Voltage Amplitude Regulation Method For Paralleling 400 Hz GPU Inverters Without Intercommunication Signals

In order to increase the available power, or for redundancy purposes, it is often required to connect two or more inverters in parallel. For increased reliability it is also desired to achieve paralleling without intercommunication signals, using frequency and amplitude drooping methods. Problems arise when high performance inverters with very low output impedance are connected in parallel through a low impedance cable, because the classic drooping method is only valid assuming large inductive impedance between the paralleled inverters. Additionally, a large drooping amplitude coefficient needs to be used in such cases, resulting in large amplitude deviation (>5%). This is a serious drawback of this method since for critical aircraft applications the typical requirement is for a maximum of 1% amplitude deviation. This paper proposes a method that allows two or more paralleled inverters to employ the principle of power sharing via drooping coefficients while still maintaining good amplitude regulation (<1%) by using a variable reference that is changed in a closed loop, based on the active power, reactive power, and the measured output voltage of the inverter.