Hybrid commutation converter, control method and system

Abstract

The invention relates to a hybrid commutation converter and a control method and system, and belongs to the technical field of HCC converter valve turn-off control. And voltage at the two ends of the to-be-commutated valve is obtained, and when the forward voltage of the to-be-commutated valve is larger than or equal to the set voltage threshold value and the next valve commutated with the to-be-commutated valve is opened, the valve switching-off condition is met, and the to-be-commutated valve is switched off. According to the scheme, the valve to be subjected to phase change is turned off before bearing the forward voltage, the voltage at the two ends of the valve to be subjected to phase change needs to be monitored in real time, and the valve to be subjected to phase change is turned off before bearing the forward voltage. Therefore, when the active turn-off of the HCC converter valve is executed, the turn-off stress of a device can be reduced, the damage of the converter valve caused by mistaken turn-off is avoided, the commutation failure is better inhibited, the control effect is better, the turn-off current is small, the stress of the device is smaller, the equipment safety can be better ensured, and the method has higher engineering application value.

Description

Technical Field

[0001] The present invention relates to a hybrid-commutated converter, a control method and a system, belonging to the technical field of HCC commutation valve turn-off control. Background Art

[0002] A hybrid-commutated converter (HCC) is a converter structure with IGCT as the basic component. The IGCT device has the ability of controllable turn-on and controllable turn-off. Therefore, compared with the line-commutated converter with thyristor as the basic component, the hybrid-commutated converter needs to study the turn-off pulse control method.

[0003] The Chinese patent application with the application publication number CN113270887A and the application publication date of August 17, 2021 discloses a DC transmission control method and system based on a controllable turn-off current source converter. This method constructs the phase information of the positive phase-locked loop and the non-full-cycle reverse phase-locked loop at the receiving end, and then compares the ignition angle with the phase information of the positive phase-locked loop, and compares the minimum extinction angle with the non-full-cycle reverse phase-locked loop information to determine the trigger turn-on pulse or turn-off pulse. This method is similar to the trigger angle control, with simple implementation and engineering application value. However, after a ground fault occurs in the AC system on the inverter side, the phase-locked loop cannot track the phase of the AC system under the fault condition in real time. At this time, the turn-off pulse is still triggered according to the phase of the phase-locked loop before the fault, which will cause a late turn-off. The commutation valve to be turned off will bear the positive voltage again, and the valve-side current will also increase again. Eventually, the real-time turn-off current at the turn-off moment increases, resulting in a more serious valve-side overvoltage and large device stress. Summary of the Invention

[0004] The purpose of the present invention is to provide a hybrid-commutated converter, a control method and a system to solve the problem of serious valve-side overvoltage caused by late turn-off of the commutation valve, resulting in large device stress.

[0005] To achieve the above purpose, the solution of the present invention includes: A control method for a hybrid-commutated converter of the present invention, the method includes: obtaining the voltage across the valve to be commutated, and when the forward voltage of the valve to be commutated is greater than or equal to the set voltage threshold and the next valve to commutate with the valve to be commutated has been turned on, the valve turn-off condition is satisfied, and the valve to be commutated is turned off; the set voltage threshold is less than 0.

[0006] Further, the set voltage threshold is the product of the set threshold coefficient and the amplitude of the AC voltage on the AC side of the hybrid-commutated converter; the set threshold coefficient is less than 0.

[0007] Further, the method further includes: when another valve in the same bridge arm as the valve to be commutated is turned on, the valve to be commutated is forced to turn off.

[0008] Furthermore, an RS flip-flop is used to generate a trigger pulse signal to control the turn-off or turn-on of the valve to be commutated. The R terminal of the RS flip-flop is connected to the turn-off signal, which is generated when the valve to be commutated meets the valve turn-off condition. The S terminal is connected to the turn-on signal of the valve to be commutated, and the turn-on signal is used to turn on the valve to be commutated.

[0009] Furthermore, when the phase-locked loop phase of the valve to be commutated is greater than or equal to the set trigger angle and the trigger angle is on the rising edge, a turn-on signal is generated.

[0010] The beneficial effects of the present invention are as follows: The turn-off pulse control method for a hybrid commutation converter of the present invention needs to detect the zero-crossing point of the forward voltage of each valve separately, and the trigger signal of the valve to be commutated needs to be associated. The voltage across the valve to be commutated is obtained. When the forward voltage of the valve to be commutated is greater than or equal to the set voltage threshold and the next valve to commutate with this valve to be commutated has been turned on, the valve turn-off condition is met, and the valve to be commutated is turned off. Thus, when the HCC commutation valve is actively turned off, the turn-off stress of the device can be reduced, the damage of the commutation valve caused by mis-turn-off can be avoided, and commutation failure can be better suppressed. The control effect of the method of the present invention is better, the turn-off current is small, and the device stress is smaller, which can better ensure the safety of the equipment. Therefore, it has higher engineering application value.

[0011] The present invention also provides a hybrid commutation converter control system, including a processor, which is used to execute a computer program to implement the steps of the hybrid commutation converter control method as described above.

[0012] The hybrid commutation converter control system can achieve the same beneficial effects as the above-mentioned hybrid commutation converter control method.

[0013] The present invention also provides a hybrid commutation converter, including a converter controller, and the converter controller includes a processor. It is characterized in that the processor is used to execute a computer program to implement the steps of the hybrid commutation converter control method as described above.

[0014] The hybrid commutation converter can achieve the same beneficial effects as the above-mentioned hybrid commutation converter control method. Description of the Drawings

[0015] Figure 1 is the topology structure of a prior art hybrid commutation converter; Figure 2 is the turn-off pulse control strategy 1 based on the zero-crossing point of the forward voltage of the present invention; Figure 3 is the turn-off pulse control strategy 2 based on the zero-crossing point of the forward voltage of the present invention; Figure 4 is the oscillogram of the turn-off pulse control based on the zero-crossing point of the forward voltage of the present invention. Detailed Implementation Manner

[0016] To make the objectives, technical solutions and advantages of the present invention clearer and more comprehensible, the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

[0017] The inventive concept of the present invention lies in: the present invention proposes a hybrid commutation converter, a control method and a system. The method includes: obtaining the voltage across the commutation valve to be commutated. When the forward voltage of the valve of the commutation valve to be commutated is greater than or equal to the set voltage threshold and the next valve to be commutated with this commutation valve has been turned on, the valve turn-off condition is satisfied, and the commutation valve to be commutated is turned off; the set voltage threshold is less than 0. The objective of the present invention is to turn off the commutation valve before it bears the forward voltage. It is necessary to monitor the voltage across the commutation valve to be commutated in real time and turn it off before the commutation valve to be commutated bears the forward voltage (i.e., at the zero crossing of the forward voltage of the commutation valve to be commutated). Thus, when performing the active turn-off of the HCC commutation valve, the turn-off stress of the device can be reduced, the damage of the commutation valve caused by mis-turn-off can be avoided, and commutation failure can be better suppressed. The control effect of the method of the present invention is better, the turn-off current is small, and the device stress is smaller, which can better ensure the safety of the equipment. Therefore, it has higher engineering application value.

[0018] Embodiment 1 of the control method of the hybrid commutation converter: The topology structure of the hybrid commutation converter targeted by this embodiment is as Figure 1 shown. The left side is the DC side, and the right side is the three-phase AC side of phase A, phase B and phase C. During the DC-to-AC conversion process, the commutation valves are turned on and off in sequence according to the ascending order of the commutation valve codes, ensuring that any one of the three commutation valves on the upper side of the bridge arm (i.e., commutation valve V2, commutation valve V6 and commutation valve V4) is turned on, and any one of the three commutation valves on the lower side of the bridge arm (i.e., commutation valve V5, commutation valve V3 and commutation valve V1) is turned on. For example, when the current commutation valves V5 and V6 are turned on, and at this time commutation valve V5 is turned off, then commutation valve V1 needs to be turned on. The next commutation valve to be turned off is commutation valve V6, then commutation valve V2 needs to be turned on, and so on. It should be noted that the two commutation valves on the same column of the bridge arm cannot be turned on simultaneously (i.e., commutation valve V1 and commutation valve V4 cannot be turned on simultaneously, commutation valve V3 and commutation valve V6 cannot be turned on simultaneously, commutation valve V2 and commutation valve V5 cannot be turned on simultaneously), otherwise the converter will short-circuit and damage the device.

[0019] For the above-introduced topology structure of the hybrid commutation converter, the following-described control method of the hybrid commutation converter can be adopted. The specific process is as Figure 2 shown, and the specific steps are as follows: An RS flip-flop is used to generate a trigger pulse signal to control the turn-off or turn-on of the commutation valve to be commutated. The R terminal of the RS flip-flop is connected to the turn-off signal, and the turn-off signal is generated when the commutation valve to be commutated meets the valve turn-off condition. The S terminal is connected to the turn-on signal of the commutation valve to be commutated, and the turn-on signal is used to turn on the commutation valve to be commutated. The specific implementation steps are as follows: The trigger signal is generated when the trigger angle is at the rising edge. Its generation strategy is the same as that of the thyristor commutation valve, that is, when the phase locked loop phase is greater than or equal to the set trigger angle ALPHA and at the rising edge of the trigger angle (i.e., S = 1 of the RS flip-flop) and when there is no commutation valve turn-off signal (i.e., R = 0 of the RS flip-flop), the turn-on signal is generated, and the output of the RS flip-flop is 1 to turn on the commutation valve to be commutated; the commutation valve turn-off signal is used as the reset signal. When the forward voltage of the commutation valve is greater than or equal to the set voltage threshold and the next valve to be commutated with this commutation valve has been turned on (i.e., R = 1 of the RS flip-flop), the valve turn-off condition is satisfied, then the output of the RS flip-flop is 0, and a turn-off pulse command is issued to turn off the commutation valve to be commutated; the set voltage threshold is less than 0.

[0020] Preferably, the set voltage threshold should not be set as a fixed constant according to the fault condition, and should be transformed according to the AC voltage amplitude U ac_psf For example, as shown in Figure 2 the threshold coefficient X1 is multiplied by the AC voltage amplitude U ac_psf as the detection voltage threshold for the zero crossing of the forward voltage of the commutation valve. In this embodiment, the threshold coefficient is -0.1 p.u.

[0021] Taking the turn-on and turn-off of the commutation valve V1 (i.e., the commutation valve to be commutated) as an example, the specific implementation steps of the commutation pulse control method for the hybrid commutation converter are as follows: When the commutation valve V1 is turned on, that is, the commutation valve V5 commutates to the commutation valve V1, the anode voltage is the A-phase voltage U A and the cathode voltage is the C-phase voltage U C . When the A-phase voltage U A is greater than the C-phase voltage U C (i.e., from the S1 moment to the S3 moment in Figure 4 ), a trigger pulse can be applied to turn it on; when the commutation valve V1 is turned off, that is, the commutation valve V1 commutates to the commutation valve V3 (i.e., the next valve to be commutated with the commutation valve to be commutated), the anode voltage is the A-phase voltage U A and the cathode voltage is the B-phase voltage U B . When the B-phase voltage U B is greater than the A-phase voltage U A (i.e., from the S2 moment to the S4 moment in Figure 4 ), the commutation can start and the natural turn-off process can start.

[0022] Figure 4 In the S1 moment is the starting moment of the phase locked loop corresponding to the commutation valve V1 (i.e., 0°), and S4 is the final moment when the commutation of the commutation valve V1 is completed. After the S4 moment, the voltage across the commutation valve V1 compared with the A-phase voltage U A is greater than the B-phase voltage U B, the commutation valve V1 will continue to bear the positive voltage and cannot turn off naturally. Moreover, as the voltage increases, the current flowing through the commutation valve V1 also increases. Therefore, it is necessary to force it to turn off before the moment S4. Then, based on the line voltage U AB crossing zero point is used as the judgment for the moment S4. When the forward voltage of the valve (U A -U B ) is greater than or equal to the set voltage threshold, the turn-off pulse is triggered. The set voltage threshold can, on the one hand, avoid being affected by the zero drift of the measurement system and resulting in frequent triggering. On the other hand, a certain measurement delay can be compensated by setting the voltage threshold to make the trigger moment of the turn-off pulse more accurate. The set voltage threshold is the threshold coefficient X1 multiplied by the amplitude U ac_psf of the AC voltage, and the threshold coefficient X1 is -0.1 p.u.

[0023] When the trigger angle on the inverter side is less than 120°, that is, it is triggered to turn on before the moment S2. At this time, the condition that the forward voltage of the valve (U A -U B ) is greater than or equal to the set voltage threshold is satisfied. However, this is a normal turn-on at this time. In order to avoid misjudging the turn-off signal, after the commutation valve V3 that commutes with the commutation valve V1 is turned on (such as after FP3 is turned on during the time from S3 to S4 in Figure 4 ), and then when this condition is satisfied again, the turn-off signal can be triggered. At this time, the commutation process has started, so there will be no mis-turn-off.

[0024] In this embodiment, it is necessary to detect the zero crossing point of the forward voltage of each valve separately, and the trigger signal of the valve that commutes with it needs to be associated. The control effect is better, the turn-off current is small, and the device stress is smaller, which can better ensure the safety of the equipment. Therefore, it has higher engineering application value.

[0025] Embodiment 2 of the control method for the hybrid commutation converter: On the basis of Method Embodiment 1, this embodiment adds a protection logic to avoid the converter short circuit caused by simultaneously turning on the commutation valves on the same bridge arm, that is, when the trigger turn-on signal of the other commutation valve on the same bridge arm of the current commutation valve is generated, the current commutation valve is forced to turn off. As shown in Figure 3 , the specific implementation steps are as follows: An RS flip-flop is used to generate a trigger pulse signal to control the turn-off or turn-on of the commutation valve to be commutated. The R terminal of the RS flip-flop is connected to the turn-off signal, and the turn-off signal is generated when the commutation valve to be commutated meets the valve turn-off condition. The S terminal is connected to the turn-on signal of the commutation valve to be commutated, and the turn-on signal is used to turn on the commutation valve to be commutated. The specific implementation steps are as follows: The trigger signal is generated when the trigger angle is at the rising edge. Its generation strategy is the same as that of the thyristor converter valve, that is, when the phase locked loop phase is greater than or equal to the set trigger angle ALPHA and at the rising edge of the trigger angle (i.e., S = 1 of the RS flip-flop) and when there is no turn-off signal for the valve to be commutated (i.e., R = 0 of the RS flip-flop), an on signal is generated, and the output of the RS flip-flop is 1 to turn on the valve to be commutated; the turn-off signal of the valve to be commutated is used as the reset signal. When the forward voltage of the valve to be commutated is greater than or equal to the set voltage threshold and the next valve commutated with the valve to be commutated has been turned on, or when another valve in the same bridge arm as the valve to be commutated is turned on (i.e., R = 1 of the RS flip-flop), the valve turn-off condition is satisfied, then the output of the RS flip-flop is 0, and a turn-off pulse command is issued to turn off the valve to be commutated; the set voltage threshold is less than 0.

[0026] Preferably, the setting of the voltage threshold should not be set as a fixed constant according to the fault condition, and should be transformed according to the AC voltage amplitude U ac_psf For the voltage threshold. As Figure 3 shown, the threshold coefficient X1 is multiplied by the AC voltage amplitude U ac_psf as the zero-crossing detection voltage threshold of the forward voltage of the converter valve. In this embodiment, the threshold coefficient is -0.1 p.u.

[0027] Taking the opening and closing of the commutation valve V1 (i.e., the valve to be commutated) as an example, the specific implementation steps of the turn-off pulse control method of the hybrid commutation converter are as follows: When the commutation valve V1 is turned on, that is, the commutation valve V5 commutates to the commutation valve V1, the anode voltage is the A-phase voltage U A , and the cathode voltage is the C-phase voltage U C , when the A-phase voltage U A is greater than the C-phase voltage U C (i.e., from the S1 moment to the S3 moment in Figure 4 ), applying a trigger pulse can turn it on; when the commutation valve V1 is turned off, that is, the commutation valve V1 commutates to the commutation valve V3 (i.e., the next valve commutated with the valve to be commutated), the anode voltage is the A-phase voltage U A , and the cathode voltage is the B-phase voltage U B , when the B-phase voltage U B is greater than the A-phase voltage U A (i.e., from the S2 moment to the S4 moment in Figure 4 ), the commutation can start and the natural turn-off process can start.

[0028] Figure 4 In A the S1 moment is the starting moment of the phase locked loop corresponding to the commutation valve V1 (i.e., 0°), and S4 is the final moment when the commutation valve V1 completes commutation. After the S4 moment, the voltage across the commutation valve V1 compared with the A-phase voltage U A is greater than the B-phase voltage U B, the commutation valve V1 will continue to bear the positive voltage and cannot turn off naturally. Moreover, as the voltage increases, the current flowing through the commutation valve V1 also increases. Therefore, it is necessary to force the commutation valve V1 to turn off before the moment S4. Then, based on the line voltage U AB crossing zero point is used as the judgment for the moment S4. When the forward voltage of the valve (U A -U B ) is greater than or equal to the set voltage threshold, the turn-off pulse is triggered. The set voltage threshold can, on the one hand, avoid frequent triggering caused by zero drift of the measurement system, and on the other hand, compensate for a certain measurement delay through the setting of the voltage threshold to make the triggering moment of the turn-off pulse more accurate. The set voltage threshold is the threshold coefficient X1 multiplied by the amplitude U ac_psf of the AC voltage, and the threshold coefficient X1 is -0.1 p.u.

[0029] When the trigger angle on the inverter side is less than 120°, that is, it is triggered to turn on before the moment S2. At this time, the condition that the forward voltage of the valve (U A -U B ) is greater than or equal to the set voltage threshold is satisfied. However, this is a normal turn-on at this time. In order to avoid misjudging the turn-off signal, after the commutation valve V3 that commutates with the commutation valve V1 is turned on (such as after FP3 is turned on during the period from S3 to S4 in Figure 4 ), and then when this condition is satisfied again, the turn-off signal can be triggered. At this time, the commutation process has started, so there will be no mis-turn-off.

[0030] There is a situation when the trigger angle is advanced. For example, when the trigger angle of the commutation valve V4 (that is, the other valve in the same bridge arm as the valve to be commutated) is advanced, there may be an intersection with the trigger pulse of the commutation valve V1, that is, there is a situation of valve short circuit. Therefore, in order to avoid the short circuit of the converter, the commutation valve V1 should be turned off before the commutation valve V4 is turned on.

[0031] In this embodiment, it is necessary to detect the zero crossing point of the forward voltage of each valve separately, and the trigger signal of the valve that commutates with it needs to be associated. The control effect is better, the turn-off current is small, and the device stress is smaller. It can better ensure the safety of the equipment and avoid the short circuit phenomenon of the converter caused by the simultaneous turn-on of the commutation valves in the same bridge arm. Therefore, it has higher engineering application value.

[0032] Embodiment of the hybrid commutation converter control system: This embodiment provides a hybrid commutation converter control system, including a processor, and this processor is used to execute a computer program to implement the steps such as those in Embodiment 1 or Embodiment 2 of the hybrid commutation converter control method.

[0033] Since the specific implementation process and principle of the hybrid commutation converter control system in this embodiment have been described in detail in Embodiment 1 or Embodiment 2 of the hybrid commutation converter control method, no further elaboration will be made here.

[0034] Example of Hybrid Commutation Converter: This embodiment provides a hybrid commutation converter, including a converter body, whose topology is as Figure 1 shown, and further includes a converter controller, which includes a processor. It is characterized in that the processor is used to execute a computer program to implement the steps of Embodiment 1 or Embodiment 2 of the hybrid commutation converter control method.

[0035] Since the specific implementation process and principle of the hybrid commutation converter in this embodiment have been described in detail in Embodiment 1 or Embodiment 2 of the hybrid commutation converter control method, no further elaboration will be provided here.

Claims

1. A control method for a hybrid commutation converter, characterized in that The method includes: obtaining the voltage across the valve to be commutated; when the forward voltage of the valve to be commutated is greater than or equal to the set voltage threshold and the next valve to be commutated with this valve to be commutated is already turned on, the valve turn-off condition is satisfied, and the valve to be commutated is turned off; the set voltage threshold is less than 0.

2. The hybrid commutation converter control method according to claim 1, wherein The set voltage threshold is the product of the set threshold coefficient and the amplitude of the AC voltage on the AC side of the hybrid commutation converter; the set threshold coefficient is less than 0.

3. The hybrid commutation converter control method according to claim 1, characterized in that, The method further includes: when another valve in the same bridge arm as the valve to be commutated is turned on, forcibly turning off the valve to be commutated.

4. The hybrid commutation converter control method according to claim 1, wherein An RS flip-flop is used to generate a trigger pulse signal to control the turn-off or turn-on of the valve to be commutated, and the R terminal of the RS flip-flop is connected to the turn-off signal, which is generated when the valve to be commutated satisfies the valve turn-off condition, and the S terminal is connected to the turn-on signal of the valve to be commutated, and the turn-on signal is used to turn on the valve to be commutated.

5. The hybrid commutation converter control method according to claim 4, wherein When the phase of the phase-locked loop of the valve to be commutated is greater than or equal to the set trigger angle and the trigger angle is at the rising edge, a turn-on signal is generated.

6. A hybrid commutation converter control system includes a processor, characterized in that, The processor is configured to execute a computer program to implement the steps of the hybrid commutation converter control method according to any one of claims 1 to 5.

7. A hybrid commutation converter, comprising a converter controller, the converter controller including a processor, characterized in that, The processor is configured to execute a computer program to implement the steps of the hybrid commutation converter control method according to any one of claims 1 to 5.

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