PID parameter tuning of proportional electro-hydraulic servo valve

In modern industrial automation control system, electro-hydraulic servo system is widely used in aerospace, machinery manufacturing, heavy equipment and other fields because of its advantages of fast response, high control accuracy and large output power. As the core control component of the system, the control performance of proportional electro-hydraulic servo valve directly affects the dynamic response and control accuracy of the whole system. In order to achieve high-precision control of servo valve, PID (Proportional-Integral-Differential) controller is usually used for closed-loop control. Therefore, reasonable tuning of PID parameters is of great significance for improving system performance.

First, the basic principle of PID control

The PID controller weights the error of the system through three parts: proportion (P), integration (I) and differentiation (D), so as to generate control signals to adjust the actuator. Specifically:

Item-P: reflects the current error and provides immediate response;
Item-I: eliminate steady-state error and improve the system error-free;
Item-D: Predict the change trend of error and enhance the stability of the system.

In the proportional electro-hydraulic servo valve system, due to the nonlinear and time-varying characteristics of the hydraulic system, the traditional PID control parameters are often difficult to meet the dynamic performance requirements of the system, so it is necessary to optimize the parameters according to the actual system characteristics.

Second, PID parameter tuning method

At present, the commonly used PID parameter tuning methods include empirical method, Ziegler-Nichols method, response curve method and self-tuning method based on optimization algorithm.

1. Empirical method
The rule of thumb depends on the engineer's empirical judgment. First, set a proportional gain, gradually add integral and differential functions, and observe the system response to adjust. Although the operation is simple, the setting efficiency is low, and it is suitable for occasions with low requirements on control accuracy.

2. Ziegler-Nichols method (critical proportion method)
By gradually increasing the proportional gain, the system enters the constant amplitude oscillation state, records the critical gain Kc and oscillation period Tc at this time, and then calculates the PI or PID parameters according to the empirical formula. This method is suitable for systems with time delay, but it may be difficult to obtain critical parameters accurately in hydraulic servo systems.

3. Response curve method (open-loop setting method)
Based on the open-loop step response of the system, model parameters, such as time constant t and delay time τ, are obtained, and then PID parameters are calculated. It is suitable for system modeling with identifiable characteristics.

4. Method based on optimization algorithm
Intelligent algorithms such as genetic algorithm, particle swarm optimization (PSO) and fuzzy control are used to optimize online parameters, which can adapt to the dynamic changes of the system, improve the control accuracy and robustness, and have a wide application prospect in complex electro-hydraulic servo systems.

Iii. Matters needing attention in practical application

In practical application, the following factors should be considered when the PID parameters of proportional electro-hydraulic servo valve are adjusted:

-Non-ideal factors such as nonlinear friction, dead zone and saturation exist in the system;
-Influence of external load disturbance on system stability;
-Matching of sampling frequency of controller and system bandwidth;
-Influence of viscosity change of hydraulic oil caused by temperature change on system performance.

In addition, it is suggested to adopt a step-by-step approach in the system debugging process, and first set the P term to ensure the basic response of the system; Then I term is introduced to eliminate the steady-state error; Finally, item D is added to improve the dynamic response and stability.

IV. Conclusion

To sum up, PID control is still one of the most commonly used and effective control strategies in proportional electro-hydraulic servo valve system. Reasonable PID parameter tuning can not only improve the response speed and control accuracy of the system, but also significantly enhance the stability and anti-interference ability of the system. With the development of intelligent control technology, a new PID parameter tuning method based on model prediction and optimization algorithm will gradually become a research hotspot, providing more possibilities for high performance control of electro-hydraulic servo system.

In the future research and engineering practice, we should combine traditional methods and modern technical means, constantly optimize PID control strategy, and promote the electro-hydraulic servo system to develop in the direction of higher precision and reliability.