Transistor inverter design, using closed-loop, pulse-width modulation control techniques, is considered. The technique of slitwidth modulation is adopted, to develop a sinusoidal voltage-source inverter. Inverter design requires a trade-off between high efficency power conversion, and low output distortion. The lowest switching frequency that provides acceptable harmonic distortion is the optimum. Developments in monolithic Darlington power transistor technology have enabled utilisation of low power base drive circuits. A 240 volt, 50Hz voltage-source inverter, operating from a nominal 96 volt d.c. supply, with worst-case efficiency of 75%, is demonstrated. Control loop phase-lead compensation reduces sensitivity to load variation. The inverter operates with full-load power factors between 0.4 leading and lagging. No harmonic voltage component exceeds 1% of the fundamental. The versatility of controlling inverter based equipment with a microcomputer, is addressed. This enhances the reconfiguration capability of the equipment, achieving maximum system utilisation. The implementation of a sinusoidally - modulated current limit regime, enables the vo1tage-source inverter to operate in a controlled-current mode. It allows a shunt connection of inverter and load to the primary a.c. power supply. The configuration forms the basis of incorporating the slitwidth inverter, with microcomputer supervisory control and health monitoring, into a multi-function power conditioning system. The regenerative nature of the slitwidth inverter, in the contro11ed-current mode, allows bi-directional power flow between inverter and a.c. supply. Power can be "exported" from d.c. source batteries to the load, or "imported" from the a.c. supply to charge the batteries. The power conditioning system is able to perform Static VAr Compensation of the mains-fed load, or to act as a UPS, providing continuous a.c. to the load.
|Date of Award||1985|