Direct-current power transmission grid-connected system stability control method, device and equipment and storage medium

Abstract

The invention discloses a stability control method, device and equipment for a direct current transmission grid-connected system and a storage medium, and the method comprises the steps: enabling the loop gain of a coupling system composed of a reactive compensation device, a receiving end converter and a weak power grid to meet a generalized Nyquist stability criterion through precisely controlling the output of the receiving end converter; therefore, the dynamic response capability and the overall stability of the system are enhanced. The method comprises the following steps: determining a direct-current voltage parameter of a receiving end side, and determining a current reference value of the receiving end side according to the direct-current voltage parameter and an outer loop controller of the high-voltage direct-current power transmission system; determining an actual current value of the receiving end side; determining a current control value of the receiving end side according to the current reference value, the current actual value and an inner ring controller of the high-voltage direct-current power transmission system; determining a grid-connected point voltage and a virtual voltage, and determining a modulation signal according to the grid-connected point voltage, the virtual voltage, the first axial current control value and the second axial current control value; and performing stable control on the receiving-end converter according to the modulation signal.

Description

Technical Field

[0001] The present application relates to the field of power system control technology, and in particular to a method, device, equipment and storage medium for stable control of a direct current transmission grid-connected system. Background Art

[0002] With the increasing penetration of renewable energy sources such as wind power and photovoltaics in the power system, their intermittency and instability pose severe challenges to the safe and stable operation of the power grid. Especially in the process of reactive power compensation devices participating in the grid connection of new energy through high-voltage direct current (HVDC), the dynamic characteristics of the HVDC system and the high-frequency switching action of power electronic devices may cause dynamic instability in the system in the low-frequency band. The stability of the power system is usually evaluated by the impedance characteristics of the system, which is mainly determined by the physical characteristics of the transmission line and power electronic devices. In the DC transmission grid-connected system, the dynamic behavior of the power electronic converter has an important influence on the system impedance characteristics. Especially under weak grid conditions, the low-frequency impedance characteristics of the HVDC system can easily induce system resonance, thereby causing stability problems. Therefore, effective control methods are urgently needed to deal with it. Summary of the invention

[0003] In view of this, the present application provides a method, device, equipment and storage medium for stable control of a direct current transmission grid-connected system, the main purpose of which is to solve the problem that in the current process of grid-connected power through high-voltage direct current (HVDC), the dynamic characteristics of the HVDC system and the high-frequency switching action of power electronic devices may cause the system to be dynamically unstable in the low-frequency band. Especially under weak grid conditions, the low-frequency impedance characteristics of the HVDC system are prone to induce system resonance, thereby causing stability problems. Therefore, an effective control method is urgently needed to address the problem.

[0004] According to a first aspect of the present application, a method for stabilizing a direct current transmission grid-connected system is provided, the method being applicable to a high voltage direct current transmission system, the method comprising:

[0005] Determine a DC voltage parameter at the receiving end, and determine a current reference value at the receiving end according to the DC voltage parameter and an outer loop controller of the high voltage direct current transmission system, wherein the DC voltage parameter includes a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value;

[0006] Determine an actual current value at the receiving end side, wherein the actual current value includes a first axial current actual value and a second axial current actual value;

[0007] Determine the current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value;

[0008] Determine a grid-connected point voltage and a virtual voltage, and determine a modulation signal according to the grid-connected point voltage, the virtual voltage, the first axial current control value, and the second axial current control value;

[0009] The receiving-end converter is stably controlled according to the modulation signal.

[0010] Optionally, determining the first axial current reference value according to the DC voltage parameter and an outer loop controller of the high voltage DC power transmission system includes:

[0011] Determine an error value between the DC voltage set value and the DC voltage actual value, and multiply the error value by the outer loop controller to obtain the first axial current reference value;

[0012] Among them, the outer loop controller is, is the proportional coefficient of the outer loop controller, is the integral coefficient of the outer loop controller, and is the complex frequency.

[0013] Optionally, determining the current control value of the receiving end side according to the current reference value, the actual current value and the inner loop controller of the high voltage direct current transmission system includes:

[0014] Calculating a difference between the first axial current reference value and the first axial current actual value, and multiplying the difference by the inner loop controller to obtain the first axial current control value;

[0015] Among them, the inner loop controller is, wherein is the proportional coefficient of the inner loop controller, is the integral coefficient of the inner loop controller, and is the complex frequency.

[0016] Optionally, determining the current control value at the receiving end side according to the current reference value, the actual current value and the inner loop controller of the high-voltage direct current transmission system also includes: calculating the difference between the second axial current reference value and the second axial current actual value, and multiplying the difference by the inner loop controller to obtain the second axial current control value.

[0017] Optionally, determining the modulation signal according to the grid connection point voltage, the virtual voltage, the first axial current control value, and the second axial current control value includes:

[0018] Determine a first axial grid-connected voltage component and a second axial grid-connected voltage component of the grid-connected voltage, and determine a first axial virtual voltage component and a second axial virtual voltage component of the virtual voltage, wherein the first axial virtual voltage component is, and the second axial virtual voltage component is, wherein is a virtual inertia coefficient and is a virtual damping coefficient;

[0019] Calculating a first product of the first axial current actual value and a target parameter, and calculating a sum of the first product and the first axial grid-connected voltage component, wherein the target parameter is a second product of a reference angular frequency and an inductance value of a filter circuit;

[0020] Calculating a first difference between the sum and the first axial current control value and the first axial virtual voltage component, and taking a ratio between the first difference and the DC voltage given value as the first axial modulation signal;

[0021] The second axial modulation signal is determined according to the second axial grid-connected voltage component, the second axial virtual voltage component, and the second axial current control value.

[0022] Optionally, determining the second axial modulation signal based on the second axial grid-connected voltage component, the second axial virtual voltage component, and the second axial current control value includes: calculating the second difference between the second axial grid-connected voltage component and the second axial current control value, the first product, and the second axial virtual voltage component, and taking the ratio of the second difference to the DC voltage given value as the second axial modulation signal.

[0023] Optionally, the stable control of the receiving-end converter according to the modulation signal includes: generating an SVPWM wave according to the first axial modulation signal and the second axial modulation signal, and using the SVPWM wave to drive a power switch of the receiving-end converter for stable control.

[0024] According to a second aspect of the present application, a DC transmission grid-connected system stability control device is provided, the device comprising:

[0025] A first determination module is used to determine a DC voltage parameter at a receiving end, and determine a current reference value at the receiving end according to the DC voltage parameter and an outer loop controller of the high voltage direct current transmission system, wherein the DC voltage parameter includes a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value;

[0026] A second determination module is used to determine an actual current value at the receiving end side, wherein the actual current value includes a first axial current actual value and a second axial current actual value;

[0027] a third determination module, configured to determine a current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value;

[0028] a fourth determination module, configured to determine a grid connection point voltage and a virtual voltage, and determine a modulation signal according to the grid connection point voltage, the virtual voltage, the first axial current control value, and the second axial current control value;

[0029] The stabilization control module is used to perform stabilization control on the receiving-end converter according to the modulation signal.

[0030] Optionally, the first determination module is used to determine the error value between the DC voltage set value and the DC voltage actual value, and multiply the error value by the outer loop controller to obtain the first axial current reference value; wherein the outer loop controller is G1(s), G1(s)=k p1 +k i1 / s,k p1 is the proportional coefficient of the outer loop controller, k i1 is the integral coefficient of the outer loop controller, and s is the complex frequency.

[0031] Optionally, the third determination module is used to calculate the difference between the first axial current reference value and the first axial current actual value, and multiply the difference by the inner loop controller to obtain the first axial current control value; wherein the inner loop controller is G2(s), G2(s)=k p2 +k i2 / s, where k p2 is the proportional coefficient of the inner loop controller, k i2 is the integral coefficient of the inner loop controller, and s is the complex frequency.

[0032] Optionally, the third determination module is used to calculate the difference between the second axial current reference value and the second axial current actual value, and multiply the difference by the inner loop controller to obtain the second axial current control value.

[0033] Optionally, the fourth determination module is used to determine a first axial grid-connected voltage component and a second axial grid-connected voltage component of the grid-connected voltage, and to determine a first axial virtual voltage component and a second axial virtual voltage component of the virtual voltage, wherein the first axial virtual voltage component is u dvir ,u dvir =(sk1+k2)·i d , the second axial virtual voltage component is u qvir ,uqvir =(sk1+k2)·i q , wherein k1 is a virtual inertia coefficient and k2 is a virtual damping coefficient; calculating a first product of the actual value of the first axial current and a target parameter, and calculating a sum of the first product and the first axial grid-connected voltage component, wherein the target parameter is a second product between a reference angular frequency and an inductance value of a filter circuit; calculating a first difference between the sum and the first axial current control value and the first axial virtual voltage component, and taking a ratio between the first difference and the given DC voltage value as the first axial modulation signal; determining the second axial modulation signal according to the second axial grid-connected voltage component, the second axial virtual voltage component and the second axial current control value.

[0034] Optionally, the fourth determination module is used to calculate the second difference between the second axial grid-connected voltage component and the second axial current control value, the first product, and the second axial virtual voltage component, and use the ratio of the second difference to the DC voltage given value as the second axial modulation signal.

[0035] Optionally, the stability control module is used to generate an SVPWM wave according to the first axial modulation signal and the second axial modulation signal, and use the SVPWM wave to drive the power switch of the receiving-end converter to perform stability control.

[0036] According to a third aspect of the present application, a computer device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of any one of the methods described in the first aspect when executing the computer program.

[0037] According to a fourth aspect of the present application, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of any one of the methods described in the first aspect are implemented.

[0038] By means of the above technical scheme, the present application provides a method, device, equipment and storage medium for stable control of a DC power transmission grid-connected system. The present application first determines the DC voltage parameters of the receiving end, and determines the current reference value of the receiving end according to the DC voltage parameters and the outer loop controller of the high-voltage DC power transmission system, wherein the DC voltage parameters include a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value. Further, the actual current value of the receiving end is determined, and the actual current value includes a first axial current actual value and a second axial current actual value. Next, according to the current reference value, the actual current value and the inner loop controller of the high-voltage DC power transmission system, the current control value of the receiving end is determined, and the current control value includes a first axial current control value and a second axial current control value. Subsequently, the grid connection point voltage and the virtual voltage are determined, and the signal is modulated according to the grid connection point voltage, the virtual voltage, the first axial current control value and the second axial current control value. Finally, the receiving end converter is stably controlled according to the modulated signal. The embodiment of the present application reshapes the output impedance of the new energy side through the software control layer without adding additional hardware equipment. This control method effectively optimizes the output impedance characteristics of the receiving end of the high-voltage direct current transmission system, and can significantly suppress the DC side oscillation problem that may be caused, especially when connected to a weak power grid. Specifically, by accurately controlling the output of the receiving-end converter, the loop gain of the coupling system consisting of the reactive compensation device, the receiving-end converter and the weak power grid meets the generalized Nyquist stability criterion, thereby enhancing the dynamic response capability and overall stability of the system. In addition, the embodiment of the present application improves the output impedance of the receiving-end converter of the high-voltage direct current transmission system by introducing a virtual impedance link, thereby improving the stability margin of the system.

[0039] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0041] Figure 1 A schematic flow chart of a DC transmission grid-connected system stability control method provided in an embodiment of the present application is shown;

[0042] Figure 2A schematic structural diagram of a receiving end of a high-voltage direct current transmission system of a direct current transmission grid-connected system stability control method provided in an embodiment of the present application is shown;

[0043] Figure 3 A schematic flow chart of a DC transmission grid-connected system stability control method provided in an embodiment of the present application is shown;

[0044] Figure 4 A schematic flow chart of a DC transmission grid-connected system stability control method provided in an embodiment of the present application is shown;

[0045] Figure 5 A schematic diagram of a Nyquist curve before and after impedance reshaping of a DC transmission grid-connected system stability control method provided by an embodiment of the present application is shown;

[0046] Figure 6 A schematic structural diagram of a DC power transmission grid-connected system stability control device provided in an embodiment of the present application is shown;

[0047] Figure 7 A schematic diagram of the device structure of a computer device provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0048] The exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0049] With the increasing penetration of renewable energy such as wind power and photovoltaic power in the power system, its intermittency and instability have posed severe challenges to the safe and stable operation of the power grid. Especially in the process of reactive power compensation devices participating in the grid connection of new energy through high-voltage direct current (HVDC), the system stability problem is more prominent, and effective control methods are urgently needed to deal with it. High-voltage direct current transmission technology has become one of the important technologies for large-scale transmission of new energy due to its low transmission loss over long distances, flexible control, and ability to effectively solve the grid connection problems that are difficult to overcome in AC systems. However, the dynamic characteristics of the HVDC system and the high-frequency switching action of power electronic devices may cause dynamic instability in the system in the low-frequency band. The stability of the power system is usually evaluated by the impedance characteristics of the system, which is mainly determined by the physical characteristics of the transmission line and the power electronic device. In the DC transmission grid-connected system, the dynamic behavior of the power electronic converter has an important influence on the system impedance characteristics. Especially under weak grid conditions, the low-frequency impedance characteristics of the HVDC system are prone to induce system resonance, thereby causing stability problems.

[0050] The present application embodiment provides a DC transmission grid-connected system stability control method, such as Figure 1 As shown, the method includes:

[0051] S10. Determine the DC voltage parameters on the receiving end side, and determine the current reference value on the receiving end based on the DC voltage parameters and the outer loop controller of the high voltage DC transmission system, wherein the DC voltage parameters include a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value.

[0052] In an embodiment of the present application, in order to solve the above technical problems, the low-frequency impedance reshaping technology adjusts the impedance characteristics of the system by changing the control parameters of the receiving-end converter or introducing active damping and other measures, which becomes an effective means to improve the stability of the system. The core of this method lies in the reshaping of the impedance characteristics of the low-frequency band, thereby improving the phase margin and gain margin of the system to enhance the dynamic response capability and overall stability of the system. The HVDC grid-connected system stability control method based on low-frequency impedance reshaping can not only effectively improve the stability and robustness of the system by optimizing the low-frequency impedance characteristics in a targeted manner, but also has important theoretical value and practical engineering application significance in solving the low-frequency oscillation problem in the process of new energy grid connection.

[0053] Specifically, first determine the HVDC transmission system to be connected to the grid. The structure diagram of the receiving end of the HVDC transmission system is as follows: Figure 2 As shown in the figure, it includes AC power grid, grid-side resistors and inductors, HVDC power transmission system receiving-end converter, converter AC-side filter inductor and converter DC-side support capacitor. The sending-end and DC-side capacitors of the HVDC power transmission system can be regarded as ideal voltage sources. Among them, C dc is the DC side support capacitor of the converter, u dc is the actual voltage on the DC side, L is the inductance of the filter circuit, u pcc is the voltage at the common coupling point (grid connection point), L g is the equivalent inductance of the AC grid, R g is the equivalent resistance of the AC grid.

[0054] Furthermore, using Figure 3 The stability margin improvement process shown in the figure is used for parameter calculation. In this step, it is necessary to determine the DC voltage given value u dcref The actual value of DC voltage u dc The error value e between them is multiplied by the outer loop controller G1(s) to obtain the first axial current reference value i dref Among them, the outer loop controller is G1(s), G1(s) = k p1 +k i1 / s,k p1 is the proportional coefficient of the outer loop controller, ki1 is the integral coefficient of the outer loop controller, and s is the complex frequency. It should be noted that in the high-voltage direct current (HVDC) grid-connected system, the concepts of the d-axis and the q-axis come from the field of motor control, especially in the control of synchronous motors and permanent magnet synchronous motors (PMSM). These two axes form a rotating coordinate system, usually called the dq coordinate system or the synchronous rotating coordinate system. In the HVDC grid-connected system, the d-axis can be compared to an axis aligned with the grid voltage phase. The d-axis current is mainly responsible for controlling the flow of active power. The d-axis current is in phase with the grid voltage, so it directly affects the active power transmission of the system. By controlling the d-axis current, the active power exchange between the transmission system and the grid can be adjusted to maintain the power balance of the grid. The q-axis is perpendicular to the d-axis, forming an orthogonal coordinate system. In the HVDC system, the q-axis can be compared to an axis perpendicular to the grid voltage phase. The q-axis current is mainly responsible for controlling the flow of reactive power. The q-axis current is 90 degrees out of phase with the grid voltage, so it mainly affects the reactive power transmission and voltage support of the system. By controlling the q-axis current, the reactive power exchange between the transmission system and the power grid can be adjusted to maintain the voltage stability of the power grid.

[0055] In the embodiment of the present application, by optimizing the current control of the d-axis and the q-axis, the DC side oscillation that may be caused when connecting to a weak power grid can be suppressed, and the stability and robustness of the system can be improved. In actual operation, the first axis is the d-axis and the second axis is the q-axis.

[0056] S20. Determine an actual current value at the receiving end side, where the actual current value includes a first axial current actual value and a second axial current actual value.

[0057] In this step, the actual value of the first axial current i can be monitored and recorded in real time through the AC side filter inductor and the DC side support capacitor of the converter at the receiving end of the high voltage direct current transmission system. d and the second axial current actual value i q Real-time monitoring data provides accurate feedback for current control, allowing the control strategy to more accurately adjust the current to achieve a predetermined reference value.

[0058] S30, determining a current control value at the receiving end side according to a current reference value, an actual current value and an inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value.

[0059] In this step, if Figure 3 As shown, the first axial current reference value i is calculated dref The actual value of the first axial current i dThe difference between them is calculated and multiplied by the inner loop controller G2(s) to obtain the first axial current control value (d-axis current control value). The inner loop controller is G2(s), G2(s)=k p2 +k i2 / s,k p2 is the proportional coefficient of the inner loop controller, k i2 is the integral coefficient of the inner loop controller, and s is the complex frequency. Further, the second axial current reference value i is calculated qref The actual value of the second axial current i q The difference between the reference value and the actual value of the first and second axial currents is calculated by multiplying the difference with the inner loop controller G2(s) to obtain the second axial current control value (q-axis current control value). In the embodiment of the present application, the current control value is accurately adjusted by accurately calculating the difference between the reference value and the actual value of the first and second axial currents, and combining the proportional and integral control effects of the inner loop controller. At the same time, the reasonable configuration of the proportional coefficient and the integral coefficient can optimize the response speed and overshoot of the system, so that the system can recover to a stable state more quickly when disturbed.

[0060] S40, determining a grid-connected point voltage and a virtual voltage, and determining a modulation signal according to the grid-connected point voltage, the virtual voltage, the first axial current control value, and the second axial current control value.

[0061] In the embodiment of the present application, in order to achieve effective control of the current and voltage in the power system and ensure the stable operation and high efficiency of the system, it is necessary to perform accurate calculation and comparison through the following steps S41 to S44. Specifically, Figure 4 As shown, in step S41, it is necessary to determine the axial components of the grid-connected voltage and the virtual voltage. In step S42, the relationship between the reference angular frequency and the inductance of the filter circuit is determined by calculating the product of the actual value of the first axial current and the target parameter, and the sum of the product and the first axial grid-connected voltage component. In step S43, the difference between the actual value and the control value of the first axial current is calculated, and the ratio of this difference to the given value of the DC voltage is used as the first axial modulation signal. Finally, in step S44, the second axial control signal is determined by calculating the difference between the second axial grid-connected voltage component and the current control value, the first product, and the virtual voltage component, and the ratio of this difference to the given value of the DC voltage is used as the second axial modulation signal.

[0062] S41, determining a first axial grid-connected voltage component and a second axial grid-connected voltage component of a grid-connected voltage, and determining a first axial virtual voltage component and a second axial virtual voltage component of a virtual voltage.

[0063] In the analysis of power system grid connection, in order to optimize the system stability and dynamic response, it is necessary to determine the first axial grid-connected voltage component u when determining the current control and modulation signal. d (d-axis grid-connected voltage component) and the second-axis grid-connected voltage component u q (q-axis grid-connected voltage component). In an actual power system, a three-phase voltage signal can be obtained by a power quality analyzer (PQAnalyzer) or similar measuring equipment, and then the α-β components in the three-phase coordinate system are converted to the synchronously rotating dq coordinate system to obtain the first axial grid-connected voltage component u d and the second axial grid-connected voltage component u q . Further, in the high-voltage direct current (HVDC) grid-connected system, the determination of the d-axis and q-axis virtual voltage components is to improve the dynamic response and stability of the system. These virtual voltage components are usually introduced based on the control strategy to simulate the virtual inertia and damping effect of the system. The virtual voltage component is a concept introduced in the control system to simulate the voltage component that does not exist in the actual power system, and then adjust the impedance characteristics of the system to improve the dynamic performance of the system. Specifically, the first axial virtual voltage component (d-axis virtual voltage component) is u dvir ,u dvir =(sk1+k2)·i d , the second axial virtual voltage component (q-axis virtual voltage component) is u qvir ,u qvir =(sk1+k2)·i q , where k1 is the virtual inertia coefficient and k2 is the virtual damping coefficient. The parameters in the virtual voltage component (such as the virtual inertia coefficient k1 and the virtual damping coefficient k2) need to be determined according to the specific needs and design goals of the system. These parameters can be determined through simulation analysis, system identification or experience-based adjustment to ensure that the system can achieve the expected stability and dynamic response after the introduction of the virtual voltage component.

[0064] S42, calculating a first product of the actual value of the first axial current and a target parameter, and calculating a sum of the first product and the first axial grid-connected voltage component, wherein the target parameter is a second product of a reference angular frequency and an inductance value of a filter circuit.

[0065] S43, calculating a first difference between the sum value and the first axial current control value and the first axial virtual voltage component, and taking a ratio between the first difference and a given DC voltage value as a first axial modulation signal.

[0066] In a high voltage direct current (HVDC) transmission system, the d-axis and q-axis modulation signals (m d and m q) is a key part of the current control strategy, which is used to generate a space vector pulse width modulation (SVPWM) wave to drive the receiving end converter. Specifically, in step S42 and step S43, the actual value of the first axial current i is calculated. d The first product of the target parameter and the first axial grid-connected voltage component u are calculated. d The target parameter is the second product of the reference angular frequency ω and the inductance value L of the filter circuit. Further, the sum value and the first axial current control value and the first axial virtual voltage component u are calculated. dvir The first difference between the first difference and the DC voltage given value u dcref The ratio between them is taken as the first axial modulation signal m d .

[0067] S44. Determine a second axial modulation signal according to the second axial grid-connected voltage component, the second axial virtual voltage component, and the second axial current control value.

[0068] Further, the second axial grid-connected voltage component u is calculated q and the second axial current control value, the first product, the second axial virtual voltage component u qvir The second difference between the two values ​​is calculated by adding the second difference to the given DC voltage value u dcref The ratio between them is taken as the second axial modulation signal m q .

[0069] S50, stably controlling the receiving-end converter according to the modulation signal.

[0070] In this step, according to the first axial modulation signal m d and the second axial modulation signal m q Generate SVPWM wave, and use the SVPWM wave to drive the power switch of the receiving-end converter to perform stable control.

[0071] The Nyquist curves before and after impedance remodeling provided in the embodiment of the present application are as follows: Figure 5 As shown in the figure, when the proposed control strategy is not adopted, the Nyquist curve of the coupled system composed of the static VAR generator, the receiving end of the HVDC transmission system and the weak power grid surrounds the point (-1, j0), and the system is in an unstable state at this time; when the proposed control strategy is adopted, the curve no longer surrounds the point (-1, j0), and the system is stable at this time. It can be seen that the proposed control strategy can effectively improve the negative damping characteristics of the receiving-end converter of the HVDC transmission system and improve the system stability margin.

[0072] The method provided in the embodiment of the present application first determines the DC voltage parameters on the receiving side, and determines the current reference value on the receiving side according to the DC voltage parameters and the outer loop controller of the high-voltage direct current transmission system, wherein the DC voltage parameters include the DC voltage set value and the DC voltage actual value, and the current reference value includes the first axial current reference value and the second axial current reference value. Further, the actual current value on the receiving side is determined, and the actual current value includes the first axial current actual value and the second axial current actual value. Next, according to the current reference value, the actual current value and the inner loop controller of the high-voltage direct current transmission system, the current control value on the receiving side is determined, and the current control value includes the first axial current control value and the second axial current control value. Subsequently, the grid connection point voltage and the virtual voltage are determined, and the signal is modulated according to the grid connection point voltage, the virtual voltage, the first axial current control value and the second axial current control value. Finally, the receiving-end converter is stably controlled according to the modulated signal. The embodiment of the present application reshapes the output impedance of the new energy side through the software control layer without adding additional hardware equipment. This control method effectively optimizes the output impedance characteristics of the receiving end of the high-voltage direct current transmission system, and can significantly suppress the DC side oscillation problem that may be caused, especially when connected to a weak power grid. Specifically, by accurately controlling the output of the receiving-end converter, the loop gain of the coupling system consisting of the reactive compensation device, the receiving-end converter and the weak power grid meets the generalized Nyquist stability criterion, thereby enhancing the dynamic response capability and overall stability of the system. In addition, the embodiment of the present application improves the output impedance of the receiving-end converter of the high-voltage direct current transmission system by introducing a virtual impedance link, thereby improving the stability margin of the system.

[0073] Further, as Figure 1 In a specific implementation of the method, the present application provides a DC transmission grid-connected system stability control device, such as Figure 6 As shown, the device includes: a first determination module 601 , a second determination module 602 , a third determination module 603 , a fourth determination module 604 , and a stability control module 605 .

[0074] The first determination module 601 is used to determine a DC voltage parameter at the receiving end, and determine a current reference value at the receiving end according to the DC voltage parameter and an outer loop controller of the high voltage direct current transmission system, wherein the DC voltage parameter includes a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value;

[0075] The second determination module 602 is used to determine the actual current value at the receiving end side, where the actual current value includes a first axial current actual value and a second axial current actual value;

[0076] The third determination module 603 is used to determine the current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value;

[0077] The fourth determination module 604 is used to determine the grid connection point voltage and the virtual voltage, and determine the modulation signal according to the grid connection point voltage, the virtual voltage, the first axial current control value and the second axial current control value;

[0078] The stability control module 605 is used to perform stability control on the receiving-end converter according to the modulation signal.

[0079] Optionally, the first determination module 601 is used to determine the error value between the DC voltage set value and the DC voltage actual value, and multiply the error value by the outer loop controller to obtain the first axial current reference value; wherein the outer loop controller is G1(s), G1(s)=k p1 +k i1 / s,k p1 is the proportional coefficient of the outer loop controller, k i1 is the integral coefficient of the outer loop controller, and s is the complex frequency.

[0080] Optionally, the third determination module 603 is used to calculate the difference between the first axial current reference value and the first axial current actual value, and multiply the difference by the inner loop controller to obtain the first axial current control value; wherein the inner loop controller is G2(s), G2(s)=k p2 +k i2 / s, where k p2 is the proportional coefficient of the inner loop controller, k i2 is the integral coefficient of the inner loop controller, and s is the complex frequency.

[0081] Optionally, the third determination module 603 is used to calculate the difference between the second axial current reference value and the second axial current actual value, and multiply the difference by the inner loop controller to obtain the second axial current control value.

[0082] Optionally, the fourth determination module 604 is used to determine a first axial grid-connected voltage component and a second axial grid-connected voltage component of the grid-connected voltage, and to determine a first axial virtual voltage component and a second axial virtual voltage component of the virtual voltage, wherein the first axial virtual voltage component is u dvir ,u dvir =(sk1+k2)·i d , the second axial virtual voltage component is uqvir ,u qvir =(sk1+k2)·i q , wherein k1 is a virtual inertia coefficient and k2 is a virtual damping coefficient; calculating a first product of the actual value of the first axial current and a target parameter, and calculating a sum of the first product and the first axial grid-connected voltage component, wherein the target parameter is a second product between a reference angular frequency and an inductance value of a filter circuit; calculating a first difference between the sum and the first axial current control value and the first axial virtual voltage component, and taking a ratio between the first difference and the given DC voltage value as the first axial modulation signal; determining the second axial modulation signal according to the second axial grid-connected voltage component, the second axial virtual voltage component and the second axial current control value.

[0083] Optionally, the fourth determination module 604 is used to calculate the second difference between the second axial grid-connected voltage component and the second axial current control value, the first product, and the second axial virtual voltage component, and use the ratio of the second difference to the DC voltage given value as the second axial modulation signal.

[0084] Optionally, the stability control module 605 is used to generate an SVPWM wave according to the first axial modulation signal and the second axial modulation signal, and use the SVPWM wave to drive the power switch of the receiving-end converter to perform stability control.

[0085] The device provided in the embodiment of the present application first determines the DC voltage parameters on the receiving side, and determines the current reference value on the receiving side according to the DC voltage parameters and the outer loop controller of the high-voltage direct current transmission system, wherein the DC voltage parameters include the DC voltage set value and the DC voltage actual value, and the current reference value includes the first axial current reference value and the second axial current reference value. Further, the actual current value on the receiving side is determined, and the actual current value includes the first axial current actual value and the second axial current actual value. Next, according to the current reference value, the actual current value and the inner loop controller of the high-voltage direct current transmission system, the current control value on the receiving side is determined, and the current control value includes the first axial current control value and the second axial current control value. Subsequently, the grid connection point voltage and the virtual voltage are determined, and the signal is modulated according to the grid connection point voltage, the virtual voltage, the first axial current control value and the second axial current control value. Finally, the receiving end converter is stably controlled according to the modulated signal. The embodiment of the present application reshapes the output impedance of the new energy side through the software control layer without adding additional hardware equipment. This control method effectively optimizes the output impedance characteristics of the receiving end of the high-voltage direct current transmission system, and can significantly suppress the DC side oscillation problem that may be caused, especially when connected to a weak power grid. Specifically, by accurately controlling the output of the receiving-end converter, the loop gain of the coupling system consisting of the reactive compensation device, the receiving-end converter and the weak power grid meets the generalized Nyquist stability criterion, thereby enhancing the dynamic response capability and overall stability of the system. In addition, the embodiment of the present application improves the output impedance of the receiving-end converter of the high-voltage direct current transmission system by introducing a virtual impedance link, thereby improving the stability margin of the system.

[0086] It should be noted that for other corresponding descriptions of the functional units involved in the DC transmission grid-connected system stability control device provided in the embodiment of the present application, reference can be made to Figures 1 to 5 The corresponding description in will not be repeated here.

[0087] In an exemplary embodiment, see Figure 7 , and also provides a device, which includes a communication bus, a processor, a memory and a communication interface, and may also include an input and output interface and a display device, wherein each functional unit can communicate with each other through the bus. The memory stores a computer program, and the processor is used to execute the program stored in the memory and execute the DC transmission grid-connected system stability control method in the above embodiment.

[0088] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the DC transmission grid-connected system stability control method.

[0089] Through the description of the above implementation methods, those skilled in the art can clearly understand that the present application can be implemented by hardware, or by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present application can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.), including a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each implementation scenario of the present application.

[0090] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of a preferred implementation scenario, and the modules or processes in the accompanying drawings are not necessarily required for implementing the present application.

[0091] Those skilled in the art will appreciate that the modules in the device in the implementation scenario can be distributed in the device in the implementation scenario according to the implementation scenario description, or can be changed accordingly and located in one or more devices different from the implementation scenario. The modules in the above implementation scenario can be combined into one module, or can be further split into multiple sub-modules.

[0092] The above application serial numbers are for description only and do not represent the advantages or disadvantages of the implementation scenarios.

[0093] The above disclosure only discloses several specific implementation scenarios of the present application. However, the present application is not limited thereto, and any changes that can be conceived by technicians in this field should fall within the scope of protection of the present application.

Claims

1. A DC power transmission grid-connected system stability control method, characterized in that: The method is applicable to a high voltage direct current transmission system, comprising: Determine a DC voltage parameter at the receiving end, and determine a current reference value at the receiving end according to the DC voltage parameter and an outer loop controller of the high voltage direct current transmission system, wherein the DC voltage parameter includes a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value; Determine an actual current value at the receiving end side, wherein the actual current value includes a first axial current actual value and a second axial current actual value; Determine the current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value; Determine a grid-connected point voltage and a virtual voltage, and determine a modulation signal according to the grid-connected point voltage, the virtual voltage, the first axial current control value, and the second axial current control value; The receiving-end converter is stably controlled according to the modulation signal.

2. The method according to claim 1, characterized in that The step of determining the first axial current reference value according to the DC voltage parameter and the outer loop controller of the high voltage DC power transmission system comprises: Determine an error value between the DC voltage set value and the DC voltage actual value, and multiply the error value by the outer loop controller to obtain the first axial current reference value; Wherein, the outer loop controller is G1(s), G1(s)=k p1 +k i1 / s,k p1 is the proportional coefficient of the outer loop controller, k i1 is the integral coefficient of the outer loop controller, and s is the complex frequency.

3. The method according to claim 1, characterized in that The determining the current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system comprises: Calculating a difference between the first axial current reference value and the first axial current actual value, and multiplying the difference by the inner loop controller to obtain the first axial current control value; Wherein, the inner loop controller is G2(s), G2(s)=k p2 +k i2 / s, where k p2 is the proportional coefficient of the inner loop controller, k i2 is the integral coefficient of the inner loop controller, and s is the complex frequency.

4. The method according to claim 1, characterized in that Determining the current control value on the receiving end side according to the current reference value, the actual current value and the inner loop controller of the high voltage direct current transmission system also includes: calculating the difference between the second axial current reference value and the second axial current actual value, and multiplying the difference by the inner loop controller to obtain the second axial current control value.

5. The method according to claim 1, characterized in that: The determining of the modulation signal according to the grid connection point voltage, the virtual voltage, the first axial current control value and the second axial current control value comprises: Determine the first axial grid-connected voltage component and the second axial grid-connected voltage component of the grid-connected voltage, and determine the first axial virtual voltage component and the second axial virtual voltage component of the virtual voltage, wherein the first axial virtual voltage component is u dvir ,u dvir =(sk1+k2)·i d , the second axial virtual voltage component is u qvir ,u qvir =(sk1+k2)·i q , where k1 is the virtual inertia coefficient and k2 is the virtual damping coefficient; Calculating a first product of the first axial current actual value and a target parameter, and calculating a sum of the first product and the first axial grid-connected voltage component, wherein the target parameter is a second product of a reference angular frequency and an inductance value of a filter circuit; Calculating a first difference between the sum and the first axial current control value and the first axial virtual voltage component, and taking a ratio between the first difference and the DC voltage given value as the first axial modulation signal; The second axial modulation signal is determined according to the second axial grid-connected voltage component, the second axial virtual voltage component, and the second axial current control value.

6. The method according to claim 5, characterized in that The second axial modulation signal is determined based on the second axial grid-connected voltage component, the second axial virtual voltage component, and the second axial current control value, including: calculating the second difference between the second axial grid-connected voltage component and the second axial current control value, the first product, and the second axial virtual voltage component, and taking the ratio of the second difference to the DC voltage given value as the second axial modulation signal.

7. The method according to claim 6, characterized in that The stable control of the receiving-end converter according to the modulation signal includes: generating an SVPWM wave according to the first axial modulation signal and the second axial modulation signal, and using the SVPWM wave to drive the power switch of the receiving-end converter to perform stable control.

8. A DC power transmission grid-connected system stability control device, characterized in that: include: A first determination module is used to determine a DC voltage parameter at a receiving end, and determine a current reference value at the receiving end according to the DC voltage parameter and an outer loop controller of the high voltage direct current transmission system, wherein the DC voltage parameter includes a DC voltage set value and a DC voltage actual value, and the current reference value includes a first axial current reference value and a second axial current reference value; A second determination module is used to determine an actual current value at the receiving end side, wherein the actual current value includes a first axial current actual value and a second axial current actual value; a third determination module, configured to determine a current control value of the receiving end side according to the current reference value, the current actual value and the inner loop controller of the high voltage direct current transmission system, wherein the current control value includes a first axial current control value and a second axial current control value; a fourth determination module, configured to determine a grid connection point voltage and a virtual voltage, and determine a modulation signal according to the grid connection point voltage, the virtual voltage, the first axial current control value, and the second axial current control value; The stabilization control module is used to perform stabilization control on the receiving-end converter according to the modulation signal.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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