Three-phase PWM converter with LCL filter optimisation including system nonlinearities
Abstract
This doctoral dissertation proposes an original method for selecting and optimizing the basic parameters of the LCL filter of a three-phase PWM inverter. The developed method is in accordance with IEC and IEEE standards on permissible current distortion and takes into account the influence of nonlinearity, especially dead time, on the characteristics of the inverter. The analysis of the influence of nonlinearity was performed at the simulation level for the case of an unregulated three-phase PWM inverter with an LCL filter. The model verification was carried out based on the comparison of simulation and experimental results. Within the framework of the developed method for selecting and optimizing the basic parameters of the LCL filter, a new criterion function based on reducing the inverter losses was defined. The validity of the developed method was verified on the example of selecting the parameters of the LCL filter of a commercial indirect frequency converter. As part of the research conducted, measurements of the total losses of the filter chokes were performed, which also include the losses of higher harmonics. Based on the results of the aforementioned measurements, an improvement of the choke model was proposed that takes into account the losses of higher harmonics. Finally, measurements of total system losses were performed and a procedure was proposed to determine the optimal carrier signal frequency for the analyzed system.
