Discharge method of flexible direct current converter valve operation test system

Abstract

The present application relates to the technical field of flexible direct current transmission, and particularly relates to a discharge method of a flexible direct current converter valve operation test system, when a stop command is issued, all power modules of the flexible direct current converter valve continue to operate discharge according to the stop command in a specific current modulation mode, until all the power modules are at the lowest set voltage, and then static discharge is performed until the voltage of all the power modules drops to a safe voltage, that is, the discharge is completed; wherein the specific current is a current less than 50% of the rated current. The stop and lock discharge strategy adopted in the present application does not require an additional discharge device, improves the discharge rate of the flexible direct current converter valve test, reduces the flexible direct current converter valve discharge waiting time, improves the production and test efficiency of the flexible direct current converter valve equipment, improves the design and type test verification speed, and improves the production routine test capacity.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, specifically to a discharge method for a flexible DC converter valve operation test system. Background Technology

[0002] Flexible DC converter valves require valve section-level operational type testing or routine testing during product design finalization and mass production trials. Each valve section contains several independently cascaded power units, each acting as an independent voltage source. After the test or if a test sample malfunctions, the traditional method is to immediately lock all power units and rely on the equalizing resistors within each unit for slow discharge. This results in a long discharge time of approximately tens of minutes, leading to low testing efficiency. Furthermore, the converter valve retains high voltage while waiting for discharge, which is detrimental to safe production.

[0003] Application No. 202210790420.9 describes adding a pneumatic switch within the power module and discharging it through external switches and resistors. However, this method further increases the cost within the power (module) unit, and power modules without the pneumatic switch still cannot discharge quickly during testing. In "An Improved Test Device for Power Modules of Flexible DC Converter Valves," after testing a single power unit, rapid discharge can be achieved through the internal resistance of the test device. However, for multi-stage series-connected power modules, the voltage levels of the valve sections connected in series are too high, making it impossible to manually connect and discharge individual modules sequentially. Even if this were possible, it would be time-consuming, laborious, and pose significant safety hazards. Summary of the Invention

[0004] To address the issue of low safety during valve section discharge in existing technologies, this invention provides a discharge method for a flexible DC converter valve operation test system.

[0005] This invention is achieved through the following technical solution: A discharge method for a flexible DC converter valve operation test system is disclosed. The test circuit of the flexible DC converter valve is equipped with a first valve section and a second valve section for counter-driving operation. When a shutdown command is issued, all power modules of the flexible DC converter valve continue to operate and discharge in a specific current modulation mode according to the shutdown command until all power modules are at the minimum set voltage. Then, static discharge is performed until the voltage of all power modules drops to a safe voltage, thus completing the discharge. The specific current is less than 50% of the rated current.

[0006] Preferably, when operating in a specific current modulation mode, all power modules discharge at a uniform rate; power modules with higher voltage are preferentially put into the discharge switch state, while power modules with lower voltage are preferentially put into the discharge switch state and discharge other power modules in turn.

[0007] Preferably, the safe voltage is less than or equal to 42V.

[0008] Preferably, the specific steps for discharging in a specific current modulation mode are as follows: S1: After the shutdown command is issued, the test control system adjusts the modulation wave in a ramp-down manner until the system current reaches the target value. S2: Determine whether the minimum voltage of all power modules has dropped from the rated operating voltage U1 to the minimum set voltage. The minimum set voltage is the internal power supply shutdown voltage U2 + 30V or 17% of the rated operating voltage U1. S3: Lock out all power modules; S4: Static waiting for residual charge to be released when the power unit is powered off.

[0009] Preferably, the discharge time is adjusted by the control system by adjusting the modulation angle difference to adjust the discharge speed, and the discharge time is adjusted by adjusting the discharge speed.

[0010] Preferably, before shutdown, when m power modules fail, with the bypass switch of the failed power module closed, the power module discharges all power modules in a specific current modulation mode. At this time, the modulation waves of the first and second valve sections are as follows: The reference voltage for the first valve section is: ; The reference voltage for the second valve section is: ; In the formula, N This represents the maximum power unit quantity in the valve section. m The number of faulty modules in any given valve section. U dc For the DC component of the modulated wave, , For the modulated wave AC component, δ This is the angle difference of the modulated wave.

[0011] Preferably, when an overload fault occurs in the test power supply circuit, after the AC power grid is disconnected, the flexible DC power unit valve section discharges in a specific current modulation mode.

[0012] Preferably, when an unexpected risk occurs in the test circuit, an emergency shutdown command is issued to lock all power modules in the internal resistance discharge mode.

[0013] Preferably, when the power module of the test valve section reports a failure to operate, all power modules are locked. Preferably, during the discharge process, if the test control system does not receive a fault signal but there is an abnormality or fault, the emergency stop interlock button is triggered to lock all power modules.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The discharge method of the flexible DC converter valve operation test system of this invention employs a shutdown-locked discharge strategy, which eliminates the need for an external discharge device. This improves the discharge rate of the flexible DC converter valve test, reduces the discharge waiting time, enhances the production and testing efficiency of the flexible DC converter valve equipment, increases the speed of design finalization testing and verification, and improves the production capacity of routine testing. When a shutdown command is issued, the power module of the flexible DC converter valve does not immediately lock out but continues to operate and discharge. During operation, the power losses of the converter valve power module are converted into heat, which consumes the energy of the internal stored capacitor. The heat is ultimately dissipated outdoors through an outdoor radiator. This electro-thermal-water cooling exchange-heat dissipation mode consumes the energy of the internal capacitor of the test converter valve, achieving rapid discharge without affecting the test chamber temperature.

[0015] Furthermore, the valve section operation modulation wave was corrected for the faulty power unit, which also improved the possibility of automatic discharge under test system failure, ensuring that the probability of unsafe events caused by human error is reduced under various possible emergencies, and increasing the safety of the test and production process.

[0016] Furthermore, the current magnitude is adaptively adjusted based on the switching frequency and discharge speed. When a faster discharge speed is required, the control system increases the current magnitude through the closed loop.

[0017] Furthermore, the system improves its applicability by classifying and determining the appropriate handling method based on the fault alarm information of the test power supply circuit and power module. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the test system for the valve section of a flexible DC converter valve. Figure 2 This is a half-bridge flexible DC module topology; Figure 3 It is a full-bridge flexible linear module topology; Figure 4 This is the discharge step; Figure 5 This is a control system adjustment diagram; Figure 6 This is the logic diagram for the emergency interlock signal; Figure 7 This is a logic diagram for judging fault conditions. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0020] A discharge method for a flexible DC converter valve operation test system, wherein a first valve section and a second valve section are set up in the valve section test circuit of the flexible DC converter valve for counter-driving operation (e.g. Figure 1 As shown in the figure, the flexible DC valve section operation test system is equipped with a lockout shutdown function button and an emergency shutdown lockout button. Unlike typical power systems that only have a single main emergency stop button, this test system has two levels of shutdown buttons to further ensure system safety during shutdown discharge. This invention proposes a corresponding discharge invention technology solution for this circuit, improving the testing efficiency of the flexible DC converter valve. The topology of the targeted power module or power unit is shown in the attached figure. Figure 2 , 3 Or as attached Figure 2 , 3 approximate.

[0021] When a shutdown command is issued, all power modules of the flexible DC converter valve continue to operate and discharge in a specific current modulation mode according to the shutdown command until all power modules are at the minimum set voltage. Then, static discharge continues until the voltage of all power modules drops to the safe voltage, thus completing the discharge. The specific current is less than 50% of the rated current, and the safe voltage is less than or equal to 42V.

[0022] When operating in a specific current modulation mode, all power modules discharge at a balanced rate; power modules with higher voltage are given priority to enter the discharge switch state, while power modules with lower voltage are given priority to enter the discharge switch state and discharge other power modules in turn.

[0023] Reference Figure 4 The specific steps for discharging in a specific current modulation mode are as follows: S1: After the shutdown command is issued, the test control system adjusts the modulation wave in a ramp-down manner until the system current reaches the target value. S2: Determine whether the minimum voltage of all power modules has dropped from the rated operating voltage U1 to the minimum set voltage. The minimum set voltage is the internal power supply shutdown voltage U2 + 30V or 17% of the rated operating voltage U1. S3: Lock out all power modules; S4: Static waiting for residual charge to be released when the power unit is powered off.

[0024] Reference Figure 5When rapid discharge is required, the discharge time is adjusted by adjusting the modulation angle difference. The adjustment of the discharge time is achieved by the control system adjusting the modulation angle difference to regulate the discharge speed. The discharge time is adjusted according to the magnitude of the controlled current. The specific adjustment method is as follows: The control system calculates the difference between the required discharge time and the expected discharge time based on feedback, and outputs the required angle difference through the modulation wave angle difference controller. When the angle difference reaches a saturation limit, a saturation signal is output, enabling the adjustment switch. The control system adjusts the modulation wave angle difference to control the operating current of the test system. Increasing the operating current increases losses, thereby dissipating the energy of the test sample capacitor. Simultaneously, the angle difference is limited within a safe range by the angle difference saturator. When the angle difference is saturated, the switch frequency adjustment is enabled. The discharge rate is adjusted by increasing the losses of the test power module through adjusting the switch frequency. Simultaneously, the switching frequency is limited within a safe range by the switch frequency limiter, thereby further adjusting the discharge time.

[0025] Before shutdown, when m power modules fail, with the bypass switch of the failed power module closed, the power module discharges all power modules in a specific current modulation mode. At this time, the modulation waves of the first and second valve sections are as follows: The reference voltage for the first valve section is: ; The reference voltage for the second valve section is: ; In the formula, N This represents the maximum power unit quantity in the valve section. m The number of faulty modules in any given valve section. U dc For the DC component of the modulated wave, , For the modulated wave AC component, δ This is the angle difference of the modulated wave.

[0026] When an overload fault occurs in the test power supply circuit, the AC mains are disconnected, and the flexible DC power unit valve section discharges in a specific current modulation mode. (Refer to...) Figure 6 The flexible DC valve section operation test system is equipped with an emergency interlock discharge button or software function signal. The emergency interlock discharge button signal and the interlock signal issued by the software are logically ANDed with the switching signals of all power modules to block the switching signals received by the power modules, so as to realize the need for manual intervention protection of the power modules in emergency situations or to stop the discharge under other factors.

[0027] When an unexpected risk occurs in the test circuit, an emergency stop command is issued to immediately lock all power modules in the internal resistance discharge mode. This is achieved by pressing the emergency stop discharge command button or issuing an emergency stop software command. At this time, the control mode changes from small current discharge to immediate and true locking of all converter valves, switching to the conventional internal resistance discharge mode.

[0028] If the power module of the test valve section reports a failure to operate, then all power modules are locked. During the discharge process, if the test control system does not receive a fault signal but there is an abnormality or fault, it will trigger the emergency stop interlock button to lock all power modules.

[0029] This invention proposes a test system that comprehensively judges the discharge mode based on fault conditions, referring to... Figure 7 The appropriate handling method is determined by classifying the fault alarm information from the test power supply circuit and power module: Case 1: If a fault signal is received from the test power supply system during the test, the power supply system circuit breaker will be disconnected and a temporary lockout signal for the power modules will be sent. After the temporary lockout is maintained for 100ms, if the signal sent by the power supply system does not change and the power modules are not faulty, the unlocked state will be restored and all power modules will be discharged in reverse in a low current mode.

[0030] Case 2: If the power module of the test valve section reports a general fault during discharge, determine whether the number of bypass modules has exceeded the bypass redundancy limit: if the number of bypass modules exceeds the bypass redundancy limit, then lock all power modules; if the number of bypass modules does not exceed the bypass redundancy limit, then lock the bypass power modules. After the bypass is locked, all power modules of the test system continue to discharge in low current mode. Case 3: If the power module of the test valve section reports a failure to operate during discharge, then all power modules will be directly locked out.

[0031] Case 4: If the system is discharging and no fault signal is received, but there is an abnormality or fault in the test system, the emergency stop interlock button can be triggered to immediately lock all power modules.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A discharge method for a flexible DC converter valve operation test system, characterized in that, The test circuit of the flexible DC converter valve is set with a first valve section and a second valve section for counter-driving operation; when a shutdown command is issued, all power modules of the flexible DC converter valve continue to operate and discharge in a specific current modulation mode according to the shutdown command until all power modules are at the lowest set voltage, and then static discharge until the voltage of all power modules drops to the safe voltage, thus completing the discharge; the specific current is less than 50% of the rated current. The specific steps for discharging in a specific current modulation mode are as follows: S1: After the shutdown command is issued, the test control system adjusts the modulation wave in a ramp-down manner until the system current reaches the target value. S2: Determine whether the minimum voltage of all power modules has dropped from the rated operating voltage U1 to the minimum set voltage. The minimum set voltage is the internal power supply shutdown voltage U2 + 30V or 17% of the rated operating voltage U1. S3: Lock out all power modules; S4: Static waiting for residual charge to be released when the power unit is powered off.

2. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, When operating in a specific current modulation mode, all power modules discharge at a balanced rate; power modules with higher voltage are given priority to enter the discharge switch state, while power modules with lower voltage are given priority to enter the discharge switch state and discharge other power modules in turn.

3. The discharge method for a flexible DC converter valve operation test system according to claim 1, characterized in that, The safe voltage is less than or equal to 42V.

4. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, The discharge time is adjusted by the control system by adjusting the modulation angle difference to adjust the discharge speed, and the discharge time is adjusted by adjusting the discharge speed.

5. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, Before shutdown, when m power modules fail, with the bypass switch of the failed power module closed, the power module discharges all power modules in a specific current modulation mode. At this time, the modulation waves of the first and second valve sections are as follows: The reference voltage for the first valve section is: ; The reference voltage for the second valve section is: ; In the formula, N This represents the maximum power unit quantity in the valve section. m The number of faulty modules in any given valve section. U dc For the DC component of the modulated wave, , For the modulated wave AC component, δ This is the angle difference of the modulated wave.

6. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, When an overload fault occurs in the test power supply circuit, the AC power grid is disconnected, and the flexible DC power unit valve section discharges in a specific current modulation mode.

7. The discharge method for a flexible DC converter valve operation test system according to claim 1, characterized in that, When an unexpected risk occurs in the test circuit, an emergency shutdown command is issued to lock all power modules in the internal resistance discharge mode.

8. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, If the power module of the test valve section reports a failure to operate, then all power modules are locked.

9. The discharge method of the flexible DC converter valve operation test system according to claim 1, characterized in that, During the discharge process, if the test control system does not receive a fault signal but there is an abnormality or fault, it will trigger the emergency stop interlock button to lock all power modules.

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