Starting of convertor-fed synchronous machine drives

The naturally commutated, convertor-fed synchronous machine is being used for drives of very high rating. At standstill and at very low speed, commutation is achieved by pulsing the current in the DC link between the supply and the machine convertors, and this gives rise to significant low-frequency disturbances to the supply system. The paper describes an alternative method, using a discontinuous current mode of operation, which gives smoother operation and less disturbance to the system. An analysis is given which shows that the method can give an average torque as high as 1.0 per unit, and permits the rapid assessment of the potential of the method for a particular application.