CN102148584B - Compensation method of direct current (DC) voltage fluctuation of photovoltaic grid-connected inverter - Google Patents

Abstract

The invention provides a compensation method of direct current (DC) voltage fluctuation of a photovoltaic grid-connected inverter, and the method can be used for improving the quality of the grid-connected current through compensating an input DC side secondary pulse voltage by adding a DC voltage pulse compensation module in a DC/AC (direction current/alternating current) high-frequency link, and eliminating a grid-connected current harmonic wave caused by the DC voltage pulse. The control performance of the system can be improved without adding a filter device and adding any extra appliance.

Description

The compensation method of photovoltaic combining inverter dc voltage fluctuation

Technical field:

The invention belongs to solar grid-connected technical field of power generation, be specifically related to a kind of compensation method of photovoltaic combining inverter dc voltage fluctuation.

Background technology:

Possesses the miniature grid-connected inverter of distributed MPPT maximum power point tracking (MPPT) because every photovoltaic module is carried out MPPT control, this inverter is particularly suitable for the photovoltaic building occasion that blocked by shade, generating efficiency that can the Effective Raise system, and that the inverse-excitation type combining inverter has is simple in structure, reliability high and be widely used in miniature grid-connected inverter as typical circuit structure.But the single-phase grid-connected inverter power output is the secondary pulsating power, and output power of photovoltaic module is firm power, certainly will need energy storage device to carry out storage and the release of energy, the inverse-excitation type combining inverter is realized power match by the input side storage capacitor, this just unavoidably causes and forms the secondary pulsating voltage on the dc bus capacitor, cause having pulsating current in the grid-connected current, affect the grid-connected current quality.Thereby general conventional method reduces dc pulse moving voltage by increasing capacitance, but the method not only increases system cost and volume, and can not eradicate dc pulse moving voltage fully, also just can not thoroughly eliminate because the pulsation grid-connected current that dc pulse moving voltage causes.

The present invention is by compensating direct current pulsating voltage in DC/AC high frequency conversion link, and the pulsating current thereby elimination is incorporated into the power networks improves the grid-connected current quality, and need not extra any equipment.

Summary of the invention

Technical problem to be solved by this invention provides a kind of do not need to increase filter or any other equipment, by adding the realization of dc voltage ripple compensating module at the DC/AC high frequency link to the compensation of input direct-current side secondary pulsating voltage, eliminate because the grid-connected current harmonic wave that dc voltage ripple causes improves the grid-connected current quality.

According to the inventive concept of appeal, the present invention adopts following technical proposals:

A kind of compensation method of photovoltaic combining inverter dc voltage fluctuation may further comprise the steps,

(1) single-phase grid-connected inverter produces the secondary pulsating voltage at input side;

(2) add the dc voltage ripple compensating module in prime DC/AC high frequency conversion link, input side dc pulse moving voltage signal is fed back to the dc voltage ripple compensating module;

(3) the dc voltage ripple compensating module generates ripple compensation signal delta D according to the pulsating voltage signal of feedback;

(4) the control signal D stack of ripple compensation signal delta D and DC/AC high frequency control module generation, generate the control signal Dref of switching tube, by the Dref signal switching tube in the high frequency conversion link is carried out the compensation control of pulsating voltage, eliminate the grid-connected current harmonic wave that mains ripple causes.

In the compensation method of above-mentioned photovoltaic combining inverter dc voltage fluctuation, the dc pulse moving voltage signal obtains instantaneous voltage U and average voltage U by the mode of filtering, sampling, calculating _Av

In the compensation method of above-mentioned photovoltaic combining inverter dc voltage fluctuation, described dc voltage ripple compensating module is according to instantaneous voltage U, average voltage U _Av, control signal D generates ripple compensation signal delta D, its ripple compensation signal is by formula Δ D=(U _Av-U) * D/U calculates.

Description of drawings

Fig. 1 is control principle drawing of the present invention.

Fig. 2 is combining inverter input side dc pulse moving voltage.

Fig. 3 is flyback transformer current waveform schematic diagram.

Embodiment

Details are as follows by reference to the accompanying drawings for the preferred embodiments of the present invention:

A kind of compensation method of photovoltaic combining inverter dc voltage fluctuation may further comprise the steps,

(1) single-phase grid-connected inverter produces the secondary pulsating voltage at input side;

(2) add the dc voltage ripple compensating module in prime DC/AC high frequency conversion link, input side dc pulse moving voltage signal is fed back to the dc voltage ripple compensating module;

(3) the dc voltage ripple compensating module generates ripple compensation signal delta D according to the pulsating voltage signal of feedback;

(4) the control signal D stack of ripple compensation signal delta D and DC/AC high frequency control module generation, generate the control signal Dref of switching tube, by the Dref signal switching tube in the high frequency conversion link is carried out the compensation control of pulsating voltage, eliminate the grid-connected current harmonic wave that mains ripple causes.

In the compensation method of above-mentioned photovoltaic combining inverter dc voltage fluctuation, the dc pulse moving voltage signal obtains instantaneous voltage U and average voltage U by the mode of filtering, sampling, calculating _Av

In the compensation method of above-mentioned photovoltaic combining inverter dc voltage fluctuation, described dc voltage ripple compensating module is according to instantaneous voltage U, average voltage U _Av, control signal D generates ripple compensation signal delta D, its ripple compensation signal is by formula Δ D=(U _Av-U) * D/U calculates.

Should be understood that; concerning the those of ordinary skill in field, place of the present invention; can be equal to accordingly according to technical scheme of the present invention and design thereof and change or replace, and all these changes or replacement, all should belong to the protection range of claims of the present invention.

The principle of photovoltaic combining inverter dc voltage fluctuation of the present invention compensation method is summarized as follows:

Figure 1 shows that the photovoltaic combining inverter control principle drawing, wherein MPPT control module sampled light photovoltaic assembly output voltage and current signal are by calculating maximum power P _Mppt, DC/AC high frequency control module is according to the P of input _MpptWith the sinusoidal envelope line peak current control of electrical network zero cross signal realization flyback transformer, wherein the current waveform of flyback transformer as shown in Figure 3.The industrial frequency control module drives signal by generating power frequency behind the detection of grid voltage zero-crossing signal, realizes that steamed bun ripple electric current is to the conversion of sine-wave current.

The former limit of flyback transformer inductance is L, main switch S ₁Duty ratio is D, and primary current is i _P, the input pulsating voltage U that the sampling of dc voltage ripple compensating module obtains calculates mean direct voltage U _Av, then have:

$L\frac{{\mathrm{di}}_p}{\mathrm{dt}}=U_{\mathrm{av}}---\left(1\right)$

Simplify:

Li _P＝U _avD (2)

Because actual DC side voltage is the instantaneous voltage U that contains fluctuating signal, in order to realize the sinusoidal envelope line traffic control of flyback transformer, need to be to switching tube S ₁Duty ratio compensate, then have:

Li _P＝U(D+ΔD)＝(U _av+U-U _av)(D+ΔD) (3)

Comparison expression (2) and formula (3):

$\mathrm{\ΔD}=\frac{(U_{\mathrm{av}}-U)D}{U}---\left(4\right)$

Claims (3)

1. the compensation method of a photovoltaic combining inverter dc voltage fluctuation is characterized in that, may further comprise the steps,

(1) single-phase grid-connected inverter produces the secondary pulsating voltage at input side;

(2) add dc voltage ripple compensation computing module in prime DC/AC high frequency conversion link, input side dc pulse moving voltage signal is fed back to dc voltage ripple compensation computing module;

(3) dc voltage ripple compensation computing module generates ripple compensation signal delta D according to the pulsating voltage signal of feedback;

(4) the control signal D stack of ripple compensation signal delta D and DC/AC high frequency control module generation, generate the control signal Dref of switching tube, by the Dref signal switching tube in the high frequency conversion link is carried out the compensation control of pulsating voltage, eliminate the grid-connected current harmonic wave that mains ripple causes.

2. the compensation method of photovoltaic combining inverter dc voltage fluctuation according to claim 1 is characterized in that, the dc pulse moving voltage signal obtains instantaneous voltage U and average voltage U by the mode of filtering, sampling, calculating _Av

3. the compensation method of photovoltaic combining inverter dc voltage fluctuation according to claim 1 is characterized in that, described dc voltage ripple compensation computing module is according to instantaneous voltage U, average voltage U _Av, control signal D generates ripple compensation signal delta D, its ripple compensation signal is by formula Δ D=(U _Av-U) * D/U calculates.

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