A modular, redundant inverter system built up with several microprocessor controlled PWM inverters working in parallel

Parallelling several inverters is not easy. Unlike rectifiers, inverters do not have an output voltage that is constant in time: not only output frequencies, but also output phases must be perfectly synchronized. Therefore each inverter must regulate its own output voltage very precisely to avoid imbalances in output currents. The feedback mechanism must react extremely quickly to assure a balanced output even with peak currents when nonlinear loads are applied. This paper describes a pulse width modulated inverter system built up with inverters that use a microprocessor governed feedback loop with a very fast settling time. Parallelling the outputs with active load sharing is guided by using a digital controlled bus. Using such a bus makes the system not only modular, but also very redundant: defect inverters are immediately switched off and isolated. Powerful possibilities, such as remote control, storing logging information and remote alarm surveillance of the inverter system, are feasible in a simple way