The Development Of Off-grid Photovoltaic Power System Controller

Solar energy is a kind of clean new energy, it has no pollution, no noise, it is inexhaustible and widely distributed. For the more and more serious problems of the supply of energy and environment, solar energy had been paid more and more attention by every country. During various applications of solar energy, PV power system has become a hot spot that every country is scrambling to develop. So off-grid PV power system and grid-connected PV power system have been developed rapidly,and off-grid power system has become the focus of national development because it can provide electricity in remote areas. Based on this, this paper will study on a 1KW off-grid PV power system control device. Aim at some of the key technical issues in off-grid power system-maximum power point tracking control of photovoltaic arrays, battery charge and discharge management and so on, this paper has carried out a detailed theoretical analysis, proposed the corresponding control algorithm, established a simulation model, and did experimental verification. This paper follows the main research:1 Based on the analysis of common off-grid PV power system, this paper has presented the technical indicators of 1KW off-grid PV power system, then selected and designed the main circuit structure and circuit parameters of system controller according to the indicators.2 Analyse operating principle and the features of photovoltaic cell and now commonly used method in maximum power point tracking control, aim at off-grid PV power system with Boost circuit, this paper proposed a simple and practical variable step method of maximum power point tracking-incremental conductance method with variable step length. System detects output voltage and output current of the PV array, compares conductance increment of photovoltaic array and instantaneous conductance, then changes the duty cycle with variable step length, achieves maximum power point tracking fast. Based on the simulation analysis, system responses fast and it can be used in the condition that atmospheric conditions change fast.3 Analyse operating principle and the features of battery and now commonly used method in battery charging and discharging, contact with battery working characteristics in off-grid PV power system, propose control method for battery charging and discharging: using two-stage charging method, constant current first and then constant voltage, in the early and late, will not damage charging circuit and battery for too large current; using discharging voltage control method, maintain the DC bus voltage and ensure the battery not discharge too much. And prove the effectiveness of the method by simulation.4 Based on the analysis and simulation in the above, design hardware and software of off-grid PV power system controller. Including the circuit for maximum power point tracking and the circuit for battery charge and discharge, and the software for algorithms, then do experimental study.The experimental results verify the feasibility of the design of off-grid PV power system, and lay foundation for industrialization of off-grid PV system controller.