Hybrid six-step operation for matrix converter in flywheel energy storage system

This paper presents a hybrid six-step operation, which utilizes both a pulse width modulation (PWM) and a conventional six-step operation of a matrix converter in order to reduce switching losses during the standby time of flywheel. In the hybrid six-step operation, a virtual AC-DC-AC conversion is applied in order to separate the control of the matrix converter into a current source rectifier (CSR) control and a voltage source inverter (VSI) control. In particular, CSR is operated in PWM and VSI is operated in the six-step operation mode. Consequently, the switching loss of VSI is reduced as compared with the PWM operation due to the conventional six-step operation mode. In addition, the input current total harmonic distortion (THD) is improved as compared with the conventional six-step operation because the CSR modulation is PWM. In the experimental result, the input current THD of the hybrid six-step operation is improved by 76.0 % compared to the conventional six-step operation. Moreover, the efficiency of hybrid six-step operation was 1.0 % lower than the conventional six-step operation. In the hybrid the six-step operation, the input current THD is improved by 76.0 % in exchange for the drops of efficiency by 1.0 %.