Abstract
Solid State Transformers (SST) may become, in the near future, key technological enablers for decentralized energy supply systems. They have the potential to unleash new technologies and operation strategies of microgrids and prosumers to move faster towards a low carbon-based economy. This work proposes a paradigm change in the hierarchically and distributed operated power systems where SSTs are used to asynchronously connect the many small low voltage (LV) distribution networks, such as clusters of prosumers or LV microgrids, to the bulk power system. The need for asynchronously coupled microgrids requires a design that allows the LV system to operate independently from the bulk grid and to rely on its own control systems. The purpose of this new approach is to achieve immune and resilient by design configurations that allow maximizing the integration of Local Renewable Energy Resources (L-RES). The paper analyses from the stability point of view, through simplified numerical simulations, the way in which SST-interconnected microgrids can become immune to disturbances that occur in the bulk power system and how sudden changes in the microgrid can damp out at the Point of Common Coupling (PCC), thus achieving better reliability and predictability in both systems and enabling strong and healthy distributed energy storage systems (DESSs). Moreover, it is shown that in a fully inverter-based microgrid there is no need for mechanical or synthetic inertia to stabilize the microgrid during power unbalances. This happens because the electrostatic energy stored in the capacitors connected behind the SST inverter can be used for a brief time interval, until automation is activated to address the power unbalance for a longer term.
Highlights
BackgroundToday the power systems operate under the paradigm of bulk networks, synchronously interconnected over wide areas, where a disturbance thatEnergies 2018, 11, 3377; doi:10.3390/en11123377 www.mdpi.com/journal/energiesEnergies 2018, 11, 3377 occurs at the highest voltage level can be experienced down to the low voltage level
Analyzing the AC currents injected by the Solid State Transformers (SST), we can see that there is only a slight change in the amplitude of the load currents, which shows that in the case of a grid outage, the microgrid is capable of maintaining its normal operation and to ensure the power balancing without any need for load shedding
The paper proposes an analysis, from the point of view of stability, of microgrid operation in the case of grid-connection via SST, which can be seen as an essential enabler of microgrids-by-design
Summary
Today the power systems operate under the paradigm of bulk networks, synchronously interconnected over wide areas (e.g., the continental zone of ENTSO-E), where a disturbance that. The key vision of the paper is that the SST allows an asynchronous interconnection between the bulk power system and the many small low voltage (LV) distribution networks This enables implementing local optimization strategies of the energy supply service while meeting the requirements for relying more and more on clean energy production at the local level.
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