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The paper presents a theoretical analysis of the correlation between carrier-based unipolar PWM (CPWM) and space-vector PWM (SVPWM) for the entire modulation-index range of multilevel invertors, including overmodulation. By presenting corresponding parameters of vector redundancies in a zero-sequence function, the carrier-based PWM has matched the SVPWM technique. Carrier-SVPWM and discontinuous-PWM methods capable of obtaining any approximate optimum offset are proposed. Among them, the minimum-common-mode PWM methods can attain a proper balancing of switching loss. A unified unipolar carrier PWM modulator is presented. Different PWM modes and the offset value can be controlled in an offset generator. Without a look-up table, linear overmodulation can be implemented simply in an active signal generator. The correlations and proposed PWM methods have been analysed mathematically and demonstrated by simulations.