Control of solid-state transformer-enabled DC microgrids
With the world-wide energy shortage and deterioration of existing power grid, microgrid becomes one of the hottest research directions in the power engineering area. Considering DC nature of many key components in the smart grid, such as photovoltaic (PV), battery, fuel cell, super capacitor, etc., as well as many DC type loads, such as light-emitting diode, DC microgrid has received more attention recently since it brings the opportunity for boosting the efficiency by eliminating the unnecessary power conversion stages. However, the existing DC microgrid can only interface with the distribution system by using a heavy and bulky passive line frequency transformer plus a rectifier, which has large space and heavy weight. Developing a more compact and active grid interface to enable an intelligent DC microgrid system is still a research focus. In this chapter, the solid-state transformer (SST)-enabled DC microgrid is presented. In addition, two system control strategies, namely, the centralized power management and hierarchical power management strategies, are proposed. In addition, an improved control strategy is proposed for increasing the penetration of distributed renewable energy resources (DRER) integration, which controls SST-enabled DC microgrid as a solid-state synchronous machine (SSSM). With the proposed control concept, frequency and voltage stability are improved in case of high-power intermittence at either DC load or DRER side. Design examples are given to illustrate the main characteristics of the presented system and control schemes.
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