CN102738825A - Novel photovoltaic grid-connected system based on modularized multi-level converter - Google Patents

Abstract

The invention discloses a novel photovoltaic grid-connected system based on a modularized multi-level converter. Each phase of the modularized multi-level converter is formed by connecting N sub-modules in series. High voltage and high power level can be realized without directly connecting devices in series. The novel photovoltaic grid-connected system is mainly applied to a high-voltage direct-current transmission system and a feed-in grid system of a wind power station at present. According to the novel photovoltaic grid-connected system provided by the invention, the modularized multi-level converter is applied to the photovoltaic grid-connected system, and is combined with a DC (Direct-Current)-DC converting circuit by combining the requirements and the characteristics of the photovoltaic grid-connected system, so that the novel photovoltaic grid-connected system based on the modularized multi-level converter is constructed. When a level value is relatively high, the quantity of required devices as the DC-AC (Alternating-Current) converting circuit is used is less than that of the required devices as an embedded multi-level converter is used, so that the control manner is simplified.

Description

Novel photovoltaic parallel in system based on the modular multilevel current transformer

Technical field

The present invention relates to the application of current transformer in photovoltaic parallel in system, the especially application of modular multilevel current transformer in photovoltaic parallel in system.

Background technology

Serious day by day along with energy crisis and environmental pollution, urgently seek a kind of new clean reproducible energy, solar energy power generating belongs to the regenerative resource of cleaning, the application of photovoltaic generation for alleviating energy crisis with reduce environmental pollution and play an important role.In photovoltaic parallel in system; The direct current that inverter sends photovoltaic battery panel changes into alternating current and sends into electrical network, in photovoltaic system, belongs to the key equipment of core, and multi-level converter is owing to can export a plurality of level alternating voltages; Make the harmonic content in the grid-connected current little; Be used widely to electric network pollution is less, the clamped formula multi-level converter of current main application is along with level number increases, and its clamped device sharply increases; And control is complicated, generally is limited in 5 level and following in the practical application; And the modular multilevel current transformer is because its modular construction, and switching device increases with level number is linear, thus at level number more for a long time; Required device will be less than the many level of clamped formula; Control is simple, and modular structure makes its autgmentability strong, is prone to realize Redundant Control; Be applied to photovoltaic system, have certain advantage compared to the many level of clamped formula.

Summary of the invention

The object of the invention is exactly in order to remedy the defective of prior art, a kind of novel photovoltaic parallel in system based on the modular multilevel current transformer that can reduce clamped formula multi-level converter main circuit number of devices to be provided.

The present invention realizes through following technical scheme:

A kind of novel photovoltaic parallel in system based on the modular multilevel current transformer; Comprise solar panel, DC-DC translation circuit, DC-AC translation circuit and three phase network; Described solar panel converts solar energy into the input as described DC-DC translation circuit of the voltage exported behind the electric energy; Described DC-DC translation circuit is by BOOST circuit, MPPT controller, pi regulator and PWM generator; Described MPPT controller detects the electric current and the output voltage of described solar panel, through the instruction of the adjusted solar panel quiescent potential of MPPT control algolithm, described instruction and solar panel output voltage values is subtracted each other; And carry out closed-loop control through described pi regulator; Produce pwm control signal, DC-DC translation circuit input voltage is controlled, realize the MPPT control of solar panel; Described DC-AC translation circuit includes three-phase three bridge arm circuit, and the two ends up and down of described three brachium pontis link to each other with the two ends of described BOOST circuit respectively, described each brachium pontis of three-phase three bridge arm circuit all comprise upper and lower two brachium pontis and on each brachium pontis and following brachium pontis be composed in series by N identical submodule and current limiting reactor; Submodule is a half-bridge circuit, the exportable unipolarity voltage of each submodule, structural module; Realize redundant easily; The last brachium pontis of described three brachium pontis and the intermediate node of following brachium pontis connect the three-phase input end of described three phase network respectively, through changing the direct voltage that submodule sum that upper and lower brachium pontis seals in obtains to expect, through changing the alternating voltage that difference that upper and lower brachium pontis seals in the submodule number obtains to expect; Wherein, Brachium pontis all comprises the N sub-module with following brachium pontis on each, exports N+1 level AC wave shape, adopts the dicyclo closure control method of outer voltage, current inner loop; Realize the unity power factor sine-wave current control of DC-AC translation circuit; Wherein, outer voltage is to realize the voltage stabilizing control of dc-link capacitance according to the principle of power-balance, and current inner loop then mainly realizes the tracking Control of DC-AC translation circuit electric current; Can obtain alternating current indirectly through obtaining alternating voltage; Carry out the control of current inner loop, obtain direct voltage, carry out the closed-loop control of the outer shroud of voltage.

BOOST circuit in the described DC-DC translation circuit also can be BUCK circuit or BUCK-BOOST circuit.

Described submodule is two switching devices and the half-bridge circuit that storage capacitor constitutes; Switching device one is the output of submodule with switching device two middle nodes; The lower end of half-bridge wall is the input of submodule; Each submodule is according to exportable 0 voltage of switching device state and storage capacitor voltage, and each switching tube only bears the submodule capacitance voltage in the submodule, and series connection reaches the higher voltage grade to the switching device of low voltage grade through submodule.

Among the present invention, last brachium pontis bridge arm voltage is u _U

$u_U=N_U\·U_C---\left(1\right)$

Following brachium pontis bridge arm voltage is u _L

$u_L=N_L\·U_C---\left(2\right)$

Wherein, N _U, N _LRepresent that respectively last brachium pontis and second arm seal in the number of submodule, U _CRepresent the capacitance voltage that single submodule is inner;

To two mesh column voltage equations up and down, alternating voltage is u by Kirchhoff's second law _V, dc voltage is Ud

$-\frac{U_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA00001752045800011.png,HDA00001752045800012.png"\; state="\{\{state\}\}">d</figure-callout>}}}{2}+u_U+u_V=0---\left(3\right)$

$-\frac{U_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA00001752045800011.png,HDA00001752045800012.png"\; state="\{\{state\}\}">d</figure-callout>}}}{2}+u_L-u_V=0---\left(4\right)$

(3) formula-(4) formula gets

$\mathrm{Uv}=\frac{U1-\mathrm{<figure-callout\; id="2"\; label="Uu"\; filenames="HDA00001752045800011.png,HDA00001752045800012.png"\; state="\{\{state\}\}">Uu</figure-callout>}}{2}=\frac{N1-\mathrm{Nu}}{2}*\mathrm{Uc}---\left(5\right)$

Promptly change the alternating voltage that difference that upper and lower bridge arm seals in the submodule number can obtain expecting.

(3) formula+(4) formula gets

Ud=?u _U+?u _L=N _U·U _C+N _L·U _C

=?（N _U+N _L）*Uc

Ud is direct voltage, and change seals in total submodule number and can obtain.

Advantage of the present invention is:

The present invention is applied to photovoltaic parallel in system with modularization multi-level converter; In conjunction with the requirement and the characteristics of photovoltaic parallel in system,, constitute novel photovoltaic parallel in system based on modularization multi-level converter with the combination of DC-DC translation circuit; When level number is higher; Owing to used the DC-AC translation circuit, required device has been simplified control mode with respect to clamped many level current transformers of formula negligible amounts.

Description of drawings

Fig. 1 is a structural representation of the present invention.

Fig. 2 is submodular circuits figure.

Embodiment

As shown in Figure 1; A kind of novel photovoltaic parallel in system based on the modular multilevel current transformer; Comprise solar panel 1, DC-DC translation circuit, DC-AC translation circuit and three phase network 7; Described solar panel 1 converts solar energy into the input as described DC-DC translation circuit of the voltage exported behind the electric energy, and described DC-DC translation circuit is made up of BOOST circuit 2, MPPT controller 3, pi regulator 4 and PWM generator 5, and described MPPT controller 3 detects the electric current and the output voltage of described solar panel 1; Instruction through adjusted solar panel 1 quiescent potential of MPPT control algolithm; Described instruction and solar panel 1 output voltage values are subtracted each other, and carry out closed-loop control, produce pwm control signal through described pi regulator 4; To controlling of DC-DC translation circuit input voltage, realize the MPPT control of solar panel 1; Described DC-AC translation circuit includes three-phase three bridge arm circuit 6, and the two ends up and down of described three brachium pontis link to each other with the two ends of described BOOST circuit 2 respectively, described three-phase three bridge arm circuit 6 each brachium pontis all comprise upper and lower two brachium pontis and on each brachium pontis and following brachium pontis be composed in series by N identical submodule SM and current limiting reactor Larm; The exportable unipolarity voltage of each submodule SM; Structural module is realized redundancy easily, and the last brachium pontis of described three brachium pontis and the intermediate node of following brachium pontis connect the three-phase input end of described three phase network 7 respectively; Through changing the direct voltage that submodule SM sum that upper and lower brachium pontis seals in obtains to expect; Through changing the alternating voltage that difference that upper and lower brachium pontis seals in submodule SM number obtains to expect, wherein, brachium pontis all comprises N sub-module SM with following brachium pontis on each; Export N+1 level AC wave shape; Adopt the dicyclo closure control method of outer voltage, current inner loop, realize the unity power factor sine-wave current control of DC-AC translation circuit, wherein; Outer voltage is to realize the voltage stabilizing control of dc-link capacitance according to the principle of power-balance; Current inner loop then mainly realizes the tracking Control of DC-AC translation circuit electric current, can obtain alternating current indirectly through obtaining alternating voltage, carries out the control of current inner loop; Obtain direct voltage, carry out the closed-loop control of the outer shroud of voltage.

BOOST circuit 2 in the described DC-DC translation circuit also can be BUCK circuit or BUCK-BOOST circuit.

As shown in Figure 2; Described submodule SM is two switching element T 1 and T2 and the half-bridge circuit that storage capacitor C0 constitutes; Node in the middle of switching device one T1 and switching device two T2 is the output of submodule SM; The lower end of half-bridge wall is the input of submodule SM; Each submodule SM is according to exportable 0 voltage of switching device state and storage capacitor voltage, and each switching tube only bears the submodule capacitance voltage among the submodule SM, and series connection reaches the higher voltage grade to the switching device of low voltage grade through submodule SM.

Claims (3)

1. novel photovoltaic parallel in system based on the modular multilevel current transformer; It is characterized in that: comprise solar panel, DC-DC translation circuit, DC-AC translation circuit and three phase network; Described solar panel converts solar energy into the input as described DC-DC translation circuit of the voltage exported behind the electric energy; Described DC-DC translation circuit includes BOOST circuit, MPPT controller, pi regulator and PWM generator; Described MPPT controller detects the electric current and the output voltage of described solar panel, through the instruction of the adjusted solar panel quiescent potential of MPPT control algolithm, described instruction and solar panel output voltage values is subtracted each other; And carry out closed-loop control through described pi regulator; Produce pwm control signal, pwm control signal is controlled the input voltage of DC-DC translation circuit, and solar panel obtains MPPT control; Described DC-AC translation circuit includes three-phase three bridge arm circuit; The two ends up and down of described three brachium pontis link to each other with the two ends of BOOST circuit respectively; Each brachium pontis of described three-phase three bridge arm circuit has included upper and lower two brachium pontis; Described on each brachium pontis include N identical submodule and current limiting reactor with following brachium pontis; The N sub-module is connected with current limiting reactor successively, and described submodule is a half-bridge circuit, and the last brachium pontis of described three brachium pontis and the intermediate node of following brachium pontis connect the three-phase input end of described three phase network respectively; Change the direct voltage that submodule sum that upper and lower brachium pontis seals in obtains expecting; Change the alternating voltage that difference that upper and lower brachium pontis seals in the submodule number obtains expectation, N+1 level AC wave shape of each brachium pontis output of three-phase three bridge arm circuit adopts the dicyclo closure control method of outer voltage, current inner loop to control the unity power factor sine-wave current of DC-AC translation circuit again.

2. the novel photovoltaic parallel in system based on the modular multilevel current transformer according to claim 1 is characterized in that: the BOOST circuit in the described DC-DC translation circuit also can be BUCK circuit or BUCK-BOOST circuit.

3. the novel photovoltaic parallel in system based on the modular multilevel current transformer according to claim 1; It is characterized in that: described submodule is two switching devices and the half-bridge circuit that storage capacitor constitutes; Switching device one is the output of submodule with switching device two middle nodes; The lower end of half-bridge arm is the input of submodule, and each submodule is according to exportable 0 voltage of switching device state and storage capacitor voltage.

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