A frequency-adaptive method for suppressing harmonics in parallel of multiple inverters with wide-frequency domain loads

Abstract

A frequency-adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method adds a typical harmonic frequency droop control link to the traditional fundamental domain droop control scheme, and uses a data sliding window method to acquire and perform FFT analysis on the grid-connected point voltage signal to obtain the typical harmonic frequency and amplitude on the load side, thereby achieving adaptive adjustment of the harmonic domain droop link and targeted offset of the load side harmonics. This invention can realize active perception of load side harmonics and active frequency-order droop control parameter adjustment, so as to achieve the purpose of actively adapting to load changes, suppressing grid-connected point harmonic distortion and improving power quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of multi-inverter parallel droop control, and in particular relates to a frequency-adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method. Background Art

[0002] As power conversion evolves toward higher voltages and higher powers, existing single inverters are no longer sufficient. Furthermore, various inverter applications often place high demands on reliability and redundancy. Consequently, multi-inverter paralleling technology has gradually developed and matured. Multi-inverter paralleling technology first emerged in UPS parallel control, and subsequently found applications in train and ship auxiliary power supplies, as well as renewable energy generation. With the widespread integration and large-scale application of renewable energy in recent years, distributed inverter paralleling technology has continued to develop and optimize, expanding its application scope. Generally speaking, it can be categorized into two control modes: grid-connected and grid-connected.

[0003] In the UPS (uninterruptible power supply) sector, auxiliary power supply, and islanded renewable energy generation, multi-inverter control often faces challenges with power sharing, current distribution, and circulating current due to the lack of voltage and frequency support from the main power grid. Currently, various multi-inverter paralleling technologies exist, including centralized control, master-slave control, distributed logic control, and interconnection-free control. Centralized control consists of a parallel control unit and each inverter submodule. The parallel control unit detects the total output current and divides it by the average value to determine the current command for each inverter submodule. When each parallel unit is controlled by a single synchronization signal, if the output voltage frequency and phase deviations are small, the current deviations between units can be assumed to be caused by inconsistent voltage amplitudes. Therefore, this control approach directly applies the current deviation as a compensation to the voltage command to each inverter power unit to eliminate current imbalances. However, centralized control relies too heavily on the centralized controller, making the entire system inoperable in the event of a failure. Furthermore, increasing or decreasing the number of submodules presents significant challenges. Furthermore, to ensure phase and frequency signals, synchronization pulses must be highly consistent, which places high demands on communication and is difficult to implement. In master-slave control, current sharing is distributed among the submodules. The master determines voltage information and all current information for the slaves to achieve current sharing. Compared to centralized control, master-slave control can achieve a certain degree of redundancy and improve reliability. However, master-slave control places higher demands on the master, and if the master fails, redundant control is still not possible. Distributed logic control truly enables each inverter power module to be independent of a centralized control unit or a master module. It can independently detect and control its operating status within the system, thereby achieving reasonable output power distribution among modules. Distributed logic parallel control technology is an independent parallel control method. It uses a control strategy that integrates the current and frequency signals of each power module in each inverter to derive compensation signals for each frequency and voltage. This method achieves true N+1 parallel operation, and the failure of one module does not affect the parallel operation of other modules. However, this solution is relatively complex and has limited practical application in actual engineering applications.

[0004] Currently, multi-machine parallel control schemes based on interconnection-free wiring are widely used in engineering practice and have achieved good results. Droop control is a representative example, effectively achieving power sharing and plug-and-play features. In this droop control scheme, each inverter simulates the droop characteristics of a generator by detecting its own output active and reactive power to adjust the output voltage amplitude and frequency. Compared to interconnection-based control schemes, this scheme does not require a power control bus or an average current bus, making it easier to implement and more practical.

[0005] With the rapid development of power electronics technology, power conversion methods have become increasingly diverse. However, the integration of various power conversion devices, such as inverters and rectifiers, has significantly increased circuit nonlinearity, posing significant challenges to grid power quality. Traditional droop control methods calculate active and reactive power based on voltage and current information within the fundamental frequency range to achieve droop control in the fundamental frequency domain. However, when nonlinear loads are connected, droop control strategies based on the fundamental frequency domain are unable to offset the generated harmonics, resulting in severe harmonic distortion at the grid connection point and affecting power quality. Summary of the Invention

[0006] In order to address the deficiencies in the prior art, the present invention proposes a frequency-adaptive multi-inverter parallel wide-band load harmonic suppression method. By adding a typical harmonic sub-droop control link to the traditional fundamental domain droop control scheme, and using a data sliding window method to acquire and perform FFT analysis on the grid-connected point voltage signal, the typical harmonic frequency and amplitude on the load side are obtained, and adaptive adjustment of the harmonic domain droop link is achieved. The load side harmonics are targetedly offset to achieve the purpose of suppressing grid-connected point harmonic distortion and improving power quality. Therefore, one of the problems to be solved by the present invention is to achieve harmonic cancellation when nonlinear loads are connected by introducing a harmonic domain frequency division droop control link on the basis of fundamental domain droop control, thereby improving the harmonic distortion on the load side and enhancing power quality. The second problem to be solved by the present invention is to use a data sliding window and FFT analysis method to more conveniently and accurately acquire load side harmonic information to achieve directional frequency division droop control.

[0007] The present invention adopts the following technical solutions.

[0008] A frequency adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method comprises the following steps:

[0009] Step 1: Collect the grid connection point voltage and the inverter side voltage and current;

[0010] Step 2: Based on the grid connection point voltage collected in step 1, the grid connection point voltage signal is acquired and FFT analyzed using a data sliding window method to obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave;

[0011] Step 3: Using the typical harmonic frequencies and amplitudes on the load side obtained in step 2, obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control. Furthermore, using the calculation results under the fundamental wave obtained in step 2, perform fundamental wave power calculations as well as calculations for active power-frequency control and reactive power-voltage control.

[0012] In step 4, according to the control parameters obtained in step 3, the fundamental wave droop control and the harmonic droop control are used to obtain the command values ​​respectively, and the obtained command values ​​are superimposed to achieve zero-difference tracking of the voltage and current commands. After superposition, the SPWM modulation command value is obtained, and the SPWM modulation command value is used to implement SPWM modulation.

[0013] Preferably, the step 2 uses a data sliding window method to acquire and perform FFT analysis on the grid connection point voltage signal to obtain the typical harmonic frequency and amplitude on the load side, specifically including:

[0014] The grid connection point voltage signal of the nth sampling sample is expressed as x n , where 0≤n≤N-1, N and n are both positive integers, and the Fourier transform is performed on these N samples, which is shown in formula (2):

[0015]

[0016] Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition.

[0017] Preferably, obtaining the calculation result under the fundamental wave in step 2 specifically includes:

[0018] According to the voltage and current on the inverter side, information processing and coordinate transformation are performed in the fundamental domain to obtain the calculation results under the fundamental domain. The information processing and coordinate transformation is to transform the voltage and current on the inverter side from a three-phase rotating coordinate system to a two-phase stationary coordinate system, which is specifically expressed as shown in formulas (3-1) and (3-2):

[0019]

[0020]

[0021] Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i cThe C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

[0022] Preferably, the typical harmonic frequency and amplitude of the load side obtained in step 2 are used in step 3 to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, specifically including:

[0023] According to formula (4), the control parameters such as voltage droop coefficient and frequency droop coefficient in frequency division droop control are obtained:

[0024]

[0025] Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E h are the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h.

[0026] Preferably, the step 3 uses the calculation result obtained in step 2 under the fundamental wave to perform fundamental wave power calculation and calculation of active power-frequency control and reactive power-voltage control, specifically including:

[0027] The fundamental power is calculated by formula (5):

[0028]

[0029] Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ;

[0030] Active power-frequency control and reactive power-voltage control are expressed as the following equations:

[0031]

[0032] Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

[0033] Preferably, the control parameters obtained in step 3 in step 4 are subjected to fundamental wave droop control and harmonic droop control to obtain command values ​​respectively, including:

[0034] Under the condition of i=1, as shown in formula (6), through the droop expression shown in formula (6) under the condition of i=1, ω is obtained according to the output power n With E n , these two variables are the frequency command value and amplitude command value of the output fundamental voltage respectively; similarly, the harmonic droop control is as shown in formula (6) under the condition of i>1. Through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively.

[0035] A frequency-adaptive multi-inverter parallel wide-frequency load harmonic suppression system comprising:

[0036] An acquisition module, which is used to collect the grid connection point voltage and the inverter side voltage and current;

[0037] A data sliding window and FFT analysis module is used to acquire and perform FFT analysis on the grid connection point voltage signal using a data sliding window method based on the collected grid connection point voltage, obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave;

[0038] a calculation module configured to use the obtained load-side typical harmonic frequencies and amplitudes to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, and to use the obtained calculation results under the fundamental wave to perform fundamental wave power calculations and calculations for active power-frequency control and reactive power-voltage control;

[0039] An adjustment module is configured to obtain command values ​​respectively through fundamental wave droop control and harmonic droop control according to the obtained control parameters, and to superimpose the obtained command values ​​to achieve error-free tracking of voltage and current commands, thereby obtaining an SPWM modulation command value after superposition, and to implement SPWM modulation through the SPWM modulation command value.

[0040] Preferably, the data sliding window and FFT analysis module is further configured to represent the grid connection point voltage signal as the nth sampling sample as x n , where 0≤n≤N-1, N and n are both positive integers, and the Fourier transform is performed on these N samples, which is shown in formula (2):

[0041]

[0042] Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition.

[0043] Preferably, the data sliding window and FFT analysis module is further used for information processing and coordinate transformation in the fundamental domain based on the inverter side voltage and current to obtain a calculation result under the fundamental domain; wherein the information processing and coordinate transformation is to perform a three-phase rotating coordinate system-two-phase stationary coordinate system transformation on the inverter side voltage and current, which is specifically expressed as shown in formula (3-1) and formula (3-2):

[0044]

[0045]

[0046] Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i c The C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

[0047] Preferably, the calculation module is further configured to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control according to formula (4):

[0048]

[0049] Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E h are the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h.

[0050] Preferably, the calculation module is further configured to calculate the fundamental wave power using formula (5):

[0051]

[0052] Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ;

[0053] Active power-frequency control and reactive power-voltage control are expressed as the following equations:

[0054]

[0055] Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

[0056] Preferably, the adjustment module is further configured to obtain ω according to the output power by using the droop expression shown in formula (6) under the condition that i=1. n With E n , these two variables are the frequency command value and amplitude command value of the output fundamental voltage respectively; similarly, the harmonic droop control is as shown in formula (6) under the condition of i>1. Through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively.

[0057] A terminal includes a processor and a storage medium;

[0058] The storage medium is used to store instructions;

[0059] The processor is configured to operate according to the instructions to execute the steps of the frequency adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method.

[0060] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the frequency-adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method.

[0061] The beneficial effect of the present invention is that, compared with the prior art, the present invention adds a typical harmonic frequency droop control link to the traditional fundamental wave domain droop control scheme, and uses a data sliding window method to acquire and perform FFT analysis on the grid connection point voltage signal to obtain the typical harmonic frequency and amplitude on the load side, thereby realizing adaptive adjustment of the harmonic domain droop link and targetedly offsetting the load side harmonics. The invention can realize active perception of load side harmonics and active frequency-order droop control parameter adjustment, thereby achieving the purpose of actively adapting to load changes, suppressing grid connection point harmonic distortion and improving power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a schematic diagram of the actual working condition of the inverter described in the present invention after being connected to a nonlinear load;

[0063] Figure 2 This is a schematic diagram of the frequency adaptive multi-inverter parallel wide-frequency load harmonic suppression method described in the present invention;

[0064] Figure 3 This is a flow chart of the frequency adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method described in the present invention;

[0065] Figure 4 This is a structural diagram of the frequency adaptive multi-inverter parallel wide-frequency load harmonic suppression system described in the present invention;

[0066] In the figure: 1: the first inverter power supply device; 2: the nth inverter power supply device; 3: the grid connection point; 4: the rectifier type nonlinear load; 5: the nonlinear resistance and inductance load; 6: the linear resistance and inductance load; 7: the inverter power supply; 8: the filter capacitor; 9: the current sampling device; 10: the filter capacitor voltage sampling device; 11: the grid connection point voltage sampling device. DETAILED DESCRIPTION

[0067] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts are all within the scope of protection of the present invention.

[0068] After the nonlinear loads represented by rectifiers and nonlinear inductors and resistors are connected, the power quality on the grid side (load side) deteriorates and the harmonic distortion is more serious, which affects the power quality of itself and other parallel electrical equipment, and even endangers the safety of the equipment.

[0069] The present invention provides a frequency adaptive multi-inverter parallel wide frequency domain load harmonic suppression method, such as Figure 2 and Figure 3 As shown, the following steps are included:

[0070] Step 1: Collect the grid connection point voltage and the inverter side voltage and current;

[0071] Specifically, in step 1, the grid connection point voltage and the inverter-side voltage and current are collected. This includes: a current sampling device 9, a filter capacitor voltage sampling device 10, and a grid connection point voltage sampling device 11 for respectively collecting the output current of the filter device, the capacitor voltage of the filter device, and the voltage information on the load side; the output current of the filter device and the capacitor voltage of the filter device form the inverter-side voltage and current. The filter capacitor voltage sampling device and the grid connection point voltage sampling device can be mutual inductors or voltage sensors, and the current sampling device can be a current sensor.

[0072] Step 2: Based on the grid connection point voltage collected in step 1, the grid connection point voltage signal is acquired and FFT analyzed using a data sliding window method to obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave;

[0073] In a preferred but non-limiting embodiment of the present invention, the step 2 uses a data sliding window method to acquire and perform FFT analysis on the grid connection point voltage signal to obtain the typical harmonic frequency and amplitude on the load side, specifically including:

[0074] The grid connection point voltage signal obtained by the data sliding window can be expressed in the time domain as shown in formula (1):

[0075]

[0076] Among them, A0 is the DC component of the grid connection point voltage signal; is the fundamental frequency component of the grid-connected voltage signal, referred to as fundamental wave, ω is the fundamental frequency, is the fundamental phasor; is the nth harmonic of the grid-connected point voltage signal, n is a positive integer, A n is the nth harmonic amplitude of the grid-connected point voltage signal, is the nth harmonic phasor;

[0077] In order to extract the harmonic amplitude and frequency, it is necessary to perform data processing through discrete Fourier transform. Assume that the grid voltage signal of the nth sampling sample is represented as x n , where 0≤n≤N-1 (i.e., there are N samples), N and n are both positive integers, and Fourier transform is performed on these N samples, as shown in formula (2):

[0078]

[0079] Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition.

[0080] Through the above data processing process, the signal amplitude information at each frequency can be calculated based on the data obtained from the data sliding window.

[0081] In a preferred but non-limiting embodiment of the present invention, obtaining the calculation result under the fundamental wave in step 2 specifically includes:

[0082] According to the voltage and current on the inverter side, information processing and coordinate transformation are performed in the fundamental domain to obtain the calculation results under the fundamental domain. Among them, the information processing and coordinate transformation is to transform the voltage and current on the inverter side from a three-phase rotating coordinate system to a two-phase stationary coordinate system, which can be specifically expressed as shown in formulas (3-1) and (3-2):

[0083]

[0084]

[0085] Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i c The C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

[0086] Through formula (3-1) and formula (3-2), we can obtain the information of voltage and current under fundamental wave in dq coordinate system.

[0087] In step 2, data sliding window and FFT analysis refers to first sliding the data window at a certain period based on the grid connection point voltage sampling data to obtain a data frame that is conducive to FFT analysis. Then, using this data frame as a sample, FFT analysis is performed to obtain grid-side harmonic frequency and amplitude information.

[0088] Step 3: Using the typical harmonic frequency and amplitude on the load side obtained in step 2, control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control are obtained to subsequently implement the droop control of the characteristic frequency. The calculation result under the fundamental wave obtained in step 2 is used to calculate the fundamental wave power and the calculation of active power-frequency control and reactive power-voltage control.

[0089] In a preferred but non-limiting embodiment of the present invention, the typical harmonic frequency and amplitude of the load side obtained in step 2 are used in step 3 to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, specifically including:

[0090] According to formula (4), the control parameters such as voltage droop coefficient and frequency droop coefficient in frequency division droop control are obtained:

[0091]

[0092] Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E h are the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h.

[0093] In a preferred but non-limiting embodiment of the present invention, the step 3 of using the calculation result under the fundamental wave obtained in step 2 to perform fundamental wave power calculation and calculation of active power-frequency control and reactive power-voltage control specifically includes:

[0094] The fundamental power can be calculated using formula (5):

[0095]

[0096] Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ;

[0097] Active power-frequency control and reactive power-voltage control can be expressed as the following equations:

[0098]

[0099] Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

[0100] Specifically, active power-frequency control and reactive power-voltage control are key links in droop control, and their main purpose is to simulate the transmission and distribution characteristics of the power grid to achieve control without interconnection lines.

[0101] In step 4, according to the control parameters obtained in step 3, command values ​​are obtained through fundamental droop control and harmonic droop control respectively, and the obtained command values ​​are superimposed to achieve error-free tracking of the voltage and current commands. After superposition, an SPWM modulation command value is obtained. SPWM modulation is implemented through the SPWM modulation command value, and finally adaptive adjustment of the harmonic domain droop link is achieved, and the load side harmonics are offset in a targeted manner.

[0102] In a preferred but non-limiting embodiment of the present invention, the control parameters obtained in step 3 in step 4 are subjected to fundamental droop control and harmonic droop control to obtain command values, respectively, including:

[0103] The fundamental wave droop control is expressed as formula (6) under the condition of i = 1. Through this droop control, the power transmission characteristics of the power grid can be simulated, thereby realizing non-interconnection line control. Under the condition of i = 1, as shown in formula (6), through the droop expression shown in formula (6) under the condition of i = 1, ω can be obtained according to the output power. n With E n , these two variables are the frequency command value and amplitude command value of the output fundamental voltage, which serve as the command and tracking target of the subsequent double closed-loop control; similarly, the harmonic droop control can also be described by a similar formula, that is, under the condition of i>1 as shown in formula (6), through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively, which serve as the command and tracking target of the subsequent dual closed-loop control.

[0104] Harmonic cancellation refers to detecting the harmonic content on the grid side and, based on the detected harmonic content, using frequency droop control to generate corresponding harmonics to compensate / offset the harmonics, thereby achieving power quality management. Adaptive adjustment refers to the fact that, because the present invention detects harmonic content and performs frequency droop control to compensate for harmonics in real time, it can adjust the harmonic compensation effect in real time based on external changes, achieving adaptive adjustment.

[0105] like Figure 1 、 Figure 2 and Figure 4 As shown, the frequency-adaptive multi-inverter parallel wide-band load harmonic suppression system of the present invention includes:

[0106] An acquisition module, which is used to collect the grid connection point voltage and the inverter side voltage and current;

[0107] Specifically, the acquisition module includes a filter capacitor voltage sampling device 10, a current sampling device 9 and a grid-connected point voltage sampling device 11; the filter capacitor voltage sampling device 10, the current sampling device 9 and the grid-connected point voltage sampling device 11 are electrically connected to the filter capacitor 8 and the inverter power supply 7 of the load, and the current sampling device 9, the filter capacitor voltage sampling device 10 and the grid-connected point voltage sampling device 11 are respectively used to collect the output current of the filter device, the capacitor voltage of the filter device and the voltage information on the load side; the inverter power supply 7 electrically connected to the filter capacitor 8 and the load forms the inverter power supply device of the first inverter power supply device 1...the nth inverter power supply device 2, and the inverter power supply 7 is electrically connected to the load through the grid-connected point 3, and the load includes a rectifier-type nonlinear load 4, a nonlinear resistor and inductor load 5 and a linear resistor and inductor load 6.

[0108] A data sliding window and FFT analysis module is used to acquire and perform FFT analysis on the grid connection point voltage signal using a data sliding window method based on the collected grid connection point voltage, obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave;

[0109] a calculation module for using the obtained load-side typical harmonic frequencies and amplitudes to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, so as to subsequently implement the droop control of the characteristic frequency, and using the obtained calculation results under the fundamental wave to perform fundamental wave power calculation and calculations for active power-frequency control and reactive power-voltage control;

[0110] An adjustment module is configured to obtain command values ​​through fundamental wave droop control and harmonic droop control according to the obtained control parameters, and to superimpose the obtained command values ​​to achieve error-free tracking of voltage and current commands. After superposition, an SPWM modulation command value is obtained. SPWM modulation is implemented using the SPWM modulation command value, ultimately achieving adaptive adjustment of the harmonic domain droop link and targeted offsetting of load-side harmonics.

[0111] In a preferred but non-limiting embodiment of the present invention, the data sliding window and FFT analysis module is further configured to represent the grid connection point voltage signal as the nth sampling sample as x n , where 0≤n≤N-1 (i.e., there are N samples), N and n are both positive integers, and Fourier transform is performed on these N samples, as shown in formula (2):

[0112]

[0113] Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition.

[0114] In a preferred but non-limiting embodiment of the present invention, the data sliding window and FFT analysis module is further configured to perform information processing and coordinate transformation in the fundamental domain based on the inverter-side voltage and current to obtain a calculation result in the fundamental domain; wherein the information processing and coordinate transformation is to perform a three-phase rotating coordinate system-two-phase stationary coordinate system transformation on the inverter-side voltage and current, which can be specifically expressed as shown in Formula (3-1) and Formula (3-2):

[0115]

[0116]

[0117] Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i c The C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

[0118] In a preferred but non-limiting embodiment of the present invention, the calculation module is further configured to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control according to formula (4):

[0119]

[0120] Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E hare the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h.

[0121] In a preferred but non-limiting embodiment of the present invention, the calculation module is further configured to calculate the fundamental wave power by formula (5):

[0122]

[0123] Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ;

[0124] Active power-frequency control and reactive power-voltage control can be expressed as the following equations:

[0125]

[0126] Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

[0127] In a preferred but non-limiting embodiment of the present invention, the adjustment module is also used for fundamental wave droop control as shown in formula (6) under the condition of i=1. Through this droop control, the power transmission characteristics of the power grid can be simulated, thereby realizing non-interconnection line control. Under the condition of i=1 as shown in formula (6), through the droop expression shown in formula (6) under the condition of i=1, ω can be obtained according to the output power. n With E n, these two variables are the frequency command value and amplitude command value of the output fundamental voltage, which serve as the command and tracking target of the subsequent double closed-loop control; similarly, the harmonic droop control can also be described by a similar formula, that is, under the condition of i>1 as shown in formula (6), through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively, which serve as the command and tracking target of the subsequent dual closed-loop control.

[0128] A terminal includes a processor and a storage medium;

[0129] The storage medium is used to store instructions;

[0130] The processor is configured to operate according to the instructions to execute the steps of the frequency adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method.

[0131] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the frequency-adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method.

[0132] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0133] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0134] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0135] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., utilizing an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions. The electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0136] Various aspects of the present disclosure are described herein with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present disclosure. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer-readable program instructions.

[0137] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, thereby producing a machine, so that when these instructions are executed by the processor of the computer or other programmable data processing device, a device is generated that implements the functions / actions specified in one or more blocks in the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium, where these instructions cause the computer, programmable data processing device, and / or other device to operate in a specific manner. Thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing various aspects of the functions / actions specified in one or more blocks in the flowchart and / or block diagram.

[0138] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device so that a series of operational steps are performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to implement the functions / actions specified in one or more blocks in the flowchart and / or block diagram.

[0139] The flow charts and block diagrams in the accompanying drawings show the possible architecture, functions and operations of the systems, methods and computer program products according to multiple embodiments of the present disclosure. In this regard, each box in the flow chart or block diagram can represent a part of a module, program segment or instruction, and the part of the module, program segment or instruction contains one or more executable instructions for realizing the prescribed logical function. In some alternative implementations, the functions marked in the box can also occur in a sequence different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the prescribed function or action, or can be implemented by a combination of dedicated hardware and computer instructions.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A frequency adaptive multi-inverter parallel wide-band load harmonic suppression method, characterized in that: The following steps are involved: Step 1: Collect the grid connection point voltage and the inverter side voltage and current; Step 2: Based on the grid connection point voltage collected in step 1, the grid connection point voltage signal is acquired and FFT analyzed using a data sliding window method to obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave; Step 3: Using the typical harmonic frequencies and amplitudes on the load side obtained in step 2, obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control. Furthermore, using the calculation results under the fundamental wave obtained in step 2, perform fundamental wave power calculations as well as calculations for active power-frequency control and reactive power-voltage control. Step 4: Based on the control parameters obtained in step 3, fundamental wave droop control and harmonic droop control are used to obtain command values ​​respectively, and the obtained command values ​​are superimposed to achieve error-free tracking of the voltage and current commands. After superposition, an SPWM modulation command value is obtained, and SPWM modulation is implemented using the SPWM modulation command value. The step 2 uses a data sliding window method to acquire and perform FFT analysis on the grid connection point voltage signal to obtain the typical harmonic frequency and amplitude on the load side, specifically including: The grid connection point voltage signal of the nth sampling sample is expressed as x n , where 0≤n≤N-1, N and n are both positive integers, and the Fourier transform is performed on these N samples, which is shown in formula (2): Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition; The step 3 uses the typical harmonic frequency and amplitude of the load side obtained in step 2 to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, specifically including: According to formula (4), the control parameters such as voltage droop coefficient and frequency droop coefficient in frequency division droop control are obtained: Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E h are the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h; The step 3 uses the calculation result obtained in step 2 under the fundamental wave to perform fundamental wave power calculation and calculation of active power-frequency control and reactive power-voltage control, specifically including: The fundamental power is calculated by formula (5): Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ; Active power-frequency control and reactive power-voltage control are expressed as the following equations: Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

2. The frequency adaptive multi-inverter parallel wide-band load harmonic suppression method according to claim 1, characterized in that: The calculation result obtained under the fundamental wave in step 2 specifically includes: According to the voltage and current on the inverter side, information processing and coordinate transformation are used in the fundamental domain to obtain the calculation results under the fundamental domain. Among them, information processing and coordinate transformation are to perform a three-phase rotating coordinate system-two-phase stationary coordinate system transformation on the voltage and current on the inverter side, which is specifically expressed as shown in formula (3-1) and formula (3-2): Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i c The C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

3. The frequency adaptive multi-inverter parallel wide-band load harmonic suppression method according to claim 2, characterized in that: In step 4, the control parameters obtained in step 3 are subjected to fundamental wave droop control and harmonic droop control to obtain command values, including: Under the condition of i=1, as shown in formula (6), through the droop expression shown in formula (6) under the condition of i=1, ω is obtained according to the output power n With E n , these two variables are the frequency command value and amplitude command value of the output fundamental voltage respectively; similarly, the harmonic droop control is as shown in formula (6) under the condition of i>1. Through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively.

4. A frequency adaptive multi-inverter parallel wide-band load harmonic suppression system, characterized in that: include: An acquisition module, which is used to collect the grid connection point voltage and the inverter side voltage and current; A data sliding window and FFT analysis module is used to acquire and perform FFT analysis on the grid connection point voltage signal using a data sliding window method based on the collected grid connection point voltage, obtain the typical harmonic frequency and amplitude on the load side, and obtain the calculation result under the fundamental wave; a calculation module configured to use the obtained load-side typical harmonic frequencies and amplitudes to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control, and to use the obtained calculation results under the fundamental wave to perform fundamental wave power calculations and calculations for active power-frequency control and reactive power-voltage control; an adjustment module configured to obtain command values ​​respectively through fundamental wave droop control and harmonic droop control according to the obtained control parameters, and to superimpose the obtained command values ​​to achieve error-free tracking of voltage and current commands, thereby obtaining an SPWM modulation command value after superposition, and to implement SPWM modulation using the SPWM modulation command value; The data sliding window and FFT analysis module is further used to represent the grid connection point voltage signal as the nth sampling sample as x n , where 0≤n≤N-1, N and n are both positive integers, and the Fourier transform is performed on these N samples, which is shown in formula (2): Among them, X k is x n The corresponding frequency domain representation, x n The numerical value indicates the corresponding frequency e -j2πkn / N The amplitude under the load side is k, which is an integer between 0 and N-1. The typical harmonic frequency and amplitude of the load side are obtained. The typical harmonic frequency of the load side is composed of all e -j2πkn / N The amplitude of the typical harmonics on the load side is composed of all x n Amplitude composition; The calculation module is also used to obtain control parameters such as the voltage droop coefficient and the frequency droop coefficient in the frequency division droop control according to formula (4): Among them, ω n is the fundamental frequency of the grid-connected voltage signal, ω h is the typical harmonic frequency on the load side, h is the corresponding typical harmonic number, P h , Q h With E h are the load-side harmonic active power, load-side harmonic reactive power, and the amplitude of the typical harmonic on the load side corresponding to the typical harmonic order h, respectively. h is the frequency droop coefficient corresponding to the typical harmonic order h, n h is the frequency droop coefficient corresponding to the typical harmonic order h; The calculation module is also used to calculate the fundamental wave power using formula (5): Among them, u od 、i od 、u oq 、i oq They represent the output voltage and output current components on the d-axis and q-axis, respectively, and u od =U0-U d ,i od =I0-I d ,u oq =U0-U q ,i oq =I0-I q ; Active power-frequency control and reactive power-voltage control can be expressed as the following equations: Where i is the harmonic order and is an integer not less than 1, ω n =ω0-m i P represents active power-frequency control, E n =E0-n i Q o Indicates reactive power-voltage control.

5. The frequency adaptive multi-inverter parallel wide-band load harmonic suppression system according to claim 4, characterized in that: The data sliding window and FFT analysis module is further used for information processing and coordinate transformation in the fundamental domain based on the voltage and current on the inverter side to obtain calculation results under the fundamental domain. The information processing and coordinate transformation is to perform a three-phase rotating coordinate system-two-phase stationary coordinate system transformation on the voltage and current on the inverter side, which is specifically expressed as shown in formulas (3-1) and (3-2): Among them, v a Indicates the a-phase voltage of the inverter side, v b Indicates the b-phase voltage of the inverter side, v c Indicates the C-phase voltage on the inverter side, i a Indicates the a-phase current of the inverter side, i b Indicates the b-phase current of the inverter side, i c The C-phase current represents the inverter side current. The left side of formula (3-1) represents the transformation result of the inverter side voltage in the two-phase stationary coordinate system, and the left side of formula (3-2) represents the transformation result of the inverter side current in the two-phase stationary coordinate system.

6. The frequency adaptive multi-inverter parallel wide-band load harmonic suppression system according to claim 5, characterized in that: The adjustment module is also used to obtain ω according to the output power through the droop expression shown in formula (6) under the condition that i=1. n With E n , these two variables are the frequency command value and amplitude command value of the output fundamental voltage respectively; similarly, the harmonic droop control is as shown in formula (6) under the condition of i>1. Through the droop expression shown in formula (6) under the condition of i>1, ω can be obtained according to the output power n With E n , at this time ω n With E n They represent the frequency command value and amplitude command value of the harmonic voltage respectively.

7. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instruction to execute the steps of the frequency adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method according to any one of claims 1 to 3.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the frequency-adaptive multi-inverter parallel wide-frequency domain load harmonic suppression method described in any one of claims 1 to 3 are implemented.

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