Parallel Operation of AC and DC Power Transmission

A preliminary account has already been given of the EHV composite ac-dc study initiated last year at the University of Wisconsin [1]. This paper presents additional results obtained in the study of parallel EHV ac-dc power transmission in a basic 2-machine equivalent system. The consequences of 3-phase faults on inverter commutation are evaluated, and circumstances leading to inverter commutation failure (shoot-through) are made clear for various conditions of initial loadings and faulting. The consequences of inverter shoot-through onsystem stability are also evaluated for the 2-machine case. The characteristics of the control arrangement for a dc line are expected to be of special significance in determining the final overall performance of composite ac-dc systems.