Research and development of conversion of direct current voltage to the quasi-sinusoidal voltage with pulse-width modulation

Resumo

Practically all widely used variable-frequency alternating-current electric drives with autonomous voltage inverters (AVIs) use pulse-width modulation (PWM) according to one of the following techniques: sinusoidal, space-vector, and relay. Fulfilling the relay PWM requires an analog–digital converter (ADC) with high resolution and sample rate. Vector PWM has a nonsinusoidal output voltage that causes additional losses in the motor. The main problem of a symmetrical (centered) sinusoidal PWM is underuse of a dc link. For a long time, the vector PWM method was taken to be most promising one due to the absence of this defect. In practice, this technique is applied in areas without a strong voltage criterion, for which reason it has limited use. Moreover, due to another significant problem, which is the “dead” time on the sector borders at the vector PWM, different modified methods for constructing the sinusoidal PWM have become widespread, especially in modern asynchronous motor control systems, with the development of digital microprocessor systems. To determine the quality of different types of PWMs, a complex model of an electric drive, incorporating an inverter control system that implements different algorithms of constructing the discrete PWM signals is developed. The model and the electric circuit are constructed in LabVIEW and NI Multisim, respectively. The obtained simulation data can be used to select the optimal method of controlling the AVI. The analysis that has been conducted allows one to select an optimal PFWM control strategy in terms of research results concerning electric power quality and mechanical properties.