A low-cost controller for mitigation of torque harmonics in mass-produced permanent magnet synchronous machines
Harmonics in the electromagnetic torque produced by permanent magnet synchronous machines (PMSM) create acoustic noise and vibration that is undesirable in numerous applications (home appliances, vehicles, manufacturing equipment, etc.). Historically, techniques for mitigating torque harmonics have focused upon the design of the magnetic system or control of the stator excitation. In most mass-produced drives, approaches to adjust the design of the magnetic system (slot/magnet geometry) are preferred. This is in large part due to the cost of additional hardware required to implement control methods and a lack of robustness in the controllers.^ In this research, a focus has been to address the shortcomings of stator excitation-based control of torque harmonics. To reduce cost, a Hall-effect-based position observer has been derived that is shown to have sufficient accuracy to control harmonics of torque and eliminates the need for a high-precision position encoder. The observer includes an initial commissioning routine to compensate for offset in placement of Hall-effect sensors and an algorithm to compensate for the sensor delay encountered when measuring torque harmonics. To improve robustness, an algorithm is derived to determine the initial position of the rotor using signatures in torque-ripple-induced vibration. The algorithm improves robustness by reducing the number of Hall-effect sensors required and improving the starting performance of the motor. Finally, future extensions to the algorithm are presented that enable vibration-based position sensing over the complete operating speed range of the machine, leading to further reductions in cost and improved robustness.^
Steven D. Pekarek, Purdue University.