Abstract
High bandwidths and accurate current controls are essential in high-performance permanent magnet synchronous (PMSM) servo drives. Compared with conventional proportional–integral control, deadbeat current control can considerably enhance the current control loop bandwidth. However, because the deadbeat current control performance is strongly affected by the variations in the electrical parameters, tuning the controller gains to achieve a satisfactory current response is crucial. Because of the prompt current response provided by the deadbeat controller, the gains must be tuned within a few control periods. Therefore, a fast online current loop tuning scheme is proposed in this paper. This scheme can accurately identify the controller gain in one current control period because the scheme is directly derived from the discrete-time motor model. Subsequently, the current loop is tuned by updating the deadbeat controller with the identified gains within eight current control periods or a speed control period. The experimental results prove that in the proposed scheme, the motor current can simultaneously have a critical-damped response equal to its reference in two current control periods. Furthermore, satisfactory current response is persistently guaranteed because of an accurate and short time delay required for the current loop tuning.
Highlights
A modern servo motor drive usually includes current, speed, and position control loops
When the current loop is implemented with a digital signal processor (DSP), because of the limited computation capability, the calculated voltage command requires one control period delay for the pulse width modulation (PWM) module to output voltage to the motor
This time delay causes an underdamped or unstable current response when a proportional–integral (PI) controller is used for motor current regulation [1,2,3,4]
Summary
A modern servo motor drive usually includes current, speed, and position control loops. When the current loop is implemented with a digital signal processor (DSP), because of the limited computation capability, the calculated voltage command requires one control period delay for the pulse width modulation (PWM) module to output voltage to the motor. The predictive current controller generates the optimal voltage vector by minimizing a specific cost function This voltage vector allows the motor current to reach its reference value as fast as possible with minimum overshoot. The effect caused by the parameter mismatch can be treated as a disturbance to the current controller To compensate for this disturbance, the compensation voltage, which was obtained through the disturbance observer in [12,17] and through adaptive control in [25], is added to the current loop. The proposed method directly identifies the gains of the deadbeat controller instead of the electrical parameters. The current loop is tuned by updating the deadbeat controller with the average gains
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