SVG control method and device of extra-high voltage SLCC system

Abstract

The invention discloses an SVG control method and device for an extra-high voltage SLCC system, and the method comprises the steps: obtaining the network side voltage and current of a converter transformer to obtain reactive power, and carrying out the reactive power control through employing the reactive power as a control variable; the reactive power controller is located at the outer ring part of the double-ring controller, and the reactive power controller is connected with the inner ring current controller of the d axis; obtaining a current reference value according to the output quantity of reactive power control, obtaining a current deviation value in combination with the SVG input current, and further obtaining a first modulation wave output by double-loop control; obtaining a characteristic harmonic wave output by the converter, and forming a second modulation wave to perform harmonic wave control; superposing the first modulation wave and the second modulation wave to obtain a third modulation wave so as to carry out SVG control; sVG control further comprises dq axis decoupling control, phase-locked loop networking control and third harmonic injection control. According to the invention, comprehensive coordination of multiple functions of the SVG can be realized, and an SVG control strategy is provided for an extra-high voltage SLCC direct current transmission project.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current (DC) transmission, and in particular to an SVG control method and device for an ultra-high voltage (UHV) SLCC system. Background Art

[0002] With the development of renewable energy power generation technology, the installed capacity of renewable energy is growing rapidly, and the demand for long-distance transmission is increasing, making conventional DC transmission difficult to adapt. SLCC (Self-Commutated Converter), a converter composed of SVG (Static Var Generator) and LCC (Line Commutated Converter), can effectively compensate for reactive power consumption and harmonic currents, reduce the need for AC filters and shunt capacitors, and thus alleviate problems such as low voltage ride-through and commutation failure. Compared with flexible DC transmission, SLCC systems have many advantages. In UHV scenarios, SLCC DC transmission systems have higher voltage levels and higher requirements for system safety and reliability. At the same time, when SLCC is used for renewable energy transmission, there are also high requirements for the voltage support capability of the SLCC system.

[0003] There is currently no precedent for UHV SLCC project construction. Further research is needed on how to construct SVG networks in UHV SLCC projects, how to achieve coordination of multiple functions, and how to design SVG control strategies. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides an SVG control method and device for a UHV SLCC system, which realizes comprehensive coordination of multiple SVG functions and provides an SVG control strategy for UHV SLCC DC transmission projects.

[0005] An embodiment of the present invention provides an SVG control method for an ultra-high voltage SLCC system, including:

[0006] Obtaining the grid-side voltage and current of the converter transformer, obtaining the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and performing reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control, and the reactive power control is connected to the inner loop current control of the d-axis;

[0007] Obtaining a current reference value according to the output of the reactive control; obtaining an SVG input current, and obtaining a current deviation according to the SVG input current and the current reference value; obtaining a first modulation wave output by the dual-loop control according to the current deviation;

[0008] Acquire characteristic harmonics output by the converter, and obtain a second modulation wave based on the characteristic harmonics to perform harmonic control;

[0009] Superimposing the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control;

[0010] The SVG control also includes dq axis decoupling control, phase-locked loop networking control and third harmonic injection control.

[0011] As an improvement to the above solution, obtaining the grid-side voltage of the converter transformer includes:

[0012] Obtaining the grid-side voltage of the converter transformer by measuring, or obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage;

[0013] The method of obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage includes:

[0014] The valve side voltage is obtained by measurement;

[0015] Obtain the phase difference between the grid-side and valve-side voltages;

[0016] According to the phase difference between the grid-side voltage and the valve-side voltage, the phase of the valve-side voltage is adjusted to obtain the grid-side voltage of the converter transformer.

[0017] As an improvement to the above solution, obtaining a current reference value according to the output of the reactive power control includes:

[0018] The deviation of the grid-side voltage of the converter transformer is obtained, and PI control is performed on the sum of the deviation and the output of the reactive control to obtain a d-axis current reference value.

[0019] As an improvement to the above solution, obtaining the current deviation according to the SVG input current and the current reference value includes:

[0020] Setting a q-axis current reference value to zero, and calculating a q-axis current deviation according to a difference between the q-axis current reference value and the q-axis component of the SVG input current;

[0021] Acquiring an input current of a commutation converter, adding a d-axis component of the input current of the commutation converter and a d-axis component of the input current of the SVG to obtain a d-axis current control amount;

[0022] The d-axis current deviation is calculated according to the difference between the d-axis current reference value and the d-axis current control value.

[0023] As an improvement to the above solution, obtaining the first modulation wave output by the dual-loop control according to the current deviation includes:

[0024] performing PI control on the d-axis current deviation and the q-axis current deviation respectively to obtain a d-axis reference voltage and a q-axis reference voltage;

[0025] A dq inverse transformation is performed according to the d-axis reference voltage and the q-axis reference voltage to obtain a first modulation wave output by the dual-loop control.

[0026] As an improvement to the above solution, the step of obtaining characteristic harmonics output by the converter and obtaining a second modulated wave according to the characteristic harmonics includes:

[0027] Obtain the 11th, 13th, 23rd, and 25th characteristic harmonics of the converter output;

[0028] Decomposing each type of characteristic harmonic into d-axis and q-axis components, performing PI control on the d-axis and q-axis components respectively to obtain output quantities, and performing dq inverse transformation on the output quantities to obtain a modulation wave corresponding to each type of characteristic harmonic;

[0029] The modulation waves corresponding to all the characteristic harmonics are superimposed to obtain a second modulation wave.

[0030] As an improvement to the above solution, the phase-locked loop network control includes:

[0031] Stator module capacitor voltage control is adopted; wherein the submodule capacitor voltage is the average value of all submodule capacitor voltages of the three phases ABC, and is reflected in the control loop in the form of a per-unit value; the submodule capacitor voltage is used as the input of virtual synchronous control, and the output of the virtual synchronous control is used as the phase adopted by the dq decomposition in the SVG control process.

[0032] As an improvement to the above solution, the dq axis decoupling control uses the valve-side voltage of the converter transformer and the current flowing through the SVG as control variables to perform complete dq axis decoupling.

[0033] As an improvement to the above solution, the third harmonic injection control includes:

[0034] When the number of sub-modules put into operation in a single bridge arm is greater than a first preset value, a third harmonic with an amplitude of 1 / 6 of the fundamental wave and a phase leading the fundamental wave voltage by 30° is injected into the third modulated wave;

[0035] When the number of sub-modules put into operation in a single bridge arm is less than a second preset value within a preset time, the injection of the third harmonic is canceled.

[0036] An embodiment of the present invention further provides an SVG control device for an ultra-high voltage SLCC system, comprising:

[0037] a reactive power control module, configured to obtain the grid-side voltage and current of the converter transformer, determine the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and perform reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control and is connected to the inner loop current control of the d-axis;

[0038] A dual-loop control module is configured to obtain a current reference value based on the output of the reactive control; obtain an SVG input current, and obtain a current deviation based on the SVG input current and the current reference value; and obtain a first modulation wave output by the dual-loop control based on the current deviation;

[0039] A harmonic control module, configured to obtain characteristic harmonics output by the converter and obtain a second modulation wave based on the characteristic harmonics for harmonic control;

[0040] a modulation wave output module, configured to superimpose the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control;

[0041] The device further includes a dq axis decoupling control module, a phase-locked loop networking control module, and a third harmonic injection control module.

[0042] Compared with the prior art, the SVG control method and device for a UHV SLCC system provided by the embodiments of the present invention have the following beneficial effects:

[0043] By monitoring the reactive power of the SLCC AC side grid connection point, the reactive power dynamic balance of the SLCC DC transmission system can be achieved. The reactive power is equivalently calculated by voltage and current parameters, without the need to increase reactive power monitoring points.

[0044] By adding SVG grid control functions to the UHV SLCC DC transmission system, the SVG voltage support capability is improved, effectively reducing the risk of SLCC commutation failure.

[0045] Through reactive power control, dual-loop control, dq-axis decoupling control, phase-locked loop (PLL) networking control, harmonic control, and dynamic third-harmonic injection control, the three-phase modulation waves output by harmonic control and dual-loop control are superimposed to form the actual modulation wave of the SVG. The voltage support, reactive power compensation, harmonic suppression, and other control links of the SVG are jointly designed, achieving comprehensive coordination of the various functions of the SVG and providing an SVG control strategy for UHV SLCC DC transmission projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 1 is a flow chart of an SVG control method for a UHV SLCC system provided by an embodiment of the present invention;

[0047] Figure 2 This is an SVG control flow chart provided by an embodiment of the present invention;

[0048] Figure 3 This is a dual-loop control and dq decoupling control flow chart provided by an embodiment of the present invention;

[0049] Figure 4 This is a control flow chart of a harmonic separation and suppression link provided by an embodiment of the present invention;

[0050] Figure 5 This is a flowchart of reactive power control, VQ slope control, and phase-locked loop network control provided by an embodiment of the present invention;

[0051] Figure 6 The figure is a schematic structural diagram of an SVG control device of an ultra-high voltage SLCC system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0053] See also Figure 1 , Figure 1 1 is a flow chart of an SVG control method for a UHV SLCC system provided by an embodiment of the present invention. The SVG control method for a UHV SLCC system includes:

[0054] S1: Obtaining the grid-side voltage and current of the converter transformer, obtaining the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and performing reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control, and the reactive power control is connected to the inner loop current control of the d-axis;

[0055] S2: obtaining a current reference value according to the output of the reactive power control; obtaining an SVG input current, and obtaining a current deviation according to the SVG input current and the current reference value; obtaining a first modulation wave output by the dual-loop control according to the current deviation;

[0056] S3: Acquire characteristic harmonics output by the converter, and obtain a second modulation wave based on the characteristic harmonics to perform harmonic control;

[0057] S4: superimposing the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control; wherein the SVG control also includes dq axis decoupling control, phase-locked loop networking control and third harmonic injection control.

[0058] Specifically, the control process of SVG is: reactive power control, dual-loop control, dq axis decoupling control, phase-locked loop network control, harmonic suppression control and dynamic third harmonic injection control, such as Figure 2 As shown in the figure, reactive power control is located in the outer loop of the d- and q-axis control systems and is connected to the inner loop current control of the d-axis. The phase used for dq decomposition is determined by the network control loop. The harmonic control link is superimposed on the three-phase modulation wave output by the dual-loop control to form the actual SVG modulation wave, thereby performing SVG control.

[0059] As one of the optional embodiments, obtaining the grid-side voltage of the converter transformer includes:

[0060] Obtaining the grid-side voltage of the converter transformer by measuring, or obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage;

[0061] The method of obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage includes:

[0062] The valve side voltage is obtained by measurement;

[0063] Obtain the phase difference between the grid-side and valve-side voltages;

[0064] According to the phase difference between the grid-side voltage and the valve-side voltage, the phase of the valve-side voltage is adjusted to obtain the grid-side voltage of the converter transformer.

[0065] Specifically, when measuring the valve-side voltage for equivalence, the dq-axis phase of the valve-side voltage needs to be adjusted. The valve-side voltage is equated to the grid-side value based on the phase difference between the grid-side and valve-side voltages. For Y / △ converter transformers, the valve-side voltage leads the grid-side voltage by 30°. Therefore, the valve-side voltage phase used for dq decomposition should be increased by 30° based on the existing controller phase. No phase adjustment is required for Y / Y converter transformers.

[0066] Furthermore, the reactive power control, during normal operation, adjusts the reactive power to zero and uses a low-pass filter to filter out medium and high frequency harmonics;

[0067] The reactive power calculation formula is:

[0068] Q=U d *I q -U q *I d

[0069] Among them, Q is reactive power, U d is the d-axis component of the grid-side voltage, U q is the q-axis component of the grid-side voltage, I d is the d-axis component of the grid-side current, I q is the q-axis component of the grid-side current.

[0070] Specifically, reactive power is calculated through grid-side voltage and current, and there is no need to add a separate grid-side reactive power measurement point.

[0071] Furthermore, the SVG controller adopts inner loop current control, which uses the current i injected into the SVG svg_d 、i svg_q To control the amount.

[0072] As one of the optional embodiments, obtaining a current reference value according to the output of the reactive power control includes:

[0073] The deviation of the grid-side voltage of the converter transformer is obtained, and PI control is performed on the sum of the deviation and the output of the reactive control to obtain a d-axis current reference value.

[0074] Specifically, the voltage monitoring quantity is the grid-side voltage of the converter transformer, and its deviation dU g The result is summed with the output of the reactive power controller and outputted by the PI controller as the inner loop d-axis current reference value I ref_d .

[0075] Furthermore, obtaining the current deviation according to the SVG input current and the current reference value includes:

[0076] Setting a q-axis current reference value to zero, and calculating a q-axis current deviation according to a difference between the q-axis current reference value and the q-axis component of the SVG input current;

[0077] Acquiring an input current of a commutation converter, adding a d-axis component of the input current of the commutation converter and a d-axis component of the input current of the SVG to obtain a d-axis current control amount;

[0078] The d-axis current deviation is calculated according to the difference between the d-axis current reference value and the d-axis current control value.

[0079] Furthermore, obtaining the first modulation wave output by the dual-loop control according to the current deviation includes:

[0080] performing PI control on the d-axis current deviation and the q-axis current deviation respectively to obtain a d-axis reference voltage and a q-axis reference voltage;

[0081] A dq inverse transformation is performed according to the d-axis reference voltage and the q-axis reference voltage to obtain a first modulation wave output by the dual-loop control.

[0082] Specifically, the q-axis current reference value I ref_q =0, q-axis current deviation di q for:

[0083] di q =I ref_q -i svg_q

[0084] Considering that the grid-side reactive power monitoring quantity of the reactive power control loop includes not only the reactive power consumed by SVG and converter transformer, but also the reactive power consumed by LCC, the d-axis current control quantity should also include the d-axis current i injected into the LCC. LCC_d , that is, the d-axis current deviation di d for:

[0085] di d =I ref_d -i svg_d -i LCC_d

[0086] Then, the inner loop current control will di d 、di q Perform PI control and output the d and q axis reference voltages, which are then transformed into a three-phase voltage modulation wave (i.e., the first modulation wave) through dq inverse transformation as the output of the dual-loop controller, as shown in the following example: Figure 3 shown.

[0087] As one of the optional embodiments, obtaining characteristic harmonics output by the converter and obtaining the second modulated wave according to the characteristic harmonics includes:

[0088] Obtain the 11th, 13th, 23rd, and 25th characteristic harmonics of the converter output;

[0089] Decomposing each type of characteristic harmonic into d-axis and q-axis components, performing PI control on the d-axis and q-axis components respectively to obtain output quantities, and performing dq inverse transformation on the output quantities to obtain a modulation wave corresponding to each type of characteristic harmonic;

[0090] The modulation waves corresponding to all the characteristic harmonics are superimposed to obtain a second modulation wave.

[0091] Specifically, a harmonic control link is added to the SVG controller. The valve sides of the high-end and low-end converter transformers are connected in Y and △ respectively. The 5th and 7th order characteristic harmonics do not flow into the grid. Therefore, the SVG only suppresses the 11th, 13th, 23rd and 25th order characteristic harmonic currents output by the converter. Figure 4As shown in the figure. To accurately extract the characteristic harmonics and avoid interference from other subharmonics, the characteristic harmonic monitoring quantity is decomposed into d- and q-axis components, each of which is subjected to PI control. The output quantity is then subjected to an inverse dq transform to form the ABC three-phase modulation wave voltage for that subharmonic. The three-phase modulation waves of all subharmonics are superimposed to form the output modulation wave of the harmonic control link (i.e., the second modulation wave). This modulation wave is superimposed with the modulation wave output by the dual-loop control to form the actual modulation wave of the SVG controller.

[0092] Furthermore, the embodiment of the present invention also adopts VQ slope control to solve the AC transient overvoltage problem, such as Figure 5 shown.

[0093] Furthermore, to address issues such as system stability and AC transient overvoltage caused by access to a weak AC grid, SVG uses network control instead of a phase-locked loop to solve system stability problems.

[0094] Furthermore, the phase-locked loop network control includes:

[0095] Stator module capacitor voltage control is adopted; wherein the submodule capacitor voltage is the average value of all submodule capacitor voltages of the three phases ABC, and is reflected in the control loop in the form of a per-unit value; the submodule capacitor voltage is used as the input of virtual synchronous control, and the output of the virtual synchronous control is used as the phase adopted by the dq decomposition in the SVG control process.

[0096] Furthermore, the dq axis decoupling control uses the valve-side voltage of the converter transformer and the current flowing through the SVG as control variables to perform complete dq axis decoupling.

[0097] Specifically, although the SVG uses the grid-side voltage as the control variable, the formula derivation shows that its dq decoupling link should use the SVG access point voltage (i.e., the converter transformer valve-side voltage) and the current flowing through the SVG as the control variables to achieve complete dq axis decoupling. The derivation process is as follows:

[0098] For SVG access nodes, the transformer equivalent leakage reactance and SVG bridge arm reactance satisfy the following equation:

[0099]

[0100] Under the three-phase symmetry condition, the small disturbance mathematical model can be simplified as follows:

[0101]

[0102] The small disturbance mathematical model of the controller for dq decoupling with the converter transformer valve-side voltage and the current flowing through the SVG as the control variables is:

[0103]

[0104] For non-characteristic subharmonic batches, ignore the harmonic control link. You can get:

[0105]

[0106] That is, the d and q axis expressions of SVG can be completely decoupled.

[0107] As one of the optional embodiments, the third harmonic injection control includes:

[0108] When the number of sub-modules put into operation in a single bridge arm is greater than a first preset value, a third harmonic with an amplitude of 1 / 6 of the fundamental wave and a phase leading the fundamental wave voltage by 30° is injected into the third modulated wave;

[0109] When the number of sub-modules put into operation in a single bridge arm is less than a second preset value within a preset time, the injection of the third harmonic is canceled.

[0110] Specifically, SVG uses dynamic third-harmonic injection control: when the number of sub-modules in a single bridge arm exceeds 97.5% of its total number, a third harmonic with an amplitude of 1 / 6 of the fundamental wave and a phase leading the fundamental voltage by 30° is injected into the modulated wave; when the number of sub-modules in a single bridge arm remains less than 95% of its total number within 200ms, the third-harmonic injection is canceled.

[0111] The embodiment of the present invention can achieve reactive dynamic balance of the SLCC DC transmission system by monitoring the reactive power of the SLCC AC-side grid connection point. The reactive power is equivalently obtained by calculating the voltage and current parameters, without adding reactive monitoring points. By adding the SVG network control function to the UHV SLCC DC transmission system, the voltage support capability of the SVG is improved, and the risk of SLCC commutation failure is effectively reduced. Through reactive power control, dual-loop control, dq-axis decoupling control, phase-locked loop network control, harmonic control, and dynamic third harmonic injection control, the three-phase modulation wave output by the harmonic control and dual-loop control is superimposed to form the actual modulation wave of the SVG. The control links of the SVG, such as voltage support, reactive power compensation, and harmonic suppression, are jointly designed to achieve comprehensive coordination of multiple functions of the SVG, and provide an SVG control strategy for the UHV SLCC DC transmission project.

[0112] Accordingly, the present invention further provides an SVG control device for an ultra-high voltage SLCC system, which can implement all processes of the SVG control method for an ultra-high voltage SLCC system in the above embodiment.

[0113] See also Figure 6 , Figure 6Schematic diagram of the structure of an SVG control device for an ultra-high voltage SLCC system provided by an embodiment of the present invention. The SVG control device for the ultra-high voltage SLCC system includes:

[0114] The reactive power control module 601 is configured to obtain the grid-side voltage and current of the converter transformer, determine the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and perform reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control and is connected to the inner loop current control of the d-axis;

[0115] The dual-loop control module 602 is configured to obtain a current reference value based on the output of the reactive power control; obtain an SVG input current, and obtain a current deviation based on the SVG input current and the current reference value; and obtain a first modulation wave output by the dual-loop control based on the current deviation;

[0116] The harmonic control module 603 is used to obtain characteristic harmonics output by the converter and obtain a second modulation wave according to the characteristic harmonics to perform harmonic control;

[0117] a modulation wave output module 604 configured to superimpose the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control;

[0118] The device further includes a dq axis decoupling control module 605 , a phase-locked loop networking control module 606 , and a third harmonic injection control module 607 .

[0119] Preferably, obtaining the grid-side voltage of the converter transformer includes:

[0120] Obtaining the grid-side voltage of the converter transformer by measuring, or obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage;

[0121] The method of obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage includes:

[0122] The valve side voltage is obtained by measurement;

[0123] Obtain the phase difference between the grid-side and valve-side voltages;

[0124] According to the phase difference between the grid-side voltage and the valve-side voltage, the phase of the valve-side voltage is adjusted to obtain the grid-side voltage of the converter transformer.

[0125] Preferably, obtaining a current reference value according to the output of the reactive power control includes:

[0126] The deviation of the grid-side voltage of the converter transformer is obtained, and PI control is performed on the sum of the deviation and the output of the reactive control to obtain a d-axis current reference value.

[0127] Preferably, obtaining the current deviation according to the SVG input current and the current reference value includes:

[0128] Setting a q-axis current reference value to zero, and calculating a q-axis current deviation according to a difference between the q-axis current reference value and the q-axis component of the SVG input current;

[0129] Acquiring an input current of a commutation converter, adding a d-axis component of the input current of the commutation converter and a d-axis component of the input current of the SVG to obtain a d-axis current control amount;

[0130] The d-axis current deviation is calculated according to the difference between the d-axis current reference value and the d-axis current control value.

[0131] Preferably, obtaining the first modulation wave output by the dual-loop control according to the current deviation includes:

[0132] performing PI control on the d-axis current deviation and the q-axis current deviation respectively to obtain a d-axis reference voltage and a q-axis reference voltage;

[0133] A dq inverse transformation is performed according to the d-axis reference voltage and the q-axis reference voltage to obtain a first modulation wave output by the dual-loop control.

[0134] Preferably, the step of acquiring characteristic harmonics output by the converter and obtaining the second modulated wave according to the characteristic harmonics includes:

[0135] Obtain the 11th, 13th, 23rd, and 25th characteristic harmonics of the converter output;

[0136] Decomposing each type of characteristic harmonic into d-axis and q-axis components, performing PI control on the d-axis and q-axis components respectively to obtain output quantities, and performing dq inverse transformation on the output quantities to obtain a modulation wave corresponding to each type of characteristic harmonic;

[0137] The modulation waves corresponding to all the characteristic harmonics are superimposed to obtain a second modulation wave.

[0138] Preferably, the phase-locked loop networking control module 606 is configured to:

[0139] Stator module capacitor voltage control is adopted; wherein the submodule capacitor voltage is the average value of all submodule capacitor voltages of the three phases ABC, and is reflected in the control loop in the form of a per-unit value; the submodule capacitor voltage is used as the input of virtual synchronous control, and the output of the virtual synchronous control is used as the phase adopted by the dq decomposition in the SVG control process.

[0140] Preferably, the dq axis decoupling control module 605 is configured to perform complete dq axis decoupling using the converter transformer valve-side voltage and the current flowing through the SVG as control variables.

[0141] Preferably, the third harmonic injection control module 607 is configured to:

[0142] When the number of sub-modules put into operation in a single bridge arm is greater than a first preset value, a third harmonic with an amplitude of 1 / 6 of the fundamental wave and a phase leading the fundamental wave voltage by 30° is injected into the third modulated wave;

[0143] When the number of sub-modules put into operation in a single bridge arm is less than a second preset value within a preset time, the injection of the third harmonic is canceled.

[0144] In specific implementation, the working principle, control process and technical effects achieved by the SVG control device of the UHV SLCC system provided by the embodiment of the present invention are the same as those of the SVG control method of the UHV SLCC system in the above embodiment, and will not be repeated here.

[0145] The embodiments of the present invention provide an SVG control method and device for an ultra-high voltage SLCC system, which has the following beneficial effects: by monitoring the reactive power of the SLCC AC-side grid connection point, the reactive power dynamic balance of the SLCC DC transmission system can be achieved, and the reactive power is equivalently obtained by calculating the voltage and current parameters, without the need to increase reactive power monitoring points; by adding the SVG network control function to the ultra-high voltage SLCC DC transmission system, the voltage support capability of the SVG is improved, and the risk of SLCC commutation failure is effectively reduced; through reactive power control, dual-loop control, dq-axis decoupling control, phase-locked loop network control, harmonic control, and dynamic third harmonic injection control, the three-phase modulation waves output by the harmonic control and dual-loop control are superimposed to form the actual modulation wave of the SVG, and the control links of the SVG, such as voltage support, reactive power compensation, and harmonic suppression, are jointly designed to achieve comprehensive coordination of multiple functions of the SVG, thereby providing an SVG control strategy for the ultra-high voltage SLCC DC transmission project.

[0146] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A SVG control method for a UHV SLCC system, characterized in that: include: Obtaining the grid-side voltage and current of the converter transformer, obtaining the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and performing reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control, and the reactive power control is connected to the inner loop current control of the d-axis; Obtaining a current reference value according to the output of the reactive control; obtaining an SVG input current, and obtaining a current deviation according to the SVG input current and the current reference value; obtaining a first modulation wave output by the dual-loop control according to the current deviation; Acquire characteristic harmonics output by the converter, and obtain a second modulation wave based on the characteristic harmonics to perform harmonic control; Superimposing the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control; The SVG control also includes dq axis decoupling control, phase-locked loop networking control and third harmonic injection control.

2. The SVG control method for the UHV SLCC system according to claim 1, wherein: The obtaining of the grid-side voltage of the converter transformer includes: Obtaining the grid-side voltage of the converter transformer by measuring, or obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage; The method of obtaining the grid-side voltage of the converter transformer by measuring the valve-side voltage and performing equivalence on the valve-side voltage includes: The valve side voltage is obtained by measurement; Obtain the phase difference between the grid-side and valve-side voltages; According to the phase difference between the grid-side voltage and the valve-side voltage, the phase of the valve-side voltage is adjusted to obtain the grid-side voltage of the converter transformer.

3. The SVG control method for the UHV SLCC system according to claim 1, wherein: The obtaining of a current reference value according to the output of the reactive power control comprises: The deviation of the grid-side voltage of the converter transformer is obtained, and PI control is performed on the sum of the deviation and the output of the reactive control to obtain a d-axis current reference value.

4. The SVG control method of the UHV SLCC system according to claim 3, characterized in that: Obtaining a current deviation according to the SVG input current and the current reference value includes: Setting a q-axis current reference value to zero, and calculating a q-axis current deviation according to a difference between the q-axis current reference value and the q-axis component of the SVG input current; Acquiring an input current of a commutation converter, adding a d-axis component of the input current of the commutation converter and a d-axis component of the input current of the SVG to obtain a d-axis current control amount; The d-axis current deviation is calculated according to the difference between the d-axis current reference value and the d-axis current control value.

5. The SVG control method for the UHV SLCC system according to claim 4, characterized in that: The step of obtaining a first modulation wave output by the dual-loop control according to the current deviation comprises: performing PI control on the d-axis current deviation and the q-axis current deviation respectively to obtain a d-axis reference voltage and a q-axis reference voltage; A dq inverse transformation is performed according to the d-axis reference voltage and the q-axis reference voltage to obtain a first modulation wave output by the dual-loop control.

6. The SVG control method for the UHV SLCC system according to claim 1, wherein: The step of obtaining characteristic harmonics output by the converter and obtaining a second modulated wave according to the characteristic harmonics includes: Obtain the 11th, 13th, 23rd, and 25th characteristic harmonics of the converter output; Decomposing each type of characteristic harmonic into d-axis and q-axis components, performing PI control on the d-axis and q-axis components respectively to obtain output quantities, and performing dq inverse transformation on the output quantities to obtain a modulation wave corresponding to each type of characteristic harmonic; The modulation waves corresponding to all the characteristic harmonics are superimposed to obtain a second modulation wave.

7. The SVG control method for a UHV SLCC system according to claim 1, wherein: The phase-locked loop network control includes: Stator module capacitor voltage control is adopted; wherein the submodule capacitor voltage is the average value of all submodule capacitor voltages of the three phases ABC, and is reflected in the control loop in the form of a per-unit value; the submodule capacitor voltage is used as the input of virtual synchronous control, and the output of the virtual synchronous control is used as the phase adopted by the dq decomposition in the SVG control process.

8. The SVG control method for a UHV SLCC system according to claim 1, wherein: The dq axis decoupling control uses the valve-side voltage of the converter transformer and the current flowing through the SVG as control variables to perform complete dq axis decoupling.

9. The SVG control method for a UHV SLCC system according to claim 1, wherein: The third harmonic injection control comprises: When the number of sub-modules put into operation in a single bridge arm is greater than a first preset value, a third harmonic with an amplitude of 1 / 6 of the fundamental wave and a phase leading the fundamental wave voltage by 30° is injected into the third modulated wave; When the number of sub-modules put into operation in a single bridge arm is less than a second preset value within a preset time, the injection of the third harmonic is canceled.

10. An SVG control device for an ultra-high voltage SLCC system, characterized in that: include: a reactive power control module, configured to obtain the grid-side voltage and current of the converter transformer, determine the reactive power of the grid-side common connection point of the converter transformer based on the grid-side voltage and current, and perform reactive power control using the reactive power as a control variable; wherein the reactive power control is located in the outer loop of the dual-loop control and is connected to the inner loop current control of the d-axis; A dual-loop control module is configured to obtain a current reference value based on the output of the reactive control; obtain an SVG input current, and obtain a current deviation based on the SVG input current and the current reference value; and obtain a first modulation wave output by the dual-loop control based on the current deviation; A harmonic control module, configured to obtain characteristic harmonics output by the converter and obtain a second modulation wave based on the characteristic harmonics for harmonic control; a modulation wave output module, configured to superimpose the first modulation wave and the second modulation wave to obtain a third modulation wave of the SVG for SVG control; The device further includes a dq axis decoupling control module, a phase-locked loop networking control module, and a third harmonic injection control module.

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