Advances in the Control of Electro-Hydraulic Servo Systems

Dear Colleagues,

Electro-hydraulic servo systems (EHSSs) play a vital role in modern engineering applications requiring high power density, rapid response, and precise motion control. They are widely utilized in aerospace, transportation, manufacturing automation, construction machinery, and energy systems, where reliability and accuracy are critical. The nonlinear dynamics of hydraulic components, such as valves, actuators, pipelines, and accumulators, combined with fluid compressibility, friction, and parameter uncertainties, make the modeling and control of EHSSs a challenging task. Over the past decades, considerable progress has been achieved through advanced modeling methods, robust control strategies, and intelligent algorithms that integrate hydraulics with modern computation. Recent research emphasizes adaptive control, sliding mode control, fuzzy logic, nonlinear observers, model predictive control, and inverse control and reference model strategies. These approaches, often enhanced by artificial intelligence and machine learning, improve robustness and adaptability under uncertainty. Alongside real-time methods, offline correction remains crucial for compensating static nonlinearities, dead zones, and hysteresis. Such techniques, based on preidentified models or iterative learning, refine control accuracy without increasing online computational burden. Moreover, EHSSs are increasingly used in rapid product prototyping and evaluation, where flexible test benches demand both precision and adaptability. Digital twins and data-driven techniques further expand the possibilities for combining offline calibration with online adaptation, supporting predictive maintenance and fault-tolerant operation. Energy-efficient control and integration into cyber-physical environments have also become key directions aligned with sustainable development and Industry 4.0 initiatives. This Special Issue on advances in the control of EHSSs aims to highlight state-of-the-art research and innovative solutions addressing theoretical, computational, and experimental challenges in this rapidly evolving field.

This Special Issue welcomes contributions that advance the state of the art in electro-hydraulic servo systems by addressing their most critical challenges and emerging applications. Particular emphasis is placed on the following topics:

• Novel approaches for nonlinear modeling and handling parameter uncertainty under fluid compressibility, leakage, friction, dead-zone effects, and operating condition variability.
• Analysis and mitigation of resonances, limit cycles, and self-excited oscillations in servo and proportional valves to enhance system stability margins.
• Methods that improve transient response, reduce overshoot, and ensure steady-state accuracy while compensating for actuation delays and nonlinearities.
• Adaptive and robust controllers that enhance performance under uncertainty and disturbances, ensuring reliability in demanding applications.
• Control strategies that provide robustness against flow pulsations, vibrations, temperature changes, and aeration to ensure reliable performance in diverse environments.
• Solutions that balance advanced control performance with practical constraints such as tuning effort, hardware costs, computational burden, and industrial feasibility.
• Innovative architectures and control schemes that increase energy efficiency, reduce hydraulic losses, and incorporate environmentally compatible working fluids.
• Contributions integrating model-free and machine learning-based methods, digital twin applications, off-line calibration and correction methods, and data-driven fault diagnosis.
• Advances in condition monitoring and diagnostics of EHSSs, including fault detection, health indicators, and predictive maintenance frameworks.
• Latest achievements on new generations of servo valves with higher switching frequencies, improved response, and enhanced durability, which might require new development of control strategies.
• Developments in modern sensor technologies enabling accurate flow, pressure, and displacement measurements, robust feedback acquisition, and advanced signal processing in EHSSs.
• Investigations into wear mechanisms, leakage, material fatigue, and predictive maintenance strategies that extend system durability and minimize downtime.

Submissions combining theoretical development, computational modeling, experimental validation, and industrial case studies are particularly encouraged. Interdisciplinary works that link hydraulics with control engineering, artificial intelligence, advanced sensor technology, and sustainable system design are also within the scope of this Special Issue.

Dr. Piotr Czop
Guest Editor

Manuscript Submission Information

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• electro-hydraulic servo systems
• nonlinear control
• adaptive control
• sliding mode control
• fuzzy logic
• model predictive control
• inverse control
• reference model strategy
• offline correction
• rapid prototyping
• transportation
• digital twin
• hydraulic accumulators
• fault diagnosis
• energy efficiency
• Industry 4.0