Alternative for control of SPM/IPM-based drives

In high performance applications we've used Closed Loop Vector with Resolver Feedback with great success in special applications at Ultra High speeds in excess of 20K RPM for SPM. In our variable torque applications using IPM we utilize Sensorless FOC with a special algorithm that provides motor efficiencies unachievable before the modifications that are required by our customers. The control of heat in these applications is critical, as well as the consistent production of torque when required. We have an IPM 10K lb•ft motor running at 275 rpm for Cooling Tower applications in a surprisingly small foot print used to directly replace the gearbox and shaft, that can handle a 32' diameter Fan. This technology will assist us in gaining efficiencies and capabilities never before achievable.

For a pure SPM (Surface ...) the FOC_OL has well known limitation at low, zero speed with an "important" external load. The estimation of Back-EMF in this range is poor. More opportunities are possible with IPM (Interior ...) due to electromechanical anisotropy in the same speed range. I suggest for this kind of motor a mix between the back-EMF estimation at mid/high speed and injection technology at low, zero speed.

DTC should be an alternative, some examples are on the market, with quite good performances (torque ripples, ~THDs).