the open state, and the main circuit breaker branch solid state switches A ₁ and B ₁ are in the open state, In order to prevent the direct current, the mechanical switches A ₇ and B ₇ are both in the off state;

( ₂ ) During normal operation, the DC current passes through the branches of the mechanical switches A3 and _B3 , that is, the mechanical switches A3 and _B3 are in the closed state, and the load transfer switches A2 and _B2 are in the open state. _The current flow path is shown in Figure ₄ shown;

( ₃ ) When the fault current is detected, the fault current rises rapidly, and the current flow path is shown in Figure 5. When the fault current reaches the turn _- off threshold of the bidirectional load transfer switch A2 and B2, the bidirectional load transfer switch is triggered immediately A ₂ and B ₂ are turned off, and the fault current is forcibly transferred to the branches of the main circuit breaker A ₁ and B _1. When the main current branch decreases to zero, the fast mechanical switches A ₃ and B ₃ act, and the fast mechanical switch A ₃ and B ₃ can be turned on at zero current, and the current flow path is shown in Figure 6;

(4) When the mechanical switches A ₃ and B ₃ are opened to a certain opening distance, that is, when the insulation strength of the mechanical switches A ₃ and B ₃ can withstand the overvoltage when they are turned off, a primary voltage isolation is formed, and the solid state of the main circuit breaker branch The switch group A ₁ and B ₁ accept the shutdown command to cut off the short-circuit fault current;

(5) After the solid-state switch group A ₁ (B ₁ ) of the main circuit breaker is turned off, the fault current starts to charge the buffer capacitor C _Q , and the voltage at both ends of the solid-state switch of the main circuit breaker rises rapidly, as shown in Figure 7;

(6) When the voltage at both ends of the snubber capacitor increases to the DC side voltage, the switches A ₇ and B ₇ are closed, and the freewheeling diode group is turned on at the same time, and the remaining inductive energy on the line is discharged nonlinearly through the freewheeling discharge circuit Resistor A ₅ (B ₅ ) discharges, the current gradually decreases to the level of the leakage current, and the breaking is completed. The current flow path is shown in Figure 8.

The above is the breaking process of the circuit breaker. The current flowing through each branch of the circuit breaker during the breaking process is shown in Figure 14(a). I ₀ is the current of the load transfer branch, and I ₁ is the current flowing through the main circuit breaker branch , I ₂ is the current flowing through the two ends of the freewheeling diode group; a fault occurs at t ₀ , and the fault current rises rapidly. When the fault current rises to I _P1 , that is, at t ₁ , the bidirectional load transfer switch is triggered to turn off, and the current is transferred from the load The branch is transferred to the branch of the main circuit breaker. When the fault current rises to I _P2 , that is, at time _t2 , it is triggered to shut down the main circuit breaker branch. On the branch of the main circuit breaker, the solid-state switch group with anti-parallel diodes is connected in series in one direction, and the fault current flows from the main circuit breaker The branch is transferred to the energy freewheeling absorption circuit, and t ₂ ~ t ₃ is the process of energy release and absorption. Fig. 14(b) shows the change process of the main circuit breaker branch voltage (U ₁ ) and the voltage (U ₂ ) at both ends of the freewheeling diode group when the circuit breaker is disconnected.

2. The closing process of the hybrid DC circuit breaker:

(1) Open the switches A ₇ and B ₇ first before closing, if the voltage across the freewheeling diode group A ₄ and B ₄ rises (that is, the voltage across the switches A ₇ and B ₇ rises), it proves that the fault has been eliminated; otherwise, The fault is not eliminated, and the closing process is suspended;

(2) Since the equivalent resistance ∑(R _Q ) of the solid-state switch in the branch circuit of the main circuit breaker is much smaller than the equivalent resistance ∑(R _D ) of the freewheeling diode in parallel, after the switch A ₇ and B ₇ are turned on, the freewheeling diode The two ends of group A ₄ (B ₄ ) bear most of the DC side voltage, and the main circuit breaker branch bears a small voltage; then the solid-state switch group with anti-parallel diodes connected in series on the main circuit breaker can be turned on under small voltage A ₁ and B ₁ , the current flow path is shown in Figure 9;

(3) Close the fast mechanical switches A ₃ and B ₃ after a certain delay, at this time, the bidirectional load changeover switch A ₂ (B ₂ ) only bears the solid-state load of the unidirectional series connection with anti-parallel diodes on the branch of the main circuit breaker A ₁ (B ₁ ). The conduction voltage drop of the switch group;

(4) After a certain delay, turn on the bidirectional load transfer switches A ₂ and B ₂ , the current flow path is shown in Figure 10, and the current is transferred from the branches of the main circuit breaker A ₁ and B ₁ to the bidirectional load transfer switches A ₂ and B ₂ At this time, the voltage across the two ends of the bidirectional load transfer switch A ₂ and B ₂ is its own conduction voltage drop, and the closing is completed.

The above is the closing process of the circuit breaker. Figure 15(b) shows the change process of the branch voltage (U ₁ ) of the main circuit breaker and the voltage (U ₂ ) at both ends of the freewheeling diode group during closing. At time t ₄ , switch A is turned on ₇ and B ₇ , since the equivalent resistance Σ(R _Q ) of the solid-state switch in the main circuit breaker branch is much smaller than the equivalent resistance Σ(R _D ) of the freewheeling diode group, the freewheeling diode group A ₄ (B ₄ ) (that is, the two ends of switch A ₇ (B ₇ )) bear most of the DC side voltage, and the solid-state switch group of the main circuit breaker branch is opened at time t ₅ , which can realize the zero-voltage opening of the solid-state switch group of the main circuit breaker branch (Zero Voltage Switching, ZVS), the fast mechanical switches A ₃ and B ₃ are closed within t ₅ ~ t ₆ , and the two-phase load transfer switches A ₂ and B ₂ are turned on at t ₆ , the starting current is transferred from the main circuit breaker branch to Load transfer branch. Figure 15(a) is the current change process of each branch at the corresponding time, I ₀ is the current flowing through the load transfer branch, I ₁ is the current flowing through the main circuit breaker branch, I ₂ is the current flowing through the freewheeling diode group A ₄ (B ₄ ) current (I ₂ is always zero during closing).

The control strategy of the hybrid DC circuit breaker: (1) Control strategy when opening: the flow of the control strategy is shown in Figure 3(a). When the instantaneous value of the DC system current exceeds the threshold value of the bidirectional load transfer switch A ₂ and B ₂ or when the line is actively cut off, the bidirectional load transfer switch A ₂ and B ₂ turn off the current and transfer it to the main circuit breaker A ₁ and B ₁ branch, When it is detected that the current flowing through the fast mechanical switches A ₃ and B ₃ is zero, the fast mechanical switches A ₃ and B ₃ are quickly opened, and when the fast mechanical switches A ₃ and B ₃ reach a certain opening distance, the main circuit breaker A is triggered ₁ and B ₁ branch solid-state switch groups are turned off, and when the main circuit breaker branch current is zero, the mechanical switches A ₇ and B ₇ are quickly closed; (2) control strategy when closing: the control strategy flow is shown in Figure 3(b) shown. Turn on the switches A ₇ and B ₇ , if the voltage across the freewheeling diode group A ₄ (B ₄ ) rises rapidly (that is, the voltage across the switch A ₇ (B ₇ ) rises rapidly), then turn on the main circuit breakers A ₁ and B in turn ₁ branch solid-state switch group, fast mechanical switches A ₃ and B ₃ , bi-directional load transfer switches A ₂ and B ₂ . If the voltage across the freewheeling diode group A ₄ (B ₄ ) does not rise, the closing process of the circuit breaker is suspended.

The dual-arm structure fast hybrid DC circuit breaker can close, carry and break current under normal circuit conditions, and can close, carry and break abnormal circuit conditions (including short circuit conditions) within a specified time The lower current improves the practical engineering applicability. By changing the number of power electronic switches connected in series in the branches of the main circuit breaker, the number of series connected freewheeling diodes and the selection of non-linear resistors, the voltage level of the circuit breaker breaking current can be changed.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (7)

1. the topological structure of the quick mixed type dc circuit breaker of a kind of both arms framework, it is characterised in that in Bridge 1 arm, main Breaker A₁Unidirectional solid-state switch group of the series connection with anti-paralleled diode of branch route is constituted, and primary current leg is opened by Quick mechanical Close A₃With two-way load transfer solid-state A₂Switch is in series, and energy afterflow absorption circuit is by a non-linear bleeder resistance A₅With Fly-wheel diode group A₄Series connection, and in A₄One in parallel of two ends are by diode A₆With Fast mechanical switch A₇Constitute series arm； In Bridge 2 arm, main circuit breaker B₁Unidirectional solid-state switch group of the series connection with anti-paralleled diode of branch route is constituted, primary current leg By Fast mechanical switch B₃With two-way load transfer solid-state switch B₂In series, energy afterflow absorption circuit is non-linear by one Bleeder resistance B₅With fly-wheel diode group B₄Series connection, and in B₄One in parallel of two ends are by diode B₆With Fast mechanical switch B₇Composition Series arm；Double arm paths pass through the connected N of current-limiting reactor L in back-to-back form₁And N₂, 1 end and 2 ends are connected directly respectively Drift net positive pole and negative pole, 3 ends and 4 ends connect opposite side direct current net positive pole and negative pole respectively；In main circuit breaker branch road A₁、B₁In, often The equal parallel connection buffer electric capacity C of one solid-state switch pipe_QWith resistance R_Q；In fly-wheel diode group A₄、B₄In each fly-wheel diode it is equal Parallel resistance R_D, wherein R_Q＜ ＜ R_D。

2. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In, in the case of normally on doube bridge arm primary current leg series connection collectively as principal current circulation branch road, during failure simultaneously Turn off two-way load transfer switch A on doube bridge arm₂And B₂, fault current is transferred to the unidirectional series connection being connected in parallel and carried instead simultaneously The solid-state switch group A of di- pole pipe₁And B₁Branch road；When primary current leg electric current is reduced to zero, rapid shut-off mechanical isolation switch A₃ And B₃, mechanical isolation switch contact non-arc breaking from.

3. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In, when mechanical switch open to it is specified open away from when, so as to protect two-way load transfer switch A₂And B₂, it is it in integrated circuit Set up primary voltage isolation；Unidirectional solid-state switch group A of the series connection with anti-paralleled diode of rapid shut-off simultaneously₁And B₁, subsequent machine Tool switchs A₇And B₇Closure, non-linear bleeder resistance A is transferred to by fault current₅(B₅) loop.

4. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In, when electric current is from left port port transmission to the right, dump energy main circuit breaker B from Bridge 2 arm₁Branch road solid-state switch group Reverse parallel connection fly-wheel diode circulates, finally the nonlinear resistance A in Bridge 1 arm₅Release；Conversely, dump energy is from Bridge 1 arm The reverse parallel connection fly-wheel diode circulation of middle main circuit breaker branch road solid-state switch group, finally, the nonlinear resistance B in Bridge 2 arm₅ Release, reach solution overvoltage and absorb energy purpose, so as to realize that DC current is turned off.

5. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In, when breaker need recover normal work when, pass through controlling switch A₇And B₇Cut-off to detect A₅And B₅Both end voltage judges straight Whether stream side failure is eliminated, due to main circuit breaker branch road solid-state switch equivalent resistance R in parallel_QMuch smaller than fly-wheel diode simultaneously The equivalent resistance R of connection_D, therefore most DC voltages are born at fly-wheel diode group two ends, it is possible to achieve main circuit breaker branch The no-voltage of road solid-state switch group is open-minded, if short trouble is not eliminated, and fly-wheel diode group both end voltage will not rise, So that N₁And N₂In ground potential；When DC side failure, which is eliminated rear breaker, needs to recover normal work, open successively main disconnected Unidirectional solid-state switch group A of the series connection with anti-paralleled diode on the device of road₁And B₁, Quick mechanical disconnecting switch A₃And B₃, it is two-way negative Carry change-over switch A₂And B₂。

6. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In described main circuit breaker A₁And B₁Unidirectional solid-state switch group of the series connection with inverse parallel fly-wheel diode is taken, by turning off A₁ And B₁Fault current is transferred to by non-linear bleeder resistance A₅(B₅) and fly-wheel diode group A₄(B₄) composition energy release back Road.

7. a kind of quick mixed type direct-current breaker topology structure of both arms framework according to claim 1, its feature exists In the nonlinear resistance A in dump energy afterflow link, bridge arm₅And B₅Voltagerating be much smaller than the overall specified electricity of direct current network Grade is pressed, while only by current-limiting reactor L, storage energy is determined the capacity that consumes energy after main circuit breaker cuts off fault current, residual energy Amount is absorbed and overvoltage protection is mainly completed by non-linear bleeder resistance.