Fast algorithms of modulation of inverter output voltage for induction motor drive

The paper describes a simplified method of direct digital pulsewidth modulation (PWM) of line-to-line output voltage of a 3-phase voltage source inverter for adjustable speed drive application. Control strategy is based on one-stage quasi-sliding scheme of modulation with approximation of voltage space vector locus by the polygon with twelve sides. This scheme provides synchronous and symmetrical variation of voltage waveform during the whole control range. Parameters of output voltage of the inverter are described by simple algebraic equations as a function of operating frequency of the drive system. The control process is characterized by large computational efficiency. This technique of PWM reduces the complexity of control software and computation time. Simple modification of the modulation algorithm also provides high quality linear control in the zone of overmodulation. The results of simulation of a drive system fed from an inverter with the proposed PWM proved high performance of the system at upper values of modulation index