Discrete pulse modulation strategies for high-frequency inverter systems

High-performance, high-frequency inverter systems for UPS (uninterruptible power system) applications cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant DC link inverter, require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. A controller that utilizes a load current feedforward strategy with a cost function current regulator to achieve excellent transient performance characteristics is presented. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this work focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well