Experience with first smart, autonomous LV-grids in Germany

Abstract

The ongoing shift towards a more decentralized and renewable energy system in Germany requires extensive modifications to existing grids and their operating principlesespecially at the distribution level. Furthermore, the integration of e-mobility will have a significant effect on distribution grids. Smart distribution systems are one way of handling these new supply scenarios. Hence, a self-sustaining monitoring and control system for LV-grids has been developed. It monitors the power flow situation and is able to control the grid if necessary. The system has been implemented in four LV-grids in Germany. The present paper describes the automation system and our initial experience with this smart grid approach.

LV-grid automation system — A technology review

“…A decentralized system for LV-grid automation has been developed and tested in several LV-grids within Germany [1], [2]. The concept of the system is shown in Fig.…”

“…Power flow calculation for LV-grids with a sparse sensor environment is a new challenge involving online monitoring of the grid state with scarce measurement data, resulting in an under-determined system of equations. Moreover, power flows at the LV-level cannot be assumed to be symmetric like at MV-level and above but are asymmetric and require phaseselective treatment [2].…”

“…nodal voltages and branch currents for each phase within the entire LV-grid. The algorithm consists of two main components [2]: -a power flow algorithm, adapted and optimized for phase-selective calculation of power flows in LVgrids considering possibly asymmetric system load -a predictive algorithm for estimating loads and feedins based on sparse measurement data to compensate for the lack of information caused by the sparse sensor environment…”

“…The calculation is executed consecutively for each element of the topology catalogue. The facultative elements of the grid's measurement topology do not enter into these calculationsthey are preserved for the next step of the technique [2]. Now, after a unique grid state estimate has been attributed to all elements of the topology catalogue, the deviation of the preserved facultative measurements from the values provided by the estimated grid state is calculated and stored in an error vector for each element of the topology catalogue [7].…”

“…Two different control strategies have been developed based on the 3-stage model [2]. In contrast to other approaches, the control process is solely performed by the LV-grid MCS within the secondary substation [11].…”