Abstract: This is a summary of experience from the front line of electromechanical integration and automation engineering, focusing on the engineering practice problem of solving the anti-interference operation of frequency converters. Keywords: Frequency converter, anti-interference, grounding signal 1 Introduction Frequency converter speed regulation of AC induction asynchronous motors is an epoch-making technological advancement in the field of electrical drives in the 20th century. With the widespread application of frequency converters, they have increasingly become the largest source of electromagnetic pollution in the field of factory automation. It is common to see dozens or even hundreds of frequency converters installed in a factory with a large number of equipment. The nonlinear equivalent load of the DC-AC inverter of the frequency converter causes the frequency converter to not only pollute the factory power supply system in many system integration projects, but also directly interfere with the automation project, causing the measurement and control system to malfunction, seriously damaging the stability of the large system, and even causing the frequency converter itself to be interfered with and trigger a "bootstrapping" type speed regulation failure. Although international standards have strict specifications for EMC (IEC 61000 series electromagnetic compatibility design) of electrical equipment, and the China National Bureau of Quality and Technical Supervision has decided to adopt them "equivalently" in China, and the Chinese national standard GB/T 14549-93 on power quality and harmonics in public power grids has been in effect for 14 years, the rapid development of China's economy and technology has made the pollution control of power electronic switching devices an urgent matter. The author, from the front line of automation integration engineering, has frequently encountered inverter interference problems in recent years, causing equipment malfunctions and halting factory production lines. Moreover, finding the cause of such problems is quite difficult. After consulting relevant materials and combining some experience in handling problems at work, this article discusses the sources and propagation methods of inverter interference, as well as some handling methods for different situations of interference problems encountered in practical applications, hoping to differ from the dogmatic teachings in textbooks. 2. Inverter Interference Analysis Inverter interference problems are generally divided into three categories: interference from the inverter itself; interference from electromagnetic waves generated by external equipment; and interference from the inverter to other weak current equipment. The frequency converter itself is a source of interference. As is well known, a frequency converter consists of two main parts: the main circuit and the control circuit. The main circuit of the frequency converter mainly consists of a rectifier circuit, an inverter circuit, and a control circuit. The rectifier circuit and the inverter circuit are composed of power electronic devices. Power and electronic devices have nonlinear characteristics. When the frequency converter is running, it needs to perform rapid switching actions, thus generating high-order harmonics. Therefore, the output waveform of the frequency converter contains a large number of high-order harmonics in addition to the fundamental wave. Regardless of the type of interference, high-order harmonics are the main cause of interference generated by the frequency converter. The frequency converter itself is a source of harmonic interference, so it will affect the equipment on the power supply side and the output side. Compared with the main circuit, the control circuit of the frequency converter is a low-energy, weak-signal circuit, which is extremely susceptible to interference from other devices. Therefore, anti-interference measures must be taken for the control circuit when installing and using the frequency converter. 3 Analysis and Handling of Frequency Converter Interference Cases 3.1 How to Determine if a Frequency Converter Has Interference Problems The interference problems of the frequency converter are mainly reflected in the operation of the motor. For example, sudden motor stoppage during operation, inconsistent motor speed, unstable operating speed, inability to stop the motor, and unresponsive buttons are all manifestations of interference affecting the frequency converter. 3.2 The general approach to handling the third type of grounding interference problem is to ensure good grounding. The general requirements for the grounding terminal are: the grounding terminal should be grounded using the "third method" (separate grounding); the grounding wire should be as short as possible and must be well grounded; shielded wires should be used for the control return line, with the far end of the shielding layer suspended and the near end grounded; wiring should be done reasonably according to product requirements, separating high-voltage and low-voltage wires and maintaining a certain distance; avoid parallel wiring of the frequency converter's power lines and signal lines, and instead, distribute the wiring; add anti-wireless interference filters, frequency converter input and output anti-interference filters or reactors; take shielding measures to prevent electromagnetic induction, and even shield the frequency converter with a metal box; appropriately reduce the carrier frequency; if using communication functions, use twisted-pair cable for RS-485 communication lines. Below, I will provide specific analyses of different interference situations in actual use. 3.3 In a three-phase five-wire power supply, a situation was encountered where the frequency converter was running continuously, and pressing the stop button had no effect. Inspection revealed that the frequency converter's ground wire was only connected to the transformer's neutral wire, while the transformer's neutral wire was not connected to the earth. Grounding the transformer's neutral wire restored normal operation of the frequency converter. The ground wire and neutral wire are strictly separated; the neutral wire in the distribution cabinet has a dedicated terminal, and the ground wire has a dedicated grounding screw. Because this user had three phase wires and one neutral wire coming from the transformer, and only connected the neutral wire to the "N" terminal, while the ground wire was not connected, even though the control wire used shielded wire and the shielding layer was connected to the grounding screw, it was not connected to the earth and therefore did not provide shielding. This caused the frequency converter to malfunction due to interference, and the motor could not be stopped. Connecting the neutral wire and ground wire in the distribution cabinet restored normal operation. Alternatively, the ground wire in the distribution cabinet can be directly connected to the earth. Many users connect the ground wire to the neutral wire, but this method has drawbacks. If the neutral wire is disconnected, starting a certain action of the machine tool may cause the machine tool to become electrified, posing a safety threat to personnel. This interference belongs to the type of interference of the frequency converter itself. 3.4 Case of interference of external equipment to frequency converter (1) Phenomenon The motor occasionally fails to stop. After inspection, the shielding layer is grounded correctly and well. Lowering the carrier frequency has no effect. Adding magnetic ring filters to the input and output sides of the frequency converter has no effect. (2) Analysis The distribution cabinet where the frequency converter is installed is too close to the power distribution room. A large current flows through the distribution cabinet in the distribution room. There is a strong magnetic field around the current, which interferes with the normal operation of the frequency converter. After moving the distribution cabinet away from the distribution room, it returns to normal. This belongs to the interference of external equipment to the frequency converter. 3.5 Case of interference of frequency converter to external equipment (1) Phenomenon After starting the frequency converter, the motor does not move. (2) The inverter is given an external 4-20mA operating frequency. The 4-20mA DC signal is sent by the transmitter. The display shows a frequency of 0.00. The output of the transmitter is measured with an ammeter and no output is found. After connecting a 100μF capacitor in parallel to the output terminal of the transmitter and restarting, the equipment returns to normal, indicating that the signal source is interfered with. In engineering practice, a simple parallel capacitor on the signal line is a frequently effective and practical method to solve major problems. This is an example of the inverter interfering with external equipment. 4 Conclusion With the rapid development of industrial automation, the use of inverters is becoming more and more common. In addition, many inverter interference problems will be encountered. Many end users often do not know how to solve this problem. It is hoped that this article can provide them with some help.