Three-level inverters with common-mode voltage cancellation based on synchronous pulsewidth modulation

A novel method of direct synchronous pulsewidth modulation (PWM) is disseminated to three-level voltage source inverters with control algorithms with elimination of the common-mode voltages in three-phase drive systems with PWM. It provides smooth pulses-ratio changing and a quarter-wave symmetry of the voltage waveforms during the whole control range including overmodulation. Continuous, discontinuous and "direct-direct" schemes of synchronous PWM with both algebraic and trigonometric control functions have been analysed and compared. Simulations give the behaviour of the proposed methods and show some advantages of synchronous PWM in comparison with asynchronous at low ratios between the switching frequency and fundamental frequency.