Staggered sampling space vector modulation for multi-motor AC-drive active front end converters

This paper proposes the use of staggered sampling SVM for multi-motor AC drive active front end converters (AFE). Particularly an 800 kVA drive comprising 22 adjustable speed drives (ASD) was considered. Under the proposed modulation scheme PWM-VSR operate with a sampling frequency of 1.2 kHz and a switching frequency of 850 Hz. Consequently reducing commutation losses by 85% compared to a multi-motor drive employing synchronized SVM. This is achieved while keeping the drive's input current THD beneath 5%. Further, the use of staggered sampling SVM in the AFE converters helped in reducing by 84% their input filters' size. All these features were accomplished by gathering AFE converters into six groups of staggered sampling, thus inducing harmonic current cancellation between them. Moreover, SVM in the AFE converters was complemented with a nonlinear control scheme, which provided them with a linearized and decoupled d-q axes dynamics. A reactive power control loop in this scheme enabled the multi-motor drive to operate as a VAr compensator. A compensating capacity of 250 kVAr was attained with the drive under study. Simulation results obtained under different operating conditions showed the feasibility of the proposed modulation scheme for multi-motor AC drive AFE converters.