Electromagnetic compatibility problems of automati

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Analysis and solution of electromagnetic compatibility problems of automatic control system in wind tunnel laboratory

Abstract: This paper introduces the example analysis and interference treatment method of frequency converter interference measurement and control system in a wind tunnel automatic control system. By adding matched filters in the input and output terminals of the frequency converter and other control circuits, and conducting a series of shielding and good grounding for the entire power supply system, the electromagnetic interference (EMI) generated by the frequency converter during operation is effectively solved. After many machine debugging and tests, the electromagnetic compatibility (EMC) of the automatic control system in the wind tunnel laboratory has been realized

key words: electromagnetic interference drafting measures of variable frequency speed regulation measurement and control system electromagnetic compatibility: This text introduced the some wind tunnel automation control system the inside the inverter interference measures solid an analysis and interferences that control the system handles method. Pass to add the filter that match features: small volume in inverter input, output carried and other control parts of electric circuits, and shield to whole power supply system proceeding a series with good connect ground, solved the inverter the work effectively the hour the creation of the electronic interaction. Adjust to try and experiment many times through whole machine,Realizes the wind tunnel laboratory automation controls the electromagnetic compatibility of the system。

Keywords: frequency conversion speed timing , control of system,Electromagnetic interence,suppression method,Electromagnetic compatibility。

The application of wind tunnel test research plays a very important role in social production. With the continuous development of production field and technology, the power demand of wind tunnel has the corresponding requirements of wide speed regulation range, high steady speed accuracy, fast dynamic response, etc. with the rapid development of power electronics technology, the successful development of variable frequency power supply and rectifier devices of various capacities and types, as well as the development of computer technology and control theory, the application field of AC speed regulation drive in speed regulation system has been continuously expanded, How to maintain the normal operation of the frequency converter control system is to engage in industrial automation 11. Automatic printing: after the experiment, the test results can be automatically printed; The practical problems faced by professional engineers and technicians are also the guarantee of improving the accuracy of wind tunnel test data

I. working principle of wind tunnel

wind tunnel is a pipe test equipment that can artificially generate and control air flow to simulate the flow of gas around aircraft or objects, measure the effect of air flow on objects, and observe physical phenomena. The power section of the wind tunnel is equipped with a motor and fan system. The data information will be displayed in the form of word tables. The motor rotates under the AC variable-frequency speed regulation to drive the blades. The electric energy is transformed into the mechanical energy of the blades, and the mechanical energy of the blades is transformed into the pressure energy of the air medium, generating the flow of the medium in the wind tunnel pipe. By trimming the air flow, it becomes a uniform and stable air flow, so as to meet the flow field for the test

II. Wind tunnel control system

2.1 wind speed control

a variable frequency speed regulation system is composed of a frequency converter, a PID regulator, supporting low-voltage electrical appliances and a pressure sensor, as shown in Figure 1. The pressure sensor in the system is responsible for detecting the system pressure difference, transforming the pressure signal into a resistance signal as a feedback input to the PID regulator, After comparing with the given signal, the deviation value uses the optimized PI algorithm to output the control signal to control the output frequency of the frequency converter to ensure the constant wind speed

2.2 angle control

the angle of the test model is often changed during the wind tunnel test, so that the test amount corresponding to each angle can be measured continuously, which saves time, improves efficiency and accuracy, and realizes full automation

III. three elements of electromagnetic compatibility

Figure 1 three elements of electromagnetic compatibility

3.1 electromagnetic disturbance source: electromagnetic energy emitted by any form of natural or electric energy devices can harm people or other organisms sharing the same environment, or cause electromagnetic harm to other equipment, subsystems or systems, resulting in performance degradation or failure, which is called electromagnetic disturbance source

3.2 coupling path: that is, the path or medium of transmission disturbance

3.3 victim: refers to people or other organisms that will be injured when they are affected by the electromagnetic energy emitted by the electromagnetic disturbance source, as well as devices, equipment, subsystems or systems that will cause electromagnetic hazards and degrade or fail in performance. Many devices, equipment, subsystems or systems are both electromagnetic disturbance sources and sensitive equipment

there must be three factors in order to cause electromagnetic compatibility problems in the system, namely, electromagnetic interference source, coupling path and sensitive equipment. Therefore, when encountering the problem of electromagnetic compatibility, we should start with these three factors, apply the right medicine to the case, and eliminate one of them, so as to solve the problem of electromagnetic compatibility

IV. analysis and solution of electromagnetic compatibility problems of frequency converter control system in wind tunnel laboratory

4.1 frequency converter interference generation mechanism

the main circuit of frequency converter is generally composed of AC-DC-AC, the external input 380v/50hz power frequency power supply is uncontrollably rectified into DC voltage signal through three-phase bridge, and is filtered into AC signal with variable frequency through filter capacitor filtering and high-power transistor switching element inversion. In the rectifier circuit, the waveform of the input current is irregular rectangular wave, and the waveform is decomposed into fundamental wave and harmonics according to Fourier series. The higher harmonics will interfere with the input power supply system. In the inverter output circuit, the output current signal is a pulse waveform modulated by PWM carrier signal. For GTR high-power inverter components, the PWM carrier frequency is 2 ~ 3kHz, while the maximum PWM carrier frequency of IGBT high-power inverter components can reach 15KHz. Similarly, the output loop current signal can also be decomposed into fundamental waves and other harmonics containing only sine waves, while the higher harmonic current directly interferes with the load. In addition, high-order harmonic currents also radiate into space through cables, interfering with adjacent 5 The assembly quality is close to that of electrical equipment

4.2 main modes of interference propagation and prevention:

4.2.1 radiated interference

radiated interference

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