Loss reduction for matrix converter with hybrid six step operation in flywheel energy storage system

This paper presents a hybrid six-step operation which utilizes both a pulse width modulation (PWM) operation and a six-step operation for a matrix converter. In the hybrid six-step operation, the control of the matrix converter is divided into a current source rectifier (CSR) control and a voltage source inverter (VSI) control. In particular, the CSR is implemented by the PWM operation and the VSI is controlled by the six-step operation. Consequently, the switching loss of the VSI with the six-step operation is reduced in compared with the PWM operation, because the switching of the VSI are only six times of the fundamental frequency. In addition, the input current total harmonic distortion (THD) is improved as compared with the six-step operation because the CSR is employed with the PWM operation. The experimental results, the converter loss of the hybrid six-step operation is reduced by 30.7% compared with the PWM operation in exchange for the increase of the input current THD by 3.71% compared with the PWM operation. Moreover, the efficiency of the charge and discharge with the hybrid six-step operation is improved by 1.80% compared with the PWM operation.