Research On Damping Control Methods For Current Source Grid-connected Converter

As an important part of photovoltaic power generation system,photovoltaic grid connected converters determine the power transmission efficiency and performance of the whole system.Compared with the voltage-source grid-connected converter,the current-source grid-connected converter does not need the front-end boost converter because of its step-up capability,which simplifies the structure of photovoltaic power system and improves conversion efficiency.A CL filter is used at the ac side of the current-source grid-connected converter,and the system is under-damped.The external disturbances easily cause the current oscillations and trigger the system stability.Therefore,this dissertation takes the single-phase current-source grid-connected converter as the research object,and conducts in-depth research and analysis on its damping control strategy.Firstly,the operation principle of the single phase current-source grid connected converter is analyzed and the mathematical model is established,which provides the theoretical foundation for the design and analysis of the grid connected control.The principles of sinusoidal pulse width modulation and one-dimensional space vector modulation are analyzed in detail and the passive damping and active damping control principle are studied,which compares and analyzes the limitations of these two traditional damping control methods and provides a theoretical basis for the research of new damping control methods.Then,in order to suppress the resonance caused by the CL filter,a new damping control scheme for current-source grid-connected converter is designed in this dissertation.The inherent damping characteristics of single-phase current-source grid-connected converters based on CL filters are analyzed,a thorough theoretical study is carried out on the relationship between the time delay and stability of single-loop controlled current source grid-connected converters with CL filters.Based on current source grid-connected converters,the ranges of time delay for system stability that suitable for any CL filter parameters is derived in the continuous s-domain and z-discrete domain respectively.When the current source grid-connected converter adopts the grid-side current single-loop control strategy,if the delay is in the stable range,it can reach a stable state,there is no need additional damping control strategy.With the inherent damping characteristics of the system,the system can operate stably.The MATLAB software is used to simulate and analyze the steady-state characteristics and dynamic response of the new damping control system.Finally,the main circuit of the single-phase current-source grid-connected converter is designed and built.Based on the TMS320F28335 DSP and Xilinx XC6SLX9-2TQG144 C FPGA control circuit,the single-phase current-source grid-connected converter modulation strategy,grid-connected steady state response,and the steady state characteristics of the new damping control and the dynamic response of current switching are experimentally studied.The experimental results verify the feasibility and effectiveness of the new damping control scheme.