Inverter And A Half Cycle Symmetric Shepwm Method Research

With the development of power electronics technology, the inverter has been widely used in a variety of power electronic devices. Pulse Width Modulation (PWM) strategy is the key technology of converters. It is not only mating with the topology of converters, directly determining whether the goal of power transformation can be realized, but also playing an important role in output quality, reducing switching losses and improvement of system efficiency. It has been a very active and important research direction.Based on several common control methods, Selected Harmonic Elimination technique is studied in detail in this dissertation. Establishments of the SHEPWM nonlinear equations for inverters with quarter symmetry, half symmetry and asymmetry phase voltage waveforms are investigated in this paper. Two half wave symmetry SHEPWM schemes for two-level voltage inverters are introduced and the corresponding formulations of SHEPWM equations are described. Taking twenty switching angles in a half cycle as an example, the SHEPWM equations for both half wave symmetry schemes are established and solved. Many more solution sets than quarter-wave symmetry are obtained. What’s more, from the view of the waveform symmetry scheme, a new method which can obtain more numerical solutions is proposed. It is demonstrated by simulations and experiments, and the results verify the effectiveness and validity of the proposed SHEPWM methods.Because of the diversity and complexity of multilevel topology, a new half wave symmetry SHEPWM method to extend the second half cycle PWM waveform is proposed. The formulas of this method are simple and the PWM waveforms are more flexible, a large number of new solutions can be obtained under this new method. What’s more, the new symmetry scheme makes the solution sets of the half cycle symmetry SHEPWM schemes for multilevel voltage inverters to be completed, and can provide more possibilities for the optimizing selections in practice. Take a five-level inverter for example, with a case of twenty switching points in a half cycle, the SHEPWM equations of the new method are established and solved, the results of simulations and experiments prove the validity and practicability.