A method for over-current shutdown test based on H-bridge type test platform

Abstract

The application relates to an overcurrent turn-off test method based on an H-bridge type operation test platform, wherein the test system comprises four bridge arm branches, wherein bridge arm 1, bridge arm 3 and bridge arm 2, bridge arm 4 form phase unit 1 and phase unit 2 respectively, the midpoints of the two phases are connected through a load reactor, each bridge arm is composed of an MMC valve and a bridge arm reactor. The two phase units have a common DC end and are connected with a DC power supply through a smoothing reactor, and the DC power supply is used for pre-charging of the sub-modules and supplementing of active loss in the test process. The application uses a target value control method, in the test operation process, the control logic of the four bridge arm test samples is changed, overcurrent turn-off tests of 1 and 2 bridge arms and overcurrent turn-off tests of 3 and 4 bridge arms are respectively completed, and the overcurrent turn-off test method of the MMC valve on the H-bridge type operation test platform is realized.

Description

Technical Field

[0001] This invention relates to the field of testing technology for flexible DC transmission converter valves, and in particular to an overcurrent shutdown test method based on an H-bridge test platform. Background Technology

[0002] The converter valve is a core module in high-voltage flexible DC transmission projects, responsible for power conversion. Its operational reliability directly affects the stability of the entire DC transmission system, thus requiring rigorous type testing. As an important test item in type testing, the overcurrent shutdown test aims to check the suitability of the converter valve design, especially the power devices and their related circuits, under specific short-circuit faults or false triggering conditions, and the effects of shutdown current and voltage stress.

[0003] Existing technologies generally employ a test system consisting of valve sections to conduct type tests on flexible DC transmission converter valves. However, the existing methods have the following problems: first, they cannot fully simulate actual field conditions; second, they use an auxiliary sub-module to test the test valve, which increases the cost of the test equipment. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a test method for overcurrent shut-off of MMC valves in flexible DC transmission based on an H-bridge test platform. This test platform can better simulate actual field conditions and further verify the quality of flexible DC transmission converter valves in practical applications.

[0005] To achieve the above objectives, a first aspect of the present invention provides an H-bridge-based operational test system, comprising four bridge arm branches, wherein bridge arm 1, bridge arm 3, bridge arm 2, and bridge arm 4 respectively form phase unit 1 and phase unit 2, the midpoints of the two phases are connected by a load reactor, and each bridge arm consists of an MMC valve and a bridge arm reactor; the two phase units have a common DC terminal and are connected to a DC power supply through a smoothing reactor, the DC power supply being used for pre-charging of the submodule and supplementing active power losses during the test process.

[0006] Accordingly, a second aspect of the present invention provides a method for conducting overcurrent shut-off tests on flexible DC converter valves using the above-described H-bridge type operating test system, characterized by the following steps:

[0007] Identify the power devices required for verification in the MMC valves connected in series in bridge arms 1, 2, 3, and 4.

[0008] The test system is started, and the sample operates under rated voltage and rated current, reaching the highest steady-state junction temperature and operating in a thermally stable state;

[0009] To facilitate the explanation of the test principle, the MMC valves of bridge arm 1 and bridge arm 2 are used as examples of overcurrent shut-off test specimens. The control logic of other bridge arm specimens is the same.

[0010] The control system issues control commands to test tube T1 of bridge arm 1 and test tube T2 of bridge arm 2 to carry out overcurrent turn-off tests, and controls test tube T1 of bridge arm 1 to be turned on and test tube T2 to be turned off, and test tube T1 of bridge arm 2 to be turned off and test tube T2 to be turned on, thereby generating the overcurrent required for the test.

[0011] After the overcurrent reaches the target value required by the test, control the T1 tube of the test specimen in bridge arm 1 to be cut off and the T2 tube to be put on, and control the T1 tube of the test specimen in bridge arm 2 to be put on and the T2 tube to be cut off, so that the overcurrent flowing through the power device to be verified in the test specimens in bridge arm 1 and bridge arm 2 gradually decreases until the overcurrent becomes zero. Then, change the control logic of bridge arm 1, bridge arm 2, bridge arm 3 and bridge arm 4 again to restore the operating state before the overcurrent shutdown test.

[0012] The control system issues control commands to test tube T2 of bridge arm 1 and test tube T1 of bridge arm 2 to carry out overcurrent turn-off tests, and controls test tube T1 of bridge arm 1 to be turned off and test tube T2 to be turned on, and test tube T1 of bridge arm 2 to be turned on and test tube T2 to be turned off, thereby generating the overcurrent required for the test.

[0013] After the overcurrent reaches the target value required by the test, control the T1 tube of the test specimen in bridge arm 1 to be put in and the T2 tube to be cut off, and control the T1 tube of the test specimen in bridge arm 2 to be cut off and the T2 tube to be put in, so that the overcurrent flowing through the power device to be verified in the test specimens in bridge arm 1 and bridge arm 2 gradually decreases until the overcurrent becomes zero. Then control the test specimens in bridge arm 1, bridge arm 2, bridge arm 3 and bridge arm 4 to be locked, and the test ends.

[0014] Furthermore, the overcurrent shutdown capability can be triggered at any time, and the resulting overcurrent can be controlled by the target value. During the test, there is no current reduction phase, and the junction temperature can be kept from dropping.

[0015] The above-described technical solution of the present invention has the following beneficial technical effects:

[0016] This invention provides a test method for overcurrent shutdown testing of flexible DC MMC valves based on an H-bridge test system. It achieves the ability to trigger overcurrent shutdown at any time, controls the end of the test by a target value, and maintains the junction temperature without dropping during the test without a current reduction phase. Attached Figure Description

[0017] Figure 1 This is a structural block diagram of an H-bridge type operation test system for overcurrent shut-off testing of converter valves in flexible DC transmission, according to the present invention.

[0018] Figure 2 This is the structural schematic diagram of the half-bridge submodule.

[0019] Figure 3 These are the overcurrent shut-off waveforms for valve T1 in bridge arm 1 and valve T2 in bridge arm 2.

[0020] Figure 4 These are the overcurrent shut-off waveforms of valve T2 in bridge arm 1MMC and valve T1 in bridge arm 2MMC. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0022] like Figure 1 As shown, this invention relates to an H-bridge operational test system for overcurrent shut-off testing of flexible DC MMC valves. It comprises four bridge arm branches, where bridge arms 1, 3, 2, and 4 form phase unit 1 and phase unit 2, respectively. The midpoints of two phases are connected via load reactors. Each bridge arm consists of the MMC valve under test and a bridge arm reactor. The two phase units share a common DC terminal ZQL and are connected to a DC power supply via a smoothing reactor. The DC power supply is obtained from the AC bus through a voltage regulator, transformer, and rectifier bridge, and is used for pre-charging of the submodules and supplementing active power losses during the test process.

[0023] When the overcurrent shut-off characteristics of the MMC valve need to be tested, the MMC valve is connected in series with the four bridge arms, and then the test is started.

[0024] In this embodiment, the converter valves to be tested are all composed of multiple half-bridge sub-modules connected in series, and the structural schematic diagram of each half-bridge module is shown below. Figure 2 As shown. In this embodiment, the power devices T1 and T2 in the half-bridge submodule are both IGBTs. Of course, in other implementations, the power devices of the half-bridge submodule can be composed of one or more of fully controlled devices such as IGBTs and IGBTs. Since the structure and working principle of the half-bridge submodule are existing technologies, they will not be described in detail here.

[0025] The H-bridge type operational test system described above for overcurrent shutdown testing of converter valves in flexible DC transmission was used to test the converter valves to be tested. The specific steps are as follows:

[0026] 1) Select the power device to be verified from the MMC valves connected in series in bridge arms 1, 2, 3, and 4. To facilitate the explanation of the test principle, the MMC valves in bridge arm 1 and 2 are used as examples for the overcurrent shutdown test. The control logic of the other bridge arm test specimens is the same.

[0027] 2) Start the test system and run the sample under rated voltage and rated current until the inlet and outlet water temperature rise remains stable. At this time, the sample reaches the highest steady-state junction temperature and runs in a thermally stable state. Then carry out the overcurrent shutdown test.

[0028] 3) The control system issues a command to conduct an overcurrent shutdown test on the MMC valve T1 tube of bridge arm 1 and the MMC valve T2 tube of bridge arm 2, so that the MMC valve of bridge arm 1 is fully engaged (voltage is at maximum Umax) and the MMC valve of bridge arm 2 is fully disengaged (voltage is 0), forming a short-circuit loop composed of bridge arm 1 and load reactor Ld, bridge arm reactors Lb1 and Lb2, causing the short-circuit current to rise continuously.

[0029] In this implementation, the MMC valves of bridge arm 1 are fully engaged. The control logic for the bridge arm 1 MMC valve is as follows: T1 is engaged, T2 is disengaged, and the DC voltage of the bridge arm 1 MMC valve is Umax. Engagement here means that current flows through the capacitor in the half-bridge submodule. The control logic for the bridge arm 2 MMC valve is as follows: T1 is disengaged, T2 is engaged, and the voltage of the bridge arm 2 MMC valve is 0. Disengagement here means that current does not flow through the capacitor in the half-bridge submodule.

[0030] At this time, since the bridge arm 1MMC valve is fully engaged and the bridge arm 2MMC valve is fully disengaged, the voltage across the bridge arm reactor and the load reactor is the voltage difference Umax between the bridge arm 1MMC valve and the bridge arm 2MMC valve, and the short-circuit current continues to rise.

[0031] After the overcurrent reaches the target value Imax required by the test, the control logic is changed to fully disconnect the valve of bridge arm 1 (voltage is 0) and fully engage the valve of bridge arm 2 (voltage is at its maximum Umax), forming a short-circuit loop consisting of bridge arm 2 and the load reactor Ld, bridge arm reactors Lb1 and Lb2, causing the short-circuit current to continuously decrease.

[0032] In this implementation case, the control logic of the bridge arm 1MMC valve is as follows: when T1 is disconnected and T2 is connected, the DC voltage of the bridge arm 1MMC valve is 0; the control logic of the bridge arm 2MMC valve is as follows: when T1 is connected and T2 is disconnected, the DC voltage of the bridge arm 2MMC valve is Umax. The voltage across the bridge arm reactor and the load reactor is the voltage difference between the bridge arm 1MMC valve and the bridge arm 2MMC valve - Umax, and the short-circuit current continuously decreases.

[0033] When the short-circuit current drops to 0, change the control logic of bridge arm 1, bridge arm 2, bridge arm 3 and bridge arm 4, and restore the control logic of continuous operation test, so that the test sample is in the operation state of continuous operation test;

[0034] The control system issues a command to conduct an overcurrent shutdown test on MMC valve T2 of bridge arm 1 and MMC valve T1 of bridge arm 2, causing all MMC valves of bridge arm 1 to be disconnected (voltage is 0) and all MMC valves of bridge arm 2 to be engaged (voltage is maximum Umax), forming a short-circuit loop consisting of bridge arm 2 and load reactor Ld, bridge arm reactors Lb1 and Lb2, causing the short-circuit current to rise continuously.

[0035] In this implementation case, the control logic is the same as described above, and will not be repeated here.

[0036] At this time, since the bridge arm 1MMC valve is completely deactivated and the bridge arm 2MMC valve is fully activated, the voltage across the bridge arm reactor and the load reactor is the voltage difference between the bridge arm 1MMC valve and the bridge arm 2MMC valve -Umax, and the short-circuit current continues to rise.

[0037] After the overcurrent reaches the target value -Imax required by the test, the control logic is changed to fully engage the valves of bridge arm 1 (maximum voltage Umax) and fully disengage the valves of bridge arm 2 (voltage is 0), forming a short-circuit loop consisting of bridge arm 1 and the load reactor Ld, and bridge arm reactors Lb1 and Lb2, causing the short-circuit current to continuously decrease.

[0038] In this implementation case, the control logic is the same as described above, and will not be repeated here.

[0039] The voltage across the bridge arm reactor and the load reactor is the voltage difference Umax between the bridge arm 1MMC valve and the bridge arm 2MMC valve, and the short-circuit current continuously decreases.

[0040] Once the short-circuit current drops to 0, lock the MMC valves of bridge arm 1, bridge arm 2, bridge arm 3, and bridge arm 4, disconnect the test circuit, and the test ends.

[0041] In the implementation case, the overcurrent shut-off waveforms of valve T1 in bridge arm 1 and valve T2 in bridge arm 2 are as follows: Figure 3 As shown, the overcurrent shut-off waveforms of valve T2 in bridge arm 1 and valve T1 in bridge arm 2 are as follows: Figure 4 As shown.

[0042] In this embodiment, the control logic for the other bridge arm samples is the same as that in the above experiment, and will not be described in detail here.

[0043] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for overcurrent shut-off testing of a flexible DC converter valve, characterized in that, The H-bridge-based operational test system includes four bridge arm branches. Bridge arms 1 and 3, and bridge arms 2 and 4 form phase unit 1 and phase unit 2, respectively. The midpoints of the two phases are connected through load reactors. Each bridge arm consists of an MMC valve and a bridge arm reactor. The two phase units have a common DC terminal and are connected to a DC power supply through a smoothing reactor. The DC power supply is used for pre-charging the submodules and supplementing active power losses during the test. The steps are as follows: Identify the power devices required for verification in the MMC valves connected in series in bridge arms 1, 2, 3, and 4. The test system is started, and the sample operates at rated voltage and rated current, reaching the highest steady-state junction temperature and operating in a thermally stable state; The control system issues control commands to test tube T1 of bridge arm 1 and test tube T2 of bridge arm 2 to carry out overcurrent turn-off tests, controlling test tube T1 of bridge arm 1 to be turned on and test tube T2 to be turned off, and test tube T1 of bridge arm 2 to be turned off and test tube T2 to be turned on, generating the overcurrent required for the test; After the overcurrent reaches the target value required by the test, control the T1 tube of the test specimen in bridge arm 1 to be cut off and the T2 tube to be put on, and control the T1 tube of the test specimen in bridge arm 2 to be put on and the T2 tube to be cut off, so that the overcurrent flowing through the power device to be verified in the test specimens in bridge arm 1 and bridge arm 2 gradually decreases until the overcurrent becomes zero. Then, change the control logic of bridge arm 1, bridge arm 2, bridge arm 3 and bridge arm 4 again to restore the operating state before the overcurrent shutdown test. The control system issues control commands to test tube T2 of bridge arm 1 and test tube T1 of bridge arm 2 to carry out overcurrent turn-off tests, controlling the disconnection of test tube T1 and the switching on of test tube T2 of bridge arm 1, and the switching on of test tube T1 and the disconnection of test tube T2 of bridge arm 2, thereby generating the overcurrent required for the test; After the overcurrent reaches the target value required by the test, control the T1 transistor of test specimen 1 to be engaged and the T2 transistor to be disengaged, and control the T1 transistor of test specimen 2 to be disengaged and the T2 transistor to be engaged, so that the overcurrent flowing through the power devices to be verified in test specimens 1 and 2 gradually decreases until the overcurrent becomes zero. Then control the test specimens 1, 2, 3 and 4 to be locked, and the test ends. The overcurrent shutdown capability can be triggered at any time, and the resulting overcurrent can be controlled by the target value. During the test, there is no current reduction phase, and the junction temperature can be kept from dropping.

Images