Current Harmonics Generated by Multiple Adjustable Speed Drives in Distribution Networks in the Frequency Range of 2-9 kHz

Adjustable-speed drives (ASDs) generate current harmonics due to their nonlinear characteristic and switching function. These current harmonics could pass through a network and deteriorate the power quality, create resonances, and increase network power loss. Higher order 2-9 kHz harmonics, among them, have become a new challenge for drive manufacturers, as these harmonics will be covered in the forthcoming IEC standards (standardization committee SC77A). To address the existing gaps, this article explores 2-9 kHz current harmonics for a common ASD type that has a diode-bridge rectifier (DR) and a dc-link filter. Through the analytical study and experimental results presented in this article, it is shown that the main source of 2-9 kHz current harmonics at the grid side of this type of ASD is its front-end DR. Moreover, it is found out that the amplitude of these current harmonics can be significantly affected by the operation power of the other ASDs in the network. Furthermore, it is analyzed that these interactions increase the 2-9 kHz current harmonics at an ASD when the other ASDs operate at different load values.