Research On Modulation And Control For Three-Phase Current Source Grid-connected Converter

PWM rectifier,as a “green” electric transition device,overcome the drawback of diode uncontrolled rectifier and thyristor phase controlled rectifier,like unidirectional power flow,poor power factor,high THD,etc.According to output characteristics,the PWM rectifier can be classified into voltage-source rectifiers(VSR)and current-source rectifiers(CSR).CSR has advantages in wide output voltage range,direct current control,inherent short-circuit protection and fast dynamic response,etc.CSR is widely employed in uninterruptible power system,motor drive,reactive power compensation in the power system,solar and wind renewable energy power generation,etc.This dissertation studied the CSR modulation technique and control strategies,including following aspects.Firstly,the operation principle of CSR is analyzed and the mathematical models in abc stationary coordinate,?? stationary coordinate and dq rotating coordinate are established,which provides a theoretical foundation for the control system analysis and design.The principles of SPWM and space vector PWM technique are analyzed and the relationship between the common mode voltage and switching state is studied.On the basis of the above analysis,a novel modulation to reduce the common mode voltage amplitude and the change rate is proposed,and the electromagnetic interference is reduced.Secondly,in order to avoid the current impulse,the soft start scheme of three-phase CSR is designed.Moreover,a double closed loop control strategy which contains inner current loop and outer voltage loop is designed for three-phase CSR in two-phase stationary coordinate.There is no need to introduce rotating coordinate transformation and decoupling.In order to effectively suppress the parallel resonance of the input LC filter,the passive damping control and the capacitor voltage feedback active damping control are designed.Meanwhile,the steady state and dynamic characteristics of the system are analyzed with MATLAB/ Simulink.In order to restrain load disturbance and improve the dynamic response speed of the system,the load current feedforward control is introduced.Finally,a three phase CSR prototype is developed.Based on TMS320F28335 DSP and Xilinx XC6SLX9-2TQG144 C FPGA digital control hardware,the modulation technique and closed-loop steady state and dynamic response under load disturbance and step changes of reference are tested.The experiment results verify the theoretical study of this thesis.