CN217956686U - Protection circuit for preventing fault expansion of alternating current side of controllable rectifier - Google Patents
Protection circuit for preventing fault expansion of alternating current side of controllable rectifier Download PDFInfo
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Abstract
The invention discloses a protection circuit for preventing the expansion of a fault at the AC side of a controllable rectifier, which comprises a current transformer, a three-phase bridge rectifier bridge ZLQ, a voltage-regulator tube D1, an isolation diode D2, a switch triode T1 and a triode T2, wherein the current transformer is connected with the three-phase bridge rectifier bridge stack ZLQ; the current transformer, the controllable rectifier, the ZLQ and the D1 cathode are sequentially connected; the positive electrode of the D1 is connected with the b electrode of the T1 after being connected with the R6 in series; the c pole of T1 is connected with the b pole of T2 after being connected with R10 in series; the c pole of T2 is connected with R9 in series and then connected with a reset button; the c pole of the T1 is also connected with a reset button after being connected with the R7 in series; the c pole of the T1 is connected with the R8 in series and then connected with the negative pole of the D2; the positive electrode of the D2 is connected with a direct-current short-circuit protection high level; the voltage of the c pole of the T1 is transmitted to a master control system as a short-circuit signal of the alternating current side of the rectifier; wherein the voltage value between R8 and D2 serves as the blocking level for the thyristor pulse circuit. The invention can detect in time and effectively block the trigger pulse signal of the thyristor when the alternating current side of the controllable rectifier is short-circuited.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a protection circuit for preventing the expansion of a fault on an alternating current side of a controllable rectifier.
Background
The high-power controllable rectifier is widely applied to industrial and mining enterprises, electric power enterprises and rail traffic, a large number of expensive high-power semiconductor device thyristors are used in the high-power rectifiers, the devices are used as key devices in the controllable rectifiers, the operation is safe and reliable, but overload and electrical impact exceeding normal working conditions exist in most high-power rectifier use occasions, the thyristors are easy to break down and damage, once one thyristor breaks down and damages, metal objects cause short circuit, conductive dust on the surface of the device and water pull electric arc short circuit cannot be isolated timely, the thyristor breaks down and damages in sequence, and great equipment loss and production loss are caused. In order to protect these key devices, a high-power fast fuse is often connected in series in a thyristor loop for protection, so that the thyristor can be prevented from being damaged due to overload, and a fault loop can be isolated, and at present, the high-power rectifier is a solution like this.
The high-power thyristor branch is connected with the fast fuse in series to protect the thyristor and isolate the fault, but the high-power thyristor branch is an inexhaustible choice, the cost of the high-power thyristor branch is higher than that of the thyristor, and the price of the high-power thyristor branch accounts for a considerable part of the equipment investment cost; the structure is complex due to large volume, the occupied space is large, the assembly and the replacement are very inconvenient, the quick fuse is disposable, once fusing protection is generated, the quick fuse needs to be replaced, the replacement is troublesome, and the operation cost is high; in addition, the fast fuse is a current conductor, and certain electric energy consumption and heating are generated under normal working conditions, so that adverse factors are brought to the running environment of equipment, and energy conservation and consumption reduction are not facilitated.
Disclosure of Invention
1. The technical problem to be solved is as follows:
aiming at the technical problems, the invention provides a protection circuit for preventing the fault expansion of the alternating current side of a controllable rectifier, which can respectively block or keep processing pulse control signals of a thyristor of the rectifier under the three conditions of normal operation, short circuit of the alternating current side of the rectifier and short circuit of the direct current side, so that the control pulses of the thyristor are blocked when the alternating current is detected to be short-circuit fault, other thyristors can not be conducted, and short-circuit fault current can not follow current at the rectifier side to be eliminated, thereby not only preventing the thyristor from being subjected to impact breakdown of the short-circuit current, but also eliminating the fault current (avoiding the fault expansion), and achieving the purpose of protecting the rectifier; meanwhile, the sampling circuit can also output short-circuit fault information of the alternating current side of the rectifier to a system main control board, after the main control board receives the signal, a control program immediately runs in a rectifier fault protection mode, and pulse sealing signals and the fault information of the alternating current side of the rectifier are sent out again by software, so that the aim of double protection is fulfilled. In order to distinguish the short-circuit condition of the direct current side, the controllable rectifier is operated in a rectification overload mode to shunt the short-circuit current flowing through the IGBT freewheeling diode in the inverter so as to achieve the purpose of protecting the IGBT.
2. The technical scheme is as follows:
a protection circuit for preventing the fault expansion of the alternating current side of a controllable rectifier is used for protecting a bidirectional converter of rail transit; the method is characterized in that: the controllable rectifier in the bidirectional converter is configured for enlarging the direct current output capability, and the controllable rectifier and the converter are connected in parallel to output power to a direct current load in a rectification mode; the master control system of the bidirectional converter coordinates the output of the controllable rectifier and the converter by controlling the trigger pulse of the thyristor of the controllable rectifier.
In the application, the bidirectional converter is a high-power electronic device which provides a driving direct-current power supply for an electric locomotive in rail transit and feeds back electric energy converted from mechanical energy to an alternating-current power supply grid system in the locomotive station entering and braking process, wherein a controllable rectifier is configured for the converter to enlarge direct-current output capacity, and the controllable rectifier and the converter are connected in parallel to output to supply power to a direct-current load in a rectification mode; the main control system of the bidirectional converter coordinates the output of the controllable rectifier and the converter by controlling the trigger pulse of the thyristor of the controllable rectifier.
The protection circuit comprises a three-phase current transformer, a three-phase bridge rectifier bridge stack ZLQ, a voltage-stabilizing tube D1, an isolating diode D2, a switch triode T1 and a triode T2; the concrete connection mode is as follows: three-phase current is respectively connected to the alternating current input end of the controllable rectifier through three current transformers, and the output ends of the current transformers are respectively connected to the three alternating current input ends of the three-phase bridge rectifier bridge stack ZLQ; the output end of the three-phase bridge rectifier bridge ZLQ is connected with the negative electrode of a voltage-stabilizing tube D1; the anode of the voltage-regulator tube D1 is connected with a resistor R6 in series and then is connected to the base electrode of the switching triode T1; the collector of the switching triode T1 is connected with the resistor R10 in series and then is connected to the base of the triode T2; the collector of the triode T2 is connected with the resistor R9 in series and then is connected to the reset button; the collector of the switching triode T1 is connected with the reset button after being connected with the resistor R7 in series; the collector of the switching triode T1 is connected with the negative electrode of the isolating diode D2 after being connected with the resistor R8 in series; the anode of the isolation diode D2 is connected with a direct-current short-circuit protection high level sent by the main control system; a voltage signal of a collector electrode of the switching triode T1 is transmitted to a main control system as a rectifier alternating current side short circuit signal;
the voltage value between the resistor R8 and the isolation diode D2 is used as a blocking level of the thyristor pulse circuit, and the main control system judges whether the rectifier AC side is short-circuited or not after receiving an abnormal large current signal at the rectifier AC side and determines whether a blocking level signal is sent to the controllable rectifier thyristor trigger pulse circuit or not.
Wherein, the voltage value between the resistor R8 and the isolation diode D2 is used as the blocking level of the thyristor pulse circuit, and the main control system receives a blocking level signal to the thyristor trigger pulse circuit of the controllable rectifier.
Further, a feedback resistor R11 is connected in parallel between the base of the switching triode T1 and the emitter of the triode T2; the output end of the three-phase current transformer is respectively connected with the converting resistors R1, R2 and R3 in series and then grounded; the output end of the three-phase bridge rectifier bridge ZLQ is connected with a resistor R4 in parallel and then is connected with a voltage stabilizing tube D1; and a resistor R5 is connected in series between the positive electrode of the voltage-stabilizing tube D1 and the negative output end of the three-phase bridge rectifier bridge stack ZLQ.
3. Has the advantages that:
after the scheme is adopted, an expensive fast fuse is saved in the controllable rectifier, the structure of the controllable rectifier is simplified, the size is reduced, the heat productivity in the controllable rectifier is reduced, the maintenance cost and the workload are reduced, more importantly, once the short-circuit fault occurs at the alternating current side of the controllable rectifier, the protection circuit can detect the short-circuit fault in time and can effectively block the thyristor trigger pulse signal, the blocking voltage Uk is only about 0.2V (rather than about 21V when the Uk normally operates at the non-fault moment), and meanwhile, the short-circuit fault signal at the alternating current side can be sent to the main control in time; thyristor I selected according to the bi-directional converter auxiliary controlled rectifier 2 t value and actual short-circuit current, the effective time from the occurrence of short-circuit fault to the blocking voltage Uk is not more than 10ms in actual measurement, which is less than half of the surge impact resistant time of the thyristor, and the aims of protecting the thyristor and eliminating a short-circuit can be completely fulfilled; when a direct-current side short-circuit test is carried out, the blocking signal is replaced by a direct-current side short-circuit protection high-level signal sent by a master controller, the rectifier can still work normally, the actually measured data rectifier can shunt over 80% of short-circuit peak current originally borne by an IGBT freewheeling diode in the converter, and the IGBT can be effectively protected from being damaged by short-circuit impact current.
Drawings
FIG. 1 is a schematic diagram of a protection circuit according to the present invention for short-circuit protection of rectifier failure;
fig. 2 is a schematic diagram of current distribution for realizing a short circuit on the dc side in a bidirectional converter by using the protection circuit of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
As shown in the attached figure 1, the scheme provides a low-cost alternating current side current sampling signal, processes the sampling signal and sends the sampling signal to a main control board, and locks or keeps processing the thyristor pulse control signal of the rectifier under the three conditions of normal operation, rectifier alternating current side short circuit and direct current side short circuit respectively, so that the thyristor control pulse is locked when the alternating current short circuit fault is detected, other thyristors can not be conducted, and the short circuit fault current can not follow current at the rectifier side to be eliminated, thereby not only preventing the thyristor from being subjected to impact breakdown of the short circuit current, but also eliminating the fault current (avoiding fault expansion), and achieving the purpose of protecting the rectifier; meanwhile, the sampling circuit can also output short-circuit fault information of the alternating current side of the rectifier to a system main control board, after the main control board receives the signal, a control program immediately runs in a rectifier fault protection mode, and software sends a pulse-sealing signal and the fault information of the alternating current side of the rectifier again, so that the aim of double protection is fulfilled. In order to distinguish the short-circuit condition of the direct current side, the controllable rectifier is operated in a rectification overload mode to shunt the short-circuit current flowing through the IGBT freewheeling diode in the inverter so as to achieve the purpose of protecting the IGBT.
In order to solve the above technical problems, the present invention takes the following measures.
Firstly, sampling current transformers CTa, CTb and CTc are added on the three-phase alternating current input side of a rectifier, the output end of each current transformer is connected with a small-resistance high-power resistor, the power is more than 20W, voltage waveforms consistent with the current waveforms are respectively generated on the sampling resistors, the three-phase voltage proportional to the three-phase alternating current is used as the voltage of the input end of a three-phase bridge rectifier bridge ZLQ, the sampling rectifier bridge ZLQ outputs a direct current voltage, the direct current output of the sampling rectifier bridge is small and only a few volts under the normal operation condition of the controllable rectifier, the stable voltage value Uz of a voltage stabilizing tube D1 cannot be in a cut-off state, a switching triode T1 is kept in a closed state, a triode T2 is kept in a saturated conduction state, uk is kept in a high-level state, and the controllable rectifier pulse can normally trigger thyristors KP 1-KP 6; when a short circuit on the alternating current side of the controllable rectifier, such as a damaged thyristor, a short circuit caused by metal objects, an arc short circuit caused by conductive dust on the surface of a device, and the like, is encountered, a large short circuit current is generated. The short-circuit current is far larger than the normal running current, so that a larger voltage signal can be generated on a sampling resistor of the current transformer, a direct-current voltage far larger than that under the normal condition is generated through the output of the ZLQ, the voltage is enough to exceed the Uz value of D1, the T1 is in saturated conduction, the output Uk of the T1 is enabled to be close to 0V output, the level controls the enabling ends of all thyristors of the controllable rectifier, the trigger pulse signal of the thyristors is blocked, all the thyristors are in a blocking state, the thyristor device is protected, meanwhile, the T2 is out of the conduction state and is switched to the blocking state due to the saturated conduction of the triode T1, the feedback voltage Uf is changed into a high level, and the triode T1 is further kept in the saturated conduction state through the R11 feedback resistor and is kept in the state all the time. And only when the normal operation of the controllable rectifier needs to be recovered after the short-circuit fault is processed, the blocking pulse signal is eliminated through the reset button, and the triode T1 is out of saturation conduction to be in a cut-off state.
On the rail transit bidirectional converter project, the alternating current fault protection does not affect the short-circuit current of an IGBT freewheeling diode in the converter which is shunted by the controllable rectifier under the condition of short circuit at the direct current side. Although the direct current side short circuit can cause the controllable rectifier to generate huge output current, the controllable rectifier can enable T1 to be in saturated conduction, when the main control detects that the direct current side short circuit exists, a high level signal is sent to the protection circuit, the blocking signal is clamped at a high level due to the effect of the isolation diode D2, the blocking signal is invalid, the controllable rectifier can share most of direct current side short circuit current in a short time by utilizing the overload capacity of the controllable rectifier, once the control system detects that the direct current side short circuit exists, the direct current power supply system can be quickly operated in a short circuit fault processing mode, and therefore the safety of direct current power supply equipment is guaranteed.
The specific embodiment is as follows:
in practical application, the rated voltage of the controllable rectifier is 1500V, and the rated current is 2000A; thyristors KP 1-KP 6 are usually of type KK28F45N, and their on-state non-repetitive current is 45KA 2 t is 10244; the sampling rectifier adopts a three-phase rectifier bridge stack with a reduced tube voltage.
As shown in the attached figure 1, three CTA, CTB and CTC current transformers (2000/5) are respectively installed on an alternating current input loop of the controllable rectifier and used for detecting alternating current input current of the controllable rectifier, the three-phase current transformers select output power larger than 15 watts, conversion resistors R1, R2 and R3 select resistors of 0.5 omega/20W, resistors R4, R5 and R6 select resistors of 1k/0.5W, resistors R7 select 1k/1W, resistors R9 select 4.7k/1W, resistors R8, R10 and R11 select 10k/0.5W, triode transistors T1 and T2 select 3DK series, a voltage regulator D1 selects 6-8V voltage regulator isolation diodes D2 select 1N1007, and VCC is 24V.
1. In a normal commutation mode: the three-phase alternating current input current is less than 1800A, the output current of three current transformers is 0-4.5A, the output direct current voltage of a three-phase bridge rectifier bridge stack ZLQ is about 4V, the voltage drop of the internal tube of the bridge stack is considered, no current passes through a voltage stabilizing tube D1 when the voltage stabilizing tube D1 is cut off, T2 is saturated and conducted, the voltage Uk of a collector of the T1 is greater than 20V, and the voltage Uf of the collector of the T2 is about 0.2V. The enabling control end of the controllable rectifier is in high level, the trigger pulse can trigger the thyristor, and the rectifier outputs normally.
2. When the AC side of the rectifier is in fault and short circuit: for example, when a thyristor in KP 1-KP 6 breaks down, a metal piece causes a short circuit, surface water or conductive dust on a device causes a surface arc short circuit, the alternating current mutual inductance detects the fault short circuit current, so that the fault short circuit current is generated and is far larger than the rated current 5A, the voltage is converted into voltage through a resistor, the output of a three-phase rectifier bridge stack ZLQ is instantly increased, the output high voltage is larger than the stable voltage Uz of D1 to conduct D1, T1 is conducted, T2 is cut off until the output voltage becomes high, current is injected into T1 through a feedback resistor R11, so that T1 is rapidly saturated and conducted, uk is about 0.2V and a trigger pulse signal of KP 1-KP 6 is blocked through R8, a low-level signal of a blocking pulse is sent to a main control board, the main control program immediately enters an alternating-current side fault short circuit processing mode, software also sends a blocking pulse signal to form double protection, KP 1-KP 6 is cut off along with the fault circuit, and the fault current cannot be cut off through the thyristor, so that other devices on the direct-current circuit are effectively protected. During the period, T1 always outputs low level, no matter whether the fault short circuit on the AC side disappears or not, the blocking signal can be unblocked only by pressing a reset button after the fault is processed, and the controllable rectifier can be operated again.
3. Direct current side short circuit condition: the protection circuit of the scheme shown in the attached figure 2 is explained by combining with the direct current side short-circuit protection of the bidirectional converter, the output of the converter and the output of the controllable rectifier are connected in parallel to supply power to a direct current side load in a bidirectional converter loop, because the converter has a high-power IGBT, although a system detects that the direct current side short-circuit fault blocks the IGBT trigger pulse of the converter in time, a freewheeling diode in the converter is in a rectification mode because the direct current side short-circuit direct current voltage is far less than the alternating current side voltage, the freewheeling diode flows a large short-circuit current and is subjected to overcurrent breakdown to directly cause damage of expensive IGBT elements, therefore, when the direct current side short-circuit occurs, the controllable rectifier needs to continue to operate, the overload capacity (far greater than that of the freewheeling diode in the IGBT) of the thyristor is fully utilized to share most of the short-circuit current flowing through the freewheeling diode in the converter, so as to protect the IGBT, therefore, a high-level signal from the direct current side short-circuit protection is required to be used to pull up a Uk low-level signal (forced to be blocked) possibly caused by the output of the large current side short-circuit under the condition that the direct current side short-circuit fault is output by the D2 through the controllable rectifier, thereby ensuring that the operation of the controllable rectifier under the direct current side short-circuit protection high-circuit, the direct current side short-circuit is further capable of isolating the isolation circuit protection of isolating the direct current side short-circuit, and the bidirectional converter, and the controllable rectifier is further capable of preventing the isolation circuit protection of the isolation circuit, and the direct current isolation circuit protection of the bidirectional converter, and the isolation circuit, and the direct current isolation circuit protection of the direct current isolation circuit, and the protection of the bidirectional converter is further expanding protection of the direct current isolation circuit.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (2)
1. A protection circuit for preventing the fault expansion of the alternating current side of a controllable rectifier is used for protecting a bidirectional converter of rail transit; the method is characterized in that: the controllable rectifier in the bidirectional converter is configured for enlarging the direct current output capacity, and the controllable rectifier and the converter are connected in parallel to output power to a direct current load in a rectification mode; the main control system of the bidirectional converter coordinates the output of the controllable rectifier and the converter by controlling the trigger pulse of the thyristor of the controllable rectifier;
the protection circuit comprises a three-phase current transformer, a three-phase bridge rectifier bridge stack ZLQ, a voltage-stabilizing tube D1, an isolation diode D2, a switch triode T1 and a triode T2; the concrete connection mode is as follows: three-phase current is respectively connected to the alternating current input end of the controllable rectifier through three current transformers, and the output ends of the current transformers are respectively connected to the three alternating current input ends of the three-phase bridge rectifier bridge stack ZLQ; the output end of the three-phase bridge rectifier bridge ZLQ is connected with the negative electrode of a voltage-stabilizing tube D1; the anode of the voltage-regulator tube D1 is connected with a resistor R6 in series and then is connected to the base electrode of the switching triode T1; the collector of the switching triode T1 is connected with the resistor R10 in series and then is connected to the base of the triode T2; the collector of the triode T2 is connected with the resistor R9 in series and then is connected to the reset button; the collector of the switching triode T1 is connected with the reset button after being connected with the resistor R7 in series; the collector of the switching triode T1 is connected with the negative electrode of the isolating diode D2 after being connected with the resistor R8 in series; the anode of the isolation diode D2 is connected with a direct-current short-circuit protection high level sent by a main control system; a voltage signal of a collector electrode of the switching triode T1 is transmitted to a main control system as a rectifier alternating current side short circuit signal;
the voltage value between the resistor R8 and the isolation diode D2 is used as a blocking level of the thyristor pulse circuit, and the main control system judges whether the rectifier AC side is short-circuited or not after receiving an abnormal large current signal at the rectifier AC side and determines whether a blocking level signal is sent to the controllable rectifier thyristor trigger pulse circuit or not.
2. The protection circuit of claim 1, wherein the protection circuit is configured to prevent the ac side fault of the controlled rectifier from propagating, and further comprises: a feedback resistor R11 is connected in parallel between the base electrode of the switching triode T1 and the emitting electrode of the triode T2; the output end of the three-phase current transformer is respectively connected with the converting resistors R1, R2 and R3 in series and then grounded; the output end of the three-phase bridge rectifier bridge ZLQ is connected with a resistor R4 in parallel and then is connected to a voltage regulator tube D1; and a resistor R5 is connected in series between the positive electrode of the voltage-stabilizing tube D1 and the negative output end of the three-phase bridge rectifier bridge stack ZLQ.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202221660032.0U CN217956686U (en) | 2022-06-29 | 2022-06-29 | Protection circuit for preventing fault expansion of alternating current side of controllable rectifier |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202221660032.0U CN217956686U (en) | 2022-06-29 | 2022-06-29 | Protection circuit for preventing fault expansion of alternating current side of controllable rectifier |
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