Comparative Efficiency Analysis in Recuperative Electrical Drives: A Study of LVDC vs. LVAC - Power Supply

Electric drives account for a significant portion of the world's demand for electrical energy. The use of direct current (DC) machines or frequency-controlled operation of alternating current (AC) machines, which require rectification, can result in substantial material and operating energy savings, leading to reduced costs and CO2 emissions. Novel DC grids enable the use of braking energy, efficient integration of renewables and storage systems, and connection of additional grid participants. This eliminates many material- and energy-intensive conversion processes compared to conventional AC supply. To quantify these savings for electric drives, a prototype of a servo drive controller with a connected linear axis on a developed test bench was measured and analyzed. Then an efficiency comparison between AC and DC power supplies was conducted with over 240 measurements. Adjustable influencing parameters were the operating mode according to IEC 60034-1, the installation angle of the axis, the mass of the transported load as well as the accelerations and speeds. The comparison was conducted with a full factorial design of experiments, the results statistically evaluated, and critically reflected. By using the braking energy in DC operation and eliminating the rectifier stage, the energy consumption of the drive controller was reduced by 12-25 % compared to AC supply. In addition, the unfavourable design ratio results in high reactive power in AC operation. The study demonstrates the great potential for DC grids, which are currently still a rarity. Due to the lack of experience with DC grids, a second part of this publication series analyses international standards and proposes two different protection concepts for the safe and regulation-compliant integration of drives into the DC grid, that the practical commissioning of the concept is possible. In order to complete the efficiency comparison of the motor controller between AC and DC operation, the losses of the switching devices required for grid integration were also measured and the losses compared with established protection concepts for AC operation. In summary, this study analyses the potential of DC grids using the case of electric drives. It provides recommendations for engineers on designing energy-efficient power supplies.