The objective of this study was to develop a reduce-dorder small-signal model of a microgrid system capable of operating in both the grid-tied and the islanded conditions. The nonlinear equations of the proposed system were derived in the dq reference frame and then linearized around stable operating points to construct a small-signal model. The high-order state matrix was then reduced using the singular perturbation technique. The dynamic equations were divided into two groups based on the small-signal model parameters ε. The “slow” states, which dominated the system's dynamics, were preserved, whereas the “fast” states were eliminated. Step responses of the model were compared to the experimental results from a hardware test to assess their accuracy and similarity to the full-order system. The proposed reduced-order model was applied to a modified IEEE-37 bus grid-tied microgrid system to evaluate system's dynamic response in grid-tied mode, islanded mode, and transition from grid-tied to islanded mode.

Healthcare facilities in the United States account for 4.8% of the total area in the commercial sector and are responsible for 10.3% of total energy consumption in this sector. The number of healthcare facilities increased by 22% since 2003, leading to a 21% rise in energy consumption and an 8% reduction in energy intensity per unit of area (544.8 kWh/m²). This study provides an analytical overview of the end-use energy consumption data in healthcare systems for hospitals in the United States. The energy intensity of the U.S. hospitals ranges from 640.7 kWh/m² in Zone 5 (very hot) to 781.1 kWh/m² in Zone 1 (very cold), with an average of 738.5 kWh/m². This is approximately 2.6 times higher than that of other commercial buildings. High energy intensity in the healthcare facilities, particularly in hospitals, along with energy costs and associated environmental concerns make energy analysis crucial for this type of facility. The proposed analysis shows that U.S. healthcare facilities have higher energy intensity than those of most other countries, especially the European ones. This necessitates the adoption of more energy-efficient approaches to the infrastructure and the management of healthcare facilities in the United States.

This paper introduces a novel approach for dynamically detecting the lowest speed threshold at which regenerative braking is effective in Electric Vehicles (EVs). The control approach is based on real-time sensing of the motor controller DC link current and disabling regenerative braking when current changes direction while the motor is operating as a generator. Various factors influencing regenerative braking capability of EVs at low speed are discussed and simulation studies are carried out to illustrate the effect of each factor on the displacement of the low-speed threshold. Based on the results obtained from the simulation studies, a dynamic Low-Speed Cutoff Point (LSCP) detection method is proposed. This method requires no hardware modification to the vehicle braking architecture and can be implemented solely by modifying the brake controller. The proposed method is tested on an experimental EV test platform for a predetermined drive cycle. It is shown that in comparison to considering a constant low-speed threshold during braking, the amount of energy recaptured through the regenerative braking process can be improved by taking advantage of the proposed method.

An improved Delayed-Signal-Cancellation (DSC) phase-locked loop (PLL) is proposed for microgrid applications. The conventional DSC-PLL suffers from phase and frequency measurement errors due to a fixed delay operation within the control loop. The source of this error is mathematically analyzed in this work. The modified DSC-PLL model overcomes the error by using a positive sequence $\alpha\beta$ detector and a notch filter. The proposed method not only rejects the double frequency oscillation appearing at the output of the PLL under unbalanced loading conditions but also offers good harmonic rejection with nonlinear loads. The proposed model adds minimal complexity to the existing DSC-PLL. To ensure a fast dynamic response as well as a stable operation, a systematic approach is proposed to design the controller gains and filter parameters. The newly designed PLL is simulated and tested for performance verification purposes.

As colleges prepare or revise their power engineering courses to include discussions on the smart grid, the microgrid, distributed energy sources and renewable energy resources, the need for new material suitable for inclusion in a typical 4-year undergraduate engineering course has never been more obvious. Toward this effort, an old machines lab was remodelled and converted into a small power network that can be operated in both grid-connected and grid-islanded microgrid modes. The intent of this paper is to devise laboratory experiments to supplement a course in conventional power systems analysis at the undergraduate level. During the remodeling process, two of six synchronous machines in the lab were converted to represent distributed generating units within a laboratory-based microgrid. The use of electromechanical distributed generators (EDG) with a low start-up time allows the system to operate as a conventional power network with provisions for frequency and voltage variations. Students can experiment with voltage control and power sharing between the EDGs in islanded mode. A Laboratory Grid Central Controller (LGCC) was developed in LabVIEW® to coordinate the operation of the EDGs, the utility grid and the loads. Its functions are similar to those of a central dispatch office, albeit on a much smaller scale. A one credit hour lab course held on this laboratory was offered for the first time during the Fall semester of 2012 at Missouri S&T.