Study On Topology And Control Method Of New Double-Frequency Grid-connected Inverter

With the development of renewable energy generation technology,single-phase inverters have been widely used in renewable energy grid-connected system,and become an indispensable power conversion device.Research on new topology and control methods to improve grid-connected power quality and inverter efficiency has become the focus of research.Based on the related research of grid-connected inverters,this paper deeply analyses the topology and working principle of a new type of double-frequency grid-connected inverters,and designs relevant parameters and control strategies according to the characteristics of the topology.The main circuit of the new double-frequency grid-connected inverter consists of power unit and harmonic elimination unit.The two units are parallel to each side of the single-phase power grid and use independent buses.The power unit works in the inverting mode and the harmonic elimination unit works in the rectifying mode.In order to improve the efficiency of grid-connected inverters,the power unit works at low switching frequency,the harmonic elimination unit works at high switching frequency,and the grid-connected current is the sum of the power unit current and the harmonic elimination unit current.Through the control system with compensation as the core,the harmonic component in grid-connected current can be effectively suppressed by controlling the current of harmonic elimination unit and the high frequency harmonic in the current of power unit.On the basis of introducing the topology and working principle of dual-frequency inverters,the steady-state model of the grid-connected inverters is established,and the parameter tuning method of the inverters is given,including the DC side voltage of the two units,the AC side inductance and the AC side capacitance of the harmonic elimination unit.Aiming at the topological structure of dual-frequency grid-connected inverters,a double closed-loop control strategy is proposed,which realizes the tracking control and harmonic suppression of grid-connected current,and the parameters of the regulator are designed.The simulation model built by Matlab/Simulink is used to verify the feasibility of the topology structure and control method as well as the correctness of parameter design.Because of the high switching frequency of the harmonic elimination unit,dead-time compensation is needed in the harmonic elimination unit because of the influence of the dead-time on the waveform quality of the harmonic elimination unit.The experimental prototype of double-frequency grid-connected inverter is built and the output waveform of the experiment is analyzed.The experimental results and the final efficiency calculation prove that the double-frequency grid-connected inverters can not only output high-quality grid power,but also have high efficiency.