Characteristics of Rotor Magnetomotive Force and Asynchronous Behavior of Variable-speed Dual-excited Synchronous Condenser

When a dual-excited synchronous condenser (DESC) provides voltage support to the system, the current diversion effect of the damping winding suppresses excitation overcurrent and prevents unit disconnection. However, the demagnetizing effect of the damping winding also reduces the inertial power, weakening its inertia support capability. To balance the voltage support capability and inertia support capability of the DESC, this paper proposes a rotor structure with symmetrical field windings. The magnetomotive force (MMF) expressions of the field windings and damping windings under two-phase AC excitation are derived. The influence of rotor MMF harmonics on the stator electromotive force (EMF) waveform is studied. The mechanism of interharmonic component generation in the stator EMF is revealed. A method to eliminate interharmonic components through rotor pitch optimization is proposed. The impact of damping winding conductivity on voltage and inertia support capabilities is studied. Based on this, an optimization method for damping winding materials that balances transient voltage support and inertia support is identified, and the optimal damping winding conductivity is determined. The research findings can provide a foundation for optimizing the rotor structure of DESCs and enhancing their transient performance.