Active protection device and protection method for DC power supply used in substation based on fault location

Abstract

A DC power active protection device and protection method for a substation based on fault location, a protection device is provided between a DC bus and each DC feeder branch, the protection device includes a single-chip control circuit and a power electronic circuit breaker and a fault detection circuit connected to the single-chip control circuit, the output end of the DC bus is connected to the input end of the power electronic circuit breaker, the output end of the power electronic circuit breaker is connected to the corresponding DC feeder branch, the control signal output end of the single-chip control circuit is connected to the control signal input end of the power electronic circuit breaker; the fault detection circuit includes a voltage and current sampling circuit and a ground fault detection circuit. The DC power active protection device of the present invention can timely detect the grounding and short circuit faults of the DC system in the substation, locate the corresponding faulty DC branch, and timely adjust the voltage output to the feeder branch according to the fault, thereby improving the continuity, reliability and safety of the DC power supply system of the substation.

Description

Technical Field

[0001] The invention relates to a DC power supply active protection device for a transformer substation based on fault location, and also relates to a protection method for the DC power supply active protection device, belonging to the technical field of electric power automation. Background Art

[0002] For the DC system of the substation, due to various reasons, grounding and short circuit faults often occur in the DC system in the station. Long-term operation of the DC system with single-point grounding in the station is not allowed. If it is not handled in time, when a grounding fault occurs at the other pole again, it will cause a short circuit in the DC system and cause DC power outage.

[0003] The existing DC system ground fault solution and fault location technology have many shortcomings: due to the poor anti-interference ability of the finder, false alarms of ground faults may occur. Any wire connected to the DC bus must be found, which requires a large amount of work and cannot achieve rapid and accurate location of ground faults. In addition, the current DC system basically relies on the passive tripping and fuse protection of circuit breakers and fuses, and cannot achieve active monitoring and active protection of DC faults. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an active DC power supply protection device for a substation based on fault location, which can not only timely detect grounding and short-circuit faults of the DC system in the substation, but also accurately locate the DC branch corresponding to the fault, and can also timely adjust the voltage output to the feeder branch according to the fault, thereby improving the continuity, reliability and safety of the DC power supply system of the substation.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] An active DC power supply protection device for a substation based on fault location, wherein the protection device is provided between the DC bus (DC power supply) and each DC feeder branch (the DC feeder branches are connected in parallel with each other), wherein the protection device comprises a single-chip control circuit and a power electronic circuit breaker and a fault detection circuit connected to the single-chip control circuit, wherein the output end of the DC bus is connected to the input end of the power electronic circuit breaker, the output end of the power electronic circuit breaker is connected to the corresponding DC feeder branch, and the control signal output end of the single-chip control circuit is connected to the control signal input end of the power electronic circuit breaker; the fault detection circuit comprises a voltage and current sampling circuit and a ground fault detection circuit;

[0007] The ground fault detection circuit includes a first isolation diode D1, a second isolation diode D2, a first electronic switch S1, a second electronic switch S2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first capacitor C1, a second capacitor C2, a first diode D30, a second diode D40, a first voltage limiting diode D3 and a second voltage limiting diode D4;

[0008] The positive electrode of the output end of the power electronic circuit breaker is connected to the positive electrode of the first isolation diode D1, the negative electrode of the first isolation diode D1 is connected to one end of the first electronic switch S1 and one end of the second resistor R2, the other end of the first electronic switch S1 is connected to one end of the first resistor R1, and the other end of the second resistor R2 is connected to one end of the fifth resistor R5; the negative electrode of the output end of the power electronic circuit breaker is connected to the negative electrode of the second isolation diode D2, the positive electrode of the second isolation diode D2 is connected to one end of the second electronic switch S2 and one end of the fourth resistor R4, the other end of the second electronic switch S2 is connected to one end of the third resistor R3, and the other end of the fourth resistor R4 is connected to one end of the sixth resistor R6; the other end of the first resistor R1 is connected to the third The other end of the resistor R3 is connected, and the other end of the fifth resistor R5 is connected to the other end of the sixth resistor R6; the junction of the first resistor R1 and the third resistor R3, and the junction of the fifth resistor R5 and the sixth resistor R6 are connected to ground, and are respectively connected to a +3.3V power supply through a first diode D30 and a forward series branch of a first voltage limiting diode D3, and are connected to a +3.3V power supply through a second diode D40 and a forward series branch of a second voltage limiting diode D4; the junction of the second resistor R2 and the fifth resistor R5 is connected to a junction of the first diode D30 and the first voltage limiting diode D3 and is grounded through a first capacitor C1, and the positive bus-to-ground voltage U is measured from the junction of the first diode D30 and the first voltage limiting diode D3 1+ The junction of the fourth resistor R4 and the sixth resistor R6 is connected to the junction of the second diode D40 and the second voltage limiting diode D4 and is grounded through the second capacitor C2, and the positive bus voltage to ground U is measured from the junction of the second diode D40 and the second voltage limiting diode D4 1- ;

[0009] The DC power supply active protection device determines the fault and implements protection in the following ways:

[0010] Step 1: The output voltage and current of the DC bus in the DC feed branch are collected through the voltage and current sampling circuit. The single chip microcomputer compares the voltage and current sampling data with the voltage and current set values, and predicts and judges the short circuit fault according to the comparison results; the single chip microcomputer samples the output voltage data and output current data at all times, and the corresponding digital quantities are U o _AD and I o_AD, set the digital quantity U_SET corresponding to the output voltage comparison threshold during short - circuit fault in the single - chip microcomputer. At the same time, set the digital quantity I_SET corresponding to the output current comparison threshold during short - circuit fault in the single - chip microcomputer; compare the magnitudes of U o _AD and U_SET, and the magnitudes of I o _AD and I_SET. When U o _AD < U_SET and I o _AD > I_SET, it indicates that a short - circuit fault has occurred in the feeder branch. The single - chip microcomputer sends a current - limiting output signal to the power electronic circuit breaker and simultaneously issues a short - circuit fault alarm signal through the fault alarm circuit;

[0011] Step 2, simultaneously sample the voltages of the positive and negative busbars to the ground in the DC feeder branch through the ground - fault detection circuit, and send the sampled data to the single - chip microcomputer for data processing and calculation, and predict and judge the ground faults of the positive and negative busbars according to the calculation results; the single - chip microcomputer calculates the insulation resistances of the positive and negative busbars to the ground based on the sampled values of the voltages of the positive and negative busbars to the ground, and obtains the insulation resistance values of the positive and negative busbars to the ground as R + and R - ; compare the obtained resistance values with the alarm thresholds of the insulation resistances of the positive and negative busbars to the ground set in the program. The alarm thresholds of the insulation resistances of the positive and negative busbars to the ground are R+_SET and R - _SET respectively. When R + < R+_SET, the single - chip microcomputer reports a fault of the decreasing insulation of the positive busbar; when R - < R - _SET, the single - chip microcomputer reports a fault of the decreasing insulation of the negative busbar;

[0012] The single - chip microcomputer samples the voltage data of the positive and negative busbars to the ground to calculate the insulation resistances of the positive and negative busbars to the ground. The calculation process is as follows, where R1 = R3, R2 = R4, R5 = R6;

[0013] Close S1, open S2, delay for a certain time, and measure the voltages of the positive and negative busbars to the ground as U 1+ 、U 1- , and get:

[0014]

[0015] Open S1, close S2, delay for a certain time, and measure the voltages of the positive and negative busbars to the ground as U 2+ 、U 2- , and get:

[0016]

[0017] Combining equations (1) and (2) gives:

[0018]

[0019] The single-chip microcomputer calculates the insulation resistances of the positive and negative busbars to the ground according to the sampled values of the voltages of the positive and negative busbars to the ground, and uses equations (3) and (4) to obtain the resistance values of the insulation resistances of the positive and negative busbars to the ground as R + and R - ; set the alarm thresholds for the insulation resistances of the positive and negative busbars to the ground, namely R+_SET and R-_SET respectively; when R+ < R+_SET, the single-chip microcomputer reports a fault of decreased insulation of the positive busbar; when R- < R-_SET, the single-chip microcomputer reports a fault of decreased insulation of the negative busbar;

[0020] Step 3: The single-chip microcomputer outputs different control signals according to the calculation results of Step 1 and Step 2 and the predicted fault types, and transmits the corresponding control signals to the power electronic circuit breaker for execution; when a grounding fault occurs in the positive busbar or the negative busbar, the single-chip microcomputer gives a control signal to control the power electronic circuit breaker to continue to work normally, and at the same time issues an alarm signal for the corresponding fault branch; when a short-circuit fault occurs, the single-chip microcomputer gives a control signal to control the power electronic circuit breaker to be in a current-limiting working state, and at the same time issues an alarm signal for the corresponding fault branch.

[0021] Wherein, the protection device further includes a fault alarm circuit, and the fault alarm circuit is connected to the single-chip microcomputer control circuit.

[0022] Wherein, the power electronic circuit breaker includes a voltage input terminal Uin, a voltage output terminal Uo, MOS transistors Q1 to Q4, a high-frequency isolation transformer T, a resonant inductor Lr, an output inductor L1, and rectifier diodes D11 to D14. The four signal driving terminals of PWM1 to PWM4 of the single-chip microcomputer are respectively connected to the four MOS transistors Q1 to Q4 of the power electronic circuit breaker, and the four signal driving terminals of PWM1 to PWM4 control the conduction and cutoff of the MOS transistors Q1 to Q4.

[0023] Wherein, the single-chip microcomputer model adopted by the single-chip microcomputer control circuit is STM32F101RBT. Ui is the input voltage sampling port AN0, Uo is the output voltage sampling port AN2, Io is the output current sampling port AN1, and AN5 and AN6 are respectively the sampling ports for the voltages of the positive and negative DC busbars to the ground in the DC feed-out branch. The four signal driving terminals of PWM1 to PWM4 are respectively connected to the four MOS transistors Q1 to Q4 of the power electronic circuit breaker.

[0024] In the active protection device for the DC power supply of the present invention, the power electronic circuit breaker uses power electronic conversion technology to realize the conversion of DC voltage, converts the input DC power into controllable DC power, and supplies power to the load of the DC feed-out branch, and has the voltage and current transmission function of the circuit breaker; in addition, by controlling the opening and closing of the power electronic circuit breaker, the control of the presence or absence of power supply to the load can be realized, and it has the opening and closing control function of the circuit breaker.

[0025] By collecting the output voltage and current of the DC bus in the feeder branch and the voltage to ground of the positive and negative busbars, the working status of the DC feeder branch can be detected in real time. Based on the sampled data, the microcontroller processes the data, calculates the relevant data results, and makes short-circuit fault information prediction and fault alarm.

[0026] According to the calculation results of the single-chip microcomputer and the predicted fault type, the single-chip microcomputer controls the power electronic circuit breaker to perform relevant active protection actions to remove or limit the fault.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] The active protection device for DC power supply of the present invention can not only realize the breaking function of the traditional circuit breaker, but also realize the rapid and accurate positioning of the fault of the fed DC branch, and predict the fault in advance, so as to perform different active protection actions according to different faults, instead of blindly tripping and shedding load like the traditional circuit breaker, thus avoiding the over-tripping fault of the traditional circuit breaker, and improving the continuity, reliability and safety of the DC power supply system of the substation; the active protection device for DC power supply of the present invention can find and locate the fault of the DC branch more quickly, reduce the engineering workload and improve timeliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a system principle diagram of the active protection device of the present invention;

[0030] Figure 2 This is the schematic diagram of the power electronic circuit breaker;

[0031] Figure 3 This is the schematic diagram of the DC feeder branch ground fault detection principle;

[0032] Figure 4 This is the schematic diagram of the output current sampling circuit;

[0033] Figure 5 This is the schematic diagram of the output voltage sampling circuit;

[0034] Figure 6 This is the schematic diagram of the single-chip microcomputer control circuit;

[0035] Figure 7 This is the flow chart for calculating the short-circuit fault of the DC feeder branch;

[0036] Figure 8 This is the flow chart for calculating the insulation resistance between the DC positive and negative busbars and the ground;

[0037] Fig. 9 It is a control flow chart of the single chip microcomputer of the present invention. DETAILED DESCRIPTION

[0038] like Figure 1As shown, the present invention is an active protection device for DC power supply for substation based on fault location, the protection device is connected in series between the DC power supply and the DC feeder branch, the protection device of the present invention is arranged between the DC bus (DC power supply) and each DC feeder branch (each DC feeder branch is connected in parallel with each other), the input end of the protection device of the present invention is connected to the DC bus (DC power supply), and the output end of the protection device of the present invention is connected to the DC feeder branch; the protection device comprises a single-chip microcomputer control circuit and a power electronic circuit breaker and a fault detection circuit connected to the single-chip microcomputer control circuit, the output end of the DC bus is connected to the input end of the power electronic circuit breaker, the output end of the power electronic circuit breaker is connected to the corresponding DC feeder branch, and the control signal output end of the single-chip microcomputer control circuit is connected to the control signal input end of the power electronic circuit breaker; the fault detection circuit comprises a voltage and current sampling circuit and a ground fault detection circuit; the protection device of the present invention also comprises a fault alarm circuit, and the fault alarm circuit is connected to the single-chip microcomputer control circuit.

[0039] Figure 2 It is a circuit schematic diagram of a power electronic circuit breaker, Uin is the input voltage of the power electronic circuit breaker, Uo is the output voltage of the power electronic circuit breaker, power tubes Q1~Q4 are MOS tubes, T is a high-frequency isolation transformer, Lr is a resonant inductor, L1 is an output inductor, and D11~D14 are fast recovery rectifier diodes; four signal driving ends of PWM1~PWM4 of the single-chip microcomputer are respectively connected to the four MOS tubes Q1~Q4 of the power electronic circuit breaker, and the four signal driving ends of PWM1~PWM4 control the on and off of the MOS tubes Q1~Q4, thereby realizing the control of whether the load is powered, that is, by changing the on time of the PWM drive signal, changing the on time of the power tube in the power electronic circuit breaker, and finally realizing the adjustment of the output voltage to keep the output voltage stable.

[0040] Figure 3 This is the detection principle diagram of the DC feeder branch grounding detection circuit. The DC 220V power supply is the output voltage of the power electronic circuit breaker. An isolation diode (the first isolation diode D1 and the second isolation diode D2) is installed on the positive and negative busbars respectively. The isolation diodes are ordinary rectifier diodes; S1 and S2 are electronic switches, the first resistor R1 and the third resistor R3 are balance bridge resistors, the second resistor R2 and the fifth resistor R5 are positive busbar to ground voltage detection resistors, the first capacitor C1 is a filter capacitor, the fourth resistor R4 and the sixth resistor R6 are negative busbar to ground voltage detection resistors, the second capacitor C2 is also a filter capacitor, the first voltage limiting diode D3 and the second voltage limiting diode D4 are positive and negative busbar to ground voltage sampling voltage limiting diodes, U+ and U- are positive and negative busbar to ground sampling voltages, and the sampling voltages of U+ and U- are sent to the AN5 and AN6 sampling ports of the single-chip microcomputer control circuit respectively. See Figure 3The ground fault detection circuit includes a first isolation diode D1, a second isolation diode D2, a first electronic switch S1, a second electronic switch S2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first capacitor C1, a second capacitor C2, a first diode D30, a second diode D40, a first voltage limiting diode D3, and a second voltage limiting diode D4. The positive electrode of the output end of the power electronic circuit breaker is connected to the positive electrode of the first isolation diode D1, the negative electrode of the first isolation diode D1 is connected to one end of the first electronic switch S1 and one end of the second resistor R2, the other end of the first electronic switch S1 is connected to one end of the first resistor R1, and the other end of the second resistor R2 is connected to one end of the fifth resistor R5; the negative electrode of the output end of the power electronic circuit breaker is connected to the negative electrode of the second isolation diode D2, the positive electrode of the second isolation diode D2 is connected to one end of the second electronic switch S2 and one end of the fourth resistor R4, the other end of the second electronic switch S2 is connected to one end of the third resistor R3, and the other end of the fourth resistor R4 is connected to one end of the sixth resistor R6; the other end of the first resistor R1 is connected to the third The other end of the resistor R3 is connected, and the other end of the fifth resistor R5 is connected to the other end of the sixth resistor R6; the junction of the first resistor R1 and the third resistor R3, and the junction of the fifth resistor R5 and the sixth resistor R6 are connected to ground, and are respectively connected to a +3.3V power supply through a first diode D30 and a forward series branch of a first voltage limiting diode D3, and are connected to a +3.3V power supply through a second diode D40 and a forward series branch of a second voltage limiting diode D4; the junction of the second resistor R2 and the fifth resistor R5 is connected to a junction of the first diode D30 and the first voltage limiting diode D3 and is grounded through a first capacitor C1, and the positive bus-to-ground voltage U is measured from the junction of the first diode D30 and the first voltage limiting diode D3 1+ The junction of the fourth resistor R4 and the sixth resistor R6 is connected to the junction of the second diode D40 and the second voltage limiting diode D4 and is grounded through the second capacitor C2, and the positive bus voltage to ground U is measured from the junction of the second diode D40 and the second voltage limiting diode D4 1- .

[0041] Figure 4 This is the output current sampling schematic diagram. The output current is sampled by the current sensor, which converts the large current into a small signal. The current signal is converted into a voltage signal through the sampling resistor R25. C23 is a filter capacitor and D21 is a voltage limiting diode to prevent the voltage entering the AN1 port of the microcontroller from being too high.

[0042] Figure 5 This is the output voltage sampling schematic diagram. The output high voltage is stepped down by R31, R32, and R33, filtered by C31, C32, and R34, and limited by the D32 diode. It is then sent to the AN2 sampling port of the microcontroller control circuit for output voltage sampling.

[0043] Figure 6 The schematic diagram of the microcontroller control circuit is shown in Figure 1. The model of the microcontroller is STM32F101RBT. Ui is the input voltage sampling port AN0, Uo is the output voltage sampling port AN2, Io is the output current sampling port AN1, Y represents the crystal oscillator, C1 and C2 are the crystal oscillator capacitors, AN3 is the temperature sampling port, AN4 is the analog input port, AN5 and AN6 are the DC positive and negative busbar voltage sampling ports to the ground in the feed branch, and the sampling input voltage comes from Figure 3 The DC positive and negative busbars sample the ground voltage (U+ and U-) in the circuit. The PWM1~PWM4 signal driver of the microcontroller is used to control the four MOS tubes of the power electronic circuit breaker. The 485R, 485T and 485C ports of the microcontroller are the RS-485 communication interfaces. The microcontroller communicates with the human-computer interaction interface through its SPI communication interface (SDI, SCK, SDO).

[0044] The protection method of the active protection device for DC power supply for substation based on fault location of the present invention is specifically as follows:

[0045] On the one hand, the active protection device for DC power supply of the present invention collects the output voltage of the DC bus in the feed branch (i.e., the voltage output to the load) through the voltage sampling circuit. After the high voltage of the DC bus is reduced, filtered, and voltage-limited, the low voltage sampling data is sent to the AD sampling pin in the single-chip microcomputer control circuit. The single-chip microcomputer converts the analog quantity into a digital quantity through AD sampling, and then after software filtering and data processing, the single-chip microcomputer obtains the final digital quantity U of the voltage sampling data. o _AD;

[0046] The DC power supply active protection device uses a current sensor to collect the output current of the DC bus in the feed branch. In the current sampling circuit, the current small signal is converted into a suitable voltage small signal through a sampling resistor, and then after filtering and voltage limiting processing, the low voltage sampling data is sent to the AD sampling pin in the single-chip microcomputer control circuit. The single-chip microcomputer converts the analog quantity into a digital quantity through AD sampling, and then after software filtering and data processing, the single-chip microcomputer obtains the final digital quantity I of the current sampling data. o _AD;

[0047] The digital value U_SET corresponding to the output voltage comparison threshold value when a short circuit fault occurs is set in the single-chip microcomputer software program. At the same time, the digital value I_SET corresponding to the output current comparison threshold value when a short circuit fault occurs is set in the single-chip microcomputer software program. The condition for output short circuit judgment is that the output voltage is less than the set value and the output current is greater than the set value, and both must be satisfied at the same time.

[0048] After the DC power active protection device works normally, the single-chip microcomputer samples the output voltage data and output current data at all times. The corresponding digital quantities of the two are U o _AD and I o _AD. In the software program, compare the magnitudes of U o _AD and U_SET, and the magnitudes of I o _AD and I_SET. When U o _AD < U_SET and I o _AD > I_SET, it indicates that a short-circuit fault has occurred in the feeder branch. The DC power active protection device performs current-limiting output and issues a short-circuit fault alarm signal, and records the time when the fault occurs.

[0049] On the other hand, the DC power active protection device collects the voltages of the positive and negative busbars to the ground in the feeder branch through the ground fault detection circuit. After the high voltage of the DC busbar is stepped down, filtered, and voltage-limited, the low-voltage sampled data is sent to the AD sampling pin in the single-chip microcomputer control circuit. The single-chip microcomputer converts the analog quantity into a digital quantity through AD sampling, and then through software filtering and data processing, the single-chip microcomputer obtains the digital quantities U + _AD and U-_AD of the final sampled data of the voltages of the positive and negative busbars to the ground.

[0050] Figure 3 In, after the DC power active protection device works normally, the single-chip microcomputer samples the voltages of the positive and negative busbars to the ground to calculate the insulation resistances of the positive and negative busbars to the ground. The calculation process is as follows, where R1 = R3, R2 = R4, R5 = R6

[0051] Close S1, open S2, delay for a certain time, and measure the voltages of the positive and negative busbars to the ground as U 1+ 、U 1- , and obtain:

[0052]

[0053] Open S1, close S2, delay for a certain time, and measure the voltages of the positive and negative busbars to the ground as U 2+ 、U 2- , and obtain:

[0054]

[0055] Combining equations (1) and (2) gives:

[0056]

[0057] The single-chip microcomputer calculates the insulation resistances of the positive and negative busbars to the ground by using equations (3) and (4) according to the sampled values of the voltages of the positive and negative busbars to the ground, and obtains the resistance values of the insulation resistances of the positive and negative busbars to the ground as R+ and R - 。Set the alarm thresholds for the insulation resistance of the positive and negative busbars to the ground in the software program, namely R+_SET and R-_SET respectively; when R + < R+_SET, the single-chip microcomputer reports the fault of the insulation degradation of the positive busbar; when R - < R-_SET, the single-chip microcomputer reports the fault of the insulation degradation of the negative busbar; the single-chip microcomputer monitors the insulation condition of the DC busbar at all times, realizes the real-time fault alarm function, records the fault occurrence time, and at the same time controls the power electronic transformer to continue to supply power to the DC load to ensure the continuity of the branch load power supply.

[0058] The control principle of the active protection device for the DC power supply used in the substation based on fault location of the present invention:

[0059] Control of the electrical transmission function: That is, the power electronic circuit breaker uses power electronic conversion technology to realize the conversion of DC voltage, converts the input DC power into controllable DC power, and supplies power to the load of the DC feed branch, with the voltage and current transmission function of the circuit breaker; in addition, by controlling the on and off of the power electronic devices, the control of the power supply to the load can be realized, with the opening and closing control function of the circuit breaker.

[0060] Control of DC fault detection and judgment: By collecting the voltage and current of the feed branch and the data of the internal DC fault detection unit, the working state of the DC feed branch is detected in real time. According to the detected sampling data, the single-chip microcomputer performs data processing, calculates the relevant data results, and makes a pre-judgment of the fault information and a fault alarm.

[0061] Control for the realization of active protection actions: According to the results calculated by the detection unit and the predicted fault types, the single-chip microcomputer controls the power electronic circuit breaker to perform relevant active protection actions to achieve the removal or limitation of the fault.

[0062] The specific implementation steps of the control method of the present invention: After the system is powered on, the control circuit of the single-chip microcomputer operates normally, the single-chip microcomputer completes initialization, and starts to execute the software program; the voltage and current data are sampled through the sampling circuit and sent to the AD sampling port of the single-chip microcomputer, and the filtering of the sampling data and relevant data processing are performed inside the single-chip microcomputer, including the short-circuit fault calculation subroutine, the ground fault calculation subroutine, and the control program.

[0063] The active protection method for the DC power supply used in the substation based on fault location of the present invention is realized as follows: that is, the single-chip microcomputer outputs a control signal according to the data after sampling and processing, controls the normal operation of the power electronic circuit breaker, and supplies power to the load of the DC feed branch; while normal power supply is in progress, by Figure 4 、 5 and 7, through sampling the output voltage and current, the single-chip microcomputer processes the sampling data and makes a prediction and judgment of the short-circuit fault according to the data results; by Figure 3 and Figure 8 It can be seen that the positive and negative bus voltages are sampled by the feeder branch grounding detection circuit and sent to the microcontroller for data processing and calculation. The positive or negative grounding fault is predicted and judged based on the calculation results. Fig. 9 It can be seen that the single-chip microcomputer outputs different control signals according to the calculation results and the predicted fault type, and the power electronic circuit breaker performs different active protection actions; when a positive or negative grounding fault occurs, the single-chip microcomputer gives a control signal to control the power electronic circuit breaker to continue to work normally, and at the same time sends out an alarm signal for the corresponding fault branch; when a short circuit fault occurs, the single-chip microcomputer gives a control signal to control the power electronic circuit breaker to be in a current limiting working state, avoiding the over-tripping of traditional circuit breakers, and at the same time sends out an alarm signal for the corresponding fault branch; maintenance personnel can quickly and accurately locate the fault branch based on the alarm signal, and quickly carry out fault troubleshooting.

[0064] Therefore, the active protection device for DC power supply of the present invention can not only realize the breaking function of the traditional circuit breaker, but also realize the function of fast and accurate positioning of the DC fault of the feeder branch, and predict the fault in advance, and perform different active protection actions according to different faults, instead of blindly tripping and cutting the load like the traditional circuit breaker, thereby avoiding the over-tripping fault of the traditional circuit breaker and improving the continuity, reliability and safety of the DC power supply system of the substation.

Claims

1. A DC power supply active protection device for a substation based on fault location, characterized in that: The protection device is provided between the DC bus and each DC feeder branch, and includes a single-chip control circuit and a power electronic circuit breaker and a fault detection circuit connected to the single-chip control circuit. The output end of the DC bus is connected to the input end of the power electronic circuit breaker, the output end of the power electronic circuit breaker is connected to the corresponding DC feeder branch, and the control signal output end of the single-chip control circuit is connected to the control signal input end of the power electronic circuit breaker; the fault detection circuit includes a voltage and current sampling circuit and a ground fault detection circuit; The ground fault detection circuit includes a first isolation diode D1, a second isolation diode D2, a first electronic switch S1, a second electronic switch S2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a first capacitor C1, a second capacitor C2, a first diode D30, a second diode D40, a first voltage limiting diode D3, and a second voltage limiting diode D4; The positive electrode of the output end of the power electronic circuit breaker is connected to the positive electrode of the first isolation diode D1, the negative electrode of the first isolation diode D1 is connected to one end of the first electronic switch S1 and one end of the second resistor R2, the other end of the first electronic switch S1 is connected to one end of the first resistor R1, and the other end of the second resistor R2 is connected to one end of the fifth resistor R5; the negative electrode of the output end of the power electronic circuit breaker is connected to the negative electrode of the second isolation diode D2, the positive electrode of the second isolation diode D2 is connected to one end of the second electronic switch S2 and one end of the fourth resistor R4, the other end of the second electronic switch S2 is connected to one end of the third resistor R3, and the other end of the fourth resistor R4 is connected to one end of the sixth resistor R6; the other end of the first resistor R1 is connected to the first resistor R2, and the other end of the fourth resistor R4 is connected to one end of the sixth resistor R6. The other end of the three resistors R3 is connected, and the other end of the fifth resistor R5 is connected to the other end of the sixth resistor R6; the junction of the first resistor R1 and the third resistor R3, and the junction of the fifth resistor R5 and the sixth resistor R6 are connected to ground, and connected to a +3.3V power supply through a forward series branch of a first diode D30 and a first voltage limiting diode D3, and connected to a +3.3V power supply through a forward series branch of a second diode D40 and a second voltage limiting diode D4; the junction of the second resistor R2 and the fifth resistor R5 is connected to a junction of the first diode D30 and the first voltage limiting diode D3 and is grounded through a first capacitor C1, and the positive bus voltage to ground U is measured from the junction of the first diode D30 and the first voltage limiting diode D3 1+ The junction of the fourth resistor R4 and the sixth resistor R6 is connected to the junction of the second diode D40 and the second voltage limiting diode D4 and is grounded through the second capacitor C2, and the positive bus voltage to ground U is measured from the junction of the second diode D40 and the second voltage limiting diode D4 1- ; Wherein, R1=R3, R2=R4, R5=R6; The DC power supply active protection device determines the fault and implements protection in the following ways: Step 1: The output voltage and current of the DC bus in the DC feed branch are collected by the voltage and current sampling circuit. The microcontroller compares the sampled voltage and current data with the set values of voltage and current, and predicts and judges the short-circuit fault according to the comparison result. The microcontroller samples the output voltage data and output current data at all times, and the corresponding digital quantities are U o _AD and I o _AD. The digital quantity U_SET corresponding to the output voltage comparison threshold during short-circuit fault is set in the microcontroller. At the same time, the digital quantity I_SET corresponding to the output current comparison threshold during short-circuit fault is set in the microcontroller. Compare the magnitudes of U o _AD and U_SET, and the magnitudes of I o _AD and I_SET. When U o _AD < U_SET and I o _AD > I_SET, it indicates that a short-circuit fault has occurred in the feed branch. The microcontroller sends a current-limiting output signal to the power electronic circuit breaker and simultaneously issues a short-circuit fault alarm signal through the fault alarm circuit; Step 2: Meanwhile, sample the voltages of the positive and negative buses to the ground in the DC outgoing branch through the ground fault detection circuit, and send the sampled data to the single-chip microcomputer for data processing and calculation. Predict and judge the ground faults of the positive and negative buses according to the calculation results. The single-chip microcomputer calculates the insulation resistances of the positive and negative buses to the ground based on the sampled values of the voltages of the positive and negative buses to the ground, and obtains the resistance values of the insulation resistances of the positive and negative buses to the ground as R + and R - ; Compare the obtained resistance values with the alarm thresholds of the insulation resistances of the positive and negative buses to the ground set in the program. The alarm thresholds of the insulation resistances of the positive and negative buses to the ground are R+_SET and R-_SET respectively. When R + < R+_SET, the single-chip microcomputer reports a fault of the decreasing insulation of the positive bus; when R - < R-_SET, the single-chip microcomputer reports a fault of the decreasing insulation of the negative bus; The single chip microcomputer samples the voltage data of the positive and negative busbars to the ground to calculate the insulation resistance of the positive and negative busbars to the ground. The calculation process is as follows; Close the first electronic switch S1, open the second electronic switch S2, delay for a certain time, and measure the voltages of the positive and negative busbars to the ground, respectively. 1+ , U 1- ,have to: Disconnect the first electronic switch S1, close the second electronic switch S2, delay for a certain time, and measure the voltages of the positive and negative busbars to ground, respectively. 2+ , U 2- ,have to: Combining equations (1) and (2) we can get: The single-chip microcomputer calculates the insulation resistances of the positive and negative busbars to the ground based on the sampled values of the voltages of the positive and negative busbars to the ground, and uses equations (3) and (4) to obtain the resistance values of the insulation resistances of the positive and negative busbars to the ground as R + and R - ; Set the alarm thresholds for the insulation resistances of the positive and negative busbars to the ground, which are R+_SET and R-_SET respectively; when R+ < R+_SET, the single-chip microcomputer reports a fault of decreased insulation of the positive busbar; when R- < R-_SET, the single-chip microcomputer reports a fault of decreased insulation of the negative busbar; Step 3, the single chip microcomputer outputs different control signals according to the calculation results of step 1 and step 2 and the predicted fault type, and transmits the corresponding control signals to the power electronic circuit breaker for execution; when a positive bus or negative bus grounding fault occurs, the single chip microcomputer gives a control signal to control the power electronic circuit breaker to continue normal operation, and at the same time sends out an alarm signal of the corresponding fault branch; when a short circuit fault occurs, the single chip microcomputer gives a control signal to control the power electronic circuit breaker to be in a current limiting working state, and at the same time sends out an alarm signal of the corresponding fault branch.

2. The DC power supply active protection device for substation based on fault location according to claim 1 is characterized in that: The protection device also includes a fault alarm circuit, which is connected to the single-chip microcomputer control circuit.

3. The DC power supply active protection device for substation based on fault location according to claim 1 is characterized in that: The power electronic circuit breaker includes a voltage input terminal Uin, a voltage output terminal Uo, a MOS tube Q1, a MOS tube Q2, a MOS tube Q3, a MOS tube Q4, a high-frequency isolation transformer T, a resonant inductor Lr, an output inductor L1, a rectifier diode D11, a rectifier diode D12, a rectifier diode D13, and a rectifier diode D14. The signal driving ends of PWM1, PWM2, PWM3, and PWM4 of the single-chip computer are respectively connected to the MOS tube Q1, MOS tube Q2, MOS tube Q3, and MOS tube Q4 of the power electronic circuit breaker.

4. The DC power supply active protection device for substation based on fault location according to claim 1 is characterized in that: The model of the single-chip microcomputer in the single-chip microcomputer control circuit is STM32F101RBT, Ui is the input voltage sampling port AN0, Uo is the output voltage sampling port AN2, Io is the output current sampling port AN1, AN5 and AN6 are the DC positive and negative bus-to-ground voltage sampling ports in the DC feed-out branch respectively, and the signal driving ends of PWM1, PWM2, PWM3, and PWM4 are connected to the MOS tubes Q1, MOS tubes Q2, MOS tubes Q3, and MOS tubes Q4 of the power electronic circuit breaker respectively.

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