Research On Control Strategy Of Dual Mode Inverter

With the rapid development of global economy and the increasing of population, energy crisis and environmental pollution have become increasingly prominent.The development and utilization of new energy has aroused widely attention. The solar energy,with its inherent advantages, such as environmentally friendly, sustainable renewable,and widely distributed, is spreading rapidly in distributed generation of the world.The inverter, as the most important part of the photovoltaic power generation system,can be classified by off-grid inverter, grid-connected inverter and dual mode inverter. Grid-connected inverter only works under normal grid; Off-grid inverter is restricted by the energy storage devices and load, the energy utilization ratio is low; And dual mode inverter incorporates the merits and demerits of the grid-connected inverter and off-grid inverter, it modulates the working mode according to environmental status automatically, enhancing the stability of the power supply and optimizing the energy utilization. Therefore, the study of dual mode inverter has theoretical and practical value.In this paper, taking the dual mode inverter for study.Firstly,analysis of the working principle of ZVS phase-shifted full-bridge topology, and realizing the voltage closed-loop control of DC-DC charger based on UC3875. Analysis of the the working principle and and mathematical model of push-pull dc convertor, Interleaved Boost converter and the bidirection full-bridge PWM converter. In regard to the two different modes of grid-connected and off-grid, proposed a switchable dual mode MPPT control method; In regard to the operating features of SPWM full-bridge inverter and PWM full-bridge rectifier, a double closed-loop control strategy of voltage and current is proposed based on the algorithm of prediction algorithm and deadbeat algorithm. Describing the work patterns of the dual mode inverter, and the energy flow between each pattern,and the switching condition between patterns in details. Proposing a control strategy of power management based on hierarchical dc-bus voltage. Detailed expounded the reasons of load voltage switching instant mutation, and proposes a uninterrupted switching method between off-grid mode and grid-connected mode. Finally, an experiment platform based on a 3KW dual mode inverter prototype has been established to test the basic function and the output performance of the dual mode inverter.The experiment shows that the design of dual mode photovoltaic inverter is feasible, and the control strategy is verified working well.