MMC different operating voltage module combined test method and device

Abstract

The application provides a MMC different operating voltage module combined test method and device, realizes two different operating voltages of modules in the same valve section in the MMC valve section test, and separates the control strategy of the tested module from the rest of the modules, separately controls the operating voltage and switching frequency of the tested module, reduces the damage risk and system energy supplement ability of the non-tested module in the test process, simultaneously reduces the one-time insulation design requirement, and provides a convenient method for the high voltage operation of the module in the valve section test in the flexible direct current transmission field. S The operating voltage of the rest of the modules is U n , the tested module is switched according to the S switching command sorted by the voltage, the modulation signal of the tested valve section is V mod1 , and the modulation signal of the accompanying valve section is V mod2 ; V mod1 is calculated according to the S switching command and the current voltage U S of the tested module.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method and apparatus for joint testing of MMC modules operating at different voltages. Background Technology

[0002] MMC converter valves are core equipment in flexible DC transmission systems, and their safety and reliability are crucial to the entire system. Valve sections are key components of the converter valve, and before formal operation, the operating characteristics of the converter valve need to be verified under actual operating conditions in the form of valve sections. In recent years, MMC converter valves have been developing towards higher voltage levels. In addition to the mature 4.5kV modules, the development of higher voltage level modules such as 6.5kV and 9kV is rapid. Due to limitations in testing conditions or special requirements, it is necessary to test the converter valves of high-voltage modules on a low-voltage valve section test platform. Therefore, this invention proposes a test method for cascading two modules of different voltage levels within a single valve section, and also proposes a test control method for this hybrid valve section. Summary of the Invention

[0003] To address the technical problems in the background art, this invention provides a method and apparatus for joint testing of MMC modules with different operating voltages. This method enables modules within the same valve section to operate at two different voltages during MMC valve section testing. Furthermore, the control strategy separates the tested module from the other modules, with the tested module's operating voltage and switching frequency differing from the individual control of other modules. This reduces the risk of damage to non-tested modules and the system's energy replenishment capability during testing, while also reducing the primary insulation design requirements. This provides a convenient method for high-voltage operation of modules in valve section testing in the field of flexible DC transmission.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A joint test method for MMC modules with different operating voltages is disclosed. The test method is for the MMC converter valve submodule and adopts a test circuit consisting of a test valve section and a test valve section directly connected. The upper ends of the test valve section and the test valve section are connected via a load reactor L. The valve section where the module under test is located is called the test valve section. The module under test is cascaded with the other modules in the valve section. The module under test is located at any position in the test valve section.

[0006] The test method described in this invention is used when the module under test and all other modules in all valve sections, except the module under test, are at two different voltage levels.

[0007] The test method is as follows: the operating voltage of the tested module is U. S The operating voltage of all valve sections except the tested module is U. n The operating voltage U of the tested module SThe operating voltage of the other modules is U n Unlike other modules, the tested module is switched according to the S-switching command ordered by voltage, and the modulation signal of the test sample valve section is V. mod1 The modulation signal for the test valve section is V. mod2 V mod1 Based on the S switching command and the current voltage U of the tested module S The calculation yielded the result.

[0008] The switching of the tested module according to the S-switching command sorted by voltage specifically includes the following:

[0009] For a half-bridge module, the AC bus is located between the upper transistor T1 and the lower transistor T2, and the current i is defined as... L The flow direction into the AC port of the test module is positive, and the equivalent voltage U of the test module is... eq Based on the average value U of the non-tested modules in the test sample valve section av The current operating voltage U of the tested module S The expected operating voltage value U of the tested module s * The calculation shows that:

[0010]

[0011] E P E is the upper limit of the sorting start threshold. N To set the lower limit of the sorting threshold, U ac Modulate the output voltage of the non-tested module in the test sample valve section.

[0012] The S-turn command includes the following branch selection:

[0013] (1) Branch 1: If the module under test was in the active state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage U of the module under test was... eq The average value U of the non-tested modules in the test sample valve section av The difference is greater than the upper limit of the sorting start threshold E. P If the subject module is changed to a cutoff command in this cycle, then S=0;

[0014] (2) Branch 2: If the module under test was in the active state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage U of the module under test was... eq The average value U of the non-tested modules in the test sample valve section av The difference is less than the upper limit of the sorting start threshold E. P If the subject module remains engaged in this cycle, then S = 1.

[0015] (3) Branch 3: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value U of the non-tested modules in the test sample valve section was... avEquivalent voltage U of the tested module eq The difference is greater than the lower limit of the sorting start threshold E. N If the subject module is changed to a cutoff command in this cycle, then S=0;

[0016] (4) Branch 4: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value U of the non-tested modules in the test sample valve section was... av Equivalent voltage U of the tested module eq The difference is less than the lower limit of the sorting start threshold E. N If the subject module remains engaged in this cycle, then S = 1.

[0017] (5) Branch 5: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The current flows in the direction of the AC outlet, and the average value U of the non-tested module in the test sample valve section is... av Equivalent voltage U of the tested module eq The difference is greater than the lower limit of the sorting start threshold E. N If the subject module is changed to the input command in this cycle, then S=1;

[0018] (6) Branch 6: If the module under test was in the off state in the previous cycle, the non-module under test modulates the output voltage U in the test sample valve section. ac Greater than the current operating voltage U of the tested module S The current flows in the direction of the AC outlet, and the average value U of the non-tested module in the test sample valve section is... av Equivalent voltage U of the tested module eq The difference is less than the lower limit of the sorting start threshold E. N If the subject module maintains the cutoff command for this cycle, then S = 0;

[0019] (7) Branch 7: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The direction of current flow out of the AC busbar; the equivalent voltage U of the module under test. eq The average value U of the non-tested modules in the test sample valve section av The difference is greater than the upper limit of the sorting start threshold E. P If the subject module is changed to the input command in this cycle, then S=1;

[0020] (8) Branch 8: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The direction of current flow out of the AC busbar; the equivalent voltage U of the module under test.eq The average value U of the non-tested modules in the test sample valve section av The difference is less than the upper limit of the sorting start threshold E. P If the subject module maintains the cutoff command for this cycle, then S = 0;

[0021] (9) Branch 9: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Less than the current operating voltage U of the tested module S If the subject module maintains the cutoff command for this cycle, then S = 0;

[0022] Based on the final voltage sorting of the S-switching commands and the current voltage U of the tested module S The modulation signal V in the NLM operation submodule of the sample valve section was calculated. mod1 =U t * -U S ×S, U t * This is the reference voltage modulation signal for the test sample valve section.

[0023] Furthermore, the modulation signal V of the test valve section mod2 The calculation method includes the following steps:

[0024] Step 1: Calculation of the overall average voltage of the test sample valve section: U S U is the current operating voltage of the module under test. av The average value of the non-tested modules in the test valve section is used to calculate the number of modules equivalent to the voltage of the tested module based on the voltage values ​​of the two. Then, the overall average voltage of the test sample valve section was calculated. SM_Num represents the number of non-test modules in the sample valve section;

[0025] Step 2: The average voltage and current of the valve segment form a voltage-current dual closed-loop control structure to maintain the balance of input and output power between the two valve segments; specifically as follows:

[0026] U av2 U represents the overall average voltage of the test valve section. av1 with U av2 The difference is output by the voltage PI regulator as the DC component setpoint of the load current between valve sections. Target peak value of AC component of load current As specified in the test requirements, After calculations based on the phase angle θ and phase difference α, a sinusoidal command signal, i.e., the AC command component, is generated. Give the communication component and DC component setpoint The summation yields the total current given between valve sections. Current feedback is i L ,Will with i L The difference is then used to obtain the control loop output U through a current PI regulator. out ;

[0027] Step 3: The reference voltage modulation signal for the test valve section is U k * Control loop output U out Modulation signal U with reference voltage of the test valve section k * The summation yields the modulation signal V of the test valve section. mod2 .

[0028] Furthermore, the experimental procedure for the subject module includes the following:

[0029] Test parameter determination: Based on the test requirements and the module's rated capacity, the following parameters need to be determined:

[0030] (1) Determine the expected operating voltage U of the tested module s * The operating voltage U of all valve sections except the module under test. n ;

[0031] (2) Determine the operating switching frequency F of the tested module. S The remaining modules operate at a switching frequency F. n ;

[0032] (3) Determine the AC component current value, DC component current value, phase angle difference, and modulation index of the system;

[0033] The specific experimental process includes the following steps:

[0034] (1) Close the disconnect switch QS01 and start the pre-charge power supply E. S The test valve section and the accompanying test valve section are charged simultaneously until all modules can operate normally.

[0035] (2) Disconnect the disconnect switch QS01 and disconnect the pre-charge power supply E. S ;

[0036] (3) Start the power supply U c ;

[0037] (4) All sub-modules are reset and configured before unlocking to ensure that the sub-modules are fault-free and reach the unlocking state;

[0038] (5) Unlock operation, the tested module is switched according to the S control command, and the test sample valve section is switched according to the modulation signal V. mod1 The test valve section is operated according to the modulation signal V.mod2 To perform NLM operation control;

[0039] (6) Gradually raise the power supply U c The output value ultimately reaches the operating voltage U of all modules except the tested module in all valve sections. n ;

[0040] (7) Gradually increase the system current until the target value is reached;

[0041] (8) According to 0.3*U respectively s * 0.6*U s * U s * The change range is adjusted by modifying the operating voltage setpoint of the module under test until the voltage of the module under test rises or falls to the desired operating voltage value U. s * ;

[0042] (9) Based on the operating switching frequency F of the remaining modules n Modify the NLM operation sorting start threshold until the switching frequency of the non-subject module meets the requirements;

[0043] (10) The switching frequency F of the tested module S Modify the upper and lower limits of the sorting start threshold of the tested module until the switching frequency of the non-tested module meets the requirements.

[0044] Furthermore, the modification rules for step (8) are as follows:

[0045] If the peak value of the current operating voltage of the tested module is too high, reduce the upper limit of the tested module's sorting and starting threshold E. P ;

[0046] If the peak value of the current operating voltage of the tested module is too low, increase the upper limit of the test module sorting start threshold E. P ;

[0047] If the current operating voltage trough value of the tested module is too small, reduce the lower limit E of the tested module sorting start threshold. N ;

[0048] If the current operating voltage trough value of the tested module is too large, increase the lower limit E of the tested module sorting start threshold. N .

[0049] Furthermore, the modification rules for step (9) are as follows:

[0050] If the current switching frequency of the non-subject module is less than F n Reduce the sorting threshold for NLM operations;

[0051] If the current switching frequency of the non-subject module is greater than F n Increase the NLM operation sorting start threshold.

[0052] Furthermore, the modification rules for step (10) are as follows:

[0053] If the current switching frequency is less than F S Reduce the upper limit of the subject module sorting priming threshold E P Increase the lower limit of the subject module ranking priming threshold E N ;

[0054] If the current switching frequency is greater than F S Increase the upper limit of the subject module sorting priming threshold E P Reduce the lower limit of the subject module sorting priming threshold E N .

[0055] Furthermore, the present invention also provides a test apparatus for implementing the aforementioned method for joint testing of MMC modules with different operating voltages, comprising: a test valve section, a test valve section, a load reactor L, a power supply Uc, a pre-charge power supply Es, a charging resistor R, and a switch QS01. The test valve section and the test valve section are connected to form a reverse test circuit. The upper ends of the test valve section and the test valve section are connected via the load reactor L, and the lower ends are grounded. The power supply Uc is connected in parallel with the DC capacitor of the power module at the ground end of the test valve section. Through the balance control between valve sections and the capacitor voltage balance control within the valve section, the power loss for the operation test is provided to all modules. The pre-charge power supply Es charges all power modules to an initial voltage that can be stably operated through the charging resistor R. After charging is completed, the switch QS01 is disconnected, and the pre-charge power supply Es is disconnected. The power modules of the test valve section and the test valve section enter the unlocked operation state according to the modulation signal of the control system, and the test system is powered by the power supply Uc.

[0056] The valve section where the module under test is located is called the test valve section. The module under test is cascaded with the other modules in the valve section. The module under test can be located at any position in the test valve section. The module under test and the other modules in all valve sections except the module under test are of two different voltage levels.

[0057] The power modules of the test valve section and the accompanying test valve section operate according to the modulation signal obtained by the MMC different operating voltage module joint test method.

[0058] Compared with the prior art, the beneficial effects of the present invention are:

[0059] This invention provides a method and apparatus for joint testing of MMC modules with different operating voltages. It enables modules within the same valve section to operate at two different voltages during MMC valve section testing. Furthermore, the control strategy separates the tested module from the other modules, with the tested module's operating voltage and switching frequency differing from the individual control of other modules. This reduces the risk of damage to non-tested modules and the system's energy replenishment capability during testing, while also reducing the primary insulation design requirements. It provides a convenient method for high-voltage operation of modules in valve section testing in the field of flexible DC transmission. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the experimental topology used in the experimental method of this invention;

[0061] Figure 2 This is a schematic diagram of the overall control scheme of the present invention;

[0062] Figure 3 This is the logic diagram of the switching signal of the test module S of the invention. Detailed Implementation

[0063] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0064] Example 1

[0065] This embodiment provides a method for joint testing of MMC modules with different operating voltages.

[0066] like Figure 1 As shown, the test method employs a counter-rotating test circuit consisting of a test valve section and a companion valve section. The upper ends of the two valve sections are connected via a load reactor L, and the lower ends are grounded. The valve section containing the module under test is called the test valve section, where the module under test is cascaded with the other modules within the section, and the module under test can be located at any position within the test valve section. The companion valve section also consists of multiple cascaded modules (non-test modules). The module described in this application is an MMC converter valve submodule.

[0067] The test method described in this invention is used when the module under test and all other modules in all valve sections, except the module under test, are at two different voltage levels.

[0068] Typically, the modulation signals between the test valve section and the auxiliary valve section are staggered by a certain phase, causing the two valve sections to generate power circulation through the load reactance. The system control structure is as follows: Figure 2 As shown.

[0069] The test method is as follows: the operating voltage of the tested module is U. S The operating voltage of all valve sections except the tested module is U. n The operating voltage U of the tested module S The operating voltage of the other modules is Un Unlike other modules, the tested module is switched according to the S-switching command ordered by voltage, and the modulation signal of the test sample valve section is V. mod1 The modulation signal for the test valve section is V. mod2 V mod1 Based on the S switching command and the current voltage U of the tested module S The calculation yielded the result.

[0070] The switching of the tested module according to the S-switching command sorted by voltage specifically includes the following:

[0071] like Figure 1 As shown, for a half-bridge module, the AC bus is located between the upper transistor T1 and the lower transistor T2, and the current i is defined. L The flow direction into the AC port of the test module is positive, and the equivalent voltage U of the test module is... eq Based on the average value U of the non-tested modules in the test sample valve section av The current operating voltage U of the tested module S The expected operating voltage value U of the tested module s * The calculation shows that:

[0072]

[0073] E P E is the upper limit of the sorting start threshold. N To set the lower limit of the sorting threshold, U ac Modulate the output voltage of the non-tested module in the test sample valve section.

[0074] Modulation signal V of the test sample valve section mod1 The test module is affected by the switching command S; S=0 is the test module removal command, and S=1 is the test module insertion command. For example... Figure 3 As shown, the S-toggle command includes the following branch selection:

[0075] (1) Branch 1: If the module under test was in the active state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage U of the module under test was... eq The average value U of the non-tested modules in the test sample valve section av The difference is greater than the upper limit of the sorting start threshold E. P If the subject module is changed to a cutoff command in this cycle, then S=0;

[0076] (2) Branch 2: If the module under test was in the active state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage U of the module under test was... eq The average value U of the non-tested modules in the test sample valve section av The difference is less than the upper limit of the sorting start threshold E. P If the subject module remains engaged in this cycle, then S = 1.

[0077] (3) Branch 3: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value U of the non-tested modules in the test sample valve section was... av Equivalent voltage U of the tested module eq The difference is greater than the lower limit of the sorting start threshold E. N If the subject module is changed to a cutoff command in this cycle, then S=0;

[0078] (4) Branch 4: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value U of the non-tested modules in the test valve section was... av Equivalent voltage U of the tested module eq The difference is less than the lower limit of the sorting start threshold E. N If the subject module remains engaged in this cycle, then S = 1.

[0079] (5) Branch 5: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The current flows in the direction of the AC outlet, and the average value U of the non-tested module in the test sample valve section is... av Equivalent voltage U of the tested module eq The difference is greater than the lower limit of the sorting start threshold E. N If the subject module is changed to the input command in this cycle, then S=1;

[0080] (6) Branch 6: If the module under test was in the off state in the previous cycle, the non-module under test modulates the output voltage U in the test sample valve section. ac Greater than the current operating voltage U of the tested module S The current flows in the direction of the AC outlet, and the average value U of the non-tested module in the test sample valve section is... av Equivalent voltage U of the tested module eq The difference is less than the lower limit of the sorting start threshold E. N If the subject module maintains the cutoff command for this cycle, then S = 0;

[0081] (7) Branch 7: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The direction of current flow out of the AC busbar; the equivalent voltage U of the module under test. eq The average value U of the non-tested modules in the test sample valve section av The difference is greater than the upper limit of the sorting start threshold E. P If the subject module is changed to the input command in this cycle, then S=1;

[0082] (8) Branch 8: If the module under test was in the off state in the previous cycle, the output voltage U of the non-module under test in the test sample valve section is modulated. ac Greater than the current operating voltage U of the tested module S The direction of current flow out of the AC busbar; the equivalent voltage U of the module under test. eq The average value U of the non-tested modules in the test sample valve section av The difference is less than the upper limit of the sorting start threshold E. P If the subject module maintains the cutoff command for this cycle, then S = 0;

[0083] (9) Branch 9: If the module under test was in the off state in the previous cycle, the non-module under test modulates the output voltage U in the test sample valve section. ac Less than the current operating voltage U of the tested module S If the subject module maintains the cutoff command for this cycle, then S = 0;

[0084] Based on the final voltage sorting of the S-switching commands and the current voltage U of the tested module S The modulation signal V in the NLM operation submodule of the sample valve section was calculated. mod1 =U t * -U S ×S, U t * This is the reference voltage modulation signal for the test sample valve section.

[0085] Example 2

[0086] This embodiment, based on Embodiment 1, proposes a modulation signal V for the test valve section. mod2 The calculation method, such as Figure 2 As shown, it includes the following steps:

[0087] Step 1: Calculation of the overall average voltage of the test sample valve section: U S U is the current operating voltage of the module under test. av The average value of the non-tested modules in the test valve section is used to calculate the number of modules equivalent to the voltage of the tested module based on the voltage values ​​of the two. Then, the overall average voltage of the test sample valve section was calculated. SM_Num represents the number of non-test modules in the sample valve section;

[0088] Step 2: The average voltage and current of the valve segment form a voltage-current dual closed-loop control structure to maintain the balance of input and output power between the two valve segments; specifically as follows:

[0089] U av2 U represents the overall average voltage of the test valve section. av1 with U av2 The difference is output by the voltage PI regulator as the DC component setpoint of the load current between valve sections. Target value of AC component of load current As specified in the test requirements, After calculations based on the phase angle θ and phase difference α, a sinusoidal command signal, i.e., the AC command component, is generated. Give the communication component and DC component setpoint The summation yields the total current given between valve sections. Current feedback is i L ,Will with i L The difference is then used to obtain the control loop output U through a current PI regulator. out ;

[0090] Step 3: The reference voltage modulation signal for the test valve section is U k * Control loop output U out Modulation signal U with reference voltage of the test valve section k * The summation yields the modulation signal V of the test valve section. mod2 Perform NLM operations.

[0091] Example 3

[0092] This embodiment, based on Embodiment 1, provides the experimental procedure for the subject module, including the following:

[0093] Test parameter determination: Based on the test requirements and the module's rated capacity, the following parameters need to be determined:

[0094] (1) Determine the expected operating voltage U of the tested module s * The operating voltage U of all valve sections except the module under test. n ;

[0095] (2) Determine the operating switching frequency F of the tested module. S The remaining modules operate at a switching frequency F. n ;

[0096] (3) Determine the AC component current value, DC component current value, phase angle difference, and modulation index of the system;

[0097] The specific experimental process includes the following steps:

[0098] (1) Close the disconnect switch QS01 and start the pre-charge power supply E. S The test valve section and the accompanying test valve section are charged simultaneously until all modules can operate normally.

[0099] (2) Disconnect the disconnect switch QS01 and disconnect the pre-charge power supply E. S;

[0100] (3) Start the power supply U c ;

[0101] (4) All sub-modules are reset and configured before unlocking to ensure that the sub-modules are fault-free and reach the unlocking state;

[0102] (5) Unlock operation, the tested module is switched according to the S control command, and the test sample valve section is switched according to the modulation signal V. mod1 The test valve section is operated according to the modulation signal V. mod2 To perform NLM operation control;

[0103] (6) Gradually raise the power supply U c The output value ultimately reaches the operating voltage U of all modules except the tested module in all valve sections. n ;

[0104] (7) Gradually increase the system current until the target value is reached;

[0105] (8) According to 0.3*U respectively s * 0.6*U s * U s * The change range is adjusted by modifying the operating voltage setpoint of the module under test until the voltage of the module under test rises or falls to the desired operating voltage value U. s * ;

[0106] (9) Based on the operating switching frequency F of the remaining modules n Modify the NLM operation sorting start threshold until the switching frequency of the non-subject module meets the requirements;

[0107] (10) The switching frequency F of the tested module S Modify the upper and lower limits of the sorting start threshold of the tested module until the switching frequency of the non-tested module meets the requirements.

[0108] Furthermore, the modification rules for step (8) are as follows:

[0109] If the peak value of the current operating voltage of the tested module is too high, reduce the upper limit of the tested module's sorting and starting threshold E. P ;

[0110] If the peak value of the current operating voltage of the tested module is too low, increase the upper limit of the test module sorting start threshold E. P ;

[0111] If the current operating voltage trough value of the tested module is too small, reduce the lower limit E of the tested module sorting start threshold. N ;

[0112] If the current operating voltage trough value of the tested module is too large, increase the lower limit E of the tested module sorting start threshold. N .

[0113] Furthermore, the modification rules for step (9) are as follows:

[0114] If the current switching frequency of the non-subject module is less than F n Reduce the sorting threshold for NLM operations;

[0115] If the current switching frequency of the non-subject module is greater than F n Increase the sorting threshold for NLM operations.

[0116] Furthermore, the modification rules for step (10) are as follows:

[0117] If the current switching frequency is less than F S Reduce the upper limit of the subject module sorting priming threshold E P Increase the lower limit of the subject module ranking priming threshold E N ;

[0118] If the current switching frequency is greater than F S Increase the upper limit of the subject module sorting priming threshold E P Reduce the lower limit of the subject module sorting priming threshold E N .

[0119] Example 4

[0120] This embodiment provides a test apparatus for implementing the aforementioned method for joint testing of MMC modules operating at different voltages.

[0121] like Figure 1 As shown, the test apparatus includes: a test valve section, a test valve section, a load reactor L, a supplementary power supply Uc, a pre-charge power supply Es, a charging resistor R, and a switch QS01. The test valve section and the test valve section are connected to form a counter-draft test circuit. The upper ends of the two valve sections are connected via the load reactor L, and the lower ends are grounded. The supplementary power supply Uc is connected in parallel with the DC capacitor of the power module at the ground terminal of the test valve section. Through the balance control between valve sections and the capacitor voltage balance control within the valve section, it provides the power loss for the operation test of all modules. The pre-charge power supply Es charges all power modules to the initial voltage that can be stably operated through the charging resistor R. After charging is completed, the switch QS01 is disconnected, and the pre-charge power supply Es is disconnected. The power modules of the test valve section and the test valve section enter the unlocked operation state according to the modulation signal of the control system, and the test system is powered by the supplementary power supply Uc.

[0122] The valve section where the module under test is located is called the test valve section. The module under test is cascaded with the other modules in the valve section. The module under test can be located at any position in the test valve section. The module under test and the other modules in all valve sections except the module under test are of two different voltage levels.

[0123] The power modules of the test valve section and the accompanying test valve section operate according to the modulation signal obtained by the MMC different operating voltage module joint test method.

[0124] In summary, this invention realizes two different operating voltage test methods for modules within the same valve section in MMC valve section testing. Furthermore, the control strategy separates the tested module from the other modules, allowing the operating voltage and switching frequency of the tested module to be controlled independently, which reduces the risk of damage to non-tested modules and the system's energy replenishment capability during testing. It also reduces the primary insulation design requirements and provides a convenient method for high-voltage operation of modules in valve section testing in the field of flexible DC transmission.

[0125] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0126] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A joint test method for MMC modules operating at different voltages, wherein the test method is a test method for MMC converter valve submodules, and adopts a counter-draft test circuit composed of a test valve section and a test valve section. The upper ends of the test valve section and the test valve section are connected via a load reactor L. The valve section where the module under test is located is called the test valve section, wherein the module under test is cascaded with the other modules in the valve section, and the module under test is located at any position in the test valve section. Its features are, The test method is used when the module under test and all other modules in all valve sections are at two different voltage levels. The test method is as follows: the operating voltage of the tested module is... The operating voltage of all valve sections except the tested module is... Operating voltage of the tested module The operating voltage of the other modules is Unlike other modules, the tested module switches according to the S-switching command ordered by voltage, and the modulation signal of the test sample valve section is... The modulation signal of the test valve section is ; Based on the S-switching command and the current voltage of the tested module Calculated; The switching of the tested module according to the S-switching command sorted by voltage specifically includes the following: For a half-bridge module, the AC bus is located between the upper transistor T1 and the lower transistor T2, defining the current... The flow direction into the AC port of the module under test is positive, and the equivalent voltage of the module under test is... Based on the average value of the non-tested modules in the test sample valve section Current operating voltage of the tested module Expected operating voltage value of the tested module The calculation shows that: definition The upper limit of the sorting threshold is set. To set the lower limit of the sorting threshold, Modulate the output voltage of the non-tested module in the test sample valve section; The S-turn command includes the following branch selection: (1) Branch 1: If the module under test was in the input state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage of the module under test was... The average value of the non-tested modules in the test sample valve section The difference is greater than the upper limit of the sorting start threshold. If the subject module is changed to a cutoff command in this cycle, then S=0; (2) Branch 2: If the module under test was in the input state in the previous cycle, the current flowed into the AC bus, and the equivalent voltage of the module under test was... The average value of the non-tested modules in the test sample valve section The difference is less than the upper limit of the sorting start threshold. If the subject module remains engaged in this cycle, then S=1. (3) Branch 3: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value of the non-tested modules in the test sample valve section was... Equivalent voltage of the module under test The difference is greater than the lower limit of the sorting start threshold. If the subject module is changed to a cutoff command in this cycle, then S=0; (4) Branch 4: If the tested module was in the input state in the previous cycle, the current was flowing out of the AC outlet, and the average value of the non-tested modules in the test sample valve section was... Equivalent voltage of the module under test The difference is less than the lower limit of the sorting start threshold. If the subject module remains engaged in this cycle, then S=1. (5) Branch 5: If the module under test was in the off state in the previous cycle, the non-module under test modulates the output voltage in the test sample valve section. Greater than the current operating voltage of the module under test The current is the direction of flow into the AC outlet, and the average value of the non-tested modules in the test sample valve section. Equivalent voltage of the module under test The difference is greater than the lower limit of the sorting start threshold. If the subject module is changed to the input command in this cycle, then S=1; (6) Branch 6: If the tested module was in the cut-off state in the previous cycle, the non-tested module in the test valve section modulates the output voltage. Greater than the current operating voltage of the module under test The current is the direction of flow into the AC outlet, and the average value of the non-tested modules in the test sample valve section. Equivalent voltage of the module under test The difference is less than the lower limit of the sorting start threshold. If the subject module maintains the cutoff command for this cycle, then S=0; (7) Branch 7: If the tested module was in the cut-off state in the previous cycle, the non-tested module in the test sample valve section modulates the output voltage. Greater than the current operating voltage of the module under test The direction of current flow out of the AC busbar; the equivalent voltage of the module under test. The average value of the non-tested modules in the sample valve section The difference is greater than the upper limit of the sorting start threshold. If the subject module is changed to the input command in this cycle, then S=1; (8) Branch 8: If the tested module was in the cut-off state in the previous cycle, the non-tested module in the test sample valve section modulates the output voltage. Greater than the current operating voltage of the module under test The direction of current flow out of the AC busbar; the equivalent voltage of the module under test. The average value of the non-tested modules in the test sample valve section The difference is less than the upper limit of the sorting start threshold. If the subject module maintains the cutoff command for this cycle, then S=0; (9) Branch 9: If the module under test was in the off state in the previous cycle, the output voltage of the non-module under test in the test sample valve section is modulated. Less than the current operating voltage of the tested module If the subject module maintains the cutoff command for this cycle, then S=0; Based on the S-switching commands sorted by the final voltage, and the current voltage of the tested module... The modulation signals of the submodules participating in the NLM operation in the sample valve section were calculated. , This is the reference voltage modulation signal for the test sample valve section.

2. The method for joint testing of MMC modules with different operating voltages according to claim 1, characterized in that, Modulation signal of the test valve section The calculation method includes the following steps: Step 1: Calculation of the overall average voltage of the test sample valve section: The current operating voltage of the module under test. The average value of the non-tested modules in the test valve section is used to calculate the number of modules equivalent to the voltage of the tested module based on the voltage values ​​of the two. Then, the overall average voltage of the test sample valve section was calculated. , This represents the number of non-tested modules in the valve section of the test sample. Step 2: The average voltage and current of the valve segment form a voltage-current dual closed-loop control structure to maintain the balance of input and output power between the two valve segments; specifically as follows: The overall average voltage of the test valve section. and The difference is output by the voltage PI regulator as the DC component setpoint of the load current between valve sections. Target peak value of AC component of load current As specified in the test requirements, After phase angle and phase difference The calculation generates a sinusoidal given signal, i.e., the AC given component. The exchange will be given a component and DC component setpoint The summation yields the total current given between valve sections. The current feedback value is ,Will and The difference is then used to obtain the output of the control loop through a current PI regulator. ; Step 3: The reference voltage modulation signal for the test valve section is... Control loop output Modulation signal with reference voltage of the test valve section The modulation signal of the test valve section is obtained by adding them together. .

3. The method for joint testing of MMC modules with different operating voltages according to claim 1, characterized in that, The experimental procedure for the subject module includes the following: Test parameter determination: Based on the test requirements and the module's rated capacity, the following parameters need to be determined: (1) Determine the expected operating voltage value of the module under test. Operating voltage of all valve sections except the module under test. ; (2) Determine the switching frequency of the tested module The operating switching frequency of the remaining modules ; (3) Determine the AC component current value and DC component current value of the system, calculate the phase angle difference and modulation degree; The specific experimental process includes the following steps: (1) Closing the disconnect switch Start the pre-charge power supply The test valve section and the accompanying test valve section are charged simultaneously until all modules can operate normally. (2) Disconnect the knife switch Exit pre-charge power ; (3) Start the power supply ; (4) All sub-modules undergo pre-unlock reset and configuration checks to ensure that the sub-modules are fault-free and reach the unlockable state; (5) Unlock operation, the tested module is switched according to the S control command, and the test sample valve section is switched according to the modulation signal. The test valve section is tested according to the modulation signal. To perform NLM operation control; (6) Gradually raise the power supply level The output value ultimately reaches the operating voltage of all modules in all valve sections except the module under test. ; (7) Gradually increase the system current until the target value is reached; (8) According to 0.3* 0.6* , The change range is adjusted by modifying the operating voltage setpoint of the module under test until the voltage of the module under test rises or falls to the desired operating voltage value. ; (9) Based on the operating switching frequency of the remaining modules Modify the NLM operation sorting start threshold until the switching frequency of the non-subject module meets the requirements; (10) Switching frequency of the tested module Modify the upper and lower limits of the sorting start threshold of the tested module until the switching frequency of the non-tested module meets the requirements.

4. The method for joint testing of MMC modules with different operating voltages according to claim 3, characterized in that, The modification rules for step (8) are as follows: If the peak voltage of the tested module is too high, reduce the upper limit of the tested module's sorting and startup threshold. ; If the peak voltage of the tested module is too low, increase the upper limit of the tested module's sorting and starting threshold. ; If the current operating voltage trough value of the tested module is too small, reduce the lower limit of the tested module sorting start threshold. ; If the current operating voltage trough value of the tested module is too large, increase the lower limit of the tested module sorting start threshold. .

5. The method for joint testing of MMC modules with different operating voltages according to claim 3, characterized in that, The modification rules for step (9) are as follows: If the current switching frequency of the non-subject module is less than Reduce the sorting threshold for NLM operations; If the current switching frequency of the non-subject module is greater than Increase the NLM operation sorting start threshold.

6. The method for joint testing of MMC modules with different operating voltages according to claim 3, characterized in that, The modification rules for step (10) are as follows: If the current switching frequency is less than Reduce the upper limit of the subject module sorting priming threshold. Increase the lower limit of the subject module sorting priming threshold. ; If the current switching frequency is greater than Increase the upper limit of the subject module sorting priming threshold. Reduce the lower limit of the subject module sorting priming threshold. .

7. A test apparatus for implementing the joint test method for MMC modules with different operating voltages as described in any one of claims 1-6, characterized in that, The system includes: a test valve section, a test valve section, a load reactor L, a power supply Uc, a pre-charge power supply Es, a charging resistor R, and a switch QS01. The test valve section and the test valve section are connected to form a reverse drag test circuit. The upper ends of the test valve section and the test valve section are connected through the load reactor L, and the lower ends are grounded. The power supply Uc is connected in parallel with the DC capacitor of the power module at the ground end of the test valve section. Through the balance control between valve sections and the capacitor voltage balance control within the valve section, the power loss for the test is provided to all modules. The pre-charge power supply Es charges all power modules to the initial voltage that can be stably operated through the charging resistor R. After charging is completed, the switch QS01 is disconnected, and the pre-charge power supply Es is disconnected. The power modules of the test valve section and the test valve section enter the unlocked operation state according to the modulation signal of the control system, and the test system is powered by the power supply Uc. The valve section where the module under test is located is called the test valve section. The module under test and the other modules in the valve section are cascaded. The module under test can be located at any position in the test valve section. The module under test and the other modules in all valve sections except the module under test are of two different voltage levels. The power modules of the test valve section and the accompanying test valve section operate according to the modulation signal obtained by the MMC different operating voltage module joint test method according to any one of claims 1-6.

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