Grid-connected point impedance control method and device, computer equipment and readable storage medium

Abstract

The invention relates to a grid-connected point impedance control method and device, computer equipment and a readable storage medium. The method comprises the following steps: when a unified power quality conditioner UPQC is in an impedance measurement mode, injecting a disturbance signal to a grid-connected point, and acquiring three-phase voltage information and three-phase current information of the grid-connected point after the disturbance signal is injected; according to the three-phase voltage information and the three-phase current information, determining the impedance of the grid-connected point in a d-q coordinate system; determining an amplitude-frequency characteristic corresponding to the impedance of the grid-connected point in the d-q coordinate system, and determining a target frequency point corresponding to low-frequency oscillation according to the amplitude-frequency characteristic; under the condition that the UPQC is not in the impedance measurement mode, the compensation voltage corresponding to the target frequency point is determined; and when the UPQC is in the damping injection mode, determining a switch control signal acting on the converter according to the compensation voltage, and adjusting the impedance of the grid-connected point based on the switch control signal. By adopting the method, the dynamic self-adaptive adjustment of the grid-connected point impedance can be realized.

Description

Technical Field

[0001] This application relates to the fields of power electronics and power grid technology, and in particular to a grid connection point impedance control method, apparatus, computer equipment, computer-readable storage medium, and computer program product. Background Technology

[0002] With the development of power electronics technology, the penetration rate of new energy sources such as wind power and photovoltaics in the power system continues to rise. However, the volatility, intermittency, and randomness of new energy power generation can easily lead to frequent fluctuations in grid-connected power, causing low-frequency oscillations, resulting in system instability or even system collapse. Furthermore, the large-scale integration of power electronic equipment and nonlinear loads further exacerbates grid harmonic problems. The non-proportional current-voltage characteristics of nonlinear loads cause current waveform distortion, generating wide-spectrum harmonics that can easily lead to resonance risks, accelerate equipment aging, cause motor overheating and relay protection malfunctions, and threaten grid safety. The Unified Power Quality Conditioner (UPQC) is a comprehensive power quality management device that combines a series active power filter (series side) and a parallel active power filter (parallel side) through a DC-side capacitor.

[0003] In traditional technologies, fixed or adjustable passive components (such as reactors and capacitors) are added to the power grid through UPQC to change the impedance characteristics of the system. However, setting fixed parameters makes it difficult to achieve dynamic adaptive adjustment of impedance and cannot effectively solve the problem of low-frequency oscillation. Summary of the Invention

[0004] Therefore, it is necessary to provide a grid connection point impedance control method, device, computer equipment, computer-readable storage medium, and computer program product that can achieve dynamic adaptive adjustment of impedance to address the above-mentioned technical problems.

[0005] In a first aspect, this application provides a grid connection point impedance control method, including:

[0006] When the Unified Power Quality Regulator (UPQC) is in impedance measurement mode, a disturbance signal is injected into the grid connection point, and the three-phase voltage and three-phase current information of the grid connection point are obtained after the disturbance signal is injected.

[0007] Based on the three-phase voltage information and the three-phase current information, determine the impedance of the grid connection point in the dq coordinate system;

[0008] Determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristic;

[0009] When the UPQC is not in impedance measurement mode, determine the compensation voltage corresponding to the target frequency point;

[0010] When the UPQC is in damped injection mode, the switching control signal applied to the converter is determined according to the compensation voltage, and the impedance of the grid connection point is adjusted based on the switching control signal.

[0011] In one embodiment, determining the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage information and the three-phase current information includes:

[0012] Perform a Fast Fourier Transform on each phase voltage information in the three-phase voltage information and each phase current information in the three-phase current information to obtain the corresponding harmonic components;

[0013] The three-phase voltage information and the three-phase current information are respectively subjected to Parker transformation to obtain the dq components in the dq coordinate system.

[0014] The impedance of the grid connection point is determined based on the linear relationship between voltage and current in the dq coordinate system, the dq component, and the harmonic component.

[0015] In one embodiment, determining the target frequency point corresponding to the low-frequency oscillation based on the amplitude-frequency characteristics includes:

[0016] The frequency point where negative damping occurs in the amplitude-frequency characteristic is taken as the target frequency point corresponding to the generation of low-frequency oscillation.

[0017] In one embodiment, determining the switching control signal applied to the converter based on the compensation voltage when the UPQC is not in impedance measurement mode includes:

[0018] When the UPQC is not in impedance measurement mode, the output voltage of the series converter is obtained, and inner loop current control is performed based on the difference between the output voltage of the series converter in the dq coordinate system and the compensation voltage to obtain the control output voltage.

[0019] Convert the control output voltage in the dq coordinate system to the control output voltage in the abc coordinate system;

[0020] The sine wave corresponding to each phase voltage information of the control output voltage in the abc coordinate system is compared with the triangular carrier wave to obtain the square wave corresponding to each phase voltage information.

[0021] The switching control signal of the converter is determined based on the square wave.

[0022] In one embodiment, the UPQC includes a series voltage compensation unit and a parallel current compensation unit; the disturbance signal includes a voltage disturbance signal or a current disturbance signal; if the grid-connected inverter connected to the grid is a grid-connected inverter, then a current disturbance signal is injected into the grid connection point through the parallel current compensation unit of the UPQC.

[0023] If the grid-connected inverter connected to the power grid is a grid-type inverter, then a voltage disturbance signal is injected into the grid connection point through the series voltage compensation unit of the UPQC.

[0024] In one embodiment, the disturbance signal includes a voltage disturbance signal; the UPQC includes a series voltage compensation unit and a parallel current compensation unit;

[0025] When the UPQC is in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is closed, and the impedance injection switch is open; the voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is closed, and the current disturbance injection switch is open.

[0026] When the UPQC is not in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is open; the voltage regulation control switch of the parallel current compensation unit is open, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open.

[0027] When the UPQC is in damped injection mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is closed; the voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open.

[0028] Secondly, this application also provides a grid connection point impedance control device, comprising:

[0029] The disturbance injection module is used to inject a disturbance signal into the grid connection point when the Unified Power Quality Conditioner (UPQC) is in impedance measurement mode, and to obtain the three-phase voltage and three-phase current information of the grid connection point after the disturbance signal is injected.

[0030] An impedance determination module is used to determine the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage information and the three-phase current information.

[0031] The frequency point determination module is used to determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and to determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristic.

[0032] A voltage determination module is used to determine the compensation voltage corresponding to the target frequency point when the UPQC is not in impedance measurement mode.

[0033] An impedance adjustment module is used to determine the switching control signal applied to the converter based on the compensation voltage when the UPQC is in damped injection mode, and to adjust the impedance of the grid connection point based on the switching control signal.

[0034] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the grid connection point impedance control method provided in the first aspect.

[0035] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the grid connection point impedance control method provided in the first aspect.

[0036] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the grid connection point impedance control method provided in the first aspect.

[0037] The aforementioned grid connection point impedance control method, device, computer equipment, computer-readable storage medium, and computer program product, by injecting a disturbance signal into the grid connection point when the UPQC is in impedance measurement mode, and acquiring the three-phase voltage and three-phase current information of the grid connection point after the disturbance signal is injected, determine the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage and three-phase current information, determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and determine the target frequency point corresponding to the low-frequency oscillation based on the amplitude-frequency characteristic. When the UPQC is not in impedance measurement mode, determine the compensation voltage corresponding to the target frequency point. When the UPQC is in damping injection mode, determine the switching control signal acting on the converter based on the compensation voltage, and adjust the impedance of the grid connection point based on the switching control signal. This enables unified impedance measurement and compensation through the UPQC, and corresponding compensation based on the measured real-time impedance information, achieving dynamic adaptive adjustment of impedance, effectively solving the low-frequency oscillation problem generated after new energy sources are connected to the grid. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is an application environment diagram of the grid connection point impedance control method in one embodiment;

[0040] Figure 2 This is a flowchart illustrating a grid connection point impedance control method in one embodiment;

[0041] Figure 3 This is a block diagram of the damping controller in one embodiment;

[0042] Figure 4 This is a flowchart illustrating the grid connection point impedance control method in another embodiment;

[0043] Figure 5 This is a control block diagram of a series voltage compensation unit in one embodiment;

[0044] Figure 6 This is a control block diagram of a parallel current compensation unit in one embodiment;

[0045] Figure 7 This is a flowchart illustrating the grid connection point impedance control method in another embodiment;

[0046] Figure 8 This is a structural block diagram of a grid connection point impedance control device in one embodiment;

[0047] Figure 9 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0049] It should be noted that the terms "first," "second," etc., used in this application can be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from the second element. The terms "comprising" and "having," and any variations thereof, used in this application, are intended to cover non-exclusive inclusion. The term "multiple" used in this application refers to two or more. The term "and / or" used in this application refers to one of the embodiments, or any combination of multiple embodiments.

[0050] The grid connection point impedance control method provided in this application embodiment can be applied to, for example... Figure 1 The application environment shown is illustrated. The Unified Power Quality Conditioner (UPQC) is a power quality conditioning device composed of a parallel active power filter and a series active power filter connected together via a common DC bus. The series active power filter is connected in series between the grid and the load via a transformer, compensating for grid-side voltage issues; the parallel active power filter is connected in parallel to the load side, compensating for load current harmonics, reactive current, and neutral current. When the UPQC is in impedance measurement mode, a disturbance signal is injected into the grid connection point, and the three-phase voltage and current information of the grid connection point after the disturbance signal is injected is acquired. Based on the three-phase voltage and current information, the impedance of the grid connection point in the dq coordinate system is determined, and the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system is determined. Based on the amplitude-frequency characteristic, the target frequency point corresponding to the low-frequency oscillation is determined. When the UPQC is not in impedance measurement mode, the compensation voltage corresponding to the target frequency point is calculated. When the UPQC is in damping injection mode, the switching control signal acting on the converter is determined based on the compensation voltage. The impedance of the grid connection point is adjusted based on the switching control signal, thereby realizing the control of the grid connection point impedance. The UPQC can be connected to a server or terminal to perform the corresponding calculations and processing.

[0051] In one exemplary embodiment, such as Figure 2 As shown, a grid connection point impedance control method is provided, which is applied to... Figure 1 Taking UPQC as an example, the explanation includes the following steps 202 to 206. Wherein:

[0052] Step 202: When the UPQC is in impedance measurement mode, a disturbance signal is injected into the grid connection point, and the three-phase voltage and three-phase current information of the grid connection point are obtained after the disturbance signal is injected.

[0053] Impedance measurement mode refers to the mode in which UPQC measures the impedance of the grid connection point. The grid connection point is the electrical connection point between a distributed generation system, energy storage device, or power electronic equipment and the power grid. A disturbance signal refers to an artificially injected voltage or current signal, which can include voltage or current disturbance signals. It is easy to understand that before the disturbance signal is injected, the grid connection point already has corresponding current and voltage signals. After the disturbance signal is injected, the obtained information is the three-phase voltage and three-phase current information of the grid connection point after the disturbance signal and the original grid signal have interacted.

[0054] In practical applications, the UPQC can be switched to impedance measurement mode by controlling the on / off state of each switch within it. In impedance measurement mode, a disturbance signal is injected into the grid connection point via the UPQC. After the disturbance signal is injected, the three-phase current information at the grid connection point is acquired and recorded. and three-phase voltage information .

[0055] Step 204: Determine the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage and three-phase current information.

[0056] The three-phase voltage and three-phase current information are both in the three-phase stationary coordinate system (abc coordinate system). After obtaining the three-phase voltage and three-phase current information at the grid connection point, it is necessary to transform from the abc coordinate system to the dq coordinate system to calculate the impedance information of the grid connection point.

[0057] For example, the three-phase voltage information and three-phase current information can be subjected to Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT) to obtain the corresponding frequency components. The frequency components can then be subjected to Park Transform to obtain the dq components in the dq coordinate system. The impedance of the grid connection point in the dq coordinate system can be determined based on the dq components.

[0058] Step 206: Determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristic.

[0059] The amplitude-frequency characteristic is used to characterize the amplitude-frequency features of the impedance. By plotting the Bode plot of the impedance at the grid connection point in the dq coordinate system, the target frequency point corresponding to the low-frequency oscillation can be determined based on the amplitude-frequency characteristic curve in the Bode plot. The target frequency point refers to the frequency position where the low-frequency oscillation occurs.

[0060] Step 208: If the UPQC is not in impedance measurement mode, determine the compensation voltage corresponding to the target frequency.

[0061] The UPQC's impedance measurement mode can be controlled via its switches. For example, if all switches are turned off, the UPQC is not in impedance measurement mode.

[0062] For example, the compensation voltage corresponding to the target frequency can be output through the damping controller in the UPQC. The damping controller can implement the control strategy on the series side. For example... Figure 3 As shown, a damping controller may include a control gain, a DC blocking filter, and a phase compensation stage. For example, the mathematical expression of the damping controller is shown in formula (1) below.

[0063] Formula (1)

[0064] Where K represents the damping control gain, and K determines the strength of the damping effect; This is a high-pass filter stage (DC blocking filter stage), whose main function is to isolate DC components; This is a phase compensation element used to modulate the phase shift of the entire damping control element at the low-frequency oscillation frequency, so as to ensure that the damping control element provides as positive a damping effect as possible. The time constant can be calculated according to formulas (2) and (3).

[0065] Formula (2)

[0066] Formula (3)

[0067] The value of m can be determined based on the compensation angle. For example, when the compensation angle is less than the threshold, m is 1; when the compensation angle is greater than or equal to the threshold, m is 2.

[0068] in other words, Figure 3 In the example shown, the frequency corresponding to the target frequency can be used as the input to the damping controller. After passing through the control gain, DC blocking filter, and phase compensation stages, the compensation voltage can be obtained. It is easy to understand that the specific parameters of the control gain, DC blocking filter, and phase compensation stages can be set according to the actual application scenario.

[0069] Step 210: When the UPQC is in damped injection mode, determine the switching control signal applied to the converter based on the compensation voltage, and adjust the impedance of the grid connection point based on the switching control signal.

[0070] The damping injection mode refers to the mode of damping injection at the grid connection point based on the compensation voltage. The compensation voltage is transformed from the three-phase coordinate system to the dq coordinate system, and then the difference between this compensation voltage and the output voltage of the series converter is modulated by PWM pulses to obtain a corresponding square wave signal. This square wave signal is used to control the on / off state of the bridge arm switches in the converter, thereby controlling the impedance of the grid connection point.

[0071] The aforementioned grid connection point impedance control method, when the UPQC is in impedance measurement mode, injects a disturbance signal into the grid connection point and acquires the three-phase voltage and current information of the grid connection point after the disturbance signal is injected. Based on the three-phase voltage and current information, the impedance of the grid connection point in the dq coordinate system is determined, and the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system is determined. Based on the amplitude-frequency characteristic, the target frequency point corresponding to the low-frequency oscillation is determined. When the UPQC is not in impedance measurement mode, the compensation voltage corresponding to the target frequency point is determined. When the UPQC is in damping injection mode, the switching control signal acting on the converter is determined based on the compensation voltage. The impedance of the grid connection point is adjusted based on the switching control signal. This method enables unified impedance measurement and compensation through the UPQC, and corresponding compensation is performed based on the measured real-time impedance information, achieving dynamic adaptive adjustment of the impedance and effectively solving the low-frequency oscillation problem generated after new energy sources are connected to the grid.

[0072] In some embodiments, determining the impedance of the grid connection point in the dq coordinate system based on three-phase voltage information and three-phase current information includes:

[0073] Perform a Fast Fourier Transform on each phase voltage information and each phase current information in the three-phase voltage information to obtain the corresponding harmonic components; perform a Park Transform on the three-phase voltage information and the three-phase current information to obtain the dq components in the dq coordinate system; determine the impedance of the grid connection point based on the linear relationship between voltage and current in the dq coordinate system, the dq components, and the harmonic components.

[0074] The harmonic components include the components of each harmonic, and each harmonic component includes amplitude and phase.

[0075] For example, by performing a Fast Fourier Transform on each phase voltage in the three-phase voltage signal and each phase current in the three-phase current information, the voltage and current components corresponding to each frequency point can be obtained. Then, a Clarke Transform is performed on the three-phase voltage and current information, i.e., from a three-phase stationary coordinate system to a two-phase stationary coordinate system, and then a Park Transform is performed, i.e., from a two-phase stationary coordinate system to a rotating coordinate system, to obtain the dq components in the dq coordinate system. For each frequency point, based on the linear relationship between voltage and current, the relationship between voltage and current corresponding to the dq components in the dq coordinate system can be established, as shown in the following formula (4).

[0076] Formula (4)

[0077] Converting formula (4) into matrix form yields the following formula (5).

[0078] Formula (5)

[0079] In formulas (4) and (5), the corresponding mathematical relationships are obtained through two injected disturbance signals (corresponding to subscripts 1 and 2). Based on formula (5), Zdd, Zdq, Zqd, and Zqq can be calculated sequentially, thereby obtaining the dq impedance matrix of the grid connection point.

[0080] In this embodiment, by performing Fast Fourier Transform on each phase voltage information and each phase current information in the three-phase voltage information, the corresponding harmonic components are obtained. By performing Park Transform on the three-phase voltage information and the three-phase current information, the dq components are obtained. Based on the relationship between voltage, current and impedance and the dq components, the impedance information of the grid connection point at each frequency can be accurately obtained, laying a solid foundation for impedance compensation of the grid connection point.

[0081] In some embodiments, determining the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristics includes: taking the frequency point in the amplitude-frequency characteristics where negative damping occurs as the target frequency point corresponding to the generation of low-frequency oscillation.

[0082] It's easy to understand that after obtaining the impedance matrix of the grid connection point in the dq coordinate system, and with the amplitude-frequency information at each frequency point, the amplitude-frequency characteristic curve corresponding to the impedance matrix can be easily obtained, i.e., the amplitude-frequency characteristic of the impedance. The frequency point where negative damping occurs is determined from the amplitude-frequency characteristic curve as the target frequency point. Negative damping refers to the phenomenon where, under certain operating conditions, the system's dynamic response not only fails to dampen oscillations but actually amplifies them, potentially leading to system instability. Negative damping causes the oscillation amplitude to gradually increase.

[0083] For example, if the amplitude-frequency characteristic curve corresponding to the impedance matrix shows negative damping (phase close to -90°) in the range of 0.1 Hz to 2 Hz, it is determined to be a low-frequency oscillation, and this frequency band is taken as the target frequency point.

[0084] In this embodiment, by taking the frequency point corresponding to the low-frequency oscillation as the target frequency point, a corresponding compensation voltage is output based on the target frequency point. When the low-frequency oscillation occurs, the impedance is adjusted according to the corresponding compensation voltage, which can effectively suppress the low-frequency oscillation.

[0085] In some embodiments, when the UPQC is not in impedance measurement mode, determining the switching control signal applied to the converter based on the compensation voltage includes:

[0086] When the UPQC is not in impedance measurement mode, the output voltage of the series converter is acquired, and inner-loop current control is performed based on the difference between the output voltage and the compensation voltage of the series converter in the dq coordinate system to obtain the control output voltage. The control output voltage in the dq coordinate system is converted into the control output voltage in the abc coordinate system. The sine wave corresponding to the voltage information of each phase of the control output voltage in the abc coordinate system is compared with the triangular carrier wave to obtain the square wave corresponding to the voltage information of each phase. The switching control signal of the converter is determined based on the square wave.

[0087] The output voltage of the series converter is used to characterize the original output voltage in the power grid. The inner loop current control aims to make the difference between the output voltage of the series converter and the compensation voltage approach zero or equal to zero.

[0088] In some examples, if the injected disturbance signal is a voltage disturbance signal, it is injected from the series side to the grid connection point and acts on the converter through the output switch control signal on the series side. If the injected disturbance signal is a current disturbance signal, it is injected from the parallel side to the grid connection point and acts on the converter through the output switch control signal on the series side.

[0089] For example, when the UPQC is not in impedance measurement mode, the output voltage of the series converter is transformed from the abc coordinate system to the dq coordinate system. The difference between the output voltage and the compensation voltage of the series converter in the dq coordinate system is used for inner-loop current control to obtain the control output voltage. The control output voltage in the dq coordinate system is then transformed back to the abc coordinate system. The sine wave corresponding to the control output voltage in the abc coordinate system is modulated by a triangular carrier wave to obtain a square wave signal. The switching control signal of the converter is determined based on this square wave signal. Each phase voltage information of the control output voltage corresponds to a square wave signal, i.e., one switching control signal. Therefore, each control output voltage can generate three switching control signals. If the converter is a three-phase three-bridge structure, each switching control signal can control the on / off state of one bridge arm to achieve impedance regulation at the grid connection point and suppress low-frequency oscillations.

[0090] In one example, a compensation current at the target frequency can also be output, and the switching control signal applied to the converter can be determined based on this compensation current. It is easy to understand that the process of current compensation is similar to that of voltage compensation. Figure 4 As shown, the output voltage of the series converter is U. g The load current is I L Compensation current and load current I L By comparison, the compensation current and the load current I are obtained. L The difference in the dq coordinate system is used for inner-loop current control to obtain the control output current. A PWM modulation is then applied to the sine wave corresponding to the control output current based on a triangular carrier wave to obtain a current square wave signal. Finally, the corresponding switch control signal is output from the series side. It's easy to understand that for a high level in the square wave, the corresponding switch control signal could be, for example, 1 / 0; for a low level in the square wave, the switch control signal could be, for example, 0 / 1, etc.

[0091] In this embodiment, the inner loop current control is performed by the difference between the output voltage and the compensation voltage of the series converter in the dq coordinate system to obtain the control output voltage. The sine wave corresponding to the voltage information of each phase of the control output voltage in the abc coordinate system is compared with the triangular carrier wave to obtain the square wave corresponding to the voltage information of each phase. The switching control signal of the converter is determined based on the square wave, so that the switching control signal of the converter can be accurately obtained.

[0092] In some embodiments, the UPQC includes a series voltage compensation unit and a parallel current compensation unit; the disturbance signal includes a voltage disturbance signal or a current disturbance signal; if the grid-connected inverter connected to the grid is a grid-connected inverter, a current disturbance signal is injected into the grid connection point through the parallel current compensation unit of the UPQC; if the grid-connected inverter connected to the grid is a grid-connected inverter, a voltage disturbance signal is injected into the grid connection point through the series voltage compensation unit of the UPQC.

[0093] The series voltage compensation unit can also be called the series side, and the parallel current compensation unit can also be called the parallel side. Grid-connected inverters are used to track grid voltage and frequency, relying on grid voltage synchronization. Grid-connected inverters are used to autonomously establish voltage and frequency, do not rely on the grid, and can operate independently.

[0094] In practical application scenarios, the type of grid-connected inverter connected to the grid is determined. If the grid-connected inverter is a grid-following type, a current disturbance signal is injected into the grid connection point through the parallel current compensation unit of UPQC. If the grid-connected inverter is a grid-connected type, a voltage disturbance signal is injected into the grid connection point through the series voltage compensation unit of UPQC.

[0095] In this embodiment, by injecting a current disturbance signal into the grid connection point through a parallel current compensation unit in the case of a grid-connected inverter, the dynamic effect of the current loop can be stimulated. This not only avoids the phase distortion problem caused by phase-locked loop (PLL) coupling in traditional voltage disturbances, but also significantly reduces the instability risk caused by PLL sensitivity under weak grid conditions. In the case of a grid-connected inverter, injecting a voltage disturbance signal into the grid connection point through a series current compensation unit can accurately match the dynamic characteristics of the voltage loop. This avoids the control instability problem caused by the forced change of output voltage due to current disturbances, and effectively stimulates the virtual inertia response. This improves the overall stability of the power grid system.

[0096] In some embodiments, the disturbance signal includes a voltage disturbance signal; the UPQC includes a series voltage compensation unit and a parallel current compensation unit;

[0097] When the UPQC is in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is closed, and the impedance injection switch is open; the voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is closed, and the current disturbance injection switch is open. When the UPQC is not in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is open; the voltage regulation control switch of the parallel current compensation unit is open, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open. When the UPQC is in damping injection mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is closed; the voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open.

[0098] For example, the control block diagram of the series voltage compensation unit is as follows: Figure 5 As shown, the control block diagram of the parallel current compensation unit is as follows: Figure 6 As shown. When the UPQC is in impedance measurement mode, the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is closed, and the impedance injection switch S4 is open; the voltage regulation control switch S5 of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch S6 is closed, and the current disturbance injection switch S7 is open, to achieve disturbance signal injection while ensuring DC side voltage stability. When the UPQC is not in impedance measurement mode, the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is open, and the impedance injection switch S4 is open; the voltage regulation control switch S5 of the parallel current compensation unit is open, the harmonic current compensation signal injection switch S6 is open, and the current disturbance injection switch S7 is open. When the UPQC is in damped injection mode, the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is open, and the impedance injection switch S4 is closed; the voltage regulation control switch S5 of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch S6 is open, and the current disturbance injection switch S7 is open.

[0099] In the series voltage compensation unit, the DC reference command voltage u of the intermediate capacitor is... ref* The comparison result is input to the PI (differential-integral) control loop, and the participation of the PI control loop is controlled by switch S1 or S5. Voltage imbalance compensation command injection switch S2 is used to connect the compensation command voltage calculated after detecting voltage sags and dips when the UPQC is used as a power quality compensation device. Disturbance voltage injection switch S3 is used to connect the d-axis and q-axis command voltages when injecting voltage disturbances. Impedance injection switch S4 is used to connect the damped injection voltage command value based on voltage compensation. Harmonic current compensation signal injection switch S6 is used to connect the compensation command current calculated after detecting grid harmonics when the UPQC is used as a power quality compensation device. Current disturbance injection switch S7 is used to connect the d-axis and q-axis command currents when injecting current disturbances. d_shc I q_shc These are used to represent the components of the feedback current of the parallel-side converter in the d and q coordinate systems, respectively. d_sec V q_sec These are used to represent the components of the feedback voltage of the series-side converter in the d and q coordinate systems, respectively. shc_abc Switching control signals used to control the switching transistors of series-side or parallel-side converters.

[0100] In this embodiment, by controlling the closing or opening of each switch in the series voltage compensation unit and the parallel current compensation unit in the UPQC, the opening or closing of the impedance measurement mode and the damping injection mode can be accurately controlled, thereby improving the accuracy of the grid connection point impedance adjustment.

[0101] In some practical applications, traditional methods have significant limitations in impedance reshaping. While active damping strategies can introduce virtual impedance through controller parameter optimization, the drastic fluctuations in renewable energy output cause rapidly changing grid conditions. Parameters need to be precisely matched to grid impedance, load characteristics, and other factors. Fixed parameter settings are difficult to achieve dynamic adaptation, easily leading to underdamping causing oscillation suppression failure or overdamping causing system response lag. Modular multilevel converters and other topologies possess impedance regulation potential, but rely on complex mathematical modeling and parameter identification processes, facing challenges of high computational load, long debugging cycles, and high costs in engineering applications. Furthermore, traditional solutions often focus on single functional modules, lacking a coordinated mechanism for measurement, analysis, and control, making it difficult to cope with the complex scenarios of multi-factor coupling after renewable energy grid connection. Therefore, this embodiment provides a grid connection point impedance adjustment method that can measure grid and load impedance in real time and adaptively inject damping through spectral analysis to solve the low-frequency oscillation problem generated after renewable energy is connected to the grid.

[0102] In an exemplary embodiment, a schematic diagram of the grid connection point impedance control process is shown below. Figure 7 As shown. This includes steps 702 to 718.

[0103] Step 702: Set the system parameters of UPQC and provide an array of disturbance frequencies.

[0104] The system parameters of UPQC include, for example, the values ​​of the filter capacitor and inductor, as well as the PI values ​​in the PI control loop. The disturbance frequency array can refer to a pre-set set of disturbance frequency points.

[0105] Step 704: Turn on impedance measurement mode.

[0106] Reference Figure 5 and Figure 6 When the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is closed, the impedance injection switch S4 is open, the voltage regulation control switch S5 of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch S6 is closed, and the current disturbance injection switch S7 is open, the UPQC is in impedance measurement mode.

[0107] Step 706: Inject a disturbance signal, detect and store the three-phase voltage and three-phase current at the grid connection point after the disturbance signal is injected.

[0108] Step 708: Convert the three-phase voltage and three-phase current signals in the time domain to the frequency domain using Fast Fourier Analysis.

[0109] Step 710: Calculate the dq impedance at the grid connection point.

[0110] The three-phase voltage and three-phase current at the grid connection point are transformed by Park to obtain the dq components in the dq coordinate system. The dq impedance of the grid connection point in the dq coordinate system is then calculated based on the dq components.

[0111] Step 712: Draw a Bode plot and analyze the oscillation frequency.

[0112] Based on the dq impedance of the grid connection point, a Bode plot is plotted, the oscillation frequency is analyzed, and the oscillation mode is identified. If the impedance curve shows negative damping (phase close to -90°) in the 0.1-2Hz frequency band, it is determined to be a low-frequency oscillation. The characteristic parameters of this frequency band, i.e. the oscillation frequency, are extracted, and the frequency point of this oscillation frequency is taken as the target frequency point.

[0113] Step 714: Turn off impedance measurement mode.

[0114] Reference Figure 5 and Figure 6If the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is open, and the impedance injection switch S4 is open; and the voltage regulation control switch S5 of the parallel current compensation unit is open, the harmonic current compensation signal injection switch S6 is open, and the current disturbance injection switch S7 is open, then the UPQC is not in impedance measurement mode.

[0115] Step 716: The damping injection voltage (i.e., compensation voltage) is obtained through the damping controller.

[0116] Step 718: Switch to damped injection mode.

[0117] When the DC voltage regulation control switch S1 of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch S2 is open, the disturbance voltage injection switch S3 is open, the impedance injection switch S4 is closed, the voltage regulation control switch S5 of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch S6 is open, and the current disturbance injection switch S7 is open, the UPQC is in damped injection mode. In damped injection mode, the switching control signal applied to the converter is determined based on the compensation voltage. The impedance at the grid connection point is adjusted based on this switching control signal to avoid low-frequency oscillations.

[0118] In the above embodiments, by leveraging the "dual-function" characteristics of UPQC, technological upgrades can be achieved while fully retaining the core functions of the original power quality management. As the core equipment for comprehensive power quality management in the power system, UPQC has functions such as voltage sag and surge compensation, harmonic suppression, and voltage imbalance regulation on its series side; while on the parallel side, it monitors and compensates reactive power in real time, filters current harmonics, and balances three-phase currents. Based on this, impedance measurement is achieved through UPQC. By actively injecting disturbance signals through dual converters and acquiring system responses, the real-time impedance characteristics of the power grid can be quickly obtained. It can also perform impedance reshaping. Based on accurate measurement data and combined with spectrum analysis to dynamically inject impedance, adaptive adjustment of the equivalent impedance at the grid connection point can be achieved. Compared to traditional measurement methods that rely on static models, this significantly improves measurement accuracy and scenario adaptability, effectively avoiding over-damping or under-damping problems caused by traditional fixed-parameter virtual impedance injection. Ultimately, UPQC not only possesses multi-dimensional power quality regulation capabilities but also overcomes the limitations of traditional devices with single functions and delayed responses, significantly improving the stability and reliability of the power system in scenarios with high penetration of new energy sources.

[0119] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0120] Based on the same inventive concept, this application also provides a grid connection point impedance control device for implementing the grid connection point impedance control method described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations of one or more embodiments of the grid connection point impedance control device provided below can be found in the limitations of the grid connection point impedance control method described above, and will not be repeated here.

[0121] In one exemplary embodiment, such as Figure 8 As shown, a grid connection point impedance control device 800 is provided, including: a disturbance injection module 802, an impedance determination module 804, a frequency point determination module 806, a voltage determination module 808, and an impedance adjustment module 810, wherein:

[0122] The disturbance injection module 802 is used to inject a disturbance signal into the grid connection point when the Unified Power Quality Regulator (UPQC) is in impedance measurement mode, and to obtain the three-phase voltage and three-phase current information of the grid connection point after the disturbance signal is injected.

[0123] Impedance determination module 804 is used to determine the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage information and the three-phase current information.

[0124] The frequency point determination module 806 is used to determine the amplitude-frequency characteristics corresponding to the impedance of the grid connection point in the dq coordinate system, and to determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristics.

[0125] The voltage determination module 808 is used to determine the compensation voltage corresponding to the target frequency point when the UPQC is not in impedance measurement mode.

[0126] The impedance adjustment module 810 is used to determine the switching control signal applied to the converter based on the compensation voltage when the UPQC is in damped injection mode, and to adjust the impedance of the grid connection point based on the switching control signal.

[0127] In some embodiments, the impedance determination module 804 is further configured to perform fast Fourier transform on each phase voltage information in the three-phase voltage information and each phase current information in the three-phase current information to obtain the corresponding harmonic components; perform Park transform on the three-phase voltage information and the three-phase current information to obtain the corresponding dq components in the dq coordinate system; and determine the impedance of the grid connection point based on the linear relationship between voltage and current in the dq coordinate system, the dq components, and the harmonic components.

[0128] In some embodiments, the frequency point determination module 806 is further configured to use the frequency point in the amplitude-frequency characteristic where negative damping occurs as the target frequency point corresponding to the generation of low-frequency oscillation.

[0129] In some embodiments, the impedance adjustment module 810 is further configured to: acquire the output voltage of the series converter when the UPQC is not in impedance measurement mode; perform inner-loop current control based on the difference between the output voltage of the series converter and the compensation voltage in the dq coordinate system to obtain a control output voltage; convert the control output voltage in the dq coordinate system to a control output voltage in the abc coordinate system; compare the sine wave corresponding to the voltage information of each phase of the control output voltage in the abc coordinate system with a triangular carrier wave to obtain a square wave corresponding to the voltage information of each phase; and determine the switching control signal of the converter based on the square wave.

[0130] In some embodiments, the UPQC includes a series voltage compensation unit and a parallel current compensation unit; the disturbance signal includes a voltage disturbance signal or a current disturbance signal; the disturbance injection module 802 is further configured to inject a current disturbance signal into the grid connection point through the parallel current compensation unit of the UPQC if the grid-connected inverter connected to the grid is a grid-connected inverter; and to inject a voltage disturbance signal into the grid connection point through the series voltage compensation unit of the UPQC if the grid-connected inverter connected to the grid is a grid-connected inverter.

[0131] Each module in the aforementioned grid connection point impedance control device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0132] In one exemplary embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 9As shown, this computer device includes a processor, memory, input / output interfaces (I / O), and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operating system and computer programs stored in the non-volatile storage media. The database stores data related to grid connection point impedance control methods. The I / O interfaces are used for information exchange between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements a grid connection point impedance control method.

[0133] Those skilled in the art will understand that Figure 9 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0134] In one exemplary embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0135] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method embodiments.

[0136] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0137] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0138] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0139] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0140] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A grid connection point impedance control method, characterized in that, The method includes: When the Unified Power Quality Regulator (UPQC) is in impedance measurement mode, a disturbance signal is injected into the grid connection point, and the three-phase voltage and three-phase current information of the grid connection point are obtained after the disturbance signal is injected. Based on the three-phase voltage information and the three-phase current information, determine the impedance of the grid connection point in the dq coordinate system; Determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristic; When the UPQC is not in impedance measurement mode, determine the compensation voltage corresponding to the target frequency point; When the UPQC is in damped injection mode, the switching control signal applied to the converter is determined according to the compensation voltage, and the impedance of the grid connection point is adjusted based on the switching control signal.

2. The method according to claim 1, characterized in that, The step of determining the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage information and the three-phase current information includes: Perform a Fast Fourier Transform on each phase voltage information in the three-phase voltage information and each phase current information in the three-phase current information to obtain the corresponding harmonic components; The three-phase voltage information and the three-phase current information are respectively subjected to Parker transformation to obtain the dq components in the dq coordinate system. The impedance of the grid connection point is determined based on the linear relationship between voltage and current in the dq coordinate system, the dq component, and the harmonic component.

3. The method according to claim 1, characterized in that, Determining the target frequency point corresponding to the low-frequency oscillation based on the amplitude-frequency characteristics includes: The frequency point where negative damping occurs in the amplitude-frequency characteristic is taken as the target frequency point corresponding to the generation of low-frequency oscillation.

4. The method according to claim 1, characterized in that, When the UPQC is not in impedance measurement mode, determining the switching control signal applied to the converter based on the compensation voltage includes: When the UPQC is not in impedance measurement mode, the output voltage of the series converter is obtained, and inner loop current control is performed based on the difference between the output voltage of the series converter in the dq coordinate system and the compensation voltage to obtain the control output voltage. Convert the control output voltage in the dq coordinate system to the control output voltage in the abc coordinate system; The sine wave corresponding to each phase voltage information of the control output voltage in the abc coordinate system is compared with the triangular carrier wave to obtain the square wave corresponding to each phase voltage information. The switching control signal of the converter is determined based on the square wave.

5. The method according to claim 1, characterized in that, The UPQC includes a series voltage compensation unit and a parallel current compensation unit; the disturbance signal includes a voltage disturbance signal or a current disturbance signal; if the grid-connected inverter connected to the grid is a grid-connected inverter, then a current disturbance signal is injected into the grid connection point through the parallel current compensation unit of the UPQC. If the grid-connected inverter connected to the power grid is a grid-type inverter, then a voltage disturbance signal is injected into the grid connection point through the series voltage compensation unit of the UPQC.

6. The method according to claim 1, characterized in that, The disturbance signal includes a voltage disturbance signal; the UPQC includes a series voltage compensation unit and a parallel current compensation unit; When the UPQC is in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is closed, and the impedance injection switch is open. The voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is closed, and the current disturbance injection switch is open. When the UPQC is not in impedance measurement mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is open. The voltage regulation control switch of the parallel current compensation unit is open, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open. When the UPQC is in damping injection mode, the DC voltage regulation control switch of the series voltage compensation unit is open, the voltage imbalance compensation command injection switch is open, the disturbance voltage injection switch is open, and the impedance injection switch is closed. The voltage regulation control switch of the parallel current compensation unit is closed, the harmonic current compensation signal injection switch is open, and the current disturbance injection switch is open.

7. A grid connection point impedance control device, characterized in that, The device includes: The disturbance injection module is used to inject a disturbance signal into the grid connection point when the Unified Power Quality Conditioner (UPQC) is in impedance measurement mode, and to obtain the three-phase voltage and three-phase current information of the grid connection point after the disturbance signal is injected. An impedance determination module is used to determine the impedance of the grid connection point in the dq coordinate system based on the three-phase voltage information and the three-phase current information. The frequency point determination module is used to determine the amplitude-frequency characteristic corresponding to the impedance of the grid connection point in the dq coordinate system, and to determine the target frequency point corresponding to the generation of low-frequency oscillation based on the amplitude-frequency characteristic. A voltage determination module is used to determine the compensation voltage corresponding to the target frequency point when the UPQC is not in impedance measurement mode. An impedance adjustment module is used to determine the switching control signal applied to the converter based on the compensation voltage when the UPQC is in damped injection mode, and to adjust the impedance of the grid connection point based on the switching control signal.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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