Abstract: According to IEC18003, many power drive systems (PDS) can operate normally in industrial environments without interference to other electrical appliances and equipment without filters. Filters that reduce interference emissions from PDS also reduce the efficiency of PDS and increase the size and cost of the device.
From an electromagnetic compatibility (EMC) perspective, incoming line filters and radio frequency filters require that any electrical equipment be able to withstand external electromagnetic interference with a certain level of immunity, while also avoiding emitting interference to other electrical equipment and causing electrical pollution. Inverters are no exception. Interference frequencies can be divided into low-frequency and high-frequency, with the dividing line defined as 9kHz in the IEC 1800 standard (some standards define it as 10kHz). In addition, there are broad-spectrum interferences such as air discharge and contact discharge. Here, we are referring to high-frequency interference, specifically radio frequency (RF).
According to IEC 18003, many power drive systems (PDS) operate normally in industrial environments without interference to other electrical appliances and equipment, even without filters. Filters that reduce PDS interference emissions also reduce PDS efficiency and increase device size and cost. In most cases, there is no interference when using the device (PDS), but for radio frequency receivers or sensitive electrical appliances (such as those used for very low voltage measurements), methods to reduce interference (such as high-frequency filtering) need to be considered. Few measurements indicate radiation emissions because there have been no complaints in this regard. Therefore, practice shows that installing filters to reduce high-frequency interference conducted through the power supply is unnecessary in most industrial environments. However, in residential building environments (with numerous radios, televisions, etc.), the installation of radio frequency filters should be considered, in addition to the higher EMC standards for frequency converters.
According to IEC standards, manufacturers should provide the harmonic content of the inverter's input current. Integrating a built-in input reactor into the inverter assembly is a suitable way to reduce harmonics. Several manufacturers, such as ABB, Schneider Electric, and VassaControl of Finland, already offer such products. It is hoped that other manufacturers will follow suit and gradually promote this approach.
Centralized installation of harmonic filters and reactive power compensation devices on low-voltage busbars, where frequency converters are widely used, is a complex and labor-intensive engineering problem, incurring significant costs and occupying considerable space. In contrast, built-in reactors within the frequency converter are simple and easy to implement, suppressing harmonics locally and preventing dissipation. Besides harmonic suppression, they offer other benefits, making them a worthwhile and widely promoted solution. When the power of the transformer and the frequency converter are comparable, the transformer already has a 4% short-circuit impedance, eliminating the need for additional line reactors in the frequency converter. Therefore, when the frequency converter power is high, whether the reactor is built-in or external, its reactance value should be tiered, such as 3%, 2%, 1%, etc., to accommodate different transformer impedances and reduce the size and cost of the equipment.
