Synchronised bus-clamping PWM strategies based on space vector approach for modulation up to six-step mode

Synchronised PWM waveforms with 3-phase, half-wave and quarter-wave symmetries are required in VSI-fed, high-power AC drives. The flexibilities of the space vector approach to modulation can be utilised for real-time generation of more than one family of synchronised PWM waveforms, maintaining all the symmetries, with any odd pulse number. Two such synchronised PWM strategies are proposed in this paper along with an overmodulation scheme for operation up to six-step mode, maintaining the modulator gain constant in the whole range. The proposed overmodulation scheme does not require any evaluation of quadratic or cubic expressions, or any look-up table except for storing sine values. These two strategies result in a harmonic distortion better than those of comparable ones at higher modulation indices for low pulse numbers of 5 and 7 A combination of these two strategies, along with two other bus-clamping strategies and the conventional space vector strategy, leads to a significant reduction in the harmonic currents in constant V/f induction motor drives as shown by the theoretical as well as experimental results.