Investigation on an AC Grid Failure Handling of Industrial DC Microgrids with an Energy Storage

Abstract

A new approach for more energy efficient industrial production processes are smart industrial direct current (DC) microgrids with one or more connections to the alternative current (AC) grid. The advantage of the DC-technology is an easier integration of renewable energies sources and energy storage systems (ESS). Different applications for ESS are possible, for instance an uninterruptible power supply (UPS) for a DC microgrid. Within this paper, a new handling concept for a mains supply failure (e.g. a blackout of the supplying AC grid) with a droop curve control is introduced. In this approach, the droop curve controlling the ESS is adapted, depending on the ESS' state of charge (SoC), which results in a droop curve with a hysteresis. This concept realizes the charging of the ESS only with recuperation energy, that occurs in the DC microgrid during the production process. Thus, all recuperation energy will be kept in the DC microgrid and a transformation of the energy in AC or an energy loss through braking resistors will be avoided. Furthermore, no additional energy is needed to charge the ESS. This increases the energy efficiency of the entire production process. The concept was verified in simulation and validated in experiment and it has shown a DC voltage deviation of less than two percent.

Load Profile Cycle Recognition for Industrial DC Microgrids with Energy Storage Systems

“…For model validation, a DC microgrid test rig (Fig. 7) was set up which has already been used in [29]- [32]. The test rig contains mains supply (sup) with adaptive droop curve control which is the main supplier to the DC microgrid.…”

“…In this work the DC microgrid model, based on [29] and [30], is simplified to an electric network with one capacity C DC between the DC terminals. If we neglect the transmission line impedances, the sum of the participants' currents i n of the DC microgrid are equal to zero.…”

Decentralized Cost-Optimized Fuzzy Control of DC Microgrids

“…The model was validated in [1] with the test setup described in [11]. The error between simulated and measured rectifier power for a 15 minute measurement is less than 4.5 %.…”

“…5 results. Optically the characteristics differ the droop curves, which were created according to [11], conventionally generated voltage droop curves. due to the decreasing of the gradient at ± 80 %, as well as the smaller plateaus in the battery curve.…”

“…. Droop curves for active grid users resulting from defuzzification in blue and in orange according to[11] conventionally generated voltage droop curves.…”