1. As you know, the HFI algorithm is only applied to control salient pole PMSMs, such as IPM motor has a high saliency ratio. And the HFI is only used during startup and low speed. In most IPMs, the saliency ratio will be reduced when the torque current increases, so you should inject a higher current if the load is very heavy. 2. You may try to increase the injection voltage and tune the coefficient of HPF. Please make sure that the dc bus voltage is enough to provide the injection voltage and torque current during the motor is running with a heavy load.
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