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.