Network-configuration type converter access system near-network-side extension constant voltage control based on impedance compensation and system

Abstract

The application discloses a kind of network type converter access system near network side extension fixed voltage control method and system based on impedance compensation, belong to network type converter access system reactive power voltage optimization control technical field.The method of the present application comprises: by impedance compensation, the voltage controlled point of network type converter access system control framework is extended to the specified fixed voltage control point closer to network side from alternating current filter capacitor outlet (converter end), while keeping control strategy still exerted on converter end and without adding electrical measurement point, actual voltage closed loop is pushed to near network side fixed voltage control point;Combining end voltage and current data and impedance compensation method, obtain near network side fixed voltage control point voltage actual value;According to the position of selected voltage control point and user demand, determine fixed voltage control point voltage reference value;Fixed voltage control point voltage actual value and its reference value are closed-loop controlled.The present application is well controlled under island and weak network conditions.

Description

Technical Field

[0001] This invention relates to the field of reactive voltage optimization control technology for grid-connected converter systems, and more specifically, to a near-grid-side extended constant voltage control system for grid-connected converter systems based on impedance compensation. Background Technology

[0002] With the increasing penetration of new energy sources and inverter-type power sources in power systems, grid strength is weakening. As a solution, grid-based control has received widespread attention. While the reactive power-voltage droop stage in traditional grid-based control has good inherent adaptability, it easily masks design deficiencies in the voltage control point, and coordinating the droop coefficient is difficult. Furthermore, the converter voltage control point is located at the generator end, far from the grid side, making it difficult for the grid-based power source capacity to achieve the expected results. Especially in typical grid integration scenarios such as new energy aggregation and transmission in my country, the coordinated control of the operating voltage of all grid-based power sources within the system should be given sufficient attention.

[0003] Currently, the grid control technologies widely used in practical engineering are mainly droop control and virtual synchronous generator (VSG) control. These are typically applied at the generator terminals (AC filter capacitor outlet) of grid-type converters, and their reactive power-voltage ratio is considered. Q - U In some respects, they exhibited relatively consistent drooping characteristics. However, existing research has shown that traditional... Q - UThe inherent adaptability of droop control can, to some extent, mask the shortcomings in the parameter design and location selection of the voltage control point, leading to the neglect of the steady-state voltage operation control problem of the grid-connected power source. This also results in the grid-connected power source's effect on supporting the grid's voltage capacity falling short of expectations. However, existing technologies focus more on the inertia and frequency support of grid-connected power sources, while paying less attention to voltage control, which is inherently more difficult. Existing grid-connected voltage control strategy improvements mainly target transient conditions, with insufficient focus on the steady-state voltage control of the grid-connected power source. Especially in typical renewable energy aggregation and transmission scenarios in my country, such as desert and Gobi areas, the grid-connected converter terminals within wind and solar power plants typically require two or more stages of voltage boosting, feeder, and transmission line transmission between the system-side bus and the grid. The equivalent electrical distance, when converted to the voltage level of the connected system, is equivalent to hundreds of kilometers of 220kV transmission lines. This poses a challenge to the voltage coordination between the grid-connected power source and the external grid, thus requiring an extension of the voltage control perspective of the grid-connected power source to the system side. As the "high-voltage and high-efficiency" characteristics of the new power system become increasingly prominent, the proportion of traditional synchronous voltage sources is declining, and the problem of "hollowing out" of system voltage support regulation is becoming increasingly serious. How to effectively leverage the role of self-synchronizing voltage sources of grid-connecting equipment, achieve coordinated operation of equipment and system at both levels, and improve the system voltage support regulation capability should be considered as soon as possible. Summary of the Invention

[0004] To address the above problems, this invention proposes a near-grid-side extended constant voltage control method for grid-connected converters based on impedance compensation, comprising: For the control framework of the grid-connected converter system, an impedance compensation link is determined. The voltage controlled object of the grid-connected converter system control framework is extended from the voltage at the output of the AC filter capacitor to the voltage at the designated constant voltage control point CVCP closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The output of the AC filter capacitor includes the converter terminal. In the impedance compensation stage, the total transmission impedance between the converter terminal and the constant voltage control point is calculated based on the location of the constant voltage control point, and the actual voltage value of the near-grid constant voltage control point is determined based on the total transmission impedance and the terminal voltage and current data. Based on the selected voltage control point location and the user's actual needs, determine the voltage control target or its reference value for the voltage control point. The voltage at the constant voltage control point is controlled in a closed loop based on the voltage reference value and the actual voltage value provided by the voltage control loop.

[0005] Optional location principles for constant voltage control points include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

[0006] Optional methods for calculating the reference value of the constant voltage control point include: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, by I q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

[0007] Optionally, the calculation method for the total transmission impedance between the converter terminal and the constant voltage control point includes: the multi-voltage level equivalent series impedance segmentation superposition method or based on... T Impedance calculation method for transmission matrix multiplication.

[0008] Furthermore, this invention also proposes a near-grid-side extended constant voltage control system for a grid-connected converter system based on impedance compensation, characterized by comprising: The location unit is used to determine the impedance compensation link for the grid-connected converter access system control framework. It extends the voltage controlled object of the grid-connected converter access system control framework from the voltage at the AC filter capacitor outlet to the specified constant voltage control point (CVCP) voltage closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The AC filter capacitor outlet includes the converter terminal. The transmission impedance and constant voltage control point voltage actual value calculation unit is used to calculate the total transmission impedance between the converter terminal and the constant voltage control point based on the location of the constant voltage control point in the impedance compensation stage, and to determine the actual voltage value of the near-grid side constant voltage control point based on the total transmission impedance and the terminal voltage and current data. The constant voltage control point voltage reference value calculation unit is used to determine the constant voltage control point voltage control target or its reference value based on the selected voltage control point location and the user's actual needs. The control unit is used to perform closed-loop control at the constant voltage control point and the voltage control target reference value based on the actual voltage value, so as to control the voltage at the constant voltage control point.

[0009] Optional location principles for constant voltage control points include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

[0010] Optional methods for calculating the reference value of the constant voltage control point include: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, by I q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

[0011] Optionally, the calculation method for the total transmission impedance between the converter terminal and the constant voltage control point includes: the multi-voltage level equivalent series impedance segmentation superposition method or based on... T Impedance calculation method for transmission matrix multiplication.

[0012] 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.

[0013] 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.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a near-grid-side extended constant voltage control method for a grid-connected converter system based on impedance compensation, comprising: a near-grid-side extended constant voltage control method for a grid-connected converter system based on impedance compensation, comprising: For the control framework of a grid-connected converter access system, an impedance compensation stage is determined. This stage extends the voltage control object of the grid-connected converter access system control framework from the voltage at the AC filter capacitor outlet to the voltage at a designated constant voltage control point (CVCP) closer to the grid side. That is, while maintaining the control strategy applied to the converter terminal without adding new voltage and current measurement points, the voltage closed loop is effectively shifted to the constant voltage control point near the grid side. The AC filter capacitor outlet includes the converter terminal. In the impedance compensation stage, the total transmission impedance between the converter terminal and the constant voltage control point is calculated based on the constant voltage control point location. The actual voltage value of the near-grid constant voltage control point is determined based on the total transmission impedance and the terminal voltage and current data. The voltage control target or its reference value for the constant voltage control point is determined based on the selected voltage control point location and the user's actual needs. Closed-loop control is then performed on the constant voltage control point voltage based on the voltage reference value and the actual voltage value provided by the voltage control stage. This invention takes a more direct approach to constant voltage control, which better aligns with the physical nature and inherent characteristics of a grid-connected power source as a controlled voltage source. It also retains the ability of the port on the right side of the voltage control point (closer to the grid side) to exhibit the malleable adaptive nonlinear QU droop characteristic (linear IU droop characteristic). Furthermore, this process does not rely on communication and requires no additional electrical measurement points. Moving the constant voltage control point from the grid-connected converter terminal towards the grid side is a crucial entry point and solution for combining equipment control objectives with system requirements. This is highly beneficial both for reassessing and determining the control objectives of power electronic converters from a system-side perspective and for enabling grid-connected power sources to fully leverage their self-synchronizing voltage source capabilities and better participate in system-side voltage support regulation. Attached Figure Description

[0015] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram illustrating the control expression of the impedance compensation stage in the method of the present invention. Figure 3 This is a schematic diagram of the power transfer model between two nodes in the method of the present invention; Figure 4 This is a schematic diagram of a cantilever beam model according to the method of the present invention; Figure 5 (ab) represents the linearity under constant voltage control of the method of the present invention. I - U and adaptive nonlinearQ - U Characteristic diagram; Figure 6 This is a schematic diagram of a refined model of a single-unit grid-connected load-carrying new energy converter according to the method of the present invention; Figure 7 This is a schematic diagram of a two-port model of the method of the present invention; Figure 8 The circuit diagram is equivalent to an approximate two-stage LC cascade structure for the method of the present invention; Figure 9 This is a schematic diagram of the updated voltage and current physical constraints and the corresponding decoupling control method of the present invention; Figure 10 A flowchart illustrating the engineering calculation method for determining the CVCP voltage reference value according to the present invention; Figure 11 This is a schematic diagram of a simulation model of the method of the present invention; Figure 12 This is a schematic diagram showing the control performance of the method of the present invention when the voltage control command changes; Figure 13 This is a schematic diagram illustrating the adaptability of the method of the present invention to load switching conditions; Figure 14 This is a schematic diagram showing the control performance of the method of the present invention under grid-side voltage fluctuation conditions. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] Example 1: This invention proposes a near-grid-side extended constant voltage control method for grid-connected converters in systems based on impedance compensation. It reshapes the reactive power-voltage control loop in traditional grid-connected droop control, improving the reactive power-voltage droop characteristics from a linear constant slope (the reciprocal of the droop coefficient) to a naturally adaptive variable-coefficient nonlinear droop. This improved control loop only requires local measurement data to achieve off-site voltage control, which can be understood as a virtual measurement. The voltage closed loop is applied to the near-grid-side constant voltage control point, no longer at the converter terminal (AC filter capacitor outlet), but the implementation can still be done at the converter terminal. The inner current loop is still retained at the AC filter inductor, which can be approximated as a two-stage LC cascade model. Extending the voltage control point from the converter terminal to a designated port closer to the system side has clear physical significance and effectively enhances the ability of grid-connected sources to participate in system-side voltage support regulation. This invention also provides examples of the location principles for the near-grid-side constant voltage control point and the design method for voltage control targets. The method proposed in this invention has good control performance in both islanded and grid-connected operating conditions, and provides a new approach to solving the problem of coordinated operation of multiple network sources and analyzing the control requirements of network sources from a system perspective.

[0019] This invention proposes a method for extending the Constant Voltage Control (CVC) point near the grid side of a grid-connected converter system based on impedance compensation. This method improves the control loop, enabling remote voltage control by acquiring only local measurement data; it can also be understood as a virtual measurement. The voltage closed loop is applied to the constant voltage control point near the grid side, no longer at the converter terminal (AC filter capacitor outlet), although the implementation can still be done at the converter terminal. The inner current loop is still retained at the AC filter inductor, which can be approximated as a two-stage cascaded LC model. Under this method, the constant voltage control point can be extended from the grid-connected converter output port (terminal) to a designated location closer to the system side, further enhancing the grid source's ability to participate in system voltage regulation and support. This provides a perspective and paradigm that combines the equipment's own control objectives with the system's coordinated operation requirements. At this point, any port of the Constant Voltage Control Point (CVCP) near the grid side will naturally exhibit adaptive nonlinearity. Q - U Sagging characteristics ( I - U The reason for linear drooping.

[0020] Meanwhile, this invention provides a corresponding improved method for the cross-decoupling term in the voltage-current dual closed loop of the proposed method, and, combined with typical topologies of wind and solar power stations in my country, presents a multi-voltage level impedance piecewise superposition method and a method based on... TThe method for solving the matrix (the matrix is ​​represented in bold italics), as well as the engineering calculation method for determining the CVCP location principle and voltage reference value, were presented. The implementation effect of the method of the present invention was verified by MATLAB / Simulink simulation and power-in-the-loop physical experiment.

[0021] Specifically, this invention proposes a near-grid-side extended constant voltage control method S100 for grid-connected converters based on impedance compensation, such as... Figure 1 As shown, it includes: S101, for the grid-connected converter access system control framework, an impedance compensation link is determined, and the voltage controlled object of the grid-connected converter access system control framework is extended from the voltage at the AC filter capacitor outlet to the specified constant voltage control point CVCP voltage closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The AC filter capacitor outlet includes: the converter terminal. S102, in the impedance compensation stage, the total transmission impedance between the converter terminal and the constant voltage control point is calculated based on the location of the constant voltage control point, and the actual voltage value of the near-grid constant voltage control point is determined based on the total transmission impedance and the terminal voltage and current data. S103, Based on the selected voltage control point location and the user's actual needs, determine the voltage control target or its reference value for the voltage control point; S104, based on the voltage reference value of the constant voltage control point given by the voltage control loop and the actual voltage value, the voltage of the constant voltage control point is controlled in a closed loop to control the voltage of the constant voltage control point.

[0022] Optional location principles for constant voltage control points include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

[0023] Optional methods for calculating the reference value of the constant voltage control point include: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, byI q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

[0024] Optionally, the calculation method for the total transmission impedance between the converter terminal and the constant voltage control point includes: the multi-voltage level equivalent series impedance segmentation superposition method or based on... T Impedance calculation method for transmission matrix multiplication.

[0025] Specifically, the overall method for achieving near-grid side constant voltage control through impedance compensation is as follows: In a typical power electronic converter topology and voltage-current closed-loop control framework, the AC filter capacitor voltage (machine terminal voltage) and the filter inductor current are usually controlled as the voltage loop and current loop, respectively. The control method proposed in this invention, without changing the original voltage control strategy implementation point (machine terminal), extends the controlled object from the original filter capacitor voltage to a designated point closer to the grid side, shifting the voltage closed loop to a near-grid side fixed voltage control point, thus achieving off-site voltage control. This process is achieved through impedance compensation.

[0026] The impedance compensation process is clearly defined: The converter terminal output voltage and current are easier to obtain as local measurements. The actual voltage value at the remote constant voltage control point is obtained by subtracting the output current from the product of the output current and the total impedance between the converter terminal and the remote constant voltage control point using the impedance compensation method. Furthermore, in the voltage control stage, closed-loop control is performed based on the given reference voltage value of the constant voltage control point and the actual voltage value obtained through the impedance compensation method. This process requires no additional measurement points or communication. This process is as follows: Figure 2 As shown, its control expression is as follows: Corresponding to typical renewable energy aggregation and transmission scenarios in my country, such as the Gobi Desert, the locations of the points of connection (POC), the proposed constant voltage control point (CVCP) based on impedance compensation, and the grid bus point (GBP) mentioned later in this invention are as described above. Figure 2 As shown. Figure 2 middle U CVCP , U o , I oThese represent the near-grid side constant voltage control point voltage, and the converter terminal voltage and current, respectively; the lower right subscript... d , q This represents the variable in dq The components of the coordinate system corresponding to the coordinate axes.

[0027] Droop characteristics under constant voltage control method: The impedance-compensated near-grid-side extended constant voltage control method for grid-connected converter systems proposed in this invention is a vector voltage control method. Compared with traditional grid-connected control methods such as droop control or virtual synchronous machine control, these methods generate voltage commands and shape voltage. Q - U The methods for addressing the droop characteristic are different. In this control scheme, the traditional voltage control strategy is replaced, but... Q - U The ability to shape sagging features is retained. (The following...) Figure 3 Taking the power transfer model between the two nodes shown as an example, and drawing an analogy with a cantilever beam model with concentrated loads, this illustrates the power transfer model under constant voltage control. Q - U The mechanism of shaping drooping characteristics.

[0028] In Figure 3, the current flowing through the line between points A and B. I and line transmission impedance Z It can be represented as: In the above formula, S B , P B , Q B , U B These represent the complex power, active power, reactive power flowing into point B, and the voltage at point B, respectively. The superscript * indicates conjugate.

[0029] With point B as the reference node, the voltage drop phasor d between points A and B is... It can be represented as: In the above formula, the real part Δ U The longitudinal component representing the voltage drop, and the imaginary part δ U The horizontal component represents the voltage drop. The vertical component, which primarily affects the voltage amplitude, can be represented as: Considering that the system impedance is inductive, X >> R It can be approximated as R≈0, at this point the above expression can be simplified to: If reactive current is used I q Describing the above equation, we have: Taking the application of constant voltage control in converters as an example, when the reactive power transmitted along the line increases, the voltage drop across the impedance between the converter and the system bus will be greater, and the system-side voltage will decrease accordingly, thus exhibiting... Q - U Droop characteristic. That is, at the right port of the constant voltage control point, a lower voltage corresponds to a larger reactive power output. This characteristic can be compared to the material mechanics model of a cantilever beam under concentrated load, where Δ U Indicates deflection. U Indicates the altitude. I q Indicates concentrated load, Q = UI q This represents the gravitational potential energy of the load. A cantilever beam model under concentrated loads, which can be used to analyze the characteristics of the source load, is as follows: Figure 4 As shown. Of course, corresponding to the droop characteristic at the right port of the constant voltage control point, there exists a droop characteristic at the left port of the constant voltage control point. Q - U The upward characteristic means that the higher the voltage, the greater the reactive power output.

[0030] The droop characteristics exhibited by traditional mesh control are directly related to the droop coefficient, which is a strong linear droop relationship with a constant slope, and its expression is as follows; However, based on the above mathematical derivation and physical model, it is clear that this strongly linear sag relationship is unnecessary and unreasonable. Correspondingly, the deflection and concentrated load of a cantilever beam only exhibit a strictly linear relationship under the premise of linear elasticity and small deformation. Under the control method of this invention, the exhibited... Q - U The characteristic is an adaptive non-linear droop characteristic, while I - U The slope between them is shaped to be the reciprocal of the equivalent transmission reactance (1 / X The linear droop relationship is an adaptive modification of the traditional mesh droop characteristics based on natural physical laws. Linearity under constant voltage control. I - U and adaptive Q - U Features are as follows Figure 5 As shown in (ab).

[0031] Total transmission impedance between converter terminals and remote constant voltage control point Z total Specific calculation method: It can be obtained by the following methods, but not limited to the following: (1) Multi-voltage level equivalent series impedance segmentation superposition method: Since the voltage control method proposed in this invention is directly applied to the converter terminal, for ease of processing, the output current of the converter terminal can be used as the current on the total transmission impedance. In this case, each actual impedance segment will be equivalently converted to the converter terminal voltage level.

[0032] Taking the grid connection process of a typical wind farm converter as an example, a refined model of a single renewable energy converter connected to the grid and carrying load is established as follows: Figure 6 As shown.

[0033] Figure 6 middle, e Represents the internal potential of the converter. L f Represents the filter inductor. C f Represents the filter capacitor. R t and L t These represent the total transmission resistance and inductance between the converter terminals and the near-grid constant voltage control point (CVCP), respectively. i l This represents the current through the filter inductor. u o This represents the converter terminal output voltage. i o This represents the current output by the converter after filtering.

[0034] The equivalent series impedance from the converter terminal to the CVCP, taking the model shown in the diagram above as an example, should be the sum of the following components: the impedance of the wind turbine tower and the 0.69-35kV transformer (no need to divide by any turns ratio); the impedance of the 35kV feeder and the 35-220kV step-up transformer (divided by the square of the transformer turns ratio); and the impedance of the 220kV outgoing line between the POC and the CVCP (divided by the square of the product of the transformer turns ratio and the main transformer turns ratio). Finally, the voltage drop across this total impedance is reduced to the voltage level of the CVCP for the next calculation. Of course, per-unit values ​​can also be used when calculating multi-voltage level systems. However, regardless of whether nominal or per-unit values ​​are used, this method of segment-by-segment conversion and superposition is applicable to obtaining the equivalent series impedance.

[0035] (2) Based on T Impedance calculation method for transmission matrix: This invention proposes to utilizeT The matrix describes the transmission impedance of each link between the machine terminal and the remote constant voltage control point, and assigns each link... T The matrices are multiplied in a concatenated order to obtain the final transfer matrix. T total This method is also more suitable for rapid computer programming solutions. For two-port networks, T Matrix can be with Y Matrix conversion. In particular, for transformers with phase-shifting function, since they no longer satisfy the reciprocity characteristic of passive circuits, their π-type equivalent circuit cannot be drawn, but the calculation method itself is not affected.

[0036] The two-port model of each transmission link between the generator terminal and the constant voltage control point of the new energy converter is as follows: Figure 7 As shown, it can be described by the following formula.

[0037] For ease of explanation, this method defines the transmission direction of the matrix (the voltage and current at port 1 are known quantities, and the voltage and current at port 2 are quantities to be determined) and the positive directions of the currents at both ports (both are positive to the right, indicating current penetration) when listing the transmission matrix. This differs from the traditional method. T The definition of a matrix differs. Therefore, strictly speaking, the name of the transfer matrix defined in this method should be different from that of the matrix used in this study. T The matrices differ to distinguish them, such as by naming them... T' Matrix, but for ease of explanation, we will continue to use it here. T The term "matrix" can also be used. (Of course, the traditional term can also be used.) T The definition and representation of matrices do not affect the implementation of this method and should also fall within the scope of protection of this invention. Two-port networks in circuit theory T The matrix equation is shown in the following equation, and the transmission matrix of the π-type equivalent circuit of the line is shown in the following equation, where Z is the line impedance and Y / 2 is the admittance of the left and right ground branches.

[0038] Taking wind turbine grid connection as an example, the converter terminal voltage typically needs to undergo two-stage voltage boosting via a transformer substation and a main transformer before grid connection. Here, the transformer's leakage reactance is considered. Z T Returning to the low-pressure side, R m , L m These are the parameters for the excitation branch; the ratio of the high-voltage to low-voltage winding voltages is the turns ratio. k Taking a more complex transformer with phase-shifting effects (such as one with Y / Δ winding connections) as an example, the turns ratio is... kSince it is a complex number, neglecting the influence of admittance or excitation branches, and based on power conservation, it is equivalent to a two-port network, matrix Y t It can be expressed as the following formula.

[0039] use T t The matrix representation is shown in the following equation.

[0040] Using the total transmission matrix T total The relationship between the terminal and the remote control point is shown in the following formula.

[0041] Total transmission matrix T total It can be expressed as shown in the following formula.

[0042] In the formula, T 1 represents the transmission matrix for the wind turbine tower lines. T 2 is the transmission matrix for 0.69-35kV box-type substations. T 3 is a 35kV feeder transmission matrix. T 4 represents the 35-220kV main transformer transmission matrix. T 5 represents the 220kV transmission matrix between the grid connection point and the constant voltage control point. k 1. k 2 represents the step-up transformer ratio of the transformer box and the main transformer, respectively. Z 1. Z T1 , Z 3. Z T2 , Z 5 represents the line impedance of the wind turbine tower, the impedance of the 0.69-35kV transformer box, the impedance of the 35kV feeder, the impedance of the 35-220kV main transformer, and the impedance of the 220kV transmission line between the grid connection point and the constant voltage control point. T Btotal The element actually represents the total transmission impedance that should be set at this time. Z total ,Right now" T Btotal × I terminal The part represents the voltage drop between the machine terminal and the constant voltage control point at the voltage level of the constant voltage control point, which is consistent with the final result obtained by using the segment-by-segment superposition method.

[0043] When implementing off-site voltage control through impedance compensation, the voltage and current dual closed loop will introduce variations under the constraints of Kirchhoff's voltage and current equations due to the change in the actual voltage control point location. Therefore, adaptive adjustments to the voltage and current dual closed loop are required.

[0044] Based on the foregoing analysis and the conclusions regarding the two-port transmission matrix, we can now write: T total The corresponding π-type circuit has two branches to ground (i.e., port-to-ground admittances). y 10 , y 20 The mathematical expression is as follows.

[0045] In the formula, det( T total )= T Atotal T Dtotal - T Btotal T Ctotal .

[0046] Furthermore, the circuit between the converter's internal potential outlet and the constant voltage control point (including filtering and control point shifting) in the refined model of a single-unit grid-connected load new energy converter can ultimately be equivalent to a circuit with an approximate two-stage LC cascade structure, such as... Figure 8 As shown.

[0047] Figure 8 middle C feq The branch represents the filter capacitor. C f and y 10 The equivalent branch after parallel connection of branch branches, C CVCP The branch road representative y 20 The equivalent ground admittance branch in which it is located.

[0048] The updated voltage and current physical constraints and corresponding decoupling control methods are as follows: Figure 9 As shown.

[0049] CVCP site selection principles: (1) The voltage control point extends to the system side: From the perspective of system requirements, it is desirable that all grid-connected power sources within the substation exhibit relatively consistent external characteristics near the grid, i.e., good compatibility. Simultaneously, it is desirable that these grid-connected power sources fully utilize their capabilities to effectively support and regulate voltage on the system side. Therefore, the CVCP (Continuous Voltage Regulator) can be extended as far as possible towards the system side, for example, by being located on a 220kV transmission line near the system side. This makes setting the CVCP's voltage control target value relatively easier; it should be as close as possible to the voltage performance of the internal potential of the equivalent high-voltage source (including other grid-connected power sources) at the connection point. This ensures that the connection of the grid-connected converter will not cause any uncoordinated impact on the power system to be connected.

[0050] (2) It cannot extend indefinitely to the power grid bus point: Based on engineering experience, even generator-transformer units of the same type and parameters can hardly achieve completely consistent control characteristics instantaneously at the voltage control point. This also means that when approaching the CVC target value, the voltage adjustment commands of different units should avoid conflicts in the adjustment direction. Therefore, the CVCP needs to be appropriately moved back towards the generator end, rather than directly setting the CVCP at the grid bus point (GBP). In this way, multiple units gathered on the same bus can use their respective droop characteristics and the buffer line impedance between the CVCP and the GBP to achieve unidirectional adjustment and coordinated operation. As stated in the text, "The method proposed in this invention does not directly set the CVCP at the GBP, but intentionally retains a certain electrical distance between the CVCP and the GBP. Within this reserved buffer distance, multiple grids can achieve adaptive adjustment and coordinated operation through their inherent droop characteristics." (3) Determine the location by considering the drooping characteristics within the adjustable range: The selection of the CVCP location will affect the droop characteristics (slope) exhibited by the grid converter. Users can further determine the appropriate location based on their specific needs. I - U ( Q - U The specific location of CVCP is determined based on the actual needs of its characteristics.

[0051] The engineering calculation method for determining the CVCP voltage reference value, with typical (but not unique) specific steps as follows: Figure 10 As shown, it includes: First, please ask the user to provide the grid bus point (GBP). I - U ( Q - U The droop characteristics and the expected value of the remaining reactive power injected into the GBP during a large-scale renewable energy generation are considered. Then, based on the voltage level of the system before renewable energy grid connection, and taking into account the actual needs provided by the user, power flow calculations are performed to obtain the GBP voltage reference value. Then, the voltage reference value is obtained...I q X or Q X / U GBP The voltage difference between CVCP and GBP is calculated and then superimposed on the GBP voltage reference value to obtain the final CVCP voltage reference value. Furthermore, for multi-machine load systems, the load distribution scheme needs to be determined first.

[0052] In general, after impedance compensation, the target reference value of the voltage control point of the source-side grid-connected converter should, in principle, be relatively close to the voltage performance of the internal potential of the equivalent large voltage source of the system to be connected (including other grid-connected sources) at the connection point. A similar method can be used for the analysis of each other grid-connected source. In this way, it can be ensured that the connection of each grid-connected converter will not have an uncoordinated impact on the power system to be connected.

[0053] The control method proposed in this invention avoids the difficulty of setting the droop coefficient while retaining... Q - U It has the ability to shape droopy characteristics, and it is more in line with the laws of physics. Q - U Variable coefficient ( I - U (Constant coefficient) droop; traditional Q - U The droop characteristic depends on the droop coefficient in the control expression. Under grid-connected operation conditions, an improperly set droop coefficient may lead to the system having no steady-state operating point. When all other parameters are constant, traditional grid-connected control methods may... Q - U Improperly set droop coefficient can lead to system instability, while the method proposed in this invention can ensure that the system has a steady-state operating point and maintains stable operation.

[0054] The control strategy of this invention exhibits excellent command tracking performance and strong control robustness; in contrast, traditional voltage control methods respond to reactive power deviations, leading to frequent changes in grid source voltage commands, making them difficult to maintain. If the traditional grid control method is used, the generator terminal voltage will inevitably decrease when the grid-side load increases. Under otherwise identical conditions, the traditional grid control method, due to sudden increases in reactive load, causes its voltage reference value to adjust in response to reactive power deviations, resulting in the voltage control point voltage becoming difficult to maintain at its original level and even decreasing. The method proposed in this invention, however, can maintain stable voltage at the voltage control point.

[0055] The control method of this invention is no longer limited to the traditional power electronic control scheme that only controls the voltage at the converter terminal. Instead, it extends the voltage control point to the grid side to better leverage its voltage support regulation capability. Traditionally, the voltage control point is located at the converter terminal, and the voltage near the grid side experiences a voltage drop due to reactive power transmission along the line, resulting in grid-connected sources performing less effectively in grid-side voltage support regulation than expected.

[0056] Overall, this method, starting from a more direct constant voltage control perspective, is more in line with the physical nature and inherent characteristics of a grid-connected source as a controlled voltage source, while retaining the port plastic adaptive nonlinearity on the right side of the voltage control point (closer to the grid side). Q - U Sagging characteristics (linear) I - U The ability to droop (and this process does not rely on communication or require additional electrical measurement points) is achieved. Moving the constant voltage control point from the generator terminal of the grid-connected converter to the grid side is a starting point and solution for combining equipment control objectives with system requirements. This is highly beneficial both for reassessing and determining the control objectives of power electronic converters from the perspective of system-side requirements, and for enabling grid-connected sources to fully utilize their self-synchronizing voltage source capabilities and better participate in system-side voltage support regulation.

[0057] In the specific implementation process, the following are established: Figure 11 The simulation model shown in this example simulates the grid-connected operation of a grid-connected converter. The converter output side is connected to the grid side via two-stage step-up transformers and the impedance of each line segment.

[0058] ① Instruction tracing effect: In respectively t =0s, t =3s, t At 6s, the CVCP voltage (line voltage) command was set to 222kV, 225kV, and 222kV. The control performance of the proposed method when the voltage control command changed was observed, and the results are as follows. Figure 12 As shown.

[0059] It is evident that, under grid-connected conditions, the CVCP point voltage can respond promptly and accurately to voltage control commands under the proposed method.

[0060] ② Adaptability to load switching and grid-side voltage fluctuation conditions: Given a constant CVCP voltage control command of 222kV (line voltage), a reactive load of 0.4pu is added at t=3s, and the added reactive load is disconnected and the system returns to its initial state at t=6s. The adaptability of the proposed method to load switching conditions is observed, and the results are as follows: Figure 13 As shown.

[0061] Given a constant CVCP voltage control command of 222kV, the grid-side voltage drops by 0.05pu at t=3s and rises by 0.05pu at t=6s, returning to its initial state. The performance of the proposed method in controlling grid-side voltage fluctuations is observed, and the results are as follows: Figure 14 As shown.

[0062] It is evident that the proposed method demonstrates excellent control performance under load switching and grid-side voltage fluctuation conditions in a grid-connected environment, ensuring that the CVCP voltage always follows the voltage command when the load changes or the grid-side voltage fluctuates.

[0063] In addition, we conducted off-grid / on-grid power-in-the-loop experiments on the grid converter prototype. The experimental results were consistent with the theoretical analysis and simulation results. The constant voltage control point could always track the voltage control command and had stable performance under all steady-state operating conditions, with good control effect. The proposed method is effective.

[0064] Example 2: Furthermore, this invention also proposes a near-grid-side extended constant voltage control system 200 for a grid-connected converter system based on impedance compensation, comprising: The location unit 201 is used to determine the impedance compensation link for the grid-connected converter access system control framework, and to extend the voltage controlled object of the grid-connected converter access system control framework from the voltage at the AC filter capacitor outlet to the specified constant voltage control point CVCP voltage closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The AC filter capacitor outlet includes the converter terminal. The transmission impedance and constant voltage control point voltage actual value calculation unit 202 is used to calculate the total transmission impedance between the converter terminal and the constant voltage control point according to the location of the constant voltage control point in the impedance compensation stage, and determine the actual voltage value of the near-grid side constant voltage control point according to the total transmission impedance and the terminal voltage and current data. The constant voltage control point voltage reference value calculation unit 203 is used to determine the constant voltage control point voltage control target or its reference value based on the selected voltage control point location and the user's actual needs. The control unit 204 is used to perform closed-loop control at the constant voltage control point and the voltage control target reference value based on the actual voltage value, so as to control the voltage at the constant voltage control point.

[0065] The selection principles for the constant voltage control point include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

[0066] The calculation method for the reference value of the constant voltage control point includes: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, by I q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

[0067] The calculation methods for the total transmission impedance between the converter terminal and the constant voltage control point include: the multi-voltage level equivalent series impedance segmentation superposition method or based on... T Impedance calculation method for transmission matrix multiplication.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0075] 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 near-grid side extended constant voltage control method for a grid-connected converter system based on impedance compensation, characterized in that, include: For the control framework of the grid-connected converter system, an impedance compensation link is determined. The voltage controlled object of the grid-connected converter system control framework is extended from the voltage at the output of the AC filter capacitor to the voltage at the designated constant voltage control point CVCP closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The output of the AC filter capacitor includes the converter terminal. In the impedance compensation stage, the total transmission impedance between the converter terminal and the constant voltage control point is calculated based on the location of the constant voltage control point, and the actual voltage value of the near-grid constant voltage control point is determined based on the total transmission impedance and the terminal voltage and current data. Based on the selected voltage control point location and the user's actual needs, determine the voltage control target or its reference value for the voltage control point. The voltage at the constant voltage control point is controlled in a closed loop based on the voltage reference value and the actual voltage value provided by the voltage control loop.

2. The near-grid side extended constant voltage control method for grid-connected converters according to claim 1, characterized in that, The selection principles for the constant voltage control point include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

3. The near-grid side extended constant voltage control method for grid-connected converters according to claim 1, characterized in that, The method for calculating the reference value of the constant voltage control point includes: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, by I q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

4. The near-grid side extended constant voltage control method for grid-connected converters according to claim 1, characterized in that, The method for calculating the total transmission impedance between the converter terminal and the constant voltage control point includes: a multi-voltage level equivalent series impedance segmentation superposition method or a method based on... T Impedance calculation method for transmission matrix multiplication.

5. A near-grid-side extended constant voltage control system for a grid-connected converter system based on impedance compensation, characterized in that, include: The location unit is used to determine the impedance compensation link for the grid-connected converter access system control framework. It extends the voltage controlled object of the grid-connected converter access system control framework from the voltage at the AC filter capacitor outlet to the specified constant voltage control point (CVCP) voltage closer to the grid side. That is, while maintaining the control strategy still applied to the converter terminal and without adding new voltage and current measurement points, the voltage closed loop is actually pushed to the constant voltage control point closer to the grid side. The AC filter capacitor outlet includes the converter terminal. The transmission impedance and constant voltage control point voltage actual value calculation unit is used to calculate the total transmission impedance between the converter terminal and the constant voltage control point based on the location of the constant voltage control point in the impedance compensation stage, and to determine the actual voltage value of the near-grid side constant voltage control point based on the total transmission impedance and the terminal voltage and current data. The constant voltage control point voltage reference value calculation unit is used to determine the constant voltage control point voltage control target or its reference value based on the selected voltage control point location and the user's actual needs. The control unit is used to perform closed-loop control at the constant voltage control point and the voltage control target reference value based on the actual voltage value, so as to control the voltage at the constant voltage control point.

6. The near-grid side extended constant voltage control system for a grid-connected converter system according to claim 5, characterized in that, The selection principles for the constant voltage control point include: (1) The voltage control point extends from the converter terminal to the system side; (2) It cannot be extended indefinitely to the power grid bus point; (3) Determine the position based on the drooping characteristics within the adjustable range.

7. The near-grid side extended constant voltage control system for a grid-connected converter system according to claim 5, characterized in that, The method for calculating the reference value of the constant voltage control point includes: Obtain the user's actual needs, including: the requirements for the GBP at the power grid bus point. I - U / Q - U Droop characteristics and expected value of residual reactive power injected into GBP during the generation of new energy sources; Based on the voltage level of the system before grid connection of new energy and the actual needs, power flow calculation is performed to obtain the GBP voltage reference value. Based on GBP voltage reference values, by I q X or QX / U GBP Calculate the voltage difference between CVCP and GBP, and then superimpose the voltage difference onto the GBP voltage reference value to obtain the CVCP voltage reference value.

8. The near-grid side extended constant voltage control system for a grid-connected converter system according to claim 5, characterized in that, The method for calculating the total transmission impedance between the converter terminal and the constant voltage control point includes: a multi-voltage level equivalent series impedance segmentation superposition method or a method based on... T Impedance calculation method for transmission matrix multiplication.

9. 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 1-4 is implemented.

10. 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 1-4.

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