Research Of Single-phase Grid-connected Photovoltaic Inverter

As the problem of energy exhausting and environment problem become increasingly serious development and utilization of new energy has became more and more important.The solar energy is accepted commonly because of its anvantages such as clean and economy.The inverter is one of the most important devices in photovoltaic(pv) grid-connected system,which directly affect the performance efficiency of solar power.This paper focous on the grid-connected single-phase photovoltaic inverter,and analyze the main circuit structure, the control method of SPWM in the process of grid-connected phase control technology.First, the current utilization situation and broad prospects are narrated, and the research content of the topic is given. The main circuit structure and working principle of current applied inverter are analyzed in detail, and the structure and function of parts are introduced.After introduce the control goals of grid-connected inverter, this paper summarizes the grid-connected operation conditions, and expounds the control methods of several inverter circuits. SPWM is the control technology based on the output voltage and current, with the advantages of stability switch frequency, convenient realized and clear physical meanings. The inverter is able to guarantee the output waveform both in independent and grid-connected mode are good, and the speed of dynamic response can meet the requirements.Secondly, this paper discussed the system software to realize the tracking of grid frequency and phase, and some parts of software like PWM interrupts that is the core part of the system are narrated in details. The software includes the A/D sampling function of dsPIC33 control chip; in view of the problem of phase lagging exists between grid voltage synchronous sampling and grid voltage, the reasons of lagging is analyzed, using the Angle fixed method to solve the problem. The paper list the flow chart of the program, and the experimental results show that the method is effective and reliable, which can make synchronization of phase and frequency of inverter output current and grid voltage, so as to achieve the purpose of power factor control.Finally, we use MICROCHIP company dsPIC33FJ128M706A as main control chip, and make a 5 kW experiment prototype. The running experimental results of independent and grid-connnected mode are given. The results show that the control strategy and the hardware circuit design meet the design requirements, and system operate stable and reliable.