Active power filter harmonic suppression system based on single-cycle dual-carrier comparison control

Abstract

The invention provides an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control, which comprises an active power filter, a measurement module, a harmonic current extraction module and a control unit, and is characterized in that the control unit comprises a frequency calculation module, a self-adaptive resonance control module, a dual-carrier comparator and a PWM (Pulse Width Modulation) module; the self-adaptive resonance control module generates a reference voltage signal based on the real-time fundamental frequency of the power grid calculated by the frequency calculation module, and the dual-carrier comparator compares the reference voltage signal with a rising type triangular carrier signal and a falling type triangular carrier signal at the same time in each switching period. And the PWM module converts the comparison result into a PWM signal for driving each switching device in the active power filter through the synergistic effect of the D trigger and the logic gate circuit. According to the method, the problems of compensation failure and insufficient multi-band harmonic collaborative suppression caused by frequency mismatch in a traditional method are solved, and the system efficiency, the dynamic performance and the working condition adaptation are remarkably improved.

Description

Technical Field

[0001] This application belongs to the field of smart grid control technology, and relates to active power filter harmonic suppression technology, specifically providing an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control. Background Technology

[0002] Since the quality of power directly affects the normal operation and lifespan of electrical equipment, providing high-quality and reliable power to load-side users is a fundamental responsibility and important goal of the power grid. In recent years, with the rapid development of power electronics technology, a large number of nonlinear loads have been connected to the power grid, leading to serious harmonic pollution problems. Power grid harmonics not only reduce power quality and cause equipment overheating and malfunctions, but may also cause grid resonance, threatening the safe and stable operation of the power system.

[0003] Active power filters (APFs) are an effective means of solving harmonic problems caused by nonlinear loads connected to the power grid by detecting harmonics in real time and injecting reverse compensation current. Conventional APFs typically extract the harmonic components of the load current based on instantaneous power theory or Fourier transform, generate a compensation reference signal, and use strategies such as hysteresis control and PI control to drive the converter to output compensation current. This control method can achieve a relatively ideal harmonic suppression effect when the fundamental frequency of the power grid is relatively stable. However, when a large number of nonlinear loads are connected to the power grid, the power grid frequency will drift as the harmonic components in the grid increase, which will seriously reduce the harmonic suppression effect of conventional APFs.

[0004] Therefore, there is an urgent need for an active power filter harmonic suppression scheme that can adaptively track the power grid frequency for high-precision harmonic extraction and dynamic compensation, and is simple in structure, reliable in operation, and easy to implement. Summary of the Invention

[0005] This application provides an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control through embodiments, including an active power filter, a measurement module, a harmonic current extraction module, and a control unit. The active power filter is used to inject a harmonic suppression signal into the power grid. The measurement module is used to measure the real-time current and voltage signals of the power grid and the harmonic suppression signal output by the active power filter. The harmonic current extraction module determines the harmonic current component signal of the power grid based on the real-time current and voltage signals of the power grid. The control unit includes: The frequency calculation module calculates the real-time fundamental frequency of the power grid based on the real-time current signal of the power grid. The adaptive resonant control module includes several parallel quasi-proportional resonant controllers for generating a reference voltage signal that can independently adjust the suppression effect of each harmonic. The transfer function of each quasi-proportional resonant controller is determined based on its corresponding harmonic order and the real-time fundamental frequency of the power grid. A dual-carrier comparator compares the reference voltage signal with two carrier signals in each switching cycle, wherein the two carrier signals are a rising triangular carrier signal and a falling triangular carrier signal; The PWM module, including D flip-flops and logic gates, generates and sends corresponding PWM drive signals to the gates of each switching device of the active power filter based on the two comparison results output by the dual-carrier comparator.

[0006] Specifically, the active power filter includes a DC power supply, an energy storage capacitor, a first bridge arm, and a second bridge arm connected in parallel; a first switching device and a second switching device are connected in series on the first bridge arm, and a third switching device and a fourth switching device are connected in series on the second bridge arm. Each switching device switches on and off based on the high and low level signals received at its gate; the midpoint of the first bridge arm and the second bridge arm are connected in parallel to the power grid through a coupling inductor.

[0007] The transfer function of the adaptive resonance control module for: , in, This is the proportionality coefficient. For the harmonic order that needs to be suppressed, For the first The resonance coefficient corresponding to the subharmonic. The cutoff frequency, For the first The resonant angular frequency corresponding to the second harmonic. The real-time fundamental frequency of the power grid. It is a complex frequency domain operator.

[0008] Furthermore, the real-time fundamental frequency of the power grid is determined based on the time interval between the two most recent consecutive positive zero crossings of the real-time current signal of the power grid.

[0009] Furthermore, the dual-carrier comparator includes: The first comparator is used to compare the reference voltage signal with the falling triangular carrier signal in real time and output a binary first logic signal. When the reference voltage signal is higher than the falling triangular carrier signal, the first logic signal is 1, and when the reference voltage signal is lower than the falling triangular carrier signal, the first logic signal is 0. The second comparator is used to compare the reference voltage signal with the rising triangular carrier signal in real time and output a binary second logic signal. When the reference voltage signal is lower than the rising triangular carrier signal, the second logic signal is 1, and when the reference voltage signal is higher than the rising triangular carrier signal, the second logic signal is 0.

[0010] Furthermore, the logic gate circuit is generated based on the following formula and sends corresponding PWM drive signals to the gates of each switching device of the active power filter: , in, , for The complementary state signal output by the trigger, The first logic signal, for complementary signals, This is the second logic signal. for complementary signals, , , , These are the PWM drive signals corresponding to the first, second, third, and fourth switching devices, respectively.

[0011] Preferably, the logic gate circuit includes a first AND gate, a second AND gate, a third AND gate, a fourth AND gate, a first OR gate, a second OR gate, a first NOT gate, and a second NOT gate; The two input terminals of the first AND gate are respectively input and The two inputs of the second AND gate are respectively input to... and The two input terminals of the third AND gate are respectively input to and The two input terminals of the fourth AND gate are respectively input to and ; The two input terminals of the first OR gate are respectively connected to the output terminal of the first AND gate and the output terminal of the second AND gate. The output terminal of the first OR gate is used to output the PWM drive signal corresponding to the first switching device. The two input terminals of the second OR gate are respectively connected to the output terminals of the third AND gate and the fourth AND gate. The output terminal of the second OR gate is used to output the PWM drive signal corresponding to the third switching device. The input terminal of the first NOT gate is connected to the output terminal of the first OR gate, and the output terminal of the first NOT gate is used to output the PWM drive signal corresponding to the fourth switching device; The input terminal of the second NOT gate is connected to the output terminal of the second OR gate, and the output terminal of the second NOT gate is used to output the PWM drive signal corresponding to the second switching device.

[0012] Preferably, the control unit further includes: The reference voltage signal detection module is used to detect the reference voltage signal. The fluctuations; The dual-carrier comparator adjusts the periods of the two carrier signals based on the fluctuations of the reference voltage signal, so that the adjusted carrier period... With a preset, system-allowed minimum base carrier period The following relationship must be satisfied: ,in, It is an integer greater than or equal to 1.

[0013] Furthermore, the reference voltage signal detection module detects the reference voltage signal output by the adaptive resonance control module according to a fixed control cycle. Sampling is performed to obtain discrete sampled signals at various times, and the fluctuation of the reference voltage signal is detected through the following steps: Step 310: Extract the sampling point corresponding to the current time and the previous time. The discrete sampled signals at n sampling points are used to construct a window with a length of n. Evaluation sequence ,in This represents the discrete sampled signal at the current moment; Step 320: Calculate the instantaneous rate of change index based on the following formula. : (6); Step 330, calculate the instantaneous rate of change index With the preset first threshold Second threshold Compare, if Then Set to 1, if Then Set as ,if Then Set as ,in, .

[0014] The technical solution of this application has at least the following beneficial effects: (1) The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control provided in this application ensures that the generation of compensation current is synchronized with the harmonic components in the opposite direction through the single-cycle dual-carrier comparison control strategy of comparator and D flip-flop working together, which significantly improves the real-time performance and accuracy of harmonic suppression.

[0015] (2) The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control provided in this application adopts multiple sets of parallel adaptive quasi-proportional resonant controllers, which can accurately compensate for harmonics of different orders and improve the harmonic suppression effect. (3) The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control provided in this application can adjust the controller parameters in real time according to the change of grid frequency, which solves the problem of the reduced compensation capability of traditional fixed parameter controllers when the grid frequency fluctuates. Attached Figure Description

[0016] Figure 1 A schematic diagram illustrating the principle of using an active power filter to suppress harmonics in a power grid connected to a nonlinear load. Figure 2 This is a framework diagram of an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control provided in Embodiment 1 of this application; Figure 3 This is a circuit diagram of an active power filter according to Embodiment 1 of this application; Figure 4 This is a schematic diagram of two carrier waves provided according to Embodiment 1 of this application; Figure 5 This is a schematic diagram of a dual-carrier comparator performing dual-carrier comparison according to Embodiment 1 of this application; Figure 6 This is a schematic diagram of the PWM module provided according to an embodiment of this application; Figure 7 This is a framework diagram of an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control provided in Embodiment 2 of this application; Figure 8 This is a schematic diagram of a dual-carrier comparator performing dual-carrier comparison according to Embodiment 2 of this application. Detailed Implementation

[0017] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0018] In the description of the embodiments of this application, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, in the description of this application, in order to distinguish different units, the terms "first," "second," etc. are used in this specification, but these are not limited by the manufacturing order, nor should they be construed as indicating or implying relative importance. Their names may differ in the detailed description and claims of this application.

[0019] The vocabulary used in this specification is for illustrative purposes and is not intended to limit the scope of this application. It should also be noted that, unless otherwise expressly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection via an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of these terms in this application.

[0020] To clearly illustrate the technical solution of this application, a brief description of existing active power filter harmonic suppression technology is first given.

[0021] Figure 1 This diagram illustrates the principle of using an Active Power Filter (APF) to suppress harmonics in a power grid connected to a nonlinear load. To suppress harmonic currents caused by the nonlinear load, a harmonic suppression system can be connected to the grid, consisting of a measurement module, a harmonic current extraction module, a harmonic suppression module, a PWM drive module, and the APF. The core structure of the APF is a bridge inverter circuit constructed from multiple switching devices (such as IGBTs and SiC MOSFETs). Depending on the application, it can be a three-phase full-bridge circuit or a single-phase full-bridge circuit. For a three-phase full-bridge circuit, the midpoint of each bridge arm is connected to the respective phase of the power grid via an inductor. For a single-phase full-bridge circuit, the midpoints of two bridge arms form an AC output port, connected between the phase line and the neutral line of the power grid via an inductor. The gates of each switching device control the switching on and off according to the high and low level signals they receive, thereby injecting harmonic current suppression signals into the power grid. This is to suppress harmonic currents in the power grid.

[0022] Harmonic current suppression signal The generation process is as follows: The measurement module acquires and measures real-time signals of the power grid on the load side (between the point of common coupling PCC and the load), including the real-time current signal of the power grid. and voltage signal The harmonic current extraction module utilizes Harmonic current detection algorithms, such as detection methods, are used to detect harmonic currents. Detection and extraction of harmonic current components The harmonic suppression module is constructed by physically replicating a pre-established harmonic suppression model. Its goal is to suppress harmonic currents in the power grid. This module first... Determine the target signal for compensation current Then, combined with feedback from the active power filter Calculation error It is converted into a reference voltage signal through a PR controller, etc. And output to the PWM driver module; the PWM driver module will It compares the signal with the built-in carrier signal in real time, generates a PWM drive signal using algorithms such as SPWM, and converts it into a high or low level output to the active power filter (APF) through the drive circuit.

[0023] The above-mentioned scheme can achieve good harmonic current suppression when the load connected to the power grid is mainly linear. However, when a large number of nonlinear loads are connected to the power grid, the fundamental frequency of the grid current will inevitably shift, and the degree of frequency shift will also increase with the increase of the proportion of harmonic components. In order to solve the problem of harmonic suppression failure caused by the fundamental frequency drift of the power grid and achieve good harmonic suppression effect over a wider frequency band, existing technologies generally focus on improving the harmonic suppression model used in the harmonic suppression module, striving to make the reference signal more accurately characterize the grid frequency shift caused by the increase of harmonic components. For example, Chinese invention patent CN119651620A discloses an active power filter control method and system suitable for frequency fluctuations. In order to improve the control bandwidth, a variable bandwidth adjustable internal model is introduced on the basis of the conventional internal model control link, and the RC is used to re-control the RC itself, and the width of the gain bandwidth is dynamically adjusted through the internal control coefficient. However, the transfer function of the control link of this method is complex and there are many control variables, which greatly increases the difficulty of hardware implementation.

[0024] This application provides an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control through embodiments. This system can adaptively track the power grid frequency to perform high-precision harmonic extraction and dynamic compensation. The entire system has a simple structure, reliable operation, low hardware cost, and is easy to implement.

[0025] Example 1 Figure 2Here is a framework diagram of an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to Embodiment 1 of this application, as shown below. Figure 2 As shown, the harmonic suppression system includes an active power filter, a measurement module, a harmonic current extraction module, and a control unit.

[0026] Active power filters are used to inject harmonic suppression signals into the power grid. ,like Figure 3 As shown, the active power filter includes DC power supplies connected in parallel. Energy storage capacitor The bridge arm consists of a first bridge arm and a second bridge arm, with a first switching device connected in series on the first bridge arm. Second switching device A third switching device is connected in series on the second bridge arm. and the fourth switching device The midpoints of the first and second bridge arms together serve as the AC output terminals, connected to the grid side and load side of the 220V AC power grid via an inductor. Each switching device switches its on / off state according to the high or low level of the PWM drive signal received at its gate, thereby controlling the DC power supply. The output DC current is converted into a varying harmonic suppression signal. Injected into the power grid.

[0027] The measurement module is installed on the load side of the power grid to measure the real-time current signal of the power grid. Real-time voltage signal and the harmonic suppression signal output by the active power filter. The measurement module can be implemented in a manner known to those skilled in the art. For example, current measurement can be performed using a Hall current sensor, a current transformer, or, in the case of low current, a sampling resistor combined with a differential amplifier circuit; voltage measurement can be performed using a voltage transformer, a resistor divider network, or an isolation operational amplifier.

[0028] In addition, the measurement module preferably also includes a conditioning circuit and an analog-to-digital (AD) conversion circuit. The conditioning circuit is used to amplify, filter and level-convert the analog signal output by the sensor. The analog-to-digital conversion circuit is composed of an ADC chip and its peripheral circuits. It synchronously samples the conditioned analog signal according to a preset sampling frequency (such as 50~100 kHz) and converts it into a digital quantity. The digital quantity is then sent to the harmonic current extraction module and the control unit as input data for subsequent harmonic detection and control operations.

[0029] The harmonic current extraction module is based on the real-time current signal output by the measurement module. and real-time voltage signal ,from Extracting harmonic current component signals In the embodiments of this application, for extraction The specific method is not limited; various harmonic separation techniques known to those skilled in the art can be used to construct the harmonic extraction module. For example, the following can be executed cyclically: Detection method implementation Extraction: Step 110: Obtain the real-time voltage signal of the power grid using a phase-locked loop. The reference phase; Step 120: Convert the real-time current signal of the power grid using Clarke transformation. Transformed into a two-phase stationary coordinate system Coordinate components , ; Step 130, using Park transformation to... , Converted to active current components in a rotating coordinate system and reactive current components ; Step 140, extract using a low-pass filter and The DC and AC components are separated and analyzed using the inverse Park transform and the inverse Clarke transform. Harmonic current component signal separated from .

[0030] The control unit uses the harmonic current components output by the harmonic current extraction module. Generate PWM drive signals for controlling the on / off states of various switching devices in the active power filter, such as... Figure 2 As shown, in this embodiment, the control unit further includes a frequency calculation module, an adaptive resonance control module, a dual-carrier comparator, and a PWM module.

[0031] Specifically: The frequency calculation module is based on the real-time current signal of the power grid. Calculate the real-time fundamental frequency of the power grid ; The adaptive resonant control module includes several parallel quasi-proportional resonant controllers used to generate reference voltage signals whose harmonic suppression effects can be independently adjusted. In this context, the transfer function of each quasi-proportional resonant controller is based on its corresponding harmonic order. and the real-time fundamental frequency of the power grid Sure; The dual-carrier comparator references the voltage signal in each switching cycle. Compare with the two carrier signals respectively; The PWM module includes D flip-flops and logic gate circuits. Based on the two comparison results output by the dual-carrier comparator, it generates and sends corresponding PWM drive signals to the gates of each switching device of the active power filter.

[0032] The following section provides a detailed introduction to the specific implementation of the control unit.

[0033] <Frequency Calculation Module> The frequency calculation module is used to realize the real-time fundamental frequency of the power grid. For precise tracking, preferably, the frequency calculation unit continuously monitors the real-time current signal of the power grid. and extract The moment it crosses midnight, and then it keeps updating. The time interval between the two most recent positive zero crossings Then, the real-time fundamental frequency of the power grid is calculated using equation (1): (1).

[0034] <Adaptive Resonance Control Module> The adaptive resonance control module obtains the values ​​calculated by the frequency calculation module. It adjusts the control parameters of its individual quasi-proportional resonant controllers in real time to adaptively generate a reference voltage signal that matches the fluctuating grid frequency. To ensure that the active power filter injects harmonic suppression signals into the power grid. It can effectively suppress harmonic current components over a wide frequency band.

[0035] Preferably, the adaptive resonance control module adaptively generates a reference voltage signal by cyclically executing the following steps. : Step 210: Determine the control parameters of each quasi-proportional resonant controller using equation (2). : (2); Step 220: Based on the harmonic current component signal output by the harmonic current extraction module... This generates a compensation current with the same amplitude but opposite polarity. ,Right now ; Step 230, compensate current Harmonic suppression signal output by active power filter The difference is input to each parallel adaptive quasi-proportional resonant controller, and the combined output is a reference current signal. The transfer function of the combined adaptive quasi-proportional resonant controllers is as follows: (3), in, This is the proportionality coefficient. For the harmonic order that needs to be suppressed (preferably, n (The harmonic order is 3, 5, 7, 11, 13, 17, 19, 23, 25). For the first The resonance coefficient corresponding to the subharmonic. The cutoff frequency, For the first The resonant angular frequency corresponding to the second harmonic. For complex frequency domain operators; Step 240, based on equation (4), the reference current signal Through gain Converted to reference voltage signal : (4), in, This is the voltage-to-current conversion gain coefficient of the control system.

[0036] The reference voltage signal obtained through steps 210 to 240 It can dynamically optimize the controller's resonant point based on the real-time fundamental frequency offset of the power grid captured by the frequency calculation module, and adjust the resonant point of each harmonic. It can independently adjust the suppression effect on each harmonic, thereby ensuring effective adaptive suppression of each harmonic component under power grid frequency fluctuation conditions.

[0037] It should be noted that, without departing from the technical concept of the transfer function of the adaptive quasi-proportional resonant controller shown in equation (3), a controller for improving the response speed and accuracy of the reference voltage signal can also be added to the adaptive resonant control module, such as the various controllers in the existing technology center analyzed above for improving the hysteresis control effect.

[0038] Dual-carrier comparator Reference voltage signal A PWM signal needs to be generated by comparing it with a carrier wave, and then converted into high and low level signals by the drive module. Existing PWM drive signal generation algorithms generally use a single form of carrier signal to compare with a reference signal. However, when a nonlinear load is connected to the power grid, the proportion of harmonic components in the current is relatively large, and the reference voltage signal... Significant fluctuations often occur. If these fluctuations cannot be effectively extracted by comparing the reference signal and the carrier signal, then even the reference voltage signal... Even though it can accurately track harmonic currents under frequency fluctuations, it cannot be converted into the on / off state of switching devices in an active power filter, leading to... Unable to Make a timely response.

[0039] To address the aforementioned issues, this application employs a dual-carrier comparator for the reference voltage signal. Compared with the carrier wave, specifically, the dual-carrier comparator references the voltage signal in each switching cycle. By comparing it with two carrier signals respectively, it is possible to capture the signal more accurately and promptly. Fluctuations.

[0040] Figure 4 Parts (a) and (b) respectively illustrate the two carrier signals used by the dual-carrier comparator in this embodiment, such as Figure 3 As shown, one of the two carrier signals is a rising triangular carrier signal, and the other is a falling triangular carrier signal. The periods of both carrier signals are equal to the switching period of the active power filter, and they have the same preset peak amplitude. V m During the same switching cycle, the amplitude of the rising triangular carrier signal linearly increases from 0 to... V m The amplitude of the falling triangular carrier signal is from V m It decreases linearly to 0.

[0041] Specifically, the dual-carrier comparator includes two comparators, namely a first comparator and a second comparator, wherein: The first comparator is used to compare the reference voltage signal in real time. Combined with a falling triangular carrier signal, and outputting the first binary logic signal A, when... When the signal is higher than the falling triangular carrier signal, the value of the first logic signal A is 1. When the signal is lower than the falling triangular carrier signal, the value of the first logic signal A is 0.

[0042] The second comparator is used to compare the reference voltage signal in real time. Combined with a rising triangular carrier signal, and outputting a binary second logic signal B, when When the signal is lower than the rising triangular carrier signal, the value of the second logic signal B is 1. When the signal is higher than the rising triangular carrier signal, the value of the second logic signal B is 0.

[0043] Figure 5 This embodiment illustrates the dual-carrier comparator for the reference voltage signal. Schematic diagram of the result of comparison with two carrier signals. The figure includes two complete switching cycles in total. Among them, in each switching cycle, according to the comparison with the two carrier signals, the output results of A and B are sequentially converted among [0, 0], [1, 0], and [1, 1]. By using a carrier with both unidirectional rising and unidirectional falling waveforms, more high and low level conversions can be triggered during the fluctuation process, so as to ensure that the fluctuation can be promptly reflected in the switching action of the switching device, and ensure that when a large number of nonlinear loads are connected to the power grid, causing a significant deviation in the power grid frequency, the active power filter can maintain good tracking of .

[0044] <PWM module> The PWM module generates and sends corresponding PWM drive signals to the gates of each switching device of the active power filter according to the two comparison results (the first logic signal A and the second logic signal B) output by the dual-carrier comparator.

[0045] Figure 6 Illustrates the schematic diagram of the D flip-flop and logic gate circuit included in the PWM module in this embodiment. In this application, by using the cooperation of the D flip-flop and logic gate circuit, high and low levels can be promptly and stably sent to the gate of the switching device, ensuring the response speed and reliability.

[0046] Specifically, as Figure 6 shown, the two output terminals of the D flip-flop are used to output complementary state signals and . Triggered by the clock signal Clock, , the state of continuously switches between [0, 1] and [1, 0].

[0047] The logic gate circuit includes a first AND gate, a second AND gate, a third AND gate, a fourth AND gate, a first OR gate, a second OR gate, a first NOT gate, and a second NOT gate, where: The two input terminals of the first AND gate are respectively input with and . The two input terminals of the second AND gate are respectively input with and . The two input terminals of the third AND gate are respectively input with and . The two input terminals of the fourth AND gate are respectively input with and ; The two inputs of the first OR gate are connected to the outputs of the first AND gate and the second AND gate, respectively. The output of the first OR gate is used to output the PWM drive signal corresponding to the first switching device. The two inputs of the second OR gate are connected to the outputs of the third AND gate and the fourth AND gate, respectively. The output of the second OR gate is used to output the PWM drive signal corresponding to the third switching device. The input of the first NOT gate is connected to the output of the first OR gate, and the output of the first NOT gate is used to output the PWM drive signal corresponding to the fourth switching device. The input of the second NOT gate is connected to the output of the second OR gate, and the output of the second NOT gate is used to output the PWM drive signal corresponding to the second switching device.

[0048] The logic gate circuit constructed in the above manner can generate the PWM drive signal corresponding to the gate of each switching device of the active power filter based on equation (5): (5), in, , for The complementary state signal output by the trigger, This is the first logic signal. for complementary signals, This is the second logic signal. for complementary signals, , , , The first switching device Second switching device Third switching device and the fourth switching device The corresponding PWM drive signal.

[0049] Example 2 Figure 7 A framework diagram of an active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to Embodiment 2 of this application is shown. The difference between Embodiment 2 and Embodiment 1 is that a reference voltage signal detection module is added to the control unit for detecting the reference voltage signal. The fluctuation situation, and at the same time, the dual-carrier comparator is based on the reference voltage signal. The fluctuations are monitored, and the periods of the two carrier signals are adjusted in real time. The adjusted carrier period... With the predetermined minimum base carrier period allowed by the system The following relationship must be satisfied: ,in, It is an integer greater than or equal to 1, which is used to adjust the carrier period of the dual-carrier comparator.

[0050] As analyzed above, the harmonic suppression system provided in this application, by switching a dual-carrier signal and a reference voltage signal in one switching cycle... By comparing and improving the ability to capture fluctuations in the reference voltage signal, it is possible to achieve better performance under conditions of grid frequency fluctuations. Good tracking is achieved because the frequency offset of the power grid is closely related to the nonlinear load conditions connected; therefore, the reference voltage signal... The fluctuations are also significantly affected by the nonlinear loads connected to the power grid.

[0051] By adding a reference voltage signal detection module to this harmonic suppression system, the reference voltage signal output by the adaptive resonance control module can be detected. The fluctuation situation is evaluated and the evaluation result is sent to the dual-carrier comparator. When fluctuations increase, a dual-carrier comparator can shorten the period of the two carrier signals. However, due to physical limitations such as the gate drive capability of IGBTs and other switching devices and the computing power of the controller, the switching period of an active power filter cannot be reduced indefinitely. Furthermore, operating with a small switching period for a long time will significantly increase the losses of the switching devices. Therefore, it is necessary to flexibly adjust the carrier period (i.e., the switching period) according to the proportion of harmonic components. When a large number of nonlinear loads are connected to the power grid, resulting in a large number of harmonic components and a severe degree of power grid frequency deviation, the carrier period should be reduced within the range allowed by the physical constraints of the system to increase the operating frequency of the switching devices and ensure the harmonic suppression effect. When the nonlinear loads in the power grid are removed or the power grid frequency deviation is small, the carrier period should be appropriately extended to reduce the operating frequency of the switching devices and improve the service life of the devices.

[0052] In some specific embodiments, the reference voltage signal detection module can detect the reference voltage signal output by the adaptive resonant control module according to a fixed control cycle. Sampling is performed to obtain discrete sampled signals at various times, and the fluctuation of the reference voltage signal is detected through the following steps: Step 310: Extract the sampling point corresponding to the current time and the previous time. The discrete sampled signals at n sampling points are used to construct a window with a length of n. Evaluation sequence ,in This represents the discrete sampled signal at the current moment.

[0053] Step 320: Calculate the instantaneous rate of change index based on the following formula. : (6).

[0054] Reference signal instantaneous rate of change index Used for quantification The degree of fluctuation directly reflects the intensity of the fluctuation. In length The maximum fluctuation slope within the evaluation window ( The value can be reasonably selected based on the frequency of sampling the reference voltage signal. The larger the value, the richer or more drastic the harmonic components.

[0055] Step 330, calculate the instantaneous rate of change index With the preset first threshold Second threshold Compare, if Then Set to 1, if Then Set as ,if Then Set as ,in, .

[0056] Specifically, when the instantaneous rate of change index Greater than the first threshold At this time, it is determined that the proportion of harmonic components is high, causing the reference voltage signal to fluctuate drastically. In this case, by ordering... With the shortest basic carrier period Drive the operation of each switching device in the active power filter to ensure the operation of the filter. Precise tracking; when Less than the second threshold When, then determine The fluctuations are gentle, at this time by... Set to larger By appropriately extending the carrier period and reducing the switching frequency, system losses can be reduced; when Greater than or equal to and less than or equal to ,Right now When, then determine When the fluctuation is moderate, output a value that is centered. Achieving a balance between performance and efficiency.

[0057] It should be understood that the parameters involved in the above steps, such as the evaluation window length, are... First threshold Second threshold And settings under different fluctuation levels , All of these can be set according to the system hardware conditions (such as the sampling frequency of the voltage reference signal) and system performance indicators (such as the specific requirements for harmonic suppression in the power grid). Obviously, the first threshold... It should be set to be greater than the second threshold. .

[0058] The reference voltage signal detection module will be After the output is sent to the dual-carrier comparator, the dual-carrier comparator is based on Real-time adjustment of the period of the two triangular carrier signals (e.g., like...) Figure 8 As shown, , Twice This enables adaptive control of the switching frequency of the active power filter.

[0059] The specific embodiments of this application have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A harmonic suppression system for an active power filter based on single-cycle dual-carrier comparison control, comprising an active power filter, a measurement module, a harmonic current extraction module, and a control unit, wherein the active power filter is used to inject a harmonic suppression signal into the power grid, the measurement module is used to measure the real-time current and voltage signals of the power grid and the harmonic suppression signal output by the active power filter, and the harmonic current extraction module determines the harmonic current component signal of the power grid based on the real-time current and voltage signals of the power grid, characterized in that... The control unit includes: The frequency calculation module calculates the real-time fundamental frequency of the power grid based on the real-time current signal of the power grid. The adaptive resonant control module includes several parallel quasi-proportional resonant controllers for generating a reference voltage signal that can independently adjust the suppression effect of each harmonic. The transfer function of each quasi-proportional resonant controller is determined based on its corresponding harmonic order and the real-time fundamental frequency of the power grid. A dual-carrier comparator compares the reference voltage signal with two carrier signals in each switching cycle, wherein the two carrier signals are a rising triangular carrier signal and a falling triangular carrier signal; The PWM module, including D flip-flops and logic gates, generates and sends corresponding PWM drive signals to the gates of each switching device of the active power filter based on the two comparison results output by the dual-carrier comparator.

2. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 1, characterized in that, The active power filter includes a DC power supply, an energy storage capacitor, a first bridge arm, and a second bridge arm connected in parallel. The first bridge arm is connected in series with a first switching device and a second switching device, and the second bridge arm is connected in series with a third switching device and a fourth switching device. Each switching device switches on and off based on the high and low level signals received at its gate. The midpoints of the first and second bridge arms are connected to the power grid in parallel via coupled inductors.

3. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 2, characterized in that, The transfer function of the adaptive resonance control module for: ， in, This is the proportionality coefficient. For the harmonic order that needs to be suppressed, For the first The resonance coefficient corresponding to the subharmonic. The cutoff frequency, For the first The resonant angular frequency corresponding to the second harmonic. The real-time fundamental frequency of the power grid. It is a complex frequency domain operator.

4. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 3, characterized in that, The real-time fundamental frequency of the power grid is determined based on the time interval between the two most recent consecutive positive zero crossings of the real-time current signal of the power grid.

5. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 2, characterized in that, The dual-carrier comparator includes: The first comparator is used to compare the reference voltage signal with the falling triangular carrier signal in real time and output a binary first logic signal. When the reference voltage signal is higher than the falling triangular carrier signal, the first logic signal is 1, and when the reference voltage signal is lower than the falling triangular carrier signal, the first logic signal is 0. The second comparator is used to compare the reference voltage signal with the rising triangular carrier signal in real time and output a binary second logic signal. When the reference voltage signal is lower than the rising triangular carrier signal, the second logic signal is 1, and when the reference voltage signal is higher than the rising triangular carrier signal, the second logic signal is 0.

6. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 5, characterized in that, The logic gate circuit is generated based on the following formula and sends corresponding PWM drive signals to the gates of each switching device of the active power filter: ， in, , for The complementary state signal output by the trigger, The first logic signal, for complementary signals, This is the second logic signal. for complementary signals, , , , These are the PWM drive signals corresponding to the first, second, third, and fourth switching devices, respectively.

7. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 6, characterized in that, The logic gate circuit includes a first AND gate, a second AND gate, a third AND gate, a fourth AND gate, a first OR gate, a second OR gate, a first NOT gate, and a second NOT gate; The two input terminals of the first AND gate are respectively input and The two inputs of the second AND gate are respectively input to... and The two input terminals of the third AND gate are respectively input to and The two input terminals of the fourth AND gate are respectively input to and ; The two input terminals of the first OR gate are respectively connected to the output terminal of the first AND gate and the output terminal of the second AND gate. The output terminal of the first OR gate is used to output the PWM drive signal corresponding to the first switching device. The two input terminals of the second OR gate are respectively connected to the output terminals of the third AND gate and the fourth AND gate. The output terminal of the second OR gate is used to output the PWM drive signal corresponding to the third switching device. The input terminal of the first NOT gate is connected to the output terminal of the first OR gate, and the output terminal of the first NOT gate is used to output the PWM drive signal corresponding to the fourth switching device; The input terminal of the second NOT gate is connected to the output terminal of the second OR gate, and the output terminal of the second NOT gate is used to output the PWM drive signal corresponding to the second switching device.

8. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 1, characterized in that, The control unit further includes: The reference voltage signal detection module is used to detect the reference voltage signal. The fluctuations; The dual-carrier comparator adjusts the periods of the two carrier signals based on the fluctuations of the reference voltage signal, so that the adjusted carrier period... With a preset, system-allowed minimum base carrier period The following relationship must be satisfied: ,in, It is an integer greater than or equal to 1.

9. The active power filter harmonic suppression system based on single-cycle dual-carrier comparison control according to claim 8, characterized in that, The reference voltage signal detection module detects the reference voltage signal output by the adaptive resonance control module according to a fixed control cycle. Sampling is performed to obtain discrete sampled signals at various times, and the fluctuation of the reference voltage signal is detected through the following steps: Step 310: Extract the sampling point corresponding to the current time and the previous time. The discrete sampled signals at n sampling points are used to construct a window with a length of n. Evaluation sequence ,in This represents the discrete sampled signal at the current moment; Step 320: Calculate the instantaneous rate of change index based on the following formula. : （6）； Step 330, calculate the instantaneous rate of change index With the preset first threshold Second threshold Compare, if Then Set to 1, if Then Set as ,if Then Set as ,in, .

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