Research On Control Problems Of Solar Photovoltaic Generation System

The problem of world energy crisis and environment pollution makes it necessary to exploit the renewable and green energy sources, in order to realize sustainable development. Solar photovoltaic (PV) generation technologies and industries have made great progress in recent year. Solar PV generation has become one of the most supplement energy, and has the potentiality to become one of the main energy.This thesis focuses on the control problems of solar PV generation system, which include modeling the PV array, maximum power point tracking (MPPT) control methods for PV arrays, the control strategies in DC/DC converters and PV gird-connected systems, islanding detection methods in PV gird-connected system, remote monitor and control for PV gird-connected systems. The main contents and results are as follows:1. The application characteristic of PV arrays is the base of research on solar PV generation system. This thesis presents four parameters engineering model of PV arrays on the base of common parameters provided by manufactures. The model can replicate the characteristic of PV arrays in any temperature and intensity. The model provides a basis for circuit simulation and system design.2. The MPPT control method is one of important means to improve system efficiency in solar PV generation system. This thesis proposes two MPPT control methods based on the analysis and introduction the constant voltage method, perturb-observe method and conductance increment method. One proposed MPPT method is the method combing constant voltage method with perturb-observe method, the other is the method combing constant voltage method with conductance increment method.3. DC/DC converters have wide application in solar PV generation system. The sliding Variable structure control strategies based on Z-A modulator are proposed for Buck and Boost converter. The exponential approach law is introduced to design sliding variable structure controller. The system has the constant switch frequency and the performance of the system can be adapted through adjusting the control parameters.4. The tracking control of grid-connected current is one of the key technologies in solar PV grid-connected generation system. The single-stage single phase grid-connected systems with L and LC filter are investigated based on sliding variable structure control. Aimed at the demand in Buck grid-connected inverter which the voltage of PV arrays is higher than the grid voltage, the Boost grid-connected inverter is investigated.5. Islanding effect must be prevented in the solar PV grid-connected system. The reason of islanding is analyzed and common islanding detection methods are introduced. The amplitude of grid-connected current should change with external environment in order to obtain maximum output power of PV arrays. The voltage of the common coupling point is equal to grid voltage when grid is connected because of the clamp effect of grid. The variation of the amplitude of grid-connected current results in the change of the voltage of the common coupling point when grid is off. Based on above, the variation of the amplitude of grid-connected current is proposed for the islanding detection.6. The software and hardware experiment set of PV grid-connected system is developed, in which the control kernel is composed of DSC and CPLD, and the power circuit is composed of IPM. Based on this, the PV grid-connected remote monitor and control system is developed based on ARM, in which remote monitor and control is realized based on Ethernet.7. Finally, this thesis makes some conclusions, and presents some issues for future research.