An integrated three-phase voltage regulated current source inverter topology

PWM current source inverters (CSI´s) are usually operated with a fixed pattern and fed from a thyristor rectifier controlled current source. Transient response of the output current is slow and input power factor is low. This paper proposes a symmetrical PWM CSI topology with a two loop control structure. A voltage regulated current source inverter ensures instantaneous output voltage control through on-line PWM current generation. The PWM rectifier maintains unity displacement power factor, thus improving the power factor. Furthermore, it maintains the DC link current to a value such that the inverter modulation index remains high at all times; this results in reduced voltage harmonic distortion at the output. The topology is particularly well suited for fast fluctuating loads. It also has regenerative capabilities, inherent short circuit protection and increased reliability. The paper describes the power circuit topology and the two control loop structure and presents controller design considerations and procedures. The complete topology is implemented on a 2 kVA unit and experimental results confirm theoretical and simulation results.