Research On Efficiency Optimization By Changing Bus Voltage In Hybrid Photovoltaic-Grid Power System

With the rapid development of economic and social, the electric power demand keeps increasing in recent years. A series of problems such as non-renewable resources exhaustion and environment pollution appear during the process of electricity generation. The new energy power generation technology can be applied as an effective method to solve the ecological and energy crisis. Photovoltaic generation has been attracting more and more attentions for its cleanness and renewability. However, solar energy is intermittent with different environment. Therefore, the power system needs a backup power source to guarantee the stability of the load power supply. To improve the stability and flexibility of solar power system, a hybrid photovoltaic-grid power system is proposed in this thesis. Furthermore, this paper carried on research on power system efficiency optimization, and proposed a efficiency optimization method.The hybrid photovoltaic-grid power system composed of a solar cell, grid, DC bus, solar cell interface converter(Boost converter+ full-bridge LLC resonant converter), grid interface converter(single-phase PWM rectifier), load interface converter(half-bridge LLC resonant converter). According to the maximum output power of photovoltaic panels and load power, the system has four different operation modes. An energy management control strategy is proposed to ensure the system steady operation in this thesis.In order to optimize the efficiency of the hybrid photovoltaic-grid power system, detailed loss analys is was applied on each converter. Each device's loss under different power and dc bus voltage was calculated by Mathcad software in the power system. And the curve of the system efficiency changed with dc bus voltage can be obtained. The analysis results show that with the change of the dc bus voltage, the system efficiency curve appears monotone increasing?monotone decreasing?single peak and multi-peak four conditions. Therefore, through real-time adjustment of the dc bus voltage under different power condition, the power system keeps working at optimal efficiency dc bus voltage. This method has achieved efficiency optimization of the hybrid photovoltaic-grid power system. Particle swarm algorithm is proposed to search optimal efficiency dc bus voltage online. For online optimization algorithm lead ing to the dc bus voltage fluctuating phenomenon, an offline system efficiency optimization method has been proposed. This method change dc bus voltage to optimal efficiency point according to the efficiency curve stored in the processor by detecting the system converter power.In order to verify the structure of the system?energy management control and efficiency optimization method,a 1000 W hybrid photovoltaic-grid power system is designed in this thesis. The system main circuit parameters are designed firstly. A simulation platform is built in MATLAB software to verify the energy management control. In addition, a set of hybrid photovoltaic-grid power system was built in the laboratory. The experimental results show that the system structure and the proposed efficiency optimization method are stable and effective.