CN111696803A - Bidirectional hybrid direct-current circuit breaker based on capacitance commutation and direct-current power transmission system - Google Patents
Bidirectional hybrid direct-current circuit breaker based on capacitance commutation and direct-current power transmission system Download PDFInfo
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- CN111696803A CN111696803A CN202010713267.0A CN202010713267A CN111696803A CN 111696803 A CN111696803 A CN 111696803A CN 202010713267 A CN202010713267 A CN 202010713267A CN 111696803 A CN111696803 A CN 111696803A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
- H01H9/547—Combinations of mechanical switches and static switches, the latter being controlled by the former
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
- H01H9/541—Contacts shunted by semiconductor devices
- H01H9/542—Contacts shunted by static switch means
- H01H2009/543—Contacts shunted by static switch means third parallel branch comprising an energy absorber, e.g. MOV, PTC, Zener
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
- H01H9/541—Contacts shunted by semiconductor devices
- H01H9/542—Contacts shunted by static switch means
- H01H2009/544—Contacts shunted by static switch means the static switching means being an insulated gate bipolar transistor, e.g. IGBT, Darlington configuration of FET and bipolar transistor
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Abstract
The invention discloses a bidirectional mixed direct current breaker based on capacitance commutation and a direct current transmission system, wherein the direct current breaker comprises: the energy absorption device comprises an ultra-fast mechanical switch unit, a load change-over switch unit, a capacitance current conversion unit and an energy absorption unit; the ultra-fast mechanical switch unit is connected with the load change-over switch unit in series, the capacitance commutation unit is connected with the ultra-fast mechanical switch unit and the load change-over switch unit which are connected in series in parallel, and the energy absorption unit is connected with the capacitance commutation unit in parallel; the capacitance commutation unit is used for providing a low-voltage branch circuit for the ultra-fast mechanical switch unit and the load transfer switch unit to ensure normal on-off when the system has short-circuit fault, and cutting off fault current by using a self-off function; the energy absorption unit is used for absorbing energy stored by a inductive element in the power system after the fault current is cut off after the fault is cut off. The bidirectional mixed direct-current circuit breaker based on capacitance commutation can realize the on-off of fault current and the energy absorption limitation of a lightning arrester.
Description
Technical Field
The invention belongs to the technical field of direct current circuit breakers, and particularly relates to a bidirectional hybrid direct current circuit breaker based on capacitance commutation and a direct current transmission system.
Background
In recent years, the total amount of new energy power generation is rapidly increased, the application of flexible direct current transmission can effectively improve the power generation utilization efficiency of renewable energy sources and reduce economic losses caused by wind and light abandonment, and high voltage direct current transmission (HVDC) is widely applied in the world as an important component of a future power system.
With the continuous expansion of the scale of the direct current power grid and the increasing complexity of the direct current power grid structure, many key problems need to be solved, one of which is direct current short circuit fault. Therefore, it is necessary to develop a dc circuit breaker capable of rapidly cutting off fault current, isolating fault points and ensuring normal operation of the system. However, the short-circuit impedance of the direct current system is small, the fault current rises quickly, so that the breaking pressure of the circuit breaker is large, and an inductive element exists in the direct current system. In order to protect the lightning arrester, reduce the breaking pressure of the circuit breaker, improve the safety of a system, save investment, have strong breaking capacity and are particularly necessary to develop the circuit breaker with small energy absorption of the lightning arrester, the scheme solves a plurality of technical problems in the operation process of the high-voltage direct-current circuit breaker and has important significance for improving the reliability and the flexibility of a direct-current power transmission system.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a bidirectional hybrid direct current breaker based on capacitance commutation, and aims to solve the technical problems that the direct current breaker is difficult to break fault current and the lightning arrester has high energy absorption in the prior art.
The invention provides a bidirectional mixed direct current breaker based on capacitance commutation, which comprises: the energy absorption device comprises an ultra-fast mechanical switch unit, a load change-over switch unit, a capacitance current conversion unit and an energy absorption unit; the ultra-fast mechanical switch unit is connected with the load change-over switch unit in series, the capacitance commutation unit is connected with the ultra-fast mechanical switch unit and the load change-over switch unit which are connected in series in parallel, and the energy absorption unit is connected with the capacitance commutation unit in parallel; the capacitance commutation unit is used for providing a low-voltage branch circuit for the ultra-fast mechanical switch unit and the load transfer switch unit to ensure normal on-off when the system has short-circuit fault, and cutting off fault current by using a self-off function; the energy absorption unit is used for absorbing energy stored by a inductive element in the power system after fault current is cut off when the power system is in a cut-off fault.
Further, the capacitance commutation cell includes: the power supply comprises a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, a commutation capacitor C, a commutation inductor L and a voltage limiting unit; a first thyristor T1 and the third thyristor T3 are connected in series, the second thyristor T2 and the fourth thyristor T4 are connected in series, and the voltage limiting unit is connected between a series connection terminal of the first thyristor T1 and the third thyristor T3 and a series connection terminal of the second thyristor T2 and the fourth thyristor T4; the commutation capacitor C and the commutation inductor L are connected in series between a series connection end of the first thyristor T1 and the third thyristor T3 and a series connection end of the second thyristor T2 and the fourth thyristor T4.
Further, the capacitance commutation cell includes: the circuit comprises a first thyristor T1, a second thyristor T2, a first mechanical switch S1, a second mechanical switch S2, a commutation capacitor C, a commutation inductor L and a voltage limiting unit; a first thyristor T1 and a first mechanical switch S1 are connected in series, a second thyristor T2 and a second mechanical switch S2 are connected in series, and a voltage limiting unit is connected between a series connection terminal of the first thyristor T1 and the first mechanical switch S1 and a series connection terminal of the second thyristor T2 and the second mechanical switch S2; the commutation capacitor C and said commutation inductor L are connected in series between the series connection of the first thyristor T1 and the first mechanical switch S1 and the series connection of the second thyristor T2 and the second mechanical switch S2.
In the invention, the required commutation capacitor has small capacity and low manufacturing cost. The commutation capacitor C is used after the ultra-fast mechanical switch reaches a certain opening distance, so that the voltages at two ends of the ultra-fast mechanical switch UFD and the load change-over switch LCS are in a lower value in the process of breaking fault current of the circuit breaker under the condition of smaller capacitor capacity, and the successful turn-off of the ultra-fast mechanical switch UFD and the load change-over switch LCS is guaranteed.
Further, the capacitance commutation cell further includes: a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4; the cathode of the first diode D1 is connected with the anode of the first thyristor T1, the anode of the second thyristor T2 and the cathode of the second diode D2; an anode of the third diode D3 is connected to a cathode of the third thyristor T3, a cathode of the fourth thyristor T4 and an anode of the fourth diode D4; the anode of the first diode D1 and the cathode of the third diode D3 are used as one end of the capacitance commutation cell, and the anode of the second diode D2 and the cathode of the fourth diode D4 are used as the other end of the capacitance commutation cell.
The purpose of symmetrical connection of the thyristor and the diode in the capacitance commutation unit is to commutate the fault current by controlling the thyristor to generate a current in any direction no matter how the polarity of the voltage of the commutation capacitor changes, and the single commutation capacitor can realize the breaking of the bidirectional fault current and the breaking of the bidirectional fault current again after reclosing, thereby having certain economic advantages.
Wherein, voltage limiting unit is used for limiting the voltage of commutation electric capacity to the setting value, and voltage limiting unit includes: a first arrester MOV1 and a third mechanical switch S connected in series in that order.
According to the invention, a charging loop is not required to be provided for the commutation capacitor C, because the breaker cuts off the fault current once, the voltage polarity of the commutation capacitor C is changed once, the absolute value of the voltage of the commutation capacitor can be limited to a specified value through the first arrester MOV1, and the breaker can not be influenced to cut off the fault current again.
When short-circuit fault occurs, the second thyristor T2 and the fourth thyristor T4 are triggered to be conducted, the load change-over switch unit is turned off, and a brake opening instruction is sent to the ultra-fast mechanical switch unit.
When the ultra-fast mechanical switch unit reaches a set opening distance, the first thyristor T1 is controlled to be conducted, current flowing to the second thyristor T2 is transferred to the first thyristor T1, when the current of the second thyristor T2 crosses zero, the current is automatically turned off, the power supply side continues to charge the commutation capacitor, the polarity of voltage of the commutation capacitor is reversed, the current flowing to the first thyristor T1 and the fourth thyristor T4 is gradually reduced, when the voltage of the commutation capacitor reaches a set value, the current flowing through the first thyristor T1 and the fourth thyristor T4 returns to zero, the first thyristor T1 and the fourth thyristor T3 are automatically turned off, the second arrester MOV acts to absorb energy stored by an inductive element of an inductive system and limit overvoltage, the third mechanical switch S of the first arrester MOV1 is controlled to be conducted, the commutation capacitor C is absorbed to store energy and limit the voltage of the commutation capacitor to a designated value, and preparation is made for next reclosing.
In the invention, when the ultra-fast mechanical switch reaches enough opening distance, the converter capacitor is put into operation, so the voltage which needs to be endured by the load change-over switch LCS is very small, a large number of semiconductor devices are not needed to be connected in series, the voltage-sharing difficulty of the load change-over switch LCS is obviously reduced, and the manufacturing cost of the load change-over switch LCS and the loss of the normal operation of a system are effectively reduced.
The invention also provides a direct current transmission system based on the hybrid direct current breaker.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) the invention obviously reduces the energy absorption pressure of the lightning arrester and the breaking pressure of the breaker. When short circuit occurs, the capacitance commutation unit provides a low-voltage commutation branch for the UFD and the LCS, so that the on-off pressure of the UFD and the LCS is reduced; the circuit breaker realizes that the fault current is gradually reduced to zero-crossing turn-off, so that the energy storage of inductive elements of the system is greatly reduced, and the energy absorption pressure of the lightning arrester is reduced.
(2) The invention does not need to provide a charging loop for the commutation capacitor of the capacitor commutation unit, and the capacitor commutation unit has rapid action and short recovery time, thereby providing effective guarantee for cutting off the fault current again after the system is reclosed.
(3) According to the invention, the converter unit can ensure that the IGBT and the ultra-fast mechanical switch do not need to bear high voltage in the switching-on and switching-off process during the switching-on and switching-off of the fault current, so that the load transfer switch unit does not need to adopt a large number of IGBTs in series connection, the manufacturing cost of the circuit breaker and the running loss of the circuit breaker are effectively reduced, and the reliability of the switching-on and switching-off fault current of the circuit breaker is improved.
(4) In the working mode of the invention, because the capacitance commutation unit is put into use in advance when a fault occurs and shunts the load transfer switch unit, the through-flow pressure of the load transfer switch unit is further reduced, the parallel connection number of the IGBTs is reduced, and the manufacturing cost of the circuit breaker and the running loss of the system are reduced.
Drawings
Fig. 1 is a schematic block diagram of a bidirectional hybrid dc circuit breaker based on capacitive commutation according to the present invention;
fig. 2 is a specific circuit structure diagram of the bidirectional hybrid dc circuit breaker based on capacitive commutation according to the present invention;
fig. 3 is a working timing diagram of the bidirectional hybrid dc circuit breaker based on capacitive commutation in the commutation preparation phase according to the present invention;
fig. 4 is a working timing diagram of the bidirectional hybrid dc circuit breaker based on capacitance commutation in the commutation stage according to the present invention;
fig. 5 is a working timing diagram of the bidirectional hybrid dc circuit breaker based on capacitive commutation in the MOV energy absorption phase of the arrester according to the present invention;
fig. 6 is a working timing diagram of the bidirectional hybrid dc circuit breaker based on capacitive commutation provided by the present invention at the stage of absorbing energy by the arrester MOV 1;
fig. 7 is a specific circuit structure diagram of the high-voltage bidirectional hybrid dc circuit breaker based on capacitive commutation according to the present invention;
the system comprises an ultra-fast mechanical switch unit 1, a load transfer switch unit 2, a commutation unit 3, an energy absorption unit 4, an ultra-fast mechanical switch UFD, a load transfer switch LCS, a commutation capacitor C, a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a first mechanical switch S1, a second mechanical switch S2, a third mechanical switch S, a smoothing reactor LS, a commutation inductor L, a first arrester MOV1 and a second arrester MOV.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a bidirectional mixed direct current breaker based on capacitance commutation, aiming at reducing the breaking pressure of the breaker and reducing the energy absorption of a lightning arrester on the basis of ensuring the rapid action and breaking large current of a high-voltage direct current breaker, and increasing the breaking reliability within the breaking capacity range.
As shown in fig. 1, the bidirectional hybrid dc circuit breaker based on capacitance commutation according to the present invention includes: the system comprises an ultra-fast mechanical switch unit 1, a load change-over switch unit 2, a capacitance current conversion unit 3 and an energy absorption unit 4; the ultra-fast mechanical switch unit 1 is connected with the load change-over switch unit 2 in series, the capacitance commutation unit 3 is connected with the ultra-fast mechanical switch unit 1 and the load change-over switch unit 2 which are connected in series in parallel, and the energy absorption unit 4 is connected with the capacitance commutation unit 3 in parallel; the capacitance commutation unit 3 is used for providing a low-voltage branch circuit for the ultra-fast mechanical switch unit 1 and the load change-over switch unit 2 to ensure normal on-off when the system has a short-circuit fault, and cutting off fault current by using a self-off function; the energy-absorbing unit 4 is used to absorb the energy stored by the inductive element in the power system after the fault current is cut off after the open fault.
Under normal working conditions, rated current passes through the ultra-fast mechanical switch unit 1 and the load transfer switch unit 2, and the running loss is small. When the system has short-circuit fault, the capacitance commutation unit 3 provides a low-voltage branch for the ultra-fast mechanical switch unit 1 and the load change-over switch unit 2 to ensure the normal on-off of the low-voltage branch, and then the capacitance commutation unit 3 cuts off the fault current by utilizing the self-off function of the capacitance commutation unit. The energy absorption unit 4 is used for absorbing energy stored by a inductive element in the power system after the fault current is cut off after the direct current breaker is disconnected.
As shown in fig. 2, in the embodiment of the present invention, the ultrafast mechanical switch unit 1 is formed of the ultrafast mechanical switch UFD, has a low on-resistance and a small operation loss, and opens the fault at zero current when a short-circuit fault occurs. The load transfer switch unit 2 is mainly composed of an IGBT, and is used to cut off a fault current under a low voltage condition when a short-circuit fault occurs, and to provide a current zero-crossing turn-off condition for the ultrafast mechanical switch. The capacitance commutation unit 3 is mainly used for providing a low-voltage branch for IGBT turn-off and ultra-fast mechanical switch brake-off during fault commutation, ensuring that the IGBT and the ultra-fast mechanical switch are not required to bear high voltage in the turn-on and turn-off process, and the capacitance commutation unit has the function of self-turn-off.
The capacitance commutation unit 3 includes: the lightning arrester comprises a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a commutation capacitor C, a commutation inductor L, a first lightning arrester MOV1 and a first mechanical switch S. A first diode D1 and a second diode D2 are connected in reverse series, and a third diode D3 and a fourth diode D4 are connected in reverse series; the first thyristor T1 and the third thyristor T3 are connected in series in the same direction, and the second thyristor T2 and the fourth thyristor T4 are connected in series in the same direction; a first arrester MOV1 and a third mechanical switch S are connected in series between the series connection of the first thyristor T1 and the third thyristor T3 and the series connection of the second thyristor T2 and the fourth thyristor T4; the commutation capacitor C and the commutation inductor L are connected in series between the series connection of the first thyristor T1 and the third thyristor T3 and the series connection of the second thyristor T2 and the fourth thyristor T4. The first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 mainly have the functions of changing the flow direction of fault current and ensuring that the circuit breaker can successfully cut off the fault current when the fault current is in any direction; the first arrester MOV1 and the third mechanical switch S are mainly used to absorb the energy of the commutation capacitor, limiting the voltage of the commutation capacitor to a specified value.
When short-circuit fault occurs, triggering a second thyristor T2 and a fourth thyristor T4 to be conducted, turning off the load transfer switch unit, and sending a brake separating instruction to the ultra-fast mechanical switch unit; when the ultra-fast mechanical switch unit reaches a proper opening distance and is enough to bear a certain voltage, the first thyristor T1 is controlled to be conducted, the current flowing to the second thyristor T2 is transferred to the first thyristor T1, when the current of the second thyristor T2 crosses zero, the power supply side continues to charge the commutation capacitor, the polarity of the voltage of the commutation capacitor is reversed, the current flowing to the first thyristor T1 and the fourth thyristor T4 is gradually reduced, when the voltage of the commutation capacitor reaches a certain value, the current flowing through the first thyristor T1 and the fourth thyristor T4 returns to zero, the first thyristor T1 and the fourth thyristor T4 are automatically turned off, the MOV action of the second arrester absorbs the energy stored by an inductive element of a system and limits the overvoltage, the third mechanical switch S of the arrester MOV1 is conducted, the energy stored by the commutation capacitor C is absorbed and limits the voltage of the commutation capacitor to a specified value, and preparation is made for next reclosing.
Due to the symmetrical design of the diodes of the capacitance commutation module, when the direction of the fault current is changed, the direction of the fault current can be corrected to the direction of the current passing through the first thyristor T1, the second thyristor T2, the third thyristor T3 and the fourth thyristor T4.
In addition, due to the arrangement of the voltage polarity of the commutation capacitor, when the commutation capacitor C is put into current limiting, the voltage at the two ends of the commutation capacitor C, namely the voltage at the two ends of the ultrafast mechanical switch UFD and the load transfer switch LCS, is reduced to zero and then is increased continuously, and the commutation capacitor C is put into use after the ultrafast mechanical switch reaches a certain opening distance, so that the voltage at the two ends of the ultrafast mechanical switch UFD and the load transfer switch LCS can be ensured to be at a lower value under the condition that the capacitance is smaller, and the successful turn-off of the ultrafast mechanical switch UFD and the load transfer switch LCS is further ensured.
The hybrid direct current breaker provided by the embodiment of the invention comprises a first arrester MOV1 and a second arrester MOV, wherein the second arrester MOV is used for absorbing energy storage of an inductive element of a system and limiting overvoltage, and the first arrester MOV1 is used for absorbing energy storage of a commutation capacitor C and limiting voltage of the commutation capacitor to a specified value after the breaker is successfully cut off a fault so as to prepare for next action of the breaker.
When the breaker successfully cuts off the fault current, only the voltage of the conversion capacitor is limited to a set value, and the energy of the voltage of the conversion capacitor C is not required to be discharged completely, so that the energy discharge time of the conversion capacitor C is effectively reduced, the next reclosing of the breaker is guaranteed, and the energy absorption of the MOV1 of the first arrester is effectively reduced.
The voltage of the commutation capacitor in the capacitor commutation unit is reduced to zero firstly and then is increased continuously, so that the current flowing through the commutation capacitor is reduced continuously, when the voltage of the commutation capacitor reaches the action voltage of the lightning arrester, the lightning arrester acts, the current of an inductive element of the system is small, the energy storage of the inductive element is small, and the MOV energy absorption of the second lightning arrester is small.
In the invention, the bidirectional hybrid direct-current circuit breaker based on capacitance commutation can quickly break the fault, the recovery time of each device in the circuit breaker is short, and the requirement of breaking the fault current again after the system is reclosed can be met. The devices with longer action time in the circuit breaker mainly comprise a first arrester MOV1, a second arrester MOV and a third mechanical switch S. The second arrester MOV is used for absorbing energy storage of an inductive element of a system and limiting overvoltage, the first arrester MOV1 is used for absorbing energy storage of a commutation capacitor C and limiting voltage of the commutation capacitor C to a specified value after a breaker successfully cuts off a fault, the voltage of the commutation capacitor C is only limited to the set value after the breaker successfully cuts off the fault current, the energy of the voltage of the commutation capacitor C is not required to be fully discharged, the energy discharge time of the commutation capacitor C is effectively reduced, guarantee is provided for next reclosing of the breaker, the energy absorption of the first arrester MOV1 is effectively reduced, the energy absorption time of the second arrester MOV and the energy absorption time of the first arrester MOV1 are both in the 10ms magnitude, the opening and closing time of the third mechanical switch S under zero current is also in the 10ms magnitude, compared with the reclosing again in hundreds of milliseconds after the fault, the internal devices of the breaker can be sufficiently recovered to the required state, the requirement of system reclosing is met.
As shown in fig. 3 to 6, the operation process of the bidirectional hybrid dc circuit breaker based on the capacitive commutation is described as follows: the bidirectional hybrid direct current breaker based on capacitance commutation cuts off fault current and is mainly divided into four stages, namely a commutation preparation stage, a commutation stage, a second arrester MOV energy absorption stage and a first arrester MOV1 energy absorption stage, and the action principle of each stage is detailed.
As shown in fig. 3, the commutation preparation stage: at the stage T0-T1, the system normally runs, and the first thyristor T1, the second thyristor T2, the third thyristor T3, the fourth thyristor T4 and the mechanical switch S are all in an off state; at time t1, the system has a short circuit fault, assuming that fault current flows from left to right. At time T2, the detection device determines that a short-circuit fault occurs in the system, immediately triggers the second thyristor T2 and the fourth thyristor T4 to conduct, sends a turn-off command to the load switch LCS and a brake-off command to the ultrafast mechanical switch UFD, and transfers the current from the branch where the load switch LCS and the ultrafast mechanical switch UFD are located to the branch where the second thyristor T2 and the fourth thyristor T4 are located. At time t3, the UFD has reached a certain opening distance and can withstand a certain voltage without arcing.
As shown in fig. 4, the commutation phase: at the time of T3, the first thyristor T1 is triggered and switched on, the current flowing to the second thyristor T2 gradually transfers to the branch where the first thyristor T1 and the commutation capacitor are located, at the time of T4, the current of the second thyristor T2 is automatically switched off after zero crossing, and after the second thyristor T2 is switched off, the voltage of the commutation capacitor is firstly reduced to zero and then continuously increased, so that it is ensured that the second thyristor T2 does not need to immediately bear high voltage after being switched off, and the reliability of switching off the second thyristor T2 is further ensured. In the stage t 4-t 5, the UFD continues to open the brake, the fault current flows from the power supply valve side to the fault point through the converter capacitor, and at the time t5, the UFD is successfully opened; at time t6, the voltage across the MOV of the second arrester reaches its operating voltage, and the voltage polarity of the commutation capacitor changes from positive right to negative left to positive left to negative left at the initial time. Then in the period from T4 to T6, the second thyristor T2 is out of operation and the arrester has not reached the action voltage for a while.
As shown in fig. 5, the second arrester MOV energy absorbing stage: at the time of t6, when the voltage at two ends of the MOV of the second arrester reaches the action voltage, the inductive element of the absorption system starts to be operated to store energy and limit overvoltage, the current flowing through the commutation capacitor gradually transfers to the arrester, and the current of the arrester gradually increases from zero; at time t7, the voltage across the arrester rises to the arrester residual voltage. And in the stage of T7-T8, the lightning arrester keeps residual voltage, the current flowing through the commutation capacitor gradually returns to zero, and at the time of T8, the currents of the first thyristor T1 and the fourth thyristor T4 are turned off in a zero-crossing mode. And in the stage t 8-t 9, the residual voltage of the lightning arrester is kept, the current flowing through the lightning arrester is gradually reduced, and the voltage of the lightning arrester begins to be reduced from the residual voltage at the moment t 9. And at the stage of t 9-t 10, the voltage of the arrester is reduced from residual voltage to the action voltage of the arrester, the current flowing through the arrester is continuously reduced, when the voltage at two ends of the arrester is reduced to the action voltage of the arrester, the current flowing through the arrester is reduced to zero, and the MOV energy absorption of the second arrester is finished.
As shown in fig. 6, the first arrester MOV1 energy absorbing phase: and at the time t11, the third mechanical switch S is controlled to be turned on, and at the time t12, the third mechanical switch S is controlled to be successfully switched on, so that the first arrester MOV1 starts to be put into operation and absorbs part of energy stored by the commutation capacitor. At time t13, the first arrester MOV1 finishes absorbing energy, and limits the voltage of the commutation capacitor to a set value, and the polarity of the voltage of the commutation capacitor is positive left and negative right. And at the time of t14, a switching-off instruction is sent to the third mechanical switch S to control the third mechanical switch S to switch off at zero current, and at the time of t15, the third mechanical switch S is controlled to be successfully switched off, so that the circuit breaker achieves all conditions for switching off the fault again, and the requirement of system reclosing can be met. At the moment t16, the fault occurs again, and at this moment, because the polarity of the commutation capacitor voltage is reversed, the capacitor commutation module can be continuously put into operation during the fault according to the symmetry of the capacitor commutation module, and the fault current cannot be influenced when the circuit breaker is cut off again. When the fault occurs again, because the polarity of the commutation capacitor voltage changes, the operation sequence of the first thyristor T1 and the second thyristor T2 is exchanged according to the symmetry of the capacitor commutation unit, and the working sequence of the third thyristor T3 and the fourth thyristor T4 is exchanged, so that the fault current can be cut off again.
As shown in fig. 7, in the embodiment of the present invention, the ultrafast mechanical switch unit 1 is formed of the ultrafast mechanical switch UFD, has a low on-resistance and a small operation loss, and opens the fault at zero current when a short-circuit fault occurs. The load transfer switch unit 2 is mainly composed of an IGBT, and is used to cut off a fault current under a low voltage condition when a short-circuit fault occurs, and to provide a current zero-crossing turn-off condition for the ultrafast mechanical switch. The capacitance commutation unit 3 is mainly used for providing a low-voltage branch for IGBT turn-off and ultra-fast mechanical switch brake-off during fault commutation, ensuring that the IGBT and the ultra-fast mechanical switch are not required to bear high voltage in the turn-on and turn-off process, and the capacitance commutation unit has the function of self-turn-off.
The capacitance commutation unit 3 includes: a first thyristor T1, a second thyristor T2, a first mechanical switch S1, a second mechanical switch S2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a commutation capacitor C, a commutation inductor L, a first arrester MOV1 and a third mechanical switch S. A first diode D1 and a second diode D2 are connected in reverse series, and a third diode D3 and a fourth diode D4 are connected in reverse series; the first thyristor T1 and the first mechanical switch S1 are connected in series, the second thyristor T2 and the second mechanical switch S2 are connected in series; a first arrester MOV1 and a third mechanical switch S are connected in series between the series connection of the first thyristor T1 and the first mechanical switch S1 and the series connection of the second thyristor T2 and the second mechanical switch S2; the commutation capacitor C and the commutation inductor L are connected in series between the series connection of the first thyristor T1 and the first mechanical switch S1 and the series connection of the second thyristor T2 and the second mechanical switch S2. The first diode D1, the second diode D2, the third diode D3 and the fourth diode D4 mainly have the functions of changing the flow direction of fault current and ensuring that the circuit breaker can successfully cut off the fault current when the fault current is in any direction; the first arrester MOV1 and the third mechanical switch S are mainly used to absorb the energy of the commutation capacitor, limiting the voltage of the commutation capacitor to a specified value.
When the system normally works, the voltage polarity of the commutation capacitor is positive right and negative left, the first thyristor T1, the second thyristor T2, the first mechanical switch S1 and the third mechanical switch S are turned off, and the second mechanical switch S2 is turned on; when short-circuit fault occurs, triggering a second thyristor T2 to be switched on and switched off the load change-over switch unit, and sending a brake-separating instruction to the ultra-fast mechanical switch unit; when the ultra-fast mechanical switch unit reaches a proper opening distance enough to endure a certain voltage, the first thyristor T1 is controlled to be conducted, the current flowing to the second thyristor T2 is transferred to the first thyristor T1, when the current of the second thyristor T2 crosses zero, the second thyristor T2 is automatically turned off, the power supply side continues to charge the commutation capacitor, the polarity of the voltage of the commutation capacitor is reversed, the current flowing to the first thyristor T1 is gradually reduced, when the voltage of the commutation capacitor reaches a certain value, the current flowing through the first thyristor T1 returns to zero, the first thyristor T1 is automatically turned off, the inductive element of the arrester MOV action absorption system stores energy and limits overvoltage, the third mechanical switch S of the first arrester MOV1 is conducted, the stored energy of the commutation capacitor C is absorbed and limits the voltage of the commutation capacitor to a specified value, then a brake-off instruction is sent to the third mechanical switch S, the third mechanical switch S is controlled to be switched off at zero current, and a brake-off instruction is sent to the second mechanical switch S2, at the moment, the first thyristor T1, the second thyristor T2 and the first mechanical switch S1 are all in an off state, the second mechanical switch S2 can be slowly switched off under zero current and zero withstand voltage, arcing risks do not exist, when the first mechanical switch S1 and the third mechanical switch S are successfully switched off, the first mechanical switch S1 sends a switching-on instruction, then the first mechanical switch S1 is successfully switched on, and therefore the breaker achieves all conditions of breaking faults again, and the requirement of system reclosing can be met. The time from the first time of breaking the fault current to the reclosing of the breaker of the direct-current power grid is generally about 300ms, and the action time of an internal device of the breaker and the action time of a mechanical switch during the fault period are far less than 300ms, so that the requirement of system reclosing can be met.
If the fault is not eliminated after reclosing or the next fault occurs, at the moment, the first mechanical switch S1 is switched on due to the fact that the voltage polarity of the commutation capacitor is reversed, according to the symmetry of the capacitor commutation module, the action sequence of the first thyristor T1 and the action sequence of the second thyristor T2 are exchanged when the fault occurs, the action sequence of the first mechanical switch S1 and the action sequence of the second mechanical switch S2 are exchanged, the action sequence of other devices of the circuit breaker is unchanged, and the fault current cannot be influenced when the circuit breaker is switched off again.
Due to the symmetrical design of the diodes of the capacitance commutation module, the direction of the fault current can be corrected to the direction of the current passing through the first thyristor T1, the second thyristor T2, the third thyristor T3 and the fourth thyristor T4 when the direction of the fault current changes, and the two thyristors are utilized to realize the bidirectional breaking and reclosing of the fault current and then the fault current is broken again.
The circuit breaker has obvious advantages when the circuit breaker is used for breaking small fault current, and can meet the requirement that the fault current of a direct current power grid is smaller than rated current. Because the capacity of the commutation capacitor of the required circuit breaker is small, the voltage of the commutation capacitor can be quickly charged to a higher value by a small fault current to block the fault current.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A bidirectional hybrid direct current circuit breaker based on capacitance commutation is characterized by comprising: the system comprises an ultra-fast mechanical switch unit (1), a load change-over switch unit (2), a capacitance commutation unit (3) and an energy absorption unit (4);
the ultra-fast mechanical switch unit (1) is connected with the load change-over switch unit (2) in series, the capacitance commutation unit (3) is connected with the ultra-fast mechanical switch unit (1) and the load change-over switch unit (2) which are connected in series in parallel, and the energy absorption unit (4) is connected with the capacitance commutation unit (3) in parallel;
the capacitance commutation unit (3) is used for providing a low-voltage branch circuit for the ultra-fast mechanical switch unit (1) and the load change-over switch unit (2) to ensure normal on-off when a system has a short-circuit fault, and cutting off a fault current by using a self-off function;
the energy absorption unit (4) is used for absorbing energy stored by a inductive element in the power system after fault current is cut off when the power system is in a break-open fault.
2. A hybrid dc circuit breaker according to claim 1, characterized in that the capacitive commutation cell (3) comprises: the power supply comprises a first thyristor T1, a second thyristor T2, a third thyristor T3, a fourth thyristor T4, a commutation capacitor C, a commutation inductor L and a voltage limiting unit;
the first thyristor T1 and the third thyristor T3 are connected in series, the second thyristor T2 and the fourth thyristor T4 are connected in series, and the voltage limiting unit is connected between a series connection terminal of the first thyristor T1 and the third thyristor T3 and a series connection terminal of the second thyristor T2 and the fourth thyristor T4; the commutation capacitor C and the commutation inductor L are connected in series between a series connection end of the first thyristor T1 and the third thyristor T3 and a series connection end of the second thyristor T2 and the fourth thyristor T4.
3. A hybrid dc circuit breaker according to claim 1, characterized in that the capacitive commutation cell (3) comprises: the circuit comprises a first thyristor T1, a second thyristor T2, a first mechanical switch S1, a second mechanical switch S2, a commutation capacitor C, a commutation inductor L and a voltage limiting unit;
the first thyristor T1 and the first mechanical switch S1 are connected in series, the second thyristor T2 and the second mechanical switch S2 are connected in series, and the voltage limiting unit is connected between the series connection of the first thyristor T1 and the first mechanical switch S1 and the series connection of the second thyristor T2 and the second mechanical switch S2; the commutation capacitor C and the commutation inductor L are connected in series between the series connection end of the first thyristor T1 and the first mechanical switch S1 and the series connection end of the second thyristor T2 and the second mechanical switch S2.
4. A hybrid direct current circuit breaker according to claim 2 or 3, characterized in that the capacitive commutation cell (3) further comprises: a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4;
the cathode of the first diode D1 is connected with the anode of the first thyristor T1, the anode of the second thyristor T2 and the cathode of the second diode D2; an anode of the third diode D3 is connected to a cathode of the third thyristor T3, a cathode of the fourth thyristor T4 and an anode of the fourth diode D4;
an anode of the first diode D1 and a cathode of the third diode D3 are used as one end of the capacitance commutation unit (3), and an anode of the second diode D2 and a cathode of the fourth diode D4 are used as the other end of the capacitance commutation unit (3).
5. A hybrid DC circuit breaker according to any of claims 2-4, characterized in that the voltage limiting unit is adapted to limit the voltage of the commutating capacitor to a set value, the voltage limiting unit comprising: a first arrester MOV1 and a third mechanical switch S connected in series in that order.
6. Hybrid direct current circuit breaker according to any of claims 1 to 5, characterized in that when a short circuit fault occurs, the second thyristor T2 and the fourth thyristor T4 are triggered to conduct and turn off the load transfer switch unit (2), giving a switch-off command to the ultra-fast mechanical switch unit (1).
7. The hybrid dc circuit breaker according to claim 6, wherein when the ultrafast mechanical switch unit (1) reaches a set opening distance, the first thyristor T1 is controlled to be turned on, the current flowing to the second thyristor T2 is diverted to the first thyristor T1, and is automatically turned off when the current of the second thyristor T2 crosses zero, the power supply side continues to charge the commutation capacitor, the polarity of the commutation capacitor voltage is reversed, the current flowing to the first thyristor T1 and the fourth thyristor T4 is gradually reduced, when the commutation capacitor voltage reaches a set value, the current flowing through the first thyristor T1 and the fourth thyristor T4 is zeroed, the first thyristor T1 and the fourth thyristor T3 are automatically turned off, the arrester MOV action absorbs the system inductive energy storage and limits the overvoltage, the third mechanical switch S is controlled to turn on the arrester MOV1, the absorption capacitor C stores energy and limits the commutation capacitor voltage to a designated value, and preparing for the next reclosing.
8. A dc transmission system comprising a hybrid dc circuit breaker according to any of claims 1 to 7.
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| CN202010713267.0A CN111696803A (en) | 2020-07-22 | 2020-07-22 | Bidirectional hybrid direct-current circuit breaker based on capacitance commutation and direct-current power transmission system |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113644636A (en) * | 2021-07-21 | 2021-11-12 | 国网冀北电力有限公司电力科学研究院 | Multi-terminal hybrid high-voltage direct-current circuit breaker based on capacitance commutation |
| CN113852051A (en) * | 2021-09-13 | 2021-12-28 | 中国科学院电工研究所 | Direct-current solid-state circuit breaker with bidirectional breaking and soft starting functions and control method |
| CN114172128A (en) * | 2021-12-02 | 2022-03-11 | 中国科学院电工研究所 | Direct current solid-state circuit breaker capable of being opened and closed bidirectionally based on hybrid device |
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2020
- 2020-07-22 CN CN202010713267.0A patent/CN111696803A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113644636A (en) * | 2021-07-21 | 2021-11-12 | 国网冀北电力有限公司电力科学研究院 | Multi-terminal hybrid high-voltage direct-current circuit breaker based on capacitance commutation |
| CN113852051A (en) * | 2021-09-13 | 2021-12-28 | 中国科学院电工研究所 | Direct-current solid-state circuit breaker with bidirectional breaking and soft starting functions and control method |
| CN114172128A (en) * | 2021-12-02 | 2022-03-11 | 中国科学院电工研究所 | Direct current solid-state circuit breaker capable of being opened and closed bidirectionally based on hybrid device |
| CN114172128B (en) * | 2021-12-02 | 2022-06-24 | 中国科学院电工研究所 | Direct current solid-state circuit breaker capable of being opened and closed bidirectionally based on hybrid device |
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