Maximum power point of photovoltaic power generation system tracking under local shadesTechnical field
The present invention relates to maximum power point of photovoltaic power generation system tracking technique field, specifically maximum power point of photovoltaic power generation system tracking under a kind of local shades.
Background technology
Along with the development of society, the energy and environmental problem more and more outstanding, sun power has good application prospect as a kind of regenerative resource.But the photoelectric transformation efficiency of photovoltaic cell is lower, and output power and intensity of sunshine and environment temperature have much relations, have significantly non-linear, need between photovoltaic device and load, connect MPPT maximum power point tracking (MPPT) circuit, to give full play to effect of photovoltaic cell.MPPT control algolithm conventional at present has constant voltage-tracing control methods, disturbance observation and conductance increment method etc.Above control algolithm is mainly based upon solar irradiation and stablizes or in the condition not having shade to affect.Many weeks, solar cell is in use easily subject to the shade impact of Adjacent Buildings trees and the aerial black clouds of electric pole and sky etc., partial radiation remitted its fury, solar cell integrated performance there will be dip, in general, the output current that the photovoltaic array output current having shade to affect affects lower than shadow-free, in like manner has photovoltaic array output power that shade affects lower than shadow-free module.Simultaneously from the P-V curve of photovoltaic array under local shades condition, unimodality affect time photovoltaic array P-U curve with shadow-free unlike, having there is multiple extreme point in the voltage power curve of whole array, also exists " pseudo-extreme point ".The maximum power point algorithm (as disturbance observation, conductance increment method etc.) of visible routine may lose efficacy when photovoltaic array is under local shades condition, occurred misjudgment phenomenon.Therefore, the local shades MPPT maximum power point tracking strategy that affects photovoltaic array in situation will be an important research topic.
Disturbance observation uses a widest algorithm in current MPPT algorithm, and the major advantage of this algorithm is that principle is simple, and it is convenient to realize, and tracking accuracy is high, and the tracking accuracy of its maximum power point can reach more than 90%.But disturbance observation also has its intrinsic shortcoming, namely near maximum power point, there is inevitably vibration thus cause extra power attenuation, and disturbance observation can produce misjudgment phenomenon.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, the invention provides the lower maximum power point of photovoltaic power generation system tracking of a kind of local shades impact, photovoltaic array can be made under local shades condition effectively to improve tracking velocity and the output power of photovoltaic generating system.
The present invention realizes with following technical scheme: maximum power point of photovoltaic power generation system tracking under a kind of local shades, is characterized in that: the output voltage U of photovoltaic array first will detectedpvwith output current Ipv, setting a switching value σ on diverter surface both sides, judging which kind of state of a control photovoltaic generating system is in by calculating sliding formwork switching function S and σ,according to the P-V family curve of solar cell,wherein: m is a constant coefficient, Poutfor the real-time power that photovoltaic cell exports, Pmaxit is the peak power that photovoltaic cell exports in normal conditions;
When diverter surface | during S| > σ, system enters sliding formwork control;
When diverter surface | during S| < σ, system enters immune PID control.
The invention has the beneficial effects as follows: compared with traditional disturbance observational technique, the method that the present invention proposes can well realize solar maximum power point Tracing Control when solar cell crested, effectively improve tracking velocity and the output efficiency of system, and curve of output is comparatively level and smooth, export vibration to reduce, improve the quality of power supply.
Accompanying drawing explanation
Below in conjunction with accompanying drawing, the invention will be further described.
Fig. 1 is control algolithm process flow diagram of the present invention,
Fig. 2 is sliding formwork control circuit figure;
Fig. 3 is sliding formwork control principle drawing;
Fig. 4 is the theory diagram of immune PID control.
Embodiment
As shown in Figure 1, because the lower photovoltaic array output characteristics of local shades impact is non-linear, the control strategy of nonlinear system can be adopted to control to realize MPPT.Because Sliding mode variable structure control can make control system slide according to the switching surface preset, thus make nonlinear control system substantially not by the impact of Parameters variation, there is good robustness.But because adopt Sliding mode variable structure control to there is high dither near sliding-mode surface, and Sliding mode variable structure control switching frequency is uncertain, cause the design comparison difficulty of subsequent filter, therefore the present invention adopts " Sliding mode variable structure control+immune PID controller " as maximum power point of photovoltaic power generation system tracking, wherein immune PID controller control system shake.
Maximum power point of photovoltaic power generation system tracking under local shades, the output voltage U of photovoltaic array first will detectedpvwith output current Ipv, setting a switching value σ on diverter surface both sides, judging to be in which kind of state of a control by calculating sliding formwork switching function S and σ,according to the P-V family curve of solar cell,wherein: m is a constant coefficient, Poutfor the real-time power that photovoltaic cell exports, Pmaxit is the peak power that photovoltaic cell exports in normal conditions;
When diverter surface | during S| > σ, system enters sliding formwork control;
When diverter surface | during S| < σ, system enters immune PID control.
As shown in Figure 2, for voltage is risen to certain amplitude, sliding formwork controls to adopt Boost circuit, and its circuit structure is simple, and it is little that MPPT searches for blind area.Described Boost comprises resistance Rs, R, inductance L, electric capacity Cs, C, diode D and MOSFET power switch pipe Q; Described resistance Rsone end be connected with photovoltaic battery panel positive pole, the other end connects one end of inductance L and electric capacity Csone end, the other end of inductance L connects the positive pole of diode D and the c pole of MOSFET power switch pipe Q, and the negative pole of diode D is connected with one end of electric capacity C and one end of resistance R respectively, electric capacity Csthe other end, the e pole of MOSFET power switch pipe Q, the other end of electric capacity C and resistance R the other end connect the negative pole of photovoltaic battery panel respectively; The b pole of MOSFET power switch pipe Q meets control signal u, and c pole connects the other end of inductance L and the positive pole of diode D, and e pole connects the negative pole of photovoltaic battery panel, and u is the control function of control MOSFET power switch pipe Q conducting,U is 1 expression switching tube conducting, and u is that 0 expression switching tube turns off; S is switching function.
As shown in Figures 3 and 4, described immune PID control adopts PID controller and connected Immunocontroller; The set-point that r (k) is photovoltaic power generation system output power, the real power output valve that y (k) is photovoltaic generating system, calculates e (k)=r (k)-y (k) for given performance number and output power value deviation; The input of the e* (k) after linear combination as Immunocontroller is calculated through PID controller,it can be used as the input of Immunocontroller, output u (k)=K (1-λ η f (Δ u (k-d))) e of Immunocontroller*k (), goes the dutycycle of gauge tap pipe PWM, realize the MPPT of PV system.At the Immunocontroller response initial stage, when namely set-point and output valve deviation are larger, now enter the Immune enhancement stage, the response speed of quickening system; In the later stage in the response, because set-point and output valve deviation diminish, and control action is still comparatively large, and now control system can produce overshoot, enters the immunosupress stage, reduces the controlled quentity controlled variable of system; In the latter stage of response, namely control system is in stable operation stage, and it is very little to enter immunity stabilization sub stage set-point and value of feedback error, and the output valve in control system equals set-point substantially, now the stablizing of keeping system.