Comparison Between Pole-Phase Modulation (PPM) Technique and Modulated Rotational Harmonic (MRH) Excitation in Nine-Phase Brushless Wound-Field Synchronous Machine

The brushless wound-field synchronous machine (BWFSM) offers a maintenance-free and cost-effective solution for various applications, eliminating the need for permanent magnets or an external exciter. This paper compares two BWFSM excitation techniques, pole-phase modulation (PPM) and modulated rotational harmonic (MRH), which utilize a multiphase stator winding to generate a main rotating magnetic flux (MRMF) for torque production and an additional rotating magnetic flux (ARMF) to power the rotor’s field winding via a rectifier. Each method employs unique pole arrangements and harmonic current injections to induce current in the auxiliary winding. To ensure a fair comparison, the stator design and rotor copper usage are kept identical for both methods. The brushless excitation is tuned to achieve the same torque output for the same total RMS stator current. Both methods produce 7% more torque than a benchmark induction motor, but PPM requires a lower harmonic-to-main current ratio, with differing excitation frequencies due to fundamental differences.