Implementation of synchronous frame harmonic control for high-performance AC power supplies

In order to achieve the reduction of voltage distortion in AC power supplies, this paper describes an implementation of synchronous frame control for selected frequencies in the output voltage. The regulation of the fundamental output voltage, as well as of some low-order harmonics, is achieved using a synchronous frame controller for each selected frequency in addition to a conventional control. The conventional part conserves good dynamic performance under load changes, while rotating frame controllers allow a slow, but very precise compensation of the residual errors within the assumption that the harmonics produced by distorting load are slowly-varying. Moreover, motivated by a fixed-point implementation, a set of refinements and modifications of the original scheme is proposed, allowing a reduction of signal processing requirements and a new control algorithm structure less sensitive to quantization and rounding errors. This solution is particularly effective for high-power fully-digital controlled AC power supplies, where the voltage loop bandwidth is usually not large enough to provide regulation at harmonic frequencies. The proposed control scheme has been implemented using a fired-point single-chip digital signal professor (ADMC401 by Analog Devices). Experimental results on a 3 kVA three-phase converter prototype show the effectiveness of the proposed approach.