Flexible power tracking method suitable for low voltage ride through working condition of photovoltaic grid-connected system

Abstract

The application provides a flexible power tracking method suitable for a low-voltage ride-through working condition of a photovoltaic grid-connected system, and belongs to the technical field of photovoltaic grid-connected power generation. The method comprises the following steps: obtaining the orthogonal components of grid voltage and grid current according to the grid voltage and the grid current, and then obtaining the reference value of grid-connected inverter output active power and the reference value of reactive power; performing active power tracking, combining the active power reference value, increasing additional sampling to eliminate the influence of reactive power on the sampling result, and obtaining a voltage reference signal; obtaining the switching signal of the grid-connected inverter according to the voltage reference signal and the reactive power reference signal; and performing power tracking control according to the switching signal of the grid-connected inverter. The application considers the sampling error of the flexible power tracking algorithm caused by the injection of reactive current in the low-voltage ride-through working condition, introduces an additional sampling, eliminates the error by reasonably setting the sampling period, and ensures the accurate output of active power and reactive power.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic grid-connected power generation technology, and in particular to a flexible power tracking method suitable for low voltage ride-through conditions in photovoltaic grid-connected systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid development of new energy sources and their increasing penetration rate, if all installed grid-connected photovoltaic (PV) power generation systems operate in Maximum Power Point Tracking (MPPT) mode, overcurrent or overvoltage issues may occur. To avoid these problems, relevant regulations and standards require PV power generation systems to have output power regulation capabilities. Therefore, MPPT in PV power generation systems should be replaced with Flexible Power Point Tracking (FPPT) to achieve flexible adjustment of output power.

[0004] For small-scale grid-connected photovoltaic (PV) systems, disconnecting from the grid during grid faults is a traditional operating method. However, disconnecting large-scale PV systems based on high grid penetration can degrade power quality and even threaten system stability. According to grid specifications, PV systems should have low voltage ride-through (LVRT) capability during grid voltage dips, meaning they should remain connected to the grid.

[0005] The inventors discovered that during the low-voltage ride-through process of a photovoltaic system, the active and reactive power output of the photovoltaic system to the grid is poorly adjusted by the grid voltage level, and it cannot effectively avoid overcurrent to ensure the safety of the grid-connected system. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flexible power point tracking method suitable for low voltage ride-through conditions in photovoltaic grid-connected systems. It considers the sampling error of the flexible power point tracking algorithm caused by reactive current injection under low voltage ride-through conditions, introduces an additional sampling, and eliminates this error by reasonably setting the sampling period, thus ensuring accurate output of active and reactive power.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a flexible power tracking method applicable to low voltage ride-through conditions in photovoltaic grid-connected systems.

[0009] A flexible power point tracking method suitable for low voltage ride-through conditions in photovoltaic grid-connected systems includes the following processes:

[0010] Based on the grid voltage and grid current, the orthogonal components of the grid voltage and grid current are obtained, and then the reference values ​​of the active power and reactive power output of the grid-connected inverter are obtained.

[0011] Perform active power tracking, combine the active power reference value, and add additional sampling to eliminate the influence of reactive power on the sampling results to obtain the voltage reference signal;

[0012] The switching signals of the grid-connected inverter are obtained based on the voltage reference signal and the reactive power reference signal;

[0013] Based on the switching signal of the grid-connected inverter and the grid operating status, the output power is adjusted. Under normal grid operating conditions, the rated active power is output, and under low voltage ride-through conditions, reactive power is injected into the grid.

[0014] As a further limitation of the first aspect of the present invention, the reference values ​​of the active power output and reactive power output of the grid-connected inverter are obtained by combining the reference values ​​of the active current and reactive current output of the grid-connected inverter with the grid voltage.

[0015] As a further limitation of the first aspect of the invention, additional sampling is added to eliminate the influence of reactive power on the sampling results, resulting in a voltage reference signal, including:

[0016] Set the sampling period T to n / 2f, where n is a positive integer and f is the power grid frequency;

[0017] When time t = (k - 1 / 2)T, k represents the k-th sampling, and an additional photovoltaic voltage v is applied. pv (k-1 / 2) and photovoltaic current i pv (k-1 / 2) sampling; when time t=kT, perform a photovoltaic voltage v sampling. pv (k) and photovoltaic current i pv (k) sampling;

[0018] Calculate the average values ​​of photovoltaic output voltage, photovoltaic output current, and photovoltaic output power at time kT;

[0019] Calculate the error Δv between the average value of the photovoltaic output voltage at time kT and (k-1)T. pv The error Δp ​​between the average photovoltaic output power at time (k) and (k-1)T is the difference between the average photovoltaic output power at time (k)T and (k-1)T. pv (k) and the error ΔP between the average photovoltaic output power and the active power reference value at time kT, based on the error Δv pv (k), Δp pvThe positive and negative generation judgment conditions S of (k) and ΔP;

[0020] If the absolute value of ΔP is within the set error threshold, the operating point position is determined: if the operating point is to the left of the maximum power point, the voltage reference value of the previous moment is added as the voltage reference value at time kT; if the operating point is to the right of the maximum power point, the voltage reference value of the previous moment is directly used as the voltage reference value at time kT. The average value of photovoltaic output voltage, average value of photovoltaic output current, average value of photovoltaic output power, and reference voltage signal value at time kT are used to participate in the next power tracking.

[0021] If the absolute value of ΔP is not within the set error threshold, the voltage reference value will continue to be determined based on the combined judgment condition S, and the average value of the photovoltaic output voltage, the average value of the photovoltaic output current, the average value of the photovoltaic output power, and the reference voltage signal at the current kT time will be used in the next power point tracking.

[0022] As a further limitation of the first aspect of the invention, when ΔP is greater than 0, X is 1; otherwise, X is 0; Δv pv When (k) is greater than 0, Y is 1; otherwise, Y is 0; Δp pv When (k) is greater than 0, Z is 1; otherwise, Z is 0. S = 4X + 2Y + Z, where X, Y and Z are the judgment criteria.

[0023] As a further limitation of the first aspect of the present invention, the error threshold is the product of the error threshold coefficient and the active power output of the grid-connected inverter.

[0024] As a further limitation of the first aspect of the present invention, the modulation signal of the inverter is obtained based on the grid current reference value, the grid-side active power reference value and the current loop PR controller, and the switching signal of the inverter is obtained by pulse width modulation based on the modulation signal of the inverter.

[0025] As a further limitation of the first aspect of the present invention, the α-axis components and β-axis components of the grid voltage and the α-axis components and β-axis components of the grid current are obtained based on the grid voltage and grid current, and then the average active power and average reactive power output by the inverter are obtained.

[0026] Based on the output voltage reference value, the output voltage sample value, and the voltage loop PI controller, the active power reference value on the grid side is obtained.

[0027] The grid current reference value is obtained based on the grid-side active power reference value, average active power, active power loop controller, reactive power loop PI controller, grid voltage α-axis and β-axis components, grid-side reactive power reference value and average reactive power.

[0028] Secondly, the present invention provides a flexible power tracking system suitable for low voltage ride-through conditions in photovoltaic grid-connected systems.

[0029] A flexible power point tracking system suitable for low voltage ride-through conditions in photovoltaic grid-connected systems includes:

[0030] The active and reactive power calculation module is configured to: obtain the orthogonal components of the grid voltage and grid current based on the grid voltage and grid current, and then obtain the reference values ​​of the active power and reactive power output of the grid-connected inverter.

[0031] The voltage reference signal calculation module is configured to: perform active power tracking, combine the active power reference value, add additional sampling to eliminate the influence of reactive power on the sampling results, and obtain the voltage reference signal;

[0032] The switching signal generation module is configured to obtain the switching signal of the grid-connected inverter based on the voltage reference signal and the reactive power reference signal.

[0033] The power point tracking control module is configured to adjust the output power according to the switching signal of the grid-connected inverter and the grid operating status. Under normal grid operating conditions, it outputs rated active power and injects reactive power into the grid when the grid voltage drops and it operates under low voltage ride-through conditions.

[0034] Thirdly, the present invention provides a computer-readable storage medium having a program stored thereon that, when executed by a processor, implements the steps of the flexible power point tracking method for low voltage ride-through conditions applicable to photovoltaic grid-connected systems as described in the first aspect of the present invention.

[0035] Fourthly, the present invention provides an electronic device including a memory, a processor, and a program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the flexible power point tracking method for low voltage ride-through conditions applicable to photovoltaic grid-connected systems as described in the first aspect of the present invention.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1. This invention innovatively proposes a flexible power point tracking strategy suitable for low voltage ride-through conditions in photovoltaic grid-connected systems. It considers the sampling error of the flexible power point tracking algorithm caused by reactive current injection under low voltage ride-through conditions, introduces an additional sampling, and eliminates this error by reasonably setting the sampling period, thus ensuring the accurate output of active and reactive power.

[0038] 2. This invention is applicable to low voltage ride-through conditions in single-phase photovoltaic grid-connected power generation systems. It can not only eliminate the sampling error of the FPPT algorithm caused by reactive power during grid voltage dips, thereby enabling active power to accurately track the given value, but also improve the control response speed, enhance the reactive power support capability of the grid-connected inverter, and realize the stable operation of the grid-connected inverter under low voltage ride-through conditions.

[0039] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 This is a structural diagram of a single-phase photovoltaic grid-connected system provided in Embodiment 1 of the present invention;

[0042] Figure 2 A schematic diagram of the traditional FPPT algorithm;

[0043] Figure 3 This is a schematic diagram of the FPPT algorithm provided in Embodiment 1 of the present invention;

[0044] Figure 4 The above is a simulation comparison diagram of the grid voltage and grid current waveforms when the grid voltage drops to 0.6 pu, and the active power and reactive power output of the inverter under the control of the traditional FPPT algorithm and the FPPT algorithm of the present invention, provided for Embodiment 1 of the present invention.

[0045] Figure 5 The above is a simulation comparison diagram of the grid voltage and grid current waveforms when the grid voltage drops to 0.4 pu, and the active and reactive power output of the inverter under the control of the traditional FPPT algorithm and the FPPT algorithm of the present invention, provided for Embodiment 1 of the present invention. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0047] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0048] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0049] Example 1:

[0050] by Figure 1 Taking the grid-connected operation of a photovoltaic grid-connected inverter as an example, the system includes photovoltaic panels (PV) and DC capacitors (C). dc Filter capacitor C f Filter inductor L1, mains resistance r g An AC power grid and a single-phase full-bridge inverter circuit consisting of four IGBT switches.

[0051] like Figure 3 As shown, the FPPT method for low voltage ride-through conditions in single-phase photovoltaic grid-connected power generation systems provided in this embodiment includes the following steps:

[0052] S1: Collect grid voltage v g , grid current i g The photovoltaic panel output voltage and current are used to generate orthogonal components of the grid voltage and current via SOGI, which are then used to calculate the average active and reactive power output of the grid-connected inverter, respectively, P. g and Q g ;

[0053] Based on the actual value of the grid voltage v g With the rated value v gn The magnitude of the power output is used to determine the operating status of the power grid (fault or normal), and to calculate the reference values ​​of the active and reactive power outputs of the grid-connected inverter, respectively, P. ref and Q ref .

[0054] S2: The FPPT module receives the active power reference value P. ref It also initiates active power tracking, adding extra sampling to eliminate the influence of reactive power on the sampling results, and then outputs a voltage reference signal v. pvref It is fed into the voltage regulator;

[0055] S3: Power control receive voltage reference signal v pvref and reactive power reference signal Q ref The modulated signal v of the grid-connected inverter is controlled by "voltage-power-current" output. inv The modulated signal is used to generate the switching signal for the grid-connected inverter using pulse width modulation technology;

[0056] S4: The grid-connected inverter receives switching signals and flexibly adjusts its output power according to the grid's operating status. Under normal grid operating conditions, it outputs rated active power, and under low voltage ride-through conditions when the grid voltage drops, it injects reactive power into the grid.

[0057] In S1, specifically, the orthogonal signals of grid voltage and current are obtained through SOGI, which are used to calculate the average active power and reactive power output of the inverter, respectively P g and Q g , can be represented as:

[0058]

[0059] In the formula, v g Indicates the actual value of the grid voltage, i g V represents the actual value of the grid current. gα and v gβ Let i represent the α-axis component and β-axis component of the grid voltage, respectively. gα and i gβ Let k represent the α-axis and β-axis components of the grid current, respectively. s ω represents the controller gain. r Indicates the cutoff frequency.

[0060] The reference values ​​I of the active and reactive current output by the grid-connected inverter are calculated using formulas under different grid voltages. d and I q When the grid voltage v g Not less than 0.9V gn When the grid voltage is below 0.9V, it is considered normal operating condition, and the inverter does not output reactive current. gn At this time, the grid-connected inverter operates in low-voltage ride-through condition. During this condition, the inverter injects a certain amount of reactive power into the grid, while simultaneously reducing active current output to ensure the current does not exceed the limit. The above process can be represented as:

[0061]

[0062] In the formula, I gmax I represents the maximum effective value of the grid current allowed after the control reaches steady state. N V represents the effective value of the rated current under normal operating conditions of the power grid. gn Indicates the rated value of the mains voltage, I d and I q These represent the d-axis and q-axis components of the grid current in the dq rotating coordinate system, respectively.

[0063] The reference values ​​P for the active and reactive power output of the grid-connected inverter are then obtained. ref and Q ref The following formula can be used to calculate:

[0064]

[0065] Specifically, S2 includes the following steps:

[0066] S2.1: Receive the active power reference value from S1, set the FPPT sampling period T, and perform an additional photovoltaic voltage V at time t = (k-1 / 2)T (where k represents the k-th sampling). pv (k-1 / 2) and current sampling i pv (k-1 / 2); When time t=kT, a photovoltaic voltage v is applied once. pv (k) and current sampling i pv (k); where the sampling period T is set according to the following formula to eliminate the sampling error of the FPPT algorithm caused by reactive power injection:

[0067]

[0068] In the formula, n represents a positive integer, and f represents the power grid frequency.

[0069] S2.2: Calculate the average values ​​of photovoltaic output voltage, current, and power at time kT using the following formulas:

[0070]

[0071]

[0072] P pva (k)=v pva (k)i pva (k)(7)

[0073] In the formula, v pva (k) represents the average value of the photovoltaic output voltage at time kT, i pva (k) represents the average value of the photovoltaic output current at time kT, p pva (k) represents the average value of the photovoltaic output power at time kT.

[0074] S2.3: Calculate the errors in photovoltaic output power and voltage between time kT and time (k-1)T, and simultaneously calculate the errors between the active power reference value and the photovoltaic output voltage at time kT, respectively:

[0075] Δv pv (k)=v pva (k)-v pva (k-1)(8)

[0076] Δp pv (k)=p pva (k)-p pva (k-1)(9)

[0077] ΔP=p pva (k)-P ref (10)

[0078] In the formula, Δv pv (k) represents the error between the average value of the photovoltaic output voltage at time kT and time (k-1)T, Δp pv (k) represents the error between the average photovoltaic output power at time kT and time (k-1)T, and ΔP represents the error between the average photovoltaic output power at time kT and the active power reference value.

[0079] S2.4: Based on the error Δv pv (k), Δp pv The conditions for determining the positive and negative values ​​of (k) and ΔP can be expressed as follows:

[0080]

[0081]

[0082]

[0083] S = 4X + 2Y + Z (14)

[0084] In the formula, X, Y, and Z are judgment flags, and S is the generated judgment condition.

[0085] Then, whether the magnitude of the error ΔP is within the set error threshold is used as a further judgment criterion.

[0086]

[0087] In the formula, dp th This represents the error threshold, where k1 is the error threshold coefficient.

[0088] S2.5: If ΔP is within the set error threshold, the operating point position is determined. If the operating point is to the left of the maximum power point, the voltage reference value from the previous moment is increased; if the operating point is to the right of the maximum power point, the voltage reference value from the previous moment is directly output. Then, the photovoltaic output voltage, current, power, and reference voltage signal results at this moment (kT moment) are recorded and used in the next FPPT algorithm. Finally, the program ends because the photovoltaic output power has reached the set value and is located to the right of the maximum power point. The above process can be represented as:

[0089]

[0090] In the formula, v pvref This represents the output voltage reference signal, v. ref_l V represents the voltage reference signal output at the previous moment. step This indicates the step size of the voltage change.

[0091] S2.6: If ΔP is not within the set error threshold, then continue according to the error Δv. pv (k), Δp pv The signs of (k) and ΔP determine the voltage reference signal, and the judgment condition can be expressed as:

[0092]

[0093] S2.7: Output voltage reference signal, and record the photovoltaic output voltage, current, power and reference voltage signal results at this moment (kT moment) to participate in the next FPPT algorithm.

[0094] In S3, specifically, the inverter's modulation signal is obtained through closed-loop control of "voltage-power-current" using the following formula:

[0095]

[0096] In the formula, v inv P represents the modulation signal of the inverter. * Indicates the reference value of active power on the grid side; i * Indicates the reference value of the mains current; G PI_u (s) represents the voltage loop PI controller, k p_u and k i_u G represents the proportional gain and integral gain of the voltage loop, respectively; PI_P (s) represents the active power loop controller, k p_P and k i_P These represent the proportional gain and integral gain of the active power loop, respectively; G PI_Q (s) represents the reactive power loop PI controller, k p_Q and k i_Q These represent the proportional gain and integral gain of the reactive power loop, respectively; G PR (s) represents the current loop PR controller, k PR K r ω0 and ω0 represent the proportional gain of the current loop, the controller gain, and the cutoff frequency, respectively.

[0097] After obtaining the modulation signal, the switching signal of the inverter can be obtained through pulse width modulation technology.

[0098] The FPPT algorithm in this invention is used to eliminate the adverse effects of reactive power on the algorithm sampling results, specifically through the following methods:

[0099] First, the AC disturbance component of the photovoltaic panel output voltage is derived, specifically:

[0100]

[0101] In the formula, V represents the AC disturbance component of the photovoltaic panel's output voltage. m and I m V represents the peak voltage and peak current of the power grid, respectively. pv This represents the average value of the photovoltaic panel's output voltage, where ω is the grid angular frequency. This indicates the phase angle by which the grid voltage leads the grid current.

[0102] according to Figure 3 The algorithm flow shown can be described as follows: The results of two samplings within one sampling period T of the FPPT algorithm can be written as follows:

[0103]

[0104] In the formula, v pv (k-1 / 2) and v pv (k) represent the first and second voltage sampling values ​​from time t0 to time (t0+kT), respectively.

[0105] According to the sampling time expression given in S2.1, taking n=1, the sampling time T can be calculated to be 0.01s, and the grid angular frequency is 100πrad / s. Substituting these values ​​into the above formula, the average value v of the two sampling results can be obtained. pva (k) is V pv ,Right now:

[0106]

[0107] As can be seen, the AC component in the DC capacitor voltage is eliminated during the sampling stage using the FPPT algorithm of this invention, thereby eliminating the phase angle during reactive power injection. The impact of changes on sampling results, and Figure 2 The traditional FPPT algorithm shown does not have this effect.

[0108] Simulations were performed on the grid-connected operation of a single-phase photovoltaic grid-connected inverter using the control method described in this embodiment, such as... Figure 4 A comparison of the control effects of the traditional FPPT algorithm and the FPPT algorithm of this invention shows that when the grid voltage drops to 0.6V... gn In this embodiment, the active power output of the inverter can be effectively controlled near a given value, and the peak value of the grid current is the same in steady state, ensuring that the limit is not exceeded; for example Figure 5 When the grid voltage drops to 0.4V gn While both the traditional FPPT algorithm and the FPPT algorithm of this invention can control active and reactive power around a given value, this implementation scheme requires a shorter control time, improves the response speed, and has a better control effect during grid voltage dips.

[0109] Example 2:

[0110] Embodiment 2 of the present invention provides a flexible power point tracking system suitable for low voltage ride-through conditions in photovoltaic grid-connected systems, comprising:

[0111] The active and reactive power calculation module is configured to: obtain the orthogonal components of the grid voltage and grid current based on the grid voltage and grid current, and then obtain the reference values ​​of the active power and reactive power output of the grid-connected inverter.

[0112] The voltage reference signal calculation module is configured to: perform active power tracking, combine the active power reference value, add additional sampling to eliminate the influence of reactive power on the sampling results, and obtain the voltage reference signal;

[0113] The switching signal generation module is configured to obtain the switching signal of the grid-connected inverter based on the voltage reference signal and the reactive power reference signal.

[0114] The power point tracking control module is configured to adjust the output power according to the switching signal of the grid-connected inverter and the grid operating status. Under normal grid operating conditions, it outputs rated active power and injects reactive power into the grid when the grid voltage drops and it operates under low voltage ride-through conditions.

[0115] The operating methods of each module of the system are the same as those of the flexible power point tracking method for low voltage ride-through conditions of photovoltaic grid-connected systems provided in Example 1, and will not be repeated here.

[0116] Example 3:

[0117] Embodiment 3 of the present invention provides a computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps of the flexible power point tracking method for low voltage ride-through conditions of photovoltaic grid-connected systems as described in Embodiment 1 of the present invention.

[0118] Example 4:

[0119] Embodiment 4 of the present invention provides an electronic device, including a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the flexible power point tracking method for low voltage ride-through conditions of photovoltaic grid-connected systems as described in Embodiment 1 of the present invention.

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flexible power point tracking method suitable for low voltage ride-through conditions in photovoltaic grid-connected systems, characterized in that, The process includes the following: Based on the grid voltage and grid current, the orthogonal components of the grid voltage and grid current are obtained, and then the reference values ​​of the active power and reactive power output of the grid-connected inverter are obtained. Perform active power tracking, combine the active power reference value, and add additional sampling to eliminate the influence of reactive power on the sampling results to obtain the voltage reference signal; The switching signals of the grid-connected inverter are obtained based on the voltage reference signal and the reactive power reference signal; Based on the switching signal of the grid-connected inverter and the grid operating status, the output power is adjusted. Under normal grid operating conditions, the rated active power is output, and under low voltage ride-through conditions, reactive power is injected into the grid. Additional sampling is added to eliminate the influence of reactive power on the sampling results, resulting in a voltage reference signal, including: Set sampling period T for n / 2f , n It is a positive integer. f The power grid frequency; When time t = ( k -1 / 2) T hour, k Indicates the first k The next sample is used to perform an additional photovoltaic voltage test. v pv ( k -1 / 2) and photovoltaic current i pv ( k -1 / 2) sampling; when time t = kT At that time, perform a photovoltaic voltage test. v pv ( k ) and photovoltaic current i pv ( k )sampling; calculate kT The average values ​​of photovoltaic output voltage, photovoltaic output current, and photovoltaic output power at any given time; calculate kT Time and ( k -1) T Error between the average values ​​of photovoltaic output voltage at different times v pv ( k ), kT Time and ( k -1) T Error between the average values ​​of photovoltaic output power at different times p pv ( k )as well as kT Error between the average photovoltaic output power and the reference value of active power at any given time P According to the error v pv ( k ), p pv ( k )and P The positive and negative generation judgment condition S; if If the absolute value of P is within the set error threshold, then the operating point position is determined: if the operating point is to the left of the maximum power point, then the voltage reference value from the previous moment is increased as... kT If the operating point is located to the right of the maximum power point, the voltage reference value at the previous moment is directly used as the reference value. kT The voltage reference value at time t, kT The average values ​​of photovoltaic output voltage, photovoltaic output current, photovoltaic output power, and reference voltage signal at each moment are used in the next power point tracking. if If the absolute value of P is not within the set error threshold, then the voltage reference value will continue to be determined based on the combined judgment condition S, and the current value will be adjusted accordingly. kT The average values ​​of photovoltaic output voltage, photovoltaic output current, photovoltaic output power, and reference voltage signal at each moment are used in the next power point tracking.

2. The flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in claim 1, characterized in that, Based on the reference values ​​of the active and reactive current outputs of the grid-connected inverter, and in conjunction with the grid voltage, the reference values ​​of the active and reactive power outputs of the grid-connected inverter are obtained.

3. The flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in claim 1, characterized in that, When P is greater than 0, X is 1; otherwise, X is 0. v pv ( k If the value is greater than 0, Y is 1; otherwise, Y is 0. p pv ( k If Z is greater than 0, Z is 1; otherwise, Z is 0. S = 4X + 2Y + Z, where X, Y and Z are the judgment criteria.

4. The flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in claim 1, characterized in that, The error threshold is the product of the error threshold coefficient and the active power output of the grid-connected inverter.

5. The flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in any one of claims 1-4, characterized in that, Based on the grid current reference value, the grid-side active power reference value, and the current loop PR controller, the inverter modulation signal is obtained. The inverter switching signal is obtained by pulse width modulation based on the inverter modulation signal.

6. The flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in any one of claims 1-4, characterized in that, The grid voltage is obtained from the grid voltage and grid current. α Axial components and β Axis components and grid current α Axial components and β The axis components are then used to obtain the average active power and average reactive power output of the inverter. Based on the output voltage reference value, the output voltage sample value, and the voltage loop PI controller, the active power reference value on the grid side is obtained. Based on the grid-side active power reference value, average active power, active power loop controller, reactive power loop PI controller, and grid voltage. α Axial components and β The grid current reference value is obtained from the axis component, the grid-side reactive power reference value, and the average reactive power.

7. A flexible power point tracking system suitable for low voltage ride-through conditions in photovoltaic grid-connected systems, characterized in that, include: The active and reactive power calculation module is configured to: obtain the orthogonal components of the grid voltage and grid current based on the grid voltage and grid current, and then obtain the reference values ​​of the active power and reactive power output of the grid-connected inverter. The voltage reference signal calculation module is configured to: perform active power tracking, combine the active power reference value, add additional sampling to eliminate the influence of reactive power on the sampling results, and obtain the voltage reference signal; The switching signal generation module is configured to obtain the switching signal of the grid-connected inverter based on the voltage reference signal and the reactive power reference signal. The power point tracking control module is configured to: adjust the output power according to the switching signal of the grid-connected inverter and the grid operating status; output rated active power under normal grid operating conditions; and inject reactive power into the grid when the grid voltage drops and the inverter operates under low voltage ride-through conditions. In the voltage reference signal calculation module, additional sampling is added to eliminate the influence of reactive power on the sampling results, resulting in a voltage reference signal, including: Set sampling period T for n / 2f , n It is a positive integer. f The power grid frequency; When time t = ( k -1 / 2) T hour, k Indicates the first k The next sample is used to perform an additional photovoltaic voltage test. v pv ( k -1 / 2) and photovoltaic current i pv ( k -1 / 2) sampling; when time t = kT At that time, perform a photovoltaic voltage test. v pv ( k ) and photovoltaic current i pv ( k )sampling; calculate kT The average values ​​of photovoltaic output voltage, photovoltaic output current, and photovoltaic output power at any given time; calculate kT Time and ( k -1) T Error between the average values ​​of photovoltaic output voltage at different times v pv ( k ), kT Time and ( k -1) T Error between the average values ​​of photovoltaic output power at different times p pv ( k )as well as kT Error between the average photovoltaic output power and the reference value of active power at any given time P According to the error v pv ( k ), p pv ( k )and P The positive and negative generation judgment condition S; if If the absolute value of P is within the set error threshold, then the operating point position is determined: if the operating point is to the left of the maximum power point, then the voltage reference value from the previous moment is increased as... kT If the operating point is located to the right of the maximum power point, the voltage reference value at the previous moment is directly used as the reference value. kT The voltage reference value at time t, kT The average values ​​of photovoltaic output voltage, photovoltaic output current, photovoltaic output power, and reference voltage signal at each moment are used in the next power point tracking. if If the absolute value of P is not within the set error threshold, then the voltage reference value will continue to be determined based on the combined judgment condition S, and the current value will be adjusted accordingly. kT The average values ​​of photovoltaic output voltage, photovoltaic output current, photovoltaic output power, and reference voltage signal at each moment are used in the next power point tracking.

8. A computer-readable storage medium having a program stored thereon, characterized in that, When executed by the processor, the program implements the steps of the flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in any one of claims 1-6.

9. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the flexible power point tracking method for low voltage ride-through conditions in photovoltaic grid-connected systems as described in any one of claims 1-6.

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