A power quality regulation method based on photovoltaic and energy storage integrated inverter

Abstract

A power quality regulation method based on a photovoltaic and energy storage integrated inverter comprises: issuing a three-phase power reference instruction by using a power adaptive control method, and issuing a three-phase reactive power reference instruction by using a reactive power regulation method; calculating a three-phase current reference value according to the three-phase power reference instruction, and performing Clark transformation, positive and negative sequence separation, and #imgabs0# transformation on the three-phase current reference value and actual value and the three-phase voltage at a PCC in sequence, so as to obtain positive, negative, and zero-sequence current reference values ​​and actual values ​​in a #imgabs1# coordinate system, and positive and negative sequence voltages at a PCC; generating a three-phase harmonic current control instruction according to an inverter residual capacity calculation method, and then performing positive, negative, and zero-sequence current inner loop control according to the positive, negative, and zero-sequence current reference values ​​and actual values, respectively, to obtain positive and negative sequence components of the output voltage in a #imgabs2# coordinate system; and obtaining switching signals #imgabs3# of four bridge arms according to the positive and negative sequence components of the output voltage and the output voltage reference value of the fourth bridge arm.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution network, and in particular to a power quality regulation method based on a photovoltaic-storage integrated inverter. Background Art

[0002] There are a large number of single-phase sources and loads with unbalanced temporal and spatial distribution in the distribution network, and the mixed access of single-phase and three-phase loads often does not fully consider the three-phase balance of the load, which makes the three-phase imbalance phenomenon long-term and widespread. In addition, the large-scale, distributed power electronic equipment connected to the power grid along with the load has caused a surge in the number of harmonic sources in the power grid, and the harmonic pollution problem in the power grid has become more serious. These power quality problems will have an adverse impact on the power supply quality and economic operation of the distribution network. A large number of distributed new energy sources such as photovoltaics have been connected to the distribution network, which has changed the direction of the power flow in the distribution network. While alleviating energy problems, it has also brought problems such as power flow reverse transmission, voltage over-limit and difficulty in absorption to the distribution network. In particular, single-phase photovoltaics have aggravated the three-phase imbalance problem in the distribution network.

[0003] The existing solutions to the three-phase imbalance problem mainly include capacitor switching, reactive power compensation and reorganization of phase sequence. Capacitor switching compensates for unbalanced current and reactive power through parallel capacitors, but it has the disadvantages of not being able to adjust continuously and only being applicable to mild imbalance. Installing reactive power compensation devices can compensate for reactive power and realize compensation for negative-sequence and zero-sequence currents, but large-scale installations involve high investment and maintenance costs. Reorganization of phase sequence dynamically adjusts the load connection phase through phase-changing switches, but the investment cost is high and requires a complex monitoring and control system, high technical requirements, and great maintenance difficulties. Summary of the invention

[0004] In order to solve the problems of three-phase imbalance and harmonics in the distribution network, the present invention proposes a power quality regulation method based on a photovoltaic and energy storage integrated inverter. The method realizes the power outer loop control and current inner loop control in the system based on a phase-locked loop and a positive and negative sequence separation method. Without adding additional reactive compensation devices and phase-changing switches, the coordinated cooperation of photovoltaics and energy storage is utilized to realize the economic optimization operation of the system in the distribution network and the rapid treatment of three-phase imbalance and harmonics problems.

[0005] In order to solve the above technical problems, the present invention adopts the following technical method: a power quality regulation method based on a photovoltaic and energy storage integrated inverter, wherein the photovoltaic and energy storage integrated inverter adopts a three-phase four-bridge arm topology structure, and the power quality regulation method comprises:

[0006] Step S1, combining the photovoltaic working state, energy storage state and actual operating conditions of the load in the system, using the power adaptive control method to issue a three-phase power reference instruction to the photovoltaic-storage integrated inverter system, and using the reactive power regulation method based on the PI regulator to issue a three-phase reactive power reference instruction to the photovoltaic-storage integrated inverter system;

[0007] Step S2, power outer loop control: calculate the three-phase current reference value according to the three-phase power reference command, and perform Clark transformation, positive and negative sequence separation, and three-phase voltage at PCC on the three-phase current reference value, the actual value of the three-phase current, and the three-phase voltage at PCC in sequence. Transform, get The positive, negative and zero sequence current reference values ​​in the coordinate system and the actual values ​​of the positive and negative sequence currents and the positive and negative sequence voltages at the PCC;

[0008] Step S3, current inner loop control: Generate three-phase harmonic current control instructions according to the inverter residual capacity calculation method, and then perform positive, negative, and zero-sequence current inner loop control according to the positive, negative, and zero-sequence current reference values ​​and the positive and negative sequence current actual values, respectively, to obtain The positive and negative sequence components of the output voltage in the coordinate system;

[0009] Step S4, according to The positive and negative sequence components of the output voltage in the coordinate system and the output voltage reference value of the fourth bridge arm of the photovoltaic and energy storage integrated inverter are used to obtain the switching signals of the four bridge arms of the photovoltaic and energy storage integrated inverter. .

[0010] Furthermore, in step S1, the photovoltaic-storage integrated inverter system includes eight typical operating conditions, and the three-phase power reference instructions under different operating conditions are as follows:

[0011] 1) In the first working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. After the photovoltaic output power provides the power source for the photovoltaic integrated inverter, the remaining power is completely absorbed by the energy storage. There is no power exchange with the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as:

[0012] (1)

[0013] In the formula, It represents the three-phase active power output by the photovoltaic and energy storage integrated inverter. ;

[0014] 2) In the second working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. The photovoltaic output power is absorbed by the energy storage after providing the power source for the photovoltaic integrated inverter. At this time, the remaining power is absorbed by the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as:

[0015] (2)

[0016] In the formula, It is represented by the input power of the photovoltaic and energy storage integrated inverter; It is expressed as the average value of the three-phase active power output by the photovoltaic and energy storage integrated inverter, and its expression is as follows:

[0017] (3)

[0018] 3) In the third working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics, and there is no power exchange with the grid. The energy storage neither absorbs nor releases power. Phase active power reference command value The same as formula (1);

[0019] 4) The fourth working condition: the input power of the photovoltaic and energy storage integrated inverter is completely provided by photovoltaic and energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1);

[0020] 5) The fifth working condition is that the input power of the photovoltaic and energy storage integrated inverter is still insufficient after being provided by photovoltaic and energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value It is expressed as:

[0021] (4)

[0022] 6) The sixth working condition is that the photovoltaic power generation is not working, and the input power of the photovoltaic-storage integrated inverter is completely provided by the energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value The same as formula (4);

[0023] 7) The seventh working condition is that the photovoltaic power generation is not working, the input power of the photovoltaic and energy storage integrated inverter is completely provided by the energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1);

[0024] 8) The eighth working condition is that the photovoltaic power is not working, the energy storage is exhausted and absorbs power, and only the grid releases power, that is, the photovoltaic storage integrated inverter absorbs the remaining power after the load in the system consumes power. Phase active power reference command value It is expressed as:

[0025] (5).

[0026] Furthermore, in step S1, the voltage reference value of each phase is calculated With voltage measurement effective value After PI adjustment of the deviation, the reactive power reference command value of each phase is obtained. .

[0027] Furthermore, step S2 includes:

[0028] S201, the measured three-phase voltage of the power grid The phase of the positive sequence component of the fundamental frequency is obtained by using a phase-locked loop and frequency ;

[0029] S202, the power factor is set to 1, and the three-phase current reference value is calculated according to the following formula;

[0030] (6)

[0031] in, , No. Phase reactive power reference command value; ; Indicates The angle between the phase voltage and current is expressed as:

[0032] (7)

[0033] S203, using Clark transformation to transform the three-phase current reference value, the three-phase current actual value and the three-phase voltage at the PCC into the stationary Coordinate system, and then separate the positive and negative sequences to obtain Positive sequence current reference value in the coordinate system , Negative sequence current reference value , zero sequence current reference value , actual value of positive sequence current , actual value of negative sequence current , and the positive sequence voltage at PCC , negative sequence voltage at PCC ; The expression of the Clark transform is as follows:

[0034] (8)

[0035] S204, according to the following formula (9), the parameters obtained in step S203 are converted from static Coordinate transformation to rotation Coordinate system, get Positive sequence current reference value in the coordinate system , actual value of positive sequence current , positive sequence voltage at PCC , negative sequence current reference value , actual value of negative sequence current , negative sequence voltage at PCC ;

[0036] (9)

[0037] in, is the grid angular frequency, It indicates the rotation angle when the positive sequence component is transformed, that is, the phase of the positive sequence component of the grid base frequency output by the phase-locked loop in real time. ,according to Can get ; The rotation angle when the negative sequence component is transformed is ,according to Can get .

[0038] Furthermore, step S3 includes:

[0039] S301, calculate the output voltage of each phase of the photovoltaic-storage integrated inverter according to the following formula (10): , and determine the peak value of the output voltage margin of each phase of the photovoltaic storage integrated inverter , as shown in formula (11);

[0040] (10)

[0041] in, is the filter inductance value of the inverter;

[0042] (11)

[0043] in, Indicates the DC input voltage of the photovoltaic-storage integrated inverter. yes The peak value of

[0044] S302, collecting grid-connected current of each phase load , and then filter it and perform Fourier transform decomposition to obtain the harmonic components of each phase, and select the harmonic with the most serious harmonic content exceeding the standard as the harmonic control target of each phase , let its peak value be , Indicates the target harmonic order of each phase; the reference value of the reverse harmonic current to be injected into each phase is calculated according to the following formula (12): ;

[0045] (12)

[0046] S303, filtering the current of each phase output by the photovoltaic and energy storage integrated inverter through a filter to obtain the actual output value of the target harmonic of each phase , and The output voltage reference value of harmonic control is obtained by making a difference and outputting it through PR control. ;

[0047] S304, perform current inner loop control according to the parameters obtained in step S204, as shown in the following formulas (13)-(16): Positive sequence component of output voltage in coordinate system , negative sequence component ;

[0048] (13)

[0049] (14)

[0050] (15)

[0051] (16)

[0052] in, They are the parameters of the PI regulator ; is the grid angular frequency.

[0053] S305, calculating the output voltage reference value of the fourth bridge arm of the photovoltaic-storage integrated inverter, that is, the zero-sequence voltage reference value, according to the following formula (17);

[0054] (17)

[0055] in, is the proportional regulator parameter.

[0056] Preferably, in step S4, the The positive and negative sequence components of the output voltage in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system. , Then, the voltage reference value of each phase Output voltage reference value for harmonic control After adding, the signals are input into the pulse width modulator to obtain the conduction signals of the first three bridge arms of the photovoltaic and energy storage integrated inverter. At the same time, the output voltage reference value of the fourth bridge arm of the photovoltaic storage integrated inverter is Input to the pulse width modulator to obtain the switching signal of the fourth bridge arm .

[0057] The beneficial effects of the present invention are:

[0058] 1. The power adaptive control method proposed in the present invention combines the photovoltaic working state, energy storage state and the actual operating conditions of the load in the system, calculates the power reference instructions of each phase and issues them to the photovoltaic and energy storage integrated inverter system. The considered operating conditions can cover the normal operating conditions.

[0059] 2. The photovoltaic-storage integrated inverter system of the present invention utilizes the synergistic cooperation of photovoltaics and energy storage to jointly achieve economic optimization of system operation and rapid management of three-phase imbalance in the distribution network without adding additional reactive compensation devices and phase-changing switches.

[0060] 3. The photovoltaic-storage integrated inverter system in the present invention can not only realize system operation during power output, but also utilize energy storage to absorb power and reverse power to realize system operation when photovoltaic power is not working and energy storage power is exhausted. Based on the inverter remaining capacity calculation method, the inverter output equivalent reverse current harmonics are used to achieve the target harmonic control with the highest harmonic content. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a block diagram of the reactive power regulation method based on PI regulator involved in the present invention;

[0062] Figure 2 is a structural diagram of a phase-locked loop involved in the present invention;

[0063] Figure 3 It is a block diagram of the positive and negative sequence separation involved in the present invention;

[0064] Figure 4 It is an overall control block diagram of the power quality regulation method involved in the present invention;

[0065] Figure 5 This is a simulation model diagram of a single-machine photovoltaic-storage integrated inverter involved in the present invention;

[0066] Figure 6 : is a three-phase active power diagram output by the photovoltaic-storage integrated inverter in an embodiment of the present invention;

[0067] Figure 7 is the three-phase voltage at the PCC before the power quality regulation method of the present invention is used in the embodiment;

[0068] Figure 8 It is the three-phase voltage at the PCC after being treated by the power quality regulation method of the present invention in the embodiment. DETAILED DESCRIPTION

[0069] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0070] The traditional photovoltaic inverter has a balanced three-phase output, and cannot provide power support for a certain phase when a three-phase imbalance occurs. The photovoltaic and energy storage integrated inverter that integrates photovoltaics and energy storage to achieve integrated management of "photovoltaics + energy storage" provides a new idea for solving problems such as three-phase imbalance, harmonics and photovoltaic absorption. Based on this, the present invention proposes a power quality regulation method based on a photovoltaic and energy storage integrated inverter, which can support the active demand of each phase based on a power adaptive control method, compensate for reactive power according to actual demand to achieve voltage support, and use PR control to achieve the inverter output equivalent reverse current harmonics according to the remaining capacity of the inverter to control the harmonics with the highest harmonic content, as follows.

[0071] like Figure 4 As shown, a power quality regulation method based on a photovoltaic and energy storage integrated inverter mainly includes four steps.

[0072] Step S1, combining the photovoltaic working state, energy storage state and the actual operating condition of the load in the system, using the power adaptive control method to issue a three-phase power reference instruction to the photovoltaic storage integrated inverter system, and using the reactive power regulation method based on the PI regulator to issue a three-phase reactive power reference instruction to the photovoltaic storage integrated inverter system, the specific steps are as follows:

[0073] First, photovoltaics have two states: working and non-working. When photovoltaics are working, in order to maximize the utilization efficiency of photovoltaics, it is assumed that they always work in the maximum power output state, that is, photovoltaics have maximum power point tracking (MPPT) function, and the output power is When the photovoltaic power is not working, the output power is 0. Energy storage has three states: charging, discharging, and neither charging nor discharging. The power states presented to the outside are respectively expressed as and 0.

[0074] Since distributed photovoltaics have the characteristics of most photovoltaic electricity being directly consumed by the load and self-generated for self-use, when photovoltaics are working, the photovoltaic power output priority is load, energy storage, and power grid, and the power source priority of the load is photovoltaics, energy storage, and power grid; when photovoltaics are not working, the power source priority of the load is energy storage and power grid.

[0075] At this time, there are eight typical operating conditions in the system. The first is that the photovoltaic system works, the energy storage system is charged, and the grid neither absorbs nor releases power; the second is that the photovoltaic system works, the energy storage system is charged, and the grid absorbs surplus power; the third is that the photovoltaic system works, the energy storage system is neither charged nor discharged, and the grid neither absorbs nor releases power; the fourth is that the photovoltaic system works, the energy storage system is discharged, and the grid neither absorbs nor releases power; the fifth is that the photovoltaic system works, the energy storage system is discharged, and the grid releases power; the sixth is that the photovoltaic system does not work, the energy storage system is discharged, and the grid releases power; the seventh is that the photovoltaic system does not work, the energy storage system is discharged, and the grid neither absorbs nor releases power. The eighth is that the photovoltaic system does not work, the energy storage system is exhausted and absorbs power, and only the grid releases power, that is, the photovoltaic system integrates the photovoltaic system and the energy storage system to absorb the remaining power after the load in the system is consumed.

[0076] The three-phase active power output by the integrated photovoltaic and energy storage inverter is expressed as , the average value It is expressed as:

[0077] (3)

[0078] The input power of the integrated photovoltaic and energy storage inverter is expressed as , according to the actual operating conditions in the system, the three-phase active power reference command value can be obtained .

[0079] 1) In the first working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. After the photovoltaic output power provides the power source for the photovoltaic integrated inverter, the remaining power is completely absorbed by the energy storage. There is no power exchange with the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as:

[0080] (1)

[0081] 2) In the second working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. The photovoltaic output power is absorbed by the energy storage after providing the power source for the photovoltaic integrated inverter. At this time, the remaining power is absorbed by the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as:

[0082] (2)

[0083] 3) In the third working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics, and there is no power exchange with the grid. The energy storage neither absorbs nor releases power. Phase active power reference command value The same as formula (1);

[0084] 4) The fourth working condition: the input power of the photovoltaic and energy storage integrated inverter is completely provided by photovoltaic and energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1);

[0085] 5) The fifth working condition is that the input power of the photovoltaic and energy storage integrated inverter is still insufficient after being provided by photovoltaic and energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value It is expressed as:

[0086] (4)

[0087] 6) The sixth working condition is that the photovoltaic power generation is not working, and the input power of the photovoltaic-storage integrated inverter is completely provided by the energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value The same as formula (4);

[0088] 7) The seventh working condition is that the photovoltaic power generation is not working, the input power of the photovoltaic and energy storage integrated inverter is completely provided by the energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1);

[0089] 8) The eighth working condition is that the photovoltaic power is not working, the energy storage is exhausted and absorbs power, and only the grid releases power, that is, the photovoltaic storage integrated inverter absorbs the remaining power after the load in the system consumes power. Phase active power reference command value It is expressed as:

[0090] (5).

[0091] The purpose of reactive power regulation is to adjust the voltage reference value of each phase With voltage measurement effective value The deviation of the output reactive power is used to adjust the voltage. After the voltage deviation is adjusted by PI, the first Phase reactive power reference command value , the reactive power regulation method based on PI regulator is as follows Figure 1 shown.

[0092] Step S2, power outer loop control: calculate the three-phase current reference value according to the three-phase power reference command, and perform Clark transformation, positive and negative sequence separation, and three-phase voltage at PCC on the three-phase current reference value, the actual value of the three-phase current, and the three-phase voltage at PCC in sequence. Transform, get The positive, negative and zero sequence current reference values ​​in the coordinate system, the actual values ​​of the positive and negative sequence currents and the positive and negative sequence voltages at the PCC, the specific steps are as follows:

[0093] S201, the measured three-phase voltage of the power grid The phase of the positive sequence component of the fundamental frequency is obtained by using a phase-locked loop and frequency The phase-locked loop used in the present invention refers to the public document "Liu Feng. Research on three-phase phase-locked loop under unbalanced power grid [D]. University of Electronic Science and Technology of China, 2013", the structure is as follows Figure 2 As shown in the figure, the harmonics of the three-phase voltage of the power grid are partially filtered out by the orthogonal signal generator (Second-Order Generalized Integrator-Quadrature-Signal Generator, SOGI-QSG) to obtain the fundamental frequency component. , and its orthogonal components , , and then decouple to obtain the positive sequence component of the fundamental frequency , Finally, the phase of the baseband positive sequence component is obtained through a phase-locked loop (Synchronous Reference Frame-PLL, SRF-PLL) based on a synchronous coordinate system. and frequency .

[0094] The current low-voltage distribution network generally adopts a three-phase four-wire power supply method. When a three-phase imbalance problem occurs in the distribution network, the three-phase current is decomposed according to the symmetrical component method to obtain negative-sequence components and zero-sequence components in addition to the positive-sequence components. In addition, the inverter with a three-phase three-bridge arm topology structure cannot provide a path for the zero-sequence component in the unbalanced current and is not suitable for solving the three-phase imbalance problem. The photovoltaic storage integrated inverter system in the present invention adopts a three-phase four-bridge arm topology structure, and the fourth bridge arm is composed of a switching device.

[0095] S202, in order to ensure that the photovoltaic-storage integrated inverter system can output power according to the command, the power factor is set to 1, and the three-phase current reference value is expressed as:

[0096] (6)

[0097] in, , No. Phase reactive power reference command value; ; Indicates The angle between the phase voltage and current is expressed as:

[0098] (7)

[0099] S203, using Clark transformation to transform the three-phase current reference value, the three-phase current actual value and the three-phase voltage at the PCC into the stationary Coordinate system, the expression of Clark transformation is as follows:

[0100] (8)

[0101] The same SOGI-QSG and decoupling calculation part as in the phase-locked loop are used to separate the positive and negative sequences of the three-phase current reference value, the three-phase current actual value and the three-phase voltage at the PCC. Taking the positive and negative sequence separation of the three-phase voltage at the PCC as an example, its structure diagram is as follows Figure 3 shown.

[0102] get Positive sequence current reference value in the coordinate system , Negative sequence current reference value , zero sequence current reference value , actual value of positive sequence current , actual value of negative sequence current , and the positive sequence voltage at PCC , negative sequence voltage at PCC ; Among them, the actual zero sequence current Obtained by measurement.

[0103] S204, according to the following formula (9), the parameters obtained in step S203 are converted from static Coordinate transformation to rotation Coordinate system, get Positive sequence current reference value in the coordinate system , actual value of positive sequence current , positive sequence voltage at PCC , negative sequence current reference value , actual value of negative sequence current , negative sequence voltage at PCC ;

[0104] (9)

[0105] in, is the grid angular frequency, It indicates the rotation angle when the positive sequence component is transformed, that is, the phase of the positive sequence component of the grid base frequency output by the phase-locked loop in real time. ,according to Can get ; The rotation angle when the negative sequence component is transformed is ,according to Can get .

[0106] Step S3, current inner loop control: Generate three-phase harmonic current control instructions according to the inverter residual capacity calculation method, and then perform positive, negative, and zero-sequence current inner loop control according to the positive, negative, and zero-sequence current reference values ​​and the positive and negative sequence current actual values, respectively, to obtain The positive and negative sequence components of the output voltage in the coordinate system, the specific steps are as follows:

[0107] S301, the three-phase voltage at PCC, that is, the voltage after filtering by LC filter As a benchmark, the voltage before LC filter filtering can be obtained, that is, the output voltage of each phase of the inverter , as follows:

[0108] (10)

[0109] in, is the filter inductance value of the inverter, The filter inductance values ​​of the three phases are equal.

[0110] Peak value of output voltage margin of each phase of photovoltaic and energy storage integrated inverter It is expressed as:

[0111] (11)

[0112] in, Indicates the DC input voltage of the photovoltaic-storage integrated inverter. yes The peak value of

[0113] S302, collecting grid-connected current of each phase load , and then filter it and perform Fourier transform decomposition to obtain the harmonic components of each phase, and select the harmonic with the most serious harmonic content exceeding the standard as the harmonic control target of each phase , let its peak value be , Indicates the target harmonic order of each phase; the reference value of the reverse harmonic current to be injected into each phase is calculated according to the following formula (12): ;

[0114] (12)

[0115] S303, filtering the current of each phase output by the photovoltaic and energy storage integrated inverter through a filter to obtain the actual output value of the target harmonic of each phase , and The output voltage reference value of harmonic control is obtained by making a difference and outputting it through PR control. ;

[0116] S304, perform current inner loop control according to the parameters obtained in step S204, as shown in the following formulas (13)-(16): Positive sequence component of output voltage in coordinate system , negative sequence component ;

[0117] (13)

[0118] (14)

[0119] (15)

[0120] (16)

[0121] in, They are the parameters of the PI regulator ; is the grid angular frequency.

[0122] S305, calculating the output voltage reference value of the fourth bridge arm of the photovoltaic-storage integrated inverter, that is, the zero-sequence voltage reference value, according to the following formula (17);

[0123] (17)

[0124] in, is the proportional regulator parameter.

[0125] Step S4, according to The positive and negative sequence components of the output voltage in the coordinate system and the output voltage reference value of the fourth bridge arm of the photovoltaic and energy storage integrated inverter are used to obtain the switching signals of the four bridge arms of the photovoltaic and energy storage integrated inverter. , the specific steps are as follows:

[0126] The result obtained in step S3 The positive and negative sequence components of the output voltage in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system. , Then, the voltage reference value of each phase Output voltage reference value for harmonic control After adding, the signals are input into the pulse width modulator to obtain the conduction signals of the first three bridge arms of the photovoltaic and energy storage integrated inverter. At the same time, the output voltage reference value of the fourth bridge arm of the photovoltaic storage integrated inverter is Input to the pulse width modulator to obtain the switching signal of the fourth bridge arm .

[0127] Next, we take a single-machine photovoltaic-storage integrated inverter as an example and build a simulation model in MATLAB / Simulink. Figure 5 As shown, the system of this embodiment includes a photovoltaic storage integrated inverter, photovoltaic, energy storage, LC filter, three-phase unbalanced load (wherein phase A is 5kW+2kVar, phase B is 5kW+2kVar, and phase C is 10kW+5kVar) and a substation transformer with an effective value of 380V at the outlet, etc. The distribution network is connected to the system in the form of a substation transformer, and the frequency is 50Hz. It should be noted that:

[0128] 1) According to the actual operating conditions in the system, the power adaptive control method is used to obtain the three-phase active power reference command value This embodiment takes the first working condition as an example, the first phase of the three-phase active power Phase active power reference command value The expression of is as shown in formula (1). The reference value of each phase voltage 220V, Figure 1 After reactive power regulation, the following can be obtained: Phase reactive power reference command value .

[0129] 2) Calculate the three-phase current reference value according to formula (6). Specifically, in this embodiment , .

[0130] The three-phase active power output by the photovoltaic-storage integrated inverter of this embodiment is as follows: Figure 6 As shown, the three-phase voltages before and after the power quality regulation method of the present invention is used at the PCC are respectively as follows: Figure 7 , 8 As shown. Figure 6-8 It can be seen that the three-phase active power is output according to the power adaptive control method, and the three-phase imbalance and harmonic problems are effectively controlled.

[0131] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0132] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A method for regulating power quality based on a photovoltaic and energy storage integrated inverter, characterized in that: The photovoltaic-storage integrated inverter adopts a three-phase four-bridge arm topology structure, and the power quality regulation method includes: Step S1, combining the photovoltaic working state, energy storage state and the actual operating condition of the load in the system, using the power adaptive control method to issue a three-phase power reference instruction to the photovoltaic-storage integrated inverter system, and using the reactive power regulation method based on the PI regulator to issue a three-phase reactive power reference instruction to the photovoltaic-storage integrated inverter system; The photovoltaic and energy storage integrated inverter system includes eight typical operating conditions. The three-phase power reference instructions under different operating conditions are as follows: 1) In the first working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. After the photovoltaic output power provides the power source for the photovoltaic integrated inverter, the remaining power is completely absorbed by the energy storage. There is no power exchange with the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as: (1) In the formula, It represents the three-phase active power output by the photovoltaic and energy storage integrated inverter. ; 2) In the second working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics. The photovoltaic output power is absorbed by the energy storage after providing the power source for the photovoltaic integrated inverter. At this time, the remaining power is absorbed by the grid. The first phase of the three-phase active power is Phase active power reference command value It is expressed as: (2) In the formula, It is represented by the input power of the photovoltaic and energy storage integrated inverter; It is expressed as the average value of the three-phase active power output by the photovoltaic and energy storage integrated inverter, and its expression is as follows: (3) 3) In the third working condition, the input power of the photovoltaic integrated inverter is completely provided by photovoltaics, and there is no power exchange with the grid. The energy storage neither absorbs nor releases power. Phase active power reference command value The same as formula (1); 4) The fourth working condition: the input power of the photovoltaic and energy storage integrated inverter is completely provided by photovoltaic and energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1); 5) The fifth working condition is that the input power of the photovoltaic and energy storage integrated inverter is still insufficient after being provided by photovoltaic and energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value It is expressed as: (4) 6) The sixth working condition is that the photovoltaic power generation is not working, and the input power of the photovoltaic-storage integrated inverter is completely provided by the energy storage. At this time, the power missing from the load is provided by the grid. Phase active power reference command value The same as formula (4); 7) The seventh working condition is that the photovoltaic power generation is not working, the input power of the photovoltaic and energy storage integrated inverter is completely provided by the energy storage, and there is no power exchange with the grid. Phase active power reference command value The same as formula (1); 8) The eighth working condition is that the photovoltaic power is not working, the energy storage is exhausted and absorbs power, and only the grid releases power, that is, the photovoltaic storage integrated inverter absorbs the remaining power after the load in the system consumes power. Phase active power reference command value It is expressed as: (5) Step S2, power outer loop control: calculate the three-phase current reference value according to the three-phase power reference command, and perform Clark transformation, positive and negative sequence separation, and three-phase voltage at PCC on the three-phase current reference value, the actual value of the three-phase current, and the three-phase voltage at PCC in sequence. αβ / dq Transform, get dq The positive, negative and zero sequence current reference values ​​in the coordinate system and the actual values ​​of the positive and negative sequence currents and the positive and negative sequence voltages at the PCC; S201, the measured three-phase voltage of the power grid The phase of the positive sequence component of the fundamental frequency is obtained by using a phase-locked loop and frequency ; S202, the power factor is set to 1, and the three-phase current reference value is calculated according to the following formula; (6) in, , No. Phase reactive power reference command value; ; Indicates The angle between the phase voltage and current is expressed as: (7) S203, using Clark transformation to transform the three-phase current reference value, the three-phase current actual value and the three-phase voltage at the PCC into a stationary Coordinate system, and then separate the positive and negative sequences to obtain Positive sequence current reference value in the coordinate system , Negative sequence current reference value , zero sequence current reference value , actual value of positive sequence current , actual value of negative sequence current , and the positive sequence voltage at PCC , negative sequence voltage at PCC ; The expression of the Clark transform is as follows: (8) S204, according to the following formula (9), the parameters obtained in step S203 are converted from static Coordinate transformation to rotation Coordinate system, get Positive sequence current reference value in the coordinate system , actual value of positive sequence current , positive sequence voltage at PCC , negative sequence current reference value , actual value of negative sequence current , negative sequence voltage at PCC ; (9) in, is the grid angular frequency, It indicates the rotation angle when the positive sequence component is transformed, that is, the phase of the positive sequence component of the grid base frequency output by the phase-locked loop in real time. ,according to Can get ; The rotation angle when the negative sequence component is transformed is ,according to Can get ; Step S3, current inner loop control: Generate three-phase harmonic current control instructions according to the inverter residual capacity calculation method, and then perform positive, negative, and zero-sequence current inner loop control according to the positive, negative, and zero-sequence current reference values ​​and the positive and negative sequence current actual values, respectively, to obtain The positive and negative sequence components of the output voltage in the coordinate system; S301, calculate the output voltage of each phase of the photovoltaic energy storage integrated inverter according to the following formula (10): , and determine the peak value of the output voltage margin of each phase of the photovoltaic storage integrated inverter , as shown in formula (11); (10) in, is the filter inductance value of the inverter; (11) in, Indicates the DC input voltage of the photovoltaic-storage integrated inverter. yes The peak value of S302, collecting grid-connected current of each phase load , and then filter it and perform Fourier transform decomposition to obtain the harmonic components of each phase, and select the harmonic with the most serious harmonic content exceeding the standard as the harmonic control target of each phase , let its peak value be , Indicates the target harmonic order of each phase; the reference value of the reverse harmonic current to be injected into each phase is calculated according to the following formula (12): ; (12) S303, filtering the current of each phase output by the photovoltaic and energy storage integrated inverter through a filter to obtain the actual output value of the target harmonic of each phase , and The output voltage reference value of harmonic control is obtained by making a difference and outputting it through PR control. ; S304, perform current inner loop control according to the parameters obtained in step S204, as shown in the following formulas (13)-(16): Positive sequence component of output voltage in coordinate system , negative sequence component ; (13) (14) (15) (16) in, They are the parameters of the PI regulator ; S305, calculating the output voltage reference value of the fourth bridge arm of the photovoltaic-storage integrated inverter, that is, the zero-sequence voltage reference value, according to the following formula (17); (17) in, is the proportional regulator parameter; Step S4, according to The positive and negative sequence components of the output voltage in the coordinate system and the output voltage reference value of the fourth bridge arm of the photovoltaic-storage integrated inverter are used to obtain the switching signals S1-S8 of the four bridge arms of the photovoltaic-storage integrated inverter.

2. The power quality regulation method based on the photovoltaic-storage integrated inverter according to claim 1 is characterized in that: In step S1, the voltage reference value of each phase is calculated With voltage measurement effective value After PI adjustment of the deviation, the reactive power reference command value of each phase is obtained. .

3. The power quality regulation method based on the photovoltaic-storage integrated inverter according to claim 1 is characterized in that: Step S4, the The positive and negative sequence components of the output voltage in the coordinate system are respectively subjected to inverse Park transformation and then added to obtain the three-phase voltage reference value in the abc coordinate system. , Then, the voltage reference value of each phase Output voltage reference value for harmonic control After addition, they are input into the pulse width modulator to obtain the conduction signals S1-S6 of the first three bridge arms of the photovoltaic and energy storage integrated inverter, and at the same time, the output voltage reference value of the fourth bridge arm of the photovoltaic and energy storage integrated inverter is The signals are input into the pulse width modulator to obtain the switching signals S7-S8 of the fourth bridge arm.

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