IGCT turn-off control method and device based on voltage zero crossing and computer storage medium

Abstract

The invention relates to an IGCT turn-off control method and device based on voltage zero crossing and a computer storage medium, and belongs to the technical field of converter valve control. The method comprises the following steps: when a converter normally runs, firstly, calculating a trigger angle of an ignition valve according to ignition time and commutation voltage zero-crossing time of the ignition valve; then the corresponding shut-off valve is determined according to the corresponding relation between the ignition valve and the shut-off valve; and finally, according to the direct current of the shut-off valve, the commutation voltage, the commutation transformer leakage reactance and the trigger angle of the ignition valve, calculating an arc extinguishing angle of the shut-off valve, and based on the obtained arc extinguishing angle of the shut-off valve and the calculated shut-off angle of the shut-off valve, controlling the IGCT of the shut-off valve to shut off according to the shut-off angle of the shut-off valve. According to the method, the trigger angle of the ignition valve is accurately calculated, and the accurate turn-off angle of the converter valve is calculated in combination with the change of the direct current, so that accurate turn-off control on the IGCT of the converter valve is realized.

Description

Technical Field

[0001] This invention relates to an IGCT turn-off control method, device, and computer storage medium based on voltage zero crossing, belonging to the field of converter valve control technology. Background Technology

[0002] Traditional conventional DC transmission uses line commutated converter technology, with thyristors (LCCs) as the commutation devices. Although the engineering technology is relatively mature and reliable, and it is widely used in my country's ultra-high voltage projects, the key characteristic of thyristors is that once they are turned on, the gate loses its control function, and they can only be turned off when the current naturally crosses zero. This method is highly dependent on the grid voltage. If a grid fault occurs (such as a voltage drop or short circuit), the current may not cross zero, causing the thyristor to remain on, leading to commutation failure and power transmission interruption. Therefore, the application of traditional conventional DC transmission technology is limited in scenarios where the receiving-end grid is relatively weak or where multiple DC feeds are used.

[0003] With technological advancements, the integrated gate commutated thyristor (IGCT) is a fully controllable device. Like a thyristor, it possesses advantages such as low on-state voltage drop and high current-carrying capacity. Simultaneously, like an IGBT, it can be turned off via a gate signal, exhibiting good resistance to commutation failure and the ability to actively interrupt commutation current. In any situation where a fault is detected (such as a short circuit or overcurrent) or a forced current interruption is required, the IGCT can be quickly turned off by resetting it via a gate trigger pulse, thereby cutting off the current path. However, current research on IGCT turn-off control mainly focuses on turn-off conditions; existing technologies do not provide a detailed process for how the IGCT turns off after receiving a turn-off signal. Summary of the Invention

[0004] The purpose of this invention is to provide an IGCT turn-off control method, device, and computer storage medium based on voltage zero crossing, so as to achieve precise control of IGCT turn-off and thereby improve the commutation success rate.

[0005] To solve the above-mentioned technical problems, this invention provides an IGCT turn-off control method based on voltage zero crossing, the method comprising: 1) Calculate the firing angle of the ignition valve based on its ignition time and voltage zero-crossing time; 2) Determine the corresponding shut-off valve by utilizing the correspondence between the ignition valve and the shut-off valve. Calculate the shut-off valve's arc-extinguishing angle based on the shut-off valve's DC current, commutation voltage, commutator leakage reactance, and ignition valve's firing angle. Then, based on the obtained shut-off valve arc-extinguishing angle and the calculated shut-off valve's shut-off angle, control the shut-off valve IGCT to shut off according to the shut-off valve's shut-off angle.

[0006] Furthermore, the formula for calculating the firing angle is: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

[0007] Furthermore, the formula for calculating the arc-extinguishing angle of the shut-off valve is: γ = Acos (Cosβ+2 Id dx / U X ) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, equal to 180°–α, α is the firing angle, Id is the DC current, and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer.

[0008] Furthermore, the formula for calculating the shut-off angle of the shut-off valve is: AlpOff = 180°-γ+γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin.

[0009] Furthermore, the method also includes generating a trigger pulse when a high-level signal is generated when the phase of the phase-locked loop is greater than the trigger angle.

[0010] Furthermore, the method also includes the following: after the next valve is ignited, if the phase of the previous valve is greater than the valve's shut-off angle or another valve in the same bridge arm is triggered, the trigger pulse disappears.

[0011] Furthermore, the voltage zero-crossing time is achieved by using a phase-locked loop to detect and track the grid voltage in real time.

[0012] Furthermore, the ignition timing of the ignition valve is obtained from the ignition control signal.

[0013] The present invention also provides an IGCT turn-off control device based on zero-voltage crossing, comprising a processor, the processor being configured to execute computer program instructions to implement the IGCT turn-off control method based on zero-voltage crossing of the present invention, the method comprising: 1) Calculate the firing angle of the ignition valve based on its ignition time and voltage zero-crossing time; 2) Determine the corresponding shut-off valve by utilizing the correspondence between the ignition valve and the shut-off valve. Calculate the shut-off valve's arc-extinguishing angle based on the DC current, commutation voltage, and leakage reactance of the commutator transformer, and the firing angle of the ignition valve. Based on the obtained arc-extinguishing angle and the calculated shut-off angle, control the shut-off valve IGCT to shut off according to the shut-off valve's shut-off angle.

[0014] Furthermore, the formula for calculating the firing angle is: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

[0015] Furthermore, the formula for calculating the arc-extinguishing angle of the shut-off valve is: γ = Acos (Cosβ+2 Id dx / U X ) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, equal to 180° – α, α is the firing angle, Id is the DC current, and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer.

[0016] Furthermore, the formula for calculating the shut-off angle of the shut-off valve is: AlpOff = 180°-γ+γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin.

[0017] Furthermore, the method also includes generating a trigger pulse when a high-level signal is generated when the phase of the phase-locked loop is greater than the trigger angle.

[0018] Furthermore, the method also includes the following: after the next valve is ignited, if the phase of the previous valve is greater than the valve's shut-off angle or another valve in the same bridge arm is triggered, the trigger pulse disappears.

[0019] Furthermore, the voltage zero-crossing time is achieved by using a phase-locked loop to detect and track the grid voltage in real time.

[0020] Furthermore, the ignition timing of the ignition valve is obtained from the ignition control signal.

[0021] The present invention also provides a computer storage medium storing a computer program to implement the IGCT turn-off control method based on voltage zero crossing as described above, the method comprising: 1) Calculate the firing angle of the ignition valve based on its ignition time and voltage zero-crossing time; 2) Determine the corresponding shut-off valve by utilizing the correspondence between the ignition valve and the shut-off valve. Calculate the shut-off valve's arc-extinguishing angle based on the shut-off valve's DC current, commutation voltage, commutator leakage reactance, and ignition valve's firing angle. Calculate the shut-off valve's shut-off angle based on the obtained arc-extinguishing angle and control the shut-off valve IGCT to shut off according to the shut-off valve's shut-off angle.

[0022] Furthermore, the formula for calculating the firing angle is: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

[0023] Furthermore, the formula for calculating the arc-extinguishing angle of the shut-off valve is: γ = Acos (Cosβ+2 Id dx / Ux) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, equal to 180°–α, α is the firing angle, Id is the DC current, and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer.

[0024] Furthermore, the formula for calculating the shut-off angle of the shut-off valve is: AlpOff = 180°-γ+γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin.

[0025] Furthermore, the method also includes generating a trigger pulse when a high-level signal is generated when the phase of the phase-locked loop is greater than the trigger angle.

[0026] Furthermore, the method also includes the following: after the next valve is ignited, if the phase of the previous valve is greater than the valve's shut-off angle or another valve in the same bridge arm is triggered, the trigger pulse disappears.

[0027] Furthermore, the voltage zero-crossing time is achieved by using a phase-locked loop to detect and track the grid voltage in real time.

[0028] Furthermore, the ignition timing of the ignition valve is obtained from the ignition control signal.

[0029] The beneficial effects of this invention are as follows: During normal operation of the converter, the firing angle of the ignition valve is first calculated based on the ignition time and the zero-crossing time of the commutation voltage. Then, the corresponding shut-off valve is determined using the correspondence between the ignition valve and the shut-off valve. The arc-extinguishing angle of the shut-off valve is calculated based on the DC current of the shut-off valve, the commutation voltage, the leakage reactance of the converter transformer, and the firing angle of the ignition valve. Based on the obtained arc-extinguishing angle and the calculated shut-off angle, the shut-off valve IGCT is controlled to shut off according to the stated shut-off angle. This invention achieves precise shut-off control of the converter valve IGCT by accurately calculating the firing angle of the ignition valve and combining it with changes in the DC current to obtain a precise shut-off angle. Attached Figure Description

[0030] Figure 1 This is a schematic diagram showing the correspondence between the ignition valve and the shut-off valve in a Y-bridge converter. Figure 2 This is a schematic diagram of the Y-bridge converter. Figure 3 This is a flowchart of the IGCT turn-off control method based on voltage zero crossing of the present invention; Figure 4 This is a schematic diagram of the trigger pulse generation logic in this invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0032] This invention calculates the trigger angle of the ignition valve precisely and, in conjunction with the change in DC current, calculates the accurate shut-off angle of the converter valve, thereby achieving precise shut-off control of the converter valve IGCT.

[0033] Implementation of IGCT Turn-off Control Method Based on Voltage Zero Crossing This invention first calculates the firing angle of the ignition valve based on its ignition time and the zero-crossing time of the commutation voltage. Then, it determines the corresponding shut-off valve using the correspondence between the ignition valve and the shut-off valve. The shut-off valve's arc-extinguishing angle is calculated based on the shut-off valve's DC current, commutation voltage, commutator leakage reactance, and the ignition valve's firing angle. Finally, based on the obtained arc-extinguishing angle and the calculated shut-off angle, the shut-off valve IGCT is controlled to shut off according to the calculated shut-off angle. The implementation flow of this method is as follows: Figure 3 As shown below, a detailed explanation will follow.

[0034] 1. Calculate the firing angle of the ignition valve.

[0035] This invention calculates the firing angle of an ignition valve based on its ignition time and voltage zero-crossing time. The voltage zero-crossing time refers to the moment when the AC phase voltage of the IGCT arm crosses zero as it transitions from the negative half-cycle to the positive half-cycle. For a three-phase bridge converter, there are three such zero-crossing points, each 120 degrees apart. This can typically be detected and tracked in real-time by a phase-locked loop (PLL), outputting a continuously changing phase signal synchronized with the grid voltage. The zero point of this phase signal corresponds to the voltage zero-crossing time. The converter valve ignition time refers to the actual delay between the voltage overcurrent moment and the issuance of the firing pulse; that is, the time difference between the voltage overcurrent moment and the issuance of the firing pulse. The firing angle refers to the electrical angle of the delay between the voltage zero-crossing moment and the issuance of the firing pulse. Therefore, there is a certain relationship between the three. The formula for calculating the firing angle used in this invention is as follows: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient. The ignition time of the ignition valve is obtained from the ignition control signal.

[0036] For a three-phase bridge converter, the ignition valve refers to the valve that is triggered to open, and the shut-off valve refers to the valve that needs to be shut off because it is triggered to open. The correspondence between the ignition valve and the shut-off valve is fixed. The following explanation uses a Y-bridge as an example. Figure 2 As shown, the converter in this embodiment has six valves: valve 1 (valve number Y1), valve 2 (valve number Y2), valve 3 (valve number Y3), valve 4 (valve number Y4), valve 5 (valve number Y5), and valve 6 (valve number Y6). Valve Y1, valve Y3, and valve Y5 form a common cathode group, that is, the cathodes of valves Y1, valve Y3, and valve Y5 are connected together to the DC positive terminal. Valve Y4, valve Y6, and valve Y2 form a common anode group, that is, the anodes of valves Y1, valve Y3, and valve Y5 are connected together to the DC negative terminal.

[0037] If the last ignition valve was Y1, then the shut-off valve number generated is Y5; if the last ignition valve was Y2, then the shut-off valve number generated is Y6; if the last ignition valve was Y3, then the shut-off valve number generated is Y1; if the last ignition valve was Y4, then the shut-off valve number generated is Y2; if the last ignition valve was Y5, then the shut-off valve number generated is Y3, and so on. If the last ignition valve was Y6, then the shut-off valve number generated is Y4. Therefore, the correspondence between the ignition valves and shut-off valves in the Y-bridge converter is as follows: Figure 1 As shown, the shut-off valve number of bridge D is similar to that of bridge Y, and will not be described in detail here.

[0038] 2. Calculate the arc-extinguishing angle of the shut-off valve.

[0039] The arc-extinguishing angle refers to the electrical angle corresponding to the time from when a thyristor (IGCT) successfully turns off during a commutation process until it begins to withstand forward voltage again. It represents the "safe time window" that the thyristor has after turn-off to restore its blocking capability. The arc-extinguishing angle of the shut-off valve is calculated based on the ignition valve's firing angle, commutation voltage, commutator leakage reactance, and DC current. The formula used in this invention for calculating the arc-extinguishing angle of the shut-off valve is as follows: γ = Acos (Cosβ+2 Id dx / U X ) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, β = 180° – α, α is the firing angle, Id is the DC current (current on the DC pole), and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer (given by the main circuit parameters).

[0040] 3. Calculate the shut-off angle.

[0041] The shut-off angle of a converter valve is the most critical indicator for measuring its operational safety. It can be directly calculated from the firing angle. The formula for calculating the shut-off angle of a shut-off valve is: AlpOff = 180° - γ + γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin, which can be set according to experience, and is generally set to 3~6°.

[0042] 4. Perform shutdown control.

[0043] After obtaining the shut-off angle, the shut-off valve can be controlled based on it. During control, the relationship between the shut-off valve phase and the shut-off angle is judged in real time. When the shut-off valve phase is greater than the shut-off angle, a reset signal is sent to the trigger pulse of the shut-off valve. When the trigger pulse disappears, the IGCT valve is shut off, thereby controlling its shutdown. The trigger angle of the valve is calculated based on the valve ignition time and the zero-crossing time of the commutation voltage. The sequence of phase commutation is: Valve 1 -> Valve 3 -> Valve 5 -> Valve 1, Valve 2 -> Valve 4 -> Valve 6 -> Valve 2. For example, in this invention, the trigger pulse of Valve 5 is controlled to shut off based on the calculated trigger angle of Valve 1.

[0044] This invention also provides a process for generating trigger pulses, such as... Figure 4As shown, when the phase of the phase-locked loop (PLL) is greater than ALPHA, a high level is generated. The rising edge of the high level is detected to set the RS flip-flop S, and the RS flip-flop outputs 1, generating a high level in the same way as before. However, the disappearance of the high level is determined by the turn-off angle of the turn-off control strategy. That is, when the valve phase is greater than the turn-off angle, a high level is generated, ANDed with the valve's already triggered state, and then ORed with the triggered state of another valve in the same bridge arm, setting the RS flip-flop R, setting the RS flip-flop output to 0, and the trigger pulse disappears, i.e., the IGCT valve is turned off. For valves with normal thyristors, such as valve 5, the disappearance of the trigger pulse is reset by the triggering of valve 1.

[0045] Implementation of IGCT turn-off control device based on voltage zero crossing This invention proposes an IGCT turn-off control device based on zero-voltage crossing, including a processor to execute computer program instructions to implement the IGCT turn-off control method based on zero-voltage crossing of this invention. The implementation flow of this control method is as follows: Figure 3 As shown, the specific process includes the following steps.

[0046] 1. Calculate the firing angle of the ignition valve.

[0047] This invention calculates the firing angle of an ignition valve based on its ignition time and voltage zero-crossing time. The voltage zero-crossing time refers to the moment when the AC phase voltage of the IGCT arm crosses zero as it transitions from the negative half-cycle to the positive half-cycle. For a three-phase bridge converter, there are three such zero-crossing points, each 120 degrees apart. This can typically be detected and tracked in real-time by a phase-locked loop (PLL), outputting a continuously changing phase signal synchronized with the grid voltage. The zero point of this phase signal corresponds to the voltage zero-crossing time. The converter valve ignition time refers to the actual delay between the voltage overcurrent moment and the issuance of the firing pulse; that is, the time difference between the voltage overcurrent moment and the issuance of the firing pulse. The firing angle refers to the electrical angle of the delay between the voltage zero-crossing moment and the issuance of the firing pulse. Therefore, there is a certain relationship between the three. The formula for calculating the firing angle used in this invention is as follows: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

[0048] The ignition timing of the ignition valve is obtained from the ignition control signal.

[0049] For a three-phase bridge converter, the ignition valve refers to the valve that is triggered to open, and the shut-off valve refers to the valve that needs to be shut off because it is triggered to open. The correspondence between ignition valves and shut-off valves is fixed. The correspondence between the ignition valves and shut-off valves in a Y-bridge converter is as follows: Figure 1 As shown, the shut-off valve number of bridge D is similar to that of bridge Y, and will not be described in detail here.

[0050] 2. Calculate the arc-extinguishing angle of the shut-off valve.

[0051] The arc-extinguishing angle refers to the electrical angle corresponding to the time from when a thyristor (IGCT) successfully turns off during a commutation process until it begins to withstand forward voltage again. It represents the "safe time window" that the thyristor has after turn-off to restore its blocking capability. The arc-extinguishing angle of the shut-off valve is calculated based on the DC current, commutation voltage, commutator leakage reactance, and ignition valve firing angle. The formula used in this invention for calculating the arc-extinguishing angle of the shut-off valve is as follows: γ = Acos (Cosβ+2 Id dx / U X ) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, β equals 180° – α, α is the firing angle, Id is the DC current (current on the DC pole), and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer.

[0052] 3. Calculate the shut-off angle.

[0053] The shut-off angle of a converter valve is the most critical indicator for measuring its operational safety. It can be directly calculated from the firing angle. The formula for calculating the shut-off angle of a shut-off valve is: AlpOff = 180° - γ + γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin, which can be set according to experience, and is generally set to 3~6°.

[0054] 4. Perform shutdown control.

[0055] After obtaining the shut-off angle, the shut-off valve can be controlled based on it. During control, the relationship between the shut-off valve phase and the shut-off angle is judged in real time. When the shut-off valve phase is greater than the shut-off angle, a reset signal is sent to the trigger pulse of the shut-off valve. When the trigger pulse disappears, the IGCT valve is shut off, thereby controlling its shutdown. The trigger angle of the valve is calculated based on the valve ignition time and the zero-crossing time of the commutation voltage. The sequence of phase commutation is: Valve 1 -> Valve 3 -> Valve 5 -> Valve 1, Valve 2 -> Valve 4 -> Valve 6 -> Valve 2. For example, in this invention, the trigger pulse of Valve 5 is controlled to shut off based on the calculated trigger angle of Valve 1.

[0056] This invention also provides a process for generating trigger pulses, such as... Figure 4 As shown, when the phase of the phase-locked loop is greater than ALPHA, a high level is generated. The rising edge of the high level is detected to set the RS flip-flop S, and the RS flip-flop outputs 1, generating a high level in the same way as the previous method. However, the disappearance of the high level is determined by the turn-off angle of the turn-off control strategy. That is, when the phase of the valve is greater than the turn-off angle, a high level is generated and ANDed with the valve's already triggered state, and then ORed with the triggered state of another valve in the same bridge arm, so that the R of the RS flip-flop is set, the RS flip-flop output is set to 0, the trigger pulse disappears, and the IGCT valve is turned off.

[0057] During implementation, the processor can be a central processing unit (CPU), a microprocessor unit (MPU), a digital signal processor (DSP), or a field programmable gate array (FPGA), etc.

[0058] Computer storage media implementation methods The IGCT turn-off control method based on voltage zero crossing, implemented by the computer program stored in the computer storage medium of the present invention, includes: 1. Calculate the firing angle of the ignition valve.

[0059] This invention calculates the firing angle of an ignition valve based on its ignition time and voltage zero-crossing time. The voltage zero-crossing time refers to the moment when the AC phase voltage of the IGCT arm crosses zero as it transitions from the negative half-cycle to the positive half-cycle. For a three-phase bridge converter, there are three such zero-crossing points, each 120 degrees apart. This can typically be detected and tracked in real-time by a phase-locked loop (PLL), outputting a continuously changing phase signal synchronized with the grid voltage. The zero point of this phase signal corresponds to the voltage zero-crossing time. The converter valve ignition time refers to the actual delay between the voltage overcurrent moment and the issuance of the firing pulse; that is, the time difference between the voltage overcurrent moment and the issuance of the firing pulse. The firing angle refers to the electrical angle of the delay between the voltage zero-crossing moment and the issuance of the firing pulse. Therefore, there is a certain relationship between the three. The formula for calculating the firing angle used in this invention is as follows: α = (FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

[0060] The ignition timing of the ignition valve is obtained from the ignition control signal.

[0061] For a three-phase bridge converter, the ignition valve refers to the valve that is triggered to open, and the shut-off valve refers to the valve that needs to be shut off because it is triggered to open. The correspondence between ignition valves and shut-off valves is fixed. The correspondence between the ignition valves and shut-off valves in a Y-bridge converter is as follows: Figure 1 As shown, the shut-off valve number of bridge D is similar to that of bridge Y, and will not be described in detail here.

[0062] 2. Calculate the arc-extinguishing angle of the shut-off valve.

[0063] The arc-extinguishing angle refers to the electrical angle corresponding to the time from when a thyristor (IGCT) successfully turns off during a commutation process until it begins to withstand forward voltage again. It represents the "safe time window" that the thyristor has after turn-off to restore its blocking capability. The arc-extinguishing angle of the shut-off valve is calculated based on the DC current, commutation voltage, commutator leakage reactance, and ignition valve firing angle. The formula used in this invention for calculating the arc-extinguishing angle of the shut-off valve is as follows: γ = Acos (Cosβ+2 Id dx / U X ) Where γ is the shut-off valve arc extinction angle, β is the lead-fire angle, β equals 180 – α, α is the firing angle, Id is the DC current, and U X dx is the commutation voltage, and dx is the leakage reactance of the commutator transformer.

[0064] 3. Calculate the shut-off angle.

[0065] The shut-off angle of a converter valve is the most critical indicator for measuring its operational safety. It can be directly calculated from the firing angle. The formula for calculating the shut-off angle of a shut-off valve is: AlpOff = 180° - γ + γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin.

[0066] 4. Perform shutdown control.

[0067] After obtaining the shut-off angle, the shut-off valve can be controlled based on it. During control, the relationship between the shut-off valve phase and the shut-off angle is judged in real time. When the shut-off valve phase is greater than the shut-off angle, a reset signal is sent to the trigger pulse of the shut-off valve. When the trigger pulse disappears, the IGCT valve is shut off, thus controlling its shut-off. The trigger angle of the valve is calculated based on the valve ignition time and the zero-crossing time of the commutation voltage. Valve 1->Valve 3->Valve 5->Valve 1----phase commutation in sequence, Valve 2->Valve 4->Valve 6->Valve 2----phase commutation in sequence. For example, in this invention, the trigger pulse of valve 5 is controlled to shut off based on the calculated trigger angle of valve 1.

[0068] This invention also provides a process for generating trigger pulses, such as... Figure 4 As shown, when the phase of the phase-locked loop (PLL) is greater than ALPHA, a high level is generated. The rising edge of the high level is detected to set the RS flip-flop S, and the RS flip-flop outputs 1, generating a high level in the same way as before. However, the disappearance of the high level is determined by the turn-off angle of the turn-off control strategy. That is, when the valve phase is greater than the turn-off angle, a high level is generated, which is then ANDed with the valve's already triggered state, and then ORed with the triggered state of another valve in the same bridge arm, setting the RS flip-flop R, setting the RS flip-flop output to 0, and the trigger pulse disappears, i.e., the IGCT valve is turned off. For valves with normal thyristors, such as valve 5, the disappearance of the trigger pulse is reset by the triggering of valve 1.

[0069] In summary, this invention can accurately calculate the firing angle of a valve based on its ignition time and the zero-crossing time of the commutation voltage. Combined with changes in DC current, it can also calculate the precise shut-off angle of the converter valve. If a valve is triggered by another valve on the same bridge arm, that valve will be immediately shut off, preventing commutation failure caused by a short circuit in the bridge arm.

Claims

1. A turn-off control method for an IGCT based on zero-crossing voltage, characterized in that, The method includes: 1) Calculate the firing angle of the ignition valve based on its ignition time and voltage zero-crossing time; 2) Determine the corresponding shut-off valve by utilizing the correspondence between the ignition valve and the shut-off valve. Calculate the shut-off valve's arc-extinguishing angle based on the shut-off valve's DC current, commutation voltage, commutator leakage reactance, and ignition valve's firing angle. Then, based on the obtained shut-off valve arc-extinguishing angle and the calculated shut-off valve's shut-off angle, control the shut-off valve IGCT to shut off according to the shut-off valve's shut-off angle.

2. The IGCT turn-off control method based on zero-crossing voltage as described in claim 1, characterized in that, The formula for calculating the firing angle is: α =(FirTime – UacZcTime) / Hptime P Where α is the firing angle, FirTime is the ignition time, UacZcTime is the voltage zero-crossing time, Hptime is the half-cycle time, and P is the conversion coefficient.

3. The IGCT turn-off control method based on zero-crossing voltage according to claim 1, characterized in that, The formula for calculating the arc extinction angle of the shut-off valve is: γ = Acos (Cosβ+2 Id dx / U X ) where γ is the extinction valve arc extinction angle, β is the advance firing angle, equal to 180° - α, α is the firing angle, Id is the direct current, U X is the commutation voltage, and dx is the converter leakage reactance.

4. The IGCT turn-off control method based on zero-crossing voltage as described in claim 1, characterized in that, The formula for calculating the shut-off angle of a shut-off valve is: AlpOff = 180° - γ + γ0 Where AlpOff is the shut-off angle of the shut-off valve, γ is the extinguishing angle of the shut-off valve, and γ0 is the shut-off angle margin.

5. The IGCT turn-off control method based on zero-crossing voltage according to any one of claims 1-4, characterized in that, The method also includes generating a trigger pulse when a high-level signal is generated when the phase of the phase-locked loop is greater than the trigger angle.

6. The IGCT turn-off control method based on zero-crossing voltage according to claim 5, characterized in that, The method also includes the following: after the next valve is ignited, if the phase of the previous valve is greater than the valve's shut-off angle or another valve in the same bridge arm is triggered, the trigger pulse disappears.

7. The IGCT turn-off control method based on zero-crossing voltage according to any one of claims 1-4, characterized in that, The voltage zero-crossing time is achieved by using a phase-locked loop to detect and track the grid voltage in real time.

8. The IGCT turn-off control method based on zero-crossing voltage according to any one of claims 1-4, characterized in that, The ignition timing of the ignition valve is obtained from the ignition control signal.

9. An IGCT turn-off control device based on voltage zero crossing, comprising a processor, characterized in that, The processor is used to execute computer program instructions to implement the IGCT turn-off control method based on voltage zero crossing as described in any one of claims 1-8.

10. A computer storage medium, characterized in that, The computer storage medium stores a computer program to implement the IGCT turn-off control method based on voltage zero crossing as described in any one of claims 1-8.

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