CN105281368B - A kind of grid-connected and power quality controlling Unified Control Strategy - Google Patents
A kind of grid-connected and power quality controlling Unified Control Strategy Download PDFInfo
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Abstract
The invention discloses a kind of grid-connected and power quality controlling Unified Control Strategy, comprise the following steps, 1) photovoltaic module output is detected in real time, adjust photovoltaic parallel in system operational mode；When being unsatisfactory for active grid-connected conditions, photovoltaic parallel in system is with power quality controlling mode operation, and when meeting active grid-connected conditions, photovoltaic parallel in system is run with active grid-connected and power quality controlling More General Form；2) when photovoltaic parallel in system is run with active grid-connected and power quality controlling More General Form, first according to the idle and priority of harmonic compensation height, the residual capacity of photovoltaic parallel in system is distributed, instantaneous power theory is then based on and integrates instruction current.The present invention makes photovoltaic parallel in system possess the function of being actively engaged in power network power quality controlling on the basis of original function is kept, improves the utilization rate of inverter, reduce the input of power quality controlling device, saved cost compared to conventional method.
Description
Technical Field
The invention relates to a photovoltaic grid-connected and power quality control unified control strategy, and belongs to the field of power electronic technology and power quality control research.
Background
With the urgent need of social development for new energy and the increasing maturity of photovoltaic power generation technology, photovoltaic power generation has entered a large-area popularization stage. However, due to the randomness and intermittence of illumination, the problems of low utilization rate of the photovoltaic inverter, poor economic benefit of the system and the like exist. On the other hand, with the occurrence of a large number of nonlinear and impact loads in the power grid, the pollution of generated harmonic waves and reactive current to the public power grid is increasingly serious, a large number of compensation devices are needed to improve the quality of electric energy, and the additional increase of the compensation devices increases the input cost of the power grid. The main circuit structure of the photovoltaic grid-connected inverter is basically consistent with that of the active filter, and only the control algorithms are different, so that the functions of the photovoltaic grid-connected inverter can be integrated and unified control is adopted. The photovoltaic grid-connected inverter with a unified control strategy is used for actively participating in power quality management of a power grid, functional expansion of a photovoltaic grid-connected system is achieved, economic benefits of photovoltaic power generation are improved, and management cost is reduced while power quality is managed.
In recent years, scholars at home and abroad carry out related research on the multifunctional photovoltaic grid-connected inverter. The students uniformly control a Static Var Generator (SVG) and grid-connected power generation, realize reactive compensation by using the residual capacity of active power grid connection, and effectively inhibit dynamic voltage fluctuation. Researchers study the unified control of the active filter and the photovoltaic grid-connected inverter, mainly expound the synthesis algorithm of active current and compensation current, and realize active grid connection and simultaneously compensate reactive power and harmonic waves. The basic strategies of the researches are to utilize the residual capacity of active grid connection to carry out power quality management, but the compensation strategy when the residual capacity cannot meet reactive harmonic full compensation is not considered; and the system operation mode is not deeply researched; most of the researches are theoretical researches and simulation verification, and complete system realization is not seen.
Disclosure of Invention
In order to solve the technical problem, the invention provides a photovoltaic grid connection and power quality management unified control strategy.
In order to achieve the purpose, the invention adopts the technical scheme that:
a photovoltaic grid connection and electric energy quality management unified control strategy comprises the following steps,
1) detecting the output of the photovoltaic module in real time, and adjusting the operation mode of the photovoltaic grid-connected system;
when the active grid-connected condition is not met, the photovoltaic grid-connected system operates in a power quality management mode, and when the active grid-connected condition is met, the photovoltaic grid-connected system operates in a unified mode of active grid-connected and power quality management;
2) when the photovoltaic grid-connected system operates in an active grid-connected and power quality management unified mode, firstly, the residual capacity of the photovoltaic grid-connected system is distributed according to the priority level of reactive power and harmonic compensation, and then, the command current is integrated based on the instantaneous power theory.
The process of adjusting the operation mode of the photovoltaic grid-connected system comprises the following steps,
defining the output current threshold value of the photovoltaic module as ipvf；
When the photovoltaic module outputs current i in real timepv＜ipvfWhen the photovoltaic grid-connected system is judged to be not capable of meeting the active grid-connected condition, the photovoltaic grid-connected system operates in an electric energy quality management mode;
when the photovoltaic module outputs current i in real timepv≥ipvfAnd in the mode, part of active power output by the photovoltaic module is used for overcoming the switching loss of the photovoltaic grid-connected system, and the other part of the active power is converted into grid-connected active current through the direct current side PI control.
According to the priority of the reactive power and harmonic compensation, the process of distributing the residual capacity of the photovoltaic grid-connected system comprises the following steps,
A1) method for detecting load electricity by adopting ip-iq methodExtracting active, reactive and harmonic currents, and calculating the effective value I of the active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenth；
A2) Defining rated capacity as IsThen remaining capacity
A3) If the residual capacity is sufficient, that isThe full compensation of reactive power and harmonic wave can be satisfied to obtain the reactive compensation coefficient kqAnd harmonic compensation coefficient kh(ii) a If the residual capacity is not sufficient, that isThen, according to the priority of the reactive power and harmonic compensation, a certain component can be compensated preferentially to obtain a reactive power compensation coefficient kqAnd harmonic compensation coefficient kh；
A4) Distributing the residual capacity according to the compensation coefficient;
the distributed reactive capacity is Iq *＝kqIqThe harmonic capacity after distribution is Ih *＝khIh。
Calculating the effective value I of the active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenthThe process of (a) is that,
B1) defining three-phase current at load side as ia、ib、ic；
Where ω t is the phase of the grid voltage,representing the phase difference between the voltage and the current n times, InRepresents n times of current;
B2) active and reactive decoupling is carried out on the three-phase current to obtain ip、iq；
Wherein,
B3) will ip、iqObtaining a DC component by a low-pass filterWherein,in order to be the active current component,is a reactive current component;
B4) will ipMinusiqMinusRespectively obtain alternating current componentsI.e. harmonic components;
B5) will be provided withPerforming inverse transformation to obtain reactive current;
wherein, C23、C-1Are respectively C32Inverse matrix of C, iaq、ibq、icqRepresenting three-phase reactive current;
will be provided withCarrying out inverse transformation to obtain harmonic current;
wherein iah、ibh、ichRepresenting three-phase harmonic currents;
B6) integrating the reactive current to obtain the effective value I of the reactive currentq；
Wherein T represents an integration period;
integrating the harmonic current to obtain the effective value I of the harmonic currenth；
B7) Since the active current is the fundamental current in phase with the grid voltage, the effective value of the active current isWherein ipdcAnd outputting active grid-connected components for the direct-current side voltage control.
The decoupled components are controlled, so that the redistribution of the residual capacity of the photovoltaic grid-connected system can be realized, and the compensation instruction current is obtained;
wherein,in order to reactive-load compensate the command current,andcompensating the command current for harmonics;
integrating reactive compensation command current, harmonic compensation command current and active current command based on an instantaneous power theory;
the integrated formula is as follows,
wherein ia *、ib *、ic *Is the integrated three-phase command current.
The invention achieves the following beneficial effects: compared with the traditional method, the photovoltaic grid-connected system has the function of actively participating in power quality management of the power grid on the basis of keeping the original functions, the utilization rate of the inverter is improved, the investment of a power quality management device is reduced, and the cost is saved.
Drawings
Fig. 1 illustrates the principle of the present invention.
Fig. 2 shows a strategy for adjusting an operation mode of a photovoltaic grid-connected system.
FIG. 3 illustrates a control strategy for integrating remaining capacity allocation and command current.
Fig. 4 is a controller software hardware structure.
FIG. 5 is an experimental protocol.
Fig. 6 shows dc side voltage waveforms in non-fully compensated/compensated and electrically connected mode of operation.
Fig. 7 shows the grid-side current waveform in the no light compensation/light compensation and power generation mode of operation.
Fig. 8 shows the effect of the power quality management mode operation.
Fig. 9 shows the waveform after the a-state compensation.
Fig. 10 shows the waveform after b-state compensation.
Fig. 11 shows the waveform after c-state compensation.
Fig. 12 shows the waveform after d-state compensation.
Fig. 13 shows the waveform after e-state compensation.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
As shown in fig. 1, a unified control strategy for photovoltaic grid connection and power quality management includes the following steps:
1) and detecting the output of the photovoltaic module in real time, and adjusting the operation mode of the photovoltaic grid-connected system.
When the active grid-connected condition is not met, the photovoltaic grid-connected system operates in a power quality management mode, and when the active grid-connected condition is met, the photovoltaic grid-connected system operates in a unified mode of active grid-connected and power quality management.
As shown in fig. 2:
defining the output current threshold value of the photovoltaic module as ipvf；
When the photovoltaic module outputs current i in real timepv＜ipvfWhen the photovoltaic grid-connected system is judged to be not capable of meeting the active grid-connected condition, the photovoltaic grid-connected system operates in an electric energy quality management mode; the reference voltage on the direct current side adopts a constant value; in the mode, the direct current side PI control overcomes the switching loss of a photovoltaic grid-connected system by adjusting the amount of active current absorbed from a power grid, maintains power balance and stabilizes voltage;
when the photovoltaic module outputs current i in real timepv≥ipvfAnd in the mode, part of active power output by the photovoltaic module is used for overcoming the switching loss of the photovoltaic grid-connected system, and the other part of the active power is converted into grid-connected active current through the direct current side PI control.
2) When the photovoltaic grid-connected system operates in an active grid-connected and power quality management unified mode, firstly, the residual capacity of the photovoltaic grid-connected system is distributed according to the priority level of reactive power and harmonic compensation, and then, the command current is integrated based on the instantaneous power theory.
On the premise of realizing the maximum active power grid connection, the residual capacity of the photovoltaic grid connection system is limited, so that the full compensation of reactive harmonics can not be met, and the residual capacity needs to be redistributed.
As shown in fig. 3, according to the priority of the reactive power and harmonic compensation, the process of allocating the remaining capacity of the photovoltaic grid-connected system is as follows:
A1) detecting load current by using an ip-iq method, extracting active, reactive and harmonic currents, and calculatingEffective value I of active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenth。
Calculating the effective value I of the active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenthThe process comprises the following steps:
B1) defining three-phase current at load side as ia、ib、ic；
Wherein, ω t is the phase of the network voltage, obtained by a phase locked loop,representing the phase difference between the voltage and the current n times, InRepresents n times of current;
B2) active and reactive decoupling is carried out on the three-phase current to obtain ip、iq；
Wherein,
B3) will ip、iqObtaining a DC component by a low-pass filterWherein,in order to be the active current component,is a reactive current component;
B4) will ipMinusiqMinusRespectively obtain alternating current componentsI.e. harmonic components;
B5) will be provided withPerforming inverse transformation to obtain reactive current;
wherein, C23、C-1Are respectively C32Inverse matrix of C, iaq、ibq、icqRepresenting three-phase reactive current;
will be provided withCarrying out inverse transformation to obtain harmonic current;
wherein iah、ibh、ichRepresenting three-phase harmonic currents;
B6) integrating the reactive current to obtain the effective value I of the reactive currentq；
Wherein T represents an integration period;
integrating the harmonic current to obtain the effective value I of the harmonic currenth；
B7) Since the active current is the fundamental current in phase with the grid voltage, the effective value of the active current isWherein ipdcAnd outputting active grid-connected components for the direct-current side voltage control.
A2) Defining rated capacity as IsThen remaining capacity
A3) If the residual capacity is sufficient, that isThe full compensation of reactive power and harmonic wave can be satisfied to obtain the reactive compensation coefficient kqAnd harmonic compensation coefficient kh(ii) a If the residual capacity is not sufficient, that isThen, according to the priority of the reactive power and harmonic compensation, a certain component can be compensated preferentially to obtain a reactive power compensation coefficient kqAnd harmonic compensation coefficient kh。
The compensation factors are shown in table one.
TABLE-PRIORITY BASED COMPENSATION POLICY
A4) Distributing the residual capacity according to the compensation coefficient;
the distributed reactive capacity is Iq *＝kqIqThe harmonic capacity after distribution is Ih *＝khIh。
As shown in fig. 4, the decoupled components are controlled, so that redistribution of the residual capacity of the photovoltaic grid-connected system can be realized, and a compensation command current is obtained;
wherein,in order to reactive-load compensate the command current,andcompensating the command current for harmonics;
integrating reactive compensation command current, harmonic compensation command current and active current command based on an instantaneous power theory;
the integrated formula is as follows,
wherein ia *、ib *、ic *Is the integrated three-phase command current.
As shown in FIG. 5, the experimental scheme utilizes 1 programmable DC power supply to simulate a photovoltaic module and 1 uncontrolled rectificationThe device simulates a harmonic source, the direct current end of the harmonic source is connected with a resistor, and 1 programmable load simulates a reactive load. 1 4-channel oscilloscope respectively collects direct-current side voltage udcVoltage e on the A phase network sideaNet side current igaInverter output current ica. A phase load current of iaThe current satisfies equation iga＝ia-ica。
As shown in fig. 6 and 7, the 0-22s photovoltaic grid-connected system operates in the power quality management mode, and the reference voltage on the direct current side is a fixed value of 360V. And (2) a photovoltaic power supply is put into the system for 22s, the condition of illumination increase is simulated, the system detects that the output current of the photovoltaic module is larger than a threshold value, the system operates in an active grid-connection and power quality control unified mode, at the moment, in order to realize maximum power grid-connection, the direct-current side reference voltage is generated by an MPPT algorithm, the system is searching for a maximum power point for 22-33 s, the amplitude of the current at the side of the visible grid is continuously increased and finally stabilized at about 345V, and the maximum power grid-connection and power quality compensation are. 41s, cutting off the analog photovoltaic power supply, suddenly weakening the analog illumination, detecting that the photovoltaic output is lower than a threshold value by the system, operating in a power quality mode, and returning the reference voltage of the direct current side to a constant value of 360V.
The photovoltaic module does not generate power, the photovoltaic grid-connected system runs in a power quality mode, an uncontrolled rectifying device is put into use, and the programmable load is adjusted to be an inductive reactive load. As shown in fig. 8, the distortion of the current on the grid side before the system is switched on is 21.2%, the power factor is 0.65, the distortion of the current on the grid side after the system is switched on is 4.3%, and the power factor is 0.96, so that the compensation effect is achieved.
When the illumination is abundant, the photovoltaic grid-connected system operates in a grid-connected and power quality management unified control mode. Under the mode, the maximum power grid connection is firstly met, the residual capacity is used for compensation, and reactive harmonic full compensation is realized when the residual capacity is sufficient; and when the residual capacity is insufficient, under-compensation is carried out according to the priority of reactive power and harmonic, and the priority is manually set according to the requirement of the power grid. And 5 possible states are simulated by adjusting the photovoltaic output and the load, wherein the state a is a state that the residual capacity is sufficient to meet the full compensation, and the rest 4 states are states that the residual capacity cannot meet the full compensation. When reactive power preferential compensation is adopted, the state b is reactive power partial compensation, and harmonic waves are not compensated; and c state is reactive full compensation and harmonic partial compensation. When the harmonic wave preferential compensation is adopted, the d state is the harmonic wave full compensation and the reactive part compensation; the e state is the harmonic partial compensation and the reactive non-compensation. The corresponding state parameters and compensation coefficients are shown in table two.
Compensation strategy for two different states of table
Compensation effect of table three different states
As shown in fig. 9, 10, 11, 12 and 13, it can be seen from table three that the power factor and distortion rate of the power grid side before and after compensation meet the compensation strategy of 5 states, and the feasibility of the strategy is verified.
In conclusion, according to the photovoltaic grid-connected and power quality management unified control strategy, when the illumination is good, the photovoltaic grid-connected system operates in a grid-connected power generation and power quality management unified mode; when the illumination is poor, the photovoltaic grid-connected system runs in an electric energy quality control mode, a photovoltaic module output-based running mode switching and direct current side voltage control method is researched, an inverter capacity distribution and command current synthesis strategy based on reactive/harmonic priority is provided, a controller based on an FPGA + RT framework is developed, an experimental grid-connected system is constructed, and the performance of the photovoltaic grid-connected system in different running modes is verified. Compared with the traditional method, the photovoltaic system has the function of actively participating in power quality management of the power grid on the basis of keeping the original functions, the utilization rate of the inverter is improved, the investment of a power quality management device is reduced, and the cost is saved.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (1)
1. A unified control strategy for photovoltaic grid connection and power quality management is characterized in that: comprises the following steps of (a) carrying out,
1) detecting the output of the photovoltaic module in real time, and adjusting the operation mode of the photovoltaic grid-connected system;
when the active grid-connected condition is not met, the photovoltaic grid-connected system operates in a power quality management mode, and when the active grid-connected condition is met, the photovoltaic grid-connected system operates in a unified mode of active grid-connected and power quality management;
2) when the photovoltaic grid-connected system operates in an active grid-connected and power quality management unified mode, firstly, the residual capacity of the photovoltaic grid-connected system is distributed according to the priority level of reactive power and harmonic compensation, and then, command current is integrated based on an instantaneous power theory;
wherein, the process of adjusting the operation mode of the photovoltaic grid-connected system in the step 1) comprises the following steps,
A1) defining the output current threshold value of the photovoltaic module as ipvf；
A2) When the photovoltaic module outputs current i in real timepv＜ipvfWhen the photovoltaic grid-connected system is judged to be not capable of meeting the active grid-connected condition, the photovoltaic grid-connected system operates in an electric energy quality management mode;
A3) when the photovoltaic module outputs current i in real timepv≥ipvfWhen the photovoltaic grid-connected system is in the active grid-connected mode, the photovoltaic grid-connected system is judged to meet the active grid-connected condition, the photovoltaic grid-connected system operates in the active grid-connected and power quality management unified mode, in the mode, one part of active power output by the photovoltaic module is used for overcoming the switching loss of the photovoltaic grid-connected system, and the other part of the active power is converted into grid-connected active current through the direct current side PI control;
wherein, the process of distributing the residual capacity of the photovoltaic grid-connected system according to the priority level of the reactive power and the harmonic compensation in the step 2) comprises the following steps,
A1) detecting load current by an ip-iq method, extracting active, reactive and harmonic currents, and calculating an effective value I of the active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenth；
A2) Defining rated capacity as IsThen remaining capacity
A3) If the residual capacity is sufficient, that isThe full compensation of reactive power and harmonic wave can be satisfied to obtain the reactive compensation coefficient kqAnd harmonic compensation coefficient kh(ii) a If the residual capacity is not sufficient, that isThen, according to the priority of the reactive power and harmonic compensation, a certain component can be compensated preferentially to obtain a reactive power compensation coefficient kqAnd harmonic compensation coefficient kh；
A4) Distributing the residual capacity according to the compensation coefficient;
the distributed reactive capacity is Iq *＝kqIqThe harmonic capacity after distribution is Ih *＝khIh；
Calculating the effective value I of the active currentpEffective value of reactive current IqAnd the effective value I of the harmonic currenthThe process of (a) is that,
B1) defining three-phase current at load side as ia、ib、ic；
Where ω t is the phase of the grid voltage,representing the phase difference between the voltage and the current n times, InRepresents n times of current;
B2) active and reactive decoupling is carried out on the three-phase current to obtain ip、iq；
Wherein,
<mrow> <mi>C</mi> <mo>=</mo> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <mi>s</mi> <mi>i</mi> <mi>n</mi> <mi>&omega;</mi> <mi>t</mi> </mrow> </mtd> <mtd> <mrow> <mo>-</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mi>&omega;</mi> <mi>t</mi> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>-</mo> <mi>c</mi> <mi>o</mi> <mi>s</mi> <mi>&omega;</mi> <mi>t</mi> </mrow> </mtd> <mtd> <mrow> <mo>-</mo> <mi>sin</mi> <mi>&omega;</mi> <mi>t</mi> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>,</mo> <msub> <mi>C</mi> <mn>32</mn> </msub> <mo>=</mo> <msqrt> <mfrac> <mn>2</mn> <mn>3</mn> </mfrac> </msqrt> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mn>1</mn> </mtd> <mtd> <mrow> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </mtd> <mtd> <mrow> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mfrac> <msqrt> <mn>3</mn> </msqrt> <mn>2</mn> </mfrac> </mtd> <mtd> <mrow> <mo>-</mo> <mfrac> <msqrt> <mn>3</mn> </msqrt> <mn>2</mn> </mfrac> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow>
B3) will ip、iqObtaining a DC component by a low-pass filterWherein,in order to be the active current component,is a reactive current component;
B4) will ipMinusiqMinusRespectively obtain alternating current componentsI.e. harmonic components;
B5) will be provided withPerforming inverse transformation to obtain reactive current;
<mrow> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>a</mi> <mi>q</mi> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>b</mi> <mi>q</mi> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>c</mi> <mi>q</mi> </mrow> </msub> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <msub> <mi>C</mi> <mn>23</mn> </msub> <msup> <mi>C</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mn>0</mn> </mtd> </mtr> <mtr> <mtd> <mover> <msub> <mi>i</mi> <mi>q</mi> </msub> <mo>&OverBar;</mo> </mover> </mtd> </mtr> </mtable> </mfenced> </mrow>
wherein, C23、C-1Are respectively C32Inverse matrix of C, iaq、ibq、icqRepresenting three-phase reactive current;
will be provided withCarrying out inverse transformation to obtain harmonic current;
<mrow> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>a</mi> <mi>h</mi> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>b</mi> <mi>h</mi> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>i</mi> <mrow> <mi>c</mi> <mi>h</mi> </mrow> </msub> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <msub> <mi>C</mi> <mn>23</mn> </msub> <msup> <mi>C</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>p</mi> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>q</mi> </msub> </mtd> </mtr> </mtable> </mfenced> </mrow>
wherein iah、ibh、ichRepresenting three-phase harmonic currents;
B6) integrating the reactive current to obtain the effective value I of the reactive currentq；
<mrow> <msub> <mi>I</mi> <mi>q</mi> </msub> <mo>=</mo> <msqrt> <mrow> <mfrac> <mn>1</mn> <mi>T</mi> </mfrac> <mrow> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>T</mi> </msubsup> <mrow> <msubsup> <mi>i</mi> <mrow> <mi>a</mi> <mi>q</mi> </mrow> <mn>2</mn> </msubsup> <mi>d</mi> <mi>t</mi> </mrow> </mrow> </mrow> </msqrt> </mrow>
Wherein T represents an integration period;
integrating the harmonic current to obtain the effective value I of the harmonic currenth；
<mrow> <msub> <mi>I</mi> <mi>h</mi> </msub> <mo>=</mo> <msqrt> <mrow> <mfrac> <mn>1</mn> <mi>T</mi> </mfrac> <mrow> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>T</mi> </msubsup> <mrow> <msubsup> <mi>i</mi> <mrow> <mi>a</mi> <mi>h</mi> </mrow> <mn>2</mn> </msubsup> <mi>d</mi> <mi>t</mi> </mrow> </mrow> </mrow> </msqrt> <mo>;</mo> </mrow>
B7) Since the active current is the fundamental current in phase with the grid voltage, the effective value of the active current isWherein ipdcOutputting active grid-connected components for direct-current side voltage control;
the decoupled components are controlled, so that the redistribution of the residual capacity of the photovoltaic grid-connected system can be realized, and the compensation instruction current is obtained;
<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msubsup> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>p</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>k</mi> <mi>h</mi> </msub> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>p</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msubsup> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>q</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>k</mi> <mi>h</mi> </msub> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>q</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mover> <msubsup> <mi>i</mi> <mi>q</mi> <mo>*</mo> </msubsup> <mo>&OverBar;</mo> </mover> <mo>=</mo> <msub> <mi>k</mi> <mi>q</mi> </msub> <mover> <msub> <mi>i</mi> <mi>p</mi> </msub> <mo>&OverBar;</mo> </mover> </mrow> </mtd> </mtr> </mtable> </mfenced>
wherein,in order to reactive-load compensate the command current,andcompensating the command current for harmonics;
integrating reactive compensation command current, harmonic compensation command current and active current command based on an instantaneous power theory;
the integrated formula is as follows,
<mrow> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <msup> <msub> <mi>i</mi> <mi>a</mi> </msub> <mo>*</mo> </msup> </mtd> </mtr> <mtr> <mtd> <mrow> <msup> <msub> <mi>i</mi> <mi>b</mi> </msub> <mo>*</mo> </msup> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msup> <msub> <mi>i</mi> <mi>c</mi> </msub> <mo>*</mo> </msup> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <msub> <mi>C</mi> <mn>23</mn> </msub> <msup> <mi>C</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <msub> <mi>i</mi> <mrow> <mi>p</mi> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>+</mo> <msubsup> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>p</mi> <mo>*</mo> </msubsup> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mover> <msubsup> <mi>i</mi> <mi>q</mi> <mo>*</mo> </msubsup> <mo>&OverBar;</mo> </mover> <mo>+</mo> <msubsup> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>q</mi> <mo>*</mo> </msubsup> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>=</mo> <msub> <mi>C</mi> <mn>23</mn> </msub> <msup> <mi>C</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced open = "[" close = "]"> <mtable> <mtr> <mtd> <mrow> <msub> <mi>i</mi> <mrow> <mi>p</mi> <mi>d</mi> <mi>c</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>k</mi> <mi>h</mi> </msub> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>p</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>k</mi> <mi>q</mi> </msub> <mover> <msub> <mi>i</mi> <mi>q</mi> </msub> <mo>&OverBar;</mo> </mover> <mo>+</mo> <msub> <mi>k</mi> <mi>h</mi> </msub> <msub> <mover> <mi>i</mi> <mo>~</mo> </mover> <mi>q</mi> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced> </mrow>
wherein ia *、ib *、ic *Is the integrated three-phase command current.
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