Large flywheel energy storage systems up to megawatt/sub-second range are needed to supply or absorb transient power for pulse loads. Due to its advantages, high power electrically excited synchronous motor is usually preferred in these systems. The Field Oriented Control and Direct Torque Control schemes are two kinds of effective methods used to achieve a stable DC-link voltage. This paper compares and analyzes these two schemes and a rotor field voltage control scheme is presented in Field Oriented Control scheme, to realize the motor unity-power factor running. Research results show the effectiveness of the presented rotor field voltage control scheme.