Design and Anti-surge Research of a Compressed Air Refrigeration Measurement and Control System

The compressed air refrigeration test is a test system that uses a pressurized turboexpander to obtain a low-temperature, various-flow airflow at a certain inlet pressure, and is mainly used to simulate the low-temperature environment of a high-altitude aeroengine. The test system is mainly composed of three parts: a constant pressure low dew point gas source section, a compressed air refrigeration test section and an engine vacuum test section. The gas source test section mainly completes the gas source required for the refrigeration test. The compressed air refrigeration test section mainly completes the state required for the test, in which the test gas flow rate is 1 15 kg/sT, the refrigeration outlet gas temperature reaches 74 ° C, and the outlet pressure is stabilized (absolute pressure).

The surge characteristics of the supercharger will affect the overall boost system and cooling efficiency. In severe cases, the whole system will be paralyzed, and even dangerous situations such as explosions will occur. Preventing the occurrence of surge phenomenon has very important practical significance for the stable and safe operation of the system.

1 measurement and control system design The whole system realizes multi-turbine refrigeration automatic control, including automatic driving, automatic parking, anti-surge control and automatic processing of emergency situations. The system is stably controlled in a certain state within the error tolerance range. Control the focus and difficulty of the entire system design.

The structure of this measurement and control system is as shown. The control system can be generally divided into: field level, lower level control level and upper management control level.

The field level consists of sensors, transmitters and actuators. Temperature sensing), male, Shaanxi, Master of Engineering, mainly engaged in the research of environmental simulation test and computer control technology.

Control technology computer measurement and control. 2014.22(4) Design of a compressed air refrigeration measurement and control system and anti-surge research Li Feng, Yang Junfeng (China Huayin Weapon Test Center, Huayin 714200, Shaanxi) Full automatic control: automatic driving, automatic parking and automatic handling of emergency situations; In addition, for the surge phenomenon that may occur in the turbocharged turboexpander refrigeration technology, multiple anti-surge methods are designed to realize the automatic control and anti-surge control of the multi-turbine refrigeration of the test system, and obtained in the actual test. A good application has a certain reference to similar problems.

Key 诃: environmental simulation; distributed measurement and control system; automatic control; surge s 褒 Li - I speed ar small instrument base two - M position control -. ~ ~ Bu position control % field 忪 computer measurement and control automatic control.

2 Automatic Control Design 1 Automatic Control Process Description The core set sound that produces low temperature gas is a pressurized turbo expander. There are 3 units in the system, each unit can generate quantity requirements, and choose single or multiple units. The environmental parameters affecting compression refrigeration include test gas flow rate, test outlet temperature, turbine pressure ratio, turbine speed, and the like.

First, prior to the compression refrigeration test, the parameters of the smart meter and the state of the actuator are initialized according to the requirements of this test. Then, the air supply pressure regulating valve is controlled so that the air source dew point and the inlet pressure are stably controlled to the control values ​​required for the normal operation of the turbine.

Finally, the emergency shut-off valve is activated and the gas enters the booster and expander. Gradually open the mouth and open the mouth of the booster. (Set the function of the return valve as shown in Figure 33), and increase the speed to the working speed. During the startup, check the bearing temperature, oil inlet pressure, sealing gas pressure and the running condition of the whole machine in real time, and automatically handle the warning. When the engine vacuum test is carried out, the back pressure will drop, adjust the turbine outlet regulating valve, and control the back pressure to be stable at 40KPa (vacuum required for the test) to ensure the safety and stability of the test.

When the test is over, the system will automatically stop in steps according to the operating state of the test unit. First, fully operate the booster return valve of the unit. Then gradually close the mouth, and at the same time detect the intake pressure, reduce the gas supply at the gas station, so as not to damage the sound. Finally, close the sealing gas and its gas source and close the emergency shut-off valve.

22 automatic control design and implementation 6.0 as a development tool, according to the description of the test system control process, design the simulation manual operation process to achieve intelligent control. The following rules are followed in the design: (1) computer software control combined with intelligent instrument control, mainly computer control. The computer software monitors the on-site operating status in real time, and controls various on-site actuators by sending control parameters to the smart meter.

3 Anti-mite method design 3.1 Surge and surge characteristic curve Under the certain inlet pressure and speed, when the inlet flow of the supercharger is less than a certain value, it will cause parameters such as compressor shaft temperature, shaft vibration and shaft displacement. When the machine changes sharply, the machine will surge. At this time, the pressure will fluctuate greatly, and a strong and reasonable anti-surge solution can effectively protect the unit from surge and provide guarantee for the safe and stable operation of the unit.

The characteristic curve of the supercharger refers to the relationship between the ratio of the outlet absolute pressure and the inlet absolute pressure (or compression ratio) and the inlet volume flow of the supercharger, as shown.

Connect the highest point of the characteristic curve of the turbocharger at different speeds. The resulting curve is the surge limit line, and the left part is called the surge zone, such as the shaded part.

Surge conditions are related to the characteristics of the pipe network. The larger the pipe network capacity, the greater the amplitude of the surge, and the lower the frequency; the smaller the pipe network capacity, the opposite.

3.2 Empirical Formula of Surge Limit Equation For the surge limit line, mathematical expressions can be obtained by theoretical derivation. This surge limit line can be approximated by a parabolic equation. The empirical formula is: where Q is the volumetric flow rate of the inlet of the supercharger, and T is the absolute temperature of the inlet of the supercharger. The decay is the inlet and outlet pressure of the supercharger. , K, a are constants, provided by the turbocharger manufacturer.

3.3 Fixed Limit Flow Method Anti-surge The surge control methods commonly used at present are mainly fixed limit flow method, variable limit flow method and general performance curve control method. Combined with the actual working conditions and related, we adopted the fixed limit flow method for surge control. Always keep the flow of the supercharger above a certain value to avoid running into the surge zone. This method is called fixed limit flow anti-surge control. Medium Qb is the fixed limit flow value. From the relevant parameters of the test and the test, QB=3.1 can be calculated. No matter how much the supercharger is running, as long as the condition of Q>Qb is satisfied, the supercharger will not surge.

The system is equipped with a return valve in the supercharger as shown. When the compressor inlet flow rate is less than Qb, the valve is opened, and the supercharger outlet gas is returned to the inlet of the supercharger via the bypass, and the inlet flow rate is increased to be greater than Qb. The occurrence of surge is prevented.

Supercharger return valve 3.4 Multiple anti-surge method design and the realization of surge is a situation that must be avoided in the system work. Therefore, there must be measures to prevent the compressor from surging on the supercharger. For system safety, multiple anti-surge measures will be designed. They are automatic software protection, automatic hardware protection and manual shut-off of emergency shut-off valves. (Continued on page 1126) Computer measurement and control should be the initial value of the PID controller parameters, quantization factor = 125, 艮 = 40, scale factor K = 1 / 320 simulation response curve as shown in curve 1.

After adding the intelligent sampling section, the simulation curve is shown as curve 2. It can be seen from the above simulation results that the addition of the intelligent sampling link improves the control quality and reduces the adverse effects brought by the hysteresis, and is more suitable for the practical application of the geothermal air circulation system.

5 Conclusions For the characteristics of the indoor air circulation system of the ground temperature central air-conditioning building, the algorithm simulation based on the embedded system, including the hardware and software design and the mathematical model for the controlled object, is designed. The results show that the intelligent control scheme has a large time-delay system control effect. Well, the dynamic performance improvement is more obvious than the conventional Pro control. Through simulation test, the deviation of each data is within the specified range, which satisfies the accuracy requirements of the system well, and realizes the intelligent control of the ground temperature central air conditioning air circulation system, which has broad application prospects.

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