Research On Group Control Technology Of Photovoltaic Pump System With Muti-machine Operation

Due to the limitation of "water threshold" in stand-alone photovoltaic pump system,a group control system with multi-machine parallel operation photovoltaic pump has been proposed.In this paper,the topology of the group control system,the characteristics and models of the group control system components,the stability of the photovoltaic array voltage and the optimal control strategy of the system have been studied.The main research work is as follows:(1)The topology of the photovoltaic pump group control system has been summarized and classified.The structure of the common DC bus type,field bus type and cascade type about photovoltaic pump group control system has been presented.The advantages and disadvantages of the three type structures are analyzed as well.In this paper,the field bus type pump group control structure is our research object.(2)The mathematical model and characteristics of the photovoltaic array,the static equivalent circuit and the dynamic model of the asynchronous motor,the basic performance and operation characteristics of the multi-pump parallel operation have been analyzed in detail,which provides support for research of the system stability and pump group control strategy.(3)The variable voltage and variable frequency(VVVF)and vector frequency control of the asynchronous motor have been introduced.The control parameters of the vector control are designed and the stability of the vector control have been verified with the theoretical analysis and the simulation.Two methods have been presented to solve the problem that the photovoltaic array voltage cannot be keeping stable in the traditional group ratio control system.A proportional control strategy based on array voltage compensation is proposed and the stability of the photovoltaic array voltage is solved by adding the array voltage compensation in the central controller.A master and slave control strategy for the pump group control system is proposed.,which the master pump is used to keep the stability of the array voltage.(4)The optimal control strategy of the photovoltaic pump system is studied.The paper proposes a disturbance observation method with constant voltage start to realize the maximum power point tracking of the PV array,analyzes the maximum power point offset problem of the group control system and gives three engineering solution.The theory shows that the total flow of the system is largest when the power of the pump is equalized.In order to realize the optimal dispatching of pumps in parallel,a pump switching scheme based on frequency determination is proposed.(5)The experimental platform of photovoltaic pump group control system with multi-machines is set up.This paper gives a detailed description of the function,software design and realization mode of the central controller.The principle of power distribution of the pump,the stability of the VVVF control and the vector control,the proportional group control strategy based on the voltage compensation are verified by experiments.