Research On Related Control Technologies Of Single Phase Grid-tied Inverter

The world today faces the dual challenge of energy crisis and environmental pollution, in this situation, distributed generation system has been paid a lot of attention. Grid-tied inverter is an important component of distributed generation system, the current control of LCL type grid-tied inverter has become a hot topic in recent years.Among the existing current control methods of LCL grid-tied inverters, the split-capacitor method divides the capacitor into two parts, which degrades the system order through the feedback of the current between the two capacitor branches. However, the cancelled poles in the deflation progress are critical steady poles. This characteristic makes the whole close-loop system incompletely controllable because the signal component at resonant frequency is not included in the current feedback. Thus, the main work of this thesis is as follows.Firstly, this thesis introduces the modeling of LCL type grid-tied inverter and its control strategy, especially introduces the current feedback model based on the split-capacitor method, and points out its shortcomings.Secondly, introduces the principle and method of zero-placement strategy. By adding one or multiple state variable feedback, a pair of conjugate zeros in the place of conjugate poles of the system transfer function is generated. Therefore the system has no resonance peak after this cancellation.Thirdly, presents an active damping control strategy of split-capacitor method, which is an effective way to attenuate the resonant peak and to improve the waveform of output current. Meanwhile, to reduce the system cost and ensure high reliability of the inverters, the filter capacitor current estimate method is adopted so that there is no need to add additional sensors when applying active damping method.Finally, the simulation and experiment results indicate the correctness of the theoretical analysis and the proposed control method.