CN105676941A - System and method for tracking maximum power point of photovoltaic array under partial shadow - Google Patents

Abstract

The invention relates to a maximum power point tracking technology of a photovoltaic array and in particular relates to a system and a method for tracking a maximum power point of a photovoltaic array under partial shadow. The maximum power point tracking system comprises the photovoltaic array, a first switch, a DC/DC (Direct Current/Direct Current) module and a load which are connected in sequence, and further comprises a tracking circuit and a controller, wherein the tracking circuit is connected with the photovoltaic array through a second switch; the tracking circuit is connected with the controller; the controller is connected with the DC/DC module. Compared with a traditional technology, the system and method for tracking the maximum power point under the partial shadow of the photovoltaic array, provided by the invention, have the advantages of simple method, rapid searching speed and high precision, and are suitable for tracking the maximum power point of the photovoltaic array under the partial shadow condition and the like.

Description

Maximum power point tracking system and method under a kind of photovoltaic array local shades

Technical field

The present invention relates to maximum power point of photovoltaic array tracer technique, be specifically related to maximum power point tracking system and method under a kind of photovoltaic array local shades.

Background technology

Photovoltaic arrays (PVArray), also known as photovoltaic array, is mechanically and electrically gone up, by several photovoltaic modulies or photovoltaic panel, the DC generation unit fitting together and having fixing supporting construction by certain way and constitute. Charging a battery, the output voltage of photovoltaic array plate necessarily be greater than the current voltage of accumulator, if the voltage of photovoltaic array plate is lower than the voltage of battery, then output electric current can be closer to 0. And traditional solar charging/discharging controller is just somewhat like manual change speed gear box, when the rotating speed of electromotor increases time, if the gear of change speed gear box does not improve accordingly, speed will certainly be affected. And the maximum power points in MPPT controller meeting real-time tracking solar panels, give play to the maximum effect of solar panels. When external environment changes, if not carrying out maximum power tracing, photovoltaic array efficiency now can not reach maximum. Theoretically, use the solar power system of MPPT controller the traditional efficiency of ratio can improve 50%, but with according to our actual test, due to surrounding environment influence and various energy losses, final efficiency can also improve 20%-30%.

MPPT maximum power point tracking (maximumpowerpointtracking, MPPT) technology is one of key technology improving photovoltaic generating system efficiency. In actual applications, local shades situation often makes power vs. voltage (P-V) characteristic curve of photovoltaic array present multiple power extreme point, now, traditional MPPT controls system and generally adopts such as disturbance observational method (perturbandobserve, P&O), conductance increment method (incrementalconductance, IC) etc., tend to be absorbed in Local Extremum and global maximum power point cannot be tracked.

Summary of the invention

The present invention provides maximum power point tracking system and method under a kind of photovoltaic array local shades, solving MPPT control system traditional in prior art and be usually absorbed in, when following the trail of maximum power point, the problem that Local Extremum causes tracking, concrete technical scheme is as follows:

Maximum power point tracking system under a kind of photovoltaic array local shades, including the photovoltaic array being linked in sequence, the first switch, DC/DC module, load, also include following the trail of circuit and controller, described tracking circuit is connected with photovoltaic array by second switch, described tracking circuit is connected with controller, and described controller connects DC/DC module.

Further, described tracking circuit includes: current sensor, electric capacity C, the 3rd switch, discharge resistance R₁, multiplier, peakvalue's checking and trigger, sampling holder and divider resistance R₂、R₃, described electric capacity C is connected to the two ends of photovoltaic array, described discharge resistance R with current sensor, the first switch after connecting₁Switch after connecting in parallel with electric capacity C with the 3rd, described divider resistance R₂、R₃For also in parallel with electric capacity C after mega-ohms resistance and series connection, input one tunnel of described multiplier connects current sensor, another road connects the centre of R2 and R3, described multiplier outputs connects peakvalue's checking and trigger, described peakvalue's checking is connected sampling holder with trigger, described sampling holder gathers the magnitude of voltage between R2 and R3, and the magnitude of voltage of described sampling holder output tracking point is to described controller.

Further, described controller is pi regulator, and its voltage sample value is sent into pi regulator by described sampling holder, and pi regulator regulates dutycycle, and output pwm pulse is to DC/DC module.

Further, described DC/DC module is booster circuit.

Further, described electric capacity C can by selecting suitable capacitance to make discharge and recharge time of electric capacity C be Millisecond.

Further, described DC/DC module includes voltage and current detection unit, and magnitude of voltage and current value that the photovoltaic array detected is exported by described voltage and current detection unit pass to controller.

Global maximum power point method for tracing under a kind of photovoltaic array local shades, comprises the steps:

S1: judge whether the difference of output P (k) that photovoltaic array output P (k+1) that current DC/DC module collects obtains with previous secondary tracking circuit exceedes setting value P_ε,, it is proceed to S2, otherwise proceeds to S6;

S2: disconnect the connecting valve K1 of photovoltaic array and the DC/DC module of rear class, connection photovoltaic array and the connecting valve K2 followed the tracks of between circuit, disconnects the discharge circuit switch K3 following the tracks of electric capacity in circuit;

S3: by following the tracks of the current value that charging initiates and end time real-time sampling photovoltaic array exports and the magnitude of voltage of electric capacity in circuit, recycling multiplier obtains photovoltaic array output power value, obtains photovoltaic array peak power output P finally by the peakvalue's checking followed the tracks of in circuit with trigger_MPPTime corresponding magnitude of voltage V_MPP, and by V_MPPInput PI controller;

S4: connection photovoltaic array and the connecting valve K1 of the DC/DC module of rear class, disconnects photovoltaic array and the connecting valve K2 followed the tracks of between circuit, and the discharge circuit switch K3 of electric capacity in circuit is followed the tracks of in connection;

S5:PI controller is according to the magnitude of voltage V obtained_MPP, output size adjustment dutycycle according to pi regulator, output pwm pulse is to DC/DC module, and makes photovoltaic array output voltage be maintained at V by the ring closure of pi regulator_MPP, and then make photovoltaic array steady operation in maximum power point.

S6: utilize the voltage detection unit in DC/DC module and the output voltage U of current detecting unit detection photovoltaic array_PVWith electric current I_PV, and calculate P (k+1)=U_PV×I_PV, proceed to S1.

It should be noted that when starting to follow the trail of, photovoltaic array disconnects the very of short duration time with load, general several milliseconds, it is connected with an external capacitive, by the voltage V following the trail of circuit acquisition maximum power point of photovoltaic array in the process that external capacitor is charged simultaneously_MPPWith electric current I_MPP, then photovoltaic array reconnects with load, the V that will obtain_MPPAs the reference voltage, photovoltaic array output voltage is made to be maintained at V by closed loop control effect_MPP, make photovoltaic array steady operation in maximum power point.

Beneficial effect:

The present invention provides maximum power point tracking system and method under a kind of photovoltaic array local shades, relative to conventional art, the present invention has that method is simple, search speed is fast, precision is high, suitable in advantages such as the trackings of maximum power point of photovoltaic array in local shades situation.

Accompanying drawing explanation

In order to be illustrated more clearly that the embodiment of the present invention or technical scheme of the prior art, the accompanying drawing used required in embodiment or description of the prior art will be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the premise not paying creative work, it is also possible to obtain other accompanying drawing according to these accompanying drawings.

Fig. 1 is overall control schematic diagram of the present invention;

Fig. 2 is for following the trail of circuit theory diagrams;

Fig. 3 is photovoltaic array under local shadow power voltage curve;

Fig. 4 is DC/DC module control principle figure;

Fig. 5 is method for tracing block diagram.

Detailed description of the invention

For making the purpose of the embodiment of the present invention, technical scheme and advantage clearly, below the technical scheme in the embodiment of the present invention is clearly and completely described, it is clear that described embodiment is a part of embodiment of the present invention, rather than whole embodiments. Based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under not making creative work premise, broadly fall into the scope of protection of the invention.

Embodiment 1:

The schematic diagram of the global maximum power point tracing system of the photovoltaic array in local shades situation is as shown in Figure 1, when carrying out global maximum power point and following the trail of, K1 (the first switch) disconnects, the DC-DC module making photovoltaic array and rear class is isolated, K2 (second switch) closes, make photovoltaic array be connected with following the trail of circuit, found the voltage U of the global maximum power point of photovoltaic array now by tracking circuit_MPPWith electric current I_MPP, now, K2 disconnects, and K1 closes; Voltage, current value are admitted to controller, and controller is by magnitude of voltage U_MPPGiving as pi regulator, makes the output voltage of photovoltaic array be maintained at magnitude of voltage U by the closed loop adjustment effect of pi regulator_MPPOn, so that photovoltaic array steady operation is in maximum power point.

Follow the trail of the principle of circuit such as shown in the surrounded part of Fig. 2 dotted line. R₂And R₃Composition potential-divider network, by sampling and can be calculated the voltage of photovoltaic array, R₂And R₃Resistance is megaohm (M Ω) level.

$u_{PV}=\frac{R_2+R_3}{R_3}{u}_{R_3}---\left(1\right)$

In formula (1), U_PVFor the voltage of photovoltaic array, U_R3For resistance R₃Both end voltage.

When carrying out global maximum power point and following the trail of, K2 closes, and now, photovoltaic array, K2, electric capacity C constitute closed-loop path (due to R₂And R₃Resistance is very big, flows through electric current negligible), photovoltaic array charges (when charging is initial, electric capacity C both end voltage is 0) to electric capacity C, in charging process, obtains the voltage U of photovoltaic array_PV(formula 1 can obtain) and electric current I_PV(being obtained by current sensor), is sent the two value into multiplier and obtains the power P of photovoltaic array_PV, this power is sent into peakvalue's checking and trigger, does not stop detection P_PV, work as P_PV(P is now corresponded to time maximum_MPP), peakvalue's checking triggers sampling holder with trigger, by voltage (the i.e. voltage U of maximum power point of now photovoltaic array_MPP) maintain, and this value is sent into controller, and thus have found the voltage of the global maximum power point of photovoltaic array, after completing tracking, K2 disconnects, and K3 (the 3rd switch) Guan Bi, electric capacity C passes through K3, resistance R₁Electric discharge, prepares for following the trail of next time.

Explained later follows the trail of the Local Extremum of circuit:

When K2 (second switch) closes, photovoltaic array charges to electric capacity C, owing to electric capacity C both end voltage is 0 before, so when just starting to charge up, electric capacity C is equivalent to short circuit, now current sensor detects that the electric current that photovoltaic array exports is short circuit current, As time goes on, electric capacity C both end voltage ceaselessly raises, until when electric capacity C both end voltage is photovoltaic array open-circuit voltage, charging process terminates. In the process of electric capacity C charging, the output voltage of photovoltaic array increases to open-circuit voltage u from 0 always_co, from figure 3, it can be seen that in the charging process of electric capacity C, the output of photovoltaic array is complete curve in Fig. 3 just, will not be absorbed in certain Local Extremum.

Electric capacity C charging interval t_cCan be obtained by formula (2)

$t_c\≈2C\frac{u_{co}}{i_{sc}}---\left(2\right)$

In formula (2), C is the capacitance of electric capacity C, u_coFor the open-circuit voltage of photovoltaic array, i_scShort circuit current for photovoltaic array.

Such as, the u of photovoltaic array_co=400V, i_sc=100A, C=500 μ F, is calculated by formula (2) and obtains electric capacity C charging interval t_c≈ 4ms, the capacitance of suitable electric capacity C is selected according to the open-circuit voltage of photovoltaic array, short circuit current, the electric capacity C charging interval can be made to be in Millisecond, and this charging interval is exactly the time of tracing global maximum power point, therefore adopts the method tracing global maximum power point required time very short.

The control principle of DC-DC module as shown in Figure 4, will obtain V_MPPAs set-point, it is compared feeding pi regulator with the voltage detection unit in DC/DC module, output size adjustment dutycycle according to pi regulator, output pwm pulse controls DC-DC module, makes photovoltaic array output voltage be maintained at V by the ring closure of pi regulator_MPP, and then make photovoltaic array steady operation in maximum power point.

The flow process of method for tracing is as it is shown in figure 5, the difference of current photovoltaic array output P (k+1) and previous power P (k) exceedes some setting value P_εTime (this value can set by the percentage ratio accounting for photovoltaic array rated output power), the ambient conditions representing extraneous there occurs change, and namely maximum power point changes, and therefore starts new tracing process once.

S1: judge whether the difference of output P (k) that photovoltaic array output P (k+1) that current DC/DC module collects obtains with previous secondary tracking circuit exceedes setting value P_ε,, it is proceed to S2, otherwise proceeds to S6;

S2: disconnect the connecting valve K1 of photovoltaic array and the DC/DC module of rear class, connection photovoltaic array and the connecting valve K2 followed the tracks of between circuit, disconnects the discharge circuit switch K3 following the tracks of electric capacity in circuit;

S3: by following the tracks of the current value that charging initiates and end time real-time sampling photovoltaic array exports and the magnitude of voltage of electric capacity in circuit, recycling multiplier obtains photovoltaic array output power value, obtains photovoltaic array peak power output P finally by the peakvalue's checking followed the tracks of in circuit with trigger_MPPTime corresponding magnitude of voltage V_MPP, and by V_MPPInput PI controller;

S4: connection photovoltaic array and the connecting valve K1 of the DC/DC module of rear class, disconnects photovoltaic array and the connecting valve K2 followed the tracks of between circuit, and the discharge circuit switch K3 of electric capacity in circuit is followed the tracks of in connection;

S5:PI controller is according to the magnitude of voltage V obtained_MPP, output size adjustment dutycycle according to pi regulator, output pwm pulse is to DC/DC module, and makes photovoltaic array output voltage be maintained at V by the ring closure of pi regulator_MPP, and then make photovoltaic array steady operation in maximum power point.

S6: utilize the voltage detection unit in DC/DC module and the output voltage U of current detecting unit detection photovoltaic array_PVWith electric current I_PV, and calculate P (k+1)=U_PV×I_PV, proceed to S1.

The present invention provides maximum power point tracking system and method under a kind of photovoltaic array local shades, relative to conventional art, the present invention has that method is simple, search speed is fast, precision is high, suitable in advantages such as the trackings of maximum power point of photovoltaic array in local shades situation.

This above example only in order to technical scheme to be described, is not intended to limit; Although the present invention being described in detail with reference to previous embodiment, it will be understood by those within the art that: the technical scheme described in foregoing embodiments still can be modified by it, or wherein portion of techniques feature is carried out equivalent replacement; And these amendments or replacement, do not make the essence of appropriate technical solution depart from the spirit and scope of various embodiments of the present invention technical scheme.

Claims (7)

1. global maximum power point tracing system under a photovoltaic array local shades, including the photovoltaic array being linked in sequence, the first switch, DC/DC module, load, it is characterized in that, also include following the trail of circuit and controller, described tracking circuit is connected with photovoltaic array by second switch, described tracking circuit is connected with controller, and described controller connects DC/DC module.

2. global maximum power point tracing system under photovoltaic array local shades as claimed in claim 1, it is characterised in that described tracking circuit includes: current sensor, electric capacity C, the 3rd switch, discharge resistance R₁, multiplier, peakvalue's checking and trigger, sampling holder and divider resistance R₂、R₃, described electric capacity C is connected to the two ends of photovoltaic array, described discharge resistance R with current sensor, the first switch after connecting₁Switch after connecting in parallel with electric capacity C with the 3rd, described divider resistance R₂、R₃For also in parallel with electric capacity C after mega-ohms resistance and series connection, input one tunnel of described multiplier connects current sensor, another road connects the centre of R2 and R3, described multiplier outputs connects peakvalue's checking and trigger, described peakvalue's checking is connected sampling holder with trigger, described sampling holder gathers the magnitude of voltage between R2 and R3, and the magnitude of voltage of described sampling holder output tracking point is to described controller.

3. global maximum power point tracing system under photovoltaic array local shades as claimed in claim 1, it is characterized in that, described controller is pi regulator, and its voltage sample value is sent into pi regulator by described sampling holder, pi regulator regulates dutycycle, and output pwm pulse is to DC/DC module.

4. global maximum power point tracing system under photovoltaic array local shades as claimed in claim 1, it is characterised in that described DC/DC module is booster circuit.

5. global maximum power point tracing system under photovoltaic array local shades as claimed in claim 4, it is characterised in that described electric capacity C can pass through the suitable capacitance of selection and make discharge and recharge time of electric capacity C be Millisecond.

6. global maximum power point tracing system under photovoltaic array local shades as claimed in claim 1, it is characterized in that, described DC/DC module includes voltage and current detection unit, and magnitude of voltage and current value that the photovoltaic array detected is exported by described voltage and current detection unit pass to controller.

7. global maximum power point method for tracing under a kind of photovoltaic array local shades as claimed in claim 1, it is characterised in that comprise the steps:

S1: judge whether the difference of output P (k) that photovoltaic array output P (k+1) that current DC/DC module collects obtains with previous secondary tracking circuit exceedes setting value P_ε, it is proceed to S2, otherwise proceeds to S6;

S2: disconnect the connecting valve K1 of photovoltaic array and the DC/DC module of rear class, connection photovoltaic array and the connecting valve K2 followed the tracks of between circuit, disconnects the discharge circuit switch K3 following the tracks of electric capacity in circuit;

S3: by following the tracks of the current value that charging initiates and end time real-time sampling photovoltaic array exports and the magnitude of voltage of electric capacity in circuit, recycling multiplier obtains photovoltaic array output power value, obtains photovoltaic array peak power output P finally by the peakvalue's checking followed the tracks of in circuit with trigger_MPPTime corresponding magnitude of voltage V_MPP, and by V_MPPInput PI controller;

S4: connection photovoltaic array and the connecting valve K1 of the DC/DC module of rear class, disconnects photovoltaic array and the connecting valve K2 followed the tracks of between circuit, and the discharge circuit switch K3 of electric capacity in circuit is followed the tracks of in connection;

S5:PI controller is according to the magnitude of voltage V obtained_MPP, regulating dutycycle, output pwm pulse is to DC/DC module, and makes photovoltaic array output voltage be maintained at V by the ring closure of pi regulator_MPP, and then make photovoltaic array steady operation in maximum power point.

S6: utilize the voltage detection unit in DC/DC module and the output voltage U of current detecting unit detection photovoltaic array_PVWith electric current I_PV, and calculate P (k+1)=U_PV×I_PV, proceed to S1.