CN103036464B - Photovoltaic array topological structure, grid-connected system based on photovoltaic array topological structure and photovoltaic array control method - Google Patents

Abstract

The invention discloses a photovoltaic array topology, a grid-connected system and a control method. The photovoltaic array includes a plurality of parallel photovoltaic branches, each photovoltaic branch includes a component branch and a compensation branch, and the component branch is composed of blocking diodes, N A photovoltaic module and a capacitor are connected in series, and the compensation circuit includes N inductors and N IGBT bridge arms; all IGBT bridge arms are connected in parallel with the component branch; each IGBT bridge arm is composed of two IGBTs; N IGBT bridge arms The N midpoints corresponding to the bridge arms are respectively connected to the N negative terminal points of the N photovoltaic modules through N inductors. The topological structure of the photovoltaic array, the grid-connected system and the control method can enable the photovoltaic module to achieve maximum power output, effectively solve the power mismatch problem of the photovoltaic array under shadow conditions, and improve the output power of the photovoltaic array.

Description

Photovoltaic array topology, grid-connected system and control method

technical field

The invention relates to a photovoltaic array topology, a grid-connected system and a control method, and belongs to the technical field of photovoltaic power generation.

Background technique

Energy is the material basis for human survival and development, and plays a key role in social development. However, with the development of society and economy, on the one hand, people's demand for energy is increasing day by day. Environmental pollution caused by energy consumption is a huge challenge, and new energy power generation technology has become a research hotspot at home and abroad to seek solutions to energy problems. Solar energy is a clean, non-polluting natural energy source, and photovoltaic power generation technology is being widely promoted and applied.

The output power of a single photovoltaic module is small. In order to meet the requirements of the load capacity, the photovoltaic modules are usually connected in series or in parallel to form a photovoltaic array that can output higher power. Photovoltaic arrays generate electricity under sunlight, and can output electricity stably for a long time under ideal conditions. However, in an actual complex working environment, due to the presence of surrounding buildings, trees, clouds, etc., it is easy to form shadows on the photovoltaic array. The local radiation intensity of the array is weakened, that is, the overall irradiation is uneven. At this time, the performance of the photovoltaic array is deteriorated, and the output power is greatly reduced. Wear and damage the battery, greatly reducing the operating efficiency and safety of the photovoltaic power generation system. Therefore, when designing a photovoltaic power generation system, it is of great practical significance to consider the partial shading conditions of the photovoltaic array and optimize the design of the photovoltaic array.

The traditional structure of the photovoltaic array is to connect a blocking diode in series in the series branch of the components to prevent the power reverse from causing damage to the photovoltaic array when the output voltage of the entire array is too low, and then to each (or several) photovoltaic cells connected in series , configure a parallel bypass diode to prevent hot spot phenomenon due to power mismatch of photovoltaic series cells under partial shadow conditions. The working mode of the photovoltaic array is that in the case of uniform illumination, the bypass diode is in the reverse cut-off state, and the photovoltaic cell works normally; when a photovoltaic cell is shaded, the component voltage becomes negative At this time, the bypass diode connected in parallel with it is turned on, which protects the photovoltaic cell from being broken down by the reverse avalanche current, but at this time, the photovoltaic cell bears the reverse pressure and becomes a load, which consumes energy and reduces the output power of the array.

The traditional photovoltaic array structure actually guarantees the normal operation of the photovoltaic array, and it is not an economical and effective optimization method to consume energy in the shaded part of the battery. Moreover, under random shading conditions, due to the existence of bypass diodes, the voltage and power output characteristics of the photovoltaic array are complicated, and the power-voltage curve has multiple local extreme points, which also causes difficulties for the maximum power point tracking control of photovoltaics. Therefore, it is necessary to design a new photovoltaic array topology, grid-connected system and control method.

Contents of the invention

The technical problem to be solved by the present invention is to provide a photovoltaic array topology, grid-connected system and control method. Reduce the power mismatch problem of the photovoltaic array and increase the output power of the photovoltaic array.

The technical solution of the invention is as follows:

A photovoltaic array topology structure, the photovoltaic array includes a plurality of parallel photovoltaic branches, each photovoltaic branch includes a component branch and a compensation branch, and the component branch is sequentially connected in series by blocking diodes, N photovoltaic modules and a capacitor, The compensation circuit includes N inductors and N IGBT bridge arms; all IGBT bridge arms are connected in parallel with component branches; each IGBT bridge arm is composed of two IGBTs; N midpoints corresponding to N IGBT bridge arms pass through N The inductors are connected to the N negative terminals of the N photovoltaic modules; N is an integer greater than or equal to 2.

Said N is 3.

A photovoltaic array control method based on the foregoing photovoltaic array topology, comprising (1) a current compensation process and (2) a voltage compensation process;

(1) The current compensation process is:

Current compensation refers to the use of N-1 IGBT bridge arms for current compensation;

For each IGBT bridge arm of the first N-1 IGBT bridge arms of each photovoltaic branch, the following controls are implemented:

Obtain the current I _Li of the inductor L _i , compare it with the compensation current I _{Li_ref} , and then compare it through the hysteresis loop to obtain the control signal G _Li of the switching tube (Vi, Vin) on the i-th IGBT bridge arm, that is, when I _{Li_ref} -I _Li <-0.1, the lower bridge arm IGBT (Vin) is turned on, when I _{Li_ref} -I _Li >0.1, the upper bridge arm IGBT (Vi) is turned on, when -0.1<I _{Li_ref} -I _Li <0.1, the control signal is 0, the upper and lower bridge arm IGBTs are not turned on;

Wherein, the compensation current I _{Li_ref} is the magnitude of the current that should be injected into the i-th inductance L _i , and I _{Li_ref} = I _Mi -I _Mi+1 , and I _Mi is the maximum power current of the i-th photovoltaic module;

(2) Voltage compensation process:

Voltage compensation refers to the voltage compensation of the capacitance in the photovoltaic branch based on the Nth IGBT bridge arm;

The compensation voltage of the jth photovoltaic branch is U _{pvj_ref} =U _pvm -U _pvmj , j=1, 2,..., M, M is the total number of photovoltaic branches;

Among them, the maximum power voltage of the branch U _pvm ＝max{U _pvmj }, where U _Mi refers to the maximum power voltage of the i-th photovoltaic module of the j-th photovoltaic branch;

The control process is: for each photovoltaic branch, the following control is implemented:

The capacitance voltage U _psj of the detection branch is compared with the compensation voltage U _{pvj_ref} , and after passing through the first PI regulator, it is compared with the first triangular wave to obtain the control of the Nth IGBT bridge arm of the switch tube (ie V _N , V _Nn ) For the signal G _C1 , if the comparison value is greater than the first triangular wave, the lower bridge arm IGBT (V _Nn ) is turned on, and if the comparison value is smaller than the first triangular wave, the upper bridge arm IGBT (V _N ) is turned on.

The proportional coefficient P _ps of the first PI regulator = 0.2, and the integral coefficient I _ps = 100; the frequency of the first triangular wave is 10kHz, [in this patent, all the amplitudes of the triangular wave vary from 0 to 1, hereby explain].

A grid-connected system based on the photovoltaic array topology, the photovoltaic array is connected to the three-phase grid through a DC/DC chopper circuit, an inverter and an LC output filter in sequence.

6. The grid-connected system according to claim 5, characterized in that, said N is 3; said inverter is an inverter based on double closed-loop control of voltage and current.

7. The control method of the grid-connected system according to claim 5 or 6, characterized in that, comprising (A) photovoltaic array control method and (B) grid-connected inverter control method;

(A) The photovoltaic array control method includes a current compensation process and a voltage compensation process;

(1) The current compensation process is:

Current compensation refers to the use of N-1 IGBT bridge arms for current compensation;

For each IGBT bridge arm of the first N-1 IGBT bridge arms of each photovoltaic branch, the following controls are implemented:

Obtain the current I _Li of the inductor L _i , compare it with the compensation current I _{Li_ref} , and then compare it through the hysteresis loop to obtain the control signal G _Li of the switching tube (Vi, Vin) on the i-th IGBT bridge arm, that is, when I _{Li_ref} -I _Li <-0.1, the lower bridge arm IGBT (Vin) is turned on, when I _{Li_ref} -I _Li >0.1, the upper bridge arm IGBT (Vi) is turned on, when -0.1<I _{Li_ref} -I _Li <0.1, the control signal is 0, the upper and lower bridge arm IGBTs are not turned on;

Wherein, the compensation current I _{Li_ref} is the magnitude of the current that should be injected into the i-th inductance L _i , I _{Li_ref} =I _Mi -I _Mi+1 , and I _Mi is the maximum power current of the i-th photovoltaic module;

(2) Voltage compensation process:

Voltage compensation refers to the voltage compensation of the capacitance in the photovoltaic branch based on the Nth IGBT bridge arm;

The compensation voltage of the jth photovoltaic branch is U _{pvj_ref} =U _pvm -U _pvmj , j=1, 2,..., M, M is the total number of photovoltaic branches;

Among them, the maximum power voltage of the branch U _pvm ＝max{U _pvmj }, where U _Mi refers to the maximum power voltage of the i-th photovoltaic module of the j-th photovoltaic branch;

The control process is: for each photovoltaic branch, the following control is implemented:

The capacitance voltage U _psj of the detection branch is compared with the compensation voltage U _{pvj_ref} , and after passing through the first PI regulator, it is compared with the first triangular wave to obtain the control of the Nth IGBT bridge arm of the switch tube (ie V _N , V _Nn ) Signal G _C1 , if the comparison value is greater than the first triangular wave, the lower bridge arm IGBT (V _Nn ) is turned on, and if the comparison value is smaller than the first triangular wave, the upper bridge arm IGBT (V _N ) is turned on;

(B) is the grid-connected inverter control method:

Control the A, B, and C phases of the inverter separately:

Compare the DC side voltage U _DC of the inverter with the set voltage U _{DC_ref} , [U _{DC_ref} generally takes a value of 800V] The comparison error is controlled by the second PI regulator, and the result is multiplied by the corresponding phase (such as A phase) grid voltage synchronization The sinusoidal signal [the amplitude of the sine wave extracted by the PLL is 1, which is a unit signal] is used as the inverter output current command signal I _inf to detect the inverter output current I _in and compare it with I _inf , and the error is passed through the third PI Regulator control, and then compared with the second triangle wave to obtain the control signal G _VSI of the inverter to control the on and off of the inverter switching device. When G _VSI > 0, control the corresponding phase (such as A phase) upper bridge arm IGBT is turned on, the lower bridge arm IGBT is turned off; when G _VSI <0, the upper bridge arm IGBT is controlled to be turned off, and the lower bridge arm IGBT is turned on.

The proportional coefficient P _dc of the second PI regulator =0.2, the integral coefficient I _dc =25; the proportional coefficient P _in of the third PI regulator =0.5, the integral coefficient I _in =300; the frequency of the second triangular wave is 10kHz.

The photovoltaic array can form a photovoltaic grid-connected system together with DC/DC chopper circuit, inverter circuit, output filter and power grid. The blocking diode is connected in series in the component branch to prevent the reverse current from causing damage to the photovoltaic array; the capacitor compensates the voltage of the branch to maintain the balance of each branch of the array; the DC/DC chopper circuit adjusts the DC of the inverter The side voltage enables the photovoltaic array to achieve the maximum power output; the inverter circuit adopts voltage and current double closed-loop control to achieve the purpose of inverter grid connection; the LC output filter filters out the harmonics in the inverter output waveform. In this photovoltaic array topology, since a compensation circuit is added to the photovoltaic branch circuit, the component current and the branch circuit voltage are compensated separately, so that each component can work at the maximum power point, improve the operating efficiency of the component, and eliminate the local shadow condition Reduce the power mismatch of photovoltaic cells and improve the safety and output power of photovoltaic arrays. The control method includes compensating current and compensating voltage control to obtain the compensating current and voltage required by the branch circuit; double-closed-loop control for inverter grid connection to ensure that the output of the inverter is accurately integrated into the grid.

Beneficial effect:

The photovoltaic array topology, grid-connected system and control method of the present invention can make each component work at the maximum power point by adding a compensation circuit to the photovoltaic branch circuit to compensate the component current and the branch circuit voltage respectively. Improve the operating efficiency of modules, eliminate the power mismatch of photovoltaic cells under partial shadow conditions, and improve the safety and output power of photovoltaic arrays. The control method includes compensating current and compensating voltage control to obtain the compensating current and voltage required by the branch circuit; double closed-loop control for inverter grid connection to ensure that the output of the inverter is accurately integrated into the grid.

The outstanding effects that the present invention has are as follows:

1) The compensation circuit composed of inductors and IGBTs is simple, feasible and easy to implement; it ensures the stable operation of the array;

2) Connecting an inductor at the lower end of the module can balance the current of the module under partial shading conditions, so that all components in the branch circuit can output power, which solves the power mismatch problem of photovoltaic modules under partial shading conditions;

3) Compensate the component current and branch circuit voltage to make the components operate at the maximum power point and maintain the stability of the branch circuit voltage, so that each component can exert the maximum efficiency and increase the output power of the photovoltaic array.

Description of drawings

Figure 1 Structural schematic diagram of photovoltaic grid-connected system;

Figure 2 Photovoltaic array compensation control flow chart;

Fig. 3 branch compensation current control block diagram;

Fig. 4 branch compensation voltage control block diagram;

Figure 5 Inverter grid-connected control block diagram;

Figure 6 Comparison of simulation effects. (figure a is a traditional photovoltaic array output power curve, and figure b is a new photovoltaic array output power curve of the present invention)

Detailed ways

The present invention will be described in further detail below in conjunction with accompanying drawing and specific embodiment:

Example 1:

Figure 1 is a structural diagram of a photovoltaic grid-connected system, which consists of a photovoltaic array, a DC/DC chopper circuit, an inverter circuit, an output filter and a power grid. Here, the photovoltaic array composed of two branches connected in parallel is analyzed as an example, and the structure of the first branch is explained as an example. The first branch is composed of three photovoltaic modules M1, M2, and M3, and D1 is a diode. C1 is a capacitor with a value of 1000uF, L1, L2, and L3 are inductors with a value of 3mH, 3mH, and 5mH respectively, and V1, V2, V3, and V1n, V2n, and V3n are switch tubes IGBT. The DC side capacitance of the inverter is 4700uF, the filter capacitance is 400uF, and the inductance is 2mH.

Figure 2 is a flowchart of photovoltaic array compensation control.

The control of the photovoltaic array branch is divided into current control and voltage control:

1) Photovoltaic branch current control. When the photovoltaic array is under partial shadow conditions, the maximum power currents of photovoltaic modules M1, M2, and M3 are respectively I _M1 , I _M2 , and I _M3 . Since the maximum power currents of the modules are not equal, that is, I _M1 ≠ I _M2 ≠ I _M3 , in order to make each component work at the maximum power point, each node should satisfy the node current law, and a certain current can be injected into the inductor branch to compensate the component current. The currents that should be injected into the inductors L1 and L2 are respectively I _{L1_ref} =I _M1 -I _M2 , I _{L2_ref} =I _M2 -I _M3 . [Whether L3 needs to inject current, and if so, how much to inject. Please explain. 】L3 is the control of the voltage, the control signal is the voltage, as shown in Figure 4

Figure 3 is a block diagram of the branch compensation current control. Here, the current compensation of the component M2 is taken as an example to illustrate. The current I _L1 of the inductor L1 branch is obtained, compared with the compensation current I _{L1_ref} , and then compared by hysteresis [parameters of hysteresis comparison , please provide], the hysteresis width is set to 0.1A, and the control signal G _L1 of the switch tube V1 and V1n is obtained. When I _{L1_ref} -I _L1 <-0.1, the lower bridge arm IGBT is turned on. When I _{L1_ref} -I _L1 > 0.1, make the upper bridge arm IGBT turn on, when -0.1≤I _{L1_ref} -I _L1 ≤0.1, the control signal is 0, and the upper and lower bridge arm IGBTs are not turned on. The control method of component M3 compensation current is the same.

The 0.1A here refers to the general situation of the components. The maximum power current of the components is generally about 5A. If 0.1A is used, the control accuracy is about 2%, which can meet the conditions.

2) Photovoltaic branch voltage control. When the photovoltaic array is under partial shadow conditions, the maximum power voltages of photovoltaic modules M1, M2 and M3 are U _M1 , U _M2 and U _M3 respectively, and the maximum power voltages of photovoltaic modules M4, M5 and M6 are U _M4 and U _M5 , U _M6 , when the two branches are under different lighting conditions, the voltages of the two branches formed by the series connection of the components are not equal, that is, U _M1 + U _M2 + U _M3 ≠ U _M4 + U _M5 + U _M6 , then it is necessary to The branch circuit voltage is compensated to maintain the stability of the branch circuit voltage. Here, the method of controlling the voltage of the branch circuit series capacitor is adopted. The maximum power voltages of the two photovoltaic branches are: U _pvml = U _M1 + U _M2 + U _M3 , U _pvm2 = U _M4 + U _M5 + U _M6 , and the maximum power voltage U _pvm = max{U _pvm1 , U _pvm2 }, then the compensation voltages for the first and second branches are respectively U _{pv1_ref} =U _pvm -U _pvm1 , U _{pv2_ref} =U _pvm -U _pvm2 .

Figure 4 is a block diagram of the branch circuit compensation voltage control. The voltage compensation of the first branch circuit is used for illustration. The capacitance voltage U _ps1 of the detection branch circuit is compared with the compensation voltage U _{pv1_ref} . After passing through the PI regulator, it is compared with the triangular wave. The triangular wave The frequency is 10kHz, and the control signal G _C1 of the switch tubes V3 and V3n is obtained. If the comparison value is greater than the triangular wave, the lower bridge arm IGBT is turned on, and if the comparison value is smaller than the triangular wave, the upper bridge arm IGBT is turned on. The control method of the compensation voltage of the second branch is the same.

The parameters of the PI regulator are set as: P _ps =0.2, I _ps =100.

Figure 5 is a block diagram of grid-connected inverter control. Compare the DC side voltage U _DC of the inverter with the set voltage U _{DC_ref} , the error is controlled by the second PI regulator, and the result is multiplied by a sinusoidal signal synchronized with the grid voltage, which is used as the inverter output current command signal I _inf to detect The inverter output current I _in is compared with I _inf , the error is controlled by the third PI regulator, and then compared with the triangular wave to obtain the control signal G _VSI of the inverter to control the on-off of the switching device of the inverter, such as A Phase, when G _VSI > 0, the upper bridge arm IGBT is controlled to be turned on, and the lower bridge arm IGBT is turned off; when G _VSI < 0, the upper bridge arm IGBT is controlled to be turned off, and the lower bridge arm IGBT is turned on. B and C phase control signals are similar. The frequency of the triangle wave is 10kHz.

The parameters of the second PI regulator are set as: P _dc =0.2, I _dc =25; the parameters of the third PI regulator are set as P _in =0.5, I _in =300.

Fig. 6 is a simulation comparison diagram, graph (a) is the output power curve of the photovoltaic array under the conventional structure, and graph (b) is the output power curve of the photovoltaic array under the method of the present invention. Under the same partial shadow condition, for the conventional array structure, the local or global maximum power tracking method is adopted, and its output power is about 715W. Using the photovoltaic array structure of the present invention, the branch voltage is controlled to make each branch reach the maximum Power, the output power is 810W, and the power is increased by 11.7%, which increases the output efficiency of the photovoltaic array and has practical significance for the operation of the photovoltaic array.

The voltage level of the IGBT in the photovoltaic array is 1200V.

Claims (6)

1. the photovoltaic array control method based on photovoltaic array topological structure, it is characterized in that, described photovoltaic array topological structure is: photovoltaic array comprises many photovoltaic branch roads in parallel, each photovoltaic branch road comprises assembly branch road and compensates branch road, assembly props up route blocking diode, N number of photovoltaic module and an electric capacity and is in series successively, and compensating circuit comprises N number of inductance and N number of IGBT brachium pontis; All IGBT brachium pontis all with assembly branch circuit parallel connection; Each IGBT brachium pontis is made up of two IGBT; N number of mid point that N number of IGBT brachium pontis is corresponding is connected to N number of negative pole end points place of N number of photovoltaic module respectively by N number of inductance; N be more than or equal to 2 integer;

Comprise (1) current compensation process and (2) voltage compensation procedure;

(1) current compensation process is:

Current compensation refers to adopt the IGBT brachium pontis described in N-1 to carry out current compensation;

To each the IGBT brachium pontis in N-1 IGBT brachium pontis before each photovoltaic branch road, all implement following control:

Obtain inductance L _ielectric current I _li, with offset current I _{li_ref}relatively, then by stagnant chain rate comparatively, the control signal G of the switching tube (Vi, Vin) on i-th IGBT brachium pontis is obtained _li, namely work as I _{li_ref}-I _li<-0.1, makes the conducting of lower brachium pontis IGBT (Vin), works as I _{li_ref}-I _li>0.1, makes brachium pontis IGBT (Vi) conducting, as-0.1<I _{li_ref}-I _li<0.1, control signal is 0, upper and lower bridge arm IGBT not conductings;

Wherein, offset current I _{li_ref}i.e. i-th inductance L _ion the size of current that should inject, and I _{li_ref}=I _mi-I _{m (i+1)}, I _miit is the maximum power electric current of i-th photovoltaic module;

(2) voltage compensation procedure:

Voltage compensation refers to and carries out voltage compensation based on N number of IGBT brachium pontis to the electric capacity in photovoltaic branch road;

The bucking voltage size of jth bar photovoltaic branch road is U _{pvj_ref}=U _pvm-U _pvmj, j=1,2 ..., M, M are the total number of photovoltaic branch road;

Wherein branch road maximum power voltage U _pvm=max{U _pvmj, wherein u _mirefer to the maximum power voltage of jth bar photovoltaic branch road i-th photovoltaic module;

Control procedure is: for each photovoltaic branch road, be all implemented as follows control:

The capacitance voltage U of detection branch _psj, with bucking voltage U _{pvj_ref}relatively, after the first pi regulator, compare with the first triangular wave, obtain the N number of IGBT brachium pontis (V of switching tube _n, V _nn) control signal G _c1, comparison value is greater than the first triangular wave then makes lower brachium pontis IGBT (V _nn) conducting, be less than the first triangular wave and then make brachium pontis IGBT (V _n) conducting.

2. photovoltaic array control method according to claim 1, is characterized in that, described N is 3.

3. photovoltaic array control method according to claim 1, is characterized in that, the proportionality coefficient P of the first pi regulator _ps=0.2, integral coefficient I _ps=100; First triangle wave frequency is 10kHz.

4. a control method for grid-connected system, is characterized in that, in described grid-connected system, photovoltaic array is connected with three phase network with LC output filter by DC/DC DC chopper circuit, inverter successively;

Described photovoltaic array topological structure is: photovoltaic array comprises many photovoltaic branch roads in parallel, each photovoltaic branch road comprises assembly branch road and compensates branch road, assembly props up route blocking diode, N number of photovoltaic module and an electric capacity and is in series successively, and compensating circuit comprises N number of inductance and N number of IGBT brachium pontis; All IGBT brachium pontis all with assembly branch circuit parallel connection; Each IGBT brachium pontis is made up of two IGBT; N number of mid point that N number of IGBT brachium pontis is corresponding is connected to N number of negative pole end points place of N number of photovoltaic module respectively by N number of inductance; N be more than or equal to 2 integer;

Described control method comprises (A) photovoltaic array control method and (B) parallel network reverse control method;

(A) photovoltaic array control method comprises current compensation process and voltage compensation procedure;

(1) current compensation process is:

Current compensation refers to adopt N-1 IGBT brachium pontis to carry out current compensation;

To each the IGBT brachium pontis in N-1 IGBT brachium pontis before each photovoltaic branch road, all implement following control:

Obtain inductance L _ielectric current I _li, with offset current I _{li_ref}relatively, then by stagnant chain rate comparatively, the control signal G of the switching tube (Vi, Vin) on i-th IGBT brachium pontis is obtained _li, namely work as I _{li_ref}-I _li<-0.1, makes the conducting of lower brachium pontis IGBT (Vin), works as I _{li_ref}-I _li>0.1, makes brachium pontis IGBT (Vi) conducting, as-0.1<I _{li_ref}-I _li<0.1, control signal is 0, upper and lower bridge arm IGBT not conductings;

Wherein, offset current I _{li_ref}i.e. i-th inductance L _ion the size of current that should inject, I _{li_ref}=I _mi-I _{m (i+1)}, I _miit is the maximum power electric current of i-th photovoltaic module;

(2) voltage compensation procedure:

Voltage compensation refers to and carries out voltage compensation based on N number of IGBT brachium pontis to the electric capacity in photovoltaic branch road;

The bucking voltage size of jth bar photovoltaic branch road is U _{pvj_ref}=U _pvm-U _pvmj, j=1,2 ..., M, M are the total number of photovoltaic branch road;

Wherein branch road maximum power voltage U _pvm=max{U _pvmj, wherein u _mirefer to the maximum power voltage of jth bar photovoltaic branch road i-th photovoltaic module;

Control procedure is: for each photovoltaic branch road, be all implemented as follows control:

The capacitance voltage U of detection branch _psj, with bucking voltage U _{pvj_ref}relatively, after the first pi regulator, compare with the first triangular wave, obtain the N number of IGBT brachium pontis (V of switching tube _n, V _nn) control signal G _c1, comparison value is greater than the first triangular wave then makes lower brachium pontis IGBT (V _nn) conducting, be less than the first triangular wave and then make brachium pontis IGBT (V _n) conducting;

(B) be parallel network reverse control method:

A, B, C three-phase of inverter is controlled respectively:

By DC side voltage of converter U _dCwith setting voltage U _{dC_ref}relatively, relative error is controlled by the second pi regulator, and result is multiplied by the sinusoidal signal synchronous with corresponding phase line voltage, as inverter output current command signal I _inf, detect inverter output current I _in, with I _infrelatively, error controls through the 3rd pi regulator, then compares with the second triangular wave, obtains the control signal G of inverter _vSI, the break-make of control inverter switching device, works as G _vSI>0, control correspondence and go up brachium pontis IGBT conducting mutually, lower brachium pontis IGBT turns off; Work as G _vSI<0, in control, brachium pontis IGBT turns off, lower brachium pontis IGBT conducting.

5. control method according to claim 4, is characterized in that, described N is 3; Described inverter is the inverter controlled based on voltage, current double closed-loop.

6. control method according to claim 5, is characterized in that, the proportionality coefficient P of the second pi regulator _dc=0.2, integral coefficient I _dc=25; The proportionality coefficient P of the 3rd pi regulator _in=0.5, integral coefficient I _in=300; Second triangle wave frequency is 10kHz.