Parallel power quality control method, system and device based on transformer-VSI coupling structure and storage medium

Abstract

The invention discloses a parallel power quality control method, system and equipment based on a transformer-VSI coupling structure, and a storage medium, and relates to the technical field of power electronics and power quality control, the method comprises the following steps: detecting the primary current of a transformer, extracting a fundamental component, and generating two paths of orthogonal fundamental reference signals; the synthesized signal controls the voltage source inverter to output controllable fundamental wave voltage to the secondary side of the transformer; continuously adjustable four-quadrant equivalent impedance is formed on a primary side through interaction of voltage and current, and reactive compensation, harmonic suppression and fault current limiting are synchronously realized by combining the harmonic low-resistance characteristic of the transformer; according to the invention, reactive, harmonic and current-limiting integrated treatment can be realized, and the number and cost of equipment are reduced; stable operation of the sensitive load is guaranteed, and complex detection hardware is omitted.

Description

Technical Field

[0001] This invention relates to the field of power electronics and power quality control technology, and in particular to a parallel power quality control method, system, device and storage medium based on a transformer-VSI coupling structure. Background Technology

[0002] With the widespread application of nonlinear loads and sensitive equipment in power systems, power quality problems are becoming increasingly prominent. How to achieve reactive power compensation, harmonic suppression and fault current limiting efficiently and economically has become a key issue in the current power control field.

[0003] In existing technologies, independent devices such as static var compensators (SVCs) and active power filters (APBs) are typically used for reactive power and harmonic mitigation. The impedance regulation achieved by semi-controlled devices exhibits a stepped change, which can easily trigger transient shocks. APBs rely on high-speed harmonic detection and complex control algorithms, which not only have stringent control bandwidth requirements but also generate switching subharmonics during the PWM (Pulse Width Modulation) conversion process. The application of negative resistance characteristics also carries the risk of inducing system oscillations. These drawbacks make existing technologies significantly inadequate in achieving multi-functional integration, continuous smooth regulation, and system stability. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention provides a method, system, device and storage medium for parallel power quality control based on transformer-VSI coupling structure.

[0005] Therefore, the technical problem solved by this invention is: how to achieve integrated control of reactive power compensation, harmonic suppression and fault current limiting in a single device, and achieve continuous and smooth impedance adjustment, while reducing system control complexity and harmonic pollution risk.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a parallel power quality control method based on a transformer-VSI coupling structure, comprising: Detect the real-time current in the primary winding of a parallel transformer and separate the fundamental component from the real-time current; Based on the separated fundamental wave components, two orthogonal fundamental wave reference signals with independently adjustable amplitudes and a 90-degree phase difference are generated; The two orthogonal reference signals are added together to form a composite command signal, which controls the voltage source inverter to output the corresponding controllable fundamental voltage to the secondary side of the transformer. By controlling the interaction between the fundamental voltage and the fundamental component, a continuously adjustable four-quadrant equivalent impedance is created on the primary side of the transformer. Based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, reactive power compensation, harmonic suppression, and fault current limiting functions are simultaneously achieved.

[0007] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The generation of two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental component includes: Based on the fundamental current component, two mutually orthogonal fundamental reference signals are generated. The first reference signal is in phase with the fundamental current component and its amplitude is adjustable. The second reference signal is obtained by performing a 90-degree phase shift lag on the fundamental current component and its amplitude is independently adjustable.

[0008] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The step of adding the two orthogonal reference signals to form a synthesized command signal and controlling the voltage source inverter to output a corresponding controllable fundamental voltage to the transformer secondary includes: The two orthogonal fundamental reference signals are combined to form a single control command; The control voltage source inverter tracks the control command and outputs a fundamental voltage with controllable amplitude and phase. The fundamental voltage is filtered to suppress high-frequency harmonic components, and the filtered fundamental voltage is applied to the secondary winding of the transformer.

[0009] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The method of creating a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction of the controllable fundamental voltage and fundamental component includes: Control the controllable fundamental voltage so that the controllable fundamental voltage and the fundamental current component form a preset amplitude-phase relationship; By using the amplitude-phase relationship, the primary side of the transformer can present an equivalent fundamental impedance; By independently adjusting two independent parameters of the controllable fundamental voltage, the resistive and reactive components of the equivalent fundamental impedance are adjusted, and the resistive and reactive components can independently exhibit positive or negative values, thereby achieving four-quadrant operation states including resistive-inductive, resistive-capacitive, negative resistive-inductive, and negative resistive-capacitive.

[0010] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The method, based on the shaped equivalent impedance and combined with the transformer's inherent low impedance characteristics to higher harmonics, simultaneously achieves reactive power compensation, harmonic suppression, and fault current limiting functions, including: By controlling the reactance component of the equivalent impedance, the primary side of the transformer can exhibit a controllable capacitive or inductive equivalent reactance, thereby dynamically compensating for the reactive power of the load.

[0011] The beneficial effects of this preferred technical solution are as follows: by adjusting the reactance component of the equivalent impedance, the device can present the required capacitive or inductive equivalent reactance in real time, thereby achieving dynamic and continuous compensation for the reactive power of the load, effectively improving the system power factor, and avoiding the current surge caused by traditional switching methods.

[0012] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The simultaneous realization of reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, also includes: By utilizing the inherent low impedance characteristics of transformer windings to high-order harmonic currents, a low-impedance return path is provided for the harmonic currents generated by the load, thereby suppressing harmonic injection into the power grid.

[0013] The advantages of this preferred technical solution are: by making full use of the inherent low impedance physical characteristics of transformer windings for high-frequency currents, a low impedance return path can be provided for load harmonic currents without the need for complex harmonic detection algorithms or active filter control, effectively suppressing harmonic injection into the power grid, simplifying the system structure, and improving reliability and economy.

[0014] As a preferred embodiment of a parallel power quality control method based on a transformer-VSI coupling structure, wherein: The simultaneous realization of reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, also includes: By controlling the equivalent impedance to exhibit positive resistance characteristics, current limiting protection is achieved by damping and limiting the fault current during system faults.

[0015] Secondly, the present invention provides a parallel power quality control system based on a transformer-VSI coupling structure, comprising: The fundamental wave detection and extraction module is used to detect the real-time current in the primary winding of the parallel transformer and separate the fundamental wave component from the real-time current. The orthogonal reference signal generation module is used to generate two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental component. The instruction synthesis and inverter output module is used to add two orthogonal reference signals to form a synthesized instruction signal and control the voltage source inverter to output the corresponding controllable fundamental voltage to the transformer secondary. The four-quadrant equivalent impedance shaping module is used to shape a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction between the controllable fundamental voltage and the fundamental component. The multi-functional power quality collaborative management module is used to simultaneously achieve reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance and the inherent low impedance characteristics of the transformer to high-order harmonics.

[0016] Thirdly, the present invention provides a computer device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the parallel power quality control method based on the transformer-VSI coupling structure.

[0017] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of a parallel power quality control method based on a transformer-VSI coupling structure.

[0018] The beneficial effects of this invention are as follows: In practical power system applications, this invention can directly replace the traditional combination of multiple separate devices such as "reactive power compensation device + active filter + current limiting reactor," integrating the three functions into a single device. This significantly reduces the number of devices, floor space, and initial investment costs in industrial user power distribution rooms. Utilizing the transformer's own physical characteristics, it provides a low-impedance path for harmonic currents, eliminating the need for expensive and easily damaged fast recovery diodes or complex harmonic detection chips, resulting in simpler and more reliable hardware and lower long-term maintenance costs. The impedance has continuous and smooth adjustment capabilities, avoiding voltage flicker and current surges caused by traditional thyristor-switched capacitor banks, making it particularly suitable for workshops with rapidly fluctuating loads, such as rolling mills and electric arc furnaces, stabilizing voltage and ensuring production. In the event of a short-circuit fault, it quickly exhibits positive resistance characteristics, suppressing short-circuit current peaks, protecting downstream circuit breakers and electrical equipment, and improving the safety and reliability of the power distribution system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is an overall flowchart of a parallel power quality control method based on a transformer-VSI coupling structure provided by the present invention.

[0021] Figure 2 This is the SPQC topology diagram in a simulation example of a parallel power quality control method based on a transformer-VSI coupling structure provided by the present invention.

[0022] Figure 3 This is a simulation example of the SPQC schematic diagram in a parallel power quality control method based on a transformer-VSI coupling structure provided by the present invention.

[0023] Figure 4 This is the equivalent circuit of the transformer to the fundamental component in a simulation example of a parallel power quality control method based on a transformer-VSI coupling structure provided by the present invention.

[0024] Figure 5 This is the equivalent circuit of the voltage source for higher harmonic components in a simulation example of a parallel power quality control method based on a transformer-VSI coupling structure provided by the present invention. Detailed Implementation

[0025] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0026] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a parallel power quality control method based on a transformer-VSI coupling structure, comprising: S1: Detect the real-time current in the primary winding of the parallel transformer and separate the fundamental component from the real-time current; S2: Based on the separated fundamental component, generate two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference; S3: Add the two orthogonal reference signals to form a composite command signal, and control the voltage source inverter to output the corresponding controllable fundamental voltage to the transformer secondary. S4: Through the interaction between the controllable fundamental voltage and the fundamental component, a continuously adjustable four-quadrant equivalent impedance is created on the primary side of the transformer. S5: Based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to high-order harmonics, it simultaneously realizes reactive power compensation, harmonic suppression and fault current limiting functions.

[0027] It should be noted that, through steps S1-S5, this invention constructs an intelligent impedance regulation system within a single physical device, based on active control of the fundamental wave signal and fully utilizing the inherent electromagnetic characteristics of the transformer. It fundamentally abandons the traditional architecture of stacked discrete devices, high-speed harmonic detection, and complex multi-objective control, instead directly shaping an arbitrary four-quadrant equivalent impedance on the primary side of the transformer that meets the real-time requirements of the system by precisely controlling the amplitude-phase relationship between the fundamental wave voltage and current. This makes the three key power quality management functions—reactive power compensation, harmonic bypass, and fault current limiting—no longer isolated actions relying on multiple independent control loops, but rather synergistic effects naturally exhibited by the same impedance regulation behavior in different frequency domains and operating states.

[0028] Example 2, refer to Figure 1 As one embodiment of the present invention, based on the previous embodiment, a parallel power quality control method based on a transformer-VSI coupling structure is provided, comprising: In this embodiment, the step S1 described above, which involves detecting the real-time current in the primary winding of the parallel transformer and separating the fundamental component from the real-time current, includes: Detecting the primary winding current of a transformer connected in parallel with a voltage source This current contains a fundamental component and harmonic components, that is... Where n represents the harmonic order; through signal processing, from the mixed real-time current The fundamental component was accurately detected and separated. This provides a unique fundamental frequency input signal for subsequent control.

[0029] In another possible implementation, the fundamental component can also be separated by a phase-locked loop-based fundamental extraction method: a sine and cosine reference signal that is strictly synchronized with the system fundamental frequency is locked from the grid voltage or current using a phase-locked loop circuit; the reference signal is used to perform coordinate transformation calculations based on instantaneous reactive power theory with the real-time current signal, thereby directly decoupling from the mixed signal and extracting the fundamental current component.

[0030] In another possible implementation, the fundamental component can also be separated by digital filtering: a linear phase finite-length unit impulse response low-pass digital filter with a cutoff frequency slightly higher than the fundamental frequency is used to filter the sampled real-time current digital sequence. This filter can effectively attenuate all higher harmonic components while maintaining the amplitude and phase information of the fundamental component to pass through with basically no distortion, thereby outputting a pure fundamental component.

[0031] In this embodiment, the step S2 above, which generates two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental components, includes: With the separated fundamental component Based on this, two orthogonal fundamental reference signals are generated.

[0032] Specifically, will It itself serves as an in-phase reference signal Its amplitude is determined by the coefficient Adjust; at the same time, A hysteresis phase shift is performed using a 90-degree phase shift circuit (e.g., an analog phase shift circuit adjusted by a potentiometer) to generate a quadrature reference signal. Its amplitude is determined by independent coefficients. Adjustment. Thus, obtain and Two signals.

[0033] In another possible implementation, the 90-degree hysteresis phase shift can also be performed using the Hilbert transform: In a digital control system, a digital Hilbert transform is applied to the discrete sampling sequence of the fundamental current component; this transform is essentially an ideal phase shifter that produces a 90-degree phase hysteresis for all frequency components, and through convolution operations or frequency domain processing, it can accurately generate a reference signal orthogonal to the original fundamental component.

[0034] In another possible implementation, a 90-degree lag phase shift can also be performed using a software algorithm based on coordinate transformation: the fundamental current component is transformed to a synchronous rotating coordinate system through Parker transformation to obtain the direct-axis component and the quadrature-axis component; the direct-axis and quadrature-axis components are swapped and the sign of one of them is changed, and then an inverse Parker transformation is performed, which can generate a digital reference signal that lags 90 degrees relative to the original fundamental component in the software, and its phase shift accuracy is guaranteed by the accuracy of the phase-locked loop.

[0035] In this embodiment, step S3 above, which involves adding the two orthogonal reference signals to form a synthesized command signal and controlling the voltage source inverter to output the corresponding controllable fundamental voltage to the transformer secondary, includes: Two orthogonal reference signals and Add them together to obtain the synthesized command signal. The voltage source inverter (VSI) uses a sinusoidal pulse width modulation strategy to track this synthesized signal. This generates a controllable fundamental voltage on the inverter output side. The voltage passes through a filter inductor. and filter capacitor An LC filter is constructed to suppress harmonics near the switching frequency. The filtered fundamental voltage... Finally, it is applied to the secondary winding of the transformer (between terminal a and terminal x). The voltage source inverter consists of a DC voltage source. It is implemented using a full-bridge circuit consisting of four power switching transistors (VT1, VT2, VT3, VT4) and four anti-parallel diodes (VD1, VD2, VD3, VD4).

[0036] In another possible implementation, the fundamental voltage can also be filtered by using an LCL filter: a filter inductor, a filter capacitor, and a second filter inductor are connected in sequence between the output of the voltage source inverter and the secondary winding of the transformer to form an LCL filter network.

[0037] In another possible implementation, the fundamental voltage can be filtered by injecting specific harmonics into the modulation strategy: by using an optimized pulse width modulation strategy, such as injecting the third harmonic into a sinusoidal pulse width modulated carrier signal or using space vector pulse width modulation, the harmonic spectrum energy of the voltage source inverter output voltage is more concentrated in a specific high-frequency band; combined with a specially designed LC filter, these concentrated harmonics can be filtered out more economically and efficiently, thereby achieving the required output waveform quality with a smaller filter size.

[0038] In this embodiment, step S4 above, which involves shaping a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction between the controllable fundamental voltage and the fundamental component, includes: Based on the transformer equivalent circuit model and the superposition theorem, the electrical quantities of the system are decomposed into fundamental and harmonic components for separate analysis. For the fundamental component, the fundamental voltage applied to the transformer secondary is controlled. The amplitude and phase of the signal are such that they are related to the primary fundamental current. A specific orthogonal relationship is formed. When control is satisfied... Under the given conditions, the equivalent fundamental impedance presented at the primary AX port of the transformer is: in , ; The transformer turns ratio This is the pulse width modulation gain of the voltage source inverter.

[0039] Through independent adjustment coefficient (control ) and (control This allows for continuous and smooth changes in the resistive component (positive or negative) and reactive component (inductive or capacitive) of the equivalent impedance, thereby enabling four-quadrant operation: resistive-inductive, resistive-capacitive, negative resistive-inductive, and negative resistive-capacitive.

[0040] In this embodiment, step S5 above, based on the shaped equivalent impedance and combined with the transformer's inherent low impedance characteristics to higher harmonics, simultaneously achieves reactive power compensation, harmonic suppression, and fault current limiting functions, including: Reactive power compensation: by controlling the equivalent impedance It exhibits pure reactive characteristics (i.e., regulation) This allows the primary winding of the transformer connected in parallel to the system to present a controllable equivalent reactance (-jβ) to the fundamental wave, dynamically generating or absorbing reactive power to compensate for the reactive power demand of the load.

[0041] Harmonic suppression: Utilizing the characteristic that the leakage inductance of transformer windings presents low impedance to high-order harmonic currents, its harmonic equivalent impedance is... ,in, and For winding resistance, and These are the leakage reactances of the primary and secondary windings (referred to as the primary winding) of the transformer, respectively. Because the leakage reactance is very small, this harmonic impedance is much smaller than the harmonic impedance of the power grid, thus preventing the generation of harmonic currents by nonlinear loads. It provides a low-impedance return path, confining it to the local loop, thereby effectively preventing harmonic current from being injected into the power grid, and this process does not require any harmonic detection algorithm.

[0042] Fault current limiting: When a fault such as a short circuit occurs in the system, the control parameters are adjusted to make the equivalent impedance present a sufficient positive resistance component (i.e., make...). This positive resistance characteristic can effectively dampen and suppress the rise of fault current, thus playing a current limiting protection role.

[0043] In another possible implementation, when taking advantage of the inherent low impedance characteristics of transformers to higher harmonics, the implementation can be enhanced by optimizing the transformer design: when designing the coupling transformer, a lower winding coupling coefficient or a specific air gap can be used to obtain a relatively large leakage inductance value while meeting the fundamental power transmission requirements; the increased leakage inductance and winding resistance together form a low impedance path for higher harmonic currents, thereby enhancing the device's bypass capability for harmonics without adding additional components.

[0044] In another possible implementation, when combined with the inherent low impedance characteristics of the transformer to higher harmonics, it can also be implemented by connecting an auxiliary branch in parallel: on the primary or secondary side of the transformer, an auxiliary high-frequency path branch consisting of a small-capacity capacitor and a resistor connected in series is connected in parallel; the parameters of this branch are designed to be high impedance at the fundamental frequency, while presenting an impedance equivalent to or lower than the transformer leakage impedance at the main harmonic frequencies (such as the 5th and 7th harmonics), thereby working in conjunction with the inherent low impedance characteristics of the transformer to further broaden and optimize the frequency range and effect of harmonic suppression.

[0045] Example 3: The above is an illustrative scheme of a parallel power quality control method based on a transformer-VSI coupling structure according to this embodiment. It should be noted that the technical solution of a parallel power quality control system based on a transformer-VSI coupling structure and the technical solution of the parallel power quality control method based on a transformer-VSI coupling structure described above belong to the same concept. Details not described in detail in the technical solution of the parallel power quality control system based on a transformer-VSI coupling structure in this embodiment can be found in the description of the technical solution of the parallel power quality control method based on a transformer-VSI coupling structure described above.

[0046] This embodiment also provides a parallel power quality control system based on a transformer-VSI coupling structure, including: The fundamental wave detection and extraction module is used to detect the real-time current in the primary winding of the parallel transformer and separate the fundamental wave component from the real-time current. The orthogonal reference signal generation module is used to generate two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental component. The instruction synthesis and inverter output module is used to add two orthogonal reference signals to form a synthesized instruction signal and control the voltage source inverter to output the corresponding controllable fundamental voltage to the transformer secondary. The four-quadrant equivalent impedance shaping module is used to shape a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction between the controllable fundamental voltage and the fundamental component. The multi-functional power quality collaborative management module is used to simultaneously achieve reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance and the inherent low impedance characteristics of the transformer to high-order harmonics.

[0047] This embodiment also provides an electronic device applicable to a parallel power quality control method based on a transformer-VSI coupling structure, including: The system includes a memory and a processor. The memory stores computer-executable instructions, and the processor executes these instructions to implement a parallel power quality control method based on a transformer-VSI coupling structure, as proposed in the above embodiments.

[0048] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a parallel power quality control method based on a transformer-VSI coupling structure as proposed in the above embodiments.

[0049] The storage medium proposed in this embodiment belongs to the same inventive concept as the parallel power quality control method based on transformer-VSI coupling structure proposed in the above embodiment. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0050] Example 4, refer to Figures 2-5 As an embodiment of the present invention, a parallel power quality control method based on a transformer-VSI coupling structure is provided. To verify the beneficial effects of the present invention, a simulation experiment is conducted for scientific demonstration.

[0051] like Figure 2 The SPQC (Shunt Power Quality Controller) topology shown mainly includes a voltage source us, a power supply impedance Ls, a transformer, a filter capacitor Cf, a filter inductor Lf, a DC voltage source Ud, a first power switch VT1, a second power switch VT2, a third power switch VT3, a fourth power switch VT4, a first diode VD1, a second diode VD2, a third diode VD3, a fourth diode VD4, a load Lo, and a load Ro. One end of the voltage source us is connected to one end of the power supply impedance Ls; The other end of the voltage source us is connected to the X terminal of the transformer at the first measurement, the cathode of the fourth diode VD4, and the anode of the second diode VD2, respectively. The other end of the power supply impedance Ls is connected to the A terminal of the transformer measured initially, the anode of the first diode VD1, and the cathode of the third diode VD3, respectively. The secondary terminal a of the transformer is connected to one end of the filter capacitor Cf and one end of the filter inductor Lf, respectively. The secondary measuring terminal of the transformer is connected to the other end of the filter capacitor Cf, the source of the second power switch VT2, and the drain of the fourth power switch VT4, respectively. The other end of Lf is connected to the source of the first power switch VT1 and the drain of the third power switch VT3, respectively. The positive terminal of the DC voltage source Ud is connected to the drain of the first power switch VT1 and the drain of the second power switch, respectively. The negative terminal of the DC voltage source Ud is connected to the source of the third power switch VT3 and the source of the fourth power switch VT4, respectively. One end of the load Lo is connected to the cathode of the first diode VD1 and the cathode of the second diode VD2, respectively; One end of load Ro is connected to the other end of load Lo; The other end of the load Ro is connected to the third diode VD3 and the fourth diode VD4, respectively. like Figure 3 The diagram shown is the schematic of SPQC. In this circuit, the variable impedance is connected in parallel with the voltage source, and its function is as a power quality controller. Figure 3 The initial current measurement of the transformer includes the fundamental component and higher harmonic components, i.e. ; Detected And delay it by 90° as a reference signal; By controlling the VSI, a reference signal is tracked to generate a controllable base frequency voltage. ; The filtered wave is then filtered by an LC filter. The signal is applied to the secondary side of the transformer; Lf and Cf are used to suppress harmonics near the switching frequency in the VSI output signal; Based on the superposition theorem, each electrical quantity can be divided into fundamental and harmonic components. For the fundamental component, the transformer voltage phasor equation is: when At that time, the equivalent impedance from terminal AX is: Based on the above formula, the equivalent circuit of the transformer for the fundamental component is generated, such as... Figure 4 As shown; Figure 5 For the equivalent circuit of the voltage source for higher harmonic components, the harmonic equivalent impedance is: The inverter is used to track the reference signal and generate a controllable fundamental voltage, which is then applied to the secondary side of the transformer. By controlling the amplitude and phase of the transformer's secondary fundamental voltage to form an orthogonal relationship with the fundamental component of the primary current for inductive compensation, the primary winding of the transformer connected in parallel to the system can present a controllable equivalent impedance to the fundamental frequency, thereby achieving compensation for fundamental reactive power. At the same time, it presents an extremely low impedance to harmonic frequencies, creating a low-impedance return path for harmonic currents generated by nonlinear loads, thus effectively preventing these harmonic currents from flowing into the public power grid.

[0052] In summary, the method of the present invention can automatically achieve a filtering effect when adjusting the reactive power of the system.

[0053] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A parallel power quality control method based on a transformer-VSI coupling structure, characterized in that, include: Detect the real-time current in the primary winding of a parallel transformer and separate the fundamental component from the real-time current; Based on the separated fundamental wave components, two orthogonal fundamental wave reference signals with independently adjustable amplitudes and a 90-degree phase difference are generated; The two orthogonal reference signals are added together to form a composite command signal, which controls the voltage source inverter to output the corresponding controllable fundamental voltage to the secondary side of the transformer. By controlling the interaction between the fundamental voltage and the fundamental component, a continuously adjustable four-quadrant equivalent impedance is created on the primary side of the transformer. Based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, reactive power compensation, harmonic suppression, and fault current limiting functions are simultaneously achieved.

2. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 1, characterized in that, The generation of two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental component includes: Based on the fundamental current component, two mutually orthogonal fundamental reference signals are generated. The first reference signal is in phase with the fundamental current component and its amplitude is adjustable. The second reference signal is obtained by performing a 90-degree phase shift lag on the fundamental current component and its amplitude is independently adjustable.

3. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 2, characterized in that, The step of adding the two orthogonal reference signals to form a synthesized command signal and controlling the voltage source inverter to output a corresponding controllable fundamental voltage to the transformer secondary includes: The two orthogonal fundamental reference signals are combined to form a single control command; The control voltage source inverter tracks the control command and outputs a fundamental voltage with controllable amplitude and phase. The fundamental voltage is filtered to suppress high-frequency harmonic components, and the filtered fundamental voltage is applied to the secondary winding of the transformer.

4. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 3, characterized in that, The method of creating a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction of the controllable fundamental voltage and fundamental component includes: Control the controllable fundamental voltage so that the controllable fundamental voltage and the fundamental current component form a preset amplitude-phase relationship; By using the amplitude-phase relationship, the primary side of the transformer can present an equivalent fundamental impedance; By independently adjusting two independent parameters of the controllable fundamental voltage, the resistive and reactive components of the equivalent fundamental impedance are adjusted, and the resistive and reactive components can independently exhibit positive or negative values, thereby achieving four-quadrant operation states including resistive-inductive, resistive-capacitive, negative resistive-inductive, and negative resistive-capacitive.

5. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 4, characterized in that, The method, based on the shaped equivalent impedance and combined with the transformer's inherent low impedance characteristics to higher harmonics, simultaneously achieves reactive power compensation, harmonic suppression, and fault current limiting functions, including: By controlling the reactance component of the equivalent impedance, the primary side of the transformer can exhibit a controllable capacitive or inductive equivalent reactance, thereby dynamically compensating for the reactive power of the load.

6. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 5, characterized in that, The simultaneous realization of reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, also includes: By utilizing the inherent low impedance characteristics of transformer windings to high-order harmonic currents, a low-impedance return path is provided for the harmonic currents generated by the load, thereby suppressing harmonic injection into the power grid.

7. The parallel power quality control method based on a transformer-VSI coupling structure as described in claim 6, characterized in that, The simultaneous realization of reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance, combined with the transformer's inherent low impedance characteristics to higher harmonics, also includes: By controlling the equivalent impedance to exhibit positive resistance characteristics, current limiting protection is achieved by damping and limiting the fault current during system faults.

8. A parallel power quality control system based on a transformer-VSI coupling structure, using the method described in any one of claims 1 to 7, characterized in that, include: The fundamental wave detection and extraction module is used to detect the real-time current in the primary winding of the parallel transformer and separate the fundamental wave component from the real-time current. The orthogonal reference signal generation module is used to generate two orthogonal fundamental reference signals with independently adjustable amplitudes and a 90-degree phase difference based on the separated fundamental component. The instruction synthesis and inverter output module is used to add two orthogonal reference signals to form a synthesized instruction signal and control the voltage source inverter to output the corresponding controllable fundamental voltage to the transformer secondary. The four-quadrant equivalent impedance shaping module is used to shape a continuously adjustable four-quadrant equivalent impedance on the primary side of the transformer through the interaction between the controllable fundamental voltage and the fundamental component. The multi-functional power quality collaborative management module is used to simultaneously achieve reactive power compensation, harmonic suppression, and fault current limiting functions based on the shaped equivalent impedance and the inherent low impedance characteristics of the transformer to high-order harmonics.

9. An electronic device, characterized in that, include: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions, which, when executed by the processor, implement the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, It stores computer-executable instructions that, when executed by a processor, implement the steps of the method according to any one of claims 1 to 7.

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