At the scene, the interference of the frequency converter appears more and more serious, and even the control system cannot be put into use, which has always been a very headache problem. . When we usually work and debug equipment, these problems occur: Common phenomenon of inverter interference 1. As soon as the inverter of the heat exchange station is turned on, the pressure transmitter jumps randomly; 2. When using the frequency converter to control the water supply, the pressure change is used as the signal to collect the pressure, and the pressure change is interfered by the frequency converter; 3. When the inverter starts the motor, the voltage change signal is unstable and the beating is severe; 4. The voltage transformer (4-20mA) jumps randomly after the inverter is started, but the nearby integrated thermal resistance (4-20mA) is not affected, and the signal lines are not shielded; These phenomena are caused by the interference of the inverter. Why does the frequency converter cause interference? First of all, we all know that the frequency converter is used to change the frequency. The inverter includes a rectifier circuit and an inverter circuit. The input AC power is converted into a DC voltage through a rectifier circuit and a smoothing circuit, and then the DC voltage is converted into a pulse voltage of different widths (called pulse width modulation voltage, PWM) through the inverter. . Using this PWM voltage to drive the motor can adjust the torque and speed of the motor. There are three types of electromagnetic interference due to this working principle: 1. Harmonic interference The rectifier circuit will generate harmonic current, which produces a voltage drop on the impedance of the power supply system, resulting in distortion of the voltage waveform. This distorted voltage interferes with many meters. The common voltage distortion is the top of the sine wave. flatten. When the harmonic current is constant, the voltage distortion is more serious in the case of weak power supply. The characteristic of this interference is that it will interfere with the equipment using the same power grid, regardless of the distance between the equipment and the inverter. 2. Radio frequency conducted emission interference Since the load voltage is pulse-shaped, the current drawn by the inverter from the power grid is also pulse-shaped. This pulse current contains a large amount of high-frequency components, causing radio frequency interference. interference, regardless of the distance between the instrument and the inverter. 3. Radio frequency radiation interference Radio frequency radiated interference comes from the input and output cables of the frequency converter. When there is radio frequency interference current on the input and output cables of the inverter, since the cables are equivalent to antennas, electromagnetic wave radiation will inevitably be generated, resulting in radiation interference. The PWM voltage transmitted on the output cable of the inverter also contains rich high-frequency components, which will generate electromagnetic wave radiation and cause radiation interference. The characteristic of radiated interference is that when other electronic equipment is close to the frequency converter, the interference phenomenon becomes serious. How to solve the interference problem? How to deal with the disturbance to the inverter 1. The inverter should be grounded at a single point, preferably a short and thick wire for grounding; 2. The signal line of the sensor adopts twisted-pair shielded wire, and the shielding layer is grounded with a cable clamp. 3. Install a power filter, a filter magnetic ring, or an isolator on the power supply of the sensor for isolation. 4. Suppress the harmonics generated by the inverter. The optional filtering products are: inverter input filter, inverter output filter, inverter input reactor, inverter output reactor, etc. Adding a reactor in series in the input circuit is an effective method to suppress lower harmonic currents. In addition, in order to prevent the frequency converter from interfering with the signal and control loop, it is necessary to use a separate isolated power supply for the controller, instrument and industrial computer. In fact, the easiest way to do it on the spot is: Keep the meter away from the inverter! However, it is not always possible to eliminate interference, and the methods still need to be tried one by one. Axial Metallized Polyester Film Capacitors Capacitor,Metallized Polypropylene Capacitor,Small Size Capacitor,X-ray Euipment Capacitor XIAN STATE IMPORT & EXPORT CORP. , https://www.shvcomponents.com