Multilevel Installation Based on Voltage Source Inverters Controlled by Synchronous Multi-Zone PWM

Method of synchronous space-vector modulation, based on direct representation of pulse patterns of voltage source inverters as function of the fundamental and switching frequencies of inverters, has been applied for adjustment of both standard three-phase inverters and diode-clamped inverters of a modular converter consisting of three voltage source inverters and multi-winding transformer. Scheme of synchronous modulation is based in this case on concept of multi-zone control, which includes continuous determination of boundary frequencies between control sub-zones (on the axis of the fundamental frequency of installation), and on alternative control correlations for determination of the pulse patterns. Systems controlled by some basic versions of synchronous pulsewidth modulation (PWM) have been investigated. The analyzed control and modulation strategies have been verified by numerical simulations.