An operating system and method for the STATCOM mode of a flexible DC transmission system

Abstract

An operating system and method for a STATCOM mode of a flexible DC transmission system provided by the present invention include an A-phase disconnector, a single-phase AC voltage generator AC, a B-phase disconnector, a C-phase disconnector, and a current-limiting resistor R. Among them, one-phase AC side of the flexible DC transmission converter valve is connected to the output end of the single-phase AC voltage generator AC through the A-phase disconnector; the remaining two-phase AC sides of the flexible DC transmission converter valve are respectively connected to the B-phase disconnector and the C-phase disconnector; the other ends of the B-phase disconnector and the C-phase disconnector are connected in parallel to the current-limiting resistor R; the other end of the current-limiting resistor R is connected to the grounding end of the single-phase AC voltage generator AC.

Description

Technical Field

[0001] The present invention belongs to the field of flexible DC power transmission, and particularly relates to an operating system and method for a STATCOM mode of a flexible DC power transmission system. Background Art

[0002] Flexible DC power transmission systems are very suitable for fields such as power grid interconnection, offshore wind power grid connection, and island power supply due to their unique technical advantages.

[0003] Before a flexible DC power transmission system is connected to the grid, a STATCOM operation test is required to test the converter valves. In the case of no grid power supply, it is usually necessary to configure a high-power diesel generator for power supply, which is costly. Especially for offshore platforms in complex marine environments, transportation is difficult, bringing great difficulties to the test. Therefore, there is an urgent need for an economical, convenient, and easily implementable method to solve the problem of converter valve testing. Summary of the Invention

[0004] The purpose of the present invention is to provide an operating system and method for a STATCOM mode of a flexible DC power transmission system, which solves the defect of high test cost in the existing converter valve testing methods.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] An operating system for a STATCOM mode of a flexible DC power transmission system provided by the present invention includes an A-phase disconnector, a single-phase AC voltage generator AC, a B-phase disconnector, a C-phase disconnector, and a current-limiting resistor R. Among them, one-phase AC side of the flexible DC power transmission converter valve is connected to the output terminal of the single-phase AC voltage generator AC through the A-phase disconnector; the remaining two-phase AC sides of the flexible DC power transmission converter valve are respectively connected to the B-phase disconnector and the C-phase disconnector; the other ends of the B-phase disconnector and the C-phase disconnector are connected in parallel to the current-limiting resistor R; the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator AC.

[0007] Preferably, the output terminal of the single-phase AC voltage generator AC is sequentially connected to the module lower-arm anti-parallel diode and the A-phase upper-arm reactor of the A-phase of the flexible DC power transmission converter valve through the A-phase disconnector; the A-phase upper-arm reactor is respectively connected to the B-phase upper-arm reactor and the C-phase upper-arm reactor of the flexible DC power transmission converter valve; the B-phase upper-arm reactor is sequentially connected to the module upper-arm anti-parallel diode and the module capacitor of the B-phase, and the B-phase disconnector; the C-phase upper-arm reactor is sequentially connected to the module upper-arm anti-parallel diode and the module capacitor of the C-phase, and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the current-limiting resistor R, and the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator;

[0008] The output terminal of the single-phase AC voltage generator AC is sequentially connected to the anti-parallel diode and the module capacitor of the upper arm of the lower bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the lower bridge arm of phase A through the isolator of phase A; the reactor of the lower bridge arm of phase A is respectively connected to the reactor of the lower bridge arm of phase B and the reactor of the lower bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the lower bridge arm of phase B is connected to the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase B and the isolator of phase B; the reactor of the lower bridge arm of phase C is connected to the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase C and the isolator of phase C; the isolators of phase B and phase C are connected in parallel and then connected to the ground terminal of the single-phase AC voltage generator AC through the current-limiting resistor R.

[0009] Preferably, the ground terminal of the single-phase AC voltage generator AC is connected in parallel to the isolators of phase B and phase C through the current-limiting resistor R; the other end of the isolator of phase B is sequentially connected to the anti-parallel diode and the reactor of the upper bridge arm of phase B of the flexible DC transmission converter valve; the other end of the isolator of phase C is sequentially connected to the anti-parallel diode and the reactor of the upper bridge arm of phase C of the flexible DC transmission converter valve; the other ends of the reactors of the upper bridge arms of phase B and phase C are both connected to the reactor of the upper bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the upper bridge arm of phase A is connected to the anti-parallel diode and the module capacitor of the upper arm of the upper bridge arm of phase A of the flexible DC transmission converter valve; the anti-parallel diode and the module capacitor of the upper arm of the upper bridge arm of phase A are connected to the output terminal of the single-phase AC voltage generator AC through the isolator of phase A;

[0010] The ground terminal of the single-phase AC voltage generator AC is connected in parallel to the isolators of phase B and phase C through the current-limiting resistor R; the other end of the isolator of phase B is sequentially connected to the anti-parallel diode, the module capacitor and the reactor of the lower bridge arm of phase B of the flexible DC transmission converter valve; the other end of the isolator of phase C is sequentially connected to the anti-parallel diode, the module capacitor and the reactor of the lower bridge arm of phase C of the flexible DC transmission converter valve; the reactors of the lower bridge arms of phase B and phase C are both connected to the reactor of the lower bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the lower bridge arm of phase A is connected to the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase A; the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase A is connected to the output terminal of the single-phase AC voltage generator through the isolator of phase A.

[0011] Preferably, the output terminal of the single-phase AC voltage generator AC is sequentially connected, through the A-phase disconnector, to the antiparallel diode of the lower arm of the module of the upper bridge arm of the A-phase of the flexible DC transmission converter valve and the reactor of the upper bridge arm of the A-phase; the reactor of the upper bridge arm of the A-phase is respectively connected to the reactor of the upper bridge arm of the B-phase and the reactor of the upper bridge arm of the C-phase of the flexible DC transmission converter valve; the reactor of the upper bridge arm of the B-phase is sequentially connected to the antiparallel diode of the upper arm of the module in the on state of the upper bridge arm of the B-phase, the module capacitor, the IGBT of the lower arm of the module in the off state, and the B-phase disconnector; the reactor of the upper bridge arm of the C-phase is sequentially connected to the antiparallel diode of the upper arm of the module in the on state of the upper bridge arm of the C-phase, the module capacitor, the IGBT of the lower arm of the module in the off state, and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through the current-limiting resistor R.

[0012] The output terminal of the single-phase AC voltage generator AC is sequentially connected, through the A-phase disconnector, to the antiparallel diode of the upper arm of the module in the on state of the lower bridge arm of the A-phase, the module capacitor, the IGBT of the lower arm of the module in the off state, and the reactor of the lower bridge arm of the A-phase of the flexible DC transmission converter valve; the reactor of the lower bridge arm of the A-phase is respectively connected to the reactor of the lower bridge arm of the B-phase and the reactor of the lower bridge arm of the C-phase of the flexible DC transmission converter valve; the reactor of the lower bridge arm of the B-phase is sequentially connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of the B-phase and the B-phase disconnector; the reactor of the lower bridge arm of the C-phase is sequentially connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of the C-phase and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through the current-limiting resistor R.

[0013] Preferably, the grounding terminal of the single-phase AC voltage generator AC is connected in parallel to the B-phase disconnector and the C-phase disconnector through the current-limiting resistor R; the B-phase disconnector is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of the B-phase and the reactor of the upper bridge arm of the B-phase of the flexible DC transmission converter valve; the C-phase disconnector is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of the C-phase and the reactor of the upper bridge arm of the C-phase of the flexible DC transmission converter valve; the reactors of the upper bridge arms of the B-phase and the C-phase are connected in parallel and then connected to the reactor of the upper bridge arm of the A-phase; the reactor of the upper bridge arm of the A-phase is sequentially connected to the antiparallel diode of the upper arm of the module in the on state of the upper bridge arm of the A-phase, the module capacitor, the IGBT of the lower arm of the module in the off state, and the A-phase disconnector; the A-phase disconnector is connected to the output terminal of the single-phase AC voltage generator AC.

[0014] The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the phase B disconnector and the phase C disconnector through a current-limiting resistor R; the other end of the phase B disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the lower bridge arm of phase B of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower arm of the module in the off state, and the reactor of the lower bridge arm of phase B; the other end of the phase C disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the lower bridge arm of phase C of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower arm of the module in the off state, and the reactor of the lower bridge arm of phase C;

[0015] The reactors of the lower bridge arm of phase B and the lower bridge arm of phase C are connected in parallel and then sequentially connected to the reactor of the lower bridge arm of phase A, the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase A, and the phase A disconnector; the phase A disconnector is connected to the output terminal of the single-phase AC voltage generator AC.

[0016] A simplified commissioning method for a flexible DC transmission converter valve system in the sea, based on the operation system of the STATCOM mode of the flexible DC transmission system described above, includes the following steps:

[0017] This commissioning method includes a charging stage and an unlocking stage. Among them, in the charging stage: the single-phase AC voltage generator AC is used to supply power to the flexible DC transmission converter valve, the current-limiting resistor R is used to limit the current in the power supply circuit, and the sub-module voltage is charged to the rated voltage value of the sub-module through the uncontrolled charging and active charging modes;

[0018] In the unlocking stage: first disconnect the wiring between the three-phase disconnector and the single-phase AC voltage generator AC, unlock the flexible DC transmission converter valve to perform no-load open-loop wave generation, and use the energy stored in the module capacitor to carry out the test of the STATCOM commissioning mode to complete the verification of the relevant functions of the flexible DC transmission converter valve.

[0019] Preferably, in step 1, disconnect the AC circuit breaker connected to the valve side of the flexible DC system transformer in the flexible DC transmission system, close the three-phase disconnector connected to the single-phase AC voltage generator AC, and connect the flexible DC transmission converter valve to the single-phase AC voltage generator AC and the current-limiting resistor R;

[0020] In step 2, slowly raise the voltage of the single-phase AC voltage generator AC to perform uncontrolled rectification charging on the flexible DC transmission converter valve module until the voltage of the single-phase AC voltage generator AC reaches the set value and then stop raising the voltage;

[0021] In step 3, cut off the part of the modules with high voltage ranking in all power sub-modules in each control cycle according to the set rising slope for controlled charging, and charge the module voltage to the rated value;

[0022] Step 4: Disconnect the three-phase disconnector connected to the single-phase AC voltage generator AC; wait for unlocking to conduct an open-loop wave generation test under no-load condition.

[0023] Step 5: Conduct an open-loop wave generation test on the flexible DC transmission converter valve under no-load condition.

[0024] Step 6: After the test is completed, end the test.

[0025] Preferably, in Step 2, when the uncontrolled rectifier charging is performed on the flexible DC transmission converter valve module, the minimum voltage of the single-phase AC voltage generator AC should satisfy the following formula:

[0026]

[0027] where U s_min is the effective value of the minimum voltage of the voltage generator, N is the number of modules in a single bridge arm of the converter valve, U sm1 is the reliable live voltage of the module energy acquisition power supply, and U R is the voltage drop across the current-limiting resistor R.

[0028] Preferably, in Step 3, remove the part of the modules with high voltage ranking in all power sub-modules within each control cycle; the upper limit of the part of the modules is:

[0029]

[0030] where N off is the upper limit that needs to be removed when the module voltage rises to the rated value, and U sm_rate is the rated voltage of the module.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. For the operation system and method of the STATCOM mode of the flexible DC transmission system provided by the present invention, the single-phase AC voltage generator is simpler in structure, lower in cost, and more convenient for transportation compared with the traditional three-phase high-power diesel generator.

[0033] 2. For the operation system and method of the STATCOM mode of the flexible DC transmission system provided by the present invention, the current-limiting resistor is connected to the grounding end of the single-phase AC voltage generator, which reduces the insulation requirement while limiting the charging current.

[0034] 3. For the operation system and method of the STATCOM mode of the flexible DC transmission system provided by the present invention, the three-phase disconnector on the AC side is disconnected during the unlocking stage, and it no longer depends on the power supply of the AC voltage generator. Instead, it relies on the energy stored in the sub-module capacitors to carry out the STATCOM operation test, further reducing the selection requirements for the AC voltage generator.

[0035] 4. The operating system and method of the STATCOM mode of the flexible DC transmission system provided by the present invention have a simple structure and convenient operation, and include three complete stages of uncontrolled charging, controllable charging, and unlocking operation, meeting the requirements for verifying the basic performance of the offshore flexible DC converter valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the topology diagram of the STATCOM debugging system of the converter valve of the flexible DC transmission system provided by the present invention;

[0037] Figure 2 is the method flow chart of the STATCOM debugging system of the converter valve of the flexible DC transmission system provided by the present invention;

[0038] Figure 3 is the path diagram of the uncontrolled rectifier charging of the positive half-wave voltage of the single-phase AC voltage generator provided by the present invention;

[0039] Figure 4 is the path diagram of the uncontrolled rectifier charging of the negative half-wave voltage of the single-phase AC voltage generator provided by the present invention;

[0040] Figure 5 is the path diagram of the controlled rectifier charging of the positive half-wave voltage of the single-phase AC voltage generator provided by the present invention;

[0041] Figure 6 is the path diagram of the controlled rectifier charging of the negative half-wave voltage of the single-phase AC voltage generator provided by the present invention;

[0042] Figure 7 is the current path diagram of the converter valve unlocking open-loop wave generation STATCOM no-load debugging mode provided by the present invention;

[0043] Figure 8 is the detailed simulation waveform diagram corresponding to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The present invention will be further described in detail below with reference to the accompanying drawings.

[0045] As Figure 1As shown in the figure, an operating system in STATCOM mode of a flexible DC transmission system provided by the present invention includes a disconnector on phase A, a single-phase AC voltage generator AC, a disconnector on phase B, a disconnector on phase C, and a current-limiting resistor R. Among them, one AC side of a phase of the flexible DC transmission converter valve is connected to the output terminal of the single-phase AC voltage generator AC through the disconnector on phase A; the remaining two AC sides of the flexible DC transmission converter valve are respectively connected to the disconnector on phase B and the disconnector on phase C; the other ends of the disconnector on phase B and the disconnector on phase C are connected in parallel to the current-limiting resistor R; the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator AC. Connecting the current-limiting resistor R to the grounding terminal of the single-phase AC voltage generator AC can reduce the voltage insulation level of the current-limiting resistor R, thereby reducing the cost of the current-limiting resistor R.

[0046] The flexible DC transmission converter valve includes six bridge arms, and each bridge arm is composed of a number of half-bridge modules.

[0047] The DC side of the flexible DC transmission converter valve is connected in an open-circuit manner.

[0048] A simplified commissioning method for a flexible DC transmission converter valve system provided by the present invention includes a charging stage and an unlocking stage. Among them, in the charging stage, the single-phase AC voltage generator AC is used to supply power to the flexible DC transmission converter valve, the current-limiting resistor R is used to limit the current in the power supply circuit, and the sub-module voltage is charged to the rated voltage value of the sub-module through the uncontrolled charging and active charging modes; in the unlocking stage, the connection between the three-phase disconnector and the single-phase AC voltage generator AC is first disconnected, the flexible DC transmission converter valve is unlocked for open-loop wave generation under no-load conditions, and the energy stored in the module capacitor is used to carry out the test of the STATCOM commissioning mode to complete the verification of the relevant functions of the flexible DC transmission converter valve.

[0049] During the charging stage, when the sub-module voltage is charged to the rated voltage value of the sub-module through the uncontrolled charging mode, the charging path of the uncontrolled rectifier charging of the positive half-wave voltage of the single-phase AC voltage generator AC is as Figure 3 shown:

[0050] The output terminal of the single-phase AC voltage generator AC is sequentially connected to the antiparallel diode of the lower arm of the module of the upper bridge arm of phase A of the flexible DC transmission converter valve and the reactor of the upper bridge arm of phase A through the isolating switch of phase A; the reactor of the upper bridge arm of phase A is respectively connected to the reactor of the upper bridge arm of phase B and the reactor of the upper bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the upper bridge arm of phase B is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of phase B, the module capacitor, and the isolating switch of phase B; the reactor of the upper bridge arm of phase C is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of phase C, the module capacitor, and the isolating switch of phase C; the isolating switches of phase B and phase C are connected in parallel and then connected to the current-limiting resistor R, and the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator; to charge the module capacitors of the upper bridge arms of phase B and phase C of the flexible DC transmission converter valve.

[0051] The output terminal of the single-phase AC voltage generator AC is sequentially connected to the antiparallel diode of the upper arm of the module of the lower bridge arm of phase A of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of phase A through the isolating switch of phase A; the reactor of the lower bridge arm of phase A is respectively connected to the reactor of the lower bridge arm of phase B and the reactor of the lower bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the lower bridge arm of phase B is connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of phase B and the isolating switch of phase B; the reactor of the lower bridge arm of phase C is connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of phase C and the isolating switch of phase C; the isolating switches of phase B and phase C are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator AC through the current-limiting resistor R; to charge the module capacitor of the lower bridge arm of phase A of the flexible DC transmission converter valve.

[0052] During the charging stage, when the sub-module voltage is charged to the rated voltage value of the sub-module through the uncontrolled charging mode, the charging path of the uncontrolled rectifier charging of the negative half-wave voltage of the single-phase AC voltage generator AC is as Figure 4 shown:

[0053] The grounding terminal of the single-phase AC voltage generator AC is connected in parallel to the isolating switches of phase B and phase C through the current-limiting resistor R; the other end of the isolating switch of phase B is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of phase B and the reactor of the upper bridge arm of phase B of the flexible DC transmission converter valve; the other end of the isolating switch of phase C is sequentially connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of phase C and the reactor of the upper bridge arm of phase C of the flexible DC transmission converter valve; the other ends of the reactors of the upper bridge arms of phase B and phase C are both connected to the reactor of the upper bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the upper bridge arm of phase A is connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of phase A and the module capacitor of the flexible DC transmission converter valve; the antiparallel diode of the upper arm of the module of the upper bridge arm of phase A and the module capacitor are connected to the output terminal of the single-phase AC voltage generator AC through the isolating switch of phase A; to charge the module capacitor of the upper bridge arm of phase A.

[0054] The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the phase B disconnector and the phase C disconnector through a current-limiting resistor R; the other end of the phase B disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the lower bridge arm of phase B of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of phase B; the other end of the phase C disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the lower bridge arm of phase C of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of phase C; the reactors of the lower bridge arms of phase B and phase C are both connected to the reactor of the lower bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the lower bridge arm of phase A is connected to the anti-parallel diode of the lower arm of the module of phase A of the lower bridge arm; the anti-parallel diode of the lower arm of the module of phase A of the lower bridge arm is connected to the output terminal of the single-phase AC voltage generator through the phase A disconnector; charging of the module capacitors of the lower bridge arms of phase B and phase C is achieved.

[0055] During the charging stage, when the sub-module voltage is charged to the rated voltage value of the sub-module through a controllable charging mode, the charging path for controllable rectifier charging of the positive half-wave voltage of the single-phase AC voltage generator AC is as Figure 5 shown:

[0056] The output terminal of the single-phase AC voltage generator AC is sequentially connected to the anti-parallel diode of the lower arm of the module of the upper bridge arm of phase A of the flexible DC transmission converter valve and the reactor of the upper bridge arm of phase A through the phase A disconnector; the reactor of the upper bridge arm of phase A is respectively connected to the reactor of the upper bridge arm of phase B and the reactor of the upper bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the upper bridge arm of phase B is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the upper bridge arm of phase B, the module capacitor, the IGBT of the lower arm in the off state, and the phase B disconnector; the reactor of the upper bridge arm of phase C is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the upper bridge arm of phase C, the module capacitor, the IGBT of the lower arm in the off state, and the phase C disconnector; the phase B disconnector and the phase C disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through a current-limiting resistor R; charging of the module capacitors of the upper bridge arms of phase B and phase C in the on state is achieved.

[0057] The output terminal of the single-phase AC voltage generator AC is sequentially connected, through the A-phase disconnector, to the anti-parallel diode of the upper arm of the module in the on state and the module capacitor of the lower bridge arm of the A-phase of the flexible DC transmission converter valve, the IGBT of the lower arm of the module in the off state, and the A-phase lower bridge arm reactor; the A-phase lower bridge arm reactor is respectively connected to the B-phase lower bridge arm reactor and the C-phase lower bridge arm reactor of the flexible DC transmission converter valve; the B-phase lower bridge arm reactor is sequentially connected to the anti-parallel diode of the lower arm of the module of the B-phase lower bridge arm and the B-phase disconnector; the C-phase lower bridge arm reactor is sequentially connected to the anti-parallel diode of the lower arm of the module of the C-phase lower bridge arm and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through the current-limiting resistor R; to charge the module capacitor of the A-phase lower bridge arm in the on state.

[0058] During the charging stage, when the sub-module voltage is charged to the rated voltage value of the sub-module through the controllable charging mode, the charging path of the controllable rectifier charging of the negative half-wave voltage of the single-phase AC voltage generator AC is as Figure 6 shown:

[0059] The grounding terminal of the single-phase AC voltage generator AC is connected in parallel to the B-phase disconnector and the C-phase disconnector through the current-limiting resistor R; the B-phase disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the B-phase upper bridge arm and the B-phase upper bridge arm reactor of the flexible DC transmission converter valve; the C-phase disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the C-phase upper bridge arm and the C-phase upper bridge arm reactor of the flexible DC transmission converter valve; the B-phase upper bridge arm reactor and the C-phase upper bridge arm reactor are connected in parallel and then connected to the A-phase upper bridge arm reactor; the A-phase upper bridge arm reactor is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state and the module capacitor of the A-phase upper bridge arm, the IGBT of the lower arm of the module in the off state, and the A-phase disconnector; the A-phase disconnector is connected to the output terminal of the single-phase AC voltage generator AC; to charge the module capacitor of the A-phase upper bridge arm in the on state.

[0060] The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the B-phase disconnector and the C-phase disconnector through a current-limiting resistor R; the other end of the B-phase disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the B-phase lower arm of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower arm of the module in the off state, and the B-phase lower arm reactor; the other end of the C-phase disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the C-phase lower arm of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower arm of the module in the off state, and the C-phase lower arm reactor; the B-phase lower arm reactor and the C-phase lower arm reactor are connected in parallel and then sequentially connected to the A-phase lower arm reactor, the anti-parallel diode of the lower arm of the module of the A-phase lower arm, and the A-phase disconnector; the A-phase disconnector is connected to the output terminal of the single-phase AC voltage generator AC; to charge the module capacitors in the on state of the B-phase lower arm and the module capacitors in the on state of the C-phase lower arm.

[0061] In the unlocking stage, unlock the flexible DC transmission converter valve to enter the no-load open-loop wave generation STATCOM no-load commissioning mode. Since the electrical connections on both the AC side and the DC side of the flexible DC transmission converter valve are disconnected, the current in the converter valve only circulates internally. The current directions of the upper and lower arms of each phase of the converter valve are the same, and the magnitudes are the same. The three-phase current of the converter valve is superimposed to zero, similar to the three-phase symmetrical current of the AC power grid; there are six current flow paths in the converter valve, which are respectively:

[0062] The first is that the current of phase A flows to phase B and phase C, that is, the module capacitor in the on state of phase A discharges, and the module capacitors in the on state of phase B and phase C are charged;

[0063] The second is that the currents of phase A and phase B flow to phase C, that is, the module capacitors in the on state of phase A and phase B discharge, and the module capacitor in the on state of phase C is charged;

[0064] The third is that the current of phase B flows to phase C and phase A, that is, the module capacitor in the on state of phase B discharges, and the module capacitors in the on state of phase C and phase A are charged;

[0065] The fourth is that the currents of phase B and phase C flow to phase A, that is, the module capacitors in the on state of phase B and phase C discharge, and the module capacitor in the on state of phase A is charged;

[0066] The fifth is that the current of phase C flows to phase A and phase B, that is, the module capacitor in the on state of phase C discharges, and the module capacitors in the on state of phase A and phase B are charged;

[0067] The sixth is that the currents of phase C and phase A flow to phase B, that is, the module capacitors in the on state of phase C and phase A discharge, and the module capacitor in the on state of phase B is charged.

[0068] TakingFigure 7 Taking the first case shown as an example, taking the current flow of phase A of the converter valve to phase B and phase C as an example, the current path 1 is as follows:

[0069] The upper IGBT and module capacitor of the modules in the on state of the upper and lower arms of phase A, the antiparallel diode of the lower arm of the module in the off state, and the arm reactor are connected to the antiparallel diode and module capacitor of the upper arm of the modules in the on state of the upper and lower arms of phase B, the IGBT of the lower arm of the module in the off state, and the arm reactor.

[0070] The current path 2 is as follows:

[0071] The upper IGBT and module capacitor of the modules in the on state of the upper and lower arms of phase A, the antiparallel diode of the lower arm of the module in the off state, and the arm reactor are connected to the antiparallel diode and module capacitor of the upper arm of the modules in the on state of the upper and lower arms of phase C, the IGBT of the lower arm of the module in the off state, and the arm reactor. The module capacitor in the on state of phase A discharges, and the module capacitors in the on state of phase B and phase C are charged.

[0072] The specific steps are as follows:

[0073] Step 1: Disconnect the AC circuit breaker connected to the valve side of the transformer in the flexible DC transmission system, close the three-phase disconnecting switches connected to the single-phase AC voltage generator AC, and connect the flexible DC transmission converter valve to the single-phase AC voltage generator AC and the current-limiting resistor R;

[0074] Step 2: To limit the charging speed of the module capacitor and reduce the supply power current, the voltage of the AC voltage generator can be slowly increased to perform uncontrolled rectifier charging on the flexible DC transmission converter valve module. When the voltage of the single-phase AC voltage generator AC reaches the set value, stop boosting;

[0075] Step 3: During the uncontrolled rectifier charging process, the power supply of the sub-module is energized and meets the condition for driving the module switching device. After the uncontrolled rectifier charging ends, enter the controllable charging stage. In the controllable charging stage, a part of the modules with high voltage ranking in all power sub-modules within each control cycle are cut off at a certain rising slope for controllable charging, and the module voltage is charged to the rated value. The upper limit of the number of modules to be cut off should enable the module voltage to reach the rated value;

[0076] Step 4: After the module voltage is charged to the rated value, disconnect the A-phase disconnecting switch connected to the single-phase AC voltage generator AC and the disconnecting switch between the parallel phases, and wait for unlocking to perform the no-load open-loop wave generation test;

[0077] Step 5: Conduct an unloaded wave - sending test on the flexible DC transmission converter valve. Specifically: Generate a three - phase symmetrical modulation wave in open - loop, then generate the conduction module numbers of the six arms of the converter valve, and generate the trigger signals of the switching devices of each module through a sorting algorithm to conduct an unloaded wave - sending functional test;

[0078] Step 6: After the test is completed, end the test and rectify the recorded test problems.

[0079] Furthermore, in Step 2, when the flexible DC transmission converter valve module is charged by uncontrolled rectification, the minimum voltage of the single - phase AC voltage generator AC should satisfy the following formula:

[0080] The final voltage after the single - phase AC voltage generator AC is boosted should enable the power sub - module energy - taking power supply to be reliably energized. The minimum voltage of the single - phase AC voltage generator AC is:

[0081]

[0082] where U s_min is the effective value of the minimum voltage of the voltage generator, N is the number of modules in a single arm of the converter valve, U sm1 is the reliable energization voltage of the module energy - taking power supply, and U R is the voltage drop across the current - limiting resistor R.

[0083] Furthermore, in Step 3, during the controllable charging stage, to increase the module voltage from the voltage after uncontrolled rectification charging to the rated voltage, a part of the modules needs to be removed to reduce the number of modules in the charging circuit, thereby increasing the module voltage. Then the upper limit of the number of removed modules is:

[0084]

[0085] where N off is the upper limit of the number of modules to be removed for the module voltage to rise to the rated value, and U sm_rate is the rated voltage of the module;

[0086] The rising slope of the number of removed modules affects the current of the AC voltage generator. The greater the rising rate, the module capacitance cannot quickly balance the potential of the charging circuit due to the charging speed, which will increase the current of the single - phase AC voltage generator AC. Therefore, it is necessary to match the module removal rate to limit the AC current within the tolerance range of the AC voltage generator.

[0087] Further, in step 5, after disconnecting the single-phase AC voltage generator AC, the converter valve has no energy replenishment power supply. However, the module energy extraction power supply, voltage equalizing resistors, the losses generated during the switching process of switching devices, and the series resistors of the valve tower continuously consume the energy in the module capacitors, causing the module voltage to continuously drop. To slow down the rate of module voltage drop, the peak value of the open-loop modulation wave can be reduced, the number of switched modules can be decreased, the switching frequency can be lowered, and the arm current can be reduced, thereby reducing the losses of the switching devices.

[0088] Further, in step 6, to ensure reliable blocking of the converter valve, the test needs to be ended before the power supply of the energy extraction power supply is cut off. When the average module voltage is lower than the set value (the set value of the average module voltage > the power-off voltage of the module energy extraction power supply), the converter valve is blocked and the test is ended. After the test is completed, the recorded test problems are rectified.

[0089] Further, the STATCOM operation strategy can solve the functional verification of the start-up of the flexible DC converter valve and open-loop wave generation.

[0090] As Figure 8 shown, the detailed simulation waveforms corresponding to the embodiments of the present invention are respectively the DC voltage, module voltage, arm current, and power supply current. Among them, in the first stage, it is uncontrolled rectifier charging. As the voltage of the AC voltage generator slowly rises, the DC voltage, module voltage, arm current, and power supply current all increase accordingly. When the AC voltage generator reaches the voltage set value, after reaching a new equilibrium state, the arm current and power supply current decrease appropriately, and the DC voltage and module voltage remain basically unchanged. In the second stage, it is controllable charging. As the number of removed modules increases, the charging voltage of the modules is less than the voltage lost by the removed modules, and the DC voltage will slightly drop. The module voltage, arm current, and power supply current all increase accordingly. When the number of removed modules reaches the upper limit, the module voltage tends to be stable. After reaching a new equilibrium state, the arm current and power supply current decrease appropriately. In the third stage, the converter valve is unlocked and open-loop wave generation enters the STATCOM no-load commissioning mode. As the energy in the module capacitors decreases, the DC voltage, module voltage, and arm current all decrease.

[0091] Finally, it should be noted that: the technical solutions of the present invention are only illustrated in combination with the above embodiments and are not limited thereby. Those of ordinary skill in the art should understand that: those skilled in the art can modify the specific embodiments of the present invention or make equivalent replacements, but these modifications or changes are all within the scope of the claims pending for approval.

Claims

1. A simplified commissioning method for a flexible DC transmission converter valve system at sea, characterized in that, An operating system based on the STATCOM mode of a flexible DC transmission system, the system includes a disconnector on phase A, a single-phase AC voltage generator AC, a disconnector on phase B, a disconnector on phase C and a current-limiting resistor R. Among them, one-phase AC side of the flexible DC transmission converter valve is connected to the output terminal of the single-phase AC voltage generator AC through the disconnector on phase A; the remaining two-phase AC sides of the flexible DC transmission converter valve are respectively connected to the disconnector on phase B and the disconnector on phase C; the other ends of the disconnector on phase B and the disconnector on phase C are connected in parallel with the current-limiting resistor R; the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator AC; Including the following steps: This debugging method includes a charging stage and an unlocking stage. Among them, the charging stage: use the single-phase AC voltage generator AC to supply power to the flexible DC transmission converter valve, use the current-limiting resistor R to limit the current of the power supply circuit, and charge the sub-module voltage to the rated voltage value of the sub-module through the uncontrolled charging and active charging modes; Unlocking stage: First, disconnect the wiring between the three-phase disconnector and the single-phase AC voltage generator AC, unlock the flexible DC transmission converter valve to perform no-load open-loop wave generation, and use the energy stored in the module capacitor to carry out the test of the STATCOM debugging mode to complete the verification of the relevant functions of the flexible DC transmission converter valve.

2. The simplified commissioning method of a flexible DC transmission converter valve system for offshore use according to claim 1, wherein Step 1, disconnect the AC circuit breaker connected to the valve side of the flexible DC system transformer in the flexible DC transmission system, close the three-phase disconnector connected to the single-phase AC voltage generator AC, and connect the flexible DC transmission converter valve to the single-phase AC voltage generator AC and the current-limiting resistor R; Step 2, slowly raise the voltage of the single-phase AC voltage generator AC to perform uncontrolled rectification charging on the flexible DC transmission converter valve module until the voltage of the single-phase AC voltage generator AC reaches the set value and then stop boosting; Step 3, cut off the part of the modules with high voltage ranking in all power sub-modules in each control cycle according to the set rising slope for controllable charging, and charge the module voltage to the rated value; Step 4, disconnect the three-phase disconnector connected to the single-phase AC voltage generator AC; wait for unlocking to perform a no-load open-loop wave generation test; Step 5, perform a no-load wave generation test on the flexible DC transmission converter valve; Step 6, after the test is completed, end the test.

3. The simplified commissioning method of a flexible DC transmission converter valve system for offshore use according to claim 2, characterized in that, In step 2, when performing uncontrolled rectification charging on the flexible DC transmission converter valve module, the minimum voltage of the single-phase AC voltage generator AC should satisfy the following formula: Among them, U s_min is the effective value of the lowest voltage of the voltage generator, N is the number of modules in a single bridge arm of the commutation valve, and U sm1 is the reliable energized voltage of the module power supply, and U R is the voltage drop across the current-limiting resistor R.

4. The simplified commissioning method of a flexible DC power transmission converter valve system for offshore use according to claim 3, characterized in that, In step 3, cut off the part of the modules with high voltage ranking in all power sub-modules in each control cycle; the upper limit of the part of the modules is: Among them, N off is the upper limit that needs to be cut off when the module voltage rises to the rated value, and U sm_rate is the rated voltage of the module.

5. A simplified commissioning method for a flexible DC transmission converter valve system in the sea according to claim 1, characterized in that, The output terminal of the single-phase AC voltage generator AC is connected in sequence, through the A-phase disconnector, to the antiparallel diode of the lower arm of the module of the upper bridge arm of the A-phase of the flexible DC transmission converter valve and the reactor of the upper bridge arm of the A-phase; the reactor of the upper bridge arm of the A-phase is respectively connected to the reactor of the upper bridge arm of the B-phase and the reactor of the upper bridge arm of the C-phase of the flexible DC transmission converter valve; the reactor of the upper bridge arm of the B-phase is connected in sequence to the antiparallel diode of the upper arm of the module of the upper bridge arm of the B-phase, the module capacitor, and the B-phase disconnector; the reactor of the upper bridge arm of the C-phase is connected in sequence to the antiparallel diode of the upper arm of the module of the upper bridge arm of the C-phase, the module capacitor, and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the current-limiting resistor R, and the other end of the current-limiting resistor R is connected to the grounding terminal of the single-phase AC voltage generator. The output terminal of the single-phase AC voltage generator AC is connected in sequence, through the A-phase disconnector, to the antiparallel diode of the upper arm of the module of the lower bridge arm of the A-phase of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of the A-phase; the reactor of the lower bridge arm of the A-phase is respectively connected to the reactor of the lower bridge arm of the B-phase and the reactor of the lower bridge arm of the C-phase of the flexible DC transmission converter valve; the reactor of the lower bridge arm of the B-phase is connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of the B-phase and the B-phase disconnector; the reactor of the lower bridge arm of the C-phase is connected to the antiparallel diode of the lower arm of the module of the lower bridge arm of the C-phase and the C-phase disconnector; the B-phase disconnector and the C-phase disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator AC through the current-limiting resistor R.

6. The simplified commissioning method of a flexible HVDC converter valve system for offshore use according to claim 1, characterized in that, The grounding terminal of the single-phase AC voltage generator AC is connected in parallel, through the current-limiting resistor R, to the B-phase disconnector and the C-phase disconnector; the other end of the B-phase disconnector is connected in sequence to the antiparallel diode of the upper arm of the module of the upper bridge arm of the B-phase and the reactor of the upper bridge arm of the B-phase of the flexible DC transmission converter valve; the other end of the C-phase disconnector is connected in sequence to the antiparallel diode of the upper arm of the module of the upper bridge arm of the C-phase and the reactor of the upper bridge arm of the C-phase of the flexible DC transmission converter valve; the other ends of the reactor of the upper bridge arm of the B-phase and the reactor of the upper bridge arm of the C-phase are both connected to the reactor of the upper bridge arm of the A-phase of the flexible DC transmission converter valve, and the reactor of the upper bridge arm of the A-phase is connected to the antiparallel diode of the upper arm of the module of the upper bridge arm of the A-phase and the module capacitor of the flexible DC transmission converter valve; the antiparallel diode of the upper arm of the module of the upper bridge arm of the A-phase and the module capacitor are connected to the output terminal of the single-phase AC voltage generator AC through the A-phase disconnector. The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the phase B disconnector and the phase C disconnector through a current-limiting resistor R; the other end of the phase B disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the lower bridge arm of phase B of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of phase B; the other end of the phase C disconnector is sequentially connected to the anti-parallel diode of the upper arm of the module of the lower bridge arm of phase C of the flexible DC transmission converter valve, the module capacitor, and the reactor of the lower bridge arm of phase C; the reactors of the lower bridge arms of phase B and phase C are both connected to the reactor of the lower bridge arm of phase A of the flexible DC transmission converter valve, and the reactor of the lower bridge arm of phase A is connected to the anti-parallel diode of the lower arm of the module of phase A; the anti-parallel diode of the lower arm of the module of phase A is connected to the output terminal of the single-phase AC voltage generator through the phase A disconnector.

7. A simplified commissioning method for a flexible DC transmission converter valve system in the sea according to claim 1, characterized in that The output terminal of the single-phase AC voltage generator AC is sequentially connected to the anti-parallel diode of the lower arm of the module of the upper bridge arm of phase A of the flexible DC transmission converter valve and the reactor of the upper bridge arm of phase A through the phase A disconnector; the reactor of the upper bridge arm of phase A is respectively connected to the reactor of the upper bridge arm of phase B and the reactor of the upper bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the upper bridge arm of phase B is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the upper bridge arm of phase B, the module capacitor, the IGBT of the lower arm of the module in the off state, and the phase B disconnector; the reactor of the upper bridge arm of phase C is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the upper bridge arm of phase C, the module capacitor, the IGBT of the lower arm of the module in the off state, and the phase C disconnector; the phase B disconnector and the phase C disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through the current-limiting resistor R; The output terminal of the single-phase AC voltage generator AC is sequentially connected to the anti-parallel diode of the upper arm of the module in the on state of the lower bridge arm of phase A of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower arm of the module in the off state, and the reactor of the lower bridge arm of phase A through the phase A disconnector; the reactor of the lower bridge arm of phase A is respectively connected to the reactor of the lower bridge arm of phase B and the reactor of the lower bridge arm of phase C of the flexible DC transmission converter valve; the reactor of the lower bridge arm of phase B is sequentially connected to the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase B and the phase B disconnector; the reactor of the lower bridge arm of phase C is sequentially connected to the anti-parallel diode of the lower arm of the module of the lower bridge arm of phase C and the phase C disconnector; the phase B disconnector and the phase C disconnector are connected in parallel and then connected to the grounding terminal of the single-phase AC voltage generator through the current-limiting resistor R.

8. The simplified commissioning method of a flexible DC power transmission converter valve system for offshore use according to claim 1, wherein The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the phase B disconnector and the phase C disconnector through a current-limiting resistor R; the phase B disconnector is sequentially connected to the anti-parallel diode of the upper module arm of the phase B upper bridge arm of the flexible DC transmission converter valve and the phase B upper bridge arm reactor; the phase C disconnector is sequentially connected to the anti-parallel diode of the upper module arm of the phase C upper bridge arm of the flexible DC transmission converter valve and the phase C upper bridge arm reactor; the phase B upper bridge arm reactor and the phase C upper bridge arm reactor are connected in parallel and then connected to the phase A upper bridge arm reactor; the phase A upper bridge arm reactor is sequentially connected to the anti-parallel diode of the upper module arm in the on state of the phase A upper bridge arm, the module capacitor, the IGBT of the lower module arm in the off state, and the phase A disconnector; the phase A disconnector is connected to the output terminal of the single-phase AC voltage generator AC; The grounding terminal of the single-phase AC voltage generator AC is connected in parallel with the phase B disconnector and the phase C disconnector through a current-limiting resistor R; the other end of the phase B disconnector is sequentially connected to the anti-parallel diode of the upper module arm in the on state of the phase B lower bridge arm of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower module arm in the off state, and the phase B lower bridge arm reactor; the other end of the phase C disconnector is sequentially connected to the anti-parallel diode of the upper module arm in the on state of the phase C lower bridge arm of the flexible DC transmission converter valve, the module capacitor, the IGBT of the lower module arm in the off state, and the phase C lower bridge arm reactor; The phase B lower bridge arm reactor and the phase C lower bridge arm reactor are connected in parallel and then sequentially connected to the phase A lower bridge arm reactor, the anti-parallel diode of the lower module arm of the phase A lower bridge arm, and the phase A disconnector; the phase A disconnector is connected to the output terminal of the single-phase AC voltage generator AC.

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