Abstract

Electrical power converter subsystems are placed between an ac-mains bus and a load in order to condition the power being transferred, to protect the load and the ac source, and to provide uninterruptible power supply (UPS) features. One method of providing the required interface in, low to medium power applications (1.0 to 150 kVA), is to connect multiple converter modules in parallel. This approach has the advantages of increased reliability, due to the redundancy of the system, and flexibility, since modules can be added or removed as needed. The successful performance of a parallel-connected system depends on (i) the modularity of the individual converter units, (ii) their response characteristics, and (iii) the quality of the power they produce. A single-phase converter module and a parallel connection circuit is proposed that meets these three objectives by using a fast control circuit for each converter, insulated-gate bipolar transistors (IGBTs), a high switching frequency (10 kHz to 20 kHz), and a frequency modulated (FM) communication scheme. Thus, the modularity is enhanced by using an FM signal in order to eliminate the wiring normally required to share the converter output current control parameters.