Parallel operation control technique of voltage source inverters in UPS

The control technique of a parallel operation system of voltage source inverters with other inverters or with utility source has been applied in many fields, especially in uninterruptible power supply (UPS). The multi-module UPS can flexibly implement expansion of power system capacities. Furthermore, it can be used to build up a parallel redundant system in order to improve the reliability of whole power system operation. This paper analyses voltage and current status of a voltage source inverter in parallel, as well as the principle of parallel redundant system. Several control strategies according to the load-sharing problem in parallel control systems are also presented, from which the research of distributed-logic-control to realize parallel operation of four 3 kVA UPSs based on TMS320F240, a kind of real time digital signal processor (DSP), is discussed and proposed in detail.