Research On The Control Of Isolated PV Inverter Parallel System

From ancient times to now,energy is an indispensable part of human survival.With the progress of society and the deterioration of living environment,the demand for clean new energy is increasing.Solar energy is one of the typical representatives of new energy Distributed photovoltaic power generation is a key research direction in today’s power network planning because of its advantages such as less energy loss,low investment and construction costs,and flexible power generation.The unique requirements of a small distributed photovoltaic power generation system include low cost,high efficiency,and tolerance to a very wide range of input voltage variations.In this paper,the stability and circulation suppression of single-phase isolated photovoltaic inverter in parallel operation are studied.First of all,through the analysis of the following requirements,including:(1)wide range voltage input;(2)need to have electrical isolation function;(3)a single photovoltaic inverter with high efficiency;(4)to ensure a single stable work and multiple parallel parallel.Thus,the front stage DC/DC circuit is the full bridge LLC resonant converter,the post stage inverter The topology of the circuit is LC filtered single-phase full bridge inverter.Secondly,in order to satisfy the requirements of stable operation of single station and multiple stable parallel operation,the topology of the proposed topology is simulated and the theoretical mathematical model is analyzed.The open loop Bode diagram of the DC/DC converter topology under the conditions of different load and different input voltage is analyzed,and a compensaton network with single pole point and two zero points with dynamic coefficients is designed to ensure the dynamic response speed of the output voltage,so as to ensure the voltage quality of the output voltage of the post stage inverter.Furthermore,by analyzing the influence of each parameter on the voltage amplitude in the closed-loop control mathematical model of a post stage inverter.The dual closed loop control system with voltage feed-forward channel voltage and current control is adopted to reduce the requirements of the double closed loop control system.The low frequency circulation caused by the impedance difference of the inverter parallel lines is suppressed through the virtual impedance load current feedforward control,and the parallel current control strategy is implemented by CAN communication synchronization to reduce the circulation of the parallel system.Finally,the experimental prototype is built on the basis of the mathematical model analysis and the correctness of the simulation verification model,and a suitable software and hardware protection circuit is designed to protect the circuit quickly under the condition of short circuit or overload,and the compensator and the circulation suppression strategy are digitized by DSP28335 Control.The experimental results show that the proposed compensator can speed up the dynamic response speed of the PV inverter.The proposed circulation suppression strategy can suppress the circulation caused by the line impedance difference.