A reactive power and voltage coordinated control method and related equipment for photovoltaic island flexible direct current transmission system

Abstract

The present invention discloses a method and related equipment for coordinated reactive power and voltage control of a photovoltaic island flexible direct current transmission system. The control and protection system collects the first three-phase instantaneous voltage of a centralized dynamic reactive compensation device at its grid connection point, and the second three-phase instantaneous voltage of each photovoltaic power generation unit at its grid connection point. Voltage closed-loop control is performed based on the first three-phase instantaneous voltage to generate a first reactive current command. Droop control is performed based on the second three-phase instantaneous voltage to generate a second reactive current command. Based on the first and second reactive current commands, the converter is called upon to output reactive currents, respectively. This reduces voltage distribution differences under reactive voltage control while effectively improving the control robustness of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of reactive power and voltage control, and in particular to a reactive power and voltage coordinated control method and related equipment for a photovoltaic island flexible direct current transmission system. Background Art

[0002] As the world responds to climate change and actively promotes energy transition, the development and utilization of solar energy, a clean and renewable energy source, has become a key path to achieving low-carbon development. However, the geographical distribution of solar-rich regions and power load centers is often uneven. This spatial mismatch between resources and demand has made large-scale photovoltaic development in remote solar-rich areas and the long-distance transmission of electricity to load centers a key goal of low-carbon development. Flexible DC transmission technology, with its advantages of long distance, large capacity, low losses, and independent control of active and reactive power, has become one of the core technologies to achieve this goal.

[0003] The application of flexible DC transmission technology in the specific scenario of large-scale, isolated PV power stations presents unique challenges. First, flexible DC replaces traditional rotating equipment, becoming the sole stable AC voltage source for the PV units, changing the traditional voltage support model. Second, the long electrical distance between the PV collection area and the flexible DC converter station consumes a large amount of reactive power. This loss of reactive power causes voltage drops on the power supply side, and in severe cases, can even cause system instability and collapse, significantly limiting the transmission capacity of PV active power. These combined factors deteriorate the voltage characteristics of the isolated transmission system, posing a risk to system stability.

[0004] In the existing technology, constant reactive power control or closed-loop constant voltage control is often used for reactive power voltage control strategies. Under the constant reactive power control mode, the voltage is difficult to adapt to changes in the system operation mode, resulting in large differences in voltage distribution when the output changes; and when multiple converter units adopt closed-loop constant voltage control, improper setting of control parameters may lead to interaction between control targets, resulting in reduced system stability. Summary of the Invention

[0005] The present invention provides a method and related equipment for coordinated reactive voltage control of a photovoltaic island flexible direct current transmission system, which solves the technical problems of large voltage distribution differences and poor control robustness of the reactive voltage at the sending end of the existing large-scale photovoltaic power station island flexible direct current transmission system under the traditional reactive voltage control method.

[0006] A first aspect of the present invention provides a method for coordinated reactive power and voltage control of a photovoltaic island flexible direct current transmission system, which is applied to a control and protection system within a sending end of the flexible direct current transmission system, wherein the control and protection system is communicatively connected to a centralized dynamic reactive power compensation device and multiple photovoltaic power generation units, respectively. The method includes:

[0007] Collecting the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and collecting the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point;

[0008] performing voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current instruction;

[0009] performing droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction;

[0010] According to the first reactive current instruction and the second reactive current instruction, the converter is called to output reactive current respectively.

[0011] Optionally, performing voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current instruction includes:

[0012] Calculating a first fundamental positive-sequence voltage amplitude and a first fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage;

[0013] Calculating a first positive-sequence voltage difference between a first positive-sequence voltage reference value and the first fundamental positive-sequence voltage amplitude;

[0014] Calculating a first negative-sequence voltage difference between a first negative-sequence voltage reference value and the first fundamental negative-sequence voltage amplitude;

[0015] Proportional integration and amplitude limiting are performed on the first positive-sequence voltage difference and the first negative-sequence voltage difference respectively to generate a first reactive current command.

[0016] Optionally, the calculating the fundamental positive-sequence voltage amplitude and the fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage includes:

[0017] Transforming the first three-phase instantaneous voltage from the positive-sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq-axis positive-sequence voltage;

[0018] Performing frequency multiplication elimination on the dq axis positive sequence voltage to obtain a dq axis positive sequence voltage component;

[0019] After low-pass filtering the dq axis positive sequence voltage component, calculating the first fundamental wave positive sequence voltage amplitude;

[0020] Transforming the first three-phase instantaneous voltage from a negative-sequence three-phase stationary coordinate system to a two-phase rotating coordinate system to obtain a dq-axis negative-sequence voltage;

[0021] Performing frequency multiplication elimination on the dq axis negative sequence voltage to obtain a negative sequence voltage component;

[0022] After low-pass filtering the dq-axis negative-sequence voltage components, the first fundamental negative-sequence voltage amplitude is calculated.

[0023] Optionally, performing droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction includes:

[0024] Calculating a second fundamental positive-sequence voltage amplitude and a second fundamental negative-sequence voltage amplitude corresponding to the second three-phase instantaneous voltage;

[0025] Calculating a second positive-sequence voltage difference between the first fundamental positive-sequence voltage amplitude and the second fundamental positive-sequence voltage amplitude;

[0026] Calculating a second negative-sequence voltage difference between the first fundamental negative-sequence voltage amplitude and the second fundamental negative-sequence voltage amplitude;

[0027] The second positive-sequence voltage difference and the second negative-sequence voltage difference are respectively proportionally controlled and limited to generate a second reactive current command.

[0028] Optionally, the proportional coefficient in the proportional control is:

[0029]

[0030] in, is the proportional coefficient of the j-th photovoltaic power generation unit connected to the grid at the unit grid connection point, is the minimum impedance among multiple photovoltaic power generation units connected to the grid at the unit grid connection point, is the preset reference coefficient, is the impedance between the jth photovoltaic power generation unit and the unit grid connection point.

[0031] Optionally, calling the converter to output reactive current respectively according to the first reactive current instruction and the second reactive current instruction includes:

[0032] generating a corresponding first reactive reference current and a second reactive reference current according to the first reactive current instruction and the second reactive current instruction respectively;

[0033] Using the first reactive reference current and the second reactive reference current, combined with a preset active reference current and an actual current signal, to perform current inner loop regulation to generate a first control signal and a second control signal;

[0034] After modulating the first control signal and the second control signal respectively, a first trigger pulse signal and a second trigger pulse signal are generated;

[0035] Using the first trigger pulse signal to trigger the converter to output reactive current to a centralized dynamic reactive power compensation device;

[0036] The second trigger pulse signal is used to trigger the converter to output reactive current to each of the photovoltaic power generation units.

[0037] Optionally, the method further includes:

[0038] According to the topology structure corresponding to the sending end of the flexible direct current transmission system, a system impedance model is constructed and an equivalent negative sequence impedance is obtained;

[0039] Calculating a ratio between a predicted negative sequence voltage value and the equivalent negative sequence impedance as a feedforward reactive compensation amount;

[0040] When the first reactive current command and the second reactive current command are generated, the feedforward reactive compensation amount is superimposed to update the first reactive current command and the second reactive current command.

[0041] A second aspect of the present invention provides a reactive power and voltage coordinated control device for a photovoltaic island flexible direct current transmission system, which is applied to a control and protection system within the sending end of the flexible direct current transmission system. The control and protection system is respectively communicatively connected to a centralized dynamic reactive power compensation device and multiple photovoltaic power generation units. The device includes:

[0042] A voltage acquisition module is used to acquire the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and to acquire the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point;

[0043] a first instruction generating module, configured to perform voltage closed-loop control according to the first three-phase instantaneous voltage and generate a first reactive current instruction;

[0044] a second instruction generating module, configured to perform droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction;

[0045] The voltage control module is used to call the converter to output reactive current respectively according to the first reactive current instruction and the second reactive current instruction.

[0046] A third aspect of the present invention provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the reactive voltage coordinated control method of the photovoltaic island flexible direct current transmission system as described in any one of the first aspects of the present invention.

[0047] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the reactive power and voltage coordinated control method of the photovoltaic island flexible direct current transmission system as described in any one of the first aspects of the present invention.

[0048] It can be seen from the above technical solutions that the present invention has the following advantages:

[0049] The present invention uses a control and protection system to collect the first three-phase instantaneous voltage of the centralized dynamic reactive compensation device at the device's grid connection point, and the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit's grid connection point. Voltage closed-loop control is performed based on the first three-phase instantaneous voltage to generate a first reactive current command. Droop control is performed based on the second three-phase instantaneous voltage to generate a second reactive current command. Based on the first and second reactive current commands, the converter is called upon to output reactive currents, respectively. This reduces voltage distribution variations under the reactive voltage control method while effectively improving the control robustness of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 A flowchart of the steps of a reactive power and voltage coordinated control method for a photovoltaic island flexible direct current transmission system provided by an embodiment of the present invention;

[0052] Figure 2 A topological structure diagram of a flexible direct current transmission system provided by an embodiment of the present invention;

[0053] Figure 3 A topological diagram of the sending end of a flexible direct current transmission system provided by an embodiment of the present invention;

[0054] Figure 4 A flow chart for calculating the fundamental positive-sequence voltage amplitude and the fundamental negative-sequence voltage amplitude provided by an embodiment of the present invention;

[0055] Figure 5 A flow chart for generating a first reactive current instruction provided by an embodiment of the present invention;

[0056] Figure 6 A flow chart for generating a second reactive current instruction provided by an embodiment of the present invention;

[0057] Figure 7 A trigger output flow chart of a converter provided by an embodiment of the present invention;

[0058] Figure 8 This is a structural block diagram of a reactive power and voltage coordinated control device for a photovoltaic island flexible direct current transmission system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The embodiment of the present invention provides a method and related equipment for coordinated reactive voltage control of a photovoltaic island flexible direct current transmission system, which is used to solve the technical problems of large voltage distribution differences and poor control robustness of the reactive voltage at the sending end of the existing large-scale photovoltaic power station island flexible direct current transmission system under the traditional reactive voltage control method.

[0060] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions 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 embodiments described below are only 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 making creative work are within the scope of protection of the present invention.

[0061] See also Figure 1 , Figure 1 A flowchart of the steps of a reactive power and voltage coordinated control method for a photovoltaic island flexible direct current transmission system provided by an embodiment of the present invention.

[0062] The present invention provides a method for coordinated reactive power and voltage control of a photovoltaic island flexible direct current transmission system, which is applied to a control and protection system within the sending end of the flexible direct current transmission system. The control and protection system is respectively connected to a centralized dynamic reactive power compensation device and multiple photovoltaic power generation units. The method includes:

[0063] Step 101: collecting the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and collecting the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point;

[0064] The flexible direct current transmission system refers to a large-scale photovoltaic power station islanded through flexible direct current transmission system. It is a new power system architecture used to solve the problem of long-distance power transmission in solar-rich areas. Its core is to use flexible direct current transmission (VSC-HVDC) technology to transmit power from large-scale photovoltaic power stations far away from the grid to load centers in an isolated manner, such as Figure 2 As shown, the sending end includes multiple photovoltaic power stations, control and protection systems, and centralized reactive power compensation devices. Each photovoltaic power station includes multiple photovoltaic power generation units. The output current at the grid connection point is converted into DC power by the sending end MMC converter and then transmitted to the receiving end AC system. The specific topological structure of the sending end is shown in the figure. Figure 3 As shown, each photovoltaic power generation unit is a generator set, which is connected to the unit grid connection point via a collection line. The centralized reactive power compensation device is connected to the converter via the device grid connection point. The control and protection system is communicated with the centralized dynamic reactive power compensation device and multiple photovoltaic power generation units respectively to achieve coordinated control of the reactive power and voltage of each device.

[0065] In an embodiment of the present invention, voltage sensors are respectively provided at the device grid-connected point and the unit grid-connected point, and the first three-phase instantaneous voltage and the second three-phase instantaneous voltage are obtained after anti-interference filtering.

[0066] Step 102: Perform voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current command;

[0067] In this embodiment, after the first three-phase instantaneous voltage is acquired, a voltage closed-loop control with positive and negative sequence separation is performed on it to generate a first reactive current instruction.

[0068] In one example of the present invention, step 102 may include the following sub-steps S11-S14:

[0069] S11. Calculate the first fundamental positive-sequence voltage amplitude and the first fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage;

[0070] Furthermore, S11 may include the following sub-steps:

[0071] The first three-phase instantaneous voltage is transformed from the positive sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq axis positive sequence voltage;

[0072] Perform frequency multiplication elimination on the dq axis positive sequence voltage to obtain the dq axis positive sequence voltage component;

[0073] After low-pass filtering the dq axis positive sequence voltage components, the first fundamental positive sequence voltage amplitude is calculated;

[0074] The first three-phase instantaneous voltage is transformed from the negative-sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq-axis negative-sequence voltage;

[0075] Perform frequency multiplication elimination on the dq axis negative sequence voltage to obtain the negative sequence voltage component;

[0076] After low-pass filtering the dq-axis negative-sequence voltage components, the first fundamental negative-sequence voltage amplitude is calculated.

[0077] See also Figure 4 , Figure 4 A calculation flow chart of the fundamental positive-sequence voltage amplitude and the fundamental negative-sequence voltage amplitude in the present invention is shown.

[0078] In this embodiment, taking the calculation of the first fundamental wave positive sequence voltage amplitude as an example, the first three-phase instantaneous voltage is transformed by the positive sequence abc / dq to obtain the dq axis voltage and , and the dq axis positive sequence voltage components are obtained through the frequency multiplication elimination link Gd. and , where the expression of the transfer function Gd is:

[0079]

[0080] Where, is the delay link, T is the voltage frequency period. The positive sequence abc / dq is transformed into:

[0081]

[0082] Among them, the positive sequence transformation matrix is:

[0083]

[0084] Where ωt is the fundamental rotation angular frequency.

[0085] dq axis positive sequence voltage component and The DC component of the dq axis positive sequence voltage is obtained through the low-pass filter Gf and , and then the first fundamental positive sequence voltage amplitude Up is obtained through the amplitude calculation link. The expression of Gf is:

[0086]

[0087] is the filtering time constant, which can be set to 0.01s, and S is a complex variable.

[0088] At the same time, the transformation of the first fundamental negative sequence voltage amplitude Un is similar, and its negative sequence transformation matrix is:

[0089]

[0090] S12, calculating a first positive-sequence voltage difference between a first positive-sequence voltage reference value and a first fundamental positive-sequence voltage amplitude;

[0091] S13, calculating a first negative-sequence voltage difference between a first negative-sequence voltage reference value and a first fundamental negative-sequence voltage amplitude;

[0092] S14 , proportionally integrating and limiting the first positive-sequence voltage difference and the first negative-sequence voltage difference respectively to generate a first reactive current command.

[0093] like Figure 5 As shown, after the first fundamental positive-sequence voltage amplitude and the first fundamental negative-sequence voltage amplitude are calculated, the first positive-sequence voltage difference and the first negative-sequence voltage difference are calculated respectively in combination with the first positive-sequence voltage reference value and the first negative-sequence voltage reference value, and after processing them through the PI proportional integral link, the reference current I is obtained. qrefip0 and I qrefin0 , after limiting, the first reactive current instruction is obtained, i.e. I qrefip and I qrefin .

[0094] Step 103, performing droop control according to the second three-phase instantaneous voltage to generate a second reactive current command;

[0095] In the embodiment of the present invention, for each photovoltaic power generation unit corresponding to the photovoltaic power generation group, after obtaining the second three-phase instantaneous voltage of its unit grid connection point, similarly Figure 4 The second fundamental positive sequence voltage amplitude and the second fundamental negative sequence voltage amplitude are calculated according to the process. After the second positive sequence voltage difference and the second negative sequence voltage difference are calculated, proportional control and amplitude limiting are performed respectively to generate the second reactive current instruction I qrefjp and I qrefjn .

[0096] In one example of the present invention, step 103 may include the following sub-steps:

[0097] Calculating a second fundamental positive-sequence voltage amplitude and a second fundamental negative-sequence voltage amplitude corresponding to the second three-phase instantaneous voltage;

[0098] Calculating a second positive-sequence voltage difference between the first fundamental positive-sequence voltage amplitude and the second fundamental positive-sequence voltage amplitude;

[0099] Calculating a second negative-sequence voltage difference between the first fundamental negative-sequence voltage amplitude and the second fundamental negative-sequence voltage amplitude;

[0100] The second positive-sequence voltage difference and the second negative-sequence voltage difference are respectively proportionally controlled and limited to generate a second reactive current command.

[0101] like Figure 6 As shown, in this embodiment, after obtaining the second fundamental positive sequence voltage amplitude Vjp and the second fundamental negative sequence voltage amplitude Vjn of the j-th photovoltaic power generation group, the second positive sequence voltage difference between the first fundamental positive sequence voltage amplitude and the second fundamental positive sequence voltage amplitude is calculated; the second negative sequence voltage difference between the first fundamental negative sequence voltage amplitude and the second fundamental negative sequence voltage amplitude is calculated, and after passing through the proportional control link, the reference current I is obtained. qrefjp0 and I qrefjn0 , after limiting, generates the second reactive current instruction I qrefjp and I qrefjn .

[0102] Among them, the proportional coefficient in proportional control is:

[0103]

[0104] in, is the proportional coefficient of the j-th photovoltaic power generation unit connected to the grid at the unit grid connection point, is the minimum impedance among multiple photovoltaic power generation units connected to the grid at the unit grid connection point, is the preset reference coefficient, is the impedance between the jth photovoltaic power generation unit and the unit grid connection point.

[0105] in, Can be set to 1.5.

[0106] In another example of the present invention, before executing step 104, the method further includes the following steps:

[0107] According to the topological structure corresponding to the sending end of the flexible DC transmission system, the system impedance model is constructed and the equivalent negative sequence impedance is obtained;

[0108] Calculate the ratio between the negative sequence voltage prediction value and the equivalent negative sequence impedance as the feedforward reactive compensation amount;

[0109] When the first reactive current command and the second reactive current command are generated, the feedforward reactive compensation amount is superimposed to update the first reactive current command and the second reactive current command.

[0110] In this embodiment, after calculating the fundamental negative-sequence voltage amplitude corresponding to the collection device's grid connection point and the unit's grid connection point, or historical negative-sequence voltage data from a period of time, a first-order inertial prediction, Kalman filtering, or model predictive control (MPC) algorithm is used to predict the negative-sequence voltage over a period of time. Simultaneously, the electrical connections at the sending end of the flexible HVDC transmission system are analyzed. Based on Kirchhoff's laws and component electromagnetic transient models, an equivalent circuit for the sending-end system is established, focusing on modeling the negative-sequence component flow path from the sending-end converter station to the photovoltaic side and centralized reactive power compensation device. The impedances of each component are connected in series or parallel according to their topological structure, and the equivalent negative-sequence impedance of the system is calculated.

[0111] The feedforward reactive compensation value is calculated by calculating the ratio between the predicted negative-sequence voltage and the equivalent negative-sequence impedance. After the calculated feedforward reactive compensation value is generated and the first and second reactive current commands are generated, this feedforward reactive compensation value is superimposed to update the first and second reactive current commands. Compared to feedforward based on measured values, the introduction of a prediction mechanism can respond to negative-sequence voltage changes in advance, making it particularly suitable for transient processes.

[0112] Step 104: In accordance with the first reactive current instruction and the second reactive current instruction, instruct the converter to output reactive current respectively.

[0113] Reactive current is used to adjust node voltage in real time and complete the coordinated control of reactive voltage at each node in the system.

[0114] In one example of the present invention, step 104 may include the following sub-steps:

[0115] generating a corresponding first reactive reference current and a second reactive reference current according to the first reactive current instruction and the second reactive current instruction respectively;

[0116] Using the first reactive reference current and the second reactive reference current, combined with the preset active reference current and the actual current signal, to perform current inner loop regulation to generate a first control signal and a second control signal;

[0117] After modulating the first control signal and the second control signal respectively, a first trigger pulse signal and a second trigger pulse signal are generated;

[0118] Using the first trigger pulse signal to trigger the converter to output reactive current to the centralized dynamic reactive power compensation device;

[0119] The second trigger pulse signal is used to trigger the converter to output reactive current to each photovoltaic power generation unit.

[0120] like Figure 7 As shown in the figure, the converter achieves reactive current output by controlling the on and off states of internal power electronic devices (such as IGBTs) to adjust the phase and amplitude of the output current. Taking a static VAR generator (SVG) converter as an example, the detection module monitors grid parameters such as voltage and current in real time. The control and calculation module calculates the amount of reactive power to be compensated based on the detection data. It then sends a control signal to the compensation output module, adjusting the on and off states of the power electronic devices in the bridge circuit. This changes the phase and amplitude of the AC output voltage or directly controls the AC current, causing the converter to output the corresponding reactive current.

[0121] In this embodiment, after calculating the corresponding first and second reactive current commands, corresponding first and second reactive reference currents are generated according to these commands. These are then combined with a preset active reference current and the actual current signal obtained through current feedback sampling, and input into the inner current loop. The reference current is a set target value based on, for example, the system's desired power output, while the current feedback sampling captures the current actual current in real time for comparison and adjustment. The inner current loop compares and analyzes the input reference current and the actual current feedback. Based on the difference between the two, a specific control algorithm (such as a proportional-integral-differential control algorithm) is used to perform calculations. This ensures that the actual current quickly and accurately tracks the reference current, minimizing the deviation between the two. After adjustment by the inner current loop, the first and second control signals are modulated to generate first and second trigger pulse signals. The modulated wave is a signal that changes according to a specific pattern and determines the subsequent operating state and output characteristics of the converter.

[0122] The first trigger pulse signal and the second trigger pulse signal act on the converter to control the on and off of the power electronic devices in the converter to output reactive current to the centralized dynamic reactive compensation device and / or each photovoltaic power generation unit.

[0123] In this embodiment of the present invention, a control and protection system collects the first three-phase instantaneous voltage of the centralized dynamic reactive compensation device at the device's grid connection point, and the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit's grid connection point. Voltage closed-loop control is performed based on the first three-phase instantaneous voltage to generate a first reactive current command. Droop control is performed based on the second three-phase instantaneous voltage to generate a second reactive current command. In response to the first and second reactive current commands, the converter is instructed to output reactive currents, respectively. This reduces voltage distribution variations under the reactive voltage control method while effectively improving the control robustness of the system.

[0124] See also Figure 8 , Figure 8 A structural block diagram of a reactive power and voltage coordinated control device for a photovoltaic island flexible direct current transmission system provided by an embodiment of the present invention is shown.

[0125] An embodiment of the present invention provides a reactive power and voltage coordinated control device for a photovoltaic island flexible direct current transmission system, which is applied to a control and protection system within the sending end of the flexible direct current transmission system. The control and protection system is respectively connected to a centralized dynamic reactive power compensation device and multiple photovoltaic power generation units. The device includes:

[0126] The voltage acquisition module 801 is used to acquire the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and to acquire the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point;

[0127] A first instruction generating module 802 is configured to perform voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current instruction;

[0128] A second instruction generating module 803 is configured to perform droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction;

[0129] The voltage control module 804 is configured to call the converter to output reactive current respectively according to the first reactive current instruction and the second reactive current instruction.

[0130] Optionally, the first instruction generating module 802 includes:

[0131] A first amplitude calculation submodule, configured to calculate a first fundamental positive-sequence voltage amplitude and a first fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage;

[0132] A first positive-sequence difference calculation submodule, configured to calculate a first positive-sequence voltage difference between a first positive-sequence voltage reference value and a first fundamental positive-sequence voltage amplitude;

[0133] A first negative-sequence difference calculation submodule, configured to calculate a first negative-sequence voltage difference between a first negative-sequence voltage reference value and a first fundamental negative-sequence voltage amplitude;

[0134] The first reactive power instruction generating submodule is configured to perform proportional integration and amplitude limiting on the first positive-sequence voltage difference and the first negative-sequence voltage difference, respectively, to generate a first reactive current instruction.

[0135] Optionally, the first amplitude calculation submodule is specifically configured to:

[0136] The first three-phase instantaneous voltage is transformed from the positive sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq axis positive sequence voltage;

[0137] Perform frequency multiplication elimination on the dq axis positive sequence voltage to obtain the dq axis positive sequence voltage component;

[0138] After low-pass filtering the dq axis positive sequence voltage components, the first fundamental positive sequence voltage amplitude is calculated;

[0139] The first three-phase instantaneous voltage is transformed from the negative-sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq-axis negative-sequence voltage;

[0140] Perform frequency multiplication elimination on the dq axis negative sequence voltage to obtain the negative sequence voltage component;

[0141] After low-pass filtering the dq-axis negative-sequence voltage components, the first fundamental negative-sequence voltage amplitude is calculated.

[0142] Optionally, the second instruction generating module 803 is specifically configured to:

[0143] Calculating a second fundamental positive-sequence voltage amplitude and a second fundamental negative-sequence voltage amplitude corresponding to the second three-phase instantaneous voltage;

[0144] Calculating a second positive-sequence voltage difference between the first fundamental positive-sequence voltage amplitude and the second fundamental positive-sequence voltage amplitude;

[0145] Calculating a second negative-sequence voltage difference between the first fundamental negative-sequence voltage amplitude and the second fundamental negative-sequence voltage amplitude;

[0146] The second positive-sequence voltage difference and the second negative-sequence voltage difference are respectively proportionally controlled and limited to generate a second reactive current command.

[0147] Optionally, the proportional coefficient within the proportional control is:

[0148]

[0149] in, is the proportional coefficient of the j-th photovoltaic power generation unit connected to the grid at the unit grid connection point, is the minimum impedance among multiple photovoltaic power generation units connected to the grid at the unit grid connection point, is the preset reference coefficient, is the impedance between the jth photovoltaic power generation unit and the unit grid connection point.

[0150] Optionally, the voltage control module 804 is specifically configured to:

[0151] generating a corresponding first reactive reference current and a second reactive reference current according to the first reactive current instruction and the second reactive current instruction respectively;

[0152] Using the first reactive reference current and the second reactive reference current, combined with the preset active reference current and the actual current signal, to perform current inner loop regulation to generate a first control signal and a second control signal;

[0153] After modulating the first control signal and the second control signal respectively, a first trigger pulse signal and a second trigger pulse signal are generated;

[0154] Using the first trigger pulse signal to trigger the converter to output reactive current to the centralized dynamic reactive power compensation device;

[0155] The second trigger pulse signal is used to trigger the converter to output reactive current to each photovoltaic power generation unit.

[0156] Optionally, the device further includes a feedforward adjustment module, specifically configured to:

[0157] According to the topological structure corresponding to the sending end of the flexible DC transmission system, the system impedance model is constructed and the equivalent negative sequence impedance is obtained;

[0158] Calculate the ratio between the negative sequence voltage prediction value and the equivalent negative sequence impedance as the feedforward reactive compensation amount;

[0159] When the first reactive current command and the second reactive current command are generated, the feedforward reactive compensation amount is superimposed to update the first reactive current command and the second reactive current command.

[0160] A third aspect of the present invention provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the reactive voltage coordinated control method of the photovoltaic island flexible direct current transmission system as described in any one of the first aspects of the present invention.

[0161] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the reactive power and voltage coordinated control method of the photovoltaic island flexible direct current transmission system as described in any one of the first aspects of the present invention.

[0162] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices and modules can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0163] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the modules is merely a logical function division. In actual implementation, there may be other division methods, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0164] The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules may be selected to achieve the purpose of the present embodiment according to actual needs.

[0165] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.

[0166] If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing an electronic device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0167] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for coordinated reactive power and voltage control of a photovoltaic island flexible direct current transmission system, characterized in that: A control and protection system applied to a sending end of a flexible direct current transmission system, wherein the control and protection system is communicatively connected to a centralized dynamic reactive power compensation device and a plurality of photovoltaic power generation units, and the method comprises: Collecting the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and collecting the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point; performing voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current instruction; performing droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction; According to the first reactive current instruction and the second reactive current instruction, calling the converter to output reactive current respectively; The performing voltage closed-loop control according to the first three-phase instantaneous voltage to generate a first reactive current instruction includes: Calculating a first fundamental positive-sequence voltage amplitude and a first fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage; Calculating a first positive-sequence voltage difference between a first positive-sequence voltage reference value and the first fundamental positive-sequence voltage amplitude; Calculating a first negative-sequence voltage difference between a first negative-sequence voltage reference value and the first fundamental negative-sequence voltage amplitude; performing proportional integration and amplitude limiting on the first positive-sequence voltage difference and the first negative-sequence voltage difference respectively to generate a first reactive current command; The performing droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction includes: Calculating a second fundamental positive-sequence voltage amplitude and a second fundamental negative-sequence voltage amplitude corresponding to the second three-phase instantaneous voltage; Calculating a second positive-sequence voltage difference between the first fundamental positive-sequence voltage amplitude and the second fundamental positive-sequence voltage amplitude; Calculating a second negative-sequence voltage difference between the first fundamental negative-sequence voltage amplitude and the second fundamental negative-sequence voltage amplitude; The second positive-sequence voltage difference and the second negative-sequence voltage difference are respectively proportionally controlled and limited to generate a second reactive current command.

2. The method according to claim 1, characterized in that The calculating the fundamental positive-sequence voltage amplitude and the fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage includes: Transforming the first three-phase instantaneous voltage from the positive-sequence three-phase stationary coordinate system to the two-phase rotating coordinate system to obtain the dq-axis positive-sequence voltage; Performing frequency multiplication elimination on the dq axis positive sequence voltage to obtain a dq axis positive sequence voltage component; After low-pass filtering the dq axis positive sequence voltage component, calculating the first fundamental wave positive sequence voltage amplitude; Transforming the first three-phase instantaneous voltage from a negative-sequence three-phase stationary coordinate system to a two-phase rotating coordinate system to obtain a dq-axis negative-sequence voltage; Performing frequency multiplication elimination on the dq axis negative sequence voltage to obtain a negative sequence voltage component; After low-pass filtering the dq-axis negative-sequence voltage components, the first fundamental negative-sequence voltage amplitude is calculated.

3. The method according to claim 1, characterized in that The proportional coefficient in the proportional control is: ； in, is the proportional coefficient of the j-th photovoltaic power generation unit connected to the grid at the unit grid connection point, is the minimum impedance among multiple photovoltaic power generation units connected to the grid at the unit grid connection point, is the preset reference coefficient, is the impedance between the jth photovoltaic power generation unit and the unit grid connection point.

4. The method according to claim 1, wherein The step of calling the converter to output reactive current respectively according to the first reactive current instruction and the second reactive current instruction includes: generating a corresponding first reactive reference current and a second reactive reference current according to the first reactive current instruction and the second reactive current instruction respectively; Using the first reactive reference current and the second reactive reference current, combined with a preset active reference current and an actual current signal, to perform current inner loop regulation to generate a first control signal and a second control signal; After modulating the first control signal and the second control signal respectively, a first trigger pulse signal and a second trigger pulse signal are generated; Using the first trigger pulse signal to trigger the converter to output reactive current to a centralized dynamic reactive power compensation device; The second trigger pulse signal is used to trigger the converter to output reactive current to each of the photovoltaic power generation units.

5. The method according to claim 1, wherein The method further comprises: According to the topology structure corresponding to the sending end of the flexible direct current transmission system, a system impedance model is constructed and an equivalent negative sequence impedance is obtained; Calculating a ratio between a predicted negative sequence voltage value and the equivalent negative sequence impedance as a feedforward reactive compensation amount; When the first reactive current command and the second reactive current command are generated, the feedforward reactive compensation amount is superimposed to update the first reactive current command and the second reactive current command.

6. A reactive power and voltage coordinated control device for a photovoltaic island flexible direct current transmission system, characterized in that: A control and protection system applied to the sending end of a flexible direct current transmission system, wherein the control and protection system is respectively connected to a centralized dynamic reactive power compensation device and multiple photovoltaic power generation units, and the device comprises: A voltage acquisition module is used to acquire the first three-phase instantaneous voltage of the centralized dynamic reactive power compensation device at the device grid connection point, and to acquire the second three-phase instantaneous voltage of each photovoltaic power generation unit at the unit grid connection point; a first instruction generating module, configured to perform voltage closed-loop control according to the first three-phase instantaneous voltage and generate a first reactive current instruction; a second instruction generating module, configured to perform droop control according to the second three-phase instantaneous voltage to generate a second reactive current instruction; a voltage control module, configured to call a converter to output reactive currents respectively according to the first reactive current instruction and the second reactive current instruction; The first instruction generation module includes: A first amplitude calculation submodule, configured to calculate a first fundamental positive-sequence voltage amplitude and a first fundamental negative-sequence voltage amplitude corresponding to the first three-phase instantaneous voltage; A first positive-sequence difference calculation submodule, configured to calculate a first positive-sequence voltage difference between a first positive-sequence voltage reference value and the first fundamental positive-sequence voltage amplitude; A first negative-sequence difference calculation submodule, configured to calculate a first negative-sequence voltage difference between a first negative-sequence voltage reference value and the first fundamental negative-sequence voltage amplitude; a first reactive current instruction generating submodule, configured to perform proportional integration and amplitude limiting on the first positive-sequence voltage difference and the first negative-sequence voltage difference, respectively, to generate a first reactive current instruction; The second instruction generation module is specifically used to: Calculating a second fundamental positive-sequence voltage amplitude and a second fundamental negative-sequence voltage amplitude corresponding to the second three-phase instantaneous voltage; Calculating a second positive-sequence voltage difference between the first fundamental positive-sequence voltage amplitude and the second fundamental positive-sequence voltage amplitude; Calculating a second negative-sequence voltage difference between the first fundamental negative-sequence voltage amplitude and the second fundamental negative-sequence voltage amplitude; The second positive-sequence voltage difference and the second negative-sequence voltage difference are respectively proportionally controlled and limited to generate a second reactive current command.

7. An electronic device, characterized in that: It includes a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the reactive voltage coordinated control method of the photovoltaic island flexible direct current transmission system as described in any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the reactive power and voltage coordinated control method of the photovoltaic island flexible direct current transmission system according to any one of claims 1 to 5 is implemented.

Images