Performance Analysis of a Novel Microprocessor-Based Controller for a Phase-Controlled Rectifier Connected to a Weak AC System

The performance analysis of a novel fast-response micro-processor-based firing and control scheme for a phase-controlled rectifier is presented. Controller performance and stability analysis are emphasized, particularly when the converter operates in a closed loop fed by a weak ac system. The firing angle control scheme, which relies on real-time projection of the firing delay angle, has been implemented and tested. In this implementation the controller responds within 20μ
_s
its to a change in the desired output voltage. The controller is synchronized to the line through a software phase-locked loop (PLL), which adapts to large variations in the line frequency. With this controller the bridge rectifier can operate properly, with a constant steady-state open-loop gain, even when a weak ac system with unregulated frequency feeds the converter. The operation and performance of the microprocessor-based converter with a current feedback loop are described. Two simple stability analyses, one based on system function simplification and the other based on exact system representation, are discussed and experimentally verified. The generation of subharmonics caused by the line inductance and the reference zero-crossing detection circuit is also studied. Experimental results are reported.