Single-phase grid-connected inverter reactive power control method, system and equipment based on improved sine waves and storage medium

Abstract

The invention discloses a single-phase grid-connected inverter reactive power control method, system and device based on an improved sine wave, and a storage medium. The method comprises the following steps: constructing the improved sine wave as a grid-connected current; fourier series decomposition is carried out on the improved sine wave; analyzing the total harmonic distortion and the power factor of the improved sine wave after Fourier series decomposition; analyzing active power and reactive power of the single-phase grid-connected inverter according to a power transmission theory based on the total harmonic distortion of the improved sine wave and a power factor; on the basis of theoretical analysis, the design of the controller is realized according to the improved sine wave; deducing a grid-connected current peak value and a phase shift angle of the grid-connected ISW waveform according to the requirements of the output active power and the power factor; and then reactive power control is carried out. The method is easy and convenient to operate, efficient and flexible, the power factor can be adjusted to 0.8 or even lower, the requirements of different power systems are met, and the method has wide application prospects.

Description

Technical Field

[0001] The present invention relates to a single-phase grid-connected inverter technology, and in particular to a reactive power control method, system, device and storage medium of a single-phase grid-connected inverter based on an improved sine wave. Background Art

[0002] With the development plan of the global power grid and the demand for large-scale distributed energy access, power grid companies around the world have put forward higher requirements for distributed energy grid connection, such as the US Rule 21 and IEEE-1547 standards. Among them, reactive power regulation function has become a key challenge in the design of micro inverters. At present, due to the limitation of circuit structure, some single-phase grid-connected inverters can only transfer energy in one direction and cannot achieve reactive power regulation. This limits the application of these inverters in markets that require reactive power regulation function to a certain extent. Therefore, it is of great practical significance to study a single-phase grid-connected inverter control method that can achieve reactive power regulation. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a single-phase grid-connected inverter reactive power control method, system, device and storage medium that realizes precise control of the reactive power of the grid-connected inverter by improving the design of the sine wave and combining the Fourier series decomposition technology.

[0004] Technical solution: The reactive power control method of a single-phase grid-connected inverter based on an improved sine wave of the present invention comprises the following steps:

[0005] (1) constructing an improved sine wave ISW as the grid-connected current, wherein the improved sine wave comprises sine waves of different frequencies, wherein the fundamental wave has a reactive component and contains harmonic components;

[0006] (2) Perform Fourier series decomposition on the improved sine wave;

[0007] (3) Analyze the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition;

[0008] (4) Based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory, the active power P and reactive power Q of the single-phase grid-connected inverter are analyzed;

[0009] (5) Based on theoretical analysis, design a controller based on the improved sine wave;

[0010] (6) According to the requirements of output active power P and power factor PF, the grid current peak value A and phase shift angle of the grid-connected ISW waveform are derived. The grid-connected ISW waveform is used as the reference current of the controller to achieve reactive power control.

[0011] Furthermore, the improved sine wave in step (1) is:

[0012]

[0013] Among them, f(t) is the grid-connected current function of generating capacitive reactive power; g(t) is the grid-connected current function of generating inductive reactive power; A is the peak value of the grid-connected current, is the phase shift angle, ω is the angular frequency, and t is the time;

[0014] The modified sine wave is used as a reference for delivering grid current.

[0015] Furthermore, in step (2), the improved sine wave is decomposed into Fourier series, specifically:

[0016] (201) The Fourier series method is used to represent the grid-connected current. The current reference current i(t) of ISW is expressed as follows:

[0017]

[0018] Where n is the harmonic number of the current reference current of ISW, ω is the angular frequency, and a n and b n Fourier series coefficients of the nth series for Fourier series analysis;

[0019] (202) Perform Fourier series analysis on ISW, a0 = 0, a0 is the DC value of the Fourier series analysis of the ISW waveform; In the interval where ISW is not 0, the grid-connected current function is integrated and calculated a n , b n :

[0020] Grid-connected current function f(t) for capacitive reactive power generation:

[0021]

[0022] The grid-connected current function g(t) for inductive reactive power generation is:

[0023]

[0024] Where, T is the period of ISW;

[0025] (203) After the integral simplification of step (202), we get a n For A, The function is as follows:

[0026] f(t):

[0027]

[0028] g(t):

[0029]

[0030] (204) After the integral simplification of step (202), we get b n For A, The function is as follows:

[0031]

[0032] (205) According to step (203) and step (204), we know that a n and b n is the ISW grid-connected current peak value A and phase shift angle The periodic signal is expanded into fundamental frequency and harmonic waves, which can be expressed as:

[0033]

[0034] Among them, I n is the amplitude of the nth harmonic, θ n is the phase angle of the nth harmonic; the parameter is obtained by the following formula:

[0035]

[0036] (206) According to step (203), step (204) and step (205), we can get n The expression is:

[0037]

[0038] Among them, K n is an intermediate variable;

[0039] (207) According to step (203), step (204) and step (205), we can get θ n The expression is:

[0040] f(t):

[0041]

[0042] g(t):

[0043]

[0044] Furthermore, in step (3), the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition are analyzed, specifically:

[0045] (301)The equation of THD and PF is:

[0046]

[0047] Where θ1 is the phase angle of the 1st harmonic;

[0048] (302) According to the amplitude of the nth harmonic I n Step (301) obtains THD with respect to the phase shift angle The expression is:

[0049]

[0050] (303) According to the phase angle θ of the nth harmonic in step n Step (302) obtains PF with respect to the phase shift angle The expression is:

[0051]

[0052] Furthermore, in step (4), based on the total harmonic distortion THD and power factor PF of the improved sine wave, according to the power transmission theory, the active power P and reactive power Q of the single-phase grid-connected inverter are analyzed; specifically:

[0053] (401) According to power transmission theory, active power is defined as:

[0054]

[0055] Among them, V s is the amplitude of the grid voltage, I1 is the amplitude of the 1st harmonic, θ1 is the phase angle of the 1st harmonic;

[0056] (402) According to power transmission theory, reactive power is defined as:

[0057]

[0058] (403) Expand i(t) to obtain:

[0059]

[0060] Step 404, compare the expression of the current reference current i(t) of ISW with step (403), and obtain:

[0061] a n =I n sinθ n

[0062] b n =I n cosθ n

[0063] (405) According to b nSubstituting n=1 into the expression, step (401) and step (404), the active power with respect to the ISW grid-connected current peak value A and the phase shift angle is obtained. The expression is:

[0064]

[0065] (406) According to a n , step (402) and step (404), substituting n=1, the reactive power with respect to the ISW grid-connected current peak value A and the phase shift angle is obtained. The expression is:

[0066]

[0067] The reactive power Q is affected by the peak current A of the ISW grid-connected current and the phase shift angle. By changing these two parameters, the photovoltaic grid-connected inverter can inject reactive power into the grid. Different parameter combinations have different THD and PF.

[0068] Furthermore, in step (5), based on theoretical analysis, the controller is designed and implemented according to the improved sine wave; specifically:

[0069] (501) An ISW ​​current reference generator is introduced. The ISW waveform is a combination of a sine wave and a linear waveform. The generator consists of a sine wave generator and a controller for converting the sine wave into an ISW. The sine wave generator outputs a sine wave synchronized with the grid voltage through a phase-locked loop, and then a part of the sine wave is linearized to obtain an ISW ​​waveform.

[0070] (502) A PI controller is used to follow the ISW grid-connected current waveform.

[0071] Furthermore, in step (6), the grid-connected current peak value A and the phase shift angle of the grid-connected ISW waveform are derived according to the requirements of the output active power P and the power factor PF. Specifically:

[0072] (601) According to the required power factor PF combined with PF about the phase shift angle The expression of

[0073] (602) The phase shift angle obtained according to step (601) Combined with THD about phase shift angle The expression of is used to solve the total harmonic distortion THD corresponding to PF;

[0074] (603) Based on the required active power P and the phase shift angle obtained in step (601) Combined with the active power P about the ISW grid current peak A and phase shift angle The expression of P and PF is solved to find the grid-connected current amplitude A corresponding to P and PF;

[0075] (604) The grid-connected current amplitude A and phase shift angle corresponding to P and PF are Used to construct the grid-connected ISW waveform as the reference current for the controller in step (5).

[0076] The control system corresponding to the control method includes:

[0077] An improved sine wave construction unit is used to construct an improved sine wave ISW as a grid-connected current, and the improved sine wave is defined as a waveform composed of sine waveforms of different frequencies, and the improved sine wave signal contains harmonics;

[0078] A Fourier transform unit, used for performing Fourier series decomposition on the improved sine wave;

[0079] Total harmonic distortion and power factor analysis unit, used to analyze the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition;

[0080] Active and reactive power analysis unit, used to analyze the active power P and reactive power Q of the single-phase grid-connected inverter based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory;

[0081] The controller design unit is used to design and implement the controller according to the improved sine wave based on theoretical analysis;

[0082] The control unit is used to derive the grid-connected current peak value A and phase shift angle of the grid-connected ISW waveform according to the requirements of the output active power P and the power factor PF. The grid-connected ISW waveform is used as the reference current of the controller to achieve reactive power control.

[0083] A control device for storing and processing the control method, comprising a processor, a communication interface, a memory and a communication bus;

[0084] Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus;

[0085] The memory is used to store computer programs;

[0086] The processor is used to implement the steps of the reactive power control method of a single-phase grid-connected inverter based on improved sine wave when executing the program stored in the memory.

[0087] A storage medium for storing and executing the control method, wherein a computer program is stored on the storage medium, and when the computer program is executed by at least one processor, the steps of the reactive power control method of a single-phase grid-connected inverter based on an improved sine wave are implemented.

[0088] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are: without adding additional hardware, efficient reactive power regulation is achieved through a simplified control strategy, including the output of inductive reactive power and capacitive reactive power; this method is not only easy to operate, but also can adjust the power factor to 0.8 or even lower, fully meeting the power factor requirements of different power systems; at the same time, the method significantly improves the power quality and system operation stability while ensuring a low total harmonic distortion (THD); for inverters in which energy can only be transmitted in one direction (such as Buck inverters, Flyback inverters, etc.), efficient and flexible reactive power regulation and power factor control are achieved, which is suitable for all inverters with unfolded circuits and has important theoretical significance and practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 is a flow chart of the method of the present invention;

[0090] Figure 2 To improve the sine wave grid-connected waveform, (a) is the capacitive reactive power waveform, (b) is the inductive reactive power waveform;

[0091] Figure 3 THD Schematic diagram of the changes;

[0092] Figure 4 PF Schematic diagram of the changes;

[0093] Figure 5 This is a schematic diagram of THD changing with PF;

[0094] Figure 6 It is a schematic diagram of ISW waveform and fundamental waveform;

[0095] Figure 7 The schematic diagram of the inverter circuit for a typical single-phase grid-connected inverter is shown below;

[0096] Figure 8 It is a schematic diagram of a single-ended flyback grid-connected inverter circuit;

[0097] Fig. 9 This is the ISW waveform grid-connected control block diagram;

[0098] Fig.10 This is an example diagram of capacitive reactive power simulation (PF = 0.8);

[0099] Fig.11 This is an example diagram of the simulation of inductive reactive power (PF=0.8). DETAILED DESCRIPTION

[0100] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0101] like Figure 1 As shown, the reactive power control method of a single-phase grid-connected inverter based on an improved sine wave according to the present invention comprises the following steps:

[0102] Step 1: construct an improved sinusoidal waveform (ISW) as the grid-connected current. The improved sinusoidal waveform is defined as a waveform composed of sinusoidal waveforms of different frequencies. The obtained waveform is close to a sine wave, but it contains harmonics in the signal.

[0103] The step 1 specifically comprises the following steps:

[0104] Step 101, analyzing the occurrence of reactive power. When the inverter output current phase lags behind the grid voltage, the inverter system transmits active power to the grid and also emits a certain amount of inductive reactive power to the grid; when the inverter output current phase leads the grid voltage, the inverter system transmits active power to the grid and also emits a certain amount of capacitive reactive power to the grid.

[0105] Step 102, analyzing the working principle of the power frequency folding bridge inverter, it is required that the zero crossing points of the grid voltage and the inverter output current are the same, and the grid current (the current after the inverter output current is connected to the grid) and the grid voltage must be in the same direction. Therefore, the improved sine wave (f(t) generates capacitive reactive power, g(t) generates inductive reactive power) is constructed as follows:

[0106]

[0107] Among them, f(t) is the grid-connected current function of generating capacitive reactive power, g(t) is the grid-connected current function of generating inductive reactive power, A is the peak value of the grid-connected current, is the phase shift angle, ω is the angular frequency, and t is the time.

[0108] Step 103, using the improved sine wave in step 102 as the grid-connected current. The waveform of the improved sine wave is divided into 4 time intervals, wherein the boundary is fixed at the zero-crossing point of the waveform. Since the properties of f(t) and g(t) are only different in terms of capacitive reactive power and inductive reactive power, f(t) is used for subsequent analysis. Figure 2 (a) and (b) are improved sine waves A=1, Waveform diagram, where (a) is the capacitive reactive power waveform and (b) is the inductive reactive power waveform.

[0109] Step 2: Based on the conclusion of step 1, perform Fourier series decomposition on the improved sine wave.

[0110] The step 2 specifically includes the following steps:

[0111] Step 201, Fourier series method is used to represent the grid-connected current. The current reference current i(t) of the ISW can be represented by the following formula:

[0112]

[0113] Where n is the harmonic number of the current reference current of ISW, ω is the angular frequency, a n for and b n Fourier series coefficients of the nth series for Fourier series analysis;

[0114] Step 202, perform Fourier series analysis on ISW. Since the integral of f(t) is zero in one cycle, a0=0, where a0 is the DC value of the Fourier series analysis of the ISW waveform. In the interval where ISW is not zero, perform an integral calculation of the grid-connected current function. n , b n :

[0115]

[0116] Among them, T is the period of ISW, which is consistent with the period of industrial frequency sinusoidal current.

[0117] Step 203, after the integral simplification of step 202, we can get a n For A, The function is as follows:

[0118]

[0119] Step 204: After the integral simplification of step 202, b can be obtained. n For A, The function is as follows:

[0120]

[0121] Step 205: According to step 203 and step 204, it can be known that a n and b n is the peak value of the ISW grid-connected current, the peak value of the grid-connected current A and the phase shift angle, the phase shift angle The waveform can therefore be adjusted by these two parameters. The periodic signal can be expanded into fundamental frequency and harmonics. The general form is:

[0122]

[0123] Among them, In is the amplitude of the nth harmonic, θ n is the phase angle of the nth harmonic. The parameters can be obtained as follows,

[0124]

[0125] Step 206: According to step 203, step 204 and step 205, it can be obtained that n The expression is:

[0126]

[0127] Among them, K n is an intermediate variable.

[0128] Step 207: According to steps 203, 204 and 205, θ n The expression is:

[0129]

[0130] Step 3: Based on the conclusion of step 2, analyze the total harmonic distortion (THD) and power factor (PF) of the improved sine wave.

[0131] The step 3 specifically comprises the following steps:

[0132] Step 301, for a grid-connected inverter, the total harmonic distortion (THD) and power factor (PF) of its grid-connected current are important indicators for measuring the reactive power control of the inverter. The general equations of THD and PF are:

[0133]

[0134]

[0135] Here, θ1 is the phase angle of the 1st harmonic.

[0136] Step 302: According to step 206 and step 301, the THD with respect to the phase shift angle can be obtained. The expression is:

[0137]

[0138] According to the functional expression of THD, THD has nothing to do with the peak value A of the ISW grid-connected current. Figure 3 THD Changes, The range is when When , the THD of ISW (pure sine wave) is 0. As the voltage increases, THD increases gradually.

[0139] Step 303: According to step 207 and step 302, the PF with respect to the phase shift angle can be obtained. The expression is:

[0140]

[0141] According to the functional expression of PF, it can be seen that PF has nothing to do with the peak value A of the ISW grid-connected current. Figure 4 PF Changes, The range is when When , the PF of ISW (pure sine wave) is 1. As , PF decreases gradually. Figure 5 This is how THD changes with PF.

[0142] Step 4: Based on the conclusion of step 3 and according to the power transmission theory, analyze the active power (P) and reactive power (Q) of the single-phase grid-connected inverter.

[0143] The step 4 specifically comprises the following steps:

[0144] For photovoltaic grid-connected inverters, active power (P) and reactive power (Q) are the key output parameters of photovoltaic inverters, which jointly determine the stability and efficiency of the power system.

[0145] Step 401, according to the power transmission theory, active power is defined as:

[0146]

[0147] Among them, V s is the amplitude of the grid voltage, I1 is the amplitude of the 1st harmonic, and θ1 is the phase angle of the 1st harmonic.

[0148] Step 402, according to the power transmission theory, reactive power is defined as:

[0149]

[0150] Figure 6 For ISW waveform A=1, Unlike its fundamental waveform, active power and reactive power are transmitted through the fundamental wave.

[0151] Step 403, according to step 205, expand i(t) to obtain:

[0152]

[0153] Step 404, comparing step 201 and step 403, we can get:

[0154]

[0155] Step 405: According to step 204, step 401 and step 404, substituting n=1, the active power with respect to the ISW grid-connected current peak value A and the phase shift angle can be obtained. The expression is:

[0156]

[0157] Step 406: According to step 203, step 402 and step 404, substituting n=1, the reactive power can be obtained in relation to the ISW grid-connected current peak value A and the phase shift angle. The expression is:

[0158]

[0159] It can be concluded that the reactive power Q is affected by the peak value A of the ISW grid-connected current and the phase shift angle By changing these two parameters, the photovoltaic grid-connected inverter can inject reactive power into the grid. Different parameter combinations have different THD and PF.

[0160] Step 5: Based on the theoretical analysis, the controller is designed and implemented according to the improved sine wave.

[0161] The step 5 specifically comprises the following steps:

[0162] A control loop is designed to generate an ISW ​​grid-connected current reference and PI control is used to make the grid-connected current follow the ISW waveform.

[0163] like Figure 7 It is a typical single-phase grid-connected inverter circuit. The front stage is a DC / DC circuit and the rear stage is a bridge inverter circuit. g is the grid voltage, i g is the grid current, P o The present invention is applicable to all inverters with unfolded bridge circuits. In this embodiment, the following inverters can be used: Figure 8 The flyback inverter circuit designs its control loop to generate an ISW ​​grid-connected current reference and uses PI control to make the grid-connected current follow the ISW waveform.

[0164] Step 501, such as Figure 8 As shown in FIG. 1 , the circuit structure of an existing flyback micro inverter mainly includes a flyback circuit at the front stage and a power frequency expansion bridge circuit at the rear stage. The input end of the flyback circuit is connected to the photovoltaic module PV, where C inThe output end of the flyback circuit is connected to the input end of the power frequency expansion bridge circuit, and the output end of the power frequency expansion bridge circuit is connected to the power grid. The flyback circuit includes a switch tube S m , transformer and diode D m , output capacitor C o , where L m is the transformer excitation inductor; the power frequency expansion bridge circuit includes bridge-connected switch tubes S1 to S4. The power grid passes through the inductor L f and capacitor C f Connected to the industrial frequency expansion bridge circuit.

[0165] Step 502, introduce an ISW ​​current reference generator. Since the ISW waveform is a combination of a sine wave and a linear waveform, the generator consists of a sine wave generator and a controller that converts the sine wave into an ISW. The sine wave generator outputs a phase-locked loop that is connected to the grid voltage u g The synchronous sine wave is calculated by mathematical calculation 1 (Formula (20) and Formula (21)) according to the output requirements of P and Q / PF to obtain the corresponding A and Input into mathematical calculation 2 (formula (1)), and then linearize part of the sine wave to obtain the ISW waveform. A PI controller is used to follow the ISW grid-connected current waveform, wherein the design of the PI controller can be the same as the PI controller when the inverter generates active power. The output of the PI controller is input into the PWM generator to obtain the main switch tube S of the flyback inverter circuit in this embodiment. m The driving signal is based on the grid voltage u g The drive signals of the expansion circuits S1, S4, S2, and S3 can be obtained through the comparator and the NOT gate module. The ISW waveform grid-connected control block diagram is shown in Fig. 9 shown.

[0166] Step 6: According to the requirements of output active power (P) and power factor PF, derive the grid-connected current peak value A and phase shift angle of the grid-connected ISW waveform.

[0167] The step 6 specifically comprises the following steps:

[0168] The following are the specific parameter calculation steps of this embodiment, including the output of capacitive reactive power and the output of inductive reactive power. For reactive power control, it is only necessary to change the grid-connected current from the same frequency and phase of the grid voltage to the improved sinusoidal ISW waveform under normal operation, and the amplitude A and the phase shift angle Different represents different active power and reactive power / power factor. In this step, combined with the characteristics of photovoltaic grid-connected inverter, how to calculate the key parameters of grid-connected current (i.e. grid-connected current amplitude A and phase shift angle) according to output requirements is explained in detail. ), and based on these parameters, an improved sinusoidal waveform (ISW) suitable for grid-connected operation is generated. This method ensures accurate regulation of reactive power (Q) and power factor (PF) through precise mathematical model analysis.

[0169] Taking the generation of capacitive reactive power as an example, the improved sinusoidal wave function adopts f(t), such as Fig.10 The figure shows an example of simulation of generating capacitive reactive power.

[0170] Step 601, based on the required power factor (PF), combined with the derivation process in step 303, calculate the phase shift angle corresponding to the target power factor In this embodiment, taking the power factor PF = 0.8 as an example, the corresponding phase shift angle can be obtained: Radians. This angle is a key parameter to ensure that the inverter can achieve reactive power regulation at a specific power factor.

[0171] Step 602, by obtaining the phase shift angle obtained in step 601 Substituting the harmonic distortion expression in step 302, the total harmonic distortion (THD) of the system can be solved. The THD value calculated in this embodiment is 23.2%. This value reflects the waveform quality of the system under this control parameter. A higher THD may have an adverse effect on the power quality, so it is necessary to weigh the relationship between this value and other performance parameters during design.

[0172] Step 603, after the phase shift angle has been determined Based on the analysis in step 405, the amplitude A of the grid-connected current is further calculated. This amplitude is related to the output active power P of the inverter and the phase shift angle In this embodiment, the active power P = 200W and As parameters, the grid-connected current amplitude A=1.66A is calculated.

[0173] Step 604: The grid-connected current amplitude A obtained in step 603 and the phase shift angle in step 601 are The input control circuit generates the corresponding grid-connected ISW waveform. This waveform will be used as the reference current of the PI controller to drive the main switch tube S of the grid-connected inverter. m And the switching signals of the industrial frequency expansion bridge circuit (S1, S4 and S2, S3).

[0174] Taking the generation of inductive reactive power as an example, the improved sinusoidal wave function adopts g(t), such as Fig.11 The figure shows an example of simulation of generating inductive reactive power.

[0175] Step 605: Based on the required power factor (PF), combined with the derivation process in step 303, calculate the phase shift angle corresponding to the target power factor. In this embodiment, taking the power factor PF = 0.8 as an example, the corresponding phase shift angle can be obtained: Radians. This angle is a key parameter to ensure that the inverter can achieve reactive power regulation at a specific power factor.

[0176] Step 606, by calculating the phase shift angle obtained in step 601 Substituting the harmonic distortion expression in step 302, the total harmonic distortion (THD) of the system can be solved. The THD value calculated in this embodiment is 23.2%. This value reflects the waveform quality of the system under this control parameter. A higher THD may have an adverse effect on the power quality, so it is necessary to weigh the relationship between this value and other performance parameters during design.

[0177] Step 607, after the phase shift angle has been determined Based on the analysis in step 405, the amplitude A of the grid-connected current is further calculated. This amplitude is related to the output active power P of the inverter and the phase shift angle In this embodiment, the active power P = 200W and As parameters, the grid-connected current amplitude A=1.66A is calculated.

[0178] Step 608: The grid-connected current amplitude A obtained in step 603 and the phase shift angle in step 601 are The input control circuit generates the corresponding grid-connected ISW waveform. This waveform will be used as the reference current of the PI controller to drive the main switch tube S of the grid-connected inverter. m And the switching signals of the industrial frequency expansion bridge circuit (S1, S4 and S2, S3).

[0179] In the simulation process, by applying the control signal to the inverter circuit, the inverter can accurately adjust the grid-connected current to meet the predetermined reactive power and power factor requirements. The simulation results show that the designed control strategy can maintain the stability of the system under different power factors, and by adjusting the control parameters, the total harmonic distortion can be effectively reduced and the output power quality can be improved.

[0180] The reactive power control method of a single-phase grid-connected inverter based on an improved sine wave of the present invention realizes effective control of the reactive power of the grid-connected inverter by designing an improved sine wave (ISW) and decomposing the same using Fourier series. First, a waveform consisting of an industrial frequency sine waveform and a linear waveform is defined, wherein the fundamental wave has a reactive component and contains harmonic components. Secondly, the improved sine wave is decomposed using Fourier series to analyze the total harmonic distortion (THD) and the power factor (PF). Then, based on the power transmission theory, the active power and reactive power of the grid-connected inverter are analyzed. The controller is designed again based on the improved sine wave to realize accurate control of the grid-connected current. Finally, the ISW sets the grid-connected current amplitude A and the phase shift angle φ according to the output requirements, and uses the obtained improved sine wave as the reference current of the PI controller. The method realizes efficient reactive power regulation through a simplified control strategy without adding additional hardware, and is suitable for power systems with high requirements for reactive power. The method can significantly reduce the total harmonic distortion (THD) under the premise of reactive power control, improve the power quality and system stability, and has important theoretical significance and practical application value for unidirectional energy transmission equipment such as photovoltaic inverters. The advantages of the present invention are simple operation, high efficiency and flexibility, and the ability to adjust the power factor to 0.8 or even lower, meeting the needs of different power systems, and having broad application prospects.

[0181] The above method corresponds to a reactive power control system of a single-phase grid-connected inverter based on an improved sine wave, comprising:

[0182] An improved sine wave construction unit is used to construct an improved sine wave ISW as a grid-connected current, and the improved sine wave is defined as a waveform composed of sine waveforms of different frequencies, and the improved sine wave signal contains harmonics;

[0183] A Fourier transform unit, used for performing Fourier series decomposition on the improved sine wave;

[0184] Total harmonic distortion and power factor analysis unit, used to analyze the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition;

[0185] Active and reactive power analysis unit, used to analyze the active power P and reactive power Q of the single-phase grid-connected inverter based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory;

[0186] The controller design unit is used to design and implement the controller according to the improved sine wave based on theoretical analysis;

[0187] The control unit is used to derive the grid-connected current peak value A and phase shift angle of the grid-connected ISW waveform according to the requirements of the output active power P and the power factor PF. The grid-connected ISW waveform is used as the reference current of the controller to achieve reactive power control.

[0188] A control device for storing and controlling the above method, including a processor, a communication interface, a memory and a communication bus;

[0189] Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus;

[0190] The memory is used to store computer programs;

[0191] The processor is used to implement the steps of the reactive power control method of a single-phase grid-connected inverter based on improved sine wave when executing the program stored in the memory.

[0192] A storage medium for storing and executing the above method, wherein a computer program is stored on the storage medium, and when the computer program is executed by at least one processor, the steps of the reactive power control method of a single-phase grid-connected inverter based on an improved sine wave are implemented.

[0193] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A reactive power control method for a single-phase grid-connected inverter based on an improved sine wave, characterized in that: The following steps are involved: (1) constructing an improved sine wave ISW as the grid-connected current, wherein the improved sine wave comprises sine waves of different frequencies, wherein the fundamental wave has a reactive component and contains harmonic components; (2) Perform Fourier series decomposition on the improved sine wave; (3) Analyze the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition; (4) Based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory, the active power P and reactive power Q of the single-phase grid-connected inverter are analyzed; (5) Based on theoretical analysis, design a controller based on the improved sine wave; (6) According to the requirements of output active power P and power factor PF, the grid current peak value A and phase shift angle of the grid-connected ISW waveform are derived. The grid-connected ISW waveform is used as the reference current of the controller to achieve reactive power control.

2. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: The improved sine wave in step (1) is: Among them, f(t) is the grid-connected current function of generating capacitive reactive power; g(t) is the grid-connected current function of generating inductive reactive power; A is the peak value of the grid-connected current, is the phase shift angle, ω is the angular frequency, and t is the time; The modified sine wave is used as a reference for delivering grid current.

3. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: In step (2), the improved sine wave is decomposed into Fourier series, specifically: (201) The Fourier series method is used to represent the grid-connected current. The current reference current i(t) of ISW is expressed as follows: Where n is the harmonic number of the current reference current of ISW, ω is the angular frequency, and a n and b n Analyze the Fourier series coefficients of the nth series for the Fourier series; (202) Perform Fourier series analysis on ISW, a0 = 0, a0 is the DC value of the Fourier series analysis of the ISW waveform; In the interval where ISW is not 0, the grid-connected current function is integrated and calculated a n , b n : Grid-connected current function f(t) for capacitive reactive power generation: The grid-connected current function g(t) for inductive reactive power generation is: Where, T is the period of ISW; (203) After the integral simplification of step (202), we get a n For A, The function is as follows: f(t): g(t): (204) After the integral simplification of step (202), we get b n For A, The function is as follows: (205) According to step (203) and step (204), we know that a n and b n is the ISW grid-connected current peak value A and phase shift angle The periodic signal is expanded into fundamental frequency and harmonic waves, which can be expressed as: Among them, I n is the amplitude of the nth harmonic, θ n is the phase angle of the nth harmonic; the parameter is obtained by the following formula: (206) According to step (203), step (204) and step (205), we can get n The expression is: Among them, K n is an intermediate variable; (207) According to step (203), step (204) and step (205), we can get θ n The expression is: f(t): g(t):

4. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: In step (3), the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition are analyzed, specifically: (301)The equation of THD and PF is: Where θ1 is the phase angle of the 1st harmonic; (302) According to the amplitude of the nth harmonic I n Step (301) obtains THD with respect to the phase shift angle The expression is: (303) According to the phase angle θ of the nth harmonic in step n Step (302) obtains PF with respect to the phase shift angle The expression is:

5. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: In step (4), based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory, the active power P and reactive power Q of the single-phase grid-connected inverter are analyzed; specifically: (401) According to power transmission theory, active power is defined as: Among them, V s is the amplitude of the grid voltage, I1 is the amplitude of the 1st harmonic, θ1 is the phase angle of the 1st harmonic; (402) According to power transmission theory, reactive power is defined as: (403) Expand i(t) to obtain: Step 404, compare the expression of the current reference current i(t) of ISW with step (403), and obtain: a n =I n sinθ n b n =I n cosθ n (405) According to b n Substituting n=1 into the expression, step (401) and step (404), the active power is obtained with respect to the ISW grid-connected current peak value A and the phase shift angle The expression is: (406) According to a n , step (402) and step (404), substituting n=1, the reactive power with respect to the ISW grid-connected current peak value A and the phase shift angle is obtained. The expression is: The reactive power Q is affected by the peak current A of the ISW grid and the phase shift angle. By changing these two parameters, the photovoltaic grid-connected inverter can inject reactive power into the grid. Different parameter combinations have different THD and PF.

6. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: In step (5), based on theoretical analysis, the controller is designed and implemented according to the improved sine wave; specifically: (501) An ISW ​​current reference generator is introduced. The ISW waveform is a combination of a sine wave and a linear waveform. The generator consists of a sine wave generator and a controller for converting the sine wave into an ISW. The sine wave generator outputs a sine wave synchronized with the grid voltage through a phase-locked loop, and then a part of the sine wave is linearized to obtain an ISW ​​waveform. (502) A PI controller is used to follow the ISW grid-connected current waveform.

7. The reactive power control method of a single-phase grid-connected inverter based on improved sine wave according to claim 1, characterized in that: In step (6), the grid-connected current peak value A and phase shift angle of the grid-connected ISW waveform are derived according to the requirements of the output active power P and the power factor PF. Specifically: (601) According to the required power factor PF combined with PF about the phase shift angle The expression of (602) The phase shift angle obtained according to step (601) Combined with THD about phase shift angle The expression of is used to solve the total harmonic distortion THD corresponding to PF; (603) Based on the required active power P and the phase shift angle obtained in step (601) Combined with the active power P about the ISW grid current peak A and phase shift angle The expression of P and PF is solved to find the grid-connected current amplitude A corresponding to P and PF; (604) The grid-connected current amplitude A and phase shift angle corresponding to P and PF are Used to construct the grid-connected ISW waveform as the reference current for the controller in step (5).

8. A reactive power control system for a single-phase grid-connected inverter based on an improved sine wave, characterized in that: include: An improved sine wave construction unit is used to construct an improved sine wave ISW as a grid-connected current, and the improved sine wave is defined as a waveform composed of sine waveforms of different frequencies, and the improved sine wave signal contains harmonics; A Fourier transform unit, used for performing Fourier series decomposition on the improved sine wave; Total harmonic distortion and power factor analysis unit, used to analyze the total harmonic distortion THD and power factor PF of the improved sine wave after Fourier series decomposition; Active and reactive power analysis unit, used to analyze the active power P and reactive power Q of the single-phase grid-connected inverter based on the total harmonic distortion THD and power factor PF of the improved sine wave and according to the power transmission theory; The controller design unit is used to design and implement the controller according to the improved sine wave based on theoretical analysis; The control unit is used to derive the grid-connected current peak value A and phase shift angle of the grid-connected ISW waveform according to the requirements of the output active power P and the power factor PF. The grid-connected ISW waveform is used as the reference current of the controller to achieve reactive power control.

9. A control device, characterized in that: including a processor, a communication interface, a memory and a communication bus; Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus; The memory is used to store computer programs; The processor is used to implement the steps of the reactive power control method of a single-phase grid-connected inverter based on an improved sine wave as described in any one of claims 1 to 7 when executing the program stored in the memory.

10. A storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by at least one processor, the steps of the reactive power control method of a single-phase grid-connected inverter based on an improved sine wave as described in any one of claims 1 to 7 are implemented.

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