Space vector methods for AC drives to achieve high efficiency and superior waveform quality.

摘要

Induction motors are the prime movers in various industrial, commercial and military applications. Voltage source inverter (VSI) fed induction motors are popularly used in variable speed applications. The performance of the VSI in terms of quality of the waveform applied to the motor and conversion efficiency depends to a large extent on the type of pulse-width modulation (PWM) technique employed. The research reported here involves new 2-level and multi-level PWM methods for VSI fed drives that result in higher efficiency and improved quality of the motor current waveform.; Real-time PWM techniques for AC motor drives have mostly been based on either triangle-comparison approach or space vector approach. Recent research has shown that the space vector approach offers additional degrees of freedom in designing PWM techniques over the classical triangle-comparison methods. Specifically, in 2-level inverters with the space vector approach, several new sequences that involve division of active vector duration can lead to improved performance. This concept of active state division can also be extended to multi-level inverters and result in even more possible sequences.; In this study, the new sequences in both 2-level and multi-level inverters have been analyzed extensively for their effects on harmonic distortion in the motor current and on inverter switching losses. The concept of stator flux ripple is used to study the distortion characteristics of the new sequences. The effects of different sequences on the switching losses are compared based on a switching loss factor defined over a subcycle. Based on this analysis, new hybrid PWM techniques that result in simultaneous reduction in line current distortion as well as switching losses have been developed.; The analysis and performance of the proposed 2-level PWM techniques have been validated on an experimental prototype comprising of a 2 kW IGBT-based inverter fed induction motor drive and a digital signal processor (DSP) based controller platform. The new multi-level PWM techniques are verified in simulation using Simulink and proved experimentally by a 10 kW IGBT-based inverter fed induction motor drive with a DSP based controller platform.