A wireless load sharing controller to improve dynamic performance of parallel-connected UPS inverters

In this paper, a new control scheme for parallel-connected inverters without communication wires is presented. This wireless control technique is based on the well-known droop method, which consists of introducing P-ω and Q-V schemes into the inverters, in order to share properly the power drawn to the loads. In the literature, the droop method has been widely discussed in applications of load sharing between different parallel-connected UPS inverters. However, there are little reports about its transient performance. Some previous works present a small signal stability analysis for parallel-connected inverter system. Nevertheless, by using the conventional droop approach, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, proper transient performance can be achieved. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance in front of conventional one.