Current compensation control for low-cost servo system

Three-phase current is very important in the vector control scheme of permanent magnet synchronous motor, and its sampling precision affects the servo control performance directly. In the low-cost servo system, to simplify the structure and reduce the volume, three-phase current is often not accurately detected because the current sensors are usually replaced by the sampling resistors, which will cause the undesirable torque ripple. Therefore, to enhance the closed-loop control performance for the low-cost servo system, an adaptive control method is proposed to compensate the current measurement error. In this approach, first, the estimated currents can be obtained online by a current state observer. Then, a three-phase current error compensator is designed based on the mathematical relation between three-phase current error and torque current. Next, based on the model reference adaptive control algorithm, two proportional–integral controllers are used to further strengthen the compensation effect. Finally, experimental results confirm that this method is effective and precise, and three-phase current error does not affect the servo control performance.

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