Scalable and robust low voltage direct current distribution (lvdc) networks require solutions allowing flexible power flow control and reliable short-circuit protection. In this paper, the continuous full-order large and small signal models of a partially rated power flow control converter (PFCC) are derived utilizing the generalized averaging method. The large signal model of the PFCC is coupled with a model of the lvdc grid. Due to the state-space representation the combined model of the PFCC and the lvdc grid is suitable for easy algorithmization, and efficient simulation. These advantages make them essential tools for studying and optimizing of scalable lvdc systems with decentralized power flow control based on the PFCC. The PFCC models provide insights into controller design and stability analysis. The models are experimentally validated, and the functionality of the PFCC is demonstrated in a laboratoryscale microgrid.
Multi-active bridge converters (MAB) have become a widely-researched candidate for the integration of multiple renewable sources, storage and loads for a variety of applications, from robust smart grids to more-electric aircraft. Connecting multiple dc ports reduces power conversion stress, improves efficiency, reduces material billing and increases power density. However, the power flows between the ports of a MAB converter are magnetically coupled via the high-frequency (HF) transformer, making it difficult to control. This paper presents a MAB converter configuration with a rigid voltage source on the magnetizing inductance of the transformer resulting in inherently decoupled power flows. As a result, the configuration allows independent power flow control tuning of the rest of the ports. The theory behind the power flow decoupling of the proposed MAB configuration is analyzed in detail using a reduced-order model. A 2-kW, 100 kHz Si-C based four-port MAB converter laboratory prototype is built and tested, showing completely decoupled control loops with fast transient response regardless of their control bandwidths. The proposed configuration therefore makes the operation and design of the MAB family of converters much more feasible for any number of ports and precludes the need for a high-performance dynamic decoupling controller.Index Terms-DC-DC converter, decoupled power flow management, multi-active-bridge converter, multiwinding transformer.
Triple active bridge (TAB) as an isolated multi-port converter is a promising integrated energy system for smart grids or electric vehicles. This paper aims to derive and analyse zero voltage switching (ZVS) regions of TAB, in which both switching losses are reduced, and EMI issues are mitigated. In the proposed closed-form solution of ZVS criteria, parameters such as the parasitic capacitance of the switches, the leakage inductance of the transformer, the switching frequency, the port voltage, the phase-shift inside and between the full-bridges are all taken into account. The analysis shows how the five degrees of freedom can be used to maintain ZVS operation in various operating points. The analysis and derived closed-form ZVS criteria are experimentally verified using a laboratory prototype. The derived analytical ZVS criteria are a powerful tool to study and optimise the operation of TAB converters.
Solid-state circuit breakers (SSCB) show great promise to become the key element in the protection of low-voltage direct current microgrids. SSCBs operate in the microsecond range and employ semi-conductor devices that have strict safe operation area limits. Therefore, the design of the SSCB needs to consider the effects of fault detection delays and semi-conductor safe operation area limitations. This paper derives SSCB design criteria that consider the effect of different detection methods with different detection delays under varying system constraints. The design space is investigated in a sensitivity analysis, which provides insights into the operation boundaries of SSCB and explains how a combination of fault detection methods can reduce the SSCB size. The insights from the theoretical and sensitivity analysis are used to propose an SSCB design flowchart. SSCB prototype is developed and tested in different scenarios under nominal grid voltage and current. The derived design constraints can be used for efficient SSCB design and also to evaluate the effects of different protection schemes on the required SSCB size.
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