CN106099878A - A kind of electric capacity charge type bidirectional, dc chopper and application thereof - Google Patents

Abstract

The invention discloses a capacitor charging type bidirectional DC circuit breaker, which comprises a parallel auxiliary branch circuit and a main branch circuit, wherein the auxiliary branch circuit is composed of a first mechanical switch and a power electronic device valve group connected in series, and the main branch circuit is formed by a single-phase uncontrollable circuit breaker. Combination of rectifier bridge and capacitor-mechanically switched capacitor series branch. The invention also discloses a DC circuit breaker, the main branch is formed by reverse parallel connection of two capacitance series branches with the same structure, one of the capacitance series branches is composed of a mechanical switch, a DC capacitor and a diode valve group in series, and the other The structure of a capacitor series branch is the same as that of the first capacitor series branch, and the connection mode is reversed. The invention also discloses a control method for fault isolation and fast reclosing of the DC circuit breaker. The invention can avoid the defect that the DC capacitance and the line inductance of the current DC circuit breaker are easy to form inductance-capacitance oscillation, and it can break the DC fault current stably and reliably, and can realize fast reclosing.

Description

A Capacitor Charging Bidirectional DC Circuit Breaker and Its Application

technical field

The invention belongs to the technical field of electric power transmission and distribution, and more specifically relates to a capacitor charging bidirectional DC circuit breaker and its application in DC fault isolation.

Background technique

With the development of modular multilevel converters, the use of modular multilevel converters to construct DC power grids has become a hot spot in the power industry in recent years. The DC power grid needs to interconnect the DC transmission lines on the DC side. When a DC fault occurs, it is necessary to quickly isolate the faulty line to avoid the voltage collapse of the DC grid. For this reason, the DC circuit breaker is an indispensable device for large-scale DC power grids.

The solid-state switching DC circuit breaker is a typical DC circuit breaker, which is composed of a large number of fully-controlled power electronic devices in series. This DC circuit breaker can break the DC fault current at a very fast speed, which can be as fast as hundreds Subtle, but the main defect of this solution is that due to the need for a large number of fully controlled power electronic devices, its cost is high, the conduction loss is high, and the series/parallel connection of multiple fully controlled power electronic devices brings voltage equalization/equalization flow difficulties.

In order to overcome the high loss defect of the solid-state switching DC circuit breaker, there is a hybrid high-voltage DC circuit breaker in the prior art, which is mainly composed of an auxiliary branch and a solid-state switching branch in parallel, wherein the auxiliary branch is composed of a fully-controlled electric power Electronic devices and fast mechanical switches are connected in series, and the solid-state switch branch is basically the same as the solid-state switch DC circuit breaker, which is composed of a large number of fully-controlled power electronic devices connected in series. During normal operation, the auxiliary branch and the solid-state switch branch are in the conduction state at the same time. Since the on-resistance of the solid-state switch branch is much higher than that of the auxiliary branch, the DC current mainly flows through the auxiliary branch, and the current on the solid-state switch branch is almost is zero, so that the hybrid high-voltage DC circuit breaker overcomes the defect of high loss of the solid-state switching DC circuit breaker. When breaking the DC fault current, the auxiliary DC fully-controlled power electronic device will be turned off first to transfer the DC current to the solid-state switch branch, and then the solid-state switch branch and its parallel arrester will isolate the DC fault current. This hybrid HVDC breaker has the advantage of low losses, but is more expensive than a solid-state switching branch because it still contains a solid-state switching branch, and its solid-state switching branch absorbs a lot of energy during shutdown , so that the solid-state switching branch cannot perform continuous shutdown operations in a short period of time, so the hybrid high-voltage DC circuit breaker does not have the ability to quickly reclose, resulting in a slow power supply speed after the fault is restored.

Patent document WO2013/093066A discloses a hybrid high-voltage DC circuit breaker, as shown in Figure 1, which includes a main branch 24 and an auxiliary branch 28, wherein the main branch 24 includes a mechanical switch 3 and a power electronic circuit breaker connected in series. Device valve group 4 , auxiliary branch 28 is connected in parallel with main branch 24 , which includes capacitor 5 . This type of DC circuit breaker realizes the isolation of DC faults by transferring the fault current to the capacitor 5 in the event of a DC fault. It can overcome the defects of high cost of the main branch of the conventional hybrid high-voltage DC circuit breaker. The current inductance 2 and the capacitor 5 form a series circuit. On the one hand, there is an inductance-capacitance resonance during the breaking of the fault current, and it takes a long time to turn off the DC fault current. Charged to a high-voltage state, it is necessary to discharge the capacitor 5 before reclosing can be realized, and it takes a certain time to discharge the capacitor 5, so the above scheme cannot realize fast reclosing, and its power electronic device valve group 4 is all controlled by a fully controlled Composition of power electronic devices, the cost of the valve group 4 of power electronic devices is relatively high.

The patent document CN105656019A discloses a capacitor charging type DC circuit breaker, which includes a parallel auxiliary branch and a main branch, wherein the auxiliary branch is composed of a first mechanical switch and a valve group of power electronic devices connected in series, and the main branch is composed of a DC capacitor and a main branch. The diode valve group is connected in series to isolate the DC fault current through the charging effect of the DC current on the DC capacitor during the DC fault. When reclosing, the reclosing command is issued only when it is detected that the DC voltage on the line side of the DC circuit breaker is higher than a certain threshold. The invention can avoid the defect that the DC capacitance and the line inductance of the current DC circuit breaker are easy to form inductance-capacitance oscillation, and it can break the DC fault current stably and reliably, and can realize fast reclosing.

However, in this scheme, since the DC fault current can only charge DC in one direction, it can only isolate the DC fault on the line side of the DC circuit breaker, and there is a problem that it cannot isolate the DC fault on the DC bus side, and it cannot be connected to the same DC bus. The other DC lines provide backup protection.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a capacitor-charging bidirectional DC circuit breaker. By improving the structure of the hybrid high-voltage DC circuit breaker, the current DC circuit breaker capacitor can be avoided when isolating a DC fault. It is easy to form the defect of inductance-capacitance oscillation with the line inductance, and it can isolate the DC fault on the DC bus side, and it can break the DC fault current stably and reliably. At the same time, it can also provide backup protection for other DC lines connected to the same DC bus.

In order to achieve the above object, according to one aspect of the present invention, a capacitor charging type bidirectional DC circuit breaker is provided, which includes an auxiliary branch circuit and a main branch circuit connected in parallel, wherein the auxiliary branch circuit includes a power electronic device valve group, The DC current flowing through the branch circuit when the DC circuit breaker is normally turned on; the main branch is composed of a single-phase uncontrollable rectifier bridge and a capacitor-mechanical switch branch composed of a DC capacitor connected in series with a mechanical switch, wherein the The input ports of the uncontrolled rectifier bridge are respectively connected to two ports of the auxiliary branch, and the capacitor-mechanical switch series branch is connected in series between the high and low voltage DC ports of the uncontrolled rectifier bridge.

In this scheme, the auxiliary branch has the function of bidirectionally isolating the DC fault current. The input port of the uncontrolled rectifier bridge of the main branch is respectively connected with the two ports of the auxiliary branch, and the high and low voltage of the uncontrolled rectifier bridge The DC capacitors are connected in series between the DC ports, so that when a DC fault occurs on the line side or the bus side, the DC capacitor can be charged; in the normal closed state, the auxiliary branch is in a closed state, and the DC current flows through the auxiliary branch to isolate the DC fault When the current is flowing, the power electronic device valve group will be turned off first to transfer the DC current to the main branch, and the DC current will charge the DC capacitor. When the DC capacitor voltage is higher than the non-fault side DC voltage, the DC current will begin to drop. and eventually drop to zero. This scheme is used to divert the fault current to the branch when it is necessary to break the DC fault current. When the voltage at both sides of the capacitor is higher than the DC voltage at the busbar side of the DC circuit breaker, the DC current starts to drop and finally drops to zero. The single-phase uncontrollable rectifier bridge can realize the bidirectional current flow capability of the main branch, and can prevent the DC current from falling to zero and further becoming a negative value, which will cause the capacitor and the line inductance to form an inductance-capacitance oscillation.

As a further preference of the present invention, a discharge branch is connected in parallel on both sides of the capacitor of the main branch for discharging the capacitor before reclosing the DC circuit breaker.

As a further preference of the present invention, the discharge branch includes a mechanical switch and a resistor connected in series.

As a further preference of the present invention, there are multiple discharge branches connected in parallel.

As a further preference of the present invention, the valve group of the power electronic device in the auxiliary branch is composed of an anti-parallel fully-controlled power electronic device and an anti-parallel thyristor connected in series.

As a further preference of the present invention, a third branch is connected in parallel to the auxiliary branch and the main branch of the DC circuit breaker, and the third branch is composed of one lightning arrester or a combination of multiple lightning arresters in series and/or in parallel.

As a further preference of the present invention, a DC current limiting inductor is connected in series outside the parallel circuit formed by the main branch circuit and the auxiliary branch circuit of the DC circuit breaker, so as to limit the rising rate of the DC fault current.

As a further preference of the present invention, a capacitor is additionally connected in parallel on the line side of the DC circuit breaker to reliably determine whether the DC fault is cleared, so as to be used for reclosing.

As a further preference of the present invention, the auxiliary branch further includes a first mechanical switch, and the first mechanical switch is connected in series with the valve group of the power electronic device to form the auxiliary branch.

As a further preference of the present invention, a second mechanical switch is connected in series to the outside of the parallel circuit composed of the main branch circuit and the auxiliary branch circuit of the DC circuit breaker, which is used to connect the DC power supply and the DC circuit breaker after breaking the DC current. A reliable insulation gap is established between them to prevent the DC voltage on the busbar side from being continuously applied to the arrester of the third branch.

As a further preference of the present invention, the power electronic device valve group of the auxiliary branch is composed of a fully controlled power electronic device (such as an insulated gate bipolar transistor) that can be turned off quickly and other power electronic devices with a slower speed such as a thyristor. , turn-off thyristors, etc. are connected in series, and the above scheme can greatly reduce the cost of the auxiliary branch.

As a further preference of the present invention, a resistor is connected in series to the extra parallel capacitor.

According to another aspect of the present invention, there is provided a method for isolating DC faults using the DC circuit breaker, wherein the method includes shutting off the power electronic valve group of the auxiliary branch circuit when a DC fault occurs, thereby dissipating the fault current Transfer to the main branch circuit to charge the DC capacitor, and when the voltage of the DC capacitor is higher than the DC voltage on the bus side of the DC circuit breaker, the fault current is extinguished to realize DC fault isolation. Or when a DC fault occurs, the valve group of the power electronic device in the auxiliary branch is first turned off, and then the first mechanical switch on the auxiliary branch is turned on.

As a further preference of the present invention, the first mechanical switch on the auxiliary branch is turned on and after the DC current drops to zero, the second external mechanical switch connected in series is turned on.

According to another aspect of the present invention, there is provided a reclosing method after DC fault isolation using the above-mentioned DC circuit breaker, wherein the method includes first closing the first mechanical switch on the auxiliary branch after receiving the reclosing command, Then open the valve group of the power electronic device; or, after receiving the reclosing command, first close the second mechanical switch connected in series outside the auxiliary branch, then close the first mechanical switch on the auxiliary branch, and finally open the power Electronic valve block.

According to another aspect of the present invention, there is provided a capacitor charging type bidirectional DC circuit breaker, which includes an auxiliary branch and a main branch connected in parallel, wherein the auxiliary branch includes a power electronic device valve group to serve as a DC circuit breaker DC current flows through the branch during normal conduction;

It is characterized in that the main branch is composed of two capacitor series branches with the same structure connected in reverse parallel, one of the capacitor series branches is composed of a mechanical switch, a DC capacitor and a diode valve group in series, and the other capacitor series branch is The structure is the same as that of the first capacitor series branch circuit element, and the wiring method is the same

According to another aspect of the present invention, there is provided a fast reclosing capacitor-charged bidirectional DC circuit breaker, which is used for fast reclosing operation without waiting for the charged capacitor to discharge after isolating a DC fault. It is characterized in that the DC circuit breaker is composed of auxiliary branch and main branch connected in parallel, among which,

The auxiliary branch is composed of a first mechanical switch and a bidirectional power electronic valve group connected in series to serve as a branch through which DC current flows during normal conduction;

The main branch is composed of a single-phase uncontrollable rectifier bridge and a plurality of capacitor series branches, wherein each group of capacitor series branches is formed by a fourth mechanical switch and a capacitor in series. The main branch is used to provide a fault path for the fault current after the auxiliary branch is turned off, so that the fault current charges the DC capacitor of the main branch. When the capacitor voltage is higher than the DC voltage of the non-fault side of the DC circuit breaker, the DC current begin to drop and eventually drop to zero for DC fault isolation. The single-phase uncontrollable rectifier bridge can realize the bidirectional current flow capacity of the main branch, so that when a DC fault occurs on either side of the DC circuit breaker, the DC circuit breaker can isolate the DC fault and prevent the DC fault after the DC current drops to zero. The DC current further becomes negative to prevent the capacitor from forming an inductance-capacitance oscillation with the line inductance,

When working normally, only the fourth mechanical switch of one group of capacitor series branches is in the closed state, and the mechanical switches of the remaining capacitor series branches are all in the off state, completing the first breaking of the DC fault After the current flow, the fourth mechanical switch that was originally in the closed state will be opened, and the fourth mechanical switch that was originally in the open state will be closed, so that the fast reclosing operation can be performed without waiting for the discharge of the charged capacitor to complete.

As a further preference of the present invention, a discharge circuit is connected in parallel to the capacitor in each capacitor series branch, and the fourth mechanical switch connected in series with the capacitor is disconnected before discharging the capacitor.

As a further preference of the present invention, the discharge circuit connected in parallel with the capacitor is formed by a third mechanical switch connected in series with a discharge resistor.

As a further preference of the present invention, a third branch is connected in parallel to the auxiliary branch and the main branch of the DC circuit breaker, and the third branch is formed by one lightning arrester or multiple lightning arresters connected in series or in parallel.

As a further preference of the present invention, a DC current limiting inductor is connected in series outside the parallel circuit formed by the main branch circuit and the auxiliary branch circuit of the DC circuit breaker, so as to limit the rising rate of the DC fault current.

As a further preference of the present invention, a second mechanical switch is connected in series to the outside of the parallel circuit composed of the main branch circuit and the auxiliary branch circuit of the DC circuit breaker, which is used to connect the DC circuit breaker and the DC system after breaking the DC current. A reliable insulation gap is established between them to prevent the DC voltage on the busbar side from being continuously applied to the arrester.

As a further preference of the present invention, the power electronic device valve group of the auxiliary branch is composed of fast full-control power electronic devices (such as insulated gate bipolar transistors) and other power electronic devices with slower speeds such as thyristors, which can be turned off Thyristors are connected in series, and each power electronic device is connected in anti-parallel so that the auxiliary branch has the ability to isolate bidirectional current.

As a further preference of the present invention, a capacitor is additionally connected in parallel on the line side of the DC circuit breaker to reliably determine whether the DC fault is cleared, so as to be used for reclosing.

As a further preference of the present invention, a resistor is connected in series to the extra parallel capacitor.

As another aspect of the present invention, a capacitor charging type bidirectional DC circuit breaker is provided, which includes a parallel auxiliary branch and a main branch, wherein,

The auxiliary branch is composed of a first mechanical switch and a valve group of bidirectional power electronic devices connected in series,

The main branch is composed of at least two capacitive series branches with the same structure connected in parallel in the direction, and each capacitive series branch is mainly composed of a DC capacitor and a diode valve group connected in series,

As a further preference of the above solution, a discharge branch is also connected in parallel at both ends of the DC capacitor;

As a further preference of the above solution, a fourth mechanical switch is connected in series outside the DC capacitor.

According to another aspect of the present invention, there is provided a method for isolating a DC fault using the fast reclosable DC circuit breaker, wherein the method includes first shutting off the valve group of the power electronic device when a DC fault occurs, and at the same time Send a breaking command to the mechanical switch on the auxiliary branch, and after the DC current in the DC line drops to zero, open one of the closed mechanical switches in the series combination to realize DC fault current isolation.

According to another aspect of the present invention, there is provided a method for using the fast reclosable DC circuit breaker to perform DC fault isolation and fast reclosing, wherein the method includes, after receiving a reclosing instruction, closing an initial Turn off the fourth mechanical switch, then close the first mechanical switch, and then open the valve group of the power electronic device to realize fast reclosing and restore the DC power supply.

As a further preference of the present invention, the reclosing command is not issued until the DC fault has been cleared.

As a further preference of the present invention, it is judged whether the DC fault has been cleared by detecting the DC voltage value on the line side of the DC circuit breaker. When the absolute value of the DC voltage on the line side of the DC circuit breaker is higher than a certain threshold, it is judged that the DC fault has been cleared. clear.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

(1) In the DC circuit breaker of the present invention, its main branch adopts a single-phase uncontrollable rectifier bridge and a mechanical switch-DC capacitor series combination scheme so that the main branch has bidirectional current flow capability, so that the present invention has bidirectional isolated DC Fault current capability, and the single-phase uncontrolled rectifier bridge eliminates the inductance-capacitance resonance problem existing in the process of breaking DC faults;

(2) In the DC circuit breaker of the present invention, the power electronic valve group of the auxiliary branch adopts a full-control type power electronic device valve group and a half-control type power electronic device valve group in series, thereby reducing the cost of the entire power electronic valve group , which greatly reduces the semiconductor cost of the auxiliary branch;

(3) In the DC circuit breaker of the present invention, the parallel combination of a plurality of "fourth mechanical switches-capacitors" replaces a single capacitor so that the designed DC circuit breaker has a fast reclosing capability, which greatly improves the recovery of power supply after the DC system fails. speed.

(4) Compared with conventional mechanical DC circuit breakers, the DC circuit breaker of the present invention does not generate arcs during the isolation of DC faults, thereby greatly improving the reliability of the DC circuit breaker for breaking DC fault currents.

Description of drawings

Figure 1 is an existing hybrid HVDC circuit breaker topology in which the main branch only consists of a single capacitor;

Figure 2 is another existing hybrid HVDC circuit breaker topology in which the main branch only consists of a single capacitor;

Fig. 3 is the topology of a capacitor charging type bidirectional DC circuit breaker according to an embodiment of the present invention;

Fig. 4 is a topology of a DC circuit breaker in which the main branch is combined with a single-phase uncontrollable rectifier bridge after connecting multiple capacitive series branches in parallel according to another embodiment of the present invention.

Fig. 5 is a DC circuit breaker topology in which capacitors are additionally connected in parallel on the line side of the DC circuit breaker according to another embodiment of the present invention;

Fig. 6 is the topology of a bidirectional capacitor charging DC circuit breaker in which the main branch is connected in reverse parallel by two "DC capacitor-diode valve group" series branches in another embodiment of the present invention;

Fig. 7 is a topology of a bidirectional capacitive charging DC circuit breaker without a first mechanical switch in the auxiliary branch according to another embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

FIG. 3 is a schematic diagram of a circuit structure of a capacitor charging bidirectional DC circuit breaker 1 according to an embodiment of the present invention. As shown in Figure 3, the DC circuit breaker 1 is mainly composed of an auxiliary branch 2 and a main branch 3 connected in parallel, wherein the auxiliary branch 2 is composed of a first mechanical switch 11 and a power electronic valve group 13 in series, and the main branch is composed of a capacitor 10. A combination of the fourth mechanical switch 9 and four diode valve groups 5a, 5b, 5c, 5d. Four diode valve groups 5a, 5b, 5c, 5d form a single-phase uncontrolled rectifier bridge, the input ends of the single-phase uncontrolled rectifier bridge are respectively connected with the two ports of the auxiliary branch 2, and the single-phase uncontrolled rectifier bridge The DC capacitor 10 is connected across the high and low voltage DC sides.

As shown in FIG. 3 , in order to prevent the capacitor voltage from rising too high, in a preferred embodiment, the auxiliary branch 2 and the main branch 3 can also be connected in parallel with a third branch formed by a lightning arrester 4 .

As shown in Figure 3, in order to prevent the DC voltage from being continuously applied to the arrester 4 to cause the arrester 4 to overheat due to leakage current, in a preferred embodiment, the outside of the parallel circuit formed by the auxiliary branch 2 and the main branch 3 can also be The second mechanical switch 15 is connected in series. In another embodiment, the second mechanical switch 15 is connected in series outside the parallel loop formed by the auxiliary branch 2 , the main branch 3 , and the third branch 4 .

The second mechanical switch 15 is used to block the leakage current of the lightning arrester after the DC circuit breaker breaks the DC fault current to prolong the service life of the lightning arrester, and can establish a reliable insulation gap between the DC power supply and the fault point so as to facilitate fault removal and communication. Troubleshooting of equipment.

As shown in FIG. 3 , in order to provide a discharge path for the capacitor 10 , in a preferred embodiment, a discharge branch 6 is connected in parallel to both ends of the capacitor 10 . The discharge branch 6 is composed of a third mechanical switch 7 and a discharge resistor 8 in series, and the capacitor 10 can be discharged through the discharge branch 6 by closing the third mechanical switch 7 .

As shown in FIG. 3 , in order to reduce the rising rate of the DC fault current during a DC fault, in a preferred embodiment, a DC current-limiting inductor 16 can be connected in series outside the parallel circuit formed by the auxiliary branch 2 and the main branch 3 . In another preferred embodiment, the parallel loop formed by the auxiliary branch 2 , the main branch 3 and the third branch 4 is externally connected in series with a DC current limiting inductor 16 .

In the normal closed state, the DC current flows through the auxiliary branch 2, and when the DC fault is broken, the DC current is transferred to the main branch 3. As shown in FIG. 3 , in the normally closed state, the second mechanical switch 15 , the first mechanical switch 11 and the power electronic valve group 13 are in the closed state, and the third mechanical switch 7 is in the open state. When switching off a DC fault, the power electronic valve group 13 will be turned off first, so that the DC fault current will be transferred to the main branch circuit 3, and the DC fault current will charge the capacitor 10. When the voltage of the capacitor 10 is higher than the bus side DC voltage 17 , the DC fault current will begin to drop, and finally drop to zero due to the absorbing effect of the arrester.

When the power electronic valve group 13 is turned off, an opening command is sent to the first mechanical switch 11. The contact of the first mechanical switch 11 starts to open after receiving the opening command and after a certain period of time, the contact between the contacts The distance reaches the rated stroke, during the contact separation of the first mechanical switch 11, the voltage of the capacitor 10 is rising and the capacitor voltage is applied to the auxiliary branch 2, the first mechanical switch 11 and the power electronics on the auxiliary branch 2 The valve group 13 shares the capacitor voltage at the same time.

In one embodiment, the power electronic valve group 13 is preferably composed of anti-parallel power electronic devices 13a and anti-parallel thyristors 13b in series. The fully-controlled power electronic device 13a has self-shutoff capability, while the thyristor 13b can only be turned off when the current crosses zero and bears the reverse blocking voltage. When the power electronic valve group 13 is turned off, a shutdown signal will be applied to the fully-controlled power electronic device 13a and the thyristor 13b at the same time. The current of the circuit drops to zero, thereby providing conditions for the shutdown of the thyristor 13b. After both 13a and 13b are turned off, 13a and 13b will share the voltage applied to the power electronic valve group 13 in series. Due to the rated voltage of the thyristor 13b Usually higher than the fully-controlled power electronic device 13a and lower in cost than the fully-controlled power electronic device 13a, the power electronic valve group 13 can be significantly reduced by using the fully-controlled power electronic device 13a and the thyristor 13b in series to form the power electronic valve group 13 13 costs.

After the DC circuit breaker completes the DC fault isolation operation, the voltage of the capacitor 10 will be charged to a higher voltage value. In order to enable the DC circuit breaker to perform a reclosing operation after completing a breaking operation, the capacitor 10 needs to be discharged first. As shown in FIG. 3 , in one embodiment, a discharge branch 6 is connected in parallel to the positive and negative poles of the capacitor 10 . The discharge branch 6 is composed of a third mechanical switch 7 and a resistor 8 connected in series, and the capacitor 10 can be discharged by closing the third mechanical switch 7 .

Before discharging the capacitor 10, it is necessary to ensure that the DC fault has been cleared. The criterion is to detect the DC voltage on the line side 14 of the DC circuit breaker. When the absolute value of the DC voltage on the line side 14 of the DC circuit breaker is continuously higher than a certain minimum threshold (such as 80% of the DC voltage), it is judged that the DC fault has been cleared.

As shown in FIG. 3 , the reclosing operation sequence of the DC circuit breaker is as follows: after receiving the reclosing command, first close the first mechanical switch 11 , and then open the power electronic valve group 13 .

In order to prevent the DC circuit breaker from reclosing due to a DC fault, it is necessary to judge whether the DC fault has been eliminated before reclosing. The criterion is to detect the DC voltage on the line side 14 of the DC circuit breaker. If it is continuously higher than a threshold greater than zero (for example, 80% of the rated DC voltage), it is judged that the DC fault has been cleared.

Before reclosing, the DC transmission line is generally in the no-load state. In one embodiment, in order to prevent excessive operating overvoltage on the DC circuit breaker line side 14, a lightning arrester 18 can be installed on the DC circuit breaker line side 14.

In order to further improve the efficiency of reclosing, shorten the waiting delay, and thus speed up the time to restore power supply, the structure of the DC circuit breaker can be further optimized, specifically increasing the number of capacitors in the main branch 3 or increasing the capacitors and corresponding The number of discharge branches, such as increasing to two or more than two capacitors, and/or at the same time correspondingly increase the corresponding discharge branches and series mechanical switches.

As shown in FIG. 4 , in one embodiment, the main branch 3 of the DC circuit breaker includes two sets of capacitors, corresponding discharge branches and series mechanical switches. As shown in Fig. 4, it includes two capacitors 10a and 10b, discharge branches 6a and 6b are connected in parallel at both ends of 10a and 10b, and mechanical switches 9a and 9b are connected in series outside the capacitors 10a and 10b. In the normal conduction state, only one of the mechanical switches in each series combination in the main branch is in the closed state, while the mechanical switches in the other series combinations are in the open state. For example, 9a is closed to connect the capacitor 10a to the main circuit, and 9b is in an open state.

In the event of a DC fault, first turn off the valve group of the power electronic device, and at the same time send an opening command to the first mechanical switch on the auxiliary branch, and after the DC current in the transmission line drops to zero, open one of the series combinations in the The fourth mechanical switch in the closed state realizes the breaking of the DC fault current. In one embodiment, there is a second mechanical switch, and then the second mechanical switch connected in series outside the auxiliary branch is turned on to realize the breaking of the DC fault current.

After the DC circuit breaker finishes breaking the DC fault current for the first time, the capacitor 10a will be charged to a high voltage. In order to facilitate subsequent rapid reclosing, when the line DC current drops to zero, the mechanical switch 9a will be opened.

After receiving the reclosing command, close a fourth mechanical switch that is initially in an open state in several series combinations inside the main branch, then close the first mechanical switch in the auxiliary branch, and finally open the power electronic device valve of the auxiliary branch group to achieve fast reclosing and restore DC power supply. Specifically, after receiving the reclosing instruction, the DC circuit breaker will close the mechanical switch 9b, the first mechanical switch 11 and the power electronic valve group 13 in sequence. When the DC circuit breaker enters a stable operating state, the mechanical switch 9a will be closed to discharge the charged capacitor 10a, so that the capacitor 10a can be used to isolate the DC fault current next time.

Similarly, in this embodiment, it is necessary to ensure that the DC fault has been cleared before reclosing the DC circuit breaker. The method for judging whether the DC fault has been cleared is to monitor the voltage on the line side 14 of the DC circuit breaker. When the absolute value of the voltage is higher than a certain threshold (for example, 80% of the rated DC voltage), it is judged that the DC fault has been cleared, and the closing operation can be started.

When the DC line is short, in order to ensure that the line side 14 of the DC circuit breaker has a sufficiently high residual voltage after the DC fault is cleared, the present invention provides an additional parallel connection with a capacitor branch on the line side 14 of the DC circuit breaker As shown in FIG. 5 , a series loop composed of a capacitor 19 and a resistor 18 is additionally connected in parallel on the line side 14 of the DC circuit breaker.

Fig. 6 shows another embodiment of a bidirectional capacitor charging type DC circuit breaker, the principle of which is similar to that of Fig. 3 and Fig. 5, the difference is that the main branch is formed by connecting two capacitive series branches with the same structure in reverse parallel, wherein The first capacitor series branch is formed by the fourth mechanical switch 9a, the DC capacitor 10a and the diode valve group 5a in series, and the discharge branch formed by the third mechanical switch 7a and the discharge resistor 8a is connected in parallel at the two ends of the DC capacitor 10a. , the structure of the second capacitor series branch is the same as that of the first capacitor series branch, and the connection mode is opposite, that is, the second capacitor series branch is composed of the diode valve group 5a, the DC capacitor 10a and the fourth mechanical switch 9a in series, and the first The fourth mechanical switch 9a of a capacitor series branch is connected to the cathode of the diode valve group 5a of the second capacitor series branch, and the negative pole of the first capacitor series branch is connected to one end of the fourth mechanical switch 9a of the second capacitor series branch .

Figure 7 shows a bidirectional capacitor charging DC circuit breaker topology for DC distribution network, its principle is similar to Figure 3-Figure 6, the difference is that the auxiliary branch only includes the power electronic valve group 13, does not include The first mechanical switch 11 . When the DC circuit breaker is in the closed state, the power electronic valve group 13 is opened; When 13 is turned off, the DC fault current can still flow through the main branch 3. Therefore, when the power electronic valve group 13 is turned off, no excessive transient voltage or transient current will be generated, thereby reducing the impact on the power electronic valve group 13. The rated DC voltage and DC current requirements. In order to increase the turn-off speed, the DC current limiting inductor 16 can also be deleted in actual use.

The capacitor charging type bidirectional DC circuit breaker provided by the present invention can be used to break the DC fault current. Charging the capacitor unidirectionally eliminates the inductance-capacitance resonance problem that exists after breaking a DC fault, and the branch has bidirectional current flow capability. In addition, the power electronic valve group of the auxiliary branch adopts the full control type power electronic device valve group and the half control type power electronic device valve group connected in series to reduce the cost of the auxiliary branch power electronic valve group. Moreover, the present invention further provides a parallel combination of multiple "mechanical switches-capacitors" instead of a single combination so that the designed DC circuit breaker has fast reclosing capability, which greatly improves the speed of system restoration of power supply after a DC fault.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (22)

1. an electric capacity charge type bidirectional, dc chopper, it auxiliary branch including parallel connection and main branch, wherein, described auxiliary Branch road includes power electronic devices valve group, to flow through branch road as DC current during dc circuit breaker normally；

It is characterized in that, described main branch is by single-phase uncontrollable rectifier bridge and the electricity that is composed in series by DC capacitor and mechanical switch Appearance-mechanical switch branch combinations forms, the input port of wherein said uncontrollable rectifier bridge respectively with two ports of auxiliary branch It is connected, electric capacity-mechanical switch series arm described in coupled in series between the high and low pressure DC port of described uncontrollable rectifier bridge.

Electric capacity charge type bidirectional, dc chopper the most according to claim 1, wherein, the capacitor both sides of described main branch Also it is parallel with discharge paths, is used for before dc circuit breaker reclosing this capacitor discharge.

Electric capacity charge type bidirectional, dc chopper the most according to claim 2, wherein, described discharge paths includes mutually going here and there The mechanical switch of connection and resistance.

4., according to the electric capacity charge type bidirectional, dc chopper described in Claims 2 or 3, wherein, described discharge paths is mutual In parallel is multiple.

5. want the electric capacity charge type bidirectional, dc chopper according to any one of 1-4, wherein, described auxiliary branch according to right Power electronic devices valve group is formed by antiparallel all-controlling power electronics device and antiparallel Thyristors in series.

6., according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 1-5, wherein, also include with described Auxiliary branch and the 3rd branch road of main branch parallel connection, the 3rd route a spark gap or by multiple spark gap connection in series-parallel Become.

7. according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 1-6, wherein, described main branch with And the outside of shunt circuit that constitutes of auxiliary branch also connected direct current current-limiting inductance, to limit the upper raising speed of direct fault current Rate.

8. according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 1-7, wherein, described direct current interruption The line side of device is additionally parallel with capacitor, is used for judging whether DC Line Fault is removed, using the condition of reclosing as whether.

9. wanting the electric capacity charge type bidirectional, dc chopper according to any one of 1-8 according to right, wherein, described auxiliary branch is also Including the first mechanical switch, this first mechanical switch and the series connection of power electronic devices valve group form described auxiliary branch；And/or, The outside of the shunt circuit that described main branch and auxiliary branch are constituted also is in series with the second mechanical switch.

10. utilize the method that the dc circuit breaker according to any one of claim 1-8 carries out DC Line Fault isolation, its In, when the method is included in generation DC Line Fault, turns off the power electronics valve group of auxiliary branch, thus fault current is transferred to Main branch charges to described DC capacitor, when this DC capacitor voltage is higher than dc circuit breaker bus bar side DC voltage, and fault Electric current is off, it is achieved DC Line Fault is isolated.

The method that 11. 1 kinds of dc circuit breakers utilized described in claim 9 carry out DC Line Fault isolation, wherein, the method bag Include when there is DC Line Fault, the power electronic devices valve group being first turned off in described auxiliary branch, then open described auxiliary and prop up The first mechanical switch on road；Or the power electronic devices valve group being first turned off in described auxiliary branch, then open described auxiliary The first mechanical switch on branch road, and after circuit DC current reduces to zero, open the second of the connection of auxiliary branch external series Mechanical switch, thus realize the isolation to DC Line Fault.

12. 1 kinds of dc circuit breakers utilized described in claim 9 carry out the reclosing method after DC Line Fault isolation, wherein, The method is included in after receiving reclosing instruction, first the first mechanical switch on Guan Bi auxiliary branch, then opens described electric power Electronic valve device group；Or, after receiving reclosing instruction, the second machinery that first Guan Bi auxiliary branch external series couples is opened Closing, then the first mechanical switch on Guan Bi auxiliary branch, finally opens described power electronic devices valve group.

13. 1 kinds of electric capacity charge type bidirectional, dc choppers, it auxiliary branch including parallel connection and main branch, wherein, described auxiliary Branch road is helped to include power electronic devices valve group, to flow through branch road as DC current during dc circuit breaker normally；

It is characterized in that, described main branch is coupled by the capacitive series branch reverse parallel connection that two structures are identical and forms, Qi Zhongyi Individual capacitive series branch is in series by mechanical switch, DC capacitor and diode valve group, another capacitive series branch and institute State that the element of a capacitive series branch is identical and the polarity of each element wiring and each element in one capacitive series branch Wiring polarity contrary.

14. electric capacity charge type bidirectional, dc choppers according to claim 13, wherein, the electric capacity of described main branch Device both sides are also parallel with discharge paths, are used for before dc circuit breaker reclosing this capacitor discharge.

15. electric capacity charge type bidirectional, dc choppers according to claim 14, wherein, described discharge paths includes mutually The mechanical switch of series connection and resistance.

16. according to the electric capacity charge type bidirectional, dc chopper described in claims 14 or 15, and wherein, described discharge paths is phase The most in parallel is multiple.

17. want the electric capacity charge type bidirectional, dc chopper according to any one of 13-16 according to right, and wherein, described auxiliary is propped up The power electronic devices valve group on road is formed by antiparallel all-controlling power electronics device and antiparallel Thyristors in series.

18. according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 13-17, wherein, also include with Described auxiliary branch and the 3rd branch road of main branch parallel connection, the 3rd route a spark gap or by multiple spark gap connection in series-parallel Form.

19. according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 13-18, and wherein, described master props up Also connected direct current current-limiting inductance in the outside of the shunt circuit that road and auxiliary branch are constituted, to limit the upper of direct fault current Rise speed.

20. according to the electric capacity charge type bidirectional, dc chopper according to any one of claim 13-19, wherein, described direct current The line side of chopper is additionally parallel with capacitor, is used for judging whether DC Line Fault is removed, using the bar of reclosing as whether Part.

21. electric capacity charge type bidirectional, dc choppers according to claim 20, wherein, by detection dc circuit breaker line The DC voltage value of trackside judges whether DC Line Fault has been cleared by, when dc circuit breaker line side DC voltage is higher than one When determining threshold value and keep a period of time, then judge that DC Line Fault has been cleared by.

22. want the electric capacity charge type bidirectional, dc chopper according to any one of 13-21 according to right, and wherein, described auxiliary is propped up Road also includes the first mechanical switch, and this first mechanical switch and the series connection of power electronic devices valve group form described auxiliary branch；With/ Or, the outside of the shunt circuit that described main branch and auxiliary branch are constituted also is in series with the second mechanical switch.