A State Space Analysis of LCI Fed Synchronous Motor Drives in the Steady State

The steady-state performance of a load-commutated in-verter (LCI) fed synchronous motor drive is computed by means of a digital computer-based state space solution of the synchronous machine equations. The computer solution permits accurate calculation of current, voltage, and torque waveforms under the assumptions of constant shaft speed and constant dc link current. Steady-state operating points are characterized by the firing angle, commutation overlap angle, and the ratio of average field current to dc link current. The two angles are specified as input to the program, and the ratio of field current to dc link current is calculated. In this way, a solution is guaranteed to exist for a given operating point. The symmetry of steady-state operation is exploited to calculate the appropriate boundary conditions for a given operating point directly, without the need to perform iterative calculations . Sample calculations for a 4500-hp LCI drive are presented, showing voltage, current, and torque waveforms, and steady-state performance characteristics with constant commutation margin angle. Consortium (WEMPEC) and in part by General Electric.