CN105024395A - Photovoltaic grid-connected power generation system input current ripple suppression device and method - Google Patents

Abstract

The invention discloses a photovoltaic grid-connected power generation system input current ripple suppression device and method. The device comprises a two-stage main power circuit formed by a Boost converter and a DC/AC converter, an AD sampling circuit, a digital processing control module, a band-pass filter, a driving circuit, an auxiliary power supply circuit and a display unit. According to the method, output voltage and current of photovoltaic cell components are sampled so as to search the maximum power tracking point; duty ratio compensation amount is calculated by sampling DC bus voltage and twice the power frequency voltage ripple quantity thereof, and MPPT calculation unit output duty ratio is adjusted via an adder so that control duty ratio of the pre-stage Boost converter is obtained; and inverter control unit output duty ratio controls working of the post-stage inversion DC/AC converter. Photovoltaic input current low-frequency ripple can be reduced with no dependence on main power system parameters and power level. Meanwhile, MPPT tracking precision and EMI performance are enhanced and heat radiation of the photovoltaic cells is reduced so that the photovoltaic grid-connected power generation system input current ripple suppression device and method have important engineering application value.

Description

A kind of device and method suppressing grid-connected photovoltaic system input current to be pulsed

Technical field

The present invention relates to the control technology field in electrical energy changer, particularly a kind of device and method suppressing grid-connected photovoltaic system input current to be pulsed.

Background technology

Direct current is transformed into alternating current by grid-connected photovoltaic system by photovoltaic cell component, and final realization is incorporated into the power networks.Grid-connected photovoltaic system has two basic functions: one is the output of photovoltaic cell component is converted to alternating current be connected to electrical network, two is the MPPT maximum power point tracking (Maximum Power Point Tracking, MPPT) realizing photovoltaic cell component.Grid-connected photovoltaic system 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, general employing two-stage type single-phase grid-connected photovoltaic power generation system, its input power opposing straight, and power output is pulsation, this power pulsations frequency is lower, it is the twice of output voltage frequency, need bus capacitor to balance Instantaneous input power and power output, bus capacitor voltage and DC bus-bar voltage are pulsed with twice work frequency, and in two-stage type single-phase grid-connected photovoltaic power generation system, the MPPT of its prime boosting (Boost) converter controls and the control (comprising DC bus-bar voltage mean value to control and grid-connected current control) of rear class DC/AC converter is independently, therefore the input current of Boost and the output current of photovoltaic cell component are also pulsed with twice work frequency, this pulsation not only reduces MPPT tracking accuracy, also (ElectroMagnetic Interference can be disturbed by exacerbate electromagnetic, and the heating of photovoltaic cell EMI), and then affect the life-span of battery.Existing technology relies on the power grade of main power circuit parameter and main circuit, or realizes input current pulsation suppression by the energy storage converter increased especially, and Measures compare is complicated, and Reliability comparotive is low.

Summary of the invention

The object of the present invention is to provide a kind of device and method of the suppression grid-connected photovoltaic system input current pulsation based on DC bus-bar voltage feedback, the electric current low frequency pulsating of input side can be reduced, improve the precision that MPPT follows the tracks of, improve EMI performance, thus reduce the heating of photovoltaic cell component and extend its life-span.

The technical solution realizing the object of the invention is: a kind of device suppressing grid-connected photovoltaic system input current to be pulsed, this device realizes input current pulsation based on DC bus-bar voltage feedback to be suppressed, specifically comprise two-stage type main power circuit, AD sample circuit, digital processing control module, band pass filter, drive circuit, auxiliary power supply circuit, the display unit of Boost and DC/AC converter composition, wherein digital processing control module comprises MPPT computing unit, adder, compensating unit and inversion control unit;

The main power circuit of described grid-connected photovoltaic system comprises photovoltaic cell component, Boost, bus capacitor C in parallel in turn _d, DC/AC converter and grid sources v _o; Wherein in main power circuit, the output voltage of the output voltage of photovoltaic cell component and electric current, DC bus-bar voltage, DC/AC converter and electric current all access AD sample circuit, and the output of AD sample circuit accesses MPPT computing unit, band pass filter and inverter control unit respectively; The output access compensating unit of band pass filter; The output of MPPT computing unit, compensating unit accesses two inputs of adder respectively, and the output of adder accesses Boost by driver element; The control output end of inverter control unit is by driver element access DC/AC converter; The output of described auxiliary power supply circuit accesses the power input of driver element, AD sample circuit, digital processing control module, display unit respectively; Described display unit is connected with the communication ends of digital processing control module.

Suppress the method that grid-connected photovoltaic system input current is pulsed, the method realizes input current pulsation based on DC bus-bar voltage feedback and suppresses, and comprises the following steps:

Step 1, creates MPPT computing unit, compensating unit, adder and inverter control unit in digital processing control module;

Step 2, AD sample circuit gathers the output voltage of photovoltaic cell component in main power circuit and electric current is input to MPPT computing unit, the output voltage and the DC bus-bar voltage that gather photovoltaic cell component in main power circuit are input to compensating unit, gather DC bus-bar voltage output variable and be input to compensating unit after band pass filter, output voltage and the electric current of collection DC bus-bar voltage, DC/AC converter are input to inverter control unit;

Step 3, the MPPT computing unit of digital processing control module carries out maximal power tracing computing according to the photovoltaic cell component output voltage current feedback signal of AD sample circuit, exports the maximum power duty ratio D of prime Boost _mPPT;

Step 4, the inverter control unit of digital processing control module compares computing according to the feedback signal of AD sample circuit, and process draws and realizes the closed-loop control of rear class by the duty ratio D that grid-connected photovoltaic system rear class DC/AC circuit is current;

Step 5, the output voltage of the photovoltaic cell component collected, DC bus-bar voltage and the DC bus-bar voltage twice power-frequency voltage component after band pass filter is carried out computing by compensatory control unit, obtains prime Boost maximum power duty ratio D _mPPTcompensation duty ratio D _ripple, through adder to the prime Boost maximum power duty ratio D exported in step 3 _mPPTadjust, the current duty cycle d obtaining prime Boost realizes the MPPT closed-loop control of prime, and formula is as follows:

d＝D _MPPT+D _ripple

Step 6, the input of gained grid-connected photovoltaic system, output valve are sent into display unit and are shown in real time by digital processing control module.

Compared with prior art, its remarkable advantage is in the present invention: (1) can adjust the control duty ratio of prime Boost circuit in real time, does not increase extra hardware cost, does not rely on main power system parameter and power grade; (2) the simple and reliable and easy Digital Implementation of method, can reduce or suppress completely the electric current low frequency pulsating of input side, improve the precision that MPPT follows the tracks of, improve EMI performance; (3) decrease the heating of photovoltaic cell and extend its life-span, there is important engineer applied and be worth.

Accompanying drawing explanation

Fig. 1 is the main power circuit figure of two-stage type single-phase grid-connected photovoltaic power generation system.

Fig. 2 is two-stage type single-phase grid-connected photovoltaic power generation system and control circuit schematic diagram thereof.

Fig. 3 is the simulation work oscillogram of input voltage, input current, busbar voltage in two-stage type single-phase grid-connected photovoltaic power generation system switch periods, and wherein (a) is input voltage V before input current pulsation suppresses _pv, input current i _pv, DC bus-bar voltage V _doscillogram, (b) is input voltage V after input current pulsation suppresses _pv, input current i _pv, DC bus-bar voltage V _doscillogram.

Embodiment

Below in conjunction with drawings and the specific embodiments, the present invention is described in further detail.

The invention provides a kind of device and method of the suppression grid-connected photovoltaic system input current pulsation based on DC bus-bar voltage feedback.

The theory deduction of 1, traditional two-stage type grid-connected photovoltaic system:

As shown in Figure 1, line voltage v is defined _o(t) be:

$v_o\left(t\right)=\sqrt{2}{V}_o\sin \mathrm{\ωt}---\left(1\right)$

Wherein V _obe the effective value 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 _ot () can be expressed as:

$i_o\left(t\right)=\sqrt{2}{I}_o\sin \mathrm{\ωt}---\left(2\right)$

Wherein I _oit is the effective value of power network current.

The instantaneous power p outputting to electrical network can be released by formula (1) and (2) _o(t) be:

$p_o\left(t\right)=v_o\left(t\right)\·i_o\left(t\right)=\sqrt{2}{V}_o\sin \mathrm{\ωt}\·\sqrt{2}{I}_o\sin \mathrm{\ωt}=V_o{I}_o(1-\cos 2\mathrm{\ωt})---\left(3\right)$

The power output p of Boost _d(t) be:

p _d(t)＝V _di _d＝V _d(I _d-i _cd(t)) (4)

Wherein: V _dthe mean value of DC bus-bar voltage, I _dthe mean value of the output current of Boost, i _cdt () is the transient current flowing through bus capacitor.

In order to make grid-connected photovoltaic system be operated in maximum power point, then its input current and photovoltaic cell component output current are without the pulsation of twice power frequency, then obtain by a power frequency period, the input-output power mean value of DC/AC converter is equal:

P _d＝V _dI _d＝P _o＝V _oI _o(5)

In formula, P _dthe mean value of Boost power output and the mean value of DC/AC converter input power, P _othe mean value that DC/AC converter outputs to grid power.

The mean value I of Boost output current can be known by formula (4) _dfor:

$I_d=\frac{V_o{I}_o}{V_d}---\left(6\right)$

The transient current i of dc-link capacitance can be flow through by formula (4), (5), (6) _cd(t) be:

$i_{\mathrm{Cd}}\left(t\right)=\frac{V_o{I}_o}{V_d}\cos 2\mathrm{\ωt}---\left(7\right)$

Instantaneous voltage v then on bus capacitor _dt () can be expressed as:

$v_d\left(t\right)=V_d+\frac{1}{C_d}\∫i_{\mathrm{Cd}}\left(t\right)\mathrm{dt}{=V}_d+\frac{V_o{I}_o}{2\mathrm{\ω}{C}_d{V}_d}\sin 2\mathrm{\ωt}---\left(8\right)$

In formula, C _dit is the capacitance of bus capacitor.

Following relation is there is between the input voltage of Boost and output voltage:

$\frac{V_d}{V_{\mathrm{PV}}}=\frac{1}{1-D_{\mathrm{MPPT}}}---\left(9\right)$

Wherein: V _dthe mean value of DC bus-bar voltage, V _pVthe mean value of photovoltaic cell output voltage when being operated in maximum power point.

And

$\frac{v_d\left(t\right)}{V_{\mathrm{pv}}}=\frac{1}{1-(D_{\mathrm{MPPT}}+D_{\mathrm{ripple}})}---\left(10\right)$

Wherein, v _dt () is the instantaneous value of DC bus-bar voltage, D _mPPTthe duty ratio of prime Boost maximum power, D _rippleprime Boost maximum power duty ratio D _mPPTcompensation duty ratio.

Then

$\begin{array}{c}\frac{V_{\mathrm{PV}}}{v_d\left(t\right)}=\frac{V_{\mathrm{PV}}}{V_d(1+\frac{V_o{I}_o}{2\mathrm{\ω}{C}_d{V}_d^2}\sin 2\mathrm{\ωt})}\\ \≅\frac{V_{\mathrm{PV}}}{V_d}(1-\frac{V_o{I}_o}{2\mathrm{\ω}{C}_d{V}_d^2}\sin 2\mathrm{\ωt})\\ =\frac{V_{\mathrm{PV}}}{V_d}-\frac{V_{\mathrm{PV}}{V}_o{I}_o}{2\mathrm{\ω}{C}_d{V}_d^3}\sin 2\mathrm{\ωt}\end{array}---\left(11\right)$

Then can be obtained by formula (9), formula (10), formula (11):

$D_{\mathrm{ripple}}=\frac{V_{\mathrm{PV}}{V}_o{I}_o}{2{\mathrm{\ωC}}_d{V}_d^3}\sin 2\mathrm{\ωt}---\left(12\right)$

The output voltage v of definition photovoltaic cell component _pv(t) be:

$v_{\mathrm{pv}}\left(t\right)=\sqrt{2}{V}_{\mathrm{pv}}\sin \mathrm{\ωt}---\left(13\right)$

When output power factor is 1, be input to the current i of Boost _pvt () can be expressed as:

$i_{\mathrm{pv}}\left(t\right)=\sqrt{2}{I}_{\mathrm{pv}}\sin \mathrm{\ωt}---\left(14\right)$

Wherein I _pvit is the effective value of photovoltaic cell component output current.

The instantaneous power p outputting to Boost can be released by formula (13) and (14) _in(t) be:

$p_{\mathrm{in}}\left(t\right)=v_{\mathrm{pv}}\left(t\right)\·i_{\mathrm{pv}}\left(t\right)=\sqrt{2}{V}_{\mathrm{pv}}\sin \mathrm{\ωt}\·\sqrt{2}{I}_{\mathrm{pv}}\sin \mathrm{\ωt}=V_{\mathrm{pv}}{I}_{\mathrm{pv}}(1-\cos 2\mathrm{\ωt})---\left(15\right)$

In a power frequency period, input power average value P _infor:

$P_{\mathrm{in}}={\∫}_0^{\mathrm{\π}}{p}_{\mathrm{in}}\left(t\right)\mathrm{d\ωt}={\∫}_0^{\mathrm{\π}}{V}_{\mathrm{pv}}{I}_{\mathrm{pv}}(1-\cos 2\mathrm{\ω})\mathrm{d\ωt}=V_{\mathrm{pv}}{I}_{\mathrm{pv}}---\left(16\right)$

Suppose that the efficiency of circuit is 100%, so in its power frequency period, the Mean Input Power of whole photovoltaic system equals power output.Can be obtained by formula (5) and (16):

P _in＝V _pvI _pv＝P _o＝V _oI _o(17)

When input power factor is 1, in half power frequency period, when Instantaneous input power is greater than power output, bus capacitor C _dcharging; When Instantaneous input power is less than power output, bus capacitor C _delectric discharge.Therefore, bus capacitor C _din half power frequency period, the maximum poor Δ E of storage power is

$\mathrm{\ΔE}={\∫}_{\mathrm{\π}/4}^{3\mathrm{\π}/4}[P_{\mathrm{in}}\left(t\right)-P_o]\mathrm{d\ωt}=\frac{P_o}{\mathrm{\ω}}---\left(18\right)$

Relation according to bus capacitor energy and its voltage has:

$\mathrm{\ΔE}=\frac{1}{2}{C}_d[{(V_d+\frac{{\mathrm{\ΔV}}_d}{2})}^2-{(V_d-\frac{{\mathrm{\ΔV}}_d}{2})}^2]=C_d{V}_d{\mathrm{\ΔV}}_d---\left(19\right)$

Wherein Δ V _dfor bus capacitor C _dripple voltage v _dpeak-to-peak value.

Bus capacitor C can be obtained by formula (18) and (19) _dwith its ripple voltage peak-to-peak value Δ V _d, average voltage V _dpass be:

$C_d=\frac{P_o}{\mathrm{\ω}{V}_d\mathrm{\Δ}{V}_d}---\left(20\right)$

Can be obtained by formula (12) and formula (20)

$D_{\mathrm{ripple}}=\frac{V_{\mathrm{PV}}{\mathrm{\ΔV}}_d}{2V_d^2}\sin 2\mathrm{\ωt}---\left(21\right)$

Based on formula (21), the grid-connected photovoltaic system input current pulsation suppression technology based on DC bus-bar voltage feedback can be obtained.

2, the present invention is based on the device and method of the suppression grid-connected photovoltaic system input current pulsation of DC bus-bar voltage feedback

Composition graphs 2, the present invention is the device suppressing the pulsation of grid-connected photovoltaic system input current, this device realizes input current pulsation based on DC bus-bar voltage feedback to be suppressed, specifically comprise two-stage type main power circuit 1, AD sample circuit 2, digital processing control module, band pass filter 10, drive circuit 7, auxiliary power supply circuit 8, the display unit 9 of Boost and DC/AC converter composition, wherein digital processing control module comprises MPPT computing unit 3, adder 5, compensating unit 4 and inversion control unit 6;

The main power circuit 1 of described grid-connected photovoltaic system comprises photovoltaic cell component, Boost, bus capacitor C in parallel in turn _d, DC/AC converter and grid sources v _o; The output that wherein in main power circuit 1, the output voltage of the output voltage of photovoltaic cell component and electric current, DC bus-bar voltage, DC/AC converter and electric current all access AD sample circuit 2, AD sample circuit 2 accesses MPPT computing unit 3, band pass filter 10 and inverter control unit 6 respectively; The output access compensating unit 4 of band pass filter 10; The output of MPPT computing unit 3, compensating unit 4 accesses two inputs of adder 5 respectively, and the output of adder 5 accesses Boost by driver element 7; DC/AC converter is accessed by driver element 7 in the control output end of inverter control unit 6; The output of described auxiliary power supply circuit 8 accesses the power input of driver element 7, AD sample circuit 2, digital processing control module, display unit 9 respectively; Described display unit 9 is connected with the communication ends of digital processing control module.Described digital processing control module is dsp chip TMS320F28335, and described display unit 9 is LCD display.

The method that the present invention suppresses grid-connected photovoltaic system input current to be pulsed, the method realizes input current pulsation based on DC bus-bar voltage feedback and suppresses, and comprises the following steps:

Step 1, creates MPPT computing unit 3, compensating unit 4, adder 5 and inverter control unit 6 in digital processing control module;

Step 2, AD sample circuit 2 gathers the output voltage of photovoltaic cell component in main power circuit 1 and electric current is input to MPPT computing unit 3, the output voltage and the DC bus-bar voltage that gather photovoltaic cell component in main power circuit are input to compensating unit 4, gather DC bus-bar voltage output variable and be input to compensating unit 4 after band pass filter 10, output voltage and the electric current of collection DC bus-bar voltage, DC/AC converter are input to inverter control unit 6;

Step 3, the MPPT computing unit 3 of digital processing control module carries out maximal power tracing computing according to the photovoltaic cell component output voltage current feedback signal of AD sample circuit 2, exports the maximum power duty ratio D of prime Boost _mPPT;

Step 4, the inverter control unit 6 of digital processing control module compares computing according to the feedback signal of AD sample circuit 2, and process draws and realizes the closed-loop control of rear class by the duty ratio D that grid-connected photovoltaic system rear class DC/AC converter is current;

Step 5, the output voltage of the photovoltaic cell component collected, DC bus-bar voltage and the DC bus-bar voltage twice power-frequency voltage component after band pass filter is carried out computing by compensatory control unit 4, obtains prime Boost maximum power duty ratio D _mPPTcompensation duty ratio D _ripple, concrete formula is as follows:

$D_{\mathrm{ripple}}=\frac{V_{\mathrm{pv}}\mathrm{\Δ}{V}_d}{{2V}_d^2}\sin 2\mathrm{\ωt}$

Wherein, V _pvthe mean value of photovoltaic cell component output voltage when being operated in maximum power point, V _dthe mean value of DC bus-bar voltage, Δ V _dfor bus capacitor C _dupper instantaneous voltage v _dtwice power frequency component peak-to-peak value, ω is the angular frequency of line voltage, and t is the time;

The prime Boost maximum power duty ratio D exported in adder 10 pairs of steps 3 _mPPTadjust, the current duty cycle d obtaining prime Boost realizes the MPPT closed-loop control of prime, and formula is as follows:

d＝D _MPPT+D _ripple

Step 6, the input of gained grid-connected photovoltaic system, output valve are sent into display unit 9 and are shown in real time by digital processing control module.

Embodiment 1

The present embodiment, based on the single-phase grid-connected electricity generation system of two-stage type, has carried out emulation experiment according to the two-stage type single-phase grid-connected photovoltaic power generation system shown in Fig. 2 and control circuit thereof.Design parameter is as follows: the power output of the maximum power point of photovoltaic cell component is 2KW; The open circuit voltage V of PV module _oc=226.5V, short circuit current I _sc=11.08A; Inductance L in Boost ₁=4mH: prime input side electric capacity C _pv=110uF, bus capacitor C _d=1500uF; Rear class DC/AC converter adopts full-bridge to export L ₂=6mH, C _ac=3.3uF.System switching frequency is: f _s=16K.

Fig. 3 (a) gives and compensates input current i under presteady state _pvwith input voltage v _pv, busbar voltage v _dsimulation waveform figure.From waveform, busbar voltage v _dpulse with the power frequency of twice, corresponding input current is also pulsed with the power frequency of twice, its twice power frequency pulsation amplitude Δ i _pv≈ 1.3A; As can be seen from waveform, input voltage is with the pulsation of the power frequency of twice and pulsation amplitude is comparatively large, its twice power frequency pulsation amplitude Δ v _pv≈ 5.8V.Fig. 3 (b) is input current i under stable state after compensation _pvwith input voltage v _pv, busbar voltage v _dsimulation waveform figure simulation waveform figure.Can find out, by adding the input current pulsation suppressing method of DC bus-bar voltage feedback, input current i _pvsubstantially without the pulsation of twice power frequency, input voltage v _pvsubstantially pulse without twice power frequency.As from the foregoing, by adopting control method of the present invention, grid-connected photovoltaic system input current and input voltage waveform more straight, pulse without twice power frequency, the electric current low frequency pulsating even eliminating input side can be reduced, improve the precision that MPPT follows the tracks of, improve EMI performance, thus reduce the heating of photovoltaic cell component and extend its life-span.

To sum up, the present invention is directed to two-stage type single-phase grid-connected photovoltaic power generation system input current low-frequency pulsation problem, provide a kind of device of the input current pulsation suppression technology research based on DC bus-bar voltage feedback, the method can when influential system normally work, reduce the low frequency pulsating even eliminating input current, improve MPPT tracking accuracy, compared to prior art, do not increase extra hardware cost, do not rely on main power system parameter and power grade, simple and reliable and the easy Digital Implementation of method, improve MPPT tracking accuracy simultaneously, the heating of EMI performance and reduction photovoltaic cell, there is important engineer applied be worth.

Claims (5)

1. the device suppressing grid-connected photovoltaic system input current to be pulsed, it is characterized in that, this device realizes input current pulsation based on DC bus-bar voltage feedback to be suppressed, specifically comprise the two-stage type main power circuit (1) of Boost and DC/AC converter composition, AD sample circuit (2), digital processing control module, band pass filter (10), drive circuit (7), auxiliary power supply circuit (8), display unit (9), wherein digital processing control module comprises MPPT computing unit (3), adder (5), compensating unit (4) and inversion control unit (6),

The main power circuit (1) of described grid-connected photovoltaic system comprises photovoltaic cell component, Boost, bus capacitor C in parallel in turn _d, DC/AC converter and grid sources v _o; Wherein the output voltage of the output voltage of photovoltaic cell component and electric current, DC bus-bar voltage, DC/AC converter and electric current all access AD sample circuit (2) in main power circuit (1), and the output of AD sample circuit (2) accesses MPPT computing unit (3), band pass filter (10) and inverter control unit (6) respectively; Output access compensating unit (4) of band pass filter (10); The output of MPPT computing unit (3), compensating unit (4) accesses two inputs of adder (5) respectively, and the output of adder (5) is by driver element (7) access Boost; The control output end of inverter control unit (6) is by driver element (7) access DC/AC converter; The output of described auxiliary power supply circuit (8) accesses the power input of driver element (7), AD sample circuit (2), digital processing control module, display unit (9) respectively; Described display unit (9) is connected with the communication ends of digital processing control module.

2. the device of suppression grid-connected photovoltaic system input current pulsation according to claim 1, it is characterized in that, described digital processing control module is dsp chip TMS320F28335.

3. the device of suppression grid-connected photovoltaic system input current pulsation according to claim 1, it is characterized in that, described display unit (9) is LCD display.

4. the method suppressing grid-connected photovoltaic system input current to be pulsed, is characterized in that, the method realizes input current pulsation based on DC bus-bar voltage feedback and suppresses, and comprises the following steps:

Step 1, creates MPPT computing unit (3), compensating unit (4), adder (5) and inverter control unit (6) in digital processing control module;

Step 2, output voltage and the electric current of the middle photovoltaic cell component of AD sample circuit (2) collection main power circuit (1) are input to MPPT computing unit (3), the output voltage and the DC bus-bar voltage that gather photovoltaic cell component in main power circuit are input to compensating unit (4), gather DC bus-bar voltage output variable and be input to compensating unit (4) after band pass filter (10), output voltage and the electric current of collection DC bus-bar voltage, DC/AC converter are input to inverter control unit (6);

Step 3, the MPPT computing unit (3) of digital processing control module carries out maximal power tracing computing according to the photovoltaic cell component output voltage current feedback signal of AD sample circuit (2), exports the maximum power duty ratio D of prime Boost _mPPT;

Step 4, the inverter control unit (6) of digital processing control module compares computing according to the feedback signal of AD sample circuit (2), process draws and realizes the closed-loop control of rear class by the duty ratio D that grid-connected photovoltaic system rear class DC/AC converter is current;

Step 5, the output voltage of the photovoltaic cell component collected, DC bus-bar voltage and the DC bus-bar voltage twice power-frequency voltage component after band pass filter is carried out computing by compensatory control unit (4), obtains prime Boost maximum power duty ratio D _mPPTcompensation duty ratio D _ripple, through adder (10) to the prime Boost maximum power duty ratio D exported in step 3 _mPPTadjust, the current duty cycle d obtaining prime Boost realizes the MPPT closed-loop control of prime, and formula is as follows:

d＝D _MPPT+D _ripple

Step 6, the input of gained grid-connected photovoltaic system, output valve are sent into display unit (9) and are shown in real time by digital processing control module.

5. the method for suppression grid-connected photovoltaic system input current pulsation according to claim 4, is characterized in that, the Boost of prime described in step 5 maximum power duty ratio D _mPPTcompensation duty ratio D _ripple, concrete formula is as follows:

$D_{\mathrm{ripple}}=\frac{V_{\mathrm{pv}}\mathrm{\Δ}{V}_d}{{2V}_d^2}\sin 2\mathrm{\ωt}$

Wherein, V _pvthe mean value of photovoltaic cell component output voltage when being operated in maximum power point, V _dthe mean value of DC bus-bar voltage, Δ V _dfor bus capacitor C _dupper instantaneous voltage v _dtwice power frequency component peak-to-peak value, ω is the angular frequency of line voltage, and t is the time.