Residual capacity harmonic compensation method for household single-phase optical storage cooperative converter

Abstract

The invention discloses a residual capacity harmonic compensation method for a household single-phase optical storage cooperative converter, and belongs to the technical field of converter control. The invention aims to provide a dynamic harmonic compensation method for household single-phase photovoltaic energy storage under limited power capacity and a residual capacity harmonic compensation method for a household single-phase photovoltaic energy storage cooperative converter based on an energy management harmonic priority compensation strategy. The household single-phase optical storage cooperative converter adopts a harmonic current priority compensation strategy, and the core of the harmonic current priority compensation strategy is to increase the residual current margin of a grid-connected inverter by utilizing photovoltaic load shedding and controlling the energy storage charging power, so that harmonic waves are completely compensated. Through a dynamic harmonic current compensation technology, when the output current of the grid-connected inverter exceeds a rated value, the harmonic current value is reduced through a harmonic current compensation factor, so that the output harmonic current value of the inverter is flexibly limited, and the harmonic current is compensated to the maximum extent while the grid-connected inverter works normally.

Description

Technical Field

[0001] The invention belongs to the technical field of converter control. Background Art

[0002] With the depletion of traditional fossil energy and the continuous improvement of environmental protection requirements, vigorously developing clean and renewable energy power generation has become the direction of global energy development. In the development of renewable energy, the application of distributed household photovoltaic power generation has attracted widespread attention due to its unique advantages such as clean and efficient, sustainable utilization, and saving land resources.

[0003] Household photovoltaic power generation is affected by natural factors. For example, changes in external conditions such as temperature and light intensity may cause greater volatility and intermittency in photovoltaic power generation, affecting the quality of electricity. In addition, remote areas have low population density, underdeveloped economy, difficulty in photovoltaic power consumption, and serious abandonment of light. Therefore, configuring energy storage equipment with reasonable capacity in household photovoltaic power generation systems is a favorable way to promote local consumption of photovoltaic systems and improve the efficiency of photovoltaic systems. Household photovoltaic storage synergy devices effectively combine residential users' photovoltaic power generation systems and energy storage systems, and can achieve reliable operation of power conversion and load supply, achieving the energy use goals expected by users.

[0004] In addition, residential users contain a large number of nonlinear power electronic equipment, which generates a large amount of harmonic current, reduces the quality of power, causes electrical equipment to overheat, generates vibration and noise, and even causes excessive line current, resulting in fire and other safety hazards.

[0005] The household single-phase photovoltaic energy storage grid-connected system contains a single-phase full-bridge grid-connected inverter, which is used to invert DC power into base-frequency AC power. The grid-connected inverter will not always be in full power during operation, and there will be a certain working margin and design margin.

[0006] Therefore, the remaining power capacity of the grid-connected inverter, that is, the current margin, can be fully utilized to actively compensate for the harmonic current of the public grid-connected point. According to the limited remaining power capacity of the grid-connected inverter, a dynamic harmonic current compensation control module is designed to dynamically compensate for all or part of the harmonic current. When the harmonic current exceeds the standard seriously, the current margin of the grid-connected inverter is adjusted by designing a harmonic current priority compensation strategy, controlling the charging power of the energy storage, and increasing the harmonic compensation capability, so that the harmonic current is fully compensated and the power quality of the grid-connected point is improved.

[0007] Therefore, the existing household single-phase photovoltaic and energy storage coordinated converter technology urgently needs a dynamic harmonic current compensation control technology and a new harmonic priority compensation energy management strategy to solve this problem. Summary of the invention

[0008] The purpose of the present invention is to provide a method for dynamic harmonic compensation of household single-phase photovoltaic energy storage under limited power capacity and a method for residual capacity harmonic compensation of household single-phase photovoltaic energy storage coordinated converter with energy management harmonic priority compensation strategy.

[0009] The household single-phase photovoltaic storage coordinated converter of the present invention adopts a harmonic current priority compensation strategy. The core of the harmonic priority compensation strategy is to utilize photovoltaic load reduction and control energy storage charging power to increase the residual current margin of the grid-connected inverter so that the harmonics can be fully compensated. S1. Working condition 5: I h ≤I y At this time, the residual current margin of the grid-connected inverter is sufficient, and there is no need to reduce the load of the photovoltaic unit and control the charging power of the energy storage unit, and the harmonic current can be fully compensated; S2, working condition six: I h >I y , SoC ≥ SoC max , the battery is in full-charge standby state, the energy storage unit cannot be charged at this time, the photovoltaic unit is unloaded, the MPPT mode is stopped, and the harmonics are compensated according to the residual current margin of the grid-connected inverter; S3, working condition seven: I h >I y , SoC<SoC max , reduce the load of the photovoltaic unit, stop using the MPPT mode, control the charging power of the energy storage unit, and adjust the residual current margin of the grid-connected inverter to fully compensate for the harmonic current.

[0010] The harmonic current detection of the present invention adopts the adaptive detection technology based on sliding Fourier transform: Assume the input current signal: i in =I m sin(2πf i t+θ0) (1) In the formula, I m is the input current peak value, f i is the input current frequency, θ0 is the initial phase of the input current; After passing through the delayed orthogonal signal generating unit, the output orthogonal current i α 、i β satisfy: Let the sampling frequency of the SFT filter in nominal working mode be f e , at sampling frequency f e In this case, two sets of two-phase signals i with unit amplitude are used. cmx and i cmy Indicates i α and i β, where m represents α or β, i cmx Composed of sine functions i cmy It is composed of cosine functions, and its expression satisfies: Perform the following sliding integration: Where, T e The detection current cycle is 1 / f when stable e , m represents α or β; When f i ≠f e When , according to formula (5) we get the integral x m and m is the time t and frequency f i 、f e The function of x α (t) and y α (t) is expressed as: With x α and α Orthogonal x β (t) and y β (t) is expressed as: In formula (6) and (7), ω d ,ω s , Δθ1, Δθ2, k1 and k2 satisfy: By superimposing equation (6) and equation (7) on each other, we can obtain: According to formula (9) and formula (10), we can get: Right now: According to formula (12), the phase angle of the input signal obtained by the above SFT method is the same as that obtained by using f e The difference between the frequency estimated angles, this phase angle difference is input into the PID controller for adjustment to obtain the required fundamental and harmonic current phase and frequency information; Subtract the fundamental current from the total current of the nonlinear load to obtain the required harmonic current: i h =i L -i1 (13) Where i his the harmonic current, i L is the load current, i1 is the fundamental current; The dynamic harmonic current compensation process is as follows: Phase 1: By sampling the current, each time a sample is taken, it is used to find i * The maximum value, and find the value of i1 and i at this time h The value of the input current i * If it is greater than the last current input value, M will store the latest maximum current i * , at this time, the components i1 and i corresponding to the maximum value h Will be stored in I1 and I h middle; Phase 2: Used to extract i * Maximum peak I m , and extract when i * When I1 and I h The value of i stored in M ​​is * The maximum value is assigned to I m , the final output is i * Maximum peak I m In addition, * When i1 and i h The values ​​of the temporary variables I1 and I h middle; Stage 3: Used to determine whether to perform partial harmonic current compensation or full harmonic current compensation, and output the corresponding harmonic compensation factor K h , change i * The maximum value of I m The rated current peak value I nm In contrast, when I m >I nm When the partial harmonic current compensation function is performed, K h Satisfying formula (14) When I m ≤I nm When , the grid-connected inverter has enough current margin to compensate all harmonic currents and perform all harmonic current compensation functions. At this time, K h =1.

[0011] Beneficial effects of the present invention: 1. The present invention adds a dynamic harmonic compensation control module to the traditional energy management strategy. During the operation of the grid-connected inverter, the grid-connected inverter can not only output the fundamental frequency current, but also use the limited current margin to output the harmonic current to offset the harmonic current in the grid-connected point, thereby improving the power quality of the grid-connected point and making full use of the remaining power capacity of the grid-connected inverter; 2. The present invention proposes an energy management harmonic priority compensation strategy. For working conditions with severe harmonics, photovoltaic load reduction and energy storage units are used to adjust the current margin of the grid-connected inverter, compensate for harmonic currents to the maximum extent, and improve the power quality of the grid-connected point; 3. The present invention adopts SFT-based adaptive harmonic current detection technology, the phase error is adjusted by the PID controller, and the detected phase and frequency are fed back to the SFT filter to achieve frequency adaptation, thereby improving the accuracy of detection and anti-interference ability; 4. The present invention uses dynamic harmonic current compensation technology, and when the output current of the grid-connected inverter exceeds the rated value, the harmonic current value is reduced by the harmonic current compensation factor to achieve flexible limitation of the inverter output harmonic current value, and the harmonic current is compensated to the maximum extent while the grid-connected inverter is working normally. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the connections of each unit of the system; Figure 2 This is the topological structure diagram of the photovoltaic and energy storage cooperative grid connection; Figure 3 It is the control structure diagram of the energy storage unit; Figure 4 It is a flow chart for judging the working condition of photovoltaic energy storage; Figure 5 It is based on the SFT adaptive harmonic current detection principle diagram; Figure 6 It is the dynamic harmonic current compensation flow chart; Figure 7 It is the waveform diagram of grid-connected inverter output current and grid current under four working conditions; Figure 8 It is the waveform diagram of the grid-connected inverter output current and grid current under the second working condition; Fig. 9 It is the waveform diagram of the grid-connected inverter output current and grid current under the seven working conditions. DETAILED DESCRIPTION

[0013] The technical problem to be solved by the present invention is to provide a method for dynamic harmonic compensation under limited power capacity for household single-phase photovoltaic energy storage and an energy management harmonic priority compensation strategy.

[0014] The traditional energy management strategy is to meet the grid dispatch and energy efficient utilization as the control goal. The energy management system controls the energy flow of photovoltaic, energy storage and grid connection points, thereby solving the problem of unstable output power of household photovoltaic power generation units, intermittent fluctuations and tracking power dispatch.

[0015] Traditional energy management strategies use heuristic algorithms to analyze each operating condition instance of the system and optimize the energy management of the operating condition instance. When analyzing the system operating condition, the following explanation is made first: When the battery's storage of charge (SoC) = SoC min When SoC=SoC max The battery should not be charged further when net I is the net power, i.e., photovoltaic power minus load power; h is the harmonic compensation amount, I y is the current margin of the grid-connected inverter. h >I y Indicates that the remaining capacity of the grid-connected inverter is insufficient to fully compensate. h ≤I y It means that the remaining capacity of the grid-connected inverter is sufficient and can be fully compensated. h , P net , I y And the size of the SoC, under the traditional energy management strategy, the system is subdivided into the following four working conditions.

[0016] (1) Working condition 1: P net ≤0, SoC≤SoC min When the photovoltaic output power is less than the load power, the load power is provided by the grid and photovoltaic, the battery is out of power, and the battery is in standby state. The harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0017] (2) Working condition 2: P net ≤0, SoC>SoC min When , the photovoltaic output power is less than the load power, the load power is provided by energy storage and photovoltaic, the battery is in a discharging state, and the harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0018] (3) Working condition 3: P net >0, SoC<SoC max When the photovoltaic output power is greater than the load power, the photovoltaic output power is given to the load and energy storage, the battery is in a charging state, and the harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0019] (4) Working condition 4: P net >0,SoC≥SoC max When the photovoltaic output power is greater than the load power, the photovoltaic output power is given to the load and the grid, the battery is fully charged, and the battery is in standby mode. Harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0020] Although the dynamic harmonic current compensation method can be used to compensate for grid harmonics under the traditional energy management strategy, when serious harmonic currents appear in the grid, the harmonic currents cannot be fully compensated under the traditional energy management strategy, which will still have a serious impact on the grid. In order to cope with the serious harmonic pollution of local loads and the harmonic control requirements of the upper management system.

[0021] Based on the conventional heuristic energy management strategy, this paper innovatively proposes a harmonic current priority compensation strategy. The core of the harmonic priority compensation strategy is to use photovoltaic load reduction and control energy storage charging power to increase the residual current margin of the grid-connected inverter, so that the harmonics can be fully compensated and the power supply quality can be guaranteed.

[0022] Under the energy management harmonic priority compensation strategy, the system is subdivided into the following three operating conditions: (1) Working condition 5: I h ≤I y At this time, the residual current margin of the grid-connected inverter is sufficient, and there is no need to reduce the load of the photovoltaic unit and control the charging power of the energy storage unit, and the harmonic current can be fully compensated.

[0023] (2) Working condition six: I h >I y , SoC ≥ SoC max , the battery is in a fully charged standby state. At this time, the energy storage unit cannot be charged, the photovoltaic unit is unloaded, the MPPT mode is stopped, and harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0024] (3) Working condition seven: I h >I y , SoC<SoC max , reduce the load of the photovoltaic unit, stop using the MPPT mode, control the charging power of the energy storage unit, and adjust the residual current margin of the grid-connected inverter to fully compensate for the harmonic current.

[0025] The current margin of the grid-connected inverter can be adjusted through the energy management harmonic priority compensation strategy. This part of the current margin can be used for harmonic compensation. Harmonic compensation is achieved through the dynamic harmonic compensation control module described in this article.

[0026] The dynamic harmonic current compensation control module includes harmonic current detection technology and dynamic harmonic current active compensation technology, and the module controls the grid-connected inverter unit. Compared with the control method of the traditional photovoltaic energy storage grid-connected inverter that can only output the fundamental frequency current, the control method of the grid-connected inverter with harmonic current compensation function introduces the harmonic current into its grid-connected current, and controls the harmonic current in the output current of the grid-connected inverter through the harmonic current compensation control module, and offsets the harmonic current in the grid-connected point to achieve on-site compensation of the harmonic current. Under this function, the power grid can not or less input harmonic components to the load, thereby improving the power quality.

[0027] The harmonic current detection technology uses an adaptive detection technology based on sliding Fourier transform (SFT). The nonlinear load current generates a corresponding orthogonal signal through the orthogonal signal generation unit, and the orthogonal current signal is calculated by the SFT adaptive detector to obtain the current amplitude and phase error Δθ f The current amplitude is filtered by a low-pass filter (LPF) to obtain the current amplitude I f . Phase error Δθ f After the proportional-integral-derivative (PID) controller, the output frequency ω is obtained. f , output frequency ω f After integration, the corresponding current phase θ is obtained f . The obtained ω f Feedback is given to the SFT adaptive detector, so that the SFT adaptive detector can adaptively change the sampling frequency and improve the immunity to spectrum leakage. The phase and amplitude of the current can be obtained by using the above SFT adaptive detection method.

[0028] The dynamic harmonic current compensation in the present invention is for all subharmonic currents, not for harmonics of a specific subfrequency. Therefore, the amplitude and phase of the fundamental current can be detected by the above method, and the required harmonic current can be obtained by subtracting the fundamental current from the total current of the nonlinear load.

[0029] Since the output current of the grid-connected inverter contains harmonic current and fundamental current components, this may cause the output current of the grid-connected inverter to exceed the rated current peak during the harmonic current compensation process. If the output current peak is simply limited, additional harmonics will be generated due to current saturation, reducing the performance of harmonic compensation.

[0030] The present invention adopts dynamic harmonic current compensation technology to realize active power priority output while performing harmonic current compensation within its limited residual current capacity. In order not to introduce additional harmonic current while ensuring the active power output of the grid-connected inverter, when the output current exceeds the rated current peak, a dynamic proportional calculation is used to reduce the harmonic compensation factor.

[0031] The harmonic current compensation technology converts the harmonic current i h , fundamental current i1, inverter current reference value i * As input, the contribution of harmonic current and fundamental current to the inverter current reference value is determined by detecting the current of one cycle, and I h and I1 represent the harmonic compensation factor K of the harmonic current that can be injected by the algorithm h To ensure that the inverter current reference value i * The peak value does not exceed the rated current peak value of the inverter.

[0032] The present invention will be further described below using drawings and embodiments:

[0033] A household single-phase photovoltaic-storage coordinated harmonic flexible compensation system is characterized by: an energy management harmonic priority compensation strategy and a dynamic harmonic current compensation control module.

[0034] The traditional energy management strategy is to use energy efficiently as the control target, and to control the energy flow of photovoltaics, energy storage and grid connection points, so as to solve the problem of unstable intermittent fluctuations in the output power of household photovoltaic power generation units and power scheduling problems.

[0035] When the harmonic current exceeds the standard seriously, the harmonic current priority compensation strategy is adopted, with full harmonic compensation as the control target, the charging power of the energy storage is controlled to adjust the current margin of the grid-connected inverter, increase the harmonic compensation capability, make the harmonic current fully compensated, and improve the power quality of the grid-connected point.

[0036] The invented energy management harmonic priority compensation strategy is a harmonic compensation priority strategy added on the basis of the traditional energy management strategy. When serious harmonic currents appear in the power grid and the upper management system has harmonic control requirements, the harmonic currents cannot be fully compensated under the traditional energy management strategy, and will still have a serious impact on the power grid. At this time, the energy management harmonic priority compensation strategy is started, and the system no longer takes efficient energy utilization as the control goal, but full harmonic compensation as the control goal. The harmonic priority compensation strategy controls the charging power of the energy storage system, which can flexibly adjust the current margin of the grid-connected inverter and increase the harmonic compensation capability, so that the grid harmonics can be fully compensated, and the power quality of the grid connection point is improved.

[0037] Single-phase photovoltaic units use the maximum power point tracking (MPPT) method to ensure that the photovoltaic unit continuously outputs the maximum energy. Turning off the MPPT will reduce the output power of the photovoltaic unit. In order to make full use of the photovoltaic unit, the MPPT method is used in most cases. The output end of the photovoltaic unit is connected to a DC boost circuit to increase the output voltage to a stable 400V and merge it into the DC bus side. The connection diagram between each unit is as follows Figure 1 shown.

[0038] The energy storage unit can release or absorb power into the system to compensate for the power fluctuation of the photovoltaic unit, playing the role of peak shaving and valley filling. A bidirectional direct current (DC) DC / DC converter is used as the energy conversion interface between the energy storage unit and the DC bus side. The current on the DC bus side is converted into AC power through a single-phase full-bridge grid-connected inverter and output to the grid and load. The output power of the grid-connected inverter comes from two parts, one is the output power of photovoltaics, and the other is the output power of energy storage, which is equivalent to the output current of the grid-connected inverter consisting of photovoltaics and energy storage. The system topology diagram is shown in the figure below. Figure 2 shown.

[0039] The energy storage unit adopts a constant power control method. Since the photovoltaic storage unit is connected to the grid connection point through the grid-connected inverter, and the grid connection point voltage is constant, controlling the output power of the energy storage unit is equivalent to controlling part of the output current of the grid-connected inverter. Under the energy management harmonic priority compensation strategy, the output power of the energy storage unit is adjusted to adjust the current margin of the grid-connected inverter, so that the harmonic current can be fully compensated. The constant power control method collects the voltage V b and current I b To calculate the instantaneous discharge power, multiply the two to get the instantaneous discharge power P of the energy storage unit b , compare the actual collected power value with the power reference value P b-ref Compare, and then use proportional-integral (PI) controller to control the difference and input it into pulse width modulation (PWM) link to generate control signal, so as to realize constant power control. The control structure diagram is shown in Figure 3 As shown. Power reference value P b-ref It is obtained by multiplying the voltage at the grid point and the harmonic current calculated by the harmonic current compensation control module. b-refThat is equivalent to controlling the current margin of the grid-connected inverter. Under the energy management harmonic priority compensation strategy, when the current margin of the grid-connected inverter is insufficient to fully compensate for the harmonic current, the current margin of the grid-connected inverter is controlled by controlling the charging power reference value of the energy storage unit, so that the harmonic current can be fully compensated.

[0040] Traditional energy management strategies take efficient energy utilization as the control goal and partially or completely compensate for harmonics under limited current margin. Traditional energy management strategies use heuristic algorithms to analyze each operating condition instance of the system and optimize the energy management of the operating condition instance. When performing system operating condition analysis, the following explanation is made first: When the battery's storage of charge (SoC) = SoC min When SoC=SoC max The battery should not be charged further when net I is the net power, i.e., photovoltaic power minus load power; h is the harmonic compensation amount, I y is the current margin of the grid-connected inverter. h >I y Indicates that the remaining capacity of the grid-connected inverter is insufficient to fully compensate. h ≤I y It means that the remaining capacity of the grid-connected inverter is sufficient and can be fully compensated. h , P net , I y And the size of the SoC, under the traditional energy management strategy, the system is subdivided into the following four working conditions.

[0041] (1) Working condition 1: P net ≤0, SoC≤SoC min When the photovoltaic output power is less than the load power, the load power is provided by the grid and photovoltaic, the battery is out of power, and the battery is in standby state. The harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0042] (2) Working condition 2: P net ≤0, SoC>SoC min When , the photovoltaic output power is less than the load power, the load power is provided by energy storage and photovoltaic, the battery is in a discharging state, and the harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0043] (3) Working condition 3: P net >0, SoC<SoC max When the photovoltaic output power is greater than the load power, the battery is in a charging state, the photovoltaic output power is given to the load and energy storage, and the harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0044] (4) Working condition 4: P net >0,SoC≥SoC max When the photovoltaic output power is greater than the load power, the photovoltaic output power is given to the load and the grid, the battery is fully charged, and the battery is in standby mode. Harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0045] When the internal harmonics exceed the standard or the external power harmonics exceed the standard, the distribution system requires the household single-phase photovoltaic storage coordinated converter to adopt a harmonic priority compensation strategy. The harmonic priority compensation strategy uses photovoltaic load reduction and controls the energy storage charging power to increase the residual current margin of the grid-connected inverter so that the harmonics are fully compensated and the power supply quality is guaranteed. Under the energy management harmonic priority compensation strategy, the system is added with the following three operating conditions. The operating condition judgment flow chart is as follows Figure 4 shown.

[0046] (1) Working condition 5: I h ≤I y At this time, the residual current margin of the grid-connected inverter is sufficient, and there is no need to reduce the load of the photovoltaic unit and control the charging power of the energy storage unit, and the harmonic current can be fully compensated.

[0047] (2) Working condition six: I h >I y , SoC ≥ SoC max , the battery is in a fully charged standby state. At this time, the energy storage unit cannot be charged, the photovoltaic unit is unloaded, the MPPT mode is stopped, and harmonics are compensated according to the residual current margin of the grid-connected inverter.

[0048] (3) Working condition seven: I h >I y , SoC<SoC max , reduce the load of the photovoltaic unit, stop using the MPPT mode, control the charging power of the energy storage unit, and adjust the residual current margin of the grid-connected inverter to fully compensate for the harmonic current.

[0049] The dynamic harmonic current compensation control module makes full use of the residual power capacity of the grid-connected inverter to actively compensate for the harmonic current of the public grid-connected point. While realizing the active power priority output, the harmonic current compensation is performed within its limited residual current capacity. Under the condition of ensuring the active power output of the grid-connected inverter, in order not to introduce additional harmonic current, when the output current exceeds the rated current peak, the harmonic compensation factor is calculated according to the limited residual power capacity of the grid-connected inverter, the harmonic current output by the grid-connected inverter is flexibly reduced, and all or part of the harmonic current of the grid-connected point is dynamically compensated.

[0050] The invented dynamic harmonic current compensation control module includes harmonic current detection technology and dynamic harmonic current active compensation technology, and the module controls the grid-connected inverter unit. Compared with the traditional photovoltaic energy storage grid-connected inverter control method, the grid-connected inverter control method with harmonic compensation function introduces harmonic current into its grid-connected output current, and adjusts the harmonic current in the grid-connected inverter output current through the harmonic current compensation control module, which offsets the harmonic current in the grid-connected point, thereby realizing on-site compensation of harmonic current. Under this function, the power grid can not or less input harmonic components to the load, thereby improving the power quality.

[0051] The harmonic current of the nonlinear load is obtained according to the harmonic current detection technology, and the fundamental component of the current is added to the harmonic component of the current to generate the output current of the grid-connected inverter. The harmonic current detection technology adopts the adaptive detection technology based on sliding Fourier transform (SFT). The nonlinear load current generates the corresponding orthogonal signal through the orthogonal signal generation unit, and the orthogonal current signal is calculated by the SFT adaptive detector to obtain the current amplitude and phase error Δθ f The current amplitude is filtered by a low-pass filter (LPF) to obtain the current amplitude I f . Phase error Δθ f After passing through the PID controller, the output frequency ω is obtained f , output frequency ω f After integration, the corresponding current phase θ is obtained f . The obtained ω f Feedback is given to the SFT adaptive detector, so that the SFT adaptive detector can adaptively change the sampling frequency and improve the immunity to spectrum leakage. The phase and amplitude of the current can be obtained by using the above SFT adaptive detection method.

[0052] The principle diagram of SFT-based adaptive harmonic current detection is as follows Figure 5 shown.

[0053] Assume that the input current signal satisfies: i in =I m sin(2πf i t+θ0) (1) In formula (1), I m is the input current peak value, f i is the input current frequency, θ0 is the initial phase of the input current.

[0054] After passing through the delayed orthogonal signal generating unit, the output orthogonal current i α 、i β satisfy:

[0055] Let the sampling frequency of the SFT filter in nominal working mode be f e , at sampling frequency f e In this case, two sets of two-phase signals i with unit amplitude are used. cmx and i cmy Indicates i α and i β , where m represents "α" or "β". cmx It is composed of sine functions, and its expression satisfies:

[0056] i cmy It is composed of cosine functions, and its expression satisfies:

[0057] To obtain the coefficients of the primitives of the sliding Fourier transform, the following sliding integration is required: Where, T e The detection current cycle is 1 / f when stable e , m represents "α" or "β".

[0058] When f i ≠f e When , according to formula (5), we can get the integral x m and m is the time t and frequency f i 、f e The function of x α (t) and y α (t) can be expressed as:

[0059] With x α and α Orthogonal x β (t) and y β (t) can be expressed as:

[0060] In formula (6) and (7), ω d ,ω s , Δθ1, Δθ2, k1 and k2 satisfy:

[0061] According to equations (6) and (7), we can know that x m With y mBoth contain high-frequency oscillations, and the output amplitude is half of the input current signal amplitude when stable. In order to eliminate the oscillation phenomenon, the high-frequency oscillations in the output of the sine and cosine filters of the two phases of equation (6) and equation (7) can offset each other. By superimposing equation (6) and equation (7) on each other, we can get:

[0062] From equations (9) and (10), we can see that x m ,y m After superposition, the output oscillation of the SFT filter disappears, the period remains unchanged, and the amplitude becomes twice as large as the original one, that is, the amplitude is equal to the input current amplitude.

[0063] According to formula (9) and formula (10), we can get:

[0064] Right now

[0065] According to formula (12), the above SFT method can be used to obtain the phase angle of the input signal and the use of f e The difference between the frequency estimated angles. This phase angle difference is input into the PID controller for adjustment to obtain the required fundamental and harmonic current phase and frequency information.

[0066] The dynamic harmonic current compensation in the present invention is for all subharmonic currents, not for harmonics of a specific subfrequency. Therefore, the amplitude and phase of the fundamental current can be detected by the above method, and the required harmonic current can be obtained by subtracting the fundamental current from the total current of the nonlinear load. i h =i L -i1 (13) Where i h is the harmonic current, i L is the load current, i1 is the fundamental current.

[0067] Since the output current generation contains harmonic current and fundamental current components, this may cause the output current of the grid-connected inverter to exceed the rated current peak during the harmonic current compensation process. By adopting dynamic harmonic current active compensation technology, that is, while ensuring active power output, the harmonic current of the nonlinear load is compensated within its maximum current capacity. The output current value of the grid-connected inverter is detected through an algorithm. In order not to change the active output of the grid-connected inverter, when the output current value exceeds the rated current peak, a dynamic proportional calculation is used to reduce the harmonic compensation factor to achieve flexible limitation of the inverter output current value.

[0068] Dynamic harmonic current active compensation technology converts the harmonic current i h , fundamental current i1, inverter current reference value i * As input, the contribution of harmonic current and fundamental current to the inverter current reference value is determined by detecting the current of one cycle, and I h and I1 represent the harmonic compensation factor K of the harmonic current that can be injected by the algorithm h , to ensure that the inverter current reference value i * The peak value does not exceed the rated current value of the inverter. The dynamic harmonic current compensation algorithm flow chart is as follows: Figure 6 shown.

[0069] Phase 1: By sampling the current, each time a sample is taken, it is used to find i * The maximum value, and find the value of i1 and i at this time h In each sampling count, if the current input current i * If it is greater than the last current input value, M will store the latest maximum current i * , at this time, the components i1 and i corresponding to the maximum value h Will be stored in I1 and I h middle.

[0070] Phase 2: Used to extract i * Maximum peak I m , and extract when i * When I1 and I h After N samplings, the value of i stored in M * The maximum value is assigned to I m , the final output is i * Maximum peak I m In addition, * When i1 and i h The values ​​of the temporary variables I1 and I h middle.

[0071] Stage 3: Used to determine whether to perform partial harmonic current compensation or full harmonic current compensation, and output the corresponding harmonic compensation factor K h . will i * The maximum value of I m The rated current peak value I nm In contrast, when I m >I nm When the partial harmonic current compensation function is performed, K h Satisfying formula (14)

[0072] When I m ≤Inm When , the grid-connected inverter has enough current margin to compensate all harmonic currents and perform all harmonic current compensation functions. At this time, K h =1.

[0073] In the simulation, the temperature is kept constant at 25°C, and the effectiveness of the proposed harmonic current compensation control strategy is verified by changing the solar radiation intensity. The initial solar radiation intensity is 1000W / m 2 .

[0074] according to Figure 7 The simulation results show that Figure 7 The simulation results correspond to working condition 4, where the solar radiation intensity is 1000W / m 2 , the photovoltaic output power is greater than the load power, the photovoltaic output power is given to the load and the grid, the battery is fully charged, and the battery is in standby mode. At this time, the grid-connected inverter works at full power, and there is no additional current margin for harmonic compensation, so the harmonic compensation factor K h The grid-connected inverter output current is a fundamental frequency sine wave with a total harmonic distortion (THD) of 2.2%, which meets the national grid-connected standard requirements (THD ≤ 5%). Since the harmonic current generated by the nonlinear load cannot be compensated, the grid current is severely distorted with a THD of 56.3%.

[0075] according to Figure 8 The simulation results show that Figure 8 The simulation result corresponds to the second working condition, when the solar radiation intensity is 850W / m 2 , the photovoltaic output power is less than the load power, the load power is provided by energy storage and photovoltaic, and the battery is in a discharge state. According to the current margin of the grid-connected inverter, partial harmonic current compensation is performed at this time, and the harmonic compensation factor K h =0.84, the grid-connected inverter output current contains harmonic current, which partially offsets the harmonic current of the grid-connected point, and the power quality of the grid current is improved to THD 20.1%.

[0076] Figure 8 The simulation proves that the current margin of the grid-connected inverter can only partially compensate for the harmonic current. Although the power quality of the grid is improved, it still does not meet the national standard requirements. At this time, the management strategy of the energy management system starts the harmonic priority compensation strategy. Fig. 9 The simulation results show that Fig. 9 The simulation results correspond to the working condition 7. h >I yIt means that the remaining capacity of the grid-connected inverter is insufficient for full compensation. The current margin of the grid-connected inverter is increased by turning off the MPPT and adjusting the charging power of the energy storage. At this time, all harmonic current compensation is performed. The harmonic compensation factor K h =1.00, the output current of the grid-connected inverter completely offsets the harmonic current of the grid-connected point, the grid current is a fundamental frequency sine wave current with a THD of 2.18%, which meets the national standard requirements, and the power quality is significantly improved, proving the effectiveness of the harmonic compensation priority strategy.

[0077] The names of the variables in the formula of the present invention are: Charge factor SoC, minimum charge factor SoC min , maximum charge factor SoC max , net power P net , harmonic compensation amount I h , grid-connected inverter current margin I y , Maximum Power Point Tracking MPPT, Sliding Fourier Transform SFT, Phase Error Δθ f , low pass filter LPF, current amplitude I f , proportional integral derivative PID, frequency ω f , current phase θ f , harmonic current i h , fundamental current i1, inverter current reference value i * , harmonic current contribution value I h , fundamental current contribution value I1, harmonic compensation factor K h , DC / DC, energy storage unit voltage V b , energy storage unit current I b , the instantaneous discharge power of the energy storage unit P b , power reference value P b-ref , proportional integral PI, pulse width modulation PWM, input current peak I m , orthogonal current i α 、i β , two groups of two-phase signals i cmx 、i cmy , input current frequency f i , input current initial phase θ0, sampling frequency f e , detection current cycle T e , load current i L , grid-connected inverter rated current peak value I nm , total harmonic distortion THD.

Claims

1. A method for compensating residual capacity harmonics of a household single-phase photovoltaic-storage cooperative converter, characterized in that: The household single-phase photovoltaic-storage cooperative converter adopts a harmonic current priority compensation strategy. The core of the harmonic priority compensation strategy is to use photovoltaic load reduction and control the energy storage charging power to increase the residual current margin of the grid-connected inverter so that the harmonics can be fully compensated. S1. Working condition 5: I h ≤I y At this time, the residual current margin of the grid-connected inverter is sufficient, and there is no need to reduce the load of the photovoltaic unit and control the charging power of the energy storage unit, and the harmonic current can be fully compensated; S2, working condition six: I h >I y , SoC ≥ SoC max , the battery is in full-charge standby state, the energy storage unit cannot be charged at this time, the photovoltaic unit is unloaded, the MPPT mode is stopped, and the harmonics are compensated according to the residual current margin of the grid-connected inverter; S3, working condition seven: I h >I y , SoC<SoC max , reduce the load of the photovoltaic unit, stop using the MPPT mode, control the charging power of the energy storage unit, and adjust the residual current margin of the grid-connected inverter to fully compensate for the harmonic current.

2. The method for compensating residual capacity harmonics of a household single-phase photovoltaic-storage coordinated converter according to claim 1 is characterized in that: Harmonic current detection uses sliding Fourier transform based adaptive detection technology: Assume the input current signal: i in =I m sin(2πf i t+θ0) (1) In the formula, I m is the input current peak value, f i is the input current frequency, θ0 is the initial phase of the input current; After passing through the delayed orthogonal signal generating unit, the output orthogonal current i α 、i β satisfy: Let the sampling frequency of the SFT filter in nominal working mode be f e , at sampling frequency f e In this case, two sets of two-phase signals i with unit amplitude are used. cmx and i cmy Indicates i α and i β , where m represents α or β, i cmx Composed of sine functions i cmy It is composed of cosine functions, and its expression satisfies: Perform the following sliding integration: Where, T e The detection current cycle is 1 / f when stable e , m represents α or β; When f i ≠f e When , according to formula (5) we get the integral x m and m is the time t and frequency f i 、f e The function of x α (t) and y α (t) is expressed as: With x α and α Orthogonal x β (t) and y β (t) is expressed as: In formula (6) and (7), ω d ,ω s , Δθ1, Δθ2, k1 and k2 satisfy: By superimposing equation (6) and equation (7) on each other, we can obtain: According to formula (9) and formula (10), we can get: Right now: According to formula (12), the phase angle of the input signal obtained by the above SFT method is the same as that obtained by using f e The difference between the frequency estimated angles, this phase angle difference is input into the PID controller for adjustment to obtain the required fundamental and harmonic current phase and frequency information; Subtract the fundamental current from the total current of the nonlinear load to obtain the required harmonic current: and h =i L -i1 (13) Where i h is the harmonic current, i L is the load current, i1 is the fundamental current; The dynamic harmonic current compensation process is as follows: Phase 1: By sampling the current, each time a sample is taken, it is used to find i * The maximum value, and find the value of i1 and i at this time h The value of the input current i * If it is greater than the last current input value, M will store the latest maximum current i * , at this time, the components i1 and i corresponding to the maximum value h Will be stored in I1 and I h middle; Phase 2: Used to extract i * Maximum peak I m , and extract when i * When I1 and I h The value of i stored in M ​​is * The maximum value is assigned to I m , the final output is i * Maximum peak I m In addition, * When i1 and i h The values ​​of the temporary variables I1 and I h middle; Stage 3: Used to determine whether to perform partial harmonic current compensation or full harmonic current compensation, and output the corresponding harmonic compensation factor K h , change i * The maximum value of I m The rated current peak value I nm In contrast, when I m >I nm When the partial harmonic current compensation function is performed, K h Satisfying formula (14) When I m ≤I nm When , the grid-connected inverter has enough current margin to compensate all harmonic currents and perform all harmonic current compensation functions. At this time, K h =1.

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