CN212137265U - A hybrid DC circuit breaker based on capacitive commutation - Google Patents

Abstract

The utility model provides a hybrid DC circuit breaker based on capacitive commutation, comprising: an ultra-fast mechanical switch unit, an auxiliary semiconductor switch unit, a capacitive commutation unit and an energy absorption unit; an ultra-fast mechanical switch unit and an auxiliary semiconductor switch unit In series connection, the capacitor commutation unit is connected in parallel with the series-connected ultra-fast mechanical switch unit and the auxiliary semiconductor switch unit, and the energy absorption unit is connected in parallel with the capacitor commutation unit; the capacitor commutation unit is an ultra-fast mechanical switch when a short-circuit fault occurs in the system The unit and the auxiliary semiconductor switch unit provide a low-voltage branch to ensure its normal switching, and use the self-shutoff function to cut off the fault current; the energy absorbing unit absorbs the energy stored by the inductive element in the power system after the fault current is cut off after the switching fault. The hybrid DC circuit breaker based on capacitive commutation provided by the utility model realizes the soft shutdown of fault current, the energy storage of system inductive elements is small during shutdown, and can realize the interruption of fault current and the limitation of energy absorption of the arrester.

Description

A hybrid DC circuit breaker based on capacitive commutation

technical field

The utility model belongs to the technical field of DC circuit breakers, and more particularly relates to a hybrid DC circuit breaker based on capacitive commutation.

Background technique

Because DC transmission is an effective measure to solve the problem of connecting green renewable energy to the power grid, and has the advantages of long transmission distance and large transmission capacity, it has been widely used in countries around the world. Due to the small impedance of the DC side of the DC transmission network, when a short-circuit fault occurs in the system, the fault current rises rapidly. If the fault is not removed in a short time, the AC circuit breaker on the converter side will be activated, and the converter valve group will be blocked, which will affect the operation of the entire system. Normal operation greatly reduces the reliability and flexibility of the transmission system.

Therefore, it is necessary to develop a DC circuit breaker that can quickly cut off the fault current, isolate the fault point, and ensure the normal operation of the system. However, due to the small short-circuit impedance of the DC system and the rapid rise of the fault current, the breaking pressure of the circuit breaker is large, and there are inductive elements in the DC system. When the breaking fault current is too large, the inductive elements store a large amount of energy, and the stored energy passes through the arrester. Absorption leads to excessive energy absorption pressure of the arrester, which increases the manufacturing difficulty of the arrester and affects the service life of the arrester.

Therefore, it is very necessary to realize the soft shut-off technology that can realize the zero-crossing shut-off of the system fault current. The soft shut-off technology can not only reduce the breaking pressure of the circuit breaker, but also effectively reduce the energy storage of the inductive components of the system and reduce the energy absorption pressure of the arrester. In order to protect the arrester, reduce the breaking pressure of the circuit breaker, improve the safety of the system, save investment, have strong breaking capacity, and develop a circuit breaker with small energy absorption by the arrester, it is particularly necessary to develop a circuit breaker. The technical problem is of great significance to improve the reliability and flexibility of the DC transmission system.

Utility model content

In view of the defects of the prior art, the purpose of this utility model is to provide a hybrid DC circuit breaker based on capacitive commutation, which aims to solve the technical problems that the DC circuit breaker is difficult to interrupt the fault current and the arrester has a large energy absorption in the prior art. .

The utility model provides a hybrid DC circuit breaker based on capacitive commutation, comprising: an ultra-fast mechanical switch unit, an auxiliary semiconductor switch unit, a capacitive commutation unit and an energy absorption unit; an ultra-fast mechanical switch unit and an auxiliary semiconductor switch unit Connected in series, the capacitive commutation unit is connected in parallel with the series-connected ultra-fast mechanical switch unit and the auxiliary semiconductor switch unit, and the energy absorption unit is connected in parallel with the capacitive commutation unit; The mechanical switch unit and auxiliary semiconductor switch unit provide low-voltage branches to ensure their normal switching, and use the self-shutoff function to cut off the fault current; the energy absorbing unit is used to absorb the fault current after the switching fault and the inductive element storage in the power system after the fault current is cut off energy of.

Further, the capacitive commutation unit includes: a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, a precharge capacitor C, a commutation inductance L, a first arrester MOV1 and a first mechanical switch S The first thyristor T1 and the fourth thyristor T4 are connected in series, the second thyristor T2 and the third thyristor T3 are connected in series, the first arrester MOV1 and the first mechanical switch S are connected in series in the series connection of the first thyristor T1 and the fourth thyristor T4 between the series connection end of the second thyristor T2 and the third thyristor T3; the precharge capacitor C and the commutation inductance L are connected in series between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the second thyristor T2 and the third thyristor T4. Between the series connection terminals of the trithyristor T3; the non-series terminal of the first thyristor T1 and the non-series terminal of the second thyristor T2 together serve as one end of the capacitive commutation unit; the non-series terminal of the third thyristor T3 and the non-series terminal of the fourth thyristor T4 The non-series terminals are collectively used as the other terminal of the capacitive commutation unit.

Further, when a short-circuit fault occurs, the second thyristor T2 and the third thyristor T3 are triggered to conduct, and the auxiliary semiconductor switch unit is turned off, and an opening command is issued to the ultra-fast mechanical switch unit; when the ultra-fast mechanical switch unit reaches When the appropriate opening distance is enough to withstand a certain voltage (different voltage levels are set with different opening distances, the higher the voltage level, the larger the set opening distance), control the first thyristor T1 to conduct, and the current flowing to the second thyristor T2 will be Transfer to the first thyristor T1, automatically shut off when the current of the second thyristor T2 crosses zero, the power supply side continues to charge the precharge capacitor, the polarity of the precharge capacitor voltage is reversed, and flows to the first thyristor T1 and the second thyristor T3. The current gradually decreases. When the precharge capacitor voltage reaches the set value (different voltage levels have different set values for the precharge capacitor voltage, the higher the voltage level, the higher the precharge capacitor voltage set value), the current The current through the first thyristor T1 and the second thyristor T3 returns to zero, the first thyristor T1 and the second thyristor T3 are automatically turned off, the arrester MOV acts to absorb the energy stored in the inductive elements of the system and limit the overvoltage, and the arrester MOV1 is turned on to control the first The mechanical switch S absorbs the stored energy of the pre-charge capacitor C and limits the voltage of the pre-charge capacitor to the specified value to prepare for the next reclosing.

Further preferably, when a short-circuit fault occurs, the second thyristor T2 and the third thyristor T3 are triggered to conduct within 1 ms after the fault.

Since the capacitive commutation unit includes the precharge capacitor C, there is no need to provide a charging circuit for the precharge capacitor C, because the voltage polarity of the precharge capacitor C changes after the fault current is disconnected. A change in voltage polarity has no effect on the circuit breaker breaking the fault current again.

In addition, due to the setting of the voltage polarity of the precharge capacitor, when the precharge capacitor C is put into current limiting, the voltage across the precharge capacitor C, that is, the voltage across the ultra-fast mechanical switch UFD and the auxiliary semiconductor switch LCS, first decreases to zero before continuing. Increase, and the pre-charge capacitor C is put into use after the ultra-fast mechanical switch reaches a certain distance, so in the case of small capacitance, it can also ensure that the voltage across the ultra-fast mechanical switch UFD and the auxiliary semiconductor switch LCS is at the same level. The lower value further guarantees the successful turn-off of the ultrafast mechanical switch UFD and the auxiliary semiconductor switch LCS.

Further, the capacitive commutation unit further includes: a first reverse thyristor T11, a second reverse thyristor T22, a third reverse thyristor T33, and a fourth reverse thyristor T44, the first reverse thyristor T11 and the The first thyristor T1 is connected in parallel, the second reverse thyristor T22 is connected in parallel with the second thyristor T2, the third reverse thyristor T33 is connected in parallel with the third thyristor T3, and the fourth reverse thyristor The fourth thyristor T4 of T44 is connected in parallel.

Among them, when the fault point of the system is on the right side of the circuit breaker, that is, the fault current flows from left to right, the working process of the hybrid bidirectional DC circuit breaker based on capacitive commutation is the same as that of the hybrid low-voltage DC circuit breaker based on capacitive commutation. . The first thyristor T1, the second thyristor T2, the third thyristor T3, the fourth thyristor T4, the first reverse thyristor T11, the second reverse thyristor T22, the third reverse thyristor T33, and the fourth reverse thyristor T44 are connected in reverse parallel The main purpose is that no matter how the voltage polarity of the precharge capacitor is changed, the fault current can be commutated by controlling the thyristor to generate a current in any direction, and a single precharge capacitor can be used to achieve bidirectional fault current breaking and bidirectional fault current. Break again after reclosing.

Further, the capacitive commutation unit includes: a first thyristor T1, a second thyristor T2, a first mechanical switch S, a second mechanical switch S1, a third mechanical switch S2, a precharge capacitor C, a commutation inductance L and a first Arrester MOV1; the first thyristor T1 and the third mechanical switch S2 are connected in series, the second thyristor T2 and the second mechanical switch S1 are connected in series, the first arrester MOV1 and the first mechanical switch S are connected in series between the first thyristor T1 and the third mechanical switch S1 Between the series connection end of the switch S2 and the series connection end of the second thyristor T2 and the second mechanical switch S1; the precharge capacitor C and the commutation inductance L are connected in series between the series connection end of the first thyristor T1 and the third mechanical switch S2 between the series connection terminal of the second thyristor T2 and the second mechanical switch S1; the non-series terminal of the first thyristor T1 and the non-series terminal of the second thyristor T2 together serve as one end of the capacitive commutation unit; the second mechanical switch S1 The non-series terminal and the non-series terminal of the third mechanical switch S2 together serve as the other terminal of the capacitive commutation unit.

In the present invention, the reason why the second mechanical switch S1 and the third mechanical switch S2 are used is that the mechanical switches are only required to break the fault under zero current and zero withstand voltage, and there is no high requirement for the action speed of the mechanical switch. In a high-voltage system, the use of the second mechanical switch S1 and the third mechanical switch S2 can greatly reduce the capacity of the required thyristor and reduce the cost of the circuit breaker.

Among them, when a short-circuit fault occurs, the second thyristor T2 is triggered to turn on, the auxiliary semiconductor switch unit is turned off, and an opening command is issued to the ultra-fast mechanical switch unit; when the ultra-fast mechanical switch unit reaches a suitable opening distance enough to withstand a certain voltage When the first thyristor T1 is controlled to be turned on, the current flowing to the second thyristor T2 will be transferred to the first thyristor T1, the current of the second thyristor T2 will be automatically turned off at zero crossing, and the power supply side will continue to charge the precharge capacitor, and the polarity of the capacitor voltage Inversion, the current flowing to the first thyristor T1 and the second mechanical switch S1 gradually decreases; when the precharge capacitor voltage reaches a certain value, the current flowing through the first thyristor T1 and the second mechanical switch S1 returns to zero, and the first thyristor T1 is automatically turned off, the arrester MOV acts to absorb the energy stored in the inductive components of the system and limits the overvoltage, and then the first mechanical switch S controlled by the arrester MOV1 is turned on to absorb the energy stored in the precharge capacitor C and limit the voltage of the precharge capacitor to the specified value. Then, an opening command is sent to the second mechanical switch S1. At this time, since the voltage across the precharge capacitor is applied to both ends of the third mechanical switch S2, the second mechanical switch S1 is opened at zero current and zero withstand voltage, and the third mechanical switch S1 is opened at zero current and zero withstand voltage. Mechanical switch S2 sends a closing command to prepare for system reclosing.

Further preferably, when a short-circuit fault occurs, the thyristor T2 is triggered to conduct within 1 ms after the fault, and a shunt branch is provided for the main branch in advance.

The hybrid DC circuit breaker provided by the utility model includes a surge arrester MOV and a surge arrester MOV1. The surge arrester MOV is used to absorb the energy storage of the system inductive elements and limit the overvoltage, and the surge arrester MOV1 is used to absorb the stored energy of the precharge capacitor C after the circuit breaker successfully cuts off the fault. And limit the precharge capacitor voltage to the specified value in preparation for the next action of the circuit breaker.

After the circuit breaker successfully cuts off the fault current, it is only necessary to limit the voltage of the precharge capacitor to the set value, and it is not necessary to discharge all the energy of the voltage of the precharge capacitor C, which effectively reduces the energy discharge time of the precharge capacitor C, which is a good solution for the circuit breaker. The next reclosing provides protection and effectively reduces the energy absorption of the arrester MOV1.

Since the voltage of the precharged capacitor in the capacitor commutation unit first decreases to zero and then continues to increase, the current flowing through the precharged capacitor continues to decrease. When the voltage of the precharged capacitor reaches the operating voltage of the arrester, the arrester operates and the system The current of the inductive element is small, the energy storage of the inductive element is small, and the energy absorption of the arrester MOV is small.

In the present invention, it is considered that once the DC fault occurs, it is difficult to eliminate it in a short period of time. Considering the existing fault detection technology, it can be determined that a short-circuit fault may occur in the system after a short-circuit fault occurs 1ms, and whether the circuit breaker needs to be disconnected can be determined after a short-circuit fault occurs 3ms, so the capacitor commutation unit can adopt the following operation methods to reduce the open circuit device cost. The low-voltage capacitor commutator unit can turn on T2 and T3 in advance 1ms after the fault, and the high-voltage capacitor commutator unit can turn on T2 in advance 1ms after the fault, providing a shunt branch for the main branch in advance, further reducing the auxiliary semiconductor switch unit LCS and The current pressure of the ultra-fast mechanical switch reduces the number of parallel IGBTs in the auxiliary semiconductor switch unit LCS, and further reduces the cost. In the process of cutting off the fault current, the action time of other units of the circuit breaker does not change. If a short-term fault occurs in the system, that is, the short-circuit fault disappears after 3ms, the self-shutdown function of the capacitor commutator unit can be used to make the capacitor commutator unit out of operation, without issuing a shutdown command to the auxiliary semiconductor switching unit LCS, and the system current can continue to pass through The auxiliary semiconductor switching unit flows to the load and will not affect the normal operation of the system.

The utility model also provides a DC power transmission system based on the above-mentioned hybrid DC circuit breaker.

In general, compared with the prior art, the following beneficial effects can be achieved through the above technical solutions conceived by the present utility model:

(1) The utility model significantly reduces the energy absorption pressure of the arrester and the breaking pressure of the circuit breaker. In the event of a short-circuit fault, the capacitor commutation unit provides a low-voltage commutation branch for the ultra-fast mechanical switch UFD and the auxiliary semiconductor switch LCS, which reduces the breaking pressure of the ultra-fast mechanical switch UFD and the auxiliary semiconductor switch LCS; The fault current is gradually reduced to zero-crossing shutdown, so the energy storage of the inductive components of the system is greatly reduced, and the energy absorption pressure of the arrester is reduced.

(2) The utility model does not need to provide a charging circuit for the pre-charging capacitor of the capacitive commutating unit, and the capacitive commutating unit operates quickly and has a short recovery time, which provides an effective guarantee for cutting off the fault current again after the system is reclosed.

(3) In the present utility model, since the commutation unit can ensure that the IGBT and the ultra-fast mechanical switch do not need to withstand high voltage during the breaking of the fault current, the auxiliary semiconductor switch unit does not need to use a large number of IGBTs in series, effectively reducing the circuit breaker. The cost of the circuit breaker and the operating loss of the circuit breaker itself improve the reliability of the circuit breaker to interrupt the fault current.

(4) In the working mode of the present utility model, since the capacitor commutation unit is put into operation in advance when a fault occurs, the auxiliary semiconductor switch unit is shunted, the current pressure of the auxiliary semiconductor switch unit is further reduced, and the number of parallel IGBTs is reduced, Reduce the cost of the circuit breaker and the operating loss of the system.

Description of drawings

1 is a schematic block diagram of a hybrid DC circuit breaker based on capacitive commutation provided by an example of the utility model;

2 is a specific circuit structure diagram of a hybrid low-voltage DC circuit breaker based on capacitive commutation provided by the first embodiment of the present utility model;

3 is a specific circuit structure diagram of a hybrid HVDC circuit breaker based on capacitive commutation provided by the second embodiment of the present invention;

4 is a specific circuit structure diagram of a hybrid bidirectional DC circuit breaker based on capacitive commutation provided by the third embodiment of the present invention;

5 is a working sequence diagram of a hybrid low-voltage DC circuit breaker based on capacitive commutation provided by an example of the utility model;

FIG. 6 is a working sequence diagram of a hybrid HVDC circuit breaker based on capacitive commutation provided by an example of the present invention.

Among them, 1 is an ultra-fast mechanical switch unit, 2 is an auxiliary semiconductor switch unit, 3 is a commutation unit, 4 is an energy absorption unit, UFD is an ultra-fast mechanical switch, LCS is an auxiliary semiconductor switch, C is a precharge capacitor, T1, T2, T3, T4, T11, T22, T33, T44 are triggerable thyristors, S1, S2, S are mechanical switches, LS is a smoothing reactor, L is an oscillating inductance, and MOV and MOV1 are lightning arresters.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present utility model more clearly understood, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not intended to limit the present invention.

The utility model provides a hybrid DC circuit breaker based on capacitive commutation, which aims to reduce the breaking pressure of the circuit breaker and reduce the suction of the arrester on the basis of ensuring that the high-voltage DC circuit breaker itself operates quickly and interrupts large currents. It can increase the reliability of breaking within the range of breaking capacity.

As shown in FIG. 1, the hybrid DC circuit breaker based on capacitive commutation provided by the present invention includes: an ultra-fast mechanical switch unit 1, an auxiliary semiconductor switch unit 2, a capacitive commutation unit 3, and an energy absorption unit 4; an ultra-fast mechanical switch unit 2; The switch unit 1 is connected in series with the auxiliary semiconductor switch unit 2, the capacitor commutation unit 3 is connected in parallel with the series-connected ultra-fast mechanical switch unit 1 and the auxiliary semiconductor switch unit 2, and the energy absorption unit 4 is connected in parallel with the capacitor commutation unit 3; The converter unit 3 is used to provide a low-voltage branch for the ultra-fast mechanical switch unit 1 and the auxiliary semiconductor switch unit 2 to ensure their normal switching when a short-circuit fault occurs in the system, and to use the self-shutoff function to cut off the fault current; the energy absorption unit 4 is used for The energy stored by the inductive elements in the power system after absorbing the fault current after the breaking fault is cut off.

Under normal operating conditions, the ultra-fast mechanical switch unit 1 and the auxiliary semiconductor switch unit 2 pass the rated current, and their running losses are small. When a short circuit fault occurs in the system, the capacitor commutation unit 3 provides a low-voltage branch for the ultra-fast mechanical switch unit 1 and the auxiliary semiconductor switch unit 2 to ensure their normal switching, and then the capacitor commutation unit 3 uses its self-shutoff function to cut off the fault current. The energy absorbing unit 4 is used for absorbing the energy stored by the inductive elements in the power system after the fault current is cut off after the DC circuit breaker is broken.

In the present invention, the ultra-fast mechanical switch unit 1 is composed of an ultra-fast mechanical switch UFD, which has low on-resistance and low operating loss, and can break the fault at zero current when a short-circuit fault occurs. The auxiliary semiconductor switch unit 2 is mainly composed of IGBT, and when a short-circuit fault occurs, it is used to interrupt the fault current in the case of low voltage, so as to provide the condition of current zero-crossing shutdown for the ultra-fast mechanical switch. Capacitive commutation unit 3 is mainly used for commutation during faults to provide a low-voltage branch for IGBT turn-off and ultra-fast mechanical switch opening, ensuring that the IGBT and ultra-fast mechanical switch do not need to withstand high voltage during the switching process. It has the function of self-shutdown.

2 shows the specific circuit structure of the hybrid low-voltage DC circuit breaker based on capacitive commutation provided by the first embodiment of the present invention; the capacitive commutation unit 3 includes: a first thyristor T1, a second thyristor T2, and a third thyristor T3, the fourth thyristor T4, the precharge capacitor C, the commutation inductance L, the first arrester MOV1 and the first mechanical switch S; the first thyristor T1 and the fourth thyristor T4 are connected in series, and the second thyristor T2 and the third thyristor T3 are connected in series connection, the first arrester MOV1 and the first mechanical switch S are connected in series between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the series connection end of the second thyristor T2 and the third thyristor T3; the precharge capacitor C and The commutation inductance L is connected in series between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the series connection end of the second thyristor T2 and the third thyristor T3; the non-series connection end of the first thyristor T1 and the second thyristor T2 The non-series terminals of the thyristor T3 and the non-series terminals of the fourth thyristor T4 together serve as one end of the capacitor commutation unit 3 ;

As shown in FIG. 5 , the working process of the hybrid low-voltage DC circuit breaker based on capacitive commutation is described in detail as follows: in the stage t ₀ to t ₁ , the system operates normally, the first thyristor T1, the second thyristor T2, the third thyristor T3 and the The fourth thyristor T4 is in the off state; at time _t1 , the system has a short-circuit fault; within the time period of _t1 - _t2 , the system determines that a short-circuit fault has occurred, and issues a breaking command to the circuit breaker; at time _t2 , the protection device sends the second thyristor to the T2, the third thyristor T3 sends a turn-on command, and sends a turn-off command to the auxiliary semiconductor switch unit, so far, the current is transferred from the branch where the auxiliary semiconductor switch LCS is located to the branch where the second thyristor T2 and the third thyristor T3 are located; t ₂ ~ In the _t3 stage, the fast mechanical switch UFD starts to open, and at _t3 time, the fast mechanical switch UFD has reached a certain opening distance, and can withstand a certain voltage without arcing; at _t3 time, the protection device turns to the first thyristor T1. A conduction signal is sent, the first thyristor T1 is turned on, and since the polarity of the capacitor is lower positive and upper negative, the current flowing to the second thyristor T2 is gradually transferred to the first thyristor T1, and then the current of the second thyristor T2 is automatically turned off when it crosses zero; During the period of t ₃ to t ₄ , the fast mechanical switch UFD continues to open, the fault current continues to flow from the power valve side to the precharge capacitor, and the voltage polarity of the precharge capacitor is reversed, from the initial lower positive upper negative to upper positive lower Negative _; at time t4, the fast mechanical switch UFD reaches a sufficient distance to successfully open the gate _; at time t5, the voltage across the arrester MOV reaches the operating voltage of the arrester MOV, the current flowing through the precharge capacitor gradually returns to zero, the first thyristor T1, the first thyristor The trithyristor T3 branch current is automatically turned off after zero crossing, and the arrester MOV starts to operate to absorb the energy stored in the inductive elements of the system and limit the overvoltage; at time t6, the first mechanical switch S is turned _{on ;} at time t7, the first mechanical switch S is closed The gate is successful, and the arrester MOV1 starts to operate to limit the precharge capacitor voltage to the set value; at t8, the arrester _MOV1 completes energy absorption, and the precharge capacitor voltage becomes positive and negative; at _t9 , to the first mechanical switch S The opening command is issued; at time t ₁₀ , the first mechanical switch S is successfully opened, so far the circuit breaker has reached all the conditions for breaking the fault current again; at time t ₁₁ , the fault occurs again, at this time due to the reverse polarity of the voltage of the precharge capacitor , according to the symmetry of the capacitive commutation unit, the capacitive commutation unit can continue to be put into operation in the event of a fault, and will not affect the breaking effect of the circuit breaker.

3 shows the specific circuit structure of the hybrid HVDC circuit breaker based on capacitive commutation provided by the second embodiment of the present invention; the capacitive commutation unit 3 includes: a first thyristor T1, a second thyristor T2, a first mechanical The switch S, the second mechanical switch S1, the third mechanical switch S2, the precharge capacitor C, the commutation inductance L and the first arrester MOV1; the first thyristor T1 and the third mechanical switch S2 are connected in series, and the second thyristor T2 and the second The mechanical switch S1 is connected in series, the first arrester MOV1 and the first mechanical switch S are connected in series between the series connection end of the first thyristor T1 and the third mechanical switch S2 and the series connection end of the second thyristor T2 and the second mechanical switch S1 ; The precharge capacitor C and the commutation inductance L are connected in series between the series connection end of the first thyristor T1 and the third mechanical switch S2 and the series connection end of the second thyristor T2 and the second mechanical switch S1; the first thyristor T1 The non-series terminal and the non-series terminal of the second thyristor T2 together serve as one end of the capacitive commutation unit 3; one end.

As shown in FIG. 6 , the working process of the hybrid HVDC circuit breaker based on capacitive commutation is as follows: in the stage t ₀ to t ₁ , the system operates normally, the first thyristor T1, the second thyristor T2, the first mechanical switch S, the third The mechanical switches S2 are all in the off state, and the second mechanical switch S1 is in the on state; at time t1, a short-circuit fault occurs in the system _; within the time period from _t1 to _t2 , the system determines that a short-circuit fault occurs, and the duration of this process is about 3ms; At time _t2 , the protection device sends a turn-on command to the second thyristor T2 and a turn-off command to the auxiliary semiconductor switch unit. At this point, the current is transferred from the branch where the auxiliary semiconductor switch unit LCS is located to the second thyristor T2 and the second mechanical switch S1. The branch where it is located; in the period of t ₂ to t ₃ , the ultra-fast mechanical switch UFD opens, and at t ₃ , the ultra-fast mechanical switch has reached a certain opening distance and can withstand a certain voltage without arcing; at t ₃ , The protection device sends a turn-on signal to the first thyristor T1, and the first thyristor T1 is turned on. Since the polarity of the capacitor is lower positive and upper negative, the current flowing through the second thyristor T2 is gradually transferred to the first thyristor T1, and the second thyristor T2 The current zero-crossing is automatically turned off; in the period of t ₃ ~ t ₄ , the fast mechanical switch UFD continues to open, and the fault current flows from the power valve side to the pre-charge capacitor. At this point, the voltage polarity of the pre-charge capacitor changes, from lower positive to upper negative to negative The upper is positive and the lower is negative; at t ₄ , the UFD reaches a sufficient distance to successfully open the gate; at t ₅ , the voltage at both ends of the arrester MOV reaches the operating voltage of the arrester MOV, the current flowing through the precharge capacitor gradually returns to zero, and the current of the first thyristor T1 exceeds Zero natural turn-off, the arrester MOV starts to operate to absorb the energy stored in the inductive components of the system and limit the overvoltage; at time t6, the first mechanical switch S is turned _{on ;} at time t7, the first mechanical switch S is successfully closed, and the arrester MOV1 begins to switch The precharge capacitor voltage is limited to the set value; at time t8, the arrester _MOV1 completes energy absorption, and the fault current shutdown process ends, and the precharge capacitor voltage becomes positive and negative at the bottom; at time _t9 , it sends a signal to the first mechanical switch S. The opening command is issued to the second mechanical switch S1 to turn off the command. At this time, the voltage across the precharge capacitor is applied to the third mechanical switch S2, and the second mechanical switch S1 can be slowly opened under the condition of zero current and zero withstand voltage. at t ₁₀ , the first mechanical switch S and the second mechanical switch S1 are successfully opened, and start to send a closing command to the third mechanical switch S2, and the third mechanical switch S2 is slowly closed; at t ₁₁ , the third mechanical switch S2 is successfully closed, so far the circuit breaker has reached all the conditions for breaking the fault again; at time _t12 , the fault occurs again. At this time, due to the reverse voltage of the pre-charged capacitor, according to the symmetry of the capacitor commutation unit, the next fault occurs. The capacitor commutation unit can continue to be put into operation without affecting the breaking effect of the circuit breaker.

The hybrid low-voltage DC circuit breaker based on capacitive commutation and the hybrid high-voltage direct current circuit breaker based on capacitive commutation provided by the utility model are only relative concepts, and are not used to limit the application occasions of the two types of structures. The capacitive commutation unit is mainly used for The thyristor is used as a breaking device. Compared with the fully controlled device, the cost is lower. The precharge capacitor only needs to generate a short-term commutation current, and the required precharge capacitor capacity is small. There are certain economic advantages in the DC transmission system.

4 shows the specific circuit structure of the hybrid bidirectional DC circuit breaker based on capacitive commutation provided by the third embodiment of the present invention; the capacitive commutation unit 3 includes: a first thyristor T1, a second thyristor T2, and a third thyristor T3, the fourth thyristor T4, the precharge capacitor C, the commutation inductance L, the first arrester MOV1, the first mechanical switch S, the first reverse thyristor T11, the second reverse thyristor T22, the third reverse thyristor T33 and the first reverse thyristor T11 Four reverse thyristors T44, the first thyristor T1 and the fourth thyristor T4 are connected in series, the second thyristor T2 and the third thyristor T3 are connected in series, and the first arrester MOV1 and the first mechanical switch S are connected in series between the first thyristor T1 and the fourth thyristor T3. Between the series connection end of the thyristor T4 and the series connection end of the second thyristor T2 and the third thyristor T3; the precharge capacitor C and the commutation inductance L are connected in series between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the third thyristor T4. Between the series connection terminals of the second thyristor T2 and the third thyristor T3; the non-series terminal of the first thyristor T1 and the non-series terminal of the second thyristor T2 together serve as one end of the capacitor commutation unit 3; the non-series terminal of the third thyristor T3 Together with the non-series terminal of the fourth thyristor T4 as the other end of the capacitive commutation unit 3; the first reverse thyristor T11 is connected in parallel with the first thyristor T1, the second reverse thyristor T22 is connected in parallel with the second thyristor T2, and the third reverse thyristor T11 is connected in parallel with the first thyristor T1. The reverse thyristor T33 is connected in parallel with the third thyristor T3, and the fourth reverse thyristor T44 is connected in parallel with the fourth thyristor T4.

The working process of the hybrid bidirectional DC circuit breaker based on capacitive commutation is as follows: Assuming that when the system is in normal operation, the working current flows from the left to the right, at this time the first thyristor T1, the second thyristor T2, the third thyristor T3, the fourth thyristor The thyristor T4, the first reverse thyristor T11, the second reverse thyristor T22, the third reverse thyristor T33, and the fourth reverse thyristor T44 are all in the off state. When the system fails at the right side of the circuit breaker, the fault current Flowing from left to right, the working process of the hybrid bidirectional DC circuit breaker based on capacitive commutation is the same as that of the hybrid low-voltage DC circuit breaker based on capacitive commutation. The first thyristor T1, the second thyristor T2, the third thyristor T3, the fourth thyristor T4, the first reverse thyristor T11, the second reverse thyristor T22, the third reverse thyristor T33, and the fourth reverse thyristor T44 are connected in reverse parallel The main purpose is that no matter how the voltage polarity of the precharge capacitor is changed, the fault current can be commutated by controlling the thyristor to generate a current in any direction, and a single precharge capacitor can be used to achieve bidirectional fault current breaking and bidirectional fault current. Breaking again after reclosing has certain economic advantages.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and replacements made within the spirit and principles of the present invention Improvements, etc., should be included within the protection scope of the present invention.

Claims (9)

1. A hybrid DC circuit breaker based on capacitive commutation, characterized in that it comprises: an ultra-fast mechanical switch unit (1), an auxiliary semiconductor switch unit (2), a capacitive commutation unit (3) and an energy absorption unit ( 4); The ultra-fast mechanical switch unit (1) is connected in series with the auxiliary semiconductor switch unit (2), and the capacitive commutation unit (3) is connected in series with the ultra-fast mechanical switch unit (1) and the auxiliary semiconductor switch connected in series The unit (2) is connected in parallel, and the energy absorbing unit (4) is connected in parallel with the capacitive commutation unit (3); The capacitive commutation unit (3) is used to provide a low-voltage branch for the ultra-fast mechanical switch unit (1) and the auxiliary semiconductor switch unit (2) to ensure their normal switching when a short-circuit fault occurs in the system, and uses The self-shut-off function cuts off the fault current; The energy absorbing unit (4) is used for absorbing the energy stored by the inductive element in the power system after the fault current is cut off after the breaking fault. 2. The hybrid DC circuit breaker according to claim 1, wherein the capacitive commutation unit (3) comprises: a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, Precharge capacitor C, commutation inductance L, first arrester MOV1 and first mechanical switch S; The first thyristor T1 and the fourth thyristor T4 are connected in series, the second thyristor T2 and the third thyristor T3 are connected in series, and the first arrester MOV1 and the first mechanical switch S are connected in series. between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the series connection end of the second thyristor T2 and the third thyristor T3; the precharge capacitor C and the commutation inductance L connected in series between the series connection end of the first thyristor T1 and the fourth thyristor T4 and the series connection end of the second thyristor T2 and the third thyristor T3; The non-series terminal of the first thyristor T1 and the non-series terminal of the second thyristor T2 together serve as one end of the capacitive commutation unit (3); the non-series terminal of the third thyristor T3 and the fourth thyristor T3 The non-series terminals of the thyristor T4 together serve as the other terminal of the capacitive commutation unit (3). 3. The hybrid DC circuit breaker according to claim 2, wherein when a short-circuit fault occurs, the second thyristor T2 and the third thyristor T3 are triggered to conduct, and the auxiliary semiconductor switch unit (2) is turned off , issue an opening command to the ultra-fast mechanical switch unit (1); When the ultra-fast mechanical switch unit (1) reaches the set opening distance, the first thyristor T1 is controlled to be turned on, and the current flowing to the second thyristor T2 will be transferred to the first thyristor T1. When the current of the second thyristor T2 exceeds the It is automatically turned off at zero time, the power supply side continues to charge the precharge capacitor, the voltage polarity of the precharge capacitor is reversed, and the current flowing to the first thyristor T1 and the second thyristor T3 gradually decreases. When the precharge capacitor voltage reaches the set value , the current flowing through the first thyristor T1 and the second thyristor T3 returns to zero, the first thyristor T1 and the second thyristor T3 are automatically turned off, the arrester MOV acts to absorb the energy stored in the inductive elements of the system and limit the overvoltage, and the control of the arrester MOV1 is turned on. The first mechanical switch S absorbs the stored energy of the pre-charge capacitor C and limits the voltage of the pre-charge capacitor to a specified value to prepare for the next reclosing. 4 . The hybrid DC circuit breaker according to claim 2 , wherein when a short-circuit fault occurs, the second thyristor T2 and the third thyristor T3 are triggered to conduct within 1 ms after the fault. 5 . 5. The hybrid DC circuit breaker according to claim 2, wherein the capacitive commutation unit (3) further comprises: a first reverse thyristor T11, a second reverse thyristor T22, and a third reverse thyristor T33, the fourth reverse thyristor T44, the first reverse thyristor T11 is connected in parallel with the first thyristor T1, the second reverse thyristor T22 is connected in parallel with the second thyristor T2, and the third reverse thyristor T22 is connected in parallel with the second thyristor T2. The forward thyristor T33 is connected in parallel with the third thyristor T3, the fourth reverse thyristor T44 and the fourth thyristor T4 are connected in parallel. 6. The hybrid DC circuit breaker according to claim 1, wherein the capacitive commutation unit (3) comprises: a first thyristor T1, a second thyristor T2, a first mechanical switch S, a second mechanical switch S1, the third mechanical switch S2, the precharge capacitor C, the commutation inductance L and the first arrester MOV1; The first thyristor T1 and the third mechanical switch S2 are connected in series, the second thyristor T2 and the second mechanical switch S1 are connected in series, and the first arrester MOV1 and the first mechanical switch S are connected in series Between the series connection terminal of the first thyristor T1 and the third mechanical switch S2 and the series connection terminal of the second thyristor T2 and the second mechanical switch S1; the precharge capacitor C and the The commutation inductance L is connected in series between the series connection end of the first thyristor T1 and the third mechanical switch S2 and the series connection end of the second thyristor T2 and the second mechanical switch S1; The non-series terminal of the first thyristor T1 and the non-series terminal of the second thyristor T2 together serve as one end of the capacitive commutation unit (3); the non-series terminal of the second mechanical switch S1 and the first The non-series terminals of the three mechanical switches S2 together serve as the other terminal of the capacitive commutation unit (3). 7. The hybrid DC circuit breaker according to claim 6, characterized in that when a short-circuit fault occurs, the second thyristor T2 is triggered to conduct, the auxiliary semiconductor switch unit (2) is turned off, and the ultra-fast mechanical switch unit is turned off. (1) Issue an opening command; When the ultra-fast mechanical switch unit (1) reaches a suitable opening distance and can withstand a certain voltage, the first thyristor T1 is controlled to be turned on, the current flowing to the second thyristor T2 will be transferred to the first thyristor T1, and the current of the second thyristor T2 will pass through. Zero automatic shutdown, the power supply side continues to charge the precharge capacitor, the capacitor voltage polarity is reversed, and the current flowing to the first thyristor T1 and the second mechanical switch S1 gradually decreases; When the voltage of the precharge capacitor reaches a certain value, the current flowing through the first thyristor T1 and the second mechanical switch S1 returns to zero, the first thyristor T1 is automatically turned off, and the arrester MOV acts to absorb the energy stored in the inductive elements of the system and limit the overvoltage. Turn on the first mechanical switch S of the arrester MOV1, absorb the energy stored in the precharge capacitor C and limit the voltage of the precharge capacitor to a specified value, and then issue an opening command to the second mechanical switch S1. Voltage is applied to both ends of the third mechanical switch S2, so the second mechanical switch S1 opens at zero current and zero withstand voltage, and sends a closing command to the third mechanical switch S2 to prepare for system reclosing. 8 . The hybrid DC circuit breaker according to claim 6 or 7 , wherein when a short-circuit fault occurs, the thyristor T2 is triggered to conduct within 1 ms after the fault, and a shunt branch is provided for the main branch in advance. 9 . 9. A DC power transmission system based on the hybrid DC circuit breaker according to any one of claims 1-8.

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