LCC-HVDC system sending end power grid transient voltage active support control method and device

Abstract

The invention relates to the technical field of photovoltaic grid connection, and particularly provides an active support control method and an active support control device for transient voltage of a transmitting end power grid of an LCC-HVDC (line commutated converter high voltage direct current power transmission) system, and the active support control method and the active support control device for the transient voltage of the transmitting end power grid of the LCC-HVDC system. Comprising the following steps: correcting an output voltage phase of a synchronization link in a virtual synchronous generator control strategy based on active power and frequency output by a network construction type photovoltaic converter, and correcting an output voltage amplitude of a voltage amplitude link in the virtual synchronous generator control strategy based on a measured value of a sending end power grid voltage; and using the virtual synchronous generator control strategy to control the network construction type photovoltaic current converter in the LCC-HVDC system containing the network construction type photovoltaic current converter. According to the technical scheme provided by the invention, the stability of photovoltaic access to the weak power grid can be improved, and the reactive power output by the converter can be automatically adjusted after the transient voltage of the sending-end power grid occurs due to the commutation failure of the LCC-HVDC system, so that the transient voltage is effectively supported, and the phenomenon of reverse adjustment of the reactive power is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid-connected technology, and in particular to a method and device for actively supporting and controlling transient voltage of a power grid at a sending end of an LCC-HVDC system. Background Art

[0002] At present, the electricity of large-scale photovoltaic bases is mainly transmitted through the line commutated converter based high voltage direct current (LCC-HVDC) system. When a commutation failure or DC fault occurs in the LCC-HVDC system, it will cause surplus reactive power in the rectifier station, causing transient voltage in the sending-end grid. The transient voltage of the sending-end grid will be further transmitted to the photovoltaic collection area, causing some photovoltaic inverters with weak fault ride-through capabilities to be disconnected from the grid, further expanding the scope of the accident and affecting the safe and stable operation of the power grid.

[0003] When the traditional grid-following control strategy is adopted, when the voltage at the grid connection point is lower than the threshold value (0.9pu), the converter can automatically output reactive power to support the grid voltage according to the voltage drop amplitude, and the dynamic response time is about 20ms. The large number of converters further increases the complexity of regulation. After the fault occurs, due to the voltage measurement link, there will be a delay problem in the process of voltage conversion from low voltage to high voltage, resulting in the delayed output of reactive power during the high voltage period, aggravating the transient overvoltage amplitude. For the transient voltage support of the LCC-HVDC system, it currently mainly relies on additional synchronous phase regulators or improving the fault ride-through capability of new energy equipment. Phase regulators can effectively improve the short-circuit ratio of the AC power grid and suppress the transient overvoltage amplitude, but greatly increase the system operation cost. By optimizing the control parameters of photovoltaic converters using grid-following control, a certain support effect can be achieved, but it is difficult to apply in large quantities in weak power grids. Summary of the invention

[0004] In order to overcome the above-mentioned defects, the present invention proposes a method and device for actively supporting and controlling transient voltage of a power grid at the sending end of an LCC-HVDC system.

[0005] In a first aspect, a method for actively supporting and controlling transient voltage of a power grid at a sending end of an LCC-HVDC system is provided. The method for actively supporting and controlling transient voltage of a power grid at a sending end of an LCC-HVDC system comprises:

[0006] The output voltage phase of the synchronization link in the virtual synchronous generator control strategy is corrected based on the active power and frequency output by the grid-forming photovoltaic converter, and the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is corrected based on the measured value of the sending-end grid voltage;

[0007] The virtual synchronous generator control strategy is used to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter.

[0008] Preferably, the LCC-HVDC system adopts a bipolar 12-pulse topology.

[0009] Preferably, the trigger angle instruction of the rectifier-side constant current controller of the LCC-HVDC system is as follows:

[0010] α r,ref =min{α r,min ,π-β r,cc}

[0011] In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows:

[0012] β r,cc =k p,rcc △I dr +k i,rcc ∫△I dr dt

[0013] In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0014] Preferably, the Echizen trigger angle instruction of the inverter-side constant current controller of the LCC-HVDC system is as follows:

[0015] β i,cc =k p,icc △I di +k i,icc ∫△I dr dt

[0016] In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I di is the second current difference, △Idi =I dr,ref -I di -0.1, I di is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0017] Preferably, the Echizen trigger angle instruction of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows:

[0018] β i,cea =k p,icea △γ+k i,icea ∫△γdt

[0019] In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, k p,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec}, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

[0020] Preferably, the output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0021] θ c =θ c1 +k d (ω c -ω0)

[0022] In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω cis the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0023]

[0024] In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), k pc is the droop coefficient, P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

[0025] Preferably, the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows:

[0026]

[0027] In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

[0028] In a second aspect, a device for actively supporting and controlling transient voltage of a power grid at a sending end of an LCC-HVDC system is provided, wherein the device for actively supporting and controlling transient voltage of a power grid at a sending end of the LCC-HVDC system comprises:

[0029] An analysis module is used to correct the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-forming photovoltaic converter, and to correct the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the sending-end grid voltage;

[0030] The control module is used to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter by using the virtual synchronous generator control strategy.

[0031] Preferably, the LCC-HVDC system adopts a bipolar 12-pulse topology.

[0032] Preferably, the trigger angle instruction of the rectifier-side constant current controller of the LCC-HVDC system is as follows:

[0033] α r,ref =min{α r,min ,π-β r,cc}

[0034] In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows:

[0035] β r,cc =k p,rcc △I dr +k i,rcc ∫△I dr dt

[0036] In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0037] Preferably, the Echizen trigger angle instruction of the inverter-side constant current controller of the LCC-HVDC system is as follows:

[0038] β i,cc =k p,icc △I di +k i,icc ∫△I dr dt

[0039] In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I diis the second current difference, △I di =I dr,ref -I di -0.1, I di is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0040] Preferably, the Echizen trigger angle instruction of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows:

[0041] β i,cea =k p,icea △γ+k i,icea ∫△γdt

[0042] In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, k p,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec}, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

[0043] Preferably, the output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0044] θ c =θ c1 +k d (ω c -ω0)

[0045] In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω cis the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0046]

[0047] In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), k pc is the droop coefficient, P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

[0048] Preferably, the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows:

[0049]

[0050] In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

[0051] In a third aspect, a computer device is provided, comprising: one or more processors;

[0052] The processor is configured to execute one or more programs;

[0053] When the one or more programs are executed by the one or more processors, the LCC-HVDC system sending-end power grid transient voltage active support control method is implemented.

[0054] In a fourth aspect, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed, the method for actively supporting and controlling transient voltage of a power grid at a sending end of an LCC-HVDC system is implemented.

[0055] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects:

[0056] The present invention provides a method and device for actively supporting and controlling transient voltage of the power grid at the sending end of an LCC-HVDC system, including: correcting the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-type photovoltaic converter, and correcting the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the voltage of the sending end power grid; and using the virtual synchronous generator control strategy to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter. The technical solution provided by the present invention can improve the stability of photovoltaic access to a weak power grid, and can automatically adjust the reactive power output by the converter by utilizing the constant voltage characteristic after a commutation failure occurs in the LCC-HVDC system causing a transient voltage to appear in the sending end power grid, thereby achieving effective support for the transient voltage and preventing the occurrence of reactive power "reverse regulation" phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic flow chart of main steps of a method for actively supporting transient voltage of a power grid at the sending end of an LCC-HVDC system according to an embodiment of the present invention;

[0058] Figure 2 1 is a schematic diagram of a bipolar 12-pulse topology structure of an embodiment of the present invention;

[0059] Figure 3 1. is a framework diagram of an LCC-HVDC system including a grid-type photovoltaic converter according to an embodiment of the present invention;

[0060] Figure 4 is a transient voltage waveform diagram caused by commutation failure of the LCC-HVDC system according to an embodiment of the present invention;

[0061] Figure 5 is a voltage reference value calculation principle diagram of an embodiment of the present invention;

[0062] Among them, 1 is a photovoltaic power generation unit, 2 is a photovoltaic inverter, 3 is an AC filter, 4 is a box-type transformer, 5 is a distributed phase regulator, 6 is a sending-end AC system, 7 is a filtering and reactive power compensation device, and 8 is an LCC-HVDC system. DETAILED DESCRIPTION

[0063] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0064] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] As disclosed in the background technology, the electric energy of large-scale photovoltaic bases is currently mainly transmitted through the line commutated converter based high voltage direct current (LCC-HVDC) system. When a commutation failure or DC fault occurs in the LCC-HVDC system, the rectifier station will have surplus reactive power, causing transient voltage in the sending-end grid. The transient voltage of the sending-end grid will be further transmitted to the photovoltaic collection area, causing some photovoltaic inverters with weak fault ride-through capabilities to be disconnected from the grid, further expanding the scope of the accident and affecting the safe and stable operation of the power grid.

[0066] When the traditional grid-following control strategy is adopted, when the voltage at the grid connection point is lower than the threshold value (0.9pu), the converter can automatically output reactive power to support the grid voltage according to the voltage drop amplitude, and the dynamic response time is about 20ms. The large number of converters further increases the complexity of regulation. After the fault occurs, due to the voltage measurement link, there will be a delay problem in the process of voltage conversion from low voltage to high voltage, resulting in the delayed output of reactive power during the high voltage period, aggravating the transient overvoltage amplitude. For the transient voltage support of the LCC-HVDC system, it currently mainly relies on additional synchronous phase regulators or improving the fault ride-through capability of new energy equipment. Phase regulators can effectively improve the short-circuit ratio of the AC power grid and suppress the transient overvoltage amplitude, but greatly increase the system operation cost. By optimizing the control parameters of photovoltaic converters using grid-following control, a certain support effect can be achieved, but it is difficult to apply in large quantities in weak power grids.

[0067] In order to improve the above problems, the present invention provides a method and device for actively supporting and controlling transient voltage in the power grid at the sending end of an LCC-HVDC system, including: correcting the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-type photovoltaic converter; correcting the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the voltage of the sending-end power grid; and controlling the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter by using the virtual synchronous generator control strategy. The technical solution provided by the present invention can improve the stability of photovoltaic access to a weak power grid, and can automatically adjust the reactive power output by the converter by using the constant voltage characteristic after a commutation failure occurs in the LCC-HVDC system causing a transient voltage in the sending-end power grid, thereby achieving effective support for the transient voltage and preventing the occurrence of reactive power "reverse regulation" phenomenon.

[0068] The above scheme is described in detail below.

[0069] Example 1

[0070] See attached Figure 1 , Figure 1 FIG. 1 is a flow chart showing the main steps of a method for actively supporting transient voltage of a power grid at the sending end of an LCC-HVDC system according to an embodiment of the present invention. Figure 1 As shown, the LCC-HVDC system sending-end grid transient voltage active support control method in the embodiment of the present invention mainly includes the following steps:

[0071] Step S101: correcting the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-forming photovoltaic converter, and correcting the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the sending-end grid voltage; in this embodiment, the correction process of the output voltage phase of the synchronization link and the output voltage phase of the synchronization link in the virtual synchronous generator control strategy can be performed simultaneously or successively;

[0072] Step S102: using the virtual synchronous generator control strategy to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter.

[0073] In this embodiment, the system architecture is implemented by using a photovoltaic inverter and an LCC-HVDC system. The overall architecture is as follows: Figure 2 As shown. Among them, 1 is a photovoltaic power generation unit, 2 is a photovoltaic inverter, 3 is an AC filter, 4 is a box-type transformer, 5 is a distributed phase regulator, 6 is a sending-end AC system, 7 is a filter and reactive power compensation device, and 8 is an LCC-HVDC system.

[0074] In this embodiment, the LCC-HVDC system adopts a bipolar 12-pulse topology structure. Figure 3 shown.

[0075] In this embodiment, the trigger angle instruction of the constant current controller on the rectifier side of the LCC-HVDC system is as follows:

[0076] α r,ref =min{α r,min ,π-β r,cc}

[0077] In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows:

[0078] β r,cc =k p,rcc △I dr +k i,rcc ∫△I dr dt

[0079] In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0080] In this embodiment, the Echizen trigger angle instruction of the inverter-side constant current controller of the LCC-HVDC system is as follows:

[0081] β i,cc =k p,icc △I di +k i,icc ∫△I dr dt

[0082] In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I di is the second current difference, △I di =I dr,ref -I di -0.1, Idi is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0083] In this embodiment, the Echizen trigger angle instruction of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows:

[0084] β i,cea =k p,icea △γ+k i,icea ∫△γdt

[0085] In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, k p,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec}, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

[0086] In this embodiment, since the active power and reactive power output by the grid-type photovoltaic inverter will change rapidly during the transient voltage change, in order to prevent output power oscillation, the output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0087] θ c =θ c1 +k d (ω c -ω0)

[0088] In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω cis the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0089]

[0090] In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), k pc is the droop coefficient, P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

[0091] In this embodiment, when using a grid-type photovoltaic inverter for transient voltage support, the reactive power output by the inverter needs to quickly match the change in transient voltage, and can quickly change from output power to absorbed reactive power after the voltage changes from low voltage to high voltage, to prevent the photovoltaic system from further raising the transient overvoltage amplitude. Therefore, it is necessary to reflect the grid voltage information in the voltage amplitude control link, and the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows:

[0092]

[0093] In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

[0094] In one embodiment, the PSCAD / EMTDC Figure 2In the model shown in Figure 1, the PV converter adopts the traditional grid-following control strategy and has the function of fault ride-through control. At t = 1.5s, a single-phase grounding fault occurs in the receiving-end AC system, causing the LCC-HVDC system to fail in commutation, resulting in transient voltage in the sending-end grid. The voltage waveform is shown in Figure 1. Figure 4 shown.

[0095] In order to improve the photovoltaic inverter's active support capability for transient voltage, the photovoltaic inverter can adopt a grid-building strategy, which can achieve self-synchronous operation without relying on an external AC power supply. Common grid-building control strategies include droop control, power synchronization control, virtual synchronous generator control, and matching control. The present invention adopts a virtual synchronous generator control strategy, and the voltage reference value V c The calculation principle is as follows Figure 5 shown.

[0096] Example 2

[0097] Based on the same inventive concept, the present invention also provides an active support control device for transient voltage of a power grid at the sending end of an LCC-HVDC system, and the active support control device for transient voltage of a power grid at the sending end of the LCC-HVDC system comprises:

[0098] An analysis module is used to correct the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-forming photovoltaic converter, and to correct the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the sending-end grid voltage;

[0099] The control module is used to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter by using the virtual synchronous generator control strategy.

[0100] Preferably, the LCC-HVDC system adopts a bipolar 12-pulse topology.

[0101] Preferably, the trigger angle instruction of the rectifier-side constant current controller of the LCC-HVDC system is as follows:

[0102] α r,ref =min{α r,min ,π-β r,cc}

[0103] In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows:

[0104] β r,cc =kp,rcc △I dr +k i,rcc ∫△I dr dt

[0105] In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0106] Preferably, the Echizen trigger angle instruction of the inverter-side constant current controller of the LCC-HVDC system is as follows:

[0107] β i,cc =k p,icc △I di +k i,icc ∫△I dr dt

[0108] In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I di is the second current difference, △I di =I dr,ref -I di -0.1, I di is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

[0109] Preferably, the Echizen trigger angle instruction of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows:

[0110] β i,cea =k p,icea △γ+k i,icea ∫△γdt

[0111] In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, kp,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec}, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

[0112] Preferably, the output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0113] θ c =θ c1 +k d (ω c -ω0)

[0114] In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω c is the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows:

[0115]

[0116] In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

[0117] Preferably, the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows:

[0118]

[0119] In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

[0120] Example 3

[0121] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the transient voltage active support control method of the sending-end power grid of the LCC-HVDC system in the above embodiment.

[0122] Example 4

[0123] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method for actively supporting the transient voltage of the power grid at the sending end of an LCC-HVDC system in the above embodiment.

[0124] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0125] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0126] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0127] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for actively supporting and controlling transient voltage of a power grid at the sending end of a power grid phase-commutated converter high voltage direct current transmission LCC-HVDC system, characterized in that: The method comprises: The output voltage phase of the synchronization link in the virtual synchronous generator control strategy is corrected based on the active power and frequency output by the grid-forming photovoltaic converter, and the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is corrected based on the measured value of the sending-end grid voltage; The virtual synchronous generator control strategy is used to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter.

2. The method according to claim 1, characterized in that The LCC-HVDC system adopts a bipolar 12-pulse topology.

3. The method according to claim 1, characterized in that The trigger angle command of the constant current controller on the rectifier side of the LCC-HVDC system is as follows: a r,ref =min{a r,min ,p-b r,cc } In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows: β r,cc =k p,rcc △I dr +k i,rcc ∫△I dr dt In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

4. The method according to claim 1, characterized in that The Echizen trigger angle command of the inverter-side constant current controller of the LCC-HVDC system is as follows: β i,cc =k p,icc △I di +k i,icc ∫△I dr dt In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I di is the second current difference, △I di =I dr,ref -I di -0.1, I di is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

5. The method according to claim 1, characterized in that The Echizen trigger angle command of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows: b i,cea =k p,icea △γ+k i,icea ∫△γdt In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, k p,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec }, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

6. The method according to claim 1, characterized in that The output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows: i c =θ c1 +k d (oh c -ω0) In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω c is the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows: In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), k pc is the droop coefficient, P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

7. The method according to claim 1, characterized in that The output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows: In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

8. An active support control device for transient voltage of power grid at the sending end of LCC-HVDC system, characterized in that: The device comprises: An analysis module is used to correct the output voltage phase of the synchronization link in the virtual synchronous generator control strategy based on the active power and frequency output by the grid-forming photovoltaic converter, and to correct the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy based on the measured value of the sending-end grid voltage; The control module is used to control the grid-type photovoltaic converter in the LCC-HVDC system containing the grid-type photovoltaic converter by using the virtual synchronous generator control strategy.

9. The device according to claim 8, characterized in that The LCC-HVDC system adopts a bipolar 12-pulse topology.

10. The device according to claim 8, characterized in that The trigger angle command of the constant current controller on the rectifier side of the LCC-HVDC system is as follows: a r,ref =min{a r,min ,p-b r,cc } In the above formula, α r,ref is the trigger angle command of the constant current controller on the rectifier side, α r,min is the lower limit of the trigger angle command of the constant current controller on the rectifier side, β r,cc is the Echizen trigger angle, wherein the Echizen trigger angle is as follows: β r,cc =k p,rcc △I dr +k i,rcc ∫△I dr dt In the above formula, k p,rcc and k i,rcc are the proportional coefficient and integral coefficient of the constant current controller on the rectifier side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr,ref is the DC current reference value obtained on the inverter side, I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

11. The device according to claim 8, characterized in that The Echizen trigger angle command of the inverter-side constant current controller of the LCC-HVDC system is as follows: β i,cc =k p,icc △I di +k i,icc ∫△I dr dt In the above formula, β i,cc is the Echizen firing angle command of the inverter side constant current controller, k p,icc and k i,icc are the proportional coefficient and integral coefficient of the constant current controller on the inverter side, △I di is the second current difference, △I di =I dr,ref -I di -0.1, I di is the DC current on the inverter side, I dr,ref is the DC current measurement value obtained on the inverter side, △I dr is the first current difference, △I dr =I dr,ref -I dr , I dr is the DC current measurement value obtained on the inverter side after filtering, and t is the time.

12. The device according to claim 8, characterized in that The Echizen trigger angle command of the inverter-side fixed shutdown angle controller of the LCC-HVDC system is as follows: b i,cea =k p,icea △γ+k i,icea ∫△γdt In the above formula, β i,cea is the Echizen trigger angle command of the inverter side fixed cut-off angle controller, k p,icea and k i,icea are the proportional coefficient and integral coefficient of the inverter side fixed turn-off angle controller, △γ is the turn-off angle deviation, △γ=max{△γ min ,γ ref -γ min +△γ cec }, △γ min is the minimum value of the turn-off angle deviation, γ ref is the cut-off angle reference value in the fixed cut-off angle controller, γ min is the lower limit of the turn-off angle in the fixed turn-off angle controller, △γ cec is the output value of the current deviation controller, and t is the time.

13. The device according to claim 8, characterized in that The output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows: i c =θ c1 +k d (oh c -ω0) In the above formula, θ c is the output voltage phase of the synchronization link in the virtual synchronous generator control strategy, θ c1 is the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy, k d is the oscillation suppression coefficient, ω c is the output angular frequency of the grid-type photovoltaic inverter, ω0 is the rated angular frequency of the power grid, wherein the initial output voltage phase of the synchronization link in the virtual synchronous generator control strategy is as follows: In the above formula, s is the Laplace operator, P refc is the active power reference value output by the grid-connected photovoltaic inverter, P refc =P refc0 -k pc (ω c -ω0), k pc is the droop coefficient, P refc0 is the active power reference value output by the initial grid-connected photovoltaic inverter, P c is the active power output by the grid-type photovoltaic converter, J is the moment of inertia of the grid-type photovoltaic converter, and D is the damping coefficient of the grid-type photovoltaic converter.

14. The device according to claim 8, characterized in that The output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy is as follows: In the above formula, V cmag is the output voltage amplitude of the voltage amplitude link in the virtual synchronous generator control strategy, k q0 is a constant droop coefficient, V acs1 is the reference value of the sending-end grid voltage, V ref is the measured value of the grid voltage at the sending end, Q refc is the reactive power reference value output by the grid-connected photovoltaic inverter, Q c is the reactive power output by the grid-connected photovoltaic inverter, k pq is the proportional coefficient of the PI controller, k iq is the integral coefficient of the PI controller, and s is the Laplace operator.

15. A computer device, characterized in that: include: one or more processors; The processor is configured to execute one or more programs; When the one or more programs are executed by the one or more processors, the method for actively supporting and controlling transient voltage of a power grid at the sending end of an LCC-HVDC system according to any one of claims 1 to 7 is implemented.

16. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the method for actively supporting and controlling transient voltage of a power grid at the sending end of an LCC-HVDC system according to any one of claims 1 to 7 is implemented.

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