A Method for Compensation of Variable Commutation Delay in Current Source Inverters

The autosequentially commutated current-fed inverter (ASCI) is widely used due to its simplicity, ruggedness, and inherent regeneration capability. It can be readily equipped with a field-oriented controller. However, the variable recharge time during commutation causes a displacement in the position of the MMF as inferred from the commutation state of the output thyristors. Therefore an error in torque angle occurs for sudden changes in torque command. The details of this problem are described quantitatively. A compensation strategy is proposed, and a circuit implementation is shown. Experimental results are included to demonstrate the effectiveness of the technique. It is concluded that this phenomenon must be taken into account for optimum performance of the drive.