Because the inverter section of a frequency converter generates SPWM control signals of a certain width and polarity through high-speed semiconductor switches, these pulse signals with sharp edges generate strong electromagnetic interference, especially the output current. These signals propagate their energy in various ways, interfering with the circuitry and equipment. Therefore, suppression measures must be taken. Grounding With the gradual expansion of the application range of frequency converters, using them to drive motors enables automatic control and significant energy savings, leading to their widespread use in industrial production. The heating center has installed over 80 frequency converters on equipment such as fans and pumps, with a total installed capacity of 2800kW. With the expansion of frequency converter applications, interference problems caused by incorrect or poor grounding frequently occur during installation, commissioning, and operation. First, it is essential to distinguish between "safety grounding" and "electromagnetic interference grounding," especially in the high-frequency region. Due to the skin effect, the junction exhibits high resistance, causing poor grounding and increasing the system's external radiation. Therefore, very low high-frequency impedance is required for electromagnetic interference grounding. When operating, the following should be noted: (1) When using the casing as a common ground, the paint or rust at the connection point needs to be removed to ensure reliable low-resistance connection. When we were installing and debugging an ABB (ACS501) frequency converter, the motor made an abnormal whistling sound when the frequency increased (automatic control), and the speed increase was very slow. The time required for this frequency converter to rise from 0Hz to 50Hz was set to 155, while the time required to rise from 0Hz to 40Hz was 1225. When the frequency rose to 41Hz, the frequency converter suddenly stopped, and when it was restarted, the above phenomenon was repeated. At a frequency of 40Hz, the voltage of the frequency converter terminal (UZvZWZ) was measured to be 702V with a multimeter, and the voltage of the main power supply terminal was measured to be 380V (UI vlWl). It was initially judged to be an electromagnetic interference fault. The grounding wire was reconnected (the paint on the casing was removed), and the two ends of the motor cable shielding layer were connected to the PE terminals of the frequency converter and the motor end, respectively. The frequency converter worked normally. If the above methods still cannot eliminate the fault, consider connecting a reactor in series in the motor cable to reduce the electromagnetic radiation interference generated in the motor cable. However, these reactors may reduce the motor terminal voltage and maximum torque. (2) Connect different grounding points together with short flat wires as much as possible. When the inverter and other equipment or multiple inverters are grounded together, each equipment is connected to the ground separately, as shown in Figure 1. It is not allowed for the grounding terminal of one equipment to be connected to the grounding terminal of another equipment before grounding, as shown in Figure 2. In any case, when the inverter is in operation, the electrical instruments around it display abnormal data. Gradually bring a working radio closer to the inverter. The radio emits noise. The closer you get to the inverter, the more you can hear howling. This indicates that the inverter is interfering with the surrounding electrical instruments. First, check the electromagnetic interference grounding. Then, install the line anti-interference filter as shown in Figure 3 at the power input and output terminals. The fault is eliminated. The line anti-interference filter is actually a coil with the smallest inductance. In practical applications, simply connect each phase to the same magnetic core and wind it four times in the same direction (incoming lines). The inductor coil between the inverter output and the motor is wound in the same way. The basic principle is that when the three-phase incoming lines pass through the magnetic core together, the resultant magnetic flux of the fundamental current component is zero, thus having no effect on the fundamental current component. However, the resultant magnetic flux of the harmonic components is not zero, thus weakening the harmonic components. When wiring, it is important to ensure that the casing, cable shielding, and motor casing are connected together. The inverter is installed inside the casing . Installing the inverter inside the casing shields the AC speed control system from radiating energy and prevents external electromagnetic waves from entering the system. When debugging an inverter, the surrounding electrical instruments displayed abnormal data. Gradually bringing a working radio closer to the inverter produced static; the closer one got to the inverter, the more a whistling sound one could hear. This indicates that the inverter was interfering with the surrounding electrical instruments. First, the electromagnetic interference grounding was checked, and then a line anti-interference filter as shown in Figure 3 was installed at the power input and output terminals, eliminating the fault. The line anti-interference filter is essentially a coil with the smallest inductance. In practice, it is only necessary to connect each phase to the same magnetic core and wind it four times in the same direction (input line). The inductor coil between the inverter output and the motor is wound in the same way. Its basic principle is: when the three-phase input lines pass through the magnetic core together, the combined magnetic flux of the fundamental current component is zero, so it has no effect on the fundamental current component. However, the combined magnetic flux of the harmonic components is not zero, thus it can weaken the harmonic components. Wiring of the control circuit : Grounding wires should not form closed loops; the grounding terminals of all equipment must be connected to the common grounding busbar. Analog control lines mainly include the input side's given signal line and feedback signal line, which can accept 0-10V voltage signals or 0-20mA current signals, and the output side's frequency signal line and current signal line. Analog signals have low anti-interference capability, therefore shielded wires must be used. The end of the shielding layer closest to the inverter should be connected to the common terminal (COM) of the control circuit, not to the inverter's ground terminal (E) or earth. The other end of the shielding layer should be left floating. Cable Installation Installing the inverter inside the casing shields it from the energy radiated outwards by the AC speed control system and prevents external electromagnetic waves from entering the system. When commissioning an inverter's input and output modules, the power cables should not run parallel to other cables to avoid interfering with control signals. Control lines should be separated from power lines and motor lines, with a minimum distance of 300mm between them.