Power-Model-Based Adaptive Overmodulation Scheme for Field-Weakening Control of PMSM

The field-weakening control can realize the operation above the base speed of a permanent magnet synchronous motor (PMSM), but the torque capacity is still limited by the power of the inverter. To further improve the torque capacity, an overmodulation technique is applied to fully utilize the dc bus voltage (
u
_dc
) of the inverter. However, the reference voltage of the field-weakening loop needs to be set to 2
u
_dc
/π in the conventional overmodulation algorithm, leading to serious current and torque harmonics. To address this problem, in this article, an adaptive overmodulation scheme is proposed to coordinate the reference voltage according to the required operation condition rather than the constant 2
u
_dc
/π. To determine the scale of reference voltage, a power model is established to monitor the working condition of the motor, including speed and torque. Then, a reasonable voltage compensation is added to the reference voltage of the field-weakening loop, which could adjust the overmodulation depth coordinating with the working condition automatically. Thus, the elimination of redundant reference voltage can be realized. The proposed scheme can realize the torque improvement in dynamic state and harmonic suppression in steady state, and its validity is verified through a 2.2 kW PMSM test bench.