Parallel control of the UPS inverters with frequency-dependent droop scheme

This paper presents a control approach for paralleling the UPS inverters with no control interconnection. The reference voltage of the inverter is generated to simulate a reactor connected between the inverter and the load at the fundamental frequency. The intention is to control the real and reactive power sharing of the inverters with the Q-V and P-ω droop scheme without connection of a true transfer reactor. At the harmonic frequency the reference voltage turns to simulate a resistor, aiming that the load harmonic current can be shared equally and the voltage distortion is low. Two 1 kVA inverters are setup for demonstrating the effectiveness of the proposed approach