Electric energy quality treatment system and method based on multiple QPR controllers

Abstract

The invention discloses an electric energy quality management system and method based on multiple QPR controllers. The actual output current of a multifunctional grid-connected inverter is detected; determining a current error signal corresponding to the multifunctional grid-connected inverter according to the difference value between the preset reference current and the actual output current; processing the current error signal by adopting a multi-QPR control strategy to generate a control signal; and generating a driving signal according to the control signal so as to drive the multifunctional grid-connected inverter to generate and inject a compensation current for suppressing harmonic waves of the power grid. High-precision current tracking and electric energy quality management based on a multi-QPR control strategy are realized, complex coordinate transformation and sub-harmonic detection in traditional PI control are avoided, the calculation complexity is reduced, and the dynamic response speed and the steady-state tracking precision of the system are improved.

Description

Technical Field

[0001] This application relates to the field of grid-connected inverter control, and in particular to a power quality management system and method based on a multi-QPR controller. Background Technology

[0002] With the increasing penetration of distributed photovoltaic power generation, grid-connected inverters, while fulfilling their basic energy conversion function, are also expected to improve power quality, thus evolving into multi-functional grid-connected inverters (MFGCIs). This integrated design can effectively address power quality issues in the power supply area, saving on additional investment in power quality control devices. It is of great significance for supporting reliable operation in nonlinear load-intensive scenarios such as electric vehicle charging stations.

[0003] However, the core of MFGCI's power quality management function lies in its current tracking control strategy. Currently, the widely used proportional-integral (PI) controller is essentially suitable for controlling DC signals because it only has high gain in the low-frequency range. To control the power frequency AC current, traditional photovoltaic inverters typically convert the sinusoidal AC quantity into two DC quantities through coordinate transformation (such as dq transformation) before PI regulation. This approach is applicable when only power frequency current is output, but when MFGCI needs to output the fundamental current and multiple harmonic compensation currents simultaneously, if PI control is still used, multiple and complex coordinate transformations and harmonic detections must be performed for each harmonic. This undoubtedly leads to a sharp increase in the system's computational load, places excessive demands on the controller's processing power, and increases system cost and complexity.

[0004] Furthermore, PI controllers inherently suffer from steady-state errors when tracking AC quantities, making zero-steady-state-error tracking impossible. They also exhibit weak resistance to disturbances such as grid frequency fluctuations and load abrupt changes, and their dynamic response speed is relatively slow. Particularly in suppressing specific harmonics, PI controllers perform poorly, often requiring additional compensation components, further increasing the complexity of control design.

[0005] Application content

[0006] This application provides a power quality management system and method based on a multi-QPR controller to solve the problems of computational complexity, steady-state error, and insufficient harmonic suppression capability of traditional PI control when tracking multi-frequency AC current.

[0007] In a first aspect, this application provides a power quality management system based on a multi-QPR controller, comprising:

[0008] Current detection module, current error calculation module, multi-QPR controller and modulation module;

[0009] The current detection module is used to detect the actual output current of the multi-functional grid-connected inverter;

[0010] The current error calculation module is used to calculate the difference between the reference current and the actual output current, so as to generate a current error signal based on the difference.

[0011] A multi-QPR controller is used to generate control signals based on current error signals. The multi-QPR controller consists of a proportional unit and multiple parallel quasi-proportional resonant units.

[0012] The proportional unit is configured with a proportional coefficient to provide full-band proportional adjustment of the current error signal and generate the first output component.

[0013] Each quasi-proportional resonant unit corresponds to a different resonant frequency, which includes the fundamental frequency and multiple harmonic frequencies. Each quasi-proportional resonant unit is configured with a resonant coefficient and a cutoff frequency to provide high gain adjustment at the corresponding resonant frequency and generate a second output component.

[0014] The multi-QPR controller superimposes the first output component and the second output component to generate a control signal;

[0015] The modulation module, connected to the multi-QPR controller, is used to generate drive signals based on control signals. The drive signals are used to drive the multi-functional grid-connected inverter to generate and inject compensation current. The compensation current is used to suppress grid harmonics and improve power quality.

[0016] Secondly, this application provides a power quality management method based on a multi-QPR controller, comprising:

[0017] Detect the actual output current of the multi-functional grid-connected inverter;

[0018] The current error signal corresponding to the multi-functional grid-connected inverter is determined based on the difference between the preset reference current and the actual output current.

[0019] A multi-QPR control strategy is used to process the current error signal to generate a control signal;

[0020] A drive signal is generated based on the control signal to drive the multi-functional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics.

[0021] This application provides a power quality management system and method based on a multi-QPR controller. The system detects the actual output current of a multi-functional grid-connected inverter; determines the current error signal corresponding to the multi-functional grid-connected inverter based on the difference between a preset reference current and the actual output current; processes the current error signal using a multi-QPR control strategy to generate a control signal; and generates a drive signal based on the control signal to drive the multi-functional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics. This achieves high-precision current tracking and power quality management based on a multi-QPR control strategy, avoiding the complex coordinate transformations and harmonic detection required in traditional PI control, reducing computational complexity, and improving the system's dynamic response speed and steady-state tracking accuracy.

[0022] The further effects of the aforementioned non-conventional preferred method will be explained below in conjunction with specific embodiments. Attached Figure Description

[0023] To more clearly illustrate the embodiments of this application or the existing technical solutions, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A schematic diagram of a power quality management system based on a multi-QPR controller is provided as an embodiment of this application;

[0025] Figure 2 A schematic flowchart illustrating a power quality management method based on a multi-QPR controller, provided as an embodiment of this application;

[0026] Figure 3 This is a schematic flowchart of another power quality management method based on a multi-QPR controller provided in an embodiment of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] With the increasing penetration of distributed photovoltaic power generation, grid-connected inverters, while fulfilling their basic energy conversion function, are also expected to improve power quality, thus evolving into multi-functional grid-connected inverters (MFGCIs). This integrated design can effectively address power quality issues in the power supply area, saving on additional investment in power quality control devices. It is of great significance for supporting reliable operation in nonlinear load-intensive scenarios such as electric vehicle charging stations.

[0029] However, the core of MFGCI's power quality management function lies in its current tracking control strategy. Currently, the widely used proportional-integral (PI) controller is essentially suitable for controlling DC signals because it only has high gain in the low-frequency range. To control the power frequency AC current, traditional photovoltaic inverters typically convert the sinusoidal AC quantity into two DC quantities through coordinate transformation (such as dq transformation) before PI regulation. This approach is applicable when only power frequency current is output, but when MFGCI needs to output the fundamental current and multiple harmonic compensation currents simultaneously, if PI control is still used, multiple and complex coordinate transformations and harmonic detections must be performed for each harmonic. This undoubtedly leads to a sharp increase in the system's computational load, places excessive demands on the controller's processing power, and increases system cost and complexity.

[0030] Furthermore, PI controllers inherently suffer from steady-state errors when tracking AC quantities, making zero-steady-state-error tracking impossible. They also exhibit weak resistance to disturbances such as grid frequency fluctuations and load abrupt changes, and their dynamic response speed is relatively slow. Particularly in suppressing specific harmonics, PI controllers perform poorly, often requiring additional compensation components, further increasing the complexity of control design.

[0031] To address this issue, this application proposes a power quality management system based on a multi-QPR controller, aiming to solve the problems of computational complexity, steady-state error, and insufficient harmonic suppression capability of traditional PI control when tracking multi-frequency AC currents. See also Figure 1 As shown, this embodiment provides a power quality management system based on a multi-QPR controller. In this embodiment, the power quality management system based on a multi-QPR controller includes: a current detection module 101, a current error calculation module 102, a multi-QPR controller 103, and a modulation module 104.

[0032] The system is applied to a multi-functional grid-connected inverter, and uses a multi-QPR control strategy to achieve synchronous tracking and compensation of the fundamental current and multiple harmonic currents, thereby effectively addressing power quality issues in the power grid. Compared with traditional PI control schemes, this system avoids multiple coordinate transformations and harmonic detection, significantly reducing computational complexity while improving current tracking accuracy and system response speed.

[0033] The current detection module 101 is used to detect the actual output current of the multi-functional grid-connected inverter.

[0034] The current detection module 101 collects the three-phase output current on the AC side of the multi-functional grid-connected inverter in real time through a current sensor. The sampling frequency is matched with the switching frequency of the control system. The detected actual output current signal is filtered and conditioned before being converted into a digital signal for use by subsequent control modules. The detection accuracy of this module directly affects the performance of the entire control system; therefore, a high-precision, low-delay current sensor is required to ensure that the control system can accurately obtain the inverter's operating status.

[0035] The current error calculation module 102 is used to calculate the difference between the reference current and the actual output current, so as to generate a current error signal based on the difference.

[0036] The reference current is calculated by the upper-level control system based on the grid status, load characteristics, and compensation requirements. It includes the fundamental active current component, reactive current component, and harmonic compensation current components. The current error calculation module 102 compares the reference current with the actual output current collected by the current detection module 101 point by point, calculates the deviation between the two, and generates a current error signal.

[0037] The current error signal reflects the difference between the actual output and the expected output of the inverter, and serves as the basis for adjusting the QPR controller. To ensure real-time control, the current error calculation is performed at high speed using a digital signal processor, with the calculation delay controlled to be within one sampling period.

[0038] The multi-QPR controller 103 is used to generate control signals based on current error signals. The multi-QPR controller consists of a proportional unit and multiple parallel quasi-proportional resonant units.

[0039] This parallel structure enables the multi-QPR controller 103 to simultaneously process current components of different frequencies. Each unit works independently yet cooperates with others to achieve accurate tracking of complex current waveforms. The proportional unit provides fast response capability across the entire frequency band, while the quasi-proportional resonant unit provides high-precision adjustment for specific frequencies. The synergistic effect of both ensures excellent performance in both dynamic and steady-state accuracy.

[0040] The quasi-proportional resonant unit includes a fundamental compensation unit for tracking the fundamental current and a harmonic compensation unit for tracking the harmonic current.

[0041] The fundamental frequency compensation unit is set to the grid fundamental frequency (50Hz or 60Hz) and is responsible for achieving zero steady-state error tracking of the fundamental active and reactive currents, ensuring the basic grid-connected function of the inverter. The harmonic compensation units are each set with a corresponding resonant frequency for different harmonic orders, and each unit independently tracks a specific frequency harmonic current component. Through the parallel operation of multiple harmonic compensation units, the system can simultaneously compensate for harmonics of multiple frequencies, effectively suppressing grid harmonic pollution and improving power supply quality.

[0042] The proportional unit is configured with a proportional coefficient to provide full-band proportional adjustment of the current error signal and generate the first output component.

[0043] The proportional unit functions similarly to the proportional element in a traditional PI controller. It amplifies the input current error signal in real time, with the amplification factor determined by the proportional coefficient. Because proportional control lacks frequency selectivity, it provides the same gain across the entire frequency range, thus enabling rapid response to changes in current error. The first output component forms the foundation of the control signal, primarily affecting the system's dynamic response characteristics and transient regulation capability.

[0044] The proportional coefficient is used to adjust the dynamic response speed of the system, and the proportional coefficient is positively correlated with the dynamic response speed.

[0045] A larger proportional gain results in a faster system response to current errors, allowing for quicker output adjustments and shorter transient response times during load surges or reference command jumps. However, an excessively large proportional gain can increase overshoot and potentially cause oscillations, reducing system stability. Therefore, a trade-off must be struck between fast response and system stability. In this embodiment, considering the system's open-loop transfer function analysis and phase margin requirements, a proportional gain of 100 is preferred, ensuring both good dynamic performance and sufficient stability margin.

[0046] Each quasi-proportional resonant unit corresponds to a different resonant frequency, which includes the fundamental frequency and multiple harmonic frequencies. Each quasi-proportional resonant unit is configured with a resonant coefficient and a cutoff frequency to provide high gain adjustment at the corresponding resonant frequency and generate a second output component.

[0047] The core characteristic of a quasi-proportional resonant unit lies in its frequency selectivity: near the resonant frequency, the gain of the controller increases sharply, thereby achieving high-precision tracking of the frequency component; while at other frequency points far from the resonant frequency, the gain decreases rapidly, avoiding unnecessary interference to other frequency components.

[0048] This frequency selectivity allows multiple quasi-proportional resonant units to operate in parallel without interfering with each other, with each unit focusing on processing the current component at its corresponding frequency. The second output component is the superposition of the outputs of all quasi-proportional resonant units, containing fine-tuning information for the fundamental frequency and each harmonic.

[0049] The resonance coefficient is used to adjust the tracking accuracy of the quasi-proportional resonant unit at the resonant frequency, and the resonance coefficient is positively correlated with the tracking accuracy.

[0050] The resonance coefficient directly determines the peak gain of the quasi-proportional resonant unit at the resonant frequency. The larger the resonance coefficient, the higher the gain at that frequency, and the smaller the tracking error of the current component at that frequency. Theoretically, zero steady-state error tracking can be achieved.

[0051] However, an excessively large resonance coefficient can cause the controller to become overly sensitive to minor disturbances near that frequency, potentially introducing harmonic components of other frequencies or amplifying noise interference, thus affecting the overall performance of the system. In this embodiment, the resonance coefficient of each harmonic controller is preferably set to 1000, ensuring high tracking accuracy while avoiding the negative impact of over-adjustment.

[0052] The cutoff frequency is used to adjust the bandwidth of the quasi-proportional resonant unit, and the cutoff frequency is positively correlated with the bandwidth.

[0053] The cutoff frequency is a key parameter that distinguishes the quasi-proportional resonant controller from the ideal proportional resonant controller. By introducing a low-pass filter characteristic, it limits the gain, which was originally infinite at the resonant frequency, to a finite value, thereby improving the practical feasibility and stability of the system.

[0054] A higher cutoff frequency results in a wider effective operating range (i.e., bandwidth) for the controller near the resonant frequency, and a stronger ability to adapt to grid frequency fluctuations. However, it also makes it easier to introduce high-frequency noise. If the cutoff frequency is too low, the controller's frequency response becomes too steep, and the bandwidth becomes too narrow. Once the grid frequency shifts, the controller gain will drop rapidly, leading to a deterioration in tracking performance.

[0055] In this embodiment, the cutoff frequency of each harmonic controller is set to a certain proportion of its resonant frequency, such as 2.6h (where h is the harmonic order). This ensures sufficient bandwidth to cope with the frequency fluctuations of the actual power grid while effectively suppressing the influence of high-frequency noise.

[0056] The harmonic order corresponding to the harmonic frequency includes multiple odd harmonics.

[0057] In power electronic systems, nonlinear loads such as uncontrolled rectifiers and switching power supplies mainly generate odd harmonic currents, while even harmonics usually cancel each other out due to symmetry. Therefore, this system focuses on compensating for odd harmonics.

[0058] Based on power quality standards and practical engineering experience, lower harmonics have larger amplitudes and more significant impacts on the power grid. Therefore, priority should be given to compensating for major odd harmonics within the 20th order, such as the 3rd, 5th, 7th, 11th, 13th, 17th, and 19th.

[0059] By configuring an independent quasi-proportional resonant unit for each target harmonic order, the system achieves synchronous and accurate tracking and compensation of multiple odd harmonics, effectively reducing the total harmonic distortion rate of the grid current and improving the sinusoidal nature of the current waveform.

[0060] The multi-QPR controller superimposes the first output component and the second output component to generate a control signal.

[0061] The first output component of the proportional unit and the second output components of all quasi-proportional resonant units are summed within the controller to form the final control signal. This control signal comprehensively reflects the system's proportional and resonant regulation of current error, containing both fast-response dynamic adjustment information and fine-grained compensation instructions for each frequency component.

[0062] The generated control signal is then sent to the modulation module 104, where it is converted into a pulse signal to drive the inverter power switching transistors through pulse width modulation. This parallel superposition control structure is simple and efficient, avoiding complex coordinate transformations and frequency separation, and significantly reducing the computational burden of the control algorithm.

[0063] The modulation module 104, connected to the multi-QPR controller 103, is used to generate a drive signal based on the control signal; wherein, the drive signal is used to drive the multi-functional grid-connected inverter to generate and inject compensation current; the compensation current is used to suppress grid harmonics and improve power quality.

[0064] The modulation module 104 receives the control signal output by the QPR controller. The control signal is essentially a continuous analog quantity or a high-resolution digital quantity, representing the AC voltage amplitude and phase information that the inverter expects to output.

[0065] The modulation module 104 uses pulse width modulation (PWM) technology to convert the control signal into a series of high-frequency switching pulses. The duty cycle and phase of these pulses precisely correspond to the requirements of the control signal. After isolation and power amplification, the drive signal directly controls the switching of power switching devices such as IGBTs or MOSFETs in the inverter bridge arm, thereby enabling the inverter to output the required compensation current. The compensation current is injected into the power grid, canceling out the harmonic current generated by the load at the point of common coupling. Simultaneously, it can regulate the fundamental active and reactive power, comprehensively improving the power quality of the grid.

[0066] The modulation module 104 generates the drive signal using space vector pulse width modulation.

[0067] Space Vector Pulse Width Modulation (SVPWM) is an advanced modulation technique. Compared to traditional Sinusoidal Pulse Width Modulation (SPWM), SVPWM offers advantages such as high DC voltage utilization, low harmonic content, and low switching losses. SVPWM treats the three-phase voltages as space vectors. By appropriately selecting adjacent basic voltage vectors and their durations, it synthesizes the desired output voltage vector, thereby achieving precise control of the inverter output.

[0068] In this embodiment, the switching frequency of the modulation module 104 can be set to 10kHz, which ensures sufficient modulation accuracy while keeping the switching losses within an acceptable range. The equivalent gain KPWM of space vector pulse width modulation is 1, which simplifies the design and parameter tuning process of the control system.

[0069] It also includes: a filter inductor, which is connected to the AC side of the multi-functional grid-connected inverter to filter out switching frequency harmonics in the drive signal.

[0070] Although the voltage waveform output by the inverter is modulated by high-frequency pulse width modulation, and its fundamental and low-order harmonic components can accurately track the requirements of the control signal, it inevitably contains high-frequency harmonic components of the switching frequency and its harmonics. If these high-frequency harmonics are directly injected into the power grid, they will cause electromagnetic interference, affect the normal operation of other equipment, and increase the high-frequency losses of the power grid.

[0071] The filter inductor utilizes its high impedance characteristics to high-frequency signals to effectively attenuate switching frequency harmonics, making the final output current waveform of the inverter approach an ideal sine wave or the required compensation waveform. In this embodiment, the inductance value of the filter inductor is preferably 5mH, which effectively filters out high-frequency harmonics while avoiding the problems of slower system dynamic response and increased size caused by excessively large inductance values. The filter inductor, modulation module 104, and multi-QPR controller 103 together form a complete current control closed loop, ensuring that the system can accurately and stably output high-quality compensation current.

[0072] As can be seen from the above technical solutions, the beneficial effects of this embodiment are:

[0073] This application provides a power quality management system based on a multi-QPR controller, comprising: a current detection module, a current error calculation module, a multi-QPR controller, and a modulation module; the current detection module is used to detect the actual output current of a multi-functional grid-connected inverter; the current error calculation module is used to calculate the difference between a reference current and the actual output current to generate a current error signal based on the difference; the multi-QPR controller is used to generate a control signal based on the current error signal, and the multi-QPR controller consists of a proportional unit and multiple parallel quasi-proportional resonant units; wherein, the proportional unit is configured with a proportional coefficient to provide full-band proportional modulation of the current error signal. The system generates a first output component. Each quasi-proportional resonant unit corresponds to a different resonant frequency, including the fundamental frequency and multiple harmonic frequencies. Each quasi-proportional resonant unit is configured with a resonant coefficient and a cutoff frequency to provide high-gain adjustment at the corresponding resonant frequency, generating a second output component. The multi-QPR controller superimposes the first and second output components to generate a control signal. A modulation module, connected to the multi-QPR controller, generates a drive signal based on the control signal. The drive signal drives the multi-functional grid-connected inverter to generate and inject compensation current. The compensation current is used to suppress grid harmonics and improve power quality. This system achieves synchronous high-precision tracking control of the fundamental current and multiple harmonic currents in a stationary coordinate system, avoiding the multiple coordinate transformations and harmonic detection required by traditional PI control, reducing the computational complexity of the control algorithm, and improving the system's dynamic response speed, steady-state tracking accuracy, and power quality management effect.

[0074] like Figure 2 The image shows a specific embodiment of a power quality management method based on a multi-QPR controller according to this application.

[0075] In this embodiment, a power quality management method based on a multi-QPR controller includes the following steps:

[0076] Step 201: Detect the actual output current of the multi-functional grid-connected inverter.

[0077] The system acquires three-phase output current signals in real time through current sensors installed on the AC side of the multi-functional grid-connected inverter. The current sensors can be Hall effect current sensors or current transformers, which have high accuracy, wide bandwidth and good linearity characteristics, and can accurately detect complete current information from DC component to high-frequency harmonic component.

[0078] The acquired analog current signal undergoes amplitude scaling and filtering by a signal conditioning circuit, and is then converted into a digital signal by a high-speed analog-to-digital converter (ADC). The sampling frequency is synchronized with the switching frequency of the control system, and is typically set to an integer multiple of the switching frequency to ensure sampling accuracy and real-time performance. In this embodiment, the switching frequency is 10kHz, and the sampling period is set to 1×10⁻⁶. -5 The sampling time is one second, meaning it is sampled once per control cycle. This satisfies the requirements of the Nyquist sampling theorem and ensures that the control system can obtain the inverter's operating status in a timely manner.

[0079] To improve detection accuracy, the system also performs digital filtering on the sampled data to remove measurement noise and interference signals, ensuring that subsequent control algorithms obtain reliable current feedback information. Accurate detection of the actual output current is fundamental to the entire control system, and its accuracy directly affects the effectiveness of current tracking control and the performance of power quality management.

[0080] Step 202: Determine the current error signal corresponding to the multi-functional grid-connected inverter based on the difference between the preset reference current and the actual output current.

[0081] The reference current is the target current that the system expects the inverter to output, which is calculated by the upper-level control strategy based on the grid status, load characteristics, and compensation requirements. The reference current typically contains multiple frequency components: the fundamental active current component is used to realize the grid-connected power generation function of the photovoltaic power generation system, the fundamental reactive current component is used to provide reactive power support and voltage regulation, and the harmonic current components are used to compensate for harmonic pollution generated by the load.

[0082] In applications such as electric vehicle charging stations, uncontrolled rectifier charging piles generate a large number of odd harmonics, such as the 3rd, 5th, and 7th harmonics. Therefore, the reference current needs to include compensation components that are equal in magnitude but opposite in phase to these harmonics. The system compares the pre-calculated or real-time detected reference current with the detected actual output current at each sampling point. The difference between the two is the current error signal. The current error signal reflects the degree and direction of deviation between the actual output and the expected output of the inverter, serving as the basis for controller adjustments.

[0083] To ensure real-time performance and accuracy of control, the calculation process is performed at high speed in a digital signal processor or field-programmable gate array (FPGA), with the calculation delay strictly controlled within one sampling period to avoid adverse effects on control performance. The generation of the current error signal is a crucial step in closed-loop control, feeding back the system's output state to the controller, enabling the controller to dynamically adjust the control strategy based on actual conditions.

[0084] Step 203: Use a multi-QPR control strategy to process the current error signal to generate a control signal.

[0085] The multi-QPR control strategy utilizes a proportional unit and multiple parallel quasi-proportional resonant units working together to selectively regulate the current error signal at the frequency. Unlike traditional PI control, which requires multiple coordinate transformations to convert AC quantities of different frequencies into DC quantities before controlling them separately, the multi-QPR controller processes each frequency component directly in a stationary coordinate system, significantly simplifying the complexity of the control algorithm.

[0086] The implementation of the control strategy involves multiple parallel processing channels: the proportional unit amplifies the current error signal across the entire frequency band, providing a fast dynamic response capability; the fundamental quasi-proportional resonant unit provides high gain adjustment for the power frequency (50Hz or 60Hz), achieving zero steady-state error tracking of the fundamental current; and the harmonic quasi-proportional resonant units provide high gain adjustment for the odd harmonic frequencies of the 3rd, 5th, 7th, 11th, 13th, 17th, and 19th harmonics, respectively, to achieve accurate compensation for each harmonic.

[0087] Each quasi-proportional resonant unit has frequency selectivity, exhibiting extremely high gain near its resonant frequency point, while the gain rapidly decays in other frequency ranges far from the resonant frequency. This characteristic allows each unit to operate independently without interfering with each other.

[0088] The controller's transfer function parameters are meticulously designed and optimized: the proportional gain is set to 100 to ensure fast response while maintaining system stability; the resonance coefficient of each resonant unit is set to 1000 to ensure high tracking accuracy; the cutoff frequency is set to a certain proportion of the resonant frequency, such as 2.6h, to provide sufficient bandwidth to cope with grid frequency fluctuations and effectively suppress high-frequency noise. The outputs of all processing channels are summed and superimposed internally within the controller to form the final control signal output. This control signal contains comprehensive adjustment information for current errors, enabling the inverter to accurately output the required compensation current.

[0089] Step 204: Generate a drive signal based on the control signal to drive the multi-functional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics.

[0090] The control signal is converted into a pulse signal to drive the power switching devices by the modulation module. The modulation module uses space vector pulse width modulation (SVM) technology to convert the continuous control signal into a high-frequency switching pulse sequence. The SVM algorithm first converts the three-phase control signal to the α-β stationary coordinate system, calculates the desired voltage space vector, then selects two adjacent basic voltage vectors according to the sector where the vector is located, calculates the duration of each basic vector using the volt-second balance principle, and finally synthesizes the switching state sequence to generate the three-phase PWM drive signal.

[0091] The generated drive signal has a frequency of 10kHz. After being amplified by optocoupler isolation and drive circuit, it controls the IGBT or MOSFET power switches in the inverter bridge arm to turn on and off in a precise timing sequence. Under the action of PWM modulation, the voltage on the DC side of the inverter is chopped into a high-frequency pulse sequence. After being filtered by the filter inductor, a smooth compensation current is finally output on the AC side.

[0092] The fundamental and harmonic components of this compensation current precisely track the requirements of the reference current. After being injected into the grid's common coupling point, they cancel each other out with the harmonic currents generated by the load, while simultaneously regulating the output of active and reactive power. The compensation current makes the total current seen from the grid side closer to the ideal sinusoidal waveform, significantly reducing the total harmonic distortion rate, improving the power factor, and enhancing the quality of the grid voltage waveform, thereby achieving effective power quality management.

[0093] The entire process forms a complete closed-loop control from current detection, error calculation, controller adjustment to drive signal generation, ensuring that the system can respond quickly, accurately and stably to changes in the power grid and load, and continuously maintain high-quality power output.

[0094] As can be seen from the above technical solution, the beneficial effects of this embodiment are: detecting the actual output current of the multi-functional grid-connected inverter; determining the current error signal corresponding to the multi-functional grid-connected inverter based on the difference between the preset reference current and the actual output current; processing the current error signal using a multi-QPR control strategy to generate a control signal; and generating a drive signal based on the control signal to drive the multi-functional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics. This achieves high-precision current tracking and power quality management based on a multi-QPR control strategy, avoiding the complex coordinate transformation and harmonic detection in traditional PI control, reducing computational complexity, and improving the system's dynamic response speed and steady-state tracking accuracy.

[0095] like Figure 3 The image shows another specific embodiment of a power quality management system based on a multi-QPR controller according to this application. This embodiment is further described based on the foregoing embodiments.

[0096] In this embodiment, a power quality management system based on a multi-QPR controller includes the following steps:

[0097] Step 301: Detect the actual output current of the multi-functional grid-connected inverter.

[0098] Step 302: Determine the current error signal corresponding to the multi-functional grid-connected inverter based on the difference between the preset reference current and the actual output current.

[0099] Step 303: Use a multi-QPR control strategy to process the current error signal to generate a control signal.

[0100] Step 304: Perform full-band proportional adjustment on the current error signal to generate the first output component.

[0101] In the implementation of the multi-QPR control strategy, the current error signal is first sent to the proportional control unit for processing. Proportional control is the most basic and direct control method. It multiplies the input current error signal by a fixed proportional coefficient, and the output is a control quantity that is proportional to the input.

[0102] The characteristic of proportional control is that it is not frequency selective, providing a constant gain across the entire frequency range, hence the name full-band control. This characteristic allows the proportional unit to respond quickly to any change in current error, whether it is a low-frequency fundamental fluctuation or a high-frequency disturbance, and to immediately generate the corresponding control action.

[0103] The amplitude of the first output component is directly related to the magnitude of the current error. The larger the error, the greater the output adjustment, thereby accelerating the system's convergence to the desired state. The rapid response characteristic of proportional control is crucial for improving the dynamic performance of the system, especially under transient conditions such as load changes, grid voltage drops, or sudden changes in reference commands. The proportional unit can quickly generate a large control output, driving the inverter to rapidly adjust the output current, shortening the transition time, and reducing current overshoot or undershoot.

[0104] However, simple proportional control cannot eliminate steady-state error. This is because the proportional unit only produces output when an error exists; if the error is zero, the output is also zero, and the system will inevitably reach equilibrium at a non-zero error point. Therefore, the proportional unit needs to be used in conjunction with a quasi-proportional resonant unit to achieve both fast and precise control.

[0105] In parameter design, the selection of the proportional gain needs to comprehensively consider response speed and stability: a proportional gain that is too small will lead to slow system response and long transition time; a proportional gain that is too large may cause excessive overshoot or even oscillation and instability. In this embodiment, by analyzing the open-loop transfer function and frequency characteristics of the system, and combining the requirements of phase margin and gain margin, the proportional gain is preferably set to 100, which ensures that the system has sufficient stability margin and good anti-interference capability while guaranteeing fast dynamic response.

[0106] Step 305: Input the current error signal to multiple parallel quasi-proportional resonant controllers respectively; each quasi-proportional resonant controller corresponds to a specific resonant frequency, which includes the fundamental frequency and harmonic frequencies.

[0107] While performing proportional regulation, the current error signal is fed in parallel to multiple quasi-proportional resonant controllers, each of which is dedicated to processing a specific frequency current component. This parallel structure is the core architecture of the multi-QPR control strategy, allowing the system to independently regulate multiple signals of different frequencies simultaneously without interference.

[0108] The number of quasi-proportional resonant controllers and the selection of their resonant frequencies are determined based on actual application requirements. In this embodiment, the system is configured with eight quasi-proportional resonant controllers. One controller's resonant frequency is set to the fundamental frequency of the power grid (50Hz or 60Hz) to track and regulate the fundamental current. The resonant frequencies of the remaining seven controllers are set to the 3rd, 5th, 7th, 11th, 13th, 17th, and 19th harmonic frequencies, respectively, to compensate for these major odd-order harmonic components.

[0109] The resonant frequency setting is based on the analysis of power quality standards and actual load characteristics: In application scenarios such as electric vehicle charging stations, uncontrolled rectifier loads mainly generate 6k±1 (k=1,2,3...) harmonics, namely the 5th, 7th, 11th, 13th, etc.; at the same time, three-phase unbalanced loads will generate the 3rd harmonic; considering that the amplitude of lower harmonics is larger and the impact is more significant, the system focuses on compensating for the main odd harmonics within the 20th order.

[0110] Each quasi-proportional resonant controller receives the same current error signal as input, but due to their different resonant frequencies, their responses to different frequency components in the input signal are quite different: when the frequency of the input signal matches the resonant frequency of the controller, the controller exhibits extremely high gain and produces a strong regulating effect; when the input frequency is far from the resonant frequency, the controller gain decays rapidly and produces almost no output.

[0111] This frequency selectivity stems from the transfer function structure of the quasi-proportional resonant controller, whose denominator contains a second-order oscillating element related to the resonant frequency. This gives the controller a narrow-band, high-gain amplitude-frequency response near the resonant frequency. By appropriately setting the parameters of each controller, it can be ensured that their frequency bands do not overlap or only slightly overlap, thereby achieving independent and precise control of each frequency component.

[0112] Step 306: Each quasi-proportional resonant controller performs high-gain adjustment on the current error signal at the corresponding resonant frequency to generate harmonic compensation components.

[0113] Each quasi-proportional resonant controller processes the input current error signal according to its transfer function, providing a gain much higher near the resonant frequency than at other frequencies. The transfer function of the quasi-proportional resonant controller is... Where K r ω is the resonance coefficient. c ω is the cutoff frequency.h It is the resonant angular frequency.

[0114] When the frequency of the input signal equals the resonant frequency, the denominator of the transfer function reaches its minimum value, and the gain reaches its peak value Kr, thus achieving strong regulation of that frequency component. High gain means that even if the amplitude of that frequency component in the current error is very small, the controller can generate a sufficiently large output to eliminate this error, theoretically achieving zero steady-state error tracking.

[0115] For example, for a quasi-proportional resonant controller with a 5th harmonic, the resonant frequency is set to 250Hz (assuming the fundamental frequency is 50Hz). When the current error signal contains a 250Hz 5th harmonic component, the controller will amplify this component with a high gain and generate a corresponding control output. However, for the 50Hz fundamental component or other harmonic components in the error signal, due to the frequency mismatch, the controller's gain is very small and it will hardly respond to them.

[0116] Each controller operates independently, generating specific harmonic compensation components for its resonant frequency. These compensation components are essentially sinusoidal signals of the corresponding frequency, amplified with high gain and phase-adjusted. Their amplitude and phase are dynamically adjusted by the controller to precisely compensate for the frequency component in the current error. Resonance coefficient K r The magnitude of K directly affects the peak gain of the controller at the resonant frequency. r The larger the value of K, the higher the tracking accuracy, but an excessively large K... r This could cause the gain to be too steep near that frequency, making it overly sensitive to slight frequency shifts, or even introducing instability. Cutoff frequency ω c This determines the controller's bandwidth, i.e., the frequency range of the high-gain region, ω. c The larger the value, the wider the bandwidth, and the stronger the adaptability to power grid frequency fluctuations, but it is also more susceptible to high-frequency noise interference. In this embodiment, the resonance coefficient of each controller is uniformly set to 1000, and the cutoff frequency is set according to ω. c The rule setting of h=2.6h, where h is the harmonic order, ensures high-precision tracking of each harmonic, provides sufficient bandwidth to cope with the fluctuation of the actual power grid frequency within the range of ±0.5Hz, and effectively suppresses the influence of high-frequency noise.

[0117] Step 307: Summarize the harmonic compensation components to generate the second output component.

[0118] The harmonic compensation components output by each quasi-proportional resonant controller are summed in the control system and combined into a unified second output component. This is a linear superposition process, which adds the fundamental compensation component output by the fundamental quasi-proportional resonant controller to the harmonic compensation components output by each harmonic quasi-proportional resonant controller.

[0119] Due to the frequency selection characteristics of each controller, each controller mainly contributes the component of its corresponding frequency, while the output of other frequency components is very small. Therefore, the summed second output component contains the adjustment information of all target frequencies, which is actually a superposition of multiple sine waves of different frequencies. This composite signal manifests as a complex periodic waveform in the time domain, with its fundamental component used to achieve zero steady-state error tracking of the fundamental current, and each harmonic component used to compensate for the corresponding current harmonics.

[0120] The second output component embodies the core advantage of the multi-QPR control strategy: through the parallel coordination of multiple resonant units, the system can simultaneously handle control tasks at multiple frequencies under a single control structure, without the need for complex coordinate transformations or frequency decomposition. The summarization process is implemented in the digital controller through simple addition operations, with minimal computational load and almost no increase in control delay.

[0121] The second output component complements the first output component: the first output component provides fast response capability across the entire frequency band and is responsible for the dynamic adjustment of the system; the second output component provides high-precision frequency-selective adjustment and is responsible for eliminating steady-state errors and compensating for harmonics at specific frequencies. Their synergistic effect enables the control system to possess both fast transient response and accurate steady-state performance, meeting the high requirements of power quality management for the control system.

[0122] Step 308: Superimpose the first output component with a set of second output components to generate a control signal.

[0123] The first output component from the proportional unit and the second output component from the quasi-proportional resonant unit are finally superimposed at the output of the multi-QPR controller to form a complete control signal. This superposition is also a linear summation operation, directly adding the two components. The generated control signal combines the dual functions of proportional and resonant regulation, including both a proportional control component that provides a fast response to current errors and a high-precision tracking control component for the fundamental frequency and various harmonics.

[0124] The control signal waveform is a complex time-varying signal in the time domain, precisely corresponding to the voltage waveform that the inverter needs to output to eliminate the current current error. This control signal is then sent to the modulation module for pulse width modulation processing, converting it into a high-frequency pulse sequence to drive the power switching devices, ultimately achieving precise control of the inverter's output current.

[0125] From a frequency domain perspective, the control signal has significant components at the fundamental frequency and each target harmonic frequency. These components drive the inverter to output compensation current at the corresponding frequency, which cancels out the harmonics generated by the load, thereby purifying the grid current.

[0126] The parallel superposition structure of the multi-QPR controllers makes the entire control algorithm simple and efficient, avoiding the complex process of multiple coordinate transformations and harmonic detection in traditional PI control. This significantly reduces the computational burden and control delay, improving the system's real-time performance and reliability. Through the rational design and optimization of the controller parameters, the system achieves zero or small steady-state error tracking of the fundamental and multiple harmonic currents while maintaining good dynamic performance, effectively improving the power quality management effect.

[0127] The entire control process forms a complete closed-loop system. From current detection, error calculation, multi-QPR adjustment to drive signal generation, each link works closely together to ensure that the multi-functional grid-connected inverter can accurately, stably and efficiently complete the power quality management task.

[0128] Step 309: Generate a drive signal based on the control signal to drive the multi-functional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics.

[0129] As can be seen from the above technical solutions, the beneficial effects of this embodiment are as follows: by providing a fast response across the entire frequency band through a proportional unit, providing high gain adjustment at their respective resonant frequencies through multiple quasi-proportional resonant units, and linearly superimposing the outputs of each unit, synchronous tracking of the fundamental current and multiple harmonic currents without steady-state error is achieved. Under a single control structure, accurate compensation of multi-frequency current components is completed, significantly improving the sinusoidal nature of the current waveform, reducing the total harmonic distortion rate, and effectively improving the power quality of the power grid.

[0130] Those skilled in the art will understand that the embodiments of this application can be provided as methods or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or a combination of software and hardware.

[0131] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0132] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0133] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A power quality management system based on a multi-QPR controller, applied to a multi-functional grid-connected inverter, characterized in that, include: Current detection module, current error calculation module, multi-QPR controller and modulation module; The current detection module is used to detect the actual output current of the multi-functional grid-connected inverter; The current error calculation module is used to calculate the difference between the reference current and the actual output current, so as to generate a current error signal based on the difference. The multi-QPR controller is used to generate a control signal based on the current error signal. The multi-QPR controller consists of a proportional unit and multiple parallel quasi-proportional resonant units. The proportional unit is configured with a proportional coefficient to provide full-band proportional adjustment of the current error signal and generate a first output component. Each of the quasi-proportional resonant units corresponds to a different resonant frequency, which includes a fundamental frequency and multiple harmonic frequencies. Each of the quasi-proportional resonant units is configured with a resonant coefficient and a cutoff frequency to provide high gain adjustment at the corresponding resonant frequency and generate a second output component. The multi-QPR controller superimposes the first output component and the second output component to generate the control signal; The modulation module, connected to the multi-QPR controller, is used to generate a drive signal according to the control signal; wherein the drive signal is used to drive the multi-functional grid-connected inverter to generate and inject compensation current; the compensation current is used to suppress grid harmonics and improve power quality.

2. The system according to claim 1, characterized in that, The harmonic frequency corresponds to multiple odd harmonics.

3. The system according to claim 1, characterized in that, The quasi-proportional resonant unit includes a fundamental compensation unit for tracking the fundamental current and a harmonic compensation unit for tracking the harmonic current.

4. The system according to claim 1, characterized in that, The proportional coefficient is used to adjust the dynamic response speed of the system, and the proportional coefficient is positively correlated with the dynamic response speed.

5. The system according to claim 1, characterized in that, The resonance coefficient is used to adjust the tracking accuracy of the quasi-proportional resonant unit at the resonant frequency, and the resonance coefficient is positively correlated with the tracking accuracy.

6. The system according to claim 1, characterized in that, The cutoff frequency is used to adjust the bandwidth of the quasi-proportional resonant unit, and the cutoff frequency is positively correlated with the bandwidth.

7. The system according to claim 1, characterized in that, The modulation module generates the driving signal using space vector pulse width modulation.

8. The system according to claim 1, characterized in that, Also includes: A filter inductor is connected to the AC side of the multi-functional grid-connected inverter and is used to filter out the switching frequency harmonics in the drive signal.

9. A power quality management method based on a multi-QPR controller, wherein the method is applied to the system described in claims 1-8, characterized in that, include: Detect the actual output current of the multi-functional grid-connected inverter; The current error signal corresponding to the multi-functional grid-connected inverter is determined based on the difference between the preset reference current and the actual output current. The current error signal is processed using a multi-QPR control strategy to generate a control signal; A drive signal is generated based on the control signal to drive the multifunctional grid-connected inverter to generate and inject compensation current for suppressing grid harmonics.

10. The method according to claim 9, characterized in that, The process of using a multi-QPR control strategy to process the current error signal to generate a control signal includes: The current error signal is proportionally adjusted across the entire frequency band to generate the first output component; The current error signal is input to multiple parallel quasi-proportional resonant controllers; each quasi-proportional resonant controller corresponds to a specific resonant frequency, which includes the fundamental frequency and harmonic frequencies. Each of the quasi-proportional resonant controllers performs high-gain adjustment on the current error signal at the corresponding resonant frequency to generate harmonic compensation components; The harmonic compensation components are combined to generate a second output component; The first output component is superimposed with a set of second output components to generate the control signal.

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