Research On Three-phase Grid-connected PWM Converter With LCL-filter For Renewable Energy Generation

This thesis mainly discusses the three-phase grid-connected converter with LCL-filter used in renewable energy generation. The determination principle and step of every element are researched in the three ways of harmonic frequency, total inductance and harmonic suppress capability of different frequency band. According to the filtering principle of the LCL-filter, the method of converter inductance design is given, and the LCL parameters especially how to choose the converter inductance is meticulous analyzed.According to its dynamic model under the synchronization reference frame, this thesis designs voltage and current two closed loop control system of the grid-connected converter with grid voltage of d axis orientate to the synchronization reference frame. The C MEX S-function is adapted to build the SVPWM simulation model which can coordinate with DSP practical program. The Matlab/Simulink module is used to emulate the LCL-filter designed and the control strategy of three-phase voltage PWM grid-connected converter. The waveforms are analyzed to check the correctness of the LCL-filter parameter design method and control strategy.The influences of feedback current and grid system impedance to stability are analyzed according to the closed loop zero-pole distribution under Z domain. It is also checked by simulation. This thesis also analyzes the influence of damping resistance to the system stability in the three ways of filtering effect, system stability and power loss. On this basis, this thesis introduces the choose principle. To resolve the power loss of damping resistance, This thesis designs and simulates the active damping, the simulation and experiments results indicate that it can reach the same effect with the damping resistance, but it avoid the problem of power loss.At last, this thesis accomplishes the hardware design and manufacture of grid-connected converter with LCL-filter. This thesis also compiles and debugs the control software, the converter experiments and analyzes the experiment data. The experiment result indicates the correctness of the LCL-filter parameter, control strategy and the design of the active damping this thesis designed.