Maximum Power Point Tracking Strategy of Disturbance Solar Panels Output Current

Abstract

Because the output of solar panels is influenced by external environment easily, and in order to ensure the energy generated by solar panel can be used as much as possible, so the maximum power point tracking technology is particularly important. In this paper, to achieve the maximum power point tracking of the solar panel output through the flyback converter. Using the method of perturbation the output current of the converter, though adjusting the duty ratio of flyback converter switch makes solar panels to the maximum power output. It has the advantages of simple structure, low cost and high efficiency. This control strategy can be applied to a system that has variety of energy supply. Introduction As the stage of solar panels on the conversion efficiency of light is relatively low, the output characteristics are nonlinear, and because of the change of the outside temperature, light and other factors on the impact to the output, the output voltage and power are instability. In order to make full use of the solar panels generate electricity, we must track its maximum power point to make the solar panels can output its maximum power [1]. In addition, because of the instable power outputted by solar panels, unable to load in a stable working condition in solar independent power supply systems, so other energy are needed to supply energy to load with solar panels together, such as batteries, electric, fuel cells. At this stage, the maximum power point tracking technology of solar panels have been relatively mature. Control algorithms commonly used are: constant voltage method (CVT), perturbation and observation method (PO Iph is photo-generated current; ID is dark current; IO is the reverse saturation current; ISC is the short circuit current of solar panels; UOC is the output voltage of the solar panel; q is the electron charge, 1.6×10 -19 C; A is the diode emission coefficient; K is the Boltzmann constant, 0.86×10 -4 eV/K;T is the cell temperature, the absolute temperature; Tref is the absolute zero temperature, -297°C; RS is the equivalent series resistance; Rsh is the equivalent parallel resistance; Ido is the reverse saturation current; Egis the Department of energy; S is illumination intensity; CT is the temperature coefficient [4]. Strategy of maximum power point tracking by controlling output current of solar panel Commonly used maximum power point tracking algorithm is by controlling the output voltage of solar panels to achieve the maximum power point tracking [5]. But in the system of solar and other energy combined power supply, control the output voltage of the solar panel is not conducive to design the double closed loop control system. The control strategy of maximum power point tracking by control the output current is proposed based on this. Following is analysis of its working principle. As can be seen from theEq.1, output current of solar panels IL is a function with the output voltage UOC as independent variable, i.e. IL=f (UOC). UL = N2 N1 D 1−D UOC (5) In Eq.5, D is the flyback converter switch duty ratio; UL is the voltage across the load;N1is the transformer primary winding; N2 is the transformer secondary winding [6]. Hypothesis devices in flyback converter are all ideal devices, no loss, so output power equal to input power. The output power of the solar panel, i.e. the input power of flyback converter is: Pin = UOCIPV = UL N1 N2 1−D D IPV (6) Suppose: Pflyback ∗ = N1 N2 1−D D IPV (7) So Pin = ULPflyback ∗ (8) Because the voltage across the load UL is stable, so the relationship of input power Pin and Pflyback ∗ is proportional. When Pflyback ∗ is maximum value, the Pin is maximum value too [7]. As can be seen from theEq.7 and Eq.8, when Pin and Pflyback ∗ are all maximum value, the switch duty ratio is the same, so we can control the duty ratio of switch to achieve maximum power point tracking [8]. Fig. 1 is a flow chart of the algorithm of maximum power point tracking of solar panel by controlling output current.