Active front-end converter input filter minimization using sequential sampling space vector modulation for multi-motor drives

Sequential sampling space vector modulation, and its equivalent the phase-shifted carrier PWM, have been used with good results in various multi-level converter structures. However, up to now they have been usually restrained to operation with a power-balanced set of converters in order to assure harmonic cancellation between the parallel or series connected converters. This paper expands the use of sequential sampling space vector modulation, and proposes its use with an unbalanced set of converters. Particularly, a 900 kVA paper machine comprising 9 induction motor drives is considered. The use of this technique among the active front-end converters of the machine effectively cancels out input current harmonics. In fact, results are such that a 0.02 pu reactor in each drive suffices to ensure 5% total input current THD. This is attained even under 100% load unbalance between motor drives. The feasibility of this method is demonstrated by showing that the current harmonics of the active front-end converters remain constant throughout the whole operating range, that is from zero to nominal power. An extensive evaluation using experimental and simulated results of the paper machine is presented for validation of the proposed method.