Modulation Signal Optimized Synchronous PWM

Suppression of low-order harmonics is important as recently large-radius machines are widely used and the generated acoustic noise is amplified through mode zero natural frequency in the audible range. Synchronous PWM is generally used to drive large machines, but cannot avoid low-order harmonics. On the other hand, optimized pulse patterns (OPPs) can eliminate arbitrary harmonics while minimizing distortion of phase current, but additionally require dedicated hardware for implementation. This paper first reveals a constraint on switching instants of synchronous PWM, and then proposes a novel modulation method based on synchronous PWM. The proposed method achieves the optimization like OPPs under the constraint, but does not require the dedicated hardware. In addition, control of the torque and stator current is simply implemented like synchronous PWM. The proposed method was verified by simulations and experiment. The results verified that the proposed method almost removes problematic harmonics caused by synchronous PWM while suppressing the current distortion and achieves almost the same transient response as synchronous PWM.