Study On Parallel Control Strategy Of Multiple Inverters With Different Capacity

Green mountains and clear waters are golden mountains of gold and silver.At present,not only China but also the developed countries in the world give top priority to sustainable and green development.Fossil fuels are limited by the fact that their formation process is non-renewable,and the huge amount of carbon dioxide produced by burning them is the root cause of global warming.Therefore,how to save energy,reduce emissions and develop new energy will be the priority of the battle to protect the blue sky.Because of its environmental friendly characteristics,microgrid has been widely concerned and opened up a new path for the development and utilization of secondary energy.In this paper,the distributed power supply with energy storage device is assumed to be an inverter,and the parallel control strategy of multiple inverters with different capacity is studied.This paper discusses the control method of secondary frequency modulation and voltage regulation for islanded microgrid and the power distribution control method for parallel connection of multiple inverters with different capacity.The main research work of this paper is as followed:(1)The application background,research value and microgrid technology are reviewed in detail.Then,four main control strategies of inverter are analyzed.Furthermore,the research status of secondary frequency and voltage regulation control strategies and parallel operation methods of multiple inverters with different capacities are analyzed in detail.(2)The mathematical model of the three-phase inverter is established,and its topology is analyzed.The difference between the controllers in the ?? and dq coordinate systems is compared,as well as the influence of the controller parameter changes on the controller performance.(3)The shortcomings of the traditional droop control,as well as common secondary frequency and voltage control methods are explained in detail,and the system characteristics after adjustment using different adjustment methods are analyzed.On this basis,an improved droop control strategy with self-healing capability is proposed.This strategy increases the no-load angular frequency and no-load voltage appropriately,and adjusts the difference between the actual output power of the inverter and the expected power through the integration link to adjust the droop coefficient,so as to achieve self-healing of frequency and voltage.This method can well solve the problem of over-limit of frequency and voltage due to limited primary frequency modulation and voltage regulation capability.Secondly,the article establishes the system small-signal modeling and analyzes the influence of the controller parameters on the system stability through the root locus method,which provides a basis for the optimal design of the controller parameters.Finally,the proposed control strategy is verified by simulation.(4)The factors affecting power distribution when multiple inverters are operated in parallel are analyzed,and a multi-inverter power distribution control strategy based on improved droop control is proposed.The accurate distribution of active and reactive power among multiple inverters with different capacities while self-healing in frequency and voltage is realized by sharing the reference of power information,setting the integration coefficient according to the capacity ratio,and controlling the size of the droop coefficient of different inverters to be proportional at all times.Finally,the effectiveness and feasibility of the proposed control strategy are verified by simulation and experiment.