Controlling excitation of synchronous motors to provide constant reactive power for varying load

Synchronous motors provide mechanical work and in contrast to all other major motor types can also provide capacitive reactive power to the system. In some cases synchronous motors are installed in power stations and substations just to improve the power factor. The amount and kind of reactive power delivered by the motor is being determined by the excitation current in the rotor. However regulating a desired constant reactive power for a synchronous motor operating in an industrial plant by simply adjusting the appropriate excitation will not work as changing mechanical load influences directly the phase of the motor's terminal impedance. The following paper hence examines the possibility to control the excitation with respect to changing mechanical load through feedback of the motors terminal phase between current and voltage via digital processing and power electronics with the prospect of providing constant reactive power.