(1) Selection Taboos for Lead and Lag Compensation In electro-hydraulic servo systems, series lag compensation is often used to improve low-frequency gain and system accuracy. Alternatively, while ensuring system accuracy, the mid-frequency gain can be reduced to decrease the crossover frequency and guarantee system stability. Because hydraulic servo systems are mainly characterized by integral and oscillatory components, phase stability margin is easy to ensure, but gain stability margin is not, making series lead compensation, which primarily improves phase margin, unsuitable. Series lag compensation is preferred instead.
(2) Series Lag Compensation Should Not Be Used Alone After applying series lag compensation, the system response characteristics are not improved. The actual system bandwidth is further reduced, and due to the decrease in phase margin and changes in the cutoff frequency during operation, the system may become conditionally stable. Therefore, series lag compensation should be used in conjunction with other corrective measures.

(3) Do Not Ignore the Difference Between Velocity Feedback Correction and Acceleration Feedback Correction Velocity feedback correction mainly improves system stiffness and bandwidth, reducing the influence of interference and non-linearity within the components enclosed in the velocity feedback loop. Acceleration feedback primarily improves system damping.

(4) Velocity and Acceleration Feedback Corrections Are Effective Depending on the needs, velocity feedback correction and acceleration feedback correction can be used individually or simultaneously.

Acceleration feedback can increase the system damping, while velocity feedback increases the natural frequency but reduces the gain and damping. If both velocity and acceleration feedback are introduced and the K1 and K2 values are appropriately selected, the damping ratio can be increased while suppressing the resonant peak, resulting in comprehensive improvements in dynamic and static performance indicators.

(5) Dynamic Pressure Feedback Is Better Than Pressure Feedback Using a dynamic pressure feedback electro-hydraulic servo valve can improve the damping ratio. If the electro-hydraulic servo valve structure is not changed, but a pressure sensor is used to measure the load pressure and convert it into a voltage signal, and a differential circuit is used to extract a voltage signal proportional to the rate of change of pressure, more components are enclosed in the feedback loop, thereby improving system stiffness. Dynamic pressure feedback only plays a feedback role during dynamic processes.

The function of pressure feedback is the same as that of a pressure feedback servo valve, which is to increase the pressure-flow coefficient K, thereby increasing the damping ratio. However, external disturbances and pressure signals can also be fed back to the input end, causing a larger static error in the system. Obviously, dynamic pressure feedback is better than pressure feedback.