Mechanical resonance is a common problem in drive systems with elastic coupling. On-line adaptive notch filter is widely used to make systems stable and the key of this method is to identify natural torsional frequency from a speed feedback signal. However, because of common adoption of digital control and expansion of system bandwidth, oscillation frequency of the system is more likely to deviate from natural torsional frequency to a higher one. When oscillation frequency is shifted, the enabled notch filter with erroneous notch frequency causes an oscillation with a lower frequency and even makes resonance more severe. In order to explain this phenomenon, the classical two-mass model based classification of resonances is checked at first. Then, by taking digital control, current loop delay, and saturation nonlinearity into consideration, an improved digital mechanical resonance model is proposed and a criterion for oscillation frequency deviation is finally obtained. Furthermore, a more widely applicable and robust notch filter tuning strategy with no oscillation rebound is presented. In the end, the validity of aforementioned analysis and strategy is verified by experimental results.

This paper aims to present a solution for torsional vibration suppression and shaft torque limitation simultaneously in servo system with backlash. The existence of backlash, which would make conventional notch filter invalid, will aggravate the mechanical vibration and bring the risk of unsafety to the system. In order to solve that problem, a novel shaft torque compensator is proposed, which would make the system similar to a rigid system with one inertia. What is more, this compensator can limit shaft torque as expected, making the system relatively safe under any situation with different load inertias and torques. The limiting control is based on the adaptive online identification of load inertia in order to improve robustness of the system and ensure not only the accuracy, but also the arbitrariness of shaft torque limit. Simulation and experimental results are presented to illustrate the favorable behavior of the drive with the robust shaft torque compensator.

Because they are economical, universal servos are chosen for most industrial applications. However, tuning them accurately poses some challenges. Accurate electrical and mechanical parameters are essential for model-based high-performance servo controller design. In motion control, the variation of inertia is much more significant than that of other parameters. Thus, inertia identification is a key to effective on-line controller parameter self-tuning, but most conventional inertia identification methods cannot be well applied in some complicated situations, such as those caused by irregularly and slowly varying speed. Additionally, traditional control parameter tuning theory displays a deep understanding of the relationship between controller gain and inertia, but lacks an analysis of the maximum bandwidth of the system. In this paper, based on a widely accepted structure which is composed of inertia identification and on-line controller self-tuning, several simple but useful modifications are proposed. Firstly, to reduce the noise from encoder quantization error and thus to improve the accuracy of inertia identification, a motor acceleration calculation method featuring an inconstant period is proposed. Then, the scope of the application is extended to make it suitable for position control by redesigning the inertia updating time of the conventional method. In addition, to guarantee the stability of servo systems, the upper constraint of the expected maximum system bandwidth is derived by taking the controller saturation nonlinearity and hardware capacity into consideration. Finally, a modified moderate systematic on-line servo controller parameter self-tuning method via variable-period inertia identification is presented. The validity, effectiveness and advantages of proposed strategies are verified by several experimental results.

This paper mainly deals with the prediction and suppression of limit cycle oscillation existed in the two-mass system with nonlinear backlash. To improve position control precision of the drive system, the full-closed-loop feedback scheme is considered. Then, a comprehensive and definite prediction of limit cycle is given via the describing function method. In order to compensate backlash nonlinearity, the state feedback control method is employed. To overcome the insufficient application of the state feedback control in the complex nonlinear system, a novel design concept is proposed. The influence of backlash on the nonlinear system is substituted with an additional compensation component to the control signal, making the system approach a linear one. Following this, a pole placement scheme is designed, which aims to establish a feedback structure that can make the system equivalent to a rigid system. In such a case, the limit cycle oscillation can be eliminated; thus, the position control precision can also be enhanced. In all cases, the validity of the proposal is verified by experimental results.

Applying high-frequency power devices, such as gallium nitride (GaN) semiconductor devices, to the motor drive can significantly reduce system volume, losses, audible noise and increase system power density. In this paper, an LC filter designed as a sine wave filter is introduced into the servo drive system based on the GaN power device. An undamped method with variable delay time is proposed to solve the electrical resonance issue caused by LC filter and stator inductor. Detailed stability analysis is conducted, and rules on parameter tuning are provided. With additional proper time delay, the system can be stable without any extra sensors or power losses. Besides, this method is suitable for resonance suppression at variable switching frequency. Moreover, a wait-free and phase-continuous spread spectrum frequency modulation is applied to solve the issue of electromagnetic interference (EMI). The field-programmable gate array (FPGA) is used to achieve high control bandwidth when implementing the control algorithm. Finally, the ideal sinusoidal drive and low conducted EMI of permanent magnet synchronous motor (PMSM) is realized. Experiments on a 100 kHz GaN inverter with LC filter verify the validity of the proposed design and method.