Hysteresis Control of Parallel-Connected Hybrid Inverters

The future naval combatant ships will feature a fully integrated power system. These systems will allow unprecedented control of shipboard power to propel the ship, sense the battlespace, and engage the enemy. One crucial enabling technology is robust power conversion modules like the hybrid dc to ac inverter. This paper is a further exploration of the hybrid inverter scheme consisting of a six-step voltage-source inverter and a hysteresis-controlled current-regulated inverter. In this implementation, the six-step controller was designed to be independent of the hysteresis controller. The hysteresis controller is fed a reference signal extracted from the total output current going to the load. The signal is filtered and modified by a closed-loop system such that the total output current approaches a perfect sine wave; the quality of which is limited only by the bandwidth of the hysteresis converter. The modified closed-loop controller was compared to previous efforts and found to improve current total harmonic distortion from 3.2% to 1.8%. This paper proves that existing power electronic technology can be used to produce high-fidelity waveforms for high-power Naval propulsion drives which have a power range of 50 MW to 100 MW.