Research On Dual-mode MPPT Control Of Solar Photovoltaic Power System

Solar PV is now widely used in various fields,including street lamps,satellites and photovoltaic power plants.With the development of smart grid,the power supply of transmission line on-line monitoring device becomes a key problem.With the development of smart grid,the power supply of transmission line on-line monitoring device becomes a key problem.Solar power is one of the primary ways of powering the system,since it can not be powered by conventional power supplies due to mounting problems and insulation problems.Usually we need to use the maximum power point tracking(MPPT)in order to improve the efficiency of photovoltaic cells.At the same time by the instability of the output of photovoltaic cells,we need to add lithium battery as a backup power supply,making the night or on a cloudy day can also keep on-line monitoring device uninterrupted power supply.The paper studies how to improve the efficiency of solar photovoltaic power generation and lithium-ion battery charging,and proposes a dual-mode MPPT control strategy.In this paper,the existing MPPT control algorithm is summarized and studied,and a new variable step size conductance incremental method is adopted to improve the dynamic response and steady-state accuracy.A dual-mode MPPT control strategy is proposed Aiming at the limitation of variable step-conductance increment method,we can not find a set of optimal maximum perturbation step size ?Dmax and scale factor N which can satisfy the MPPT tracking demand at the same time when the illumination intensity changes greatly.The maximum power point tracking method is adopted in different lighting conditions.The new incremental step size conductance algorithm is used in strong illumination and the perturbation and observation algorithm is used in weak illumination.Lithium-ion battery charging method directly affects its charging efficiency and service life,PI control is used to achieve CC/CV charging program.When the light intensity decreases,the photovoltaic cell can only shallow and inefficient lithium-ion battery trickle charge,extended lithium-ion battery charging time.A dual-mode lithium-ion battery charging strategy is proposed in order to improve the utilization of solar energy and the charging efficiency of lithium-ion battery.This paper presents a dual-mode lithium-ion battery charging scheme,the photovoltaic cells directly charge the lithium-ion battery in strong illumination;when in weak illumination the super-capacitor store energy and charge lithium-ion battery.A new circuit topology is adopted to solve the problem that MPPT can not be realized in the early stage of super capacitor charging.This paper selects low-power&high-performance micro-controller MSP430F5132 as the control core.The feasibility of the proposed scheme is verified by the experimental study on the design of the lithium battery charging device based on MSP430F5132.