CN114530836B - Bidirectional direct current fault current limiter based on coupling inductor and control method thereof - Google Patents

Abstract

The invention discloses a bidirectional direct current fault current limiter based on a coupling inductor and a control method thereof, wherein the bidirectional direct current fault current limiter comprises the coupling inductor, a discharge loop module and an energy absorption module; the coupling inductor is used for limiting the rise of fault current; the discharging loop module consists of a pre-charging capacitor and a current-limiting trigger switch module; the energy absorption module comprises a diode and a metal oxide lightning arrester; the coupling inductor is of a three-winding structure, a primary winding is connected in series with a main circuit and plays a role in limiting current, and a secondary winding is provided with two windings and is respectively used for limiting forward fault current and reverse fault current; the current-limiting trigger switch module is formed by connecting thyristors in series and comprises a forward switch and a reverse switch. According to the invention, only the primary winding of the coupling inductor is connected in series with the main circuit, the on-state loss is low, and only a half-control device is used, so that the cost is reduced; the pre-charging capacitor is used for discharging, a large reverse voltage is generated in the coupling inductor, the fault current can be reduced to a lower level in a short time, the fault clearing time is shortened, and the cost of the control module is reduced.

Description

A bidirectional DC fault current limiter based on coupled inductors and its control method

technical field

The invention relates to the technical field of high-voltage direct current transmission fault current limiters, in particular to a bidirectional direct current fault current limiter based on coupled inductance and a control method thereof.

Background technique

The application of flexible direct current transmission system is more and more extensive, but its development is subject to many restrictions, among which the fault clearing method of flexible direct current transmission system is a bottleneck. The DC side of the flexible DC transmission system contains a large capacitance, the short-circuit current rise rate of the system can reach 10kA/ms, and the current amplitude can even reach thousands of amperes, and because the DC system has a small damping, after a fault occurs on the DC side, the fault current The ascent is fast and can cause damage to equipment in the system. The flexible DC transmission system has high requirements on the breaking capacity of the DC circuit breaker, and will put forward stricter requirements on technology and investment. Therefore, it is necessary to study the DC fault current limiter to limit the fault current and achieve the purpose of reducing the pressure of the DC circuit breaker.

There are many topologies of DC fault current limiters that have been proposed, mainly divided into two categories: resistive current limiter and inductive current limiter. Among them, the resistive current limiter is mainly a superconducting current limiter, which uses the quenching of superconducting materials and presents the characteristics of large resistance to limit current, but requires a cooling system, which increases the volume and cost, and the recovery speed of superconducting materials is slow. The inductive current limiter is divided into: 1) Magnetic flux coupling type, which mainly uses the principle of electromagnetic induction to generate a magnetic field according to the current and change the inductance value so that it presents a large inductance for current limiting when a fault occurs. This scheme is the most widely used, The easiest to realize; 2) Saturated iron core type, using DC power supply or permanent magnet to provide a magnetic field to make the iron core enter a pre-saturation state, showing a small inductance value, when a fault occurs, the magnetic field generated by the fault current and the pre-saturation magnetic field cancel, and the iron core desaturation Thus presenting a large inductance value, the current limiter has a fast response speed, but the introduction of a DC power supply or a permanent magnet is costly and bulky; 3) The solid-state switch type is mainly based on power electronic devices for fault current transfer, and then uses current limiting The component performs current limiting, but a large number of power electronic devices are used, and the current limiter has high on-state loss and high cost. Therefore, it is necessary to propose a DC fault current limiter with better comprehensive performance.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a bidirectional DC fault current limiter based on coupled inductors and its control method, which has low conduction loss, good current limiting effect, only uses half-controlled devices, low cost, and simple control. Can significantly reduce fault current levels. The technical scheme is as follows:

A bidirectional DC fault current limiter based on a coupled inductor, including a coupled inductor, a discharge circuit module, and an energy absorption module;

The coupled inductor includes three windings, the primary winding is a current-limiting coil L ₁ connected in series to the main circuit to limit the rise of the fault current; the secondary winding has two windings: forward induction coil L ₂ and reverse induction coil L ₃ , respectively used to limit the forward fault current and reverse fault current;

The discharge circuit module includes a pre-charging capacitor C and a current-limiting trigger switch module; the current-limiting trigger switch module includes _two sets of thyristors in series, and a group of thyristors in series is used as a forward switch, and its anode is connected to the forward induction coil L2 The opposite end; another set of thyristors in series is used as a reverse switch, and its anode is connected to the end of the same name of the reverse induction coil L3 _; one end of the precharge capacitor C is connected to the end of the same name of the forward induction coil _L2 and the reverse induction coil Between the opposite ends of L ₃ , the other end is connected to the cathodes of two sets of thyristors in series at the same time, forming a forward fault discharge circuit and a reverse fault discharge circuit;

The energy absorbing module includes an energy absorbing branch composed of series diodes and metal oxide arresters, and the energy absorbing branch is connected in parallel to both ends of the pre-charging capacitor C.

Further, it also includes a hybrid DC circuit breaker used in conjunction with the current limiter, the hybrid DC circuit breaker includes a series fast mechanical switch and a current transfer switch, and a main break switch connected in series to the main circuit; fast The mechanical switch + current transfer switch, and the main break switch are also connected in parallel at both ends of the metal oxide arrester.

Furthermore, during normal operation: the precharge capacitor C is charged to the system voltage through the grounding resistor, the normal operating current flows through the current-limiting coil L ₁ on the primary side of the coupled inductor, and the current-limit trigger switch is locked:

In the event of a DC system failure:

S1: After detecting a fault, judge whether the fault is a forward fault or a reverse fault;

S2: After fault detection and judgment, select the forward switch or reverse switch of the current-limiting trigger switch according to the fault direction;

S3: The pre-charge capacitor C starts to discharge, and the discharge current flows into the forward induction coil L ₂ or the reverse induction coil L ₃ on the secondary side of the coupled inductor, and an induced voltage opposite to the system voltage is generated in the current-limiting coil L ₁ to suppress Fault current rises;

S4: After the DC circuit breaker cuts off the fault, the fault current begins to drop, and the capacitor is discharged and reversely charged. When the reverse charging voltage of the capacitor reaches the operating voltage of the metal oxide arrester, the energy absorption module is turned on, and the capacitor and the part of the DC system remain Energy is absorbed by energy absorbing modules.

Furthermore, in S1 and S2, after detecting a fault, open the current transfer switch of the hybrid DC circuit breaker, and simultaneously judge whether the fault is a forward fault or a reverse fault, and if it is forward, turn on the forward switch module; Reverse, turn on the reverse switch module; where the fault current rise characteristic is:

Among them, if is the fault current, V _dc is the _{DC voltage, R dc is} the line resistance, I _N is the normal operating current of the system, τ ₁ is the line charging time constant, which is determined by formula (2); L is the limit of the current limiter Inductance value of the current winding, L _line is the line inductance; t ₀ is the time when the fault occurs, and t is any time after the fault occurs and before the action of the protection device;

The value of the induced voltage in the S3 is:

为放电电流在一次侧的磁通量。Among them, v _LM is the induced voltage, N _L the number of turns of the current-limiting winding,

is the magnetic flux on the primary side of the discharge current.

The beneficial effects of the present invention are: the present invention only couples the primary winding of the inductor in series with the main circuit, the on-state loss is low, only half-controlled devices are used, thereby reducing the cost; the discharge of the pre-charged capacitor is used to generate a large reverse in the coupled inductor Voltage, can reduce the fault current to a lower level in a short time, shorten the fault clearing time, and the control logic is simple, reducing the cost of the control module.

Description of drawings

Figure 1 is a schematic circuit diagram of a bidirectional DC fault current limiter based on coupled inductors.

Fig. 2 is a control flow chart of a bidirectional DC fault current limiter based on a coupled inductor.

Figure 3 is a circuit schematic diagram of a hybrid DC circuit breaker.

Fig. 4 is a simulation result diagram of a bidirectional DC fault current limiter based on a coupled inductor.

Fig. 5 is a diagram of the bidirectional current limiting simulation result of a bidirectional DC fault current limiter based on a coupled inductor.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a bidirectional DC fault current limiter based on a coupled inductor includes a coupled inductor, a discharge loop module, and an energy absorbing module; the coupled inductor is used to limit the rise of the fault current; the discharge loop module consists of a precharge capacitor, a The current trigger switch module; the energy absorbing module includes a series diode and a metal oxide arrester (MOV), and is connected in parallel to both ends of the pre-charging capacitor C.

The coupled inductor has a three-winding structure. The primary winding is a current-limiting coil L ₁ connected in series to the main circuit to limit the rise of the fault current; the secondary winding has two windings: forward induction coil L ₂ and reverse induction coil L ₃ , which are used to limit the forward fault current and reverse fault current respectively.

The discharge circuit module includes a pre-charging capacitor C and a current-limiting trigger switch module; the current-limiting trigger switch module includes _two sets of thyristors in series, and a group of thyristors in series is used as a forward switch, and its anode is connected to the forward induction coil L2 The opposite end; another group of thyristors in series is used as a reverse switch, and its anode is connected to the same end of the reverse induction coil L3 _; one end of the precharge capacitor C is connected to the same end of the forward induction coil _L2 and the reverse induction coil Between the opposite ends of L ₃ , the other end is simultaneously connected to the cathodes of two sets of thyristors connected in series to form a forward fault discharge circuit and a reverse fault discharge circuit.

The current limiter cooperates with the hybrid DC circuit breaker connected in series to the main circuit. The action flow after the fault is shown in Figure 2, and the circuit schematic diagram of the hybrid DC circuit breaker is shown in Figure 3. The hybrid DC circuit breaker includes A fast mechanical switch and a current transfer switch connected in series, and a main break switch connected in series to the main circuit; a fast mechanical switch + a current transfer switch, and a main break switch are also connected in parallel at both ends of the metal oxide arrester.

In the event of a DC system failure:

a) Perform fault detection. After detecting the fault, turn on the current transfer switch of the hybrid DC circuit breaker, and judge whether the fault is a forward fault or a reverse fault. If it is forward, turn on the forward switch module; if it is reverse, turn it on Reverse switch module; where the fault current rise characteristic is:

Among them, if is the fault current, V _dc is the _{DC voltage, R dc is} the line resistance, I _N is the normal operating current of the system, τ ₁ is the line charging time constant, which is determined by formula (2), and L is a coupling inductor based The current-limiting winding inductance of the bidirectional DC fault current limiter, L _line is the line inductance, t ₀ is the time when the fault occurs, and t is any time after the fault occurs and before the protection device operates.

b) The capacitor starts to discharge, and the discharge current flows into the secondary side of the coupled inductor, and an induced voltage opposite to the system voltage is generated in the primary winding of the coupled inductor, thereby suppressing the rise of the fault current. The induced voltage value is:

为放电电流在一次侧的磁通量。该感应电压的大小决定了限流效果。Among them, v _LM is the induced voltage, N _L the number of turns of the current-limiting winding,

is the magnetic flux on the primary side of the discharge current. The magnitude of the induced voltage determines the current limiting effect.

c) After a certain current-limiting time, turn on the main break switch of the hybrid DC circuit breaker, and the fault current begins to drop;

d) After the DC circuit breaker cuts off the fault, the fault current begins to drop, and the capacitor is discharged and reversely charged. When the reverse charge voltage of the capacitor reaches the MOV operating voltage, the energy absorption module is turned on, and part of the remaining energy of the capacitor and the DC system is converted by the energy The simulation results of absorbing and current limiting effects of the absorbing module are shown in Figure 4, and the simulation results of bidirectional current limiting effects are shown in Figure 5. It can be seen that the peak value of the fault current is reduced by 51.2%, and the fault clearing time is reduced by 48.6%.

Claims (4)

1. A bidirectional direct current fault current limiter based on a coupling inductor is characterized by comprising the coupling inductor, a discharge loop module and an energy absorption module;

the coupling inductor comprises three windings, and the primary winding is a current-limiting coil L connected in series with the main circuit ₁ For limiting the rise of the fault current; the secondary winding has two windings: forward direction induction coil L ₂ And a reverse induction coil L ₃ For limiting forward fault current and reverse fault current, respectively;

the discharging loop module comprises a pre-charging capacitor C and a current-limiting trigger switch module; the current-limiting trigger switch module comprises two groups of thyristors which are connected in series and one group of thyristors which are connected in seriesThe tube acts as a forward switch, the anode of which is connected to the forward induction coil L ₂ The synonym end of (2); another group of thyristors connected in series as a reverse switch having their anodes connected to a reverse induction coil L ₃ The same name end of (1); one end of a pre-charging capacitor C is connected to the forward induction coil L ₂ End of same name and reverse induction coil L ₃ The other end of the positive-polarity-difference-voltage power supply is connected to the cathodes of two groups of thyristors in series connection to form a positive fault discharge loop and a reverse fault discharge loop;

the energy absorption module comprises an energy absorption branch consisting of a diode and a metal oxide arrester which are connected in series, and the energy absorption branch is connected in parallel with two ends of the pre-charging capacitor C.

2. The coupled inductance based bidirectional dc fault current limiter of claim 1 further comprising a hybrid dc circuit breaker for use with said current limiter, said hybrid dc circuit breaker including a fast mechanical switch and a current transfer switch in series, and a main disconnect switch in series into a main circuit; the quick mechanical switch, the current transfer switch and the main breaking switch are also connected in parallel at two ends of the metal oxide lightning arrester.

3. A method for controlling a coupled inductor based bidirectional dc fault current limiter according to claim 2, comprising:

when the normal work is carried out: the pre-charging capacitor C is charged to the system voltage through the grounding resistor, and the normal operation current flows through the current-limiting coil L on the primary side of the coupling inductor ₁ And current-limiting trigger switch locking:

when the direct current system fails:

s1: after the fault is detected, judging whether the fault is a forward fault or a reverse fault;

s2: after fault detection and judgment, a forward switch or a reverse switch of the current-limiting trigger switch is selected to be switched on according to the fault direction;

s3: the pre-charging capacitor C begins to discharge, and the discharge current flows into the positive induction coil L of the secondary side of the coupling inductor ₂ Or a reverse induction coil L ₃ At the current limiting coil L ₁ Generating an induced voltage in a direction opposite to a system voltage to suppress a fault current from rising;

s4: after the direct current breaker breaks down, the fault current begins to drop, the capacitor finishes discharging and reversely charges, when the reverse charging voltage of the capacitor reaches the action voltage of the metal oxide arrester, the energy absorption module is conducted, and the capacitor and part of residual energy of the direct current system are absorbed by the energy absorption module.

4. The control method according to claim 3, wherein in S1 and S2, after detecting the fault, the current transfer switch of the hybrid dc circuit breaker is turned on, and meanwhile, whether the fault is a forward fault or a reverse fault is determined, and if the fault is a forward fault, the forward switch module is turned on; if the direction is reverse, the reverse switch module is conducted; the fault current rise characteristic is as follows:

wherein i _f For fault current, V _dc Is a direct voltage, R _dc Is a line resistance, I _N For normal operating current of the system, τ ₁ Is the line charging time constant, determined by equation (2); l is the inductance of the current-limiting winding of the current limiter, L _line Is a line inductance; t is t ₀ The moment when the fault occurs, t is any moment after the fault occurs and before the protection device acts;

the induced voltage value in S3 is as follows:

wherein v is _L-M To induce a voltage, N _L Current limitingThe number of winding turns is set,

is the magnetic flux of the discharge current at the primary side.

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