Case study: variable-voltage DC bus with energy recovery system for industrial plants

Abstract

Direct current (DC) buses and microgrids have drawn significant attention owing to the simple integration of distinct sources and energy storage systems. However, most research efforts refer to the use of DC buses for residential, datacenter, and telecommunications applications rather than manufacturing industry, where processes are controlled by alternating current (AC) motor drivers. This work proposes a novel approach of a DC bus used as primary power supply in manufacturing industrial plants for replacing the traditional AC bus. Unlike most applications, the DC bus voltage presents a variable magnitude and allows energy recovery aiming to improve energy efficiency. This arrangement employs a capacitor bank directly to the DC bus, which is responsible for storing the energy that, otherwise, would be lost during the motor braking. Simulation in PSIM software and experimental results on an industrial plant involving a real polyvinyl chloride (PVC) injection machine supplied directly by the DC bus, in which the voltage varies between 535 V and 600 V, are presented and discussed to validate the proposed approach. The obtained results show that the DC bus does not require a rigid control of the voltage magnitude, thus allowing a reduction of up to 5.05% in energy consumption.