image: This diagram comprehensively reveals the entire process from the input of the reference signal to the achievement of precise control within the system. Within this closed-loop control system, the reference displacement signal, serving as the initial input for the control target, is precisely transmitted to the CRLADRC controller of the displacement loop. The controller processes the reference displacement signal in real-time through its internal complex algorithms.
Credit: Kaiyu Shan
Research content
During the startup of the hydraulic turbine generators, the hybrid magnetic bearing support system exhibits displacement fluctuations, and the nonlinearity and strong coupling characteristics of the magnetic bearings limit the accuracy of rotor modeling, making traditional control methods difficult to adapt to parameter variations. To suppress startup disturbances and achieve a control strategy with low computational complexity and high precision, this paper proposes a five-degree-of-freedom hybrid magnetic bearing control strategy based on an improved cascaded reduced-order linear active disturbance rejection controller (CRLADRC). The front-stage reduced-order linear extended state observer (FRLESO) reduces the system’s computational complexity, enabling the system to maintain stability during motor startup disturbances. The second-stage reduced-order linear extended state observer (SRLESO) further enhances the system’s disturbance estimation accuracy while maintaining low computational complexity. Furthermore, the disturbance rejection and noise suppression capabilities are analyzed in the frequency domain and the stability of the proposed control method is proven using Lyapunov theory. Experimental results indicate that the proposed strategy effectively reduces displacement fluctuations in the hybrid magnetic bearing support system during motor startup, significantly enhancing the system’s robustness.
The research results and their significance
This research addresses the issue of insufficient disturbance rejection performance of the magnetic bearing support system displacement fluctuations during the startup of hydraulic turbine generators. A control strategy for HMB system based on an improved CRLADRC is proposed, followed by theoretical analysis and experimental verification.
Initially, the proposed cascaded structure reduces the computational complexity of the system. Below the shear frequency, the cascaded reduced-order linear extended state observer (CRLESO) exhibits performance comparable to that of a wide-bandwidth single-stage reduced-order linear extended state observer (RLESO). Near the shear frequency, the CRLESO has an accelerated attenuation rate, which enables it to more swiftly suppress disturbances and enhance the system’s dynamic response performance. Above the shear frequency, the gain rapidly decreases, showing that CRLESO has a strong attenuation effect on disturbances and noise. Through Lyapunov equation, the stability of the controller is demonstrated.
Meanwhile, Experimental results show that, compared to the traditional RLADRC control method, the CRLADRC control method offers higher tracking accuracy under static levitation, dynamic levitation during motor startup, and steady-state operation. Additionally, this method significantly reduces the displacement vibration amplitude of the five-degree-of-freedom magnetic bearing, demonstrating strong disturbance rejection capabilities.
Future outlook
Looking to the Future: Further Breakthroughs in Magnetic Bearing Control Algorithms
Looking ahead, the research team plans to further optimize the control algorithms to enhance the disturbance rejection and stability of the magnetic bearing system. Continuous improvements in observer structure and compensation mechanisms are expected to push the control accuracy and stability margin of the motor rotor to new heights. "Our next goal is to develop a more robust intelligent control architecture to cope with more complex operating conditions," the researcher explained.
The successful validation of the improved cascaded active disturbance rejection control strategy proposed in this study not only provides a solution for performance breakthroughs in hybrid magnetic bearings but also lays a foundation for the stable operation of magnetic bearing systems under complex disturbance environments.
The full study is accessible by DOI: 10.30941/CESTEMS.2025.00024
Journal
CES Transactions on Electrical Machines and Systems
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Control Strategy for Hybrid Magnetic Bearing Based on Improved Cascaded Reduced-Order Active Disturbance Rejection Controller
Article Publication Date
16-Sep-2025