Apparatus and methods for space-vector domain control in uninterruptible power supplies

Abstract

Uninterruptible power supplies (UPSs), power conversion apparatus and power conversion methods are provided which may improve phase regulation of polyphase AC voltages in the presence of load imbalances. According to one embodiment, a UPS includes a DC voltage generating circuit that produces a DC voltage. A space vector domain controlled inverter couples the DC voltage generating circuit to an AC load, and produces a polyphase AC output voltage at the load by sensing a plurality of voltages at the load, transforming the plurality of sensed voltages according to a space vector (d-q) transformation to produce an output space vector, generating an error space vector from the output space vector and a reference space vector, and selectively coupling the DC voltage generating circuit to the load responsive to the error space vector. In this manner, a voltage control loop is closed in the d-q domain, which may improve per-phase regulation of the polyphase AC output. Preferably, compensation is applied to the error space vector to produce a control space vector that compensates for poles or other transfer characteristics of the forward path of the voltage control loop. In another embodiment, the reference space vector is generated by an outer voltage amplitude loop that compares a sum of the plurality of output voltages at the load to a reference voltage amplitude, generating an error amplitude voltage which is compensated and then transformed according to a space vector transformation to produce the reference space vector that serves as the set point for the inner space vector domain control loop.