CN103633866A - Device and method for inhibiting single-phase photovoltaic grid-connected inverter input current low frequency pulsation - Google Patents

Abstract

The invention discloses a device and a method for inhibiting single-phase photovoltaic grid-connected inverter input current low frequency pulsation. The device comprises a two-stage main power circuit consisting of a Boost circuit and an inverter circuit, an auxiliary power supply circuit, a driving circuit, a signal conditioning circuit, a digital processing control module and a display unit. The method is characterized in that by comprising the steps of detecting the output voltage and current of a solar cell assembly, direct current bus voltage and the output voltage and current of a DC/AC inverter circuit, outputting the output voltage and current of the solar cell assembly, the direct current bus voltage and the output voltage and current of the DC/AC inverter circuit to a preceding stage control unit and a backward stage control unit, adjusting an output control signal of the preceding stage control unit by a low frequency pulsation inhibiting unit to obtain and output the current duty ratio D of a preceding stage Boost circuit, and obtaining the current duty ratio D of the inverter circuit through the backward stage control unit. Under the condition of not influencing the normal work of the system, the low frequency pulsation of the input current is reduced and even eliminated, the MPPT (maximum power point tracking) precision is improved, the EMI (electro-magnetic interference) and the heating of photovoltaic cells are reduced, and significance practical value is obtained.

Description

Restraining device and the method for the pulsation of single-phase photovoltaic grid-connected inverter input current low-frequency

Technical field

The invention belongs to the control technology field in electrical energy changer, particularly a kind of restraining device and method of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation.

Background technology

Solar photovoltaic battery component is transformed into alternating current by inverter by direct current, and final realization is incorporated into the power networks.Photovoltaic combining inverter has two basic functions: the one, and the output of solar cell is converted to alternating current and is connected to electrical network, the 2nd, realize the MPPT maximum power point tracking (Maximum Power Point Tracking, MPPT) of solar cell.Combining inverter directly has influence on the energy output of whole solar photovoltaic generation system and operation stability, high efficiency, fail safe, is the key equipment of whole system.In middle low power applications, the general two-stage type single-phase grid-connected inverter that adopts, its input power is relatively straight, and power output is pulsed, this power pulsations frequency is lower, it is the twice of output voltage frequency, need storage capacitor to come the instantaneous input power of balance and power output, storage capacitor voltage is that DC bus-bar voltage is pulsed with twice work frequency, and in two-stage type single-phase grid-connected inverter, its prime boosts that the MPPT of (Boost) converter controls and the control of rear class inverter (comprise DC bus-bar voltage mean value is controlled and grid-connected current control) is independently, therefore the input current of Boost converter is that photovoltaic cell output current is also pulsed with twice work frequency, this pulsation has not only reduced MPPT tracking accuracy, also can worsen electromagnetic interference (Electro Magnetic Interference, EMI) and the heating of photovoltaic cell, and then affect life-span of battery.

Summary of the invention

The object of the present invention is to provide a kind of restraining device and method of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation, can reduce even to eliminate the electric current low frequency pulsating of input side, improve the precision that MPPT follows the tracks of, improve EMI performance, thereby reduce the heating of photovoltaic cell component, postpone its life-span.

The technical solution that realizes the object of the invention is: a kind of restraining device of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation, the main power circuit, auxiliary power supply circuit, drive circuit, signal conditioning circuit, digital processing control module and the display unit that comprise two-stage type single-phase photovoltaic grid-connected inverter, wherein digital processing control module comprises that prime control unit, rear class control unit, sample circuit and low frequency pulsating suppress unit;

The main power circuit of described two-stage type single-phase photovoltaic grid-connected inverter comprises input solar module, Boost booster circuit, bus capacitor group C in parallel in turn _b, DC/AC inverter circuit and grid sources v _g; Wherein in main power circuit, the output voltage of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit and electric current all access sample circuit, and the output of sample circuit accesses respectively prime control unit and rear class control unit; Prime control unit suppresses unit with low frequency pulsating and is connected, and low frequency pulsating suppresses unit and rear class control unit all accesses signal conditioning circuit; The output of signal conditioning circuit is connected with drive circuit, and the control signal of drive circuit output accesses respectively Boost booster circuit and the DC/AC inverter circuit of main power circuit; The output of described auxiliary power supply circuit accesses respectively the power input of each chip in drive circuit, signal conditioning circuit, digital processing control module, display unit; Described display unit is connected with the output of digital processing control module.

An inhibition method for single-phase photovoltaic grid-connected inverter input current low-frequency pulsation, comprises the following steps:

Step 1 creates prime control unit, rear class control unit, sample circuit and low frequency pulsating and suppresses unit in digital processing control module;

Step 2, output voltage and the electric current of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit in the main power circuit of sample circuit collection two-stage type single-phase photovoltaic grid-connected inverter, and export to respectively prime control unit and rear class control unit;

Step 3, prime control unit compares computing according to the feedback signal of sample circuit, realizes the MPPT closed-loop control of prime, processes the maximal power tracing control duty ratio D that draws prime Boost booster circuit _mPPT;

Step 4, rear class control unit compares computing according to the feedback signal of sample circuit, realizes the closed-loop control of rear class, processes the duty ratio D that draws rear class DC/AC inverter circuit ₂;

Step 5, low frequency pulsating suppresses unit and the output control signal of prime control unit is adjusted to reduce the ripple amplitude of prime solar module output current, the duty ratio d of output prime Boost converter;

Step 6, the output signal that signal conditioning circuit suppresses unit, rear class control unit by low frequency pulsating is converted to analog quantity by digital quantity, and being adjusted into the magnitude of voltage matching with drive circuit input, drive circuit carries out power amplification to drive the switching tube of Boost converter and DC/AC converter by input signal;

Step 7, digital processing control module is sent parameters such as the input of the system of gained, output valves into display unit and is shown in real time.

Compared with prior art, remarkable advantage of the present invention is: (1) adjusts the control duty ratio of prime Boost circuit in real time, has suppressed the electric current low frequency pulsating of input side; (2) improve the precision that MPPT follows the tracks of, improved EMI performance; (3) reduce the heating of photovoltaic cell component, postpone its life-span.

Accompanying drawing explanation

Fig. 1 is the structural representation of main power circuit in two-stage type single-phase photovoltaic grid-connected inverter of the present invention.

Fig. 2 is the work wave of output current, busbar voltage and input current in two-stage type single-phase photovoltaic grid-connected inverter switch periods of the present invention, wherein (a) is output current voltage before input current pulsation suppresses, input-output power, busbar voltage and input current waveform figure, is (b) the input current waveform figure after input current pulsation suppresses.

Fig. 3 is the restraining device structural representation of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation of the present invention.

Wherein: Δ I _pvthe ripple value of-Boost converter input current pulsation, v _pv-input voltage, i _pv-input current, C _b-bus capacitor group, V _b-busbar voltage, v _g-grid sources voltage, i _g-grid sources electric current.

Embodiment

Below in conjunction with drawings and the specific embodiments, the present invention is made to further description.

The present invention designs a kind of restraining device and method of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation.

1, the theory of traditional two-stage type photovoltaic combining inverter is derived:

In conjunction with Fig. 1～2, traditional two-stage type photovoltaic combining inverter is derived as follows.

Definition line voltage v _g(t) be

v _g(t)＝V _gsinωt (1)

V wherein _gbe the amplitude of line voltage, ω is the angular frequency of line voltage, and t is the time.

When output power factor is 1, be input to the current i of electrical network _g(t) can be expressed as

i _g(t)＝I _gsinωt (2)

I wherein _git is the amplitude that is input to the electric current of electrical network.

By formula (1) and (2), can release the instantaneous power p that outputs to electrical network _g(t) be:

p _g(t)＝v _g(t)v _g(t)＝V _gI _gsin ²ωt (3)

In a power frequency period, power output average value P _gfor

$P_g=\frac{1}{\mathrm{\π}}{\∫}_0^{\mathrm{\π}}{p}_g\left(t\right)\mathrm{d\ωt}=\frac{1}{\mathrm{\π}}{\∫}_0^{\mathrm{\π}}{V}_g{I}_g{\sin }^2\mathrm{\ωtd\ωt}=\frac{V_g{I}_g}{2}---\left(4\right)$

For Boost converter, its input/output relation is

$\frac{v_B}{v_{\mathrm{PV}}}=\frac{1}{1-d}---\left(5\right)$

V wherein _bthat Boost converter output voltage is DC bus-bar voltage, v _pVthat Boost converter input voltage is photovoltaic cell output voltage, the duty ratio that d is converter.

So, DC bus-bar voltage is

$v_B=\frac{v_{\mathrm{PV}}}{1-d}---\left(6\right)$

The power output of photovoltaic cell is

p _PV＝v _PV·i _PV＝v _PV·f(v _PV) (7)

I wherein _pVthat Boost converter input current is photovoltaic cell output current.

The power of processing on dc-link capacitance is

$p_{C_B}\left(t\right)=p_{\mathrm{PV}}-p_g=v_{\mathrm{PV}}\·f\left(v_{\mathrm{PV}}\right)-2P_g{\sin }^2\mathrm{\ωt}---\left(8\right)$

Instantaneous energy on dc-link capacitance is

$e_{C_B}\left(t\right)=\frac{1}{2}{C}_B{v}_B^2=E_{C_B}\left(0\right)+{\∫}_0^t{p}_{C_B}\left(t\right)\mathrm{dt}\≈\frac{1}{2}{C}_B{V}_B^2+{\∫}_0^t{p}_{C_B}\left(t\right)\mathrm{dt}---\left(9\right)$

Wherein

(0) be the energy of storing on zero moment dc-link capacitance, V _bfor DC bus-bar voltage mean value.

By formula (6), formula (8), formula (9) simultaneous, can be obtained

$\frac{1}{2}{C}_B{\left(\frac{v_{\mathrm{PV}}}{1-D}\right)}^2=\frac{1}{2}{C}_B{V}_B^2+{\∫}_0^t[v_{\mathrm{PV}}\·f\left(v_{\mathrm{PV}}\right)-2P_g{\sin }^2\mathrm{\ωt}]\mathrm{dt}---\left(10\right)$

C in formula (10) _b, D, V _b, P _gbe fixed value, by formula (10), can solve photovoltaic cell voltage v _pV, then can obtain DC bus-bar voltage v according to formula (6) _b.

If making combining inverter input current is photovoltaic cell output current pulse free, it should be operated in maximum power point, by input-output power mean value in a power frequency period, is equated to obtain

P _PV＝V _PVI _PV＝P _g (11)

V wherein _pVfor maximum power of photovoltaic cell point voltage, I _pVfor maximum power of photovoltaic cell point electric current.

Power on dc-link capacitance is

$p_{C_B}\left(t\right)=P_{\mathrm{PV}}-p_g=P_g-2P_g{\sin }^2\mathrm{\ωt}=P_g\cos \left(2\mathrm{\ωt}\right)---\left(12\right)$

And can obtain according to the relation between capacitance voltage and capacitance stores energy

$\begin{array}{c}{e}_{C_B}\left(t\right)=\frac{1}{2}{C}_B{v}_B^2=E_{C_B}\left(0\right)+{\∫}_0^t{p}_{C_B}\left(t\right)\mathrm{dt}=E_{C_B}\left(0\right)+{\∫}_0^t{P}_g\cos \left(2\mathrm{\ωt}\right)\mathrm{dt}\\ \≅\frac{1}{2}{C}_B{V}_B^2+{\∫}_0^t{P}_g\cos \left(2\mathrm{\ωt}\right)\mathrm{dt}\end{array}---\left(13\right)$

And then can obtain

$v_B\left(t\right)=\sqrt{\frac{2e_{C_B}}{C_B}}=\sqrt{V_B^2+\frac{P_g}{\mathrm{\&omega;}{C}_B}\sin 2\mathrm{\&omega;t}}={\mathrm{<figure-callout\; id="1"\; label="V\; B"\; filenames="HDA0000425980860000012.png"\; state="\{\{state\}\}">V</figure-callout>}}_B\sqrt{1+\frac{P_g}{\mathrm{\&omega;}{C}_B{V}_B^2}\sin 2\mathrm{\&omega;t}}---\left(14\right)$

The expression formula that can be obtained variable duty cycle by Boost converter input/output relation is

$\begin{array}{c}d=1-\frac{V_{\mathrm{PV}}}{v_B\left(t\right)}=1-\frac{V_{\mathrm{<figure-callout\; id="1"\; label="PV\; V\; B"\; filenames="HDA0000425980860000012.png"\; state="\{\{state\}\}">PV</figure-callout>}}}{V_B}\&cong;1-\frac{V_{\mathrm{PV}}}{V_B}(1-\frac{P_g}{2\mathrm{\&omega;}{C}_B{V}_B^2}\sin 2\mathrm{\&omega;t})\\ =1-\frac{V_{\mathrm{PV}}}{V_B}+\frac{V_{\mathrm{PV}}{P}_g}{2\mathrm{\&omega;}{C}_{\mathrm{<figure-callout\; id="3"\; label="B\; V\; B"\; filenames="HDA0000425980860000021.png"\; state="\{\{state\}\}">B</figure-callout>}}{V}_B^{}{}_3^{}}\sin 2\mathrm{\&omega;t}=1-\frac{V_{\mathrm{PV}}}{V_B}+\frac{V_g}{2\mathrm{\&omega;}{C}_B{V}_B^3}{V}_{\mathrm{PV}}{I}_g\sin 2\mathrm{\&omega;t}=D_{\mathrm{MPPT}}+d_{\mathrm{ripple}}\end{array}---\left(15\right)$

Wherein

$D_{\mathrm{MPPT}}=1-\frac{V_{\mathrm{PV}}}{V_B}---\left(16\right)$

d _ripple＝kV _PVI _gsin2ωt (17)

$k=\frac{V_g}{2\mathrm{\&omega;}{C}_B{V}_B^3}---\left(18\right)$

Wherein, D _mPPTfor maximal power tracing is controlled duty ratio, d _ripplefor ripple voltage is adjusted duty ratio.Based on formula (16), (17), can obtain two-stage type single-phase photovoltaic grid-connected inverter input current low-frequency pulsation inhibition method.

2, restraining device and the method for single-phase photovoltaic grid-connected inverter input current low-frequency pulsation of the present invention

The restraining device of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation of the present invention, the main power circuit 1, auxiliary power supply circuit 8, drive circuit 7, signal conditioning circuit 6, digital processing control module and the display unit 9 that comprise two-stage type single-phase photovoltaic grid-connected inverter, wherein digital processing control module comprises that prime control unit 4, rear class control unit 3, sample circuit 2 and low frequency pulsating suppress unit 5;

The main power circuit 1 of described two-stage type single-phase photovoltaic grid-connected inverter comprises input solar module, Boost booster circuit, bus capacitor group C in parallel in turn _b, DC/AC inverter circuit and grid sources v _g; Wherein in main power circuit, the output voltage of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit and electric current all access sample circuit 2, and the output of sample circuit 2 accesses respectively prime control unit 4 and rear class control unit 3; Prime control unit 4 suppresses unit 5 with low frequency pulsating and is connected, and low frequency pulsating suppresses unit 5 and rear class control unit 3 all accesses signal conditioning circuit 6; The output of signal conditioning circuit 6 is connected with drive circuit 7, and the control signal of drive circuit 7 outputs accesses respectively Boost booster circuit and the DC/AC inverter circuit of main power circuit 1; The output of described auxiliary power supply circuit 8 accesses respectively the power input of each chip in drive circuit 7, signal conditioning circuit 6, digital processing control module, display unit 9; Described display unit 9 is connected with the output of digital processing control module, realizes point-to-point communication between the two.Described signal processing module is dsp chip TMS320F28335, and described display unit 9 is 1602 LCDs.

Auxiliary power supply circuit 8 offers the electric energy of foregoing circuit chips need of work; 6 pairs of low frequency pulsatings of signal conditioning circuit suppress the output signal of unit, rear class control unit to be adjusted, and finally realizes the closed-loop control of digital processing control module to whole system.

The inhibition method of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation of the present invention, comprises the following steps:

Step 1 creates prime control unit 4, rear class control unit 3, sample circuit 2 and low frequency pulsating and suppresses unit 5 in digital processing control module;

Step 2, output voltage and the electric current of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit in the main power circuit of sample circuit 2 collection two-stage type single-phase photovoltaic grid-connected inverters, and export to respectively prime control unit 4 and rear class control unit 3;

Step 3, prime control unit 4 compares computing according to the feedback signal of sample circuit, realizes the MPPT closed-loop control of prime, processes the maximal power tracing control duty ratio D that draws prime Boost booster circuit _mPPT;

Step 4, rear class control unit 3 compares computing according to the feedback signal of sample circuit, realizes the closed-loop control of rear class, processes the duty ratio D that draws rear class DC/AC inverter circuit ₂;

Step 5, the output control signal of the 5 pairs of prime control units 4 in low frequency pulsating inhibition unit adjusts to reduce the ripple amplitude of prime solar module output current, the duty ratio d of output prime Boost converter, as shown in formula (15)～(18);

Step 6, the output signal that signal conditioning circuit 6 suppresses unit 5, rear class control unit 3 by low frequency pulsating is converted to analog quantity by digital quantity, and being adjusted into the magnitude of voltage matching with drive circuit 7 inputs, drive circuit 7 carries out power amplification to drive the switching tube of Boost converter and DC/AC converter by input signal;

Step 7, digital processing control module is sent parameters such as the input of the system of gained, output valves into display unit 9 and is shown in real time.

The present invention is directed to two-stage type single-phase photovoltaic grid-connected inverter input current low-frequency pulsation problem, designed and a kind ofly can suppress two-stage type single-phase photovoltaic grid-connected inverter input current low-frequency pulsation restraining device and method, the method can be in the situation that not impact system works, reduce the low frequency pulsating of even eliminating input current, improved MPPT tracking accuracy, reduce the heating of EMI and photovoltaic cell, there is important practical value.

Claims (5)

1. the restraining device of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation, it is characterized in that, the main power circuit (1), auxiliary power supply circuit (8), drive circuit (7), signal conditioning circuit (6), digital processing control module and the display unit (9) that comprise two-stage type single-phase photovoltaic grid-connected inverter, wherein digital processing control module comprises that prime control unit (4), rear class control unit (3), sample circuit (2) and low frequency pulsating suppress unit (5);

The main power circuit of described two-stage type single-phase photovoltaic grid-connected inverter (1) comprises input solar module, Boost booster circuit, bus capacitor group C in parallel in turn _b, DC/AC inverter circuit and grid sources v _g; Wherein in main power circuit, the output voltage of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit and electric current all access sample circuit (2), and the output of sample circuit (2) accesses respectively prime control unit (4) and rear class control unit (3); Prime control unit (4) suppresses unit (5) with low frequency pulsating and is connected, and low frequency pulsating suppresses unit (5) and rear class control unit (3) all accesses signal conditioning circuit (6); The output of signal conditioning circuit (6) is connected with drive circuit (7), and the control signal of drive circuit (7) output accesses respectively Boost booster circuit and the DC/AC inverter circuit of main power circuit (1); The output of described auxiliary power supply circuit (8) accesses respectively the power input of each chip in drive circuit (7), signal conditioning circuit (6), digital processing control module, display unit (9); Described display unit (9) is connected with the output of digital processing control module.

2. the restraining device of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation according to claim 1, is characterized in that, described signal processing module is dsp chip TMS320F28335.

3. the restraining device of single-phase photovoltaic grid-connected inverter input current low-frequency pulsation according to claim 1, is characterized in that, described display unit (9) is 1602 LCDs.

4. an inhibition method for single-phase photovoltaic grid-connected inverter input current low-frequency pulsation, is characterized in that, comprises the following steps:

Step 1 creates prime control unit (4), rear class control unit (3), sample circuit (2) and low frequency pulsating and suppresses unit (5) in digital processing control module;

Step 2, output voltage and the electric current of the output voltage of solar module and electric current, DC bus-bar voltage, DC/AC inverter circuit in the main power circuit of sample circuit (2) collection two-stage type single-phase photovoltaic grid-connected inverter, and export to respectively prime control unit (4) and rear class control unit (3);

Step 3, prime control unit (4) compares computing according to the feedback signal of sample circuit, realizes the MPPT closed-loop control of prime, processes the maximal power tracing control duty ratio D that draws prime Boost booster circuit _mPPT;

Step 4, rear class control unit (3) compares computing according to the feedback signal of sample circuit, realizes the closed-loop control of rear class, processes the duty ratio D that draws rear class DC/AC inverter circuit ₂;

Step 5, low frequency pulsating suppresses unit (5) and the output control signal of prime control unit (4) is adjusted to reduce the ripple amplitude of prime solar module output current, the duty ratio d of output prime Boost converter;

Step 6, the output signal that signal conditioning circuit (6) suppresses unit (5), rear class control unit (3) by low frequency pulsating is converted to analog quantity by digital quantity, and being adjusted into the magnitude of voltage matching with drive circuit (7) input, drive circuit (7) carries out power amplification to drive the switching tube of Boost converter and DC/AC converter by input signal;

Step 7, digital processing control module is sent parameters such as the input of the system of gained, output valves into display unit (9) and is shown in real time.

5. the inhibition method that single-phase photovoltaic grid-connected inverter input current low-frequency according to claim 4 is pulsed, it is characterized in that, it is as follows that low frequency pulsating suppresses the concrete formula unit (5) adjusted by the output control signal of prime control unit (4) described in step 5:

d＝D _MPPT+d _ripple

$D_{\mathrm{MPPT}}=1-\frac{V_{\mathrm{PV}}}{V_B}$

d _ripple＝kV _PVI _gsin2ωt

$k=\frac{V_g}{2\mathrm{\&omega;}{C}_B{V}_B^3}$

Wherein, d is the duty ratio of output prime Boost converter, D _mPPTfor maximal power tracing is controlled duty ratio, d _ripplefor ripple voltage is adjusted duty ratio, V _pVfor maximum power of photovoltaic cell point voltage, V _bfor DC bus-bar voltage mean value, V _gthe amplitude of line voltage, C _bbe dc-link capacitance value, ω is the angular frequency of line voltage, I _gbe the amplitude that is input to the electric current of electrical network, t is the time.

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