High-order-filter-based Grid-Tied Inverter Damper Stragety Research And Simulation

Renewable resources have been used more and more widely in recent years.Grid-connected inverters are often used to transfer the electricity generated by renewable energy to the power grid.Pulse width modulation(PWM)is a widely used modulation method for grid-connected inverters,while PWM will introduce high frequency switching harmonics into the power grid,which is not conducive to the current quality of the power grid.Grid-connected inverter filters are often used to connected the grid-connected inverters and power grids to remove the switching harmonics.Single-inductor filter was first used,its control is simple,but the volume is large,and the cost is high.Compared with the single-inductance filter,the high-order filter LCL-filter has a small volume.The LLCL filter introduces a series resonance circuit,which can further reduce the filter volume.However,LCL-and LLCL-filters will introduce resonance,which will lead to the power grid instability.The effective damping method is required to suppress resonance.The existing damping methods include passive damping and active damping.The passive damping methods suppress the resonance peak of high order filter by passive device.And its control method is simple.The active damping methods introduce the circuit state variables or the digital filter to damp the resonance peaks.The active damping method will not introduce additional losses,but its control method is difficult.In this paper,we first model the high order filter and analyze the effect of each component on the performance of the high order filter.Then the paper summarizes the existing damping scheme of high order filter,and analyzes the stability of the high-order-filter-based grid-connected inverter when the grid parameters vary in a wide range.In order to solve this problem,combined with the advantages of passive and active damping methods,this paper proposes a hybrid damping method which stabilizes the high-order-filter-based grid-connected inverter when the grid parameters vary in a wide range.A parallelled resistor-capacitor passive damping has been include in the hybrid damping method,then a digital filter is introduced to expand the effective range of damping method,to ensure the system stability in the case of a large scale power grid parameter variation.The main contents of this paper are as follows:(1)The paper modeled the high-order filter and analyze its characteristics.Then the paper summarized the existing high-order filter grid-connected inverter damping methods;(2)A hybrid damping methods for the high-order-filter-based grid-connected inverter is designed.A biquadratic filter combined with a paralleled resistor-capacitor damping method is added together into the high-order-filter-based grid-connected inverter.The detail design steps are given.In order to effectively suppress the low-order harmonics of the power grid,the proportional-resonant controller is used as the controller of the high-order-filter-based grid-connected inverter.The stability analysis of the designed system is given.(3)The current mainstream control methods for high-order-filter-based grid-connected inverter are introduced,which include linear control and nonlinear control methods.(4)PSIM is used to simulate the designed system.The feasibility and correctness of the design method was verified through simulation.The hybrid damping scheme designed in this paper introduced low losses and cost.The design method can be easily implemented and has strong practicability in industrial application.