CN100379113C - An integrated method to realize grid-connected power generation and grid reactive power compensation at the same time - Google Patents

Abstract

The present invention relates to an integrated method for realizing parallel network power generation and power network reactive power compensation simultaneously, which belongs to the technical field of solar power generation and power electrons. The present invention adopts park transformation to transform the current output from a three-phase inverter onto rotary dp coordinates, so the active current and reactive current are separated; the quantities and the directions of the active current and the reactive current are respectively controlled to transform the direct current of a photovoltaic cell into alternating current, and reactive power compensation is simultaneously carried out for local networks. When the photovoltaic cell has enough energy to output, photovoltaic parallel network power generation and reactive compensation are realized at the same time. When the photovoltaic cell stops outputting, the inverter singly carries out reactive compensation for networks. The present invention can transform and transmit direct current output from photovoltaic arrays onto three-phase 380 V alternating current networks through the inverter, and can realize a certain amount of reactive compensation for other reactive loads on local networks, so that the power quality of networks is improved.

Description

An integrated method to realize grid-connected power generation and grid reactive power compensation at the same time

technical field

The invention relates to an integrated method for simultaneously realizing grid-connected power generation and grid reactive power compensation, in particular to an integrated method capable of simultaneously realizing grid-connected power generation of photovoltaic cells and grid reactive power compensation. It belongs to the technical field of solar power generation and power electronics.

Background technique

At present, the application of photovoltaic is mainly in three aspects: DC power supply, independent inverter AC power supply and grid-connected power supply. Considering that most electrical equipment is currently powered by AC, converting the DC output from the photovoltaic array into AC has become a research focus in this field. For an independent low-power photovoltaic system, the inverter is used as a current conversion device to realize the power supply of the PV array to the AC equipment, so that the utilization value of photovoltaic cells is increased and it is easy to use. With the improvement of photovoltaic cell quality, its generating power and conversion efficiency are also greatly improved, which provides the possibility for large-scale grid-connected power generation. The key to grid-connected power generation is to maximize the energy generated by the PV array and transfer it to the grid. Related methods have been reported in many papers. However, there is a major shortcoming in photovoltaic grid-connected power generation, that is, when the sunshine intensity is very low or at night, the photovoltaic cells actually lose their output capacity. At this time, the entire system must be withdrawn from the grid. When the value is certain, the system will be paralleled with the power grid. In this way, not only the whole set of equipment is in an idle state when the system is shut down, but also the frequent paralleling and decoupling actions make it difficult to control the system, increase the wear and tear of some equipment and shorten the service life.

Through literature search, it is found that Multi-function photovoltaic power supply system with grid-connection and power factor correction features. Source: PESC Record-IEEE Annual Power Electronics Specialists Conference, v 3, 2000, p1185-1190 ("multi-function photovoltaic Functional photovoltaic grid-connected power generation system", IEEE Power Electronics Annual Conference 2000 Proceedings), T.-F.Wu et al. proposed a method to combine photovoltaic grid-connected power generation with three-phase rectification technology, that is, in the inverter The DC side of the inverter is connected in parallel with the DC load. When the photovoltaic cell generates power, the system works in the inverter state, and the DC side load is separated from the system through the relay; when the photovoltaic cell stops outputting, the additional relay pulls in, and the inverter acts as a rectifier to supply power to the DC load. , this method improves the utilization rate of the system to a certain extent. However, in this grid-connected system, the DC load is connected in parallel on the DC side of the inverter, which undoubtedly reduces the flexibility of the entire system application. Moreover, in this method, a large number of relays are used to switch between the two functions, so that the control of the entire system becomes complicated and the reliability is reduced.

Contents of the invention

The purpose of the present invention is to address the above-mentioned shortcomings in the background technology, and provide an integrated method for realizing grid-connected power generation and grid reactive power compensation at the same time, so that it can convert the direct current output from the photovoltaic array to three Phase 380V AC power grid, at the same time, it can also realize a certain amount of reactive power compensation for other reactive loads on the local power grid, and improve the power quality of the power grid. The present invention can be used for grid-connected power generation and power grid reactive power compensation at the same time when the photovoltaic cell generates power without adding hardware equipment; when the photovoltaic cell does not generate power (such as at night), it can still perform reactive power compensation for the power grid. So as to solve the problem of low utilization rate of traditional photovoltaic grid-connected power generation system, and achieve the effect of simple and reliable system structure, high conversion efficiency and flexible use.

The present invention is realized through the following technical solutions. Based on the theory of instantaneous reactive power, the present invention uses park transformation to convert the output current of the three-phase inverter to the rotating dq coordinates, thereby realizing the separation of active current and reactive current. Controlling the size and direction of active current and reactive current respectively realizes the transformation of the direct current of the photovoltaic cell into alternating current, and at the same time performs reactive power compensation to the local power grid. When the photovoltaic cells have sufficient energy output, photovoltaic grid-connected power generation and reactive power compensation are realized at the same time. When the photovoltaic cell stops outputting (the output power is lower than a certain value), the inverter alone performs reactive power compensation to the grid, and the reactive power compensation function is not affected by the photovoltaic output capability. Since the system is always in working condition on the power grid, the output energy of photovoltaic cells can be transmitted at any time, which saves repeated paralleling and decoupling actions and improves the reliability of the photovoltaic system.

The realization of the method of the present invention specifically includes three parts: grid-connected power generation of photovoltaic cells, reactive power compensation, and synchronous realization of grid-connected power generation and reactive power compensation, wherein the synchronous realization of grid-connected power generation of photovoltaic cells and reactive power compensation is The core technology of the present invention. Each part of the inventive method is described in detail below:

1. Grid-connected power generation of photovoltaic cells

The voltage transformer is used to sample the phase voltage of the three-phase grid in real time, and the frequency and phase of the grid voltage are obtained through vector transformation, which are used as the frequency and phase reference for inverter current control. The inverter adopts full-bridge sinusoidal pulse width modulation technology (SPWM) to control the inverter current instantaneously. All the mathematical conversion and control algorithms are programmed by the digital controller. The input of the digital controller is the sampling value or reference value of voltage and current, and its output is the six-way PWM pulse wave that controls the operation of the inverter.

In order to maintain the voltage stability of the DC side, this method introduces a closed-loop control of the DC side voltage, that is, the error between the DC side voltage and the reference voltage is used as the reference value of the active current output by the inverter after passing through the PI regulator. This control method can ensure that when the photovoltaic battery has enough energy output, the inverter can transfer this part of energy to the grid to the maximum extent, because when the DC side voltage remains constant, the current flowing through the DC side capacitor Very small, all the current output from the photovoltaic cells is delivered to the grid by the inverter. At the same time, when the photovoltaic cell stops outputting power, through the closed-loop control of the DC side voltage, the inverter absorbs part of the active current from the grid to maintain a constant DC side voltage to meet the needs of reactive power compensation later. The present invention is characterized in that the DC side voltage control is different from the traditional error comparison. In this method, the DC side voltage reference value is used as the negative terminal input of the error comparator, and its positive terminal input is the DC side voltage feedback signal. When the DC side voltage is higher than the reference voltage, the error signal is positive, and the reference value of the active current output by the inverter increases positively, that is, it provides active energy to the grid; otherwise, when the DC side voltage is lower than the reference voltage, the inverter The bypass diode of the switching tube forms a rectifier bridge, which absorbs active energy from the grid to maintain a constant DC side voltage. Since the DC side capacitor itself does not consume active energy, this part of energy is only used to compensate the loss of the inverter switching tube, so the active current absorbed from the grid is very small. This strategy makes reasonable use of the energy transmission direction, has a large degree of control freedom, and is simple and reliable to implement.

Since the grid-connected power generation mentioned here mainly refers to converting solar energy into active energy and transmitting it to the grid, its essence is to control the active current of the inverter. The current output by the inverter is the vector sum of the active component and the reactive component. To control the active current alone, the decoupling of the active component and the reactive component must be realized. H.Akagi and others proposed the theory of instantaneous reactive power in the αβ0 coordinate system. Although the purpose of this theory is to explain the concept of instantaneous reactive power, the current component after coordinate transformation just realizes the active current and reactive current. separation. The present invention is based on such a method, respectively controls the active current and the reactive current, and realizes the dual functions of the active power output of the inverter and the reactive power compensation of the grid. Considering that active components and reactive components are simultaneously obtained through park transformation, specific detection and control methods are given in the following text.

2. Reactive power compensation

Connect the three-phase inverter bridge circuit in parallel to the power grid through the reactor, properly adjust the amplitude of the output voltage of the AC side of the bridge circuit, and form a certain voltage drop at both ends of the reactor, so that the circuit absorbs or emits no voltage that meets the requirements. Work current, to achieve the purpose of dynamic reactive power compensation. Its essence is to use the voltage difference between the inverter output voltage and the grid voltage on the inverter output reactor to form the required reactive power compensation current. By controlling the amplitude of the inverter output voltage, it can control its reactive power absorption. The nature and magnitude of power. This method uses tracking PWM control technology to feedback and control the instantaneous value of the inverter output current waveform, and its response speed and control accuracy are much higher than the indirect control method of controlling the amplitude and phase of the inverter voltage fundamental wave. improvement.

Transform the voltage and current of the abc three-phase system into vectors on the αβ0 coordinate system, define the dot product of voltage and current vectors as instantaneous active power, and define the cross product of voltage and current vectors as instantaneous reactive power, and thus obtain instantaneous Reactive power and instantaneous reactive current. Let the instantaneous values of the voltage and current of each phase of the three-phase circuit be e _a , e _b , e _c and i _a , i _b , i _c respectively. Through park transformation, they can be transformed into the rotating dq coordinate system. The transformation The relationship can be expressed as follows:

i _dq0 =Ci _abc , i _abc =C ^-1 i _dq0

Among them, i _dq0 =[i _d , i _q , i ₀ ] ^T , i _abc =[i _a , i _b , i _c ] ^T , C is the park transformation matrix, namely

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}}\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}& \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}& \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right]$

Since C is an orthogonal matrix, there is C ^-1 ＝ C ^T , so

${\mathrm{<span\; class="notranslate">\; C</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; 3</span>}}}\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&omega;t</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right]$

Here, ω is the frequency of the grid voltage. Take the rotation speed of dq coordinates to be consistent with ω. According to the theory of instantaneous reactive power, i _d and i _q at this time are the instantaneous active current and instantaneous reactive current in the rotating coordinate system.

3. Synchronous realization of grid-connected power generation and reactive power compensation

The present invention realizes the separation of active current and reactive current through dq conversion, and uses the error between the detection voltage on the DC side and the reference voltage on the DC side to be the reference value of the active current component after PI adjustment; at the same time, by detecting the reactive component of the load current of the local power grid , which is used as the reference value of the inverter to compensate the reactive current, that is, to realize the synchronous control of photovoltaic grid-connected power generation and reactive power compensation. By controlling the magnitude and direction of the voltage on the inverter output filter inductor, that is, controlling the direction of the inductor current, this method can compensate both inductive reactive power and capacitive reactive power. When the inverter output voltage is higher than the grid voltage, the inverter outputs inductive reactive power; when the inverter output voltage is lower than the grid voltage, the inverter outputs capacitive reactive power. When the inverter sends active power to the grid, the inverter output voltage phase leads the grid voltage phase; when the inverter absorbs active power from the grid, the inverter output voltage phase lags the grid voltage phase. It should be noted that when the reactive power demand of the load (such as 1KVar) is small, its reactive current component can be directly used as the reactive current reference value output by the inverter. If the reactive power demand of the actual load is large and the compensation capacity of the inverter is limited, the detected reactive current component can be considered to be scaled down and then used as the reactive current reference value of the inverter, and the remaining part will be provided by other power grids. Compensation device provided. In addition, it is also possible not to detect the reactive current of the load, but to directly give a reference value according to its own capacity, and the rest is still provided by other compensation devices of the power grid. This not only reduces the number of detection points, but also completely ignores the working conditions of the load, making the use and maintenance of the system more convenient. The variables to be detected by the inverter system include: DC side voltage U _dc , grid voltage u _abc , inverter current i _abc and load current i _Labc . The phase-locked loop control, signal error comparison, PI adjustment, park conversion and inverse conversion, and PWM generation are all programmed by the digital signal processor, and the PWM output can directly drive the inverter switch.

The present invention has substantive features and significant progress. It can transform the direct current output by the photovoltaic array to the three-phase 380V AC power grid through the inverter, and can also realize a certain amount of reactive power compensation for other reactive loads on the local power grid. Improve grid power quality. The analysis results show that this method makes the output of the active current of the inverter follow the output of the photovoltaic cell. When the photovoltaic cell is at the maximum power output, the active current of the inverter also outputs the maximum; The active current output of the inverter gradually decreases and has a certain negative value, which means that the inverter absorbs active energy from the grid to maintain a constant DC side voltage. The reactive current component is not affected by the photovoltaic output capability. Within the allowable range of capacity, the reactive current component always follows the reactive component of the load current.

In addition, in order to improve the efficiency of photovoltaic grid-connected power generation, the present invention adopts the maximum power point tracking technology based on the admittance increment method to maximize the output power of photovoltaic cells. That is, a BOOST conversion circuit is added between the output terminal of the photovoltaic cell and the inverter to detect the output voltage and current of the photovoltaic cell in real time, and judge the current working state of the photovoltaic cell according to these two sampling values and the sampling value of the previous cycle. If the operating point deviates from the maximum power point output by the photovoltaic cell, change the duty cycle of the BOOST circuit switch to make the operating point of the photovoltaic cell approach the maximum power point until it finally stabilizes at the maximum power point. This measure can greatly improve the conversion efficiency of electricity from solar energy to the grid.

Detailed ways

The following examples are provided in conjunction with the content of the inventive method:

Establish a photovoltaic grid-connected power generation system, which is composed of photovoltaic arrays, BOOST conversion circuits, three-phase full-bridge inverters, voltage and current detection devices, and digital controllers. The short-circuit current of the photovoltaic cell is 3.4A, the open-circuit voltage is 360V, and the maximum output power is 1.2KW; the sampling period of the output voltage and current of the photovoltaic cell is 2ms, the scan time of the module realized by the MPPT algorithm is 0.2ms, and the duty cycle reference voltage increment is 0.01V , the BOOST switching frequency is 40KHz, the DC side voltage of the inverter is 800V; the grid load is an inductive load, and its absorbed reactive power is set to 1 KVar; the output capacity of the inverter is 5KVA, and the carrier frequency is 20KHz.

The specific implementation steps are as follows: 1) Detect the output voltage u _PV and current i _PV of the photovoltaic cell, input the sampled value to the digital signal processor, and the program processes the sampled data according to the MPPT algorithm, and calculates the BOOST circuit duty in the next sampling period 2) Detect grid voltage u _abc , obtain the reference frequency and phase value required for dq transformation through vector transformation; 3) detect inverter current detection i _abc , and obtain the current inverter current after park transformation Active component and reactive component; 4) Detect the DC side voltage U _dc and compare it with the reference voltage U _dc ^* , and the error is adjusted by the internal digital PI as the reference value of the active current of the inverter; 5) Detect the grid flowing into the load The current grid i _Labc is used as the reference value of the reactive current of the inverter after dq transformation; 6) The reference value of the active current and reactive current of the inverter is compared with the current actual value respectively, and the error is adjusted by PI as the reference value The input value of the dq inverse transformation; 7) The output of the dq inverse transformation is used as the input of the SPWM generator, that is, the modulation wave, and finally forms six PWM pulse waves as the output of the digital signal processor; 8) The six PWM pulse waves control the three phases respectively The six switching tubes of the inverter are turned on and off to adjust the output current of the inverter.

In this embodiment, when the photovoltaic cell outputs maximum power, the duty cycle of the BOOST circuit switch is about 75%. After the output of photovoltaic cells is stable, it basically maintains near the maximum power point (1.2KW), and fluctuates about 30W downward. At this time, the active component of the inverter output current is about 2.1A, the reactive component is about 2.5A, the reactive component on the grid is close to zero, and the reactive power compensation effect of the system is obvious. When the sunlight intensity weakens and the output power of the photovoltaic cell is zero, the active component of the output current of the inverter is about -0.6A, while the effect of reactive power compensation remains unchanged.

Claims (4)

1. realize simultaneously generating electricity by way of merging two or more grid systems and the integral method of power system reactive power compensation for one kind, it is characterized in that, adopt the park conversion that three-phase grid photovoltaic DC-to-AC converter output current is transformed on the rotation dq coordinate, realization separates active current and reactive current, regulate the size and Orientation of controlling active current and reactive current respectively by PI, realize generating electricity by way of merging two or more grid systems of photovoltaic cell, simultaneously local power grid is carried out reactive power compensation, when photovoltaic cell stops to export, the three-phase grid photovoltaic DC-to-AC converter carries out reactive power compensation to electrical network separately, when photovoltaic cell had enough energy to export, parallel network power generation and reactive power compensation realized simultaneously.

2. the integral method that realization is generated electricity by way of merging two or more grid systems and power system reactive power compensates simultaneously according to claim 1 is characterized in that, generating electricity by way of merging two or more grid systems of described photovoltaic cell is specific as follows:

With voltage transformer real-time sampling three phase network phase voltage, obtain the frequency and the phase place of line voltage by transform vector, as frequency and phase reference to three-phase grid photovoltaic DC-to-AC converter Current Control, the three-phase grid photovoltaic DC-to-AC converter adopts full-bridge sinusoidal pulse width modulation technology, with regulate through PI and the inverter current waveform of dp inverse transformation as modulating wave, inverter current is carried out Instantaneous Control, mathematic(al) manipulation and control algolithm are realized by the digitial controller programming, digitial controller be input as voltage and current sampled value or reference value, it is output as six road pwm pulse ripples of control three-phase grid photovoltaic DC-to-AC converter work.

3. the integral method that realization is generated electricity by way of merging two or more grid systems and power system reactive power compensates simultaneously according to claim 1 is characterized in that, described reactive power compensation is specific as follows:

The three-phase grid photovoltaic DC-to-AC converter is connected in parallel on the electrical network by reactor, regulate inverter AC side output voltage amplitude, control the character and the size of its absorbing reactive power, the current signal that forms with the dc voltage closed-loop control is as three-phase grid photovoltaic DC-to-AC converter output current reference value, adopt following-up type PWM control method, the instantaneous meritorious and idle value of three-phase grid photovoltaic DC-to-AC converter output current wave is carried out FEEDBACK CONTROL.

4. according to claim 1ly realize simultaneously generating electricity by way of merging two or more grid systems and the integral method of power system reactive power compensation, it is characterized in that, described synchronous realization of generating electricity by way of merging two or more grid systems with reactive power compensation, specific as follows:

The error of utilizing DC side to detect voltage and DC side reference voltage is regulated the reference value of back as the active current component through PI, simultaneously by detecting the idle component of local power grid load current, with its reference value as three-phase grid photovoltaic DC-to-AC converter compensating reactive power electric current, regulate and the dq inverse transformation will be gained merit and the output voltage of reactive current coupling adjusting three-phase grid photovoltaic DC-to-AC converter by PI, promptly realize the Synchronization Control of parallel network power generation and reactive power compensation.