A Dual Mode Excitation Control of Synchronous Machine for Suppressing its Hunting

To suppress the hunting of synchronous machine caused by stepwise load change, a dual mode field excitation control was investigated for conventional (one-axis) machine and 2-axis machine. For one-axis machine, a dual mode is applied successively, the first one being a bang-bang suboptimal control mode decided by use of energy function instead of Pontryagin´s switching function, this mode is applicable to dynamic equation described in nonlinear form. The second one is a linear feedback control mode composed of a linear combination of state variables, and it will be adopted to the range near the steady state operating point where the equation will be linearized. For 2-axis machine at the instant of load change the original excitation introduced by mixing these two controls is efficiently applied. From the results of the investigation it is recognized that the employment of 2-axis synchronous machine is a potential means for the improvement of system stability.