A low voltage capacitor high speed switching compensation module and control method thereof

Abstract

The present invention belongs to the field of low-voltage capacitor switching compensation, and provides a low-voltage capacitor high-speed switching compensation module and a control method thereof. The compensation module includes a circuit breaker, a switching switch, a reactor, a capacitor and a module control board; a digital phase-locking unit and a no-inrush switching logic unit are arranged on the module control board; the digital phase-locking unit is used to phase-lock the three-phase voltage of the power grid; the no-inrush switching logic unit is used to find the peak point of the three-phase voltage of the power grid after phase locking, and trigger the switching switch at the peak point of the three-phase voltage of the power grid after receiving an external input command and input the capacitor; the switching switch is composed of a thyristor and a diode connected in anti-parallel; when the thyristor in the switching switch is turned off, the capacitor will be charged through the diode, and when the diode is turned off, that is, when the switching switch is turned off, the capacitor will be charged to the voltage at the peak of the line voltage, so as to wait for the switching instruction to be responded to again to achieve the purpose of high-speed switching.

Description

Technical Field

[0001] The invention belongs to the field of low-voltage capacitor switching compensation, and in particular relates to a low-voltage capacitor high-speed switching compensation module and a control method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The traditional thyristor switching capacitor compensation uses thyristor terminal voltage zero-crossing detection or power supply voltage zero-crossing phase-locked detection as its synchronous triggering method. When the thyristor terminal voltage zero-crossing detection method switches the capacitor of the series reactor, it takes a certain discharge time after removal before it can be put into operation again, resulting in slow response time or short-term phase loss operation. During high-power impact loads or phase-changing short-circuit processes of phase-controlled rectifier equipment, a large voltage drop will occur, resulting in power supply voltage zero-crossing phase-locked detection errors; in situations where industrial loads have large harmonics, the influence of harmonics will also cause power supply voltage zero-crossing phase-locked detection errors.

[0004] Traditional capacitor compensation cannot determine the attenuation of the compensation branch capacitor and the problem of excessive branch current harmonics. The attenuation of the capacitor will cause the reactance rate to decrease and the absorbed harmonics to become larger. The long-term excessive current harmonics in the compensation loop will cause the capacitor to heat up and damage faster, and then there will be capacitor explosion accidents. Traditional capacitor compensation uses fuses or circuit breakers in series with the branch for protection. Since these protection currents are generally large, according to national standards, they need to be above 1.43In. By the time these external devices are protected, the fault has expanded, and it is impossible to provide protection at the initial stage of device damage and prevent accidents.

[0005] In the traditional thyristor switching capacitor compensation device, the breakdown voltage of the thyristor will drop due to aging and other factors. In addition, the overvoltage of the power grid will also cause the breakdown voltage of the thyristor to be insufficient. Therefore, the thyristor will break down and conduct, or it will turn on and off automatically at a certain critical point after the breakdown voltage drops. When the thyristor breaks down and conducts, it often brings problems of imbalance or compensation error; when the thyristor breakdown voltage drops to the critical point and turns on and off automatically, it will cause inrush current to damage the capacitor. When the effective current does not reach the protection value of the external protection device, the fault will continue to expand. When the external device is protected, the accident is relatively large, and the capacitor often explodes. Therefore, when the thyristor breaks down and conducts or the breakdown voltage drops to the critical point and turns on and off automatically, the traditional capacitor compensation branch cannot be timely cut off at the early stage of the fault for protection. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a low-voltage capacitor high-speed switching compensation module and a control method thereof. The main circuit adopts a switching switch, a reactor, and a capacitor in series to form an angle internal connection method, wherein the switching switch is composed of a diode and a thyristor in anti-parallel connection. When the capacitor is not switched on or the capacitor is cut off, the capacitor will be charged to the voltage at the peak of the line voltage. The module control board uses a digital phase-locked technology to achieve phase locking of the grid voltage, which can be free from the influence of harmonics and voltage drops, and can accurately find the time of the peak point of the grid line voltage. After receiving an external input command, the three thyristors of the switching switch are respectively triggered at the peak points of the three line voltages of the grid to enable the capacitor to be switched on without inrush current, and the capacitor can be immediately switched on again after being cut off, which solves the problem that the response time of the thyristor terminal voltage zero-crossing detection of the capacitor compensation using thyristor switching is slow, and the synchronous triggering method using the power supply voltage zero-crossing phase-locked detection is easily affected by harmonics and voltage drops, and can be adapted to the occasions of rapid reactive power fluctuations with large harmonics and voltage drop impacts.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a low-voltage capacitor high-speed switching compensation module.

[0009] A low-voltage capacitor high-speed switching compensation module, comprising a circuit breaker, a switching switch, a reactor, a capacitor and a module control board, wherein the switching switch, the reactor and the capacitor are connected in series to form an inner triangle and connected to the outgoing line side of the circuit breaker, and the incoming line side of the circuit breaker is connected to a power supply;

[0010] The module control board is provided with a digital phase-locking unit and a no-inrush current switching logic unit; the digital phase-locking unit is used to phase-lock the three-phase voltage of the power grid; the no-inrush current switching logic unit is used to find the peak point of the three-phase line voltage of the power grid after phase locking, and trigger the switching switch at the peak point of the three-phase line voltage of the power grid after receiving an external input command to input the capacitor without inrush current;

[0011] The switching switch is composed of a thyristor and a diode connected in anti-parallel; when the thyristor in the switching switch is turned off, the capacitor will be charged through the diode, and when the diode is cut off, that is, when the switching switch is turned off, the capacitor will be charged to the voltage at the peak of the line voltage.

[0012] Furthermore, the input end of the no-inrush current switching logic unit receives the grid phase signal and phase sequence signal after digital phase locking, and the no-inrush current switching logic unit is used to switch the no-inrush current input phase point according to the grid phase sequence signal. When the actual phase is consistent with the no-inrush current input phase point, the trigger signal of the thyristor in the corresponding switching switch is output to input the capacitor.

[0013] Furthermore, a capacitance attenuation protection unit is also provided on the module control board, and its input end is connected to the grid voltage, compensation current and voltage frequency after digital phase locking, and the capacitance of the capacitor and the capacitance attenuation rate are calculated online by combining the actual reactance rate and the capacitance value on the capacitor nameplate. When the capacitance attenuation rate exceeds the set value, an alarm shutdown signal is output.

[0014] Furthermore, a harmonic protection unit is also provided on the module control board, and its input end is connected to the grid voltage and compensation current. The fundamental wave value and harmonic wave value are calculated according to the sampled grid voltage and compensation current, and the harmonic content of the grid voltage and compensation current are calculated respectively. When the respective set protection values ​​are exceeded, an alarm shutdown signal is output.

[0015] Furthermore, a thyristor breakdown protection unit is also provided on the module control board, and its input end receives a trigger instruction and a compensation current, obtains the state of the thyristor according to the trigger instruction and the compensation current, and outputs a trip signal to the opening coil of the circuit breaker after a breakdown is detected.

[0016] Furthermore, the module control board is also provided with a full-duplex communication unit, which has a full-duplex communication interface, receives high-speed switching communication instructions from an external controller in a broadcast instruction listening manner and sends status information of the module control board in a full-duplex manner.

[0017] Furthermore, a temperature protection unit is also provided on the module control board, which is used to sample the temperature of the capacitor, the temperature of the reactor, the temperature of the radiator on the switching switch and the ambient temperature. The temperature protection unit is used to calculate the temperature or temperature rise of the capacitor, the reactor and the radiator on the switching switch. Once the temperature or temperature rise of the capacitor, the reactor and the radiator on the switching switch exceeds the set protection value, an alarm shutdown signal is output.

[0018] Furthermore, the low-voltage capacitor high-speed switching compensation module also includes a current transformer. There are three current transformers in total, whose primary sides are respectively connected in series in the three corner inner loops of the triangle connection, and whose secondary sides are respectively connected to the three current input terminals of the module control board.

[0019] Furthermore, the circuit breaker is provided with a tripping coil, and a control end of the tripping coil is connected to a tripping terminal of the module control board.

[0020] Furthermore, a radiator is also provided on the switching switch, a temperature sensor is installed on the radiator, and the temperature sensor is connected to the radiator temperature terminal of the module control board.

[0021] Furthermore, the reactor is composed of three windings, each winding has an independent line-in terminal and an outlet terminal, and each winding is equipped with a temperature sensor, which is respectively connected to the reactor temperature terminal of the module control board.

[0022] Furthermore, the capacitor is composed of three groups of independent single-phase capacitors, each group of capacitors has an input terminal and an output terminal, and each group of capacitors is installed with a temperature sensor, which is respectively connected to the capacitor temperature terminal of the module control board.

[0023] Furthermore, the digital phase locking unit comprises:

[0024] Three AD conversion units, used to convert the three-phase voltage analog signals of the power grid into digital signals respectively;

[0025] A first adder and a second adder, which are used to make a difference between the A-phase and C-phase voltage digital signals and the B-phase voltage digital signal respectively;

[0026] A first proportional regulator connected to an output terminal of the first adder;

[0027] a second proportional regulator connected to an output terminal of the second adder;

[0028] A first multiplier, one input end of which is connected to the first proportional regulator, and the other input end of which is connected to the output end of the first sine operator, and the input end of the first sine operator is connected to the output end of the integrator with a reset end;

[0029] a second multiplier, one input end of which is connected to the second proportional regulator, and the other input end of which is connected to the output end of the second sine operator, the input end of the second sine operator is connected to the fourth adder, and the two input ends of the fourth adder are respectively connected to the output end of the integrator with a reset end and the first constant;

[0030] a third adder, configured to accumulate output results of the first multiplier and the second multiplier;

[0031] A low-pass filter, used for filtering harmonic signals, wherein an input end of the low-pass filter is connected to an output end of the third adder;

[0032] A PI regulator, whose input end is connected to the output end of the low-pass filter, and whose output end is connected to the input end of the second absolute value operator, and whose output end is an angular frequency signal;

[0033] A third proportional regulator, an input end of which is connected to an output end of the PI regulator;

[0034] an integrator with a reset terminal, one input terminal of which is connected to the output terminal of the third proportional regulator, and the other input terminal of which is connected to the output terminal of the comparator;

[0035] The comparator has a positive input terminal connected to the output terminal of the first absolute value operator, an input terminal of the first absolute value operator connected to the output terminal of the integrator with a reset terminal, and a negative input terminal of the comparator connected to the second constant.

[0036] A second aspect of the present invention provides a control method for a low-voltage capacitor high-speed switching compensation module.

[0037] A control method for a low-voltage capacitor high-speed switching compensation module, comprising:

[0038] Digital phase-locked grid three-phase voltage obtains the phase sequence and phase of the grid voltage;

[0039] When the compensation module receives the external input command, it determines the phase according to the grid voltage phase sequence to find the positive peak point of the grid three-phase line voltage, and sends a triggering thyristor instruction in the switching switch at the positive peak point of the grid three-phase line voltage to input the capacitor;

[0040] When the compensation module receives the external removal command, it determines the phase according to the current grid voltage phase sequence, finds the positive zero-crossing point of the three-phase line voltage of the grid (that is, the current of the diode in the switching switch corresponds to the peak value when the line voltage changes from negative to positive), and issues a stop triggering thyristor instruction in the switching switch. The thyristor will naturally turn off at zero current, and then the diode will turn on and off after half a power frequency cycle, completing the capacitor removal. At this time, the three groups of capacitors have been fully charged through the diodes, and the compensation module can immediately respond to the external input command again to re-input the capacitor to achieve the purpose of high-speed switching.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The three-phase voltage of the power grid is phase-locked by a digital phase-locked unit, which can improve the reliability of the phase-locked synchronous triggering technology. The inrush-free switching logic unit is then used to find the moment of the positive peak point of the three-phase line voltage of the power grid. After receiving the external input command, the switching switch is triggered at the positive peak point of the three-phase line voltage of the power grid and the capacitor is input. This solves the problem of slow response time of the thyristor terminal voltage zero-crossing detection for capacitor compensation of thyristor switching and the problem that the synchronous triggering method using the power supply voltage zero-crossing phase-locked detection is easily affected by harmonics and voltage drops. It can be adapted to occasions with large harmonics and rapid reactive power fluctuations with voltage drop impacts.

[0043] (2) The switching device of the present invention is composed of a thyristor and a diode connected in anti-parallel. When receiving an external removal command, the switching device stops triggering at the forward zero crossing point of the three-phase line voltage of the power grid after phase locking (that is, at the forward peak current of the diode), which can avoid the problem of the diode delaying opening for half a cycle caused by harmonics when the thyristor stops triggering near the fundamental zero current, resulting in slow shutdown of the switching device. When the thyristor in the switching device stops triggering, it will naturally shut down at zero current, and then after half a power frequency cycle, the capacitor will be fully charged through the diode in the switching device, and at this time it can immediately respond to the switching command again, so as to achieve the purpose of high-speed switching.

[0044] (3) The present invention also provides a capacitance attenuation protection unit, a harmonic protection unit, a thyristor breakdown protection unit, and a temperature protection unit on the module control board, which solves the problem of monitoring and protection in the early stage of capacitor compensation branch fault and can avoid the expansion of accidents.

[0045] (4) The digital phase-locked unit of the present invention is composed of hardware logic devices, which avoids digital phase-locked programming and improves the reliability of digital phase-locked synchronous triggering technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0047] Figure 1 It is a structural schematic diagram of a low-voltage capacitor high-speed switching compensation module according to an embodiment of the present invention;

[0048] Figure 2 is a principle block diagram of a digital phase-locked unit according to an embodiment of the present invention;

[0049] Figure 3 It is a flow chart of the no-inrush current switching logic unit of an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0051] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0052] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0053] Terminology explanation:

[0054] The low voltage in the low-voltage capacitor high-speed switching compensation module of the present invention refers to AC 1140V and below.

[0055] like Figure 1As shown, the low-voltage capacitor high-speed switching compensation module of this embodiment comprises a circuit breaker (1), a switching switch (3), a reactor (4), a capacitor (5) and a module control board (6); the switching switch (3), the reactor (4) and the capacitor (5) are connected in series to form an inner triangle and are connected to the outgoing line side of the circuit breaker (1); the incoming line side of the circuit breaker (1) is connected to a power supply;

[0056] The module control board (6) is provided with a digital phase-locking unit and a no-inrush current switching logic unit; when the circuit breaker (1) is closed, so that the entire low-voltage capacitor high-speed switching compensation module is connected to the power supply, the module control board (6) is used to sample the three-phase voltage of the power grid, and after being phase-locked by the digital phase-locking unit, the no-inrush current switching logic unit finds the moment of the positive peak point of the three-phase line voltage of the power grid, and after receiving the input command of the external controller, the switching switch (3) is triggered at the positive peak point of the three-phase line voltage of the power grid and the capacitor (5) is input; when the thyristor in the switching switch (3) is turned off, the capacitor (5) is charged through the diode, and when the diode is turned off, that is, when the switching switch (3) is turned off, the capacitor (5) is charged to the voltage at the peak of the line voltage, and at this time, it can immediately respond to the switching command again, so as to achieve the purpose of high-speed switching.

[0057] In a specific implementation, the circuit breaker (1) is equipped with a trip coil (7), and the control end of the trip coil (7) is connected to the trip terminal of the module control board (6). The trip coil is a wire winding with a movable iron core in the middle; when the rated voltage is applied to both ends of the trip coil, current will pass through the winding, generate a magnetic field, attract the iron core, and then push the mechanism to trip. The trip coil of this embodiment is used to disconnect the fault circuit breaker, and is controlled to trip by the module control board (6).

[0058] In a specific implementation, a thyristor and a diode are connected in anti-parallel to form a switching switch (3), wherein the anode of the diode is connected to the outgoing line side of the circuit breaker (1), the cathode is connected in series with the reactor (4), and the trigger end of the thyristor is connected to the trigger terminal of the module control board (6). The thyristor is a high-power electrical component, also known as a thyristor.

[0059] In a specific implementation, a radiator is also provided on the switching switch (3), and a temperature sensor is installed on the radiator, and the temperature sensor is connected to the radiator temperature terminal of the module control board (6). The temperature sensor is used to detect the temperature of the switching switch in real time and transmit it to the module control board (6) to realize temperature monitoring of the switching switch.

[0060] In a specific implementation, the reactor (4) is composed of three windings, each winding has an independent input terminal and an output terminal, and each winding is equipped with a temperature sensor, which is respectively connected to the reactor temperature terminal of the module control board (6). The reactor and the capacitor form a partial harmonic circuit, absorb or suppress harmonic currents of a specific order, and can also limit the closing charging current and fault current of the low-voltage capacitor high-speed switching compensation module. The temperature sensor on the reactor (4) is used to monitor the temperature of the reactor in real time to avoid excessive temperature, which may damage the reactor and cause the low-voltage capacitor high-speed switching compensation module to fail.

[0061] In a specific implementation, the capacitor (5) is composed of three groups of independent single-phase capacitors, each group of capacitors has an input terminal and an output terminal, and each group of capacitors is installed with a temperature sensor (8), and the temperature sensor (8) is respectively connected to the capacitor temperature terminal of the module control board (6). The capacitor is a component that generates capacitive reactive power compensation current, and the temperature sensor (8) on the capacitor is used to monitor the temperature of the capacitor in real time to avoid excessive temperature, which may damage the capacitor and cause failure of the low-voltage capacitor high-speed switching compensation module.

[0062] In another specific embodiment, the low-voltage capacitor high-speed switching compensation module further includes a current transformer (2), wherein there are three current transformers (2), the primary sides of which are respectively connected in series in the three corner inner loops of the triangle connection method, and the secondary sides of which are respectively connected to the three current input terminals of the module control board. The current transformer is an instrument that converts a large current on the primary side into a small current on the secondary side for measurement based on the principle of electromagnetic induction. The current transformer is composed of a closed iron core and a winding. The current transformer is connected in series in the circuit of the current to be measured.

[0063] Wherein, the digital phase locking unit comprises:

[0064] Three AD conversion units, used to convert the three-phase voltage analog signals of the power grid into digital signals respectively;

[0065] A first adder and a second adder, which are used to make a difference between the A-phase and C-phase voltage digital signals and the B-phase voltage digital signal respectively;

[0066] A first proportional regulator connected to an output terminal of the first adder;

[0067] a second proportional regulator connected to an output terminal of the second adder;

[0068] A first multiplier, one input end of which is connected to the first proportional regulator, and the other input end of which is connected to the output end of the first sine operator, and the input end of the first sine operator is connected to the output end of the integrator with a reset end;

[0069] A second multiplier, one input end of which is connected to the second proportional regulator, and the other input end of which is connected to the output end of the second sine operator, the input end of the second sine operator is connected to the output end of the fourth adder, and two input ends of the fourth adder are respectively connected to the output end of the integrator with a reset end and a first constant (for example: 120);

[0070] a third adder, configured to accumulate output results of the first multiplier and the second multiplier;

[0071] A low-pass filter, used for filtering harmonic signals, wherein an input end of the low-pass filter is connected to an output end of the third adder;

[0072] A PI regulator, wherein an input end is connected to an output end of the low-pass filter, an output end is connected to an input end of a second absolute value operator, an output end of the second absolute value operator is an angular frequency signal, and another output end of the PI regulator is a phase sequence signal;

[0073] A third proportional regulator, an input end of which is connected to an output end of the PI regulator;

[0074] An integrator with a reset terminal, one input terminal of which is connected to the output terminal of the third proportional regulator, and the other reset input terminal of which is connected to the output terminal of the comparator, and the output terminal of the integrator with a reset terminal is a phase signal;

[0075] A comparator, whose positive input terminal is connected to the output terminal of the first absolute value operator, whose input terminal is connected to the output terminal of the integrator with a reset terminal, and whose negative input terminal is connected to the second constant (for example: 360).

[0076] In the specific implementation, Figure 2As shown, the digital phase-locked unit is composed of an AD conversion unit I (11), an AD conversion unit II (12), an AD conversion unit III (13), an adder I (14), an adder II (15), an adder III (20), an adder IV (29), a proportional regulator I (16), a proportional regulator II (17), a proportional regulator III (23), a multiplier I (18), a multiplier II (19), a low-pass filter (21), a PI regulator (22), a sine operator I (25), a sine operator II (28), an integrator with a reset terminal (24), a comparator (27), an absolute value operator I (26), and an absolute value operator II (30); wherein the input terminal of the AD conversion unit I (11) is The input terminal of AD conversion unit Ⅱ (12) is connected to voltage Ua, and the output terminal is connected to the "+" input terminal of adder Ⅰ (14); the input terminal of AD conversion unit Ⅱ (12) is connected to voltage Ub, and there are two output terminals, one output terminal is connected to the "-" input terminal of adder Ⅰ (14), and the other output terminal is connected to the "-" input terminal of adder Ⅱ (15); the input terminal of AD conversion unit Ⅲ (13) is connected to voltage Uc, and the output terminal is connected to the "+" input terminal of adder Ⅱ (15); the input terminal of proportional regulator Ⅰ (16) is connected to the output terminal of adder Ⅰ (14), and the output terminal thereof is connected to an input terminal of multiplier Ⅰ (18); the input terminal of proportional regulator Ⅱ (17) is connected to the output terminal of adder Ⅱ (15), and the output terminal thereof is connected to an input terminal of multiplier Ⅱ (19); adder Ⅲ One "+" input terminal of (20) is connected to the output terminal of multiplier I (18), and the other "+" input terminal thereof is connected to the output terminal of multiplier II (19), and the output terminal thereof is connected to the input terminal of low-pass filter (21); the input terminal of PI regulator (22) is connected to the output terminal of low-pass filter (21), and it has three output terminals, one output terminal is connected to the input terminal of proportional regulator III (23), one output terminal is connected to the input terminal of absolute value operator II (30), and one output terminal is a phase sequence output signal Ps; the signal input terminal of integrator (24) with reset terminal is connected to the input terminal of proportional regulator III (23), and the reset input terminal thereof is connected to the output terminal of comparator (27), and it has four output terminals, which are respectively connected to the input terminals of sine operator I (25) and the output terminals of sine operator II (25). The comparator (27) comprises a first input terminal, a "+" input terminal of an adder IV (29), an input terminal of an absolute value operator (26), and a phase output signal α; a "+" input terminal of a comparator (27) is connected to the output terminal of the absolute value operator (26), and a "-" input terminal thereof is connected to a second constant; another "+" input terminal of the adder IV (29) is connected to the first constant, and an output terminal thereof is connected to a sine operator II (28); an output terminal of the sine operator I (25) is connected to another input terminal of a multiplier I (18), and an output terminal of the sine operator II (28) is connected to another input terminal of a multiplier II (19); an output terminal of the absolute value operator II (30) is an angular frequency signal ω; wherein the value of the proportional regulator III (23) is a constant (e.g., 180 / π).

[0077] This embodiment implements the digital phase locking unit through the above hardware structure, thereby preventing the software phase locking program from running away or becoming invalid, thereby achieving reliable phase locking of the three-phase voltage of the power grid.

[0078] In a specific implementation, the no-inrush current switching logic unit is used for phase judgment of no-inrush current switching. The input end of the no-inrush current switching logic unit is connected to the grid phase signal and phase sequence signal output by the digital phase-locked unit. The no-inrush current input phase point is switched according to the grid phase sequence signal. When the actual phase is consistent with the no-inrush current input phase point, the trigger signal of the corresponding thyristor is output to input the capacitor.

[0079] like Figure 3 As shown, the working process of the no-inrush current switching logic unit is as follows: after receiving the input command, the phase sequence output signal Ps is judged. If the phase sequence signal Ps>0, the corresponding thyristor is switched according to the following phase output signal α: judging α, when α is 150, the thyristor trigger signal Drab between AB is set to 1, and the thyristor between AB is switched; judging α, when α is 270, the thyristor trigger signal Drbc between BC is set to 1, and the thyristor between BC is switched; judging α, when α is 30, the thyristor trigger signal Drca between CA is set to 1, and the thyristor between CA is switched. Judge the phase sequence signal Ps. If the phase sequence output signal Ps≤0, switch the corresponding thyristor according to the following phase output signal α: judge α. When α is -210, set the thyristor trigger signal Drab between AB to 1, and switch the thyristor between AB; judge α. When α is -90, set the thyristor trigger signal Drbc between BC to 1, and switch the thyristor between BC; judge α. When α is -330, set the thyristor trigger signal Drca between CA to 1, and switch the thyristor between CA.

[0080] In a specific embodiment, the module control board (6) is further provided with a capacitance attenuation protection unit, which is used for detecting and protecting the attenuation rate of the capacitance. The input end of the capacitance attenuation protection unit is connected to the grid voltage, the compensation current and the voltage frequency output by the digital phase-locked unit, and the capacitance of the capacitor and the attenuation rate of the capacitor are calculated online by combining the actual reactance rate and the capacitance value on the capacitor nameplate. When the capacitance attenuation rate exceeds the set value, an alarm shutdown signal is output.

[0081] In a specific implementation, the module control board (6) is also provided with a harmonic protection unit, which is used for monitoring and protecting the harmonic content of the voltage and the compensation current. Its input end is connected to the grid voltage and the compensation current, and the fundamental wave value and the harmonic wave value are calculated based on the sampled grid voltage and the compensation current, and the harmonic content of the grid voltage and the compensation current are calculated respectively. When the harmonic content exceeds the respective set protection value, an alarm shutdown signal is output.

[0082] In a specific embodiment, the module control board (6) is also provided with a thyristor breakdown protection unit, which is used for judging and protecting the thyristor breakdown state. Its input end is connected to the trigger instruction and the compensation current, and the state of the thyristor is obtained according to the trigger instruction and the compensation current. When a breakdown is detected, a trip signal is output to the opening coil of the circuit breaker.

[0083] The capacitance attenuation protection unit, harmonic protection unit and thyristor breakdown protection unit of this embodiment solve the problem of monitoring and protection in the early stage of capacitor compensation branch fault, thereby avoiding the expansion of accidents.

[0084] Specifically, the module control board (6) is also provided with a full-duplex communication unit, which has a full-duplex communication interface, receives high-speed switching communication instructions from an external controller in a broadcast instruction listening manner and sends status information of the module control board in a full-duplex manner.

[0085] In a specific embodiment, the module control board (6) is also provided with a temperature protection unit, which is used to sample the temperature of the capacitor (5), the temperature of the reactor, the temperature of the heat sink on the switching switch and the ambient temperature. The temperature protection unit is used to calculate the temperature rise of the capacitor (5), the reactor (4) and the heat sink on the switching switch (3). When the temperature or temperature rise of the capacitor (5), the reactor (4) and the heat sink on the switching switch (3) exceeds the set protection value, an alarm shutdown signal is output.

[0086] A control method of a low-voltage capacitor high-speed switching compensation module in this embodiment includes:

[0087] When the circuit breaker (1) is closed, the three-phase voltage of the power grid is sampled by using the module control board (6), and then the phase sequence and phase of the power grid voltage are obtained after being phase-locked by the digital phase-locking unit;

[0088] When the compensation module receives an external input command, the inrush current switching logic unit determines the phase according to the grid voltage phase sequence to find the positive peak point of the grid three-phase line voltage, and issues a triggering instruction for the thyristor in the switching switch (3) at the positive peak point of the grid three-phase line voltage to input the capacitor (5);

[0089] When the compensation module receives the external removal command, it determines the phase according to the current grid voltage phase sequence, finds the positive zero-crossing point of the grid three-phase line voltage (i.e., the current of the diode in the switching switch is the peak value when the line voltage changes from negative to positive), and issues a stop triggering thyristor command in the switching switch (3). The thyristor will naturally turn off at zero current, and then the diode will turn on and off after half a power frequency cycle, completing the capacitor removal. At this time, the three groups of capacitors (5) are fully charged through the diodes, and the compensation module can immediately respond to the external input command again to re-input the capacitors (5) to achieve the purpose of high-speed switching.

[0090] When the module control board (6) is composed of a digital phase-locked unit, a no-inrush current switching logic unit, a capacitance attenuation protection unit, a harmonic protection unit, a thyristor breakdown protection unit, a full-duplex communication unit and a temperature protection unit, the corresponding control method of the low-voltage capacitor high-speed switching compensation module is:

[0091] When the module control board (6) is connected to the power supply and the circuit breaker (1) is closed, the three groups of capacitors in the capacitor (5) are charged to the positive peak point of the grid line voltage through the diodes inside the switching switch (3), and the module control board (6) samples the three-phase voltage of the grid, and after the digital phase locking unit locks the phase, the phase sequence and phase of the grid voltage are obtained; when the compensation module receives the external input command, the phase is determined by the inrush current switching logic unit according to the grid voltage phase sequence to find the positive peak point of the grid three-phase line voltage, and the thyristor instructions in the switching switch (3) are respectively issued at the positive peak point of the grid three-phase line voltage to input the capacitor (5);

[0092] When the compensation module receives the external removal command, it determines the phase according to the current grid voltage phase sequence, finds the positive zero-crossing point of the grid three-phase line voltage (i.e., the current of the diode in the switching switch is the peak value when the line voltage changes from negative to positive), and issues a stop triggering thyristor command in the switching switch (3). The thyristor will naturally turn off at zero current, and then the diode will turn on and off after half a power frequency cycle, completing the capacitor removal. At this time, the three groups of capacitors (5) are fully charged through the diodes, and the compensation module can immediately respond to the external input command again to re-input the capacitors (5) to achieve the purpose of high-speed switching.

[0093] The capacitance attenuation protection unit first analyzes the fundamental voltage and fundamental compensation current based on the sampled three-phase voltage Ua, Ub, Uc and the compensation current Iab, Ibc, Ica in the three-phase angle inner loop through the Fourier algorithm, and then calculates the capacitance attenuation rate based on the fundamental voltage, fundamental compensation current, and the voltage frequency output by the phase-locked unit, combined with the actual reactance rate and the capacitance parameters on the capacitor nameplate. If the capacitance attenuation rate exceeds the set protection value, an alarm shutdown signal will be output;

[0094] The harmonic protection unit analyzes the fundamental voltage, fundamental compensation current, harmonic voltage, harmonic compensation current based on the sampled three-phase voltage Ua, Ub, Uc and the compensation current Iab, Ibc, Ica in the three-phase angle inner loop through Fourier algorithm, and calculates the voltage harmonic content and compensation current harmonic content. If the respective set protection values ​​are exceeded, an alarm shutdown signal will be output;

[0095] The module control board (6) samples the temperature of the capacitor (5), the temperature of the reactor (4), the temperature of the radiator of the switching switch (3) and the ambient temperature, and respectively calculates the temperature rise of the capacitor (5), the reactor (4) and the radiator of the switching switch (3). When the temperature or temperature rise of the capacitor (5), the reactor (4) and the radiator of the switching switch (3) exceeds the set protection value, an alarm shutdown signal is output;

[0096] The thyristor breakdown protection unit detects the compensation currents Iab, Ibc, and Ica in real time. If the compensation current is detected when there is no thyristor trigger signal, it means that the thyristor has a breakdown or critical breakdown phenomenon. The thyristor breakdown protection unit will send a module tripping instruction to the tripping coil (7) to disconnect the module circuit breaker (1) from the main circuit.

[0097] The full-duplex communication unit of the module control board (6) has a full-duplex communication interface, receives the high-speed switching communication command of the external controller in a broadcast command listening mode and sends the status information of the module in a full-duplex mode.

[0098] The control method based on the above-mentioned low-voltage capacitor high-speed switching compensation module includes:

[0099] Digital phase-locked grid three-phase voltage obtains the phase sequence and phase of the grid voltage;

[0100] When the compensation module receives the external input command, it determines the phase according to the grid voltage phase sequence to find the positive peak point of the grid three-phase line voltage, and sends a triggering thyristor instruction in the switching switch at the positive peak point of the grid three-phase line voltage to input the capacitor;

[0101] When the compensation module receives the external removal command, it determines the phase according to the current grid voltage phase sequence, finds the positive zero-crossing point of the three-phase line voltage of the grid (that is, the current of the diode in the switching switch corresponds to the peak value when the line voltage changes from negative to positive), and issues a stop triggering thyristor instruction in the switching switch. The thyristor will naturally turn off at zero current, and then the diode will turn on and off after half a power frequency cycle, completing the capacitor removal. At this time, the three groups of capacitors have been fully charged through the diodes, and the compensation module can immediately respond to the external input command again to re-input the capacitor to achieve the purpose of high-speed switching.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low voltage capacitor high speed switching compensation module, characterized in that: It includes a circuit breaker, a switching switch, a reactor, a capacitor and a module control panel. The switching switch, the reactor and the capacitor are connected in series to form an inner triangle and connected to the outgoing line side of the circuit breaker. The incoming line side of the circuit breaker is connected to the power supply. The module control board is provided with a digital phase-locking unit and a no-inrush current switching logic unit; the digital phase-locking unit is used to phase-lock the three-phase voltage of the power grid; the no-inrush current switching logic unit is used to find the peak point of the three-phase voltage of the power grid after phase locking, and trigger the switching switch at the peak point of the three-phase voltage of the power grid after receiving an external input command to input the capacitor; The switching switch is composed of a thyristor and a diode connected in anti-parallel. When the thyristor in the switching switch is turned off, the capacitor will be charged through the diode. When the diode is cut off, that is, when the switching switch is turned off, the capacitor will be charged to the voltage at the peak of the line voltage, waiting to respond to the switching instruction again to achieve the purpose of high-speed switching. The input end of the no-inrush current switching logic unit receives the grid phase signal and phase sequence signal after digital phase locking, and the no-inrush current switching logic unit is used to switch the no-inrush current input phase point according to the grid phase sequence signal, and when the actual phase is consistent with the no-inrush current input phase point, output a trigger signal of the thyristor in the corresponding switching switch to input the capacitor; The digital phase locking unit comprises: Three AD conversion units, used to convert the three-phase voltage analog signals of the power grid into digital signals respectively; A first adder and a second adder, which are used to make a difference between the A-phase and C-phase voltage digital signals and the B-phase voltage digital signal respectively; A first proportional regulator connected to an output terminal of the first adder; a second proportional regulator connected to the output terminal of the second adder; A first multiplier, one input end of which is connected to the first proportional regulator, and the other input end of which is connected to the output end of the first sine operator, and the input end of the first sine operator is connected to the output end of the integrator with a reset end; a second multiplier, one input end of which is connected to the second proportional regulator, and the other input end of which is connected to the output end of the second sine operator, the input end of the second sine operator is connected to the output end of the fourth adder, and two input ends of the fourth adder are respectively connected to the output end of the integrator with a reset end and the first constant; a third adder, configured to accumulate output results of the first multiplier and the second multiplier; A low-pass filter, used for filtering harmonic signals, wherein an input end of the low-pass filter is connected to an output end of the third adder; A PI regulator, whose input end is connected to the output end of the low-pass filter, and whose output end is connected to the input end of the second absolute value operator, whose output end is an angular frequency signal, and whose other output end is a phase sequence signal; A third proportional regulator, an input end of which is connected to an output end of the PI regulator; An integrator with a reset terminal, one input terminal of which is connected to the output terminal of the third proportional regulator, and the other reset input terminal of which is connected to the output terminal of the comparator, and the output terminal of the integrator with a reset terminal is a phase signal; The comparator has a positive input terminal connected to the output terminal of the first absolute value operator, an input terminal of the first absolute value operator connected to the output terminal of the integrator with a reset terminal, and a negative input terminal of the comparator connected to the second constant.

2. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The module control board is also provided with a capacitance attenuation protection unit, whose input end is connected to the grid voltage, compensation current and voltage frequency after digital phase locking, and combines the actual reactance rate and the capacitance value on the capacitor nameplate to online simulate and calculate the capacitance value and the capacitance attenuation rate. When the capacitance attenuation rate exceeds the set value, an alarm shutdown signal is output.

3. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The module control board is also provided with a harmonic protection unit, whose input end is connected to the grid voltage and compensation current, and the fundamental wave value and harmonic wave value are calculated according to the sampled grid voltage and compensation current, and the harmonic content of the grid voltage and compensation current are calculated respectively, and an alarm shutdown signal is output when the respective set protection values ​​are exceeded.

4. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The module control board is also provided with a thyristor breakdown protection unit, whose input end receives a trigger instruction and a compensation current, obtains the state of the thyristor according to the trigger instruction and the compensation current, and outputs a trip signal to the opening coil of the circuit breaker when a breakdown is detected.

5. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The module control board is also provided with a full-duplex communication unit, which has a full-duplex communication interface, receives high-speed switching communication instructions of an external controller in a broadcast instruction listening manner and sends status information of the module control board in a full-duplex manner.

6. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The module control board is also provided with a temperature protection unit, which is used to sample the temperature of the capacitor, the temperature of the reactor, the temperature of the radiator on the switching switch and the ambient temperature. The temperature protection unit is used to calculate the temperature or temperature rise of the capacitor, the reactor and the radiator on the switching switch. Once the temperature or temperature rise of the capacitor, the reactor and the radiator on the switching switch exceeds the set protection value, an alarm shutdown signal is output.

7. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The low-voltage capacitor high-speed switching compensation module also includes a current transformer, whose primary side is respectively connected in series to the three corner inner loops of the triangle connection, and whose secondary side is respectively connected to the three current input terminals of the module control board.

8. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The circuit breaker is equipped with a trip coil, and the control end of the trip coil is connected to the trip terminal of the module control board.

9. The low-voltage capacitor high-speed switching compensation module according to claim 1, characterized in that: The switching switch is also provided with a radiator, on which a temperature sensor is installed, and the temperature sensor is connected to the radiator temperature terminal of the module control board; Or the reactor is composed of three windings, each winding has an independent incoming line terminal and an outgoing line terminal, and each winding is equipped with a temperature sensor, which is respectively connected to the reactor temperature terminal of the module control board; Or the capacitor is composed of three groups of independent single-phase capacitors, each group of capacitors has an input terminal and an output terminal, each group of capacitors is installed with a temperature sensor, and the temperature sensors are respectively connected to the capacitor temperature terminals of the module control board.

10. A control method using the low-voltage capacitor high-speed switching compensation module according to any one of claims 1 to 9, characterized in that: include: Digital phase-locked grid three-phase voltage obtains the phase sequence and phase of the grid voltage; When the compensation module receives the external input command, it determines the phase according to the grid voltage phase sequence to find the positive peak point of the grid three-phase line voltage, and sends a triggering thyristor instruction in the switching switch at the positive peak point of the grid three-phase line voltage to input the capacitor; When the compensation module receives the external removal command, it determines the phase according to the current grid voltage phase sequence, finds the moment when the three-phase line voltage of the grid crosses zero in the positive direction, and issues instructions to stop triggering the thyristor in the switching switch. The thyristor will naturally turn off at zero current, and then the diode will be turned on and cut off after half a power frequency cycle, completing the capacitor removal. At this time, the three groups of capacitors have been fully charged through the diodes, and the compensation module immediately responds to the external input command again to re-input the capacitor to achieve the purpose of high-speed switching.

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