A method, system, medium, and apparatus for harmonic compensation and stability enhancement

Abstract

The application discloses a harmonic compensation and stability improvement method, system, medium and equipment, filters components of a grid voltage in a two-phase static coordinate system to obtain corresponding fundamental components; subtracts the fundamental components of the grid voltage from the components of the grid voltage in the two-phase static coordinate system to obtain total harmonic components of the grid voltage; filters the total harmonic components of the grid voltage by using multiple band-pass filters to obtain multiple harmonic components corresponding to frequencies; subtracts reference current instructions of an active power filter from the multiple harmonic components, and inputs the result as a new current reference instruction into a current controller; and based on a virtual harmonic admittance method, outputs harmonic compensation currents through current inner loop control in the two-phase static coordinate system to realize harmonic compensation on a nonlinear load with frequency coupling characteristics and suppression of harmonic compensation oscillation. The application can adapt to various complex grid environments and has relatively practical engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of power quality and harmonic compensation control technology, specifically relating to a harmonic compensation and stability improvement method, system, medium and equipment. Background Technology

[0002] In recent years, with the widespread application of distributed generation devices for new energy sources, a large number of harmonics have been generated in the power grid, seriously affecting the power quality. Due to the high requirements for power quality for the normal and stable operation of the power grid, the need for harmonic control methods for nonlinear loads is becoming increasingly urgent.

[0003] Among existing harmonic mitigation solutions, parallel active power filters (SAPFs) are the most widely used and effective method. Current research mainly focuses on harmonic detection, current control, topology optimization, and control loop design within the SAPF device itself, enabling the SAPF device to quickly and accurately compensate for detected harmonics.

[0004] However, when SAPF (Short-Area Power Filter) performs harmonic compensation in practical applications, resonance often occurs under various complex power grid environments, severely impacting its harmonic compensation effectiveness. Existing research primarily focuses on the SAPF itself, with limited attention paid to this resonance phenomenon. In complex power grid environments, SAPF typically forms a complex multi-source load interaction system with the power grid and nonlinear loads. This interaction system leads to system stability issues arising from the dynamic characteristics of SAPF across various frequency bands. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a harmonic compensation and stability improvement method, system, medium and device to address the shortcomings of the prior art, and to solve the technical problem of harmonic compensation oscillation and system stability caused by the frequency coupling characteristics of nonlinear loads in multi-source load interaction systems.

[0006] The present invention adopts the following technical solution:

[0007] A method for harmonic compensation and stability improvement includes the following steps:

[0008] S1. Perform Clark transformation on the grid voltage connected to the active power filter to obtain the components of the grid voltage in the two-phase stationary coordinate system.

[0009] S2. Determine the fundamental component of the grid voltage and the multiple pairs of fundamental bandpass filters that produce multiple harmonic pairs that generate resonance phenomena.

[0010] S3. Use the fundamental bandpass filter obtained in step S2 to filter the components of the grid voltage in the two-phase stationary coordinate system obtained in step S1 to obtain the corresponding fundamental component.

[0011] S4. Subtract the fundamental component obtained in step S3 from the components of the grid voltage in the two-phase stationary coordinate system obtained in step S1 to obtain the total harmonic components of the grid voltage.

[0012] S5. Use the multiple bandpass filters obtained in step S2 to filter the total harmonic component of the grid voltage obtained in step S4 to obtain the multiple harmonic components of the corresponding frequency.

[0013] S6. Subtract the reference current command of the active power filter from the multiple harmonic components obtained in step S5, and use the result as a new current reference command to input into the current controller. Based on the virtual harmonic admittance method, the harmonic compensation current is output through the current inner loop control in the two-phase stationary coordinate system to realize harmonic compensation for nonlinear loads with frequency coupling characteristics and suppression of harmonic compensation oscillation.

[0014] Specifically, in step S1, the component v of the grid voltage in the two-phase stationary coordinate system α and v β Specifically:

[0015]

[0016] Among them, v a v b and v c This is the sampled three-phase voltage signal.

[0017] Specifically, in step S2, the bandpass filter A(s) is:

[0018] A(s)=∑A k (s)

[0019] Among them, A k (s) represents multiple pairs of bandpass filters.

[0020] Furthermore, the frequencies of multiple harmonic pairs are symmetrical about the fundamental frequency, and multiple bandpass filters A k (s) is:

[0021]

[0022] Among them, K VAk σ represents the compensation coefficient of the correlated bandpass filter. k is the bandwidth coefficient of the correlated bandpass filter, and s is the complex frequency.

[0023] Specifically, in step S6, the virtual harmonic admittance method involves obtaining the current command i from harmonic detection.ref In the method of subtracting virtual harmonic admittance, the grid voltage v g The compensation signal obtained through the bandpass filter A(s) is then passed through the current control circuit H. i (s) controls the output voltage of the active power filter through PWM modulation.

[0024] Specifically, in step S6, the compensation coefficient and bandwidth settings of the bandpass filter that needs to compensate for the symmetrical subharmonics that exhibit resonance are consistent.

[0025] Specifically, in step S6, the bandpass filter for a specific harmonic is implemented using vector resonance discrete control, as follows:

[0026]

[0027] Among them, u nα u nβ For the input signal, y nα y nβ The output signal for this control cycle is y. (n-1)α y (n-1)β The output signal of the previous control cycle is given by K, where T is the discrete control cycle and K is the output signal of the previous control cycle. VAk σ represents the compensation coefficient of the correlated bandpass filter. k ω is the bandwidth coefficient of the correlated bandpass filter, and kω1 is the angular frequency of the compensation harmonic.

[0028] Secondly, embodiments of the present invention provide a harmonic compensation and stability enhancement system, comprising:

[0029] The transformation module performs Clark transformation on the grid voltage connected to the active power filter to obtain the grid voltage components in a two-phase stationary coordinate system.

[0030] The design module determines the fundamental component of the grid voltage and multiple pairs of fundamental bandpass filters that generate multiple harmonic pairs to produce resonance phenomena.

[0031] The filtering module uses the fundamental bandpass filter obtained by the design module to filter the grid voltage components in the two-phase stationary coordinate system obtained by the transformation module to obtain the corresponding fundamental component.

[0032] The calculation module uses the components of the grid voltage in the two-phase stationary coordinate system obtained by the transformation module to subtract the fundamental component obtained by the filtering module, and then obtains the total harmonic components of the grid voltage.

[0033] The processing module uses multiple bandpass filters obtained from the design module to filter the total harmonic component of the grid voltage obtained from the calculation module, thereby obtaining the multiple harmonic components of the corresponding frequencies.

[0034] The control module subtracts the reference current command from the active power filter from the multiple harmonic components obtained by the processing module, and uses the result as a new current reference command to input into the current controller. Based on the virtual harmonic admittance method, the output harmonic compensation current is controlled by the inner current loop in the two-phase stationary coordinate system to achieve harmonic compensation for nonlinear loads with frequency coupling characteristics, as well as harmonic compensation oscillation suppression.

[0035] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described harmonic compensation and stability improvement method.

[0036] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described harmonic compensation and stability improvement method.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] This invention proposes a harmonic compensation and stability enhancement method. Based on theoretical research and analysis of the overall harmonic compensation effect and stability of a SAPF harmonic compensation system, this invention presents a control method for improving the harmonic compensation effect and system stability of an active power filter (APF) for nonlinear loads with frequency coupling characteristics. The method involves sampling the grid voltage and adding a bandpass filter result of the symmetrical subharmonic pair of the grid voltage to the current command of the traditional current inner loop control with a certain weight. This improves the harmonic compensation effect and increases system stability. The harmonic virtual impedance method makes the grid voltage admittance of the SAPF current inner loop control loop approach resistive, providing damping for the SAPF parasitic feedback system and effectively suppressing the generation of right-half-plane poles in the control system, thereby suppressing the harmonic compensation oscillation phenomenon that easily occurs in traditional methods. Simultaneously, for nonlinear loads with frequency coupling characteristics, a method for simultaneously stabilizing symmetrical subharmonics is proposed. Compared with other stabilization methods, this method specifically improves the harmonic compensation effect of the active power filter and enhances the overall system stability. The existing implementation steps do not require adding new sensors or other hardware to the existing active power filter equipment. Furthermore, the implementation steps are clear and straightforward, the method is simple and efficient, and the increased computational cost is relatively small. Therefore, this invention has excellent applicability and transferability, and has high practical value in engineering practice.

[0039] Furthermore, the grid voltage component v in the two-phase stationary coordinate system is obtained by using coordinate transformation. α and v βAs a key input signal for the harmonic virtual impedance method, its parameter values ​​in the two-phase coordinate system can be obtained using coordinate transformation, which is more convenient and faster. In traditional SAPF systems, commonly used phase-locked loops acquire this parameter. Therefore, acquiring this parameter for virtual impedance adjustment does not require additional sensors, making the harmonic virtual impedance method easier to apply and migrate.

[0040] Furthermore, the core principle of the harmonic virtual impedance method lies in adjusting the system characteristics at the compensation harmonic frequency. Therefore, a bandpass filter is used to precisely adjust the characteristics of the SAPF without affecting the characteristics at other frequency points of the system. The bandpass filter can selectively extract the components of each compensation harmonic frequency, helping to achieve precise adjustment of the characteristics at specific frequency points.

[0041] Furthermore, due to the frequency coupling characteristics of the nonlinear load, the symmetrical sub-compensated harmonics share their oscillation characteristics. Therefore, harmonic pair filters centered on the fundamental frequency, such as the -5th and 7th harmonic pairs, are set up. This allows for simultaneous sedation of the symmetrical sub-harmonics, improving the sedation effect. SAPF harmonic oscillations are caused by line impedance and load impedance, and their range of influence is wide. Therefore, it is necessary to sedate all compensation harmonic pairs in the dangerous resonance region. Setting up multiple pairs of bandpass filters can simultaneously sedate harmonics in the dangerous region, effectively improving system stability and harmonic compensation performance.

[0042] Furthermore, harmonic virtual admittance is mainly achieved by adding a control loop corresponding to the harmonic to the inner current loop, thereby adjusting the overall grid admittance of the system to tend towards resistivity. Resistive grid admittance suppresses the resonance effect of SAPF with the load and grid line impedance, effectively achieving harmonic oscillation suppression.

[0043] Furthermore, since symmetrical subharmonics share oscillation characteristics, their resonance characteristics are essentially the same. Therefore, the compensation coefficients and bandwidth settings of the bandpass filters for symmetrical subharmonics should be consistent. This prevents situations where the oscillation of one harmonic leads to the simultaneous oscillation of its symmetrical subharmonics due to different parameter settings. Consistent parameter settings are more conducive to achieving harmonic oscillation stabilization and also reduce the difficulty of parameter design. In addition, based on the frequency domain characteristics A(s) of the designed bandpass filter, the improvement effect of the harmonic virtual admittance method in different system environments can be adjusted more simply and efficiently by adjusting the compensation coefficients and bandwidth parameters.

[0044] Furthermore, vector discrete control is a common control method. It offers high control accuracy, is relatively easy to implement in engineering, requires less computation, and has lower performance requirements. Simultaneously, its implementation structure is simple, facilitating the adjustment of control parameters and monitoring of the control process, and exhibits good control stability. It can effectively digitally implement the harmonic virtual impedance method, improving system stability and filtering performance.

[0045] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0046] In summary, this invention, based on the existing control method of active power filters, incorporates the harmonic components of the grid voltage into the command value of the current control inner loop of the active power filter through a bandpass filter. This adjusts the grid voltage admittance of the active power filter to be more resistive, thereby suppressing harmonic compensation resonance and improving the harmonic compensation effect. The flexible and adjustable bandpass filter settings allow this invention to adapt to various system operating environments, exhibiting wide applicability and portability. In practical applications, this invention can better achieve harmonic compensation and improve the overall stability of the system. Furthermore, a simulation model of an active power filter applied to compensate for nonlinear load harmonics was built, and the proposed control method and related algorithms were verified through simulation, demonstrating the correctness, practicality, and reliability of the method. This invention exhibits good stability, low implementation cost, simple and efficient structure, wide applicability, and adaptability to various complex power grid environments, possessing significant practical engineering application value.

[0047] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating the operation of the present invention in an active power filter compensating for a nonlinear load system.

[0049] Figure 2 This is a system control block diagram of a specific implementation scheme of the present invention;

[0050] Figure 3 The figures show the simulated waveforms of the grid voltage and current before and after harmonic compensation of the nonlinear load using the proposed method, as well as the harmonic analysis diagram after harmonic compensation. (a) shows the simulated waveforms of the grid voltage and current before and after harmonic compensation without using the present invention; (b) shows the harmonic analysis diagram of the grid voltage and current after harmonic compensation without using the present invention; (c) shows the simulated waveforms of the grid voltage and current before and after harmonic compensation using the present invention; and (d) shows the harmonic analysis diagram of the grid voltage and current after harmonic compensation using the present invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0053] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0054] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" relationship.

[0055] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0056] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0057] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0058] This invention provides a harmonic compensation and stability improvement method. Based on a small-signal dynamic model of a complex source-load interaction system including grid impedance, a nonlinear load with frequency coupling characteristics, and a SAPF (Simplified Power Filter), a series of theoretical analyses and derivations are performed to analyze the corresponding resonance and system stability issues. Building upon the existing control theory and dynamic model of active power filters, this invention proposes a harmonic virtual admittance method. By adjusting the grid admittance in the traditional current inner-loop control method of the active power filter, it simultaneously sedates two mutually symmetrical harmonics to achieve a good sedation effect. This solves the problem of harmonic compensation oscillations and system stability caused by system resonance in multi-source-load interaction systems due to the frequency coupling characteristics of nonlinear loads.

[0059] This invention discloses a method for harmonic compensation and stability improvement, comprising the following steps:

[0060] S1, sampling the grid voltage v connected to the active power filter. g Then, a Clark transformation is performed to obtain the components v of the grid voltage in the two-phase stationary coordinate system. gα v gβ ;

[0061] The Clark transform converts the sampled three-phase voltage signal v a v b and v c Component v converted to two-phase stationary coordinate system α v β The transformation equation is:

[0062]

[0063] S2. Design multiple bandpass filters A1(s) symmetrically centered on the fundamental voltage component ω1 and the frequency at which resonance occurs, containing multiple harmonic pairs (k+1)ω1 and (-k+1)ω1. k+1 (s), A -k+1 (s);

[0064] Bandpass filter A1(s), A k+1 (s), A -k+1 (s) is designed as follows:

[0065]

[0066] Among them, K VAk σ represents the compensation coefficient of the correlated bandpass filter. k This represents the bandwidth coefficient of the correlated bandpass filter.

[0067] The characteristics of bandpass filter A(s) are the superposition of multiple bandpass filters:

[0068] A(s)=∑A k (s)

[0069] S3. Using the fundamental bandpass filter A1(s) designed in step S2, apply the voltage component v in the stationary coordinate system of the grid voltage obtained in step S1. gα v gβ Filtering is performed to obtain its fundamental component v g1α v g1β ;

[0070] S4. Use the original grid voltage v from step S1. gα v gβ Subtract the fundamental component v obtained in step S3 g1α v g1β The total harmonic component v in the grid voltage is obtained. ghα v ghβ ;

[0071] S5. Use the multiple bandpass filters A designed in step S2. k+1 (s), A -k+1 (s) Filter the total harmonic component obtained in step S4 to obtain the multiple harmonic components v with corresponding frequencies of (k+1)w1, (-k+1)w1, etc. g(k+1)α v g(k+1)β and v g(-k+1)α v g(-k+1)β ;

[0072] S6. The reference current command I of the traditional active power filter. refα I refβ The voltage component v of the specific multiple harmonics obtained in step S5 g(k+1)α v g(k+1)β and v g(-k+1)α v g(-k+1)β After the difference is calculated, it serves as a new current reference command. Through the current control inner loop in the two-phase stationary coordinate system, the harmonic compensation current output by the inverter is controlled, thereby achieving harmonic compensation for nonlinear loads with frequency coupling characteristics and suppression of harmonic compensation oscillations.

[0073] The bandpass filter compensation coefficient at the fundamental frequency is set to 1, and the bandwidth is less than 4 Hz to ensure that the bandpass filter has a good filtering effect. When compensating for symmetrical subharmonics in the dangerous resonance region, the compensation coefficient and bandwidth of the bandpass filter should be set to be consistent and within 6 Hz.

[0074] The design is mainly based on the grid voltage admittance of the inner loop control of the regulating current to resistive. The specific implementation of the bandpass filter for a certain harmonic is vector resonant discrete control, as shown below:

[0075]

[0076] Among them, u nα u nβ For the input signal, y nα y nβ The output signal for this control cycle is y. (n-1)α y (n-1)β The output signal of the previous control cycle is given by K, where T is the discrete control cycle and K is the output signal of the previous control cycle. VAk σ represents the compensation coefficient of the correlated bandpass filter. k ω is the bandwidth coefficient of the correlated bandpass filter, and kω1 is the angular frequency of the compensation harmonic.

[0077] In another embodiment of the present invention, a harmonic compensation and stability enhancement system is provided. This system can be used to implement the above-mentioned harmonic compensation and stability enhancement method. Specifically, the harmonic compensation and stability enhancement system includes a transformation module, a design module, a filtering module, a calculation module, a processing module, and a control module.

[0078] The transformation module performs Clark transformation on the grid voltage connected to the active power filter to obtain the grid voltage components in a two-phase stationary coordinate system.

[0079] The design module determines the fundamental component of the grid voltage and multiple pairs of fundamental bandpass filters that generate multiple harmonic pairs to produce resonance phenomena.

[0080] The filtering module uses the fundamental bandpass filter obtained by the design module to filter the grid voltage components in the two-phase stationary coordinate system obtained by the transformation module to obtain the corresponding fundamental component.

[0081] The calculation module uses the components of the grid voltage in the two-phase stationary coordinate system obtained by the transformation module to subtract the fundamental component obtained by the filtering module, and then obtains the total harmonic components of the grid voltage.

[0082] The processing module uses multiple bandpass filters obtained from the design module to filter the total harmonic component of the grid voltage obtained from the calculation module, thereby obtaining the multiple harmonic components of the corresponding frequencies.

[0083] The control module subtracts the reference current command from the active power filter from the multiple harmonic components obtained by the processing module, and uses the result as a new current reference command to input into the current controller. Based on the virtual harmonic admittance method, the output harmonic compensation current is controlled by the inner current loop in the two-phase stationary coordinate system to achieve harmonic compensation for nonlinear loads with frequency coupling characteristics, as well as harmonic compensation oscillation suppression.

[0084] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment of the present invention can be used for the operation of harmonic compensation and stability improvement methods, including:

[0085] Clark transformation is performed on the grid voltage connected to the active power filter to obtain the grid voltage components in a two-phase stationary coordinate system. The fundamental component of the grid voltage and multiple pairs of fundamental bandpass filters that generate multiple harmonic pairs are determined. The fundamental bandpass filters are used to filter the grid voltage components in the two-phase stationary coordinate system to obtain the corresponding fundamental components. The fundamental component is subtracted from the grid voltage components in the two-phase stationary coordinate system to obtain the total harmonic components of the grid voltage. The total harmonic components of the grid voltage are filtered using multiple bandpass filters to obtain the multiple harmonic components of the corresponding frequencies. The difference between the reference current command of the active power filter and the multiple harmonic components is used as a new current reference command input to the current controller. Based on the virtual harmonic admittance method, the harmonic compensation current is output through the inner current loop control in the two-phase stationary coordinate system to achieve harmonic compensation for nonlinear loads with frequency coupling characteristics and suppression of harmonic compensation oscillations.

[0086] In another embodiment of the present invention, a storage medium is also provided, specifically a computer-readable storage medium (memory). This computer-readable storage medium is a memory device in a terminal device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and extended storage media supported by the terminal device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device.

[0087] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the harmonic compensation and stability improvement methods in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps:

[0088] Clark transformation is performed on the grid voltage connected to the active power filter to obtain the grid voltage components in a two-phase stationary coordinate system. The fundamental component of the grid voltage and multiple pairs of fundamental bandpass filters that generate multiple harmonic pairs are determined. The fundamental bandpass filters are used to filter the grid voltage components in the two-phase stationary coordinate system to obtain the corresponding fundamental components. The fundamental component is subtracted from the grid voltage components in the two-phase stationary coordinate system to obtain the total harmonic components of the grid voltage. The total harmonic components of the grid voltage are filtered using multiple bandpass filters to obtain the multiple harmonic components of the corresponding frequencies. The difference between the reference current command of the active power filter and the multiple harmonic components is used as a new current reference command input to the current controller. Based on the virtual harmonic admittance method, the harmonic compensation current is output through the inner current loop control in the two-phase stationary coordinate system to achieve harmonic compensation for nonlinear loads with frequency coupling characteristics and suppression of harmonic compensation oscillations.

[0089] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0090] Please see Figure 1 The specific application scenarios for harmonic compensation and stability improvement control methods for nonlinear loads are as follows:

[0091] The power grid supplies power to a nonlinear load. An active power filter is connected in parallel at the front end of the nonlinear load to sample the grid connection point voltage v. g Load current i L The harmonic current command i is generated by extracting the harmonic components from the load current through the harmonic detection stage. ref Then, the current controller tracks the harmonic current command to generate each compensation harmonic current i. c Compensating for harmonic current i c The input to the power grid is fed through an active power filter to compensate for harmonics generated by nonlinear loads. The virtual harmonic admittance method uses the sampled grid connection point v. g By using the designed filter A(s), multiple harmonic components requiring compensation are obtained. These harmonic components are then used as negative feedback to generate a new harmonic compensation current command. This achieves the harmonic compensation effect of the active power filter and uses the virtual harmonic admittance method to improve system stability and ensure the harmonic compensation effect.

[0092] Please see Figure 2 The control block diagram of the active power filter using the virtual harmonic admittance method is as follows:

[0093] Current command i is obtained from harmonic detection ref In the method of subtracting virtual harmonic admittance, the grid voltage v g The compensation signal obtained through the bandpass filter A(s) is then passed through the current control circuit H. i (s) controls the output voltage of the active power filter through PWM modulation. The actual output current i is sampled. cAs negative feedback, it is input into the current command. Analyzing this control block diagram, it can be seen that the virtual harmonic admittance method adjusts the grid impedance characteristics of the active power filter, making it more resistive, suppressing the occurrence of harmonic compensation oscillations, and improving the stability of the system.

[0094] Please see Figure 3 In the simulation, the nonlinear load is a three-phase uncontrolled rectifier. Traditional harmonic compensation and virtual harmonic admittance method harmonic compensation are added at 1s respectively. The negative 11th order and positive 13th order harmonics that are prone to harmonic compensation oscillation are compensated. Among them, (a) is the waveform of the grid current before and after traditional harmonic compensation, (b) is the harmonic analysis of the grid current after traditional harmonic compensation, (c) is the waveform of the grid current before and after virtual harmonic admittance method harmonic compensation, and (d) is the waveform of the grid current before and after virtual harmonic admittance method harmonic compensation.

[0095] As can be seen from the simulation results (a) and (b), after performing traditional harmonic compensation for 1 second, the system exhibits harmonic compensation resonance, and the grid voltage and grid current are significantly distorted; the harmonics generated by the nonlinear load are not effectively compensated for by the negative eleventh and positive thirteenth harmonics at the resonant frequency.

[0096] Simulation results (c) and (d) show that incorporating the virtual harmonic admittance method proposed in this invention into the traditional control loop effectively suppresses harmonic oscillations and improves system stability. It also effectively compensates for harmonics at various frequency points caused by nonlinear loads.

[0097] In summary, this invention provides a harmonic compensation and stability enhancement method, system, medium, and device. Building upon existing active power filter control methods, it incorporates harmonic components of the grid voltage into the command value of the active power filter's current control inner loop using a bandpass filter. This adjusts the grid voltage admittance of the active power filter to be more resistive, thereby suppressing harmonic compensation resonance. For nonlinear loads, it achieves better harmonic compensation and improves overall system stability. Furthermore, a simulation model of an active power filter applied to compensate for harmonics in nonlinear loads was built, and the proposed control method and related algorithms were verified through simulation, demonstrating the correctness, practicality, and reliability of the method. This invention exhibits good stability, low implementation cost, simple and efficient structure, wide applicability, and adaptability to various complex power grid environments, possessing significant practical engineering application value.

[0098] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0099] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0100] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0101] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0102] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0103] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0104] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0105] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0106] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0107] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0108] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for harmonic compensation and stability improvement, characterized in that, Includes the following steps: S1. The grid voltage connected to the active power filter is... The transformation yields the components of the grid voltage in the two-phase stationary coordinate system. S2. Determine the fundamental component of the grid voltage and the multiple pairs of fundamental bandpass filters that produce multiple harmonic pairs that generate resonance phenomena. S3. Use the fundamental bandpass filter obtained in step S2 to filter the components of the grid voltage in the two-phase stationary coordinate system obtained in step S1 to obtain the corresponding fundamental component. S4. Subtract the fundamental component obtained in step S3 from the components of the grid voltage in the two-phase stationary coordinate system obtained in step S1 to obtain the total harmonic components of the grid voltage. S5. Use the multiple bandpass filters obtained in step S2 to filter the total harmonic component of the grid voltage obtained in step S4 to obtain the multiple harmonic components of the corresponding frequency. S6. Subtract the reference current command of the active power filter from the multiple harmonic components obtained in step S5, and use the result as a new current reference command input to the current controller. Based on the virtual harmonic admittance method, the harmonic compensation current is output through the inner current loop control in the two-phase stationary coordinate system to achieve harmonic compensation for nonlinear loads with frequency coupling characteristics and suppression of harmonic compensation oscillations. The compensation coefficient and bandwidth settings of the bandpass filter for the symmetrical subharmonics that need to be compensated for resonance are consistent. The implementation method of the bandpass filter for a specific harmonic is vector resonance discrete control, specifically: in, , For input signal, , This is the output signal for this control cycle. , This is the output signal of the previous control cycle. For discrete control periods, These are the compensation coefficients for the correlated bandpass filter. The bandwidth coefficient of the correlated bandpass filter. To compensate for the angular frequency of harmonics.

2. The harmonic compensation and stability improvement method according to claim 1, characterized in that, In step S1, the components of the grid voltage in the two-phase stationary coordinate system and Specifically: in, , and This is the sampled three-phase voltage signal.

3. The harmonic compensation and stability improvement method according to claim 1, characterized in that, In step S2, the bandpass filter for: in, It consists of multiple pairs of bandpass filters.

4. The harmonic compensation and stability improvement method according to claim 3, characterized in that, Multiple harmonic pairs have frequencies symmetrical about the fundamental frequency, and multiple bandpass filters. for: in, These are the compensation coefficients for the correlated bandpass filter. The bandwidth coefficient of the correlated bandpass filter. It is a complex frequency.

5. The harmonic compensation and stability improvement method according to claim 1, characterized in that, In step S6, the virtual harmonic admittance method specifically involves obtaining the current command from harmonic detection. In the method of subtracting virtual harmonic admittance, the grid voltage Through bandpass filter The obtained compensation signal then passes through the current control circuit. The output voltage of the active power filter is controlled by PWM modulation.

6. A harmonic compensation and stability enhancement system, characterized in that, include: The conversion module converts the grid voltage connected to the active power filter. The transformation yields the components of the grid voltage in the two-phase stationary coordinate system. The design module determines the fundamental component of the grid voltage and multiple pairs of fundamental bandpass filters that generate multiple harmonic pairs to produce resonance phenomena. The filtering module uses the fundamental bandpass filter obtained by the design module to filter the grid voltage components in the two-phase stationary coordinate system obtained by the transformation module to obtain the corresponding fundamental component. The calculation module uses the components of the grid voltage in the two-phase stationary coordinate system obtained by the transformation module to subtract the fundamental component obtained by the filtering module, and then obtains the total harmonic components of the grid voltage. The processing module uses multiple bandpass filters obtained from the design module to filter the total harmonic component of the grid voltage obtained from the calculation module, thereby obtaining the multiple harmonic components of the corresponding frequencies. The control module subtracts the reference current command from the active power filter from the multiple harmonic components obtained by the processing module, and inputs the result as a new current reference command to the current controller. Based on the virtual harmonic admittance method, it outputs harmonic compensation current through the inner current loop control in a two-phase stationary coordinate system. This achieves harmonic compensation for nonlinear loads with frequency coupling characteristics, as well as harmonic compensation oscillation suppression. The compensation coefficients and bandwidth settings of the bandpass filter for the symmetrical subharmonics exhibiting resonance phenomena are consistent. The implementation of the bandpass filter for a specific harmonic is vector resonance discrete control, specifically: in, , For input signal, , This is the output signal for this control cycle. , This is the output signal of the previous control cycle. For discrete control periods, These are the compensation coefficients for the correlated bandpass filter. The bandwidth coefficient of the correlated bandpass filter. To compensate for the angular frequency of harmonics.

7. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform the method of any one of claims 1 to 5.

8. A computing device, characterized in that, include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including steps for performing the method of any one of claims 1 to 5.

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