Abstract
The new concept of integrating electric springs (ESs) and multi-port transformers (MTPs) as an active solution for energy management in alternating current (AC) microgrids is proposed. With an ES located at the port where storage devices previously were, the so-called critical flux is regulated to a constant value within the core of the transformer. The voltage on each winding is then clamped so that critical load (CL) voltage is regulated to a predefined value. The integration of ESs and MPTs can ensure a safer environment for ES utilization. Thus, the power generated by renewable energy sources can be safely used at residential locations with no need to worry about voltage fluctuations across CLs. Moreover, users can sell electricity to the power companies considered as CLs when the electricity generation of the AC microgrids or the home-installed renewable energy resources exceeds the personal consumption. In the paper, isolated topologies for ESs with three- and four-port transformers are examined, and a theoretical analysis of the ES operation is carried out. Then, equivalent circuits of the isolated ES topologies have been derived. Analysis of the ES operation and effectiveness of the isolated ES topologies are validated by both simulations and experiments.
Highlights
alternating current (AC) microgrids with renewable energy sources (RESs) are becoming more and more popular all over the world; they may contain various energy sources, such as wind and solar, and loads along with batteries for the energy storage [1]
Switch S1 is of bypass type: when open, smart loads (SLs) is line voltage is subjected to changes, especially if the line is fed by power sources like RESs that exhibit activated; when closed, SL is deactivated and capacitor C is shortened to prevent possible oscillating uncontrolled variations in their output voltage
The concept of integrating electric springs (ESs) and multi-port transformers (MPTs) has been proposed as an effective solution to comply with the voltage requirements of critical load (CL) when supplied by AC microgrids with prevalent RES power generation and, at the same time, to extend the applicative potentials of the original ES equipment
Summary
AC microgrids with renewable energy sources (RESs) are becoming more and more popular all over the world; they may contain various energy sources, such as wind and solar, and loads along with batteries for the energy storage [1]. A fully isolated ES greatly extends the applications of the ES equipment because of its many features, documented later on, like the voltage magnitude stabilization of more CLs operating at different voltage levels and the opportunity for the users to sell high-quality electricity to the power companies when the electricity generation of the AC microgrids or the home-installed RESs exceed the personal consumption For this reason, the concept of fully isolated ES can be regarded as the fourth version (ES-4) of ESs. Compared to MPCs, the fully isolated ESs enjoy the known ES merits, namely they need only one converter and eliminate any charging-discharging process of the DC source feeding ES when operated in reactive power compensation mode. Throughout the paper the time-variable quantities are denoted with lower case letters, the DC and rms quantities with upper case letters and the vector quantities with upper case letters topped by an arrow
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