Alternating current (ac) machines (e.g., IPM machines) are extensively used in loaders, combines or other heavy equipment machinery vehicle electric drive because they provide a higher efficiency than direct current (dc) machines. Of the ac machines, an Interior Permanent Magnet (IPM) machine has high drive efficiency and a wider constant power operating range. An IPM machine controller also called an inverter, controls operation of the IPM machine. The controller produces ac control signals which are applied to the terminals of the IPM machine.
In an IPM machine, extra high machine terminal voltage could detrimentally cause current regulation collapse, introduce additional harmonics in the inverter voltage output, cause degraded current regulation quality and associated side effects such as torque ripple, rotor magnet and stator winding heating, acoustic noise, etc. The extra high machine terminal voltage may depend on d/q-axis voltage commands, manufacturing and raw material tolerance such as permanent magnet, stator/rotor steel saturation characteristics can cause variance in the machine terminal voltage, accuracy of a position offset calibration, ambient and cooling temperatures, accuracy of the inverter onboard a current transducer (CT), etc.
Typically the controller controls the IPM machine based on a plurality of information. For example, an accurate estimation of the actual inverter or terminal voltage of the IPM machine, together with position information of the machine, may provide a better estimation of a torque output of the IPM machine, which in turn may complete the torque control loop.