A Novel Current Control Strategy Based on Harmonic Voltage Injection for Power Losses Reduction of PMSMs with Non-Sinusoidal Back-EMF

In terms of permanent magnet synchronous machine (PMSM) design, high power density and a low manufacturing cost can be achieved by sacrificing sinusoidal back-EMF. Those machines suffer from higher torque ripple due to the flux harmonics. Additionally, the non-sinusoidal backEMF introduces current harmonics in the case where the conventional d-q axis current controller is adopted. This introduces additional copper losses in machine stator windings and conduction losses in inverter switches. A novel current control strategy based on harmonic voltage injection is presented for PMSMs with non-sinusoidal back-EMF to reduce the copper losses due to harmonic current components in a high speed region. Based on the harmonic back-EMF information of the machine, the harmonic voltages are injected to cancel out the harmonic components in the back-EMF waveforms so that machine current can be controlled with lower THD and copper losses. This method can be easily applied to the conventional PI current controller without non-sinusoidal coordinate transformation.