A method and system for virtual impedance-based grid-forming converter voltage control and voltage-reactive power droop shaping

Abstract

This invention discloses a method and system for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-connected converter based on virtual impedance, belonging to the field of converter optimization control technology. The method includes: selecting any point between the generator terminal and the grid side of the grid-connected converter as a constant voltage control point; setting a constant voltage control target value for the constant voltage control point; obtaining a generator terminal voltage reference command value based on the voltage drop between the generator terminal and the constant voltage control point; and performing closed-loop control of the generator terminal voltage through a voltage loop based on the generator terminal voltage reference command value, thereby controlling the voltage at the constant voltage control point under the action of virtual impedance to improve the voltage support capability of the grid-connected converter. Compared to the problem that traditional virtual impedance values ​​lack physical meaning and are difficult to determine, the virtual impedance values ​​in this invention have clear physical meaning, corresponding to the equivalent line impedance between the generator terminal droop control application point and the grid-side constant voltage control point.

Description

Technical Field

[0001] This invention relates to the field of converter optimization control technology, and more specifically, to a method and system for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-type converter based on virtual impedance. Background Technology

[0002] my country's new power system exhibits a "double high" characteristic of high proportion of renewable energy and high proportion of power electronic equipment, resulting in reduced system inertia and weakened grid strength. In recent years, grid-type control strategies applicable to weak grid environments have become a research focus in related fields. In the most common grid-type control technologies, whether using droop control or virtual synchronous machine control, the voltage-reactive power droop characteristics are satisfied. At the same time, grid-type equipment is required to have the ability to autonomously construct and maintain internal potential amplitude and frequency, and to exhibit voltage source characteristics externally. Taking droop control as an example, current grid-type control technologies often generate reference values ​​for the voltage amplitude of the grid source through the self-synchronization mechanism of the reactive power outer loop, as shown in equation (1).

[0003] (1) In the formula, f , U These are the converter output frequency and voltage amplitude, respectively. K p , K q These are the active and reactive power droop coefficients, both positive numbers; the subscript 0 represents the initial rated value of the variable, variables without subscripts represent their actual values, and the subscript ref represents their reference values.

[0004] Unlike grid-connected converters that employ power control, the voltage of a grid-connected source is a controlled variable, while reactive power is an uncontrolled free variable. However, under traditional grid control strategies, especially the droop control or virtual synchronous machine control most commonly used in engineering, the terminal voltage reference value of the grid-connected converter will adaptively adjust with the reactive power deviation. However, this response may weaken the voltage support capability and effectiveness of the grid-connected converter because its voltage reference value is constantly being adjusted.

[0005] In addition, traditional droop control is usually applied to the converter terminal. For new energy power plants, especially considering the overall control requirements from a system perspective, it is usually more necessary to pay attention to the voltage at the grid connection point, high-voltage bus, etc.

[0006] Traditional droop control is essentially a compensatory differential regulation, reflecting how the valve side responds when grid-side conditions and parameters change. Under droop control, the converter can adjust accordingly to changes in grid-side operating conditions, exhibiting good natural adaptability. However, this response may weaken the voltage support capability and effectiveness of grid-connected converters because their voltage reference value is constantly adjusted. Furthermore, the traditional voltage control mechanism of grid-connected converters is applied at the converter terminal, only controlling the terminal voltage and failing to clearly define and improve the voltage-reactive power support level from a system-side perspective. Summary of the Invention

[0007] Unlike grid-connected converters that employ power control, the voltage of a grid-connected source is a controlled variable, while reactive power is an uncontrolled free variable. However, under traditional grid control strategies, especially the droop control or virtual synchronous machine control most commonly used in engineering, the terminal voltage reference value of the grid-connected converter will adaptively adjust with the reactive power deviation. However, this response may weaken the voltage support capability and effectiveness of the grid-connected converter because its voltage reference value is constantly being adjusted.

[0008] Furthermore, traditional droop control is usually applied at the converter terminal. For new energy power plants, especially considering the overall control requirements from a system perspective, it is usually more important to pay attention to the voltage at the grid connection point, high-voltage bus, etc. Therefore, a new control scheme needs to be proposed that can shift the voltage control point from the generator terminal to the grid side, ensure the voltage support capability of the grid-connected power source, and continue to have the ability to shape the voltage-reactive power droop characteristics of the system side port.

[0009] To further leverage the voltage support and grid-connection capabilities of grid-connected converters as external voltage sources, this patent proposes a method for shaping the voltage-reactive power droop characteristics and enhancing the voltage support capability of grid-connected converters based on virtual impedance and AC-side vector constant voltage control. This method can completely replace the voltage-reactive power control scheme in traditional grid-connected control strategies. Specifically, instead of generating the voltage reference value command change ΔU through the power outer loop self-synchronization mechanism, it directly assigns a clear and constant voltage amplitude generation command to control the AC-side voltage vector. This method is also more consistent with its physical nature as a voltage source.

[0010] Therefore, by employing virtual impedance technology, this invention can shift the voltage control point to any designated location on the grid side without changing the traditional application point of droop control (based on the framework of traditional power electronic equipment LC filters, etc., to ensure the universality of the method proposed in this patent). This achieves off-site voltage control and shapes the voltage-reactive droop characteristics required by the user and the system at any port on the right side of the fixed voltage control point (close to the grid side). It also greatly improves the voltage control capability on the system side and the voltage-reactive output level of the grid source.

[0011] To address the problem that traditional virtual impedance values ​​lack physical meaning and are difficult to determine, the virtual impedance values ​​in this invention have clear physical meaning, corresponding to the equivalent line impedance between the generator terminal droop control application point and the grid-side constant voltage control point. Based on this, this invention proposes a method for constant voltage control and voltage-reactive power droop characteristic shaping of grid-connected converters based on virtual impedance, including: By using the AC side vector constant voltage control method, any point between the generator terminal and the grid side of the grid-type converter is selected as the constant voltage control point. Based on the location of the constant voltage control point in the system and the actual operating conditions, set the constant voltage control target value of the constant voltage control point; Based on the voltage reference value of the constant voltage control point and the voltage drop between the machine terminal and the constant voltage control point, the machine terminal voltage reference command value is obtained; Based on the reference command value of the terminal voltage, the terminal voltage is controlled in a closed loop through a voltage loop, and then the voltage at the constant voltage control point is controlled under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

[0012] Optionally, the voltage loop is applied at the generator terminal of the grid-connected converter, and the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. In this case, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

[0013] Optionally, under closed-loop control, a constant voltage control point is used as the boundary between the source side and the load side; When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

[0014] Optionally, in closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U CqThese represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

[0015] Optional, the expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the converter terminals, respectively. R ∑ , X ∑ These are the equivalent impedances between the converter terminals and the constant voltage control point, with the real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U C Let be the converter terminal voltage, and j be the imaginary part.

[0016] Furthermore, this invention also proposes a constant voltage control and voltage-reactive power droop characteristic shaping system for grid-type converters based on virtual impedance, comprising: The selected unit is used to select any point between the generator terminal and the grid side of the grid-type converter as the constant voltage control point by means of the AC side vector constant voltage control method. The target value setting unit is used to set the constant voltage control target value of the constant voltage control point according to the location of the constant voltage control point in the system and the actual operating conditions. The calculation unit is used to obtain the terminal voltage reference command value based on the voltage reference value of the constant voltage control point and the voltage drop between the terminal and the constant voltage control point; The control unit is used to perform closed-loop control of the terminal voltage through a voltage loop based on the terminal voltage reference command value, and then control the constant voltage control point voltage under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

[0017] Optionally, the voltage loop is applied at the generator terminal of the grid-connected converter, and the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. In this case, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

[0018] Optionally, under closed-loop control, a constant voltage control point is used as the boundary between the source side and the load side; When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

[0019] Optionally, in closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

[0020] Optional, the expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the line ports, respectively. R ∑ , X ∑ These are the equivalent impedances between the two ports of the line, with real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U C Let be the converter terminal voltage, and j be the imaginary part.

[0021] In another aspect, the present invention also provides a computing device, comprising: one or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described above is implemented.

[0022] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the method described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-connected converter based on virtual impedance. The method includes: selecting any point between the generator terminal and the grid side of the grid-connected converter as a constant voltage control point using AC-side vector constant voltage control; setting a constant voltage control target value for the constant voltage control point based on its location in the system and actual operating conditions; obtaining a generator terminal voltage reference command value based on the voltage reference value of the constant voltage control point and the voltage drop between the generator terminal and the constant voltage control point; and performing closed-loop control of the generator terminal voltage using a voltage loop based on the generator terminal voltage reference command value, thereby controlling the voltage of the constant voltage control point under the action of virtual impedance to improve the voltage support capability of the grid-connected converter. Compared to the problem that traditional virtual impedance values ​​lack physical meaning and are difficult to determine, the virtual impedance values ​​in this invention have clear physical meaning, corresponding to the equivalent line impedance between the generator terminal droop control application point and the grid-side constant voltage control point. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of a constant voltage control method for a grid-type converter based on virtual impedance, as described in an embodiment of the present invention. Figure 3 This is a schematic diagram of the entire constant voltage control scheme in an embodiment of the method of the present invention; Figure 4 This is a schematic diagram of the constant voltage controlled virtual impedance addition method in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the voltage-related variable relationships in an embodiment of the method of the present invention; Figure 6 This is a schematic diagram of an off-grid load system model of a grid-type converter according to an embodiment of the method of the present invention; Figure 7 This is a diagram illustrating the control effect of the constant voltage control point in an off-grid system according to an embodiment of the method of the present invention. Figure 8 (ab) are voltage-reactive power characteristic curves of the generator end and load side under this scenario, respectively, according to the embodiment of the method of the present invention; Figure 9 This is a schematic diagram of a grid-connected load-carrying system model of a grid-type converter as an embodiment of the method of the present invention; Figure 10 This is a structural diagram of the system of the present invention. Detailed Implementation

[0025] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0026] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0027] Example 1: This invention proposes a method S100 for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-type converter based on virtual impedance, such as... Figure 1 As shown, it includes: S101, by using the AC side vector constant voltage control method, any point between the generator terminal and the grid side of the grid-type converter is selected as the constant voltage control point; S102, Based on the location of the constant voltage control point in the system and the actual operating conditions, set the constant voltage control target value of the constant voltage control point; S103, Based on the voltage reference value of the constant voltage control point and the voltage drop between the machine terminal and the constant voltage control point, obtain the machine terminal voltage reference command value; S104, based on the terminal voltage reference command value, the terminal voltage is controlled in a closed loop through the voltage loop, and then the voltage at the constant voltage control point is controlled under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

[0028] The voltage loop is applied at the generator terminal of the grid-connected converter, while the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. At this time, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

[0029] Among them, under closed-loop control, the constant voltage control point is used as the boundary between the source side and the load side; and even when completely replacing the original grid-type voltage control method, it still has the characteristics and ability of the traditional grid-type control strategy to shape the voltage-reactive power droop characteristics of the load side (grid side). When the reactive power demand on the load side (grid side) increases, the voltage on the load side (grid side) will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

[0030] In closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

[0031] The expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the converter terminals, respectively. R ∑ , X ∑ These are the equivalent impedances between the converter terminals and the constant voltage control point, with the real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U CLet be the converter terminal voltage, and j be the imaginary part.

[0032] The invention will be further illustrated below with specific examples: The specific implementation process is as follows: The AC-side vector constant voltage control method replaces the original grid-type voltage control scheme. A certain point (any point between the generator terminal and the grid side, which can be selected according to control requirements) is selected as the constant voltage control point. Based on the location of this point in the system and the actual operating conditions, the constant voltage control target value of this point is set. The voltage drop between the generator terminal and the constant voltage control point is added to the voltage reference value of the constant voltage control point to obtain the generator terminal voltage reference command value. Then, the generator terminal voltage is controlled in a closed loop through the voltage loop.

[0033] At this point, although the voltage closed-loop is ostensibly applied at the converter terminal, it actually controls the voltage at a remote constant voltage control point closer to the grid side. The virtual impedance value at this time corresponds to the actual impedance between the converter terminal and the constant voltage control point, such as... Figure 2 As shown.

[0034] Under constant voltage control, the constant voltage control point serves as the boundary between the "source side" and the "load side (system side)". When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an "upward" characteristic where the higher the voltage, the greater the reactive power.

[0035] Under this control architecture, the original voltage-reactive power droop loop will be replaced, and only the frequency-active power droop loop needs to be retained to stabilize the active power output and generate the frequency. The overall control framework is as follows: Figure 3 As shown. It should be noted that the method proposed in this invention can be applied, but is not limited to, converters under grid-connected droop control and virtual synchronous machine control. It is applicable to all grid-connected sources, and even scenarios such as multi-machine parallel operation systems and multiple renewable energy power plants can utilize the method proposed in this patent to control the voltage-reactive power levels at different voltage levels and locations. In other words, the constant voltage control point in this invention can be set at any point between the generator terminal and the grid-side bus, possessing universality.

[0036] The virtual impedance in this invention differs from conventional virtual impedance in its addition to the control circuit. Conventional virtual impedance, introduced to suppress fault overcurrent, has its voltage drop subtracted from the reference value of the terminal voltage. However, the virtual impedance in this invention has its voltage drop added to the control target value at the constant voltage control point; that is, the two types of virtual impedance have opposite signs when introduced into the system. The control block diagram of the virtual impedance in the method proposed in this invention is as follows: Figure 4As shown, the expression is shown in equation (2). It should be noted that the grid converter in the new energy power station is usually connected to the grid after multi-stage voltage boosting. If the current on the virtual impedance is considered to be the current at the output port of the converter, then in the process of calculating the virtual impedance, the actual impedance of each segment should be converted to the output voltage level of the converter before being superimposed.

[0037] Figure 4 middle, I oabc For the converter output current, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are virtual resistance and virtual reactance, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the voltage at the converter terminal (at the filter capacitor), respectively. U Cd , U Cq These represent the d-axis and q-axis components of the target value for the constant voltage control point, respectively, with the subscript ref indicating its reference value.

[0038] (2) The value of virtual impedance is directly related to its effect. In traditional overcurrent suppression applications, although improved methods such as adaptive virtual impedance exist, a significant problem is that the virtual impedance value lacks a clear physical meaning. In contrast, the method proposed in this invention explicitly corresponds to the line impedance between the generator terminal and the constant voltage control point, providing a clear physical meaning. This approach to virtual impedance can also be extended to solve the problem of power distribution among multiple generators at different spatial locations or network nodes. By compensating for the transmission impedance between each generator unit and the grid connection point through virtual impedance, each converter can achieve a more ideal reactive power distribution and regulation according to demand.

[0039] The following is a method for calculating the voltage drop across a section of a line based on the line impedance and the transmitted power. The voltage-related variables are as follows: Figure 5 As shown.

[0040] (3) In equation (3), P C , QC These represent the active and reactive power transmitted at the line ports, respectively. R ∑ , X ∑ These are the equivalent impedances between the two ports of the line. The real part Δ in equation (3) U The vertical component is ΔU, and the horizontal component is the imaginary component. The magnitude of the voltage drop is mainly determined by the vertical component ΔU. U Based on this, the voltage drop between the converter terminal and the constant voltage control point can be calculated using relevant data, and then the voltage control of the constant voltage control point can be achieved at the converter terminal through virtual impedance technology.

[0041] When the grid-connected converter is operating in off-grid / island mode, the setting of the constant voltage control point target value is relatively arbitrary; when the grid-connected converter is operating in grid-connected mode, the setting of the constant voltage control point voltage reference value should be such that the grid source can coordinate with the grid-side large voltage source of equivalent value when connected to the grid.

[0042] The method of this invention completely replaces the voltage-reactive power control scheme in the original grid control strategy. That is, instead of generating the change amount ΔU of the voltage reference value command through the power outer loop self-synchronization mechanism, it assigns a specified voltage amplitude command value to it and performs AC side vector constant voltage control. This method is more in line with its physical nature as a voltage source, and also significantly improves the voltage-reactive power support effect, voltage control accuracy and grid construction capability of the grid-connected converter as an external voltage source.

[0043] Meanwhile, the method proposed in this invention uses virtual impedance technology to move the voltage control point to any position on the grid side without changing the voltage control application point, thereby achieving off-site voltage control. Furthermore, it can shape the voltage-reactive power droop characteristics required by the user and the system at any port on the right side (close to the grid side) of the fixed voltage control point.

[0044] It is worth noting that, compared to the traditional problem that virtual impedance values ​​have no physical meaning and are difficult to determine, the virtual impedance values ​​in this invention have clear physical meaning and correspond to the equivalent line impedance between the machine terminal droop control application point and the grid side constant voltage control point.

[0045] The above method will be explained below with specific applications: Construct a model of an off-grid load system for a grid-connected converter, such as... Figure 6 As shown.

[0046] The effective values ​​of the constant voltage control point voltage control target were set to 220V, 230V, 240V, and 220V at t=0s, t=1s, t=2s, and t=3s, respectively. The adaptability of the proposed constant voltage control scheme to different constant voltage control targets in the off-grid system was verified. The results are as follows: Figure 7As shown, the constant voltage control point effectively tracks the set control target value.

[0047] The simulation results above show that, under constant voltage control, the constant voltage control point serves as the boundary between the "source side" and the "load side (system side)". When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, a voltage-reactive power droop characteristic appears at the port to the right of the constant voltage control point, where the lower the voltage, the greater the reactive power. Figure 8 As shown in (ab), the internal potential of the source side will rise accordingly, that is, the left port of the constant voltage control point exhibits the voltage-reactive power "rise" characteristic of the higher the voltage and the greater the reactive power.

[0048] Construct a grid-connected load system model for a grid-connected converter, such as... Figure 9 As shown.

[0049] Simulation and physical experiment results show that the proposed method exhibits excellent control performance and voltage-reactive power characteristics in both off-grid and grid-connected scenarios. Furthermore, this patented method has also been validated in a multi-unit off-grid / grid-connected operation model of a grid-connected converter, with control performance and voltage-reactive power characteristics consistent with the aforementioned analysis.

[0050] Example 2: Furthermore, this invention also proposes a constant voltage control and voltage-reactive power droop characteristic shaping system 200 for a grid-type converter based on virtual impedance, such as... Figure 10 As shown, it includes: Select unit 201 is used to select any point between the generator terminal and the grid side of the grid-type converter as the constant voltage control point by means of AC side vector constant voltage control method; The target value setting unit 202 is used to set the constant voltage control target value of the constant voltage control point according to the position of the constant voltage control point in the system and the actual operating conditions. The calculation unit 203 is used to obtain the terminal voltage reference command value based on the voltage reference value of the constant voltage control point and the voltage drop between the terminal and the constant voltage control point; The control unit 204 is used to perform closed-loop control of the terminal voltage through a voltage loop based on the terminal voltage reference command value, and then control the constant voltage control point voltage under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

[0051] The voltage loop is applied at the generator terminal of the grid-connected converter, while the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. At this time, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

[0052] In closed-loop control, the constant voltage control point serves as the boundary between the source side and the load side. When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

[0053] In closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

[0054] The expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the converter terminals, respectively. R ∑ , X ∑ These are the equivalent impedances between the two ports of the line, with real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U C Let be the converter terminal voltage, and j be the imaginary part.

[0055] Compared to the traditional problem that virtual impedance values ​​have no physical meaning and are difficult to determine, the virtual impedance values ​​in this invention have clear physical meaning and correspond to the equivalent line impedance between the machine terminal droop control application point and the grid-side constant voltage control point.

[0056] Example 3: Based on the same inventive concept, this invention also provides a computer device, which includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement corresponding method flows or corresponding functions, thereby implementing the steps of the methods in the above embodiments.

[0057] Example 4: Based on the same inventive concept, this invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiments.

[0058] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0059] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0060] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0061] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0062] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0063] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-type converter based on virtual impedance, characterized in that, include: By using the AC side vector constant voltage control method, any point between the generator terminal and the grid side of the grid-type converter is selected as the constant voltage control point. Based on the location of the constant voltage control point in the system and the actual operating conditions, set the constant voltage control target value of the constant voltage control point; Based on the voltage reference value of the constant voltage control point and the voltage drop between the machine terminal and the constant voltage control point, the machine terminal voltage reference command value is obtained; Based on the reference command value of the terminal voltage, the terminal voltage is controlled in a closed loop through a voltage loop, and then the voltage at the constant voltage control point is controlled under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

2. The method for improving voltage support capability according to claim 1, characterized in that, The voltage loop is applied at the generator terminal of the grid-connected converter, while the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. At this time, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

3. The method for improving voltage support capability according to claim 1, characterized in that, Under closed-loop control, the constant voltage control point is used as the boundary between the source side and the load side; When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

4. The method for improving voltage support capability according to claim 1, characterized in that, In closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

5. The method for improving voltage support capability according to claim 1, characterized in that, The expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the converter terminals, respectively. R ∑ , X ∑ These are the equivalent impedances between the converter terminals and the constant voltage control point, with the real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U C Let be the converter terminal voltage, and j be the imaginary part.

6. A system for constant voltage control and voltage-reactive power droop characteristic shaping of a grid-type converter based on virtual impedance, characterized in that, include: The selected unit is used to select any point between the generator terminal and the grid side of the grid-type converter as the constant voltage control point by means of the AC side vector constant voltage control method. The target value setting unit is used to set the constant voltage control target value of the constant voltage control point according to the location of the constant voltage control point in the system and the actual operating conditions. The calculation unit is used to obtain the terminal voltage reference command value based on the voltage reference value of the constant voltage control point and the voltage drop between the terminal and the constant voltage control point; The control unit is used to perform closed-loop control of the terminal voltage through a voltage loop based on the terminal voltage reference command value, and then control the constant voltage control point voltage under the action of virtual impedance to improve the voltage support capability of the grid-type converter.

7. The voltage support capability enhancement system according to claim 6, characterized in that, The voltage loop is applied at the generator terminal of the grid-connected converter, while the actual control is closer to the voltage at the off-site constant voltage control point on the grid side. At this time, the virtual impedance value corresponds to the actual impedance between the generator terminal and the constant voltage control point.

8. The voltage support capability enhancement system according to claim 6, characterized in that, Under closed-loop control, the constant voltage control point is used as the boundary between the source side and the load side; When the reactive power demand on the load side increases, the load side voltage will decrease accordingly. That is, the right port of the constant voltage control point exhibits a drooping characteristic where the lower the voltage, the greater the reactive power. At the same time, the internal potential on the source side will rise accordingly. That is, the left port of the constant voltage control point exhibits an upward characteristic where the higher the voltage, the greater the reactive power.

9. The voltage support capability enhancement system according to claim 6, characterized in that, In closed-loop control, a virtual impedance is introduced, and the voltage drop is added to the control target value at the constant voltage control point. The control expression for the virtual impedance is as follows: in, I d , I q These are the d-axis and q-axis components of the converter output current, respectively. R V , ωL V These are the virtual resistance and virtual reactance equivalent to the terminal voltage level, respectively. U Cd , U Cq These represent the d-axis and q-axis components of the converter terminal voltage, respectively, with the subscript "ref" indicating its reference value. U Cd , U Cq These are the d-axis and q-axis components of the target value for the constant voltage control point, respectively.

10. The voltage support capability enhancement system according to claim 6, characterized in that, The expression for calculating the pressure drop is as follows: in, P C , Q C These represent the active and reactive power transmitted at the converter terminals, respectively. R ∑ , X ∑ These are the equivalent impedances between the converter terminals and the constant voltage control point, with the real part Δ. U The vertical component is δ, and the imaginary part is δ. U The amplitude of the voltage drop is mainly determined by the longitudinal component Δ, which is the horizontal component. U Decide, U C Let be the converter terminal voltage, and j be the imaginary part.

11. A computer device, characterized in that, include: One or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described in any one of claims 1-5 is implemented.

12. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements the method as described in any one of claims 1-5.

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