Distortion Analysis and Duty Ratio Correction Algorithm for Asymmetric Modulation of Two-Stage Matrix Converter

When applying the two-stage matrix converter (TSMC) to the aero variable-speed constant-frequency generation system, the high input frequency varying between 360 and 800 Hz becomes a great challenge to its control. One of the most commonly used modulation methods for TSMC is the dual space vector modulation (DSVM). Simulation and experiments show that despite its advantages such as simplicity and low switching loss, the asymmetric DSVM causes distortion both in the output voltages and input currents of the TSMC. In this paper, the conception of “pulse orthocenter” (PO) is introduced via a BUCK model, and the influence of PO's fluctuation upon the actual output is revealed. Based on the PO theory, the spectra of TSMC's output voltages and input currents are then analyzed, indicating that asymmetric modulation causes $3n\omega_{\rm in}\pm(3m\pm 1)\omega_{o}$ harmonics in the output voltages and $(3n\pm 1)\omega_{\rm in}$ harmonics in the input currents. In order to suppress these harmonics, a duty ratio correction (DRC) algorithm is proposed to improve the waveform quality without increasing switching loss. The DRC formula is provided and the available range of related parameters discussed. The correctness of distortion analysis is testified via simulation, and the validity and feasibility of the DRC algorithm is verified via experiments.