Investigation of an Easy-Structured and Cost-Effective Energy-Storage System in the DC-Bus

This paper presents a new approach of an energy-storage technique for feedback-energy of drive-systems. A well known state of the art technology for high-power application, is to feed the energy back into the grid using a three-phase full-bridge. However, for smaller drive-systems this is not feasible due to cost and efficiency reasons. Here it is more advantageous to store the fed-back energy directly in the DC-bus. The simplest approach of storing energy directly in the capacitor of the rectifier is limited due to capacitance and voltage issues. Using additional large storage capacitors, like ultra-capacitors, directly in the DC-bus is limited by their voltage ratings. Therefore, a prior and bidirectional DC/DC-conversion is required, which has also disadvantages in terms of costs and efficiency. The new approach presented in this paper allows storage capacitors to be operated directly in the DC-bus without prior DC/DC-conversion, which reduces costs, increases the efficiency, and results in an optimal cost-benefit ratio. The principal function of this new current-source based energy-storage is shown by a detailed description of the topology, its modeling, and an evaluation using simulations and measurements. It turns out that the disclosed new approach is a promising alternative to the prior DC/DC-conversion.