Control of high-performance switched-mode rectifier system

A novel high-performance switched-mode rectifier system for high-power applications is introduced. The rectifier system comprises a three-level neutral-point-diode clamped (NPC) AC/DC rectifier, which is interfaced to the DC load through a DC/DC buck converter. The NPC converter provides a tightly regulated DC voltage at the input of the buck converter; the buck converter provides a rapid current control for the load. This novel arrangement has the following technical merits: (i) fast transient response, (ii) operation at unity power factor, (iii) low distortion AC-side currents, and (iv) capability to operate at high-voltage levels with commercially available power switches rated at lower voltage levels, (v) elimination of multi-winding transformers, and (vi) decoupling between the DC load and the supply system in terms of rapid transients of AC and DC sides. Dynamic models and control schemes for the proposed rectifier system are presented. The control schemes include the buck converter control, the NPC capacitor voltage balancer, the DCbus voltage control and the AC-side current control. Superior performance of the proposed rectifier system is validated through digital time-domain simulation studies in the PSCAD/EMTDC environment.