A dynamical modulation strategy of the virtual DC-Link voltage for matrix converters under input voltage unbalance

The matrix converter is a single stage ac-ac power conversion device without dc-link energy storage elements. Any disturbance in the input voltages will be immediately reflected to the output voltages. Line voltage source unbalances can result in unwanted input harmonic currents. In order to eliminate the harmonic contents of the input current, the paper proposes a new switching strategy for a matrix converter under unbalanced conditions. In this control strategy, the virtual dc-link voltage is modulated based on the positive and negative sequence components of the input voltages and the motor speed. By using this strategy, the output current ripples are obviously reduced and input current harmonics can be effectively eliminated. Thus power quality can be improved. The matrix converter is also used to drive a PMSM servo motor. A nonlinear adaptive backstepping controller is proposed to improve the position response of the drive system. By using this controller, the system can track a time varying speed and position commands. All the control loops, including the switching strategy, current-loop, and position-loop, are implemented by TMS320LF2407A digital signal processor. The hardware circuit is very simple. Several experimental results are shown to validate the theoretical analysis.