Reduce operation noise and energy cost with torque current control and torque forward compensation

Noise in mechanical systems often arises from mechanical vibration due to an unbalance load. Such unwanted torque spikes arise from load-torque ripples on the motor shaft, and delays in motor-winding current commutation.

By Control Engineering Staff

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Austin, TX —Noise in mechanical systems often arises from mechanical vibration due to an unbalance load. Such unwanted torque spikes arise from load-torque ripples on the motor shaft, and delays in motor-winding current commutation. Charlie Wu, senior. system and application engineer in the Microcontroller Division at Freescale Semiconductor suggests that the company’s digital signal controllers can be used to eliminate audio-frequency instabilities in mechatronic systems caused by torque ripple.

“Most motor control systems can be implemented by an 8-bit microcontroller (MCU),” Wu says, “but performance is often poor because of lack of current feedback loop.”

“Without a current control loop plus torque forward compensation, acoustic noises caused by torque ripple cannot easily be eliminated,” Wu continues. “It is difficult to add a current control loop into control system based on an 8-bit MCU because the processor cannot perform the intense math calculations at the required loop bandwidth.”

Wu points out that, on the other hand, a DSC implemented as a monolithic integrated circuit can reduce acoustic noise, mechanic noise, material cost, and complexity of control circuits and algorithms.

“Add current feedback loop with proper torque forward compensation,” he advises. “The torque forward compensation signal follows the estimated rotor position.”

— C.G. Masi , senior editor, Control Engineering