Abstract
The conventional bidirectional DC-DC converter (BDC), which employs a half-bridge configuration, has some major disadvantages, including a controller designed for one direction with poor performance in the other direction, a bidirectional operation which does not have symmetrical voltage gain resulting in asymmetrical operation, and step-up and step-down switches that are simultaneously modulated, thereby increasing switching losses. To overcome these drawbacks, this paper proposes a new, nonisolated, DC-DC converter for the bidirectional power flow of battery energy storage applications in DC and hybrid microgrids (HMGs). The proposed converter uses two back-to-back Boost converters with two battery voltage levels, which eliminates step-down operation to obtain symmetric gains and dynamics in both directions. In discharge mode, two battery sections are in parallel connection at a voltage level lower than the grid voltage. In charge mode, two battery sections are in series connection at a voltage level higher than the grid voltage. Simulations demonstrate the efficacy of the proposed converter in the MATALB\Simulink environment. The results show that the proposed converter has promising performance compared to that of the conventional type. Moreover, the novel converter adds no complexity to the control system and does not incur considerable power loss or capital cost.
Highlights
The popularity of DC microgrids and their operation along with AC microgrids is increasing due to the elevated level of DC power renewable generations and ubiquitous DC loads
Case I—Grid-connected Hybrid microgrids (HMGs): In this state, the DC grid is connected to the main grid through a grid-following interlinking converter (ILC)
This study proposed a novel bidirectional DC-DC converter for energy storage applications in DC microgrid and HMG systems composed of two back-to-back Boost converters in the power stage
Summary
The popularity of DC microgrids and their operation along with AC microgrids is increasing due to the elevated level of DC power renewable generations and ubiquitous DC loads. Hybrid microgrids (HMGs) are evolving from the concept stage to real-world practice, as they combine the functionalities of both AC and DC load/generation systems into a synthetic power distribution system. HMGs, in islanded operation, are prone to instability and power fluctuations due to the intermittent nature of renewable energy sources (RES) and the stochastic behavior of the loads. Converter-interfaced battery energy storage systems (BESS) [4] are well demonstrated to be the most reliable, technically suitable, and economically available solutions to manage voltage/frequency deviations and to enhance the dynamic performance of microgrids [5]. In an HMG, the DC side BESS is connected to the grid through a bidirectional DC-DC converter (BDC) to control grid voltage or power. The converter is driven to exchange energy between the battery bank and grid to control grid voltage or power mismatches due to power under/oversupply.
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