Method for Discontinuous Current Mode Compensation of Line-Commutated Converters

The implementation of a new method to control line-commutated converters in discontinuous conduction mode is presented. The method is based on the modification of the thyristor's firing angle alpha using a linear approximation, yielding nearly the same dynamic performance as in continuous conduction mode. The firing angle is corrected by adding a supplementary angle Deltaalpha, calculated by estimating the average output current. The proposed technique significantly reduces computational burden, thus being suitable for online calculation. Both simulations and experimental results are presented on a 1-kW laboratory prototype.

I. Introduction

Line-Commutated rectifiers for large power conversion are preferably used in continuous conduction mode (CCM) due to their better dynamic response. Under such condition, the converter has a well-known small-signal behavior, which, along with its intrinsic robustness, makes it a natural choice for a specific range of applications, including large dc motor drives, HVdc power transmission, and high-power high-precision current sources, among others [1]–[5].