A Precise Model of DC-Link Current in Adjustable Speed Drives for the Harmonic Analysis of Electrical Networks

Abstract

Adjustable Speed Drives (ASDs) deteriorate the power quality in distribution networks by increasing the harmonic distortions. These harmonics can also cause serious electromagnetic interference-related issues in the network, as they have a high value above 2 kHz. To prevent these issues, the harmonics above 2 kHz have been considered in recent decades by different standardization committees. Therefore, manufacturers seek precise models to analyze ASD harmonics for complying with the forthcoming standards, and network operators need analytical models to estimate these harmonics in networks that include multiple ASDs. In this paper, a new mathematical model is developed for estimating the inverter-side current harmonics that flow through the DC-link in an ASD. The proposed model is found by considering a precise model of voltage ripples across DC-link for calculating the current harmonics at the load side of the ASD. Then, a mathematical approach is used to find the current harmonics that pass through DC-link according to the load side currents. This model demonstrates a higher accuracy to find an ASD’s harmonics over the existing methods due to modeling the effects of voltage ripple across DC-link and the load-side harmonics. The proposed model and the conclusions from the analysis are validated by experimental and simulation results.

Keywords

• Adjustable speed drives
• distribution networks
• harmonic estimation
• power quality
• supraharmonics
• 2–9 kHz current harmonics