This article, written by Wang Meng of the Automation Department of Laiwu Steel, briefly introduces the electro-hydraulic servo control system, its technical characteristics, composition, and working principle in the TRT automatic control system of the 1880m³ blast furnace in Laiwu Steel's large H-type production line. Electro-hydraulic servo control technology has many advantages, the most prominent being its fast response speed, high output power, and high control precision. Therefore, it has been widely used in aviation, aerospace, military, metallurgy, transportation, and engineering machinery fields. 1. Introduction TRT is short for Blast-Furnace Top Pressure Recovery Turbine Unit. It is an energy recovery device that utilizes the pressure and heat energy contained in the blast furnace outlet gas to power the turbine expander and drive the generator to generate electricity. This achieves energy saving, noise reduction, and environmental protection, possessing excellent economic and social benefits. It is currently recognized as an energy-saving and environmentally friendly device by modern international and domestic steel enterprises. The TRT automatic control system consists of six systems: main gas system, lubricating oil system, electro-hydraulic servo control system (power oil system), turbine shaft motion detection system, nitrogen sealing system, and water system. 2. Overview of Electro-hydraulic Servo Control Technology Electro-hydraulic servo control technology, serving as a bridge connecting modern microelectronics, computer technology, and hydraulic technology, has become an important component of modern control technology. Due to its significant advantages such as good linearity, small dead zone, high sensitivity, good dynamic performance, fast response, and high precision, it has been widely used. This paper addresses this issue by designing an electro-hydraulic servo control system suitable for TRT automatic control systems, utilizing electro-hydraulic servo control technology and computer technology. [IMG=Figure 1 Principle Block Diagram of Electro-hydraulic Servo Control System]/uploadpic/THESIS/2007/11/20071116120707309407.jpg[/IMG] Figure 1 Principle Block Diagram of Electro-hydraulic Servo Control System [IMG=Figure 2 Power Oil System Control Block Diagram]/uploadpic/THESIS/2007/11/2007111612072263712W.jpg[/IMG] Figure 2 Power Oil System Control Block Diagram 3 Composition, Function and Working Principle of Electro-hydraulic Servo Control System 3.1 Composition of Electro-hydraulic Servo Control System The electro-hydraulic servo control system consists of three main parts: the hydraulic control unit, the servo cylinder, and the power oil. The hydraulic control unit includes the speed control valve control unit and the turbine vane control unit. Each unit consists of an electro-hydraulic servo valve, a jogging solenoid valve, a quick-closing solenoid valve, an oil circuit block, and a base. The servo cylinder has a double piston rod structure, with very low friction and good sealing performance. The power oil station consists of an oil tank, variable displacement pump, oil filter, cooler, pipeline valves, and monitoring instruments. 3.2 Role of the Electro-hydraulic Servo Control System The electro-hydraulic servo control system is one of the main systems in the TRT unit. Based on instructions from the main control room, it controls the TRT's start-up, shutdown, speed, furnace top pressure, and process monitoring. To achieve the functional control of these systems, the turbine speed must ultimately be controlled. Controlling the turbine speed requires controlling the opening of the speed control valve or turbine stator. The means of controlling the stator or speed control valve opening is the electro-hydraulic servo control system. The accuracy and error of the control system directly affect the control of each stage of the TRT system. Therefore, the system's position and role in the TRT are extremely important. 3.3 Working Principle of the Electro-hydraulic Servo Control System The electro-hydraulic servo control system consists of mechanical, electrical, and hydraulic components, and its control block diagram is shown in Figure 1. The command signal issued by the automatic control system is compared with the actual position signal of the cylinder in the servo controller. The resulting error signal is amplified and sent to the electro-hydraulic servo valve. The servo valve converts the current signal into hydraulic oil flow at a certain ratio, driving the cylinder to move. The feedback signal from the position sensor changes continuously until it equals the command signal, at which point the cylinder stops moving. The cylinder stops at the designated position, stabilizing the turbine vane at a certain opening. The linear motion of the cylinder is converted into the rotational motion of the valve plate (vane) through a crank, changing the working opening of the valve plate or vane. As the system signal changes continuously, the opening of the turbine vane will also change continuously, and the change in the vane opening achieves the purpose of controlling the revolutions, controlling the gas flow, and controlling the turbine output. Its power oil system control diagram is shown in Figure 2. 3.4 Main Control Equipment in the Electro-hydraulic Servo Control System The most important control equipment in the TRT is the turbine vane and the quick-opening bypass valve. They are both closed-loop systems driven by hydraulic servo. The main control equipment includes a servo controller, servo valve, LVDT feedback position sensor, hydraulic motor, and solenoid valve. By controlling the gain and loss of the solenoid valve, the valve and vane can be quickly opened and closed. 3.4.1 Servo Controller The servo controller (model ESA-3E) is mainly used for servo control of axial compressor stator angle, TRT differential pressure power generation, position control, and other related electro-hydraulic actuators. This controller has two circuit boards: the PARKER control board compares the control command signal and the sensor feedback signal, performs proportional and integral calculations and power amplification, and sends out the corresponding current signal to drive the servo valve; the signal conditioning board is used to condition the feedback signal, convert between positive and negative actions, and provides two alarm functions for command signal loss and feedback signal loss, as well as a 4-20mA position indication signal. 3.4.2 Servo Valve Under the control of the servo valve, the servo valve converts the 4-20mA signal output by the servo controller into hydraulic oil flow to drive the servo cylinder. The feedback signal from the position sensor continuously changes until it equals the adjustment signal. At this point, the hydraulic oil flow signal output by the servo valve becomes 0, the servo cylinder stops moving, and thus drives the turbine stator and quick-opening bypass valve to the expected position, achieving the purpose of position adjustment. 3.4.3 A hydraulic lock is a hydraulically controlled directional valve, whose main function is to provide protection for the actuator in the event of power failure or pressure drop. 3.4.4 Position Sensors Position sensors (angular displacement sensors or linear displacement sensors) are used to measure the actual position signal and convert it into a corresponding current signal (4-20mA) or voltage signal (-3V-3V) sent to the ESA-3E servo controller as a feedback signal. The controller also receives 4-20mA command signals from the position command signal regulator in the main control room. 4. Functional Applications of the Electro-hydraulic Servo Control System The main function of the electro-hydraulic servo control system is applied to the speed control of the turbine. The main object of speed control is the stator vane. By controlling the opening degree of the stator vane, the speed of the turbine is controlled, thereby achieving stable control of the blast furnace top pressure. Speed ​​control in electro-hydraulic servo control systems can be roughly divided into three processes: 4.1 Speed-up process: All system startup conditions are met, and there are no major fault signals in the unit. After receiving the "electrical start-up permission" signal from the electrical system and the "TRT start-up permission" signal from the blast furnace main control room, it is confirmed that the blast furnace pressure reducing valve group is under automatic control and the blast furnace top pressure and gas temperature are stable within the process range, thus the unit is ready to increase speed. 4.2 Speed ​​process: This process includes both automatic and manual control, with the stationary vane as the controlled object. 4.2.1 Automatic speed-up: The automatic speed-up control process involves the setpoint of a speed PID regulator continuously increasing over time. This process is achieved through the inverse functions of the stationary vane control time curve and the speed setpoint speed-up curve. When the deviation between the measured and setpoint top pressure exceeds 2 kPa, the speed is not allowed to increase. The stationary vane control time curve is a broken-line function of the speed setpoint and the stationary vane control time, and is an inverse function of the speed-up curve. The stationary vane control time is calculated based on the current speed setpoint. Then, based on this stationary vane control time and the speed increase curve, the next speed setpoint is obtained. This cycle repeats, continuously increasing the speed setpoint. 4.2.2 Manual Speed ​​Increase: In manual mode, a manual speed increase command is sent to the system. The speed is controlled by manually adjusting the inlet hydraulic valve and the opening of the stationary vane on the system screen. 4.3 Automatic Synchronization Process: When the automatic synchronizing device is engaged, automatic grid connection is achieved through fine-tuning of the speed during grid connection. When the speed reaches 2850 rpm, the PLC sends an automatic synchronizing activation signal. Automatic synchronizing only works when the speed control is in automatic mode. When a speed increase command is sent to the system, the automatic synchronizing device controls speed increase/decrease at ±5 rpm; when no speed increase command is sent, the automatic synchronizing device controls speed increase/decrease at ±1 rpm. 5. Conclusion The widespread application of electro-hydraulic servo control technology in TRT control systems has fully highlighted its significant advantages, including good linearity, small dead zone, high sensitivity, good dynamic performance, and fast response. During normal operation, TRT equipment can recover approximately 30% of the energy required by the blast furnace blower. It requires no fuel, does not alter the quality of the blast furnace gas, and purifies the gas while improving pressure control at the furnace top without affecting the normal use of existing gas users, thus creating considerable economic and social benefits for steel enterprises. (Proceedings of the 2nd Servo and Motion Control Forum; Proceedings of the 3rd Servo and Motion Control Forum)