Power grid supporting type high-voltage direct-current power transmission system

Abstract

The invention discloses a power grid supporting type high-voltage direct-current power transmission system, and belongs to the technical field of power systems. The system comprises a converter transformer, a static synchronous phase modifier, an LCC converter valve and an amplitude-phase corrector. The converter transformers are connected in parallel, the network side of each converter transformer is connected with a converter bus, and the valve side of each converter transformer is connected with an LCC converter valve; the static synchronous phase modifier is connected with the converter bus or the valve side of each converter transformer, and the amplitude-phase corrector is connected with the converter bus. According to the method, a 100% new energy unit can be configured, a conventional thermal power or hydroelectric generating set support is not needed, a static synchronous phase modifier replaces a conventional synchronous unit to maintain the system voltage stability, stable sending of island 100% new energy power generation is guaranteed, the equipment operation and maintenance complexity is greatly reduced, and characteristic harmonic waves generated by an LCC converter valve on a network side are reduced. Harmonic waves with low frequency are filtered by the static synchronous phase modifier, and harmonic waves with high frequency and high-frequency harmonic waves generated by the power electronic equipment are filtered by the amplitude-phase corrector.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a grid-supported high-voltage direct current transmission system. Background Technology

[0002] The core equipment of a conventional high-voltage direct current (LCC-HVDC) transmission system is the LCC converter valve. The LCC converter valve works by controlling the thyristors to conduct at a fixed angle within the power frequency cycle, thereby converting alternating current (AC) into direct current (DC). Because thyristors are semi-controlled switching devices, their commutation relies on a high-strength AC system. In isolated or weak AC systems, the LCC converter valve cannot operate normally. This prevents high-voltage direct current transmission from transmitting a high proportion of renewable energy sources, requiring the use of large-capacity hydropower or thermal power units. This significantly limits the application scenarios of high-voltage direct current technology. Furthermore, higher-frequency harmonics in the LCC converter valve cannot be filtered out.

[0003] Flexible DC transmission based on fully controllable devices (VSC-HVDC) can achieve large-scale new energy transmission without relying on AC grid support. However, the cost of converter valves for flexible DC transmission is very high, and its economic efficiency is far inferior to that of conventional DC transmission. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a grid-supported high-voltage direct current transmission system that can be configured with 100% new energy generating units. The static synchronous condenser replaces the conventional synchronous generator to maintain system voltage stability, ensuring the stable transmission of 100% new energy power generation from isolated areas.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution: This invention provides a grid-supported high-voltage direct current transmission system, including a converter transformer, a static synchronous condenser, an LCC converter valve, and an amplitude-phase corrector; Each converter transformer is connected in parallel, and each converter transformer is connected to a converter bus on the grid side and an LCC converter valve on the valve side. The static synchronous condenser is connected to the converter bus or the valve side of each converter transformer, and the amplitude-phase corrector is connected to the converter bus.

[0006] Optionally, the converter transformer is a Y / Y converter transformer or a Y / D converter transformer; The Y / Y converter transformer and Y / D converter transformer are connected to the DC line and grounding electrode for transmitting DC power through the LCC converter valve; the converter bus is connected to the new energy power station for generating AC power.

[0007] Optionally, the static synchronous condenser is connected to the converter bus or the valve side of each converter transformer in a direct-connect or step-down topology.

[0008] Optionally, the static synchronous condenser includes a VSC converter valve, which includes multiple bridge arm sub-modules. The bridge arm sub-modules are connected in a star, triangle, or double star configuration.

[0009] Optionally, when the bridge arm submodules are connected in a star or delta configuration, each bridge arm submodule is a full-bridge submodule, and a supercapacitor is connected in parallel on the DC side of the full-bridge submodule.

[0010] Optionally, when the bridge arm submodules are connected in a double star configuration, each bridge arm submodule is a half-bridge submodule or a full-bridge submodule, and a common capacitor is connected in parallel on the DC side of the half-bridge submodule or the full-bridge submodule. A DC bridge arm submodule is connected in series between the positive and negative terminals of the VSC converter valve. Each DC bridge arm submodule is a half-bridge submodule. A supercapacitor is connected in parallel on the DC side of the half-bridge module. A buffer inductor is connected between the negative terminal of the VSC converter valve and the DC bridge arm submodule.

[0011] Optionally, the voltage source of the static synchronous condenser is obtained by pulse modulation calculation of the phase of the internal potential of the static synchronous condenser, the amplitude of the internal potential of the static synchronous condenser, and the harmonic voltage reference signal of the static synchronous condenser; the frequency of the static synchronous condenser is controlled by the LCC converter valve firing angle command. The phase and amplitude of the electromotive force within the static synchronous condenser are calculated using a grid-type control method. The harmonic voltage reference signal of the static synchronous condenser is calculated using an active filtering control method. The LCC converter valve firing angle command is calculated using a frequency control method.

[0012] Optionally, the calculation steps for the potential phase within the static synchronous condenser include: Obtain the reference value of the capacitor voltage of the static synchronous condenser. V dref Measured value of capacitor voltage of stationary synchronous condenser V d and reference frequency oh 0ref ; Reference value of capacitor voltage of static synchrotron V dref Measurement of capacitor voltage of stationary synchronous condenser V d By taking the difference, we obtain the first deviation. ΔV dref ; the first deviation ΔV drefActive power regulation signals are generated through a capacitor voltage controller. ΔP Vd The active power regulation signal ΔP Vd Damping power at the current moment as calculated ΔP Damp By subtracting the values, we obtain the signal difference. ΔP SSCref ; to the signal difference ΔP SSCref The frequency change is obtained through the inertia element of the network structure. Give The change in frequency Give The damping power at the next moment is obtained through the network damping mechanism. ΔP Damp ';The change in frequency Give Superimposed reference frequency oh 0ref To obtain the control frequency oh ; control frequency oh The phase of the internal potential of the static synchronous condenser is obtained through integration. i ; The calculation steps for the potential amplitude of the static synchronous condenser include: Obtain reactive power reference value Q ref reactive power measurement value Q out AC voltage measurement value V g AC voltage reference value V gref Internal potential reference value E 0ref reactive current amplitude I and droop coefficient k ; Calculate reactive power reference value Q ref With reactive power measurement value Q out The second deviation between ΔQ Calculate the reactive current amplitude I With droop coefficient k reactive power direction sgn( Q out The product of reactive power between ) ΔV I ; The second deviation ΔQ The reactive power regulation signal is obtained through the reactive power controller. ΔV Q AC voltage reference value V gref AC voltage measurement value Vg The difference is calculated to obtain the third deviation, which is then superimposed with the reactive power regulation signal. ΔV Q Product of reactive power ΔV I The voltage deviation was obtained. ΔV gref ; to reduce voltage deviation ΔV gref The change in internal potential is generated by an AC voltage controller. DE ref The change in internal potential DE ref Superimposed internal potential reference value E 0ref The amplitude of the internal potential of the stationary synchronous modulator is obtained. E .

[0013] Optionally, the calculation steps for the harmonic voltage reference signal of the static synchronous modulator include: Obtain the AC side current of the LCC converter valve i LCC Measurement value of AC side current of stationary synchronous condenser i SSC ; The AC side current of the LCC converter valve i LCC The opposite of the measured value of the AC side current of the stationary synchronous condenser. i SSC The difference is used to obtain the harmonic current deviation. Yes har To reduce harmonic current deviation Yes har A harmonic voltage reference signal for a static synchronous condenser is generated using a harmonic current controller. V ref_har .

[0014] Optionally, the calculation steps for the LCC converter valve firing angle command include: Obtain the frequency change of the stationary synchronous modulator. Give LCC DC power reference value P DCref DC power measurement value P DC ; Change in the frequency of the stationary synchronous modulator Give Frequency modulation power is obtained through a frequency controller. ΔP ω , frequency modulation power ΔP ω Superimposed LCC DC power reference value P DCref Then compared with DC power measurement value PDC By taking the difference, we obtain the fourth bias. ΔP DC The fourth deviation ΔP DC The LCC converter valve firing angle command is obtained through the DC power controller. α ord .

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention can be configured with 100% new energy units without the need for conventional thermal or hydropower units, and without the need for a large number of AC filters and capacitors. It has a smaller footprint. The static synchronous condenser replaces the conventional synchronous generator to maintain system voltage stability, ensuring the stable transmission of 100% new energy power generation from isolated areas. It does not require additional conventional synchronous condensers, greatly reducing the complexity of equipment operation and maintenance and reducing losses. The characteristic harmonics generated by the LCC converter valve on the grid side are filtered out by the static synchronous condenser. The lower frequency harmonics are filtered out by the static synchronous condenser, while the higher frequency harmonics and the high frequency harmonics generated by the VSC converter valve, new energy power generation equipment and other power electronic equipment in the static synchronous condenser are filtered out by the amplitude and phase corrector. Attached Figure Description

[0016] Figure 1 The diagram shown is a structural schematic of a grid-supported high-voltage direct current transmission system according to one embodiment of the present invention. Figure 2 The diagram shown is a schematic diagram of the principle of the static synchronous condenser VSC converter valve with star connection in one embodiment of the present invention. Figure 3 The diagram shown is a schematic diagram of the principle of the stationary synchronous condenser VSC converter valve with a triangular connection in one embodiment of the present invention. Figure 4 The diagram shown is a schematic diagram of the principle of the static synchronous condenser VSC converter valve with double star connection with DC bus in one embodiment of the present invention. Figure 5 The diagram shown is a schematic diagram of the control principle of the LCC converter valve and VSC converter valve in one embodiment of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0018] The term "and / or" simply describes a relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. Additionally, the character " / " generally indicates an "or" relationship between the related objects.

[0019] Example 1

[0020] like Figure 1 As shown, this embodiment introduces a grid-supported high-voltage direct current transmission system. By replacing conventional synchronous generators with static synchronous condensers, the system voltage is maintained and the stable transmission of 100% renewable energy power generation from isolated areas is ensured. The system includes a converter transformer, a static synchronous condenser, an LCC converter valve, and an amplitude-phase corrector. The converter transformers are connected in parallel. Each converter transformer is connected to the converter bus on the grid side and to the LCC converter valve on the valve side. The static synchronous condenser is connected to the converter bus or the valve side of each converter transformer. The amplitude and phase corrector is connected to the converter bus.

[0021] This embodiment can be configured with 100% new energy units without the need for conventional thermal or hydropower units, and without the need for a large number of AC filters and capacitors. It has a smaller footprint. The static synchronous condenser replaces the conventional synchronous generator to maintain system voltage stability, ensuring the stable transmission of 100% new energy power generation from the island. It does not require additional conventional synchronous condensers, which greatly reduces the complexity of equipment operation and maintenance and reduces losses. In addition, the characteristic harmonics generated by the LCC converter valve on the grid side are filtered out by the static synchronous condenser. The lower frequency harmonics are filtered out by the static synchronous condenser, while the higher frequency harmonics and the high frequency harmonics generated by the VSC converter valve, new energy power generation equipment and other power electronic equipment in the static synchronous condenser are filtered out by the amplitude and phase corrector.

[0022] Example 2

[0023] This embodiment introduces a grid-supported high-voltage direct current transmission system. Figure 1 This is a schematic diagram of a high-voltage direct current transmission grid system with a single-pole twelve-pulse converter. The actual system is usually a bipolar direct current system with symmetrical positive and negative pole structures. The negative pole circuit is omitted here.

[0024] The equipment in the converter station includes converter transformers, converter valves, static synchronous condensers, and amplitude-phase correctors. Each twelve-pulse converter consists of a Y / Y bridge six-pulse converter and a Y / D bridge six-pulse converter. The converter transformers are connected in parallel. Each converter transformer is connected to the converter bus on the grid side and to the LCC converter valve on the valve side. The static synchronous condensers are centrally connected to the converter bus on the grid side through buffer inductors, or they are distributed on the valve side of each converter transformer. The amplitude-phase correctors are connected to the converter bus through capacitors, and the other end of the amplitude-phase correctors is grounded.

[0025] External equipment of the converter station includes new energy power plants such as wind farms and photovoltaic power stations, DC lines, and grounding electrodes. After the new energy power plants are aggregated, they are connected to the converter bus. Y / Y converter transformers and Y / D converter transformers are connected to the DC lines and grounding electrodes through LCC converter valves. The DC lines and grounding electrodes are used for DC power transmission. A buffer inductor is connected between the LCC converter valve and the DC line, and a buffer inductor is also connected between the LCC converter valve and the grounding electrode.

[0026] The converter transformer is used to connect the grid side and the valve side, and to match the LCC converter valve with the AC system voltage. The LCC converter valve is based on thyristor switching devices. After rectification by the LCC converter valve, the power is transmitted to the other end converter station through a DC line.

[0027] The static synchronous condenser includes energy storage components, VSC converter valves, and grid connection components. It is connected to the grid using a direct-connect or step-down topology, with the connection point located on the converter bus or the valve side of each converter transformer.

[0028] The energy storage elements of a static synchronous condenser are energy storage devices such as double-layer supercapacitors or lithium-ion supercapacitors. Double-layer supercapacitors can achieve active power output capabilities at the second level, thus providing support for system inertia. Lithium-ion supercapacitors can achieve active power output capabilities at the minute level, further providing primary frequency regulation capabilities for the power grid.

[0029] VSC converter valves can adopt various topologies. In the high-pressure field, the Modular Multilevel Converter (MMC) topology is the most commonly used topology. VSC converter valves include multiple bridge arm sub-modules, which are connected in star, delta, or double star configurations.

[0030] Star connection method Figure 2 As shown, the triangle connection method is as follows: Figure 3 As shown, in both methods, each bridge arm submodule is a full-bridge submodule, and a supercapacitor is connected in parallel on the DC side of the full-bridge submodule.

[0031] The connection method of the double star with DC bus is as follows Figure 4 As shown, in this method, the three-phase six-arm converter valve submodule can be a half-bridge submodule or a full-bridge submodule, or a combination of both. This submodule only needs to be connected in parallel with a common capacitor on the DC side, without the need for a supercapacitor. A DC bridge arm submodule is connected in series between the positive and negative terminals of the VSC converter valve. Each DC bridge arm submodule is a half-bridge module. A supercapacitor is connected in parallel on the DC side of the half-bridge module. A buffer inductor is connected between the negative terminal of the VSC converter valve and the DC bridge arm submodule.

[0032] The LCC converter valve generates a characteristic harmonic of 12k±1 on the grid side. Lower frequency harmonics are filtered out by the static synchronous condenser (SSC). Higher frequency harmonics, as well as high-frequency harmonics generated by power electronic equipment such as the VSC converter valve in the SSC and renewable energy generation equipment, are filtered out by an amplitude-phase corrector. The amplitude-phase corrector consists of passive components such as resistors, capacitors, and inductors. Figure 1 As shown, it has high-pass characteristics, which can filter out high-frequency harmonic currents in the converter bus and improve voltage and power quality.

[0033] Figure 5 This paper presents schematic diagrams illustrating the control principles of LCC and VSC converter valves. A static synchronous condenser employs a grid-type control strategy to construct a voltage source, providing the ideal synchronization voltage required by the LCC converter valves and new energy power generation equipment. Specifically: The grid-type voltage source, through virtual inertia and virtual damping link 1, possesses inertia and damping characteristics similar to a synchronous generator; through the additional frequency control link 2 of the LCC converter valve, it possesses primary and secondary frequency regulation characteristics similar to a synchronous generator; through the virtual excitation link 3, it possesses reactive voltage regulation characteristics similar to a synchronous generator excitation system; in addition, through the active filtering link 4, the static synchronous condenser can compensate for the harmonic current generated by the LCC converter valve, replacing most of the passive filters.

[0034] That is: the voltage source of the static synchronous condenser is obtained by pulse modulation calculation of the phase of the internal potential of the static synchronous condenser, the amplitude of the internal potential of the static synchronous condenser and the harmonic voltage reference signal of the static synchronous condenser; the frequency of the static synchronous condenser is controlled by the LCC converter valve firing angle command. The phase and amplitude of the electromotive force within the stationary synchronous condenser are calculated using a grid-type control method. The calculation steps for the phase of the electromotive force within the stationary synchronous condenser include: Obtain the reference value of the capacitor voltage of the static synchronous condenser. V dref Measured value of capacitor voltage of stationary synchronous condenser V d and reference frequency oh 0ref ; Reference value of capacitor voltage of static synchrotron V dref Measurement of capacitor voltage of stationary synchronous condenser V d By taking the difference, we obtain the first deviation. ΔV dref ; the first deviation ΔV dref Active power regulation signals are generated through a capacitor voltage controller. ΔP Vd The active power regulation signal ΔP Vd Damping power at the current moment as calculated ΔP Damp By subtracting the values, we obtain the signal difference. ΔP SSCref ; to the signal difference ΔP SSCref The frequency change is obtained through the inertia element of the network structure. Give The change in frequency Give The damping power at the next moment is obtained through the network damping mechanism. ΔP Damp ';The change in frequency Give Superimposed reference frequency oh 0ref To obtain the control frequency oh ; control frequency oh The phase of the internal potential of the static synchronous condenser is obtained through integration. i ; The steps for calculating the potential amplitude of a stationary synchronous condenser include: Obtain reactive power reference value Q ref reactive power measurement value Q out AC voltage measurement value V g AC voltage reference value V gref Internal potential reference value E 0ref reactive current amplitude I and droop coefficient k ; Calculate reactive power reference value Q ref With reactive power measurement value Q out The second deviation between ΔQ Calculate the reactive current amplitude I With droop coefficient k reactive power direction sgn( Q out The product of reactive power between ) ΔV I ; The second deviation ΔQ The reactive power regulation signal is obtained through the reactive power controller. ΔV Q AC voltage reference value V gref AC voltage measurement value V g The difference is calculated to obtain the third deviation, which is then superimposed with the reactive power regulation signal. ΔV QProduct of reactive power ΔV I The voltage deviation was obtained. ΔV gref ; to reduce voltage deviation ΔV gref The change in internal potential is generated by an AC voltage controller. DE ref The change in internal potential DE ref Superimposed internal potential reference value E 0ref The amplitude of the internal potential of the stationary synchronous modulator is obtained. E .

[0035] The harmonic voltage reference signal of the stationary synchronous condenser is calculated using an active filtering control method. The calculation steps for the harmonic voltage reference signal of the stationary synchronous condenser include: Obtain the AC side current of the LCC converter valve i LCC Measurement value of AC side current of stationary synchronous condenser i SSC ; The AC side current of the LCC converter valve i LCC The opposite of the measured value of the AC side current of the stationary synchronous condenser. i SSC The difference is used to obtain the harmonic current deviation. Yes har To reduce harmonic current deviation Yes har A harmonic voltage reference signal for a static synchronous condenser is generated using a harmonic current controller. V ref_har .

[0036] The LCC converter valve firing angle command is calculated using a frequency control method. The calculation steps for the LCC converter valve firing angle command include: Obtain the frequency change of the stationary synchronous modulator. Give LCC DC power reference value P DCref DC power measurement value P DC ; Change in the frequency of the stationary synchronous modulator Give Frequency modulation power is obtained through a frequency controller. ΔP ω , frequency modulation power ΔP ω Superimposed LCC DC power reference value P DCref Then compared with DC power measurement value P DCBy taking the difference, we obtain the fourth bias. ΔP DC The fourth deviation ΔP DC The LCC converter valve firing angle command is obtained through the DC power controller. α ord .

[0037] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A grid-supported high-voltage direct current transmission system, characterized in that, This includes converter transformers, static synchronous condensers, LCC converter valves, and amplitude-phase correctors; Each converter transformer is connected in parallel, and each converter transformer is connected to a converter bus on the grid side and an LCC converter valve on the valve side. The static synchronous condenser is connected to the converter bus or the valve side of each converter transformer, and the amplitude-phase corrector is connected to the converter bus.

2. The grid-supported high-voltage direct current transmission system according to claim 1, characterized in that, The converter transformer is a Y / Y converter transformer or a Y / D converter transformer; The Y / Y converter transformer and Y / D converter transformer are connected to the DC line and grounding electrode for transmitting DC power through the LCC converter valve; the converter bus is connected to the new energy power station for generating AC power.

3. The grid-supported high-voltage direct current transmission system according to claim 1, characterized in that, The static synchronous condenser is connected to the converter bus or the valve side of each converter transformer in a direct-connect or step-down topology.

4. The grid-supported high-voltage direct current transmission system according to claim 1, characterized in that, The static synchronous condenser includes a VSC converter valve, which includes multiple bridge arm sub-modules. The bridge arm sub-modules are connected in a star, triangle, or double star configuration.

5. The grid-supported high-voltage direct current transmission system according to claim 4, characterized in that, When the bridge arm submodules are connected in a star or delta configuration, each bridge arm submodule is a full-bridge submodule, and a supercapacitor is connected in parallel on the DC side of the full-bridge submodule.

6. The grid-supported high-voltage direct current transmission system according to claim 4, characterized in that, When the bridge arm submodules are connected in a double star configuration, each bridge arm submodule is a half-bridge submodule or a full-bridge submodule, and a common capacitor is connected in parallel on the DC side of the half-bridge submodule or the full-bridge submodule. A DC bridge arm submodule is connected in series between the positive and negative terminals of the VSC converter valve. Each DC bridge arm submodule is a half-bridge submodule. A supercapacitor is connected in parallel on the DC side of the half-bridge module. A buffer inductor is connected between the negative terminal of the VSC converter valve and the DC bridge arm submodule.

7. The grid-supported high-voltage direct current transmission system according to claim 1, characterized in that, The voltage source of the static synchronous condenser is obtained by pulse modulation calculation of the phase of the internal potential of the static synchronous condenser, the amplitude of the internal potential of the static synchronous condenser, and the harmonic voltage reference signal of the static synchronous condenser. The frequency of the static synchronous condenser is controlled by the LCC converter valve firing angle command. The phase and amplitude of the electromotive force within the static synchronous condenser are calculated using a grid-type control method. The harmonic voltage reference signal of the static synchronous condenser is calculated using an active filtering control method. The LCC converter valve firing angle command is calculated using a frequency control method.

8. The grid-supported high-voltage direct current transmission system according to claim 7, characterized in that, The calculation steps for the internal potential phase of the static synchronous condenser include: Obtain the reference value of the capacitor voltage of the static synchronous condenser. V dref Measured value of capacitor voltage of stationary synchronous condenser V d and reference frequency ω 0ref ; Reference value of capacitor voltage of static synchrotron V dref Measurement of capacitor voltage of stationary synchronous condenser V d By taking the difference, we obtain the first deviation. ΔV dref ; the first deviation ΔV dref Active power regulation signals are generated through a capacitor voltage controller. ΔP Vd The active power regulation signal ΔP Vd Damping power at the current moment as calculated ΔP Damp By subtracting the values, we obtain the signal difference. ΔP SSCref ; to the signal difference ΔP SSCref The frequency change is obtained through the inertia element of the network structure. Δω The change in frequency Δω The damping power at the next moment is obtained through the network damping mechanism. ΔP Damp ';The change in frequency Δω Superimposed reference frequency ω 0ref To obtain the control frequency ω ; control frequency ω The phase of the internal potential of the static synchronous condenser is obtained through integration. θ ; The calculation steps for the potential amplitude of the static synchronous condenser include: Obtain reactive power reference value Q ref reactive power measurement value Q out AC voltage measurement value V g AC voltage reference value V gref Internal potential reference value E 0ref reactive current amplitude I and droop coefficient k ; Calculate reactive power reference value Q ref With reactive power measurement value Q out The second deviation between ΔQ Calculate the reactive current amplitude I With droop coefficient k reactive power direction sgn( Q out The product of reactive power between ) ΔV I ; The second deviation ΔQ The reactive power regulation signal is obtained through the reactive power controller. ΔV Q AC voltage reference value V gref AC voltage measurement value V g The difference is calculated to obtain the third deviation, which is then superimposed with the reactive power regulation signal. ΔV Q Product of reactive power ΔV I The voltage deviation was obtained. ΔV gref ; to reduce voltage deviation ΔV gref The change in internal potential is generated by an AC voltage controller. ΔE ref The change in internal potential ΔE ref Superimposed internal potential reference value E 0ref The amplitude of the internal potential of the stationary synchronous modulator is obtained. E .

9. The grid-supported high-voltage direct current transmission system according to claim 7, characterized in that, The calculation steps for the harmonic voltage reference signal of the static synchronous modulator include: Obtain the AC side current of the LCC converter valve i LCC Measurement value of AC side current of stationary synchronous condenser i SSC ; The AC side current of the LCC converter valve i LCC The opposite of the measured value of the AC side current of the stationary synchronous condenser. i SSC The difference is used to obtain the harmonic current deviation. Δi har To reduce harmonic current deviation Δi har A harmonic voltage reference signal for a static synchronous condenser is generated using a harmonic current controller. V ref_har .

10. The grid-supported high-voltage direct current transmission system according to claim 7, characterized in that, The calculation steps for the LCC converter valve firing angle command include: Obtain the frequency change of the stationary synchronous modulator. Δω LCC DC power reference value P DCref DC power measurement value P DC ; Change in the frequency of the stationary synchronous modulator Δω Frequency modulation power is obtained through a frequency controller. ΔP ω , frequency modulation power Δ P ω Superimposed LCC DC power reference value P DCref Then compared with DC power measurement value P DC By taking the difference, we obtain the fourth bias. ΔP DC The fourth deviation ΔP DC The LCC converter valve firing angle command is obtained through the DC power controller. α ord .

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