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Building and microgrid designs with highly-distributed electrical storage have potential advantages over today's conventional topologies with centralized storage. This paper studies the capital cost benefits of several residential behind-the-meter distributed-storage topologies, including AC and DC versions of systems with load-packaged batteries and resilient sub-networks. The study begins by defining the block configuration of each topology. This work then develops a model for the cost of the power electronics necessary to interface with the storage elements. Finally, the analysis develops a model for the total cost of each storage topology, incorporating the installation and soft costs. The results suggest that while the cost of power electronics is lower in centralized topologies, the total cost is lower for distributed storage due to the avoided costs of installation and permitting. This paper also explores the benefits of load-packaged batteries for savings in electrical infrastructure.

LEDs have finally emerged as the dominant lighting technology. As such, the lighting industry values power converters that have high efficiency, unity power factor, minimal flicker, dimming, low cost, and a small form factor. This paper presents an integrated circuit (IC) LED driver that is designed to achieve these goals. It introduces multilevel converters with sigma–delta modulation to the power IC space. The driver features a pair of sigma–delta-controlled multilevel converters. The first is a multilevel rectifier responsible for power factor correction and dimming. The second is a bidirectional multilevel inverter used to cancel ac power ripple from the dc bus. The system also contains an output stage that powers the LEDs with dc and provides for galvanic isolation. The IC LED driver has been simulated and prototyped on a silicon fabrication process. Its functional performance indicates that integrated multilevel converters are a viable topology for lighting or other similar applications.

Today’s selection of DC buildings features a diverse set of electrical topologies and turnkey solutions, and each has specific design trade-offs and optimizations. Designers desperately need standardized metrics and procedures for measurement and verification (M&V) to analyze and compare the advantages of each DC solution to traditional AC building networks. This work develops the Measurement-Informed Modeling (MIM) method, which can be used to determine full-building efficiency and energy savings. The MIM M&V procedure develops a building model, and refines the model with metered data. This work demonstrates the MIM method by measuring the full-building efficiency of two DC buildings operated by the Institute of Building Research in Shenzhen, China. The MIM procedure can ultimately be used to compare and improve the efficiency of various DC topologies.

DC microgrids have become a prevalent topic in research in part due to the expected superior efficiency of DC/DC converters compared to their AC/DC counterparts. Although numerous side-by-side analyses have quantified the efficiency benefits of DC power distribution, these studies all modeled converter loss based on product data that varied in component quality and operating voltage. To establish a fair efficiency comparison, this work derives a formulaic loss model of a DC/DC and an AC/DC PFC boost converter. These converters are modeled with identical components and an equivalent input and output voltage. Simulated designs with real components show AC/DC boost converters between 100 W to 500 W having up to 2.5 times more loss than DC/DC boost converters. Although boost converters represent a fraction of electronics in buildings, these loss models can eventually work toward establishing a comprehensive model-based full-building analysis.

Today's selection of DC microgrid buildings features a diverse set of electrical topologies and turnkey solutions, each with specific design trade-offs and optimizations. Designers desperately need standardized metrics and procedures for measurement and verification (M&V) to analyze and compare the advantages of each DC solution to traditional AC building networks. This work develops M&V procedures for quantifying and comparing the energy efficiency and power quality in buildings. To calculate full-building efficiency, this work introduces the measurement-informed modeling method, a procedure that develops and refines a building's energy model with metered data. To quantify power quality, this work defines a new voltage quality index that applies to both AC and DC buildings. This article describes the equipment, instrumentation, and operation necessary to calculate the efficiency and power quality. It then demonstrates these methods with a set of field tests. These M&V procedures can ultimately be used to compare and improve the efficiency and power quality of various DC topologies.

With distributed generation and battery storage technologies thriving in microgrids, the use of direct current (DC) microgrids in the building sector offers multiple advantages in energy efficiency and power quality compared with alternating current (AC) systems. This study developed a new concept of a loose-coupled bipolar DC building power system. The concept was used to design a real-world office building in Shenzhen, China. A power system model was developed to study the stability and control of the DC power system and to verify DC power quality. The design and modeling of the DC power control system is discussed in detail. The study developed a few common fault scenarios in DC building microgrids that were simulated in the MATLAB-Simulink environment to validate the design of a loose-coupled bipolar DC system. The results indicate that the proposed loose-coupled bipolar DC system schema, when implemented with proper control algorithms, can achieve good fault-tolerant performance with reliable power quality, even during disruptive system events.

Despite the recent interest in direct current (DC) power distribution in buildings, the market for DC-ready loads remains small. The existing DC loads in various products or research test beds are not always designed to efficiently leverage the benefits of DC. This work addresses a pressing need for a study into the development of efficient DC loads. In particular, it focuses on documenting and demonstrating how to best leverage a DC input to eliminate or improve conversion stages in a load’s power converter. This work identifies how typical building loads can benefit from DC input, including bath fans, refrigerators, wall adapters, task lights, and zone lighting. It then details the development of several prototypes that demonstrate efficiency savings with DC. The most efficient direct-DC loads are explicitly designed for DC from the ground up, rather than from an AC modification.

Despite the recent interest in direct current (DC) power distribution in buildings, the market for DC-ready loads remains small. The existing DC loads in various products or research test beds are not always designed to efficiently leverage the benefits of DC. This work addresses a pressing need for a study into the development of efficient DC loads. In particular, it focuses on documenting and demonstrating how to best leverage a DC input to eliminate or improve conversion stages in a load’s power converter. This work identifies how typical building loads can benefit from DC input, including bath fans, refrigerators, task lights, and zone lighting. It then details the development of several prototypes that demonstrate efficiency savings with DC. The most efficient direct-DC loads are explicitly designed for DC from the ground up, rather than from an AC modification.

This paper compares several electrical load models for estimating the efficiency of DC vs. AC distribution in micro-grids. Candidate models include energy balance, harmonic power flow, and time-domain modeling. Model results are compared with numerical studies and validated with experimental measurements. Based on quantitative and qualitative considerations, the most appropriate load modeling approach for larger-scale DC distribution efficiency studies is proposed.

Studies have shown the efficiency benefits of DC distribution systems are largely due to the superior performance of DC/DC converters. Nonetheless, these studies are often based on product data that differs widely in manufacturer and operating voltage. This work develops a rigorous loss model to theoretically compare the efficiency of a DC/DC and an AC/DC PFC boost converter. It ensures each converter has the same components and equivalent operating voltages. The results show AC boost converters below 500 W to have 2.9 to 4.2 times the loss of DC.

Author(s): Meier, Alan; Brown, Richard E; Gerber, Daniel; Khandekar, Aditya; Kloss, Margarita; Koyanagi, Hidemitsu; Liou, Richard; Rainer, Leo; SANDERS, Seth | Abstract: Plug loads are the devices plugged into common electrical outlets. Modern buildings contain hundreds of these devices which, together, are responsible for at least 25 percent of the energy use in California buildings. Energy consumed by plug loads is increasing because the “Internet of Things” is, to a great extent, the “Internet of Plug Loads.” This project developed technologies that will reduce the energy use of plug loads. Two crosscutting strategies were investigated in detail: (1) technologies to reduce standby power use to near zero, and (2) methods to increase the use of direct current (DC) as a power source. Two new approaches to reduce standby to near zero were developed and have potential applicability to a wide range of devices. Prototype DC appliances were developed to demonstrate energy savings by bypassing power supplies and avoiding other losses. Networks of DC-powered devices can save even more energy and provide other benefits, such as resiliency during power outages. A unique category of energy-using devices was identified that provide life safety, health, and security to building occupants. Their installation or use is dictated by building codes, health providers, insurance companies, and other entities—none of whom would ordinarily prioritize energy efficiency. In the case of ground fault circuit interrupts (GFCIs), savings of 80 percent appear possible, simply by adopting the most efficient designs. Home medical equipment, particularly oxygen concentrators, are a rising category of energy use where significant savings are possible. This report also reviews the codes, standards, and other policies that affect energy use of plug loads.

This paper presents a hybrid-switched-capacitor-resonant (HSCR) light-emitting diode (LED) driver based on a stackable switched-capacitor (SC) converter IC rated for 15-20-W applications. Bulky transformers have been replaced with an SC ladder to perform high-efficiency voltage step-down conversion; an LC-resonant output network provides almost lossless current regulation and demonstrates the potential of capacitive galvanic isolation. The integrated SC modules can be stacked in the voltage domain to handle a large range of input voltage ranges that largely exceed the voltage limitation of the medium-voltage-rated 120-V silicon technology. The LED driver demonstrates >91% efficiency over a rectified input dc voltage range from 160 to 180 Vdc with two stacked ICs; using a stack of four ICs >89.6% efficiency is demonstrated over an input range from 320 to 360 Vdc. The LED driver can dim its output power to around 10% of the rated power while maintaining >70% efficiency with a pulsewidth modulation-controlled clock gating circuit.

Improvements in building end-use efficiency have significantly reduced the energy intensity of new buildings, but diminishing returns make it a challenge to build very-low energy buildings cost-effectively. A largely untapped efficiency strategy is to improve the efficiency of power distribution within buildings. Direct current (DC) distribution with modern power electronics has the potential to eliminate much of the power conversion loss in alternating current (AC) building distribution networks that include photovoltaics and DC end uses. Previous literature suggests up to 15% energy savings from DC power distribution in very energy efficient buildings with onsite generation and battery storage. This paper extends prior energy modeling of DC versus AC distribution in buildings, to consider the cost of implementing DC systems on a life-cycle basis. A techno-economic analysis framework based on commercially available products that evaluates the cost-effectiveness of DC systems is presented. The analysis is conducted for three commercial building types in two California climate zones and for various PV and battery storage capacities. Monte Carlo simulation is used to compute the payback period and lifecycle cost savings of DC versus AC distribution systems. A future-market scenario is also examined, which evaluates how future efficiency improvements in power converters and changes in electricity tariffs may affect cost savings. This analysis shows that DC systems can be cost-effective in all scenarios that include large capacities of battery storage and onsite solar, whereas for systems without storage, DC distribution is generally not cost-effective.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. Despite recent efforts to reduce standby power consumption in plug loads, new trends in the miniaturization and wide distribution of electronics necessitates devices with zero standby consumption. This work introduces two zero standby solutions that wake a device using an external input of energy harvested from a 5 mW laser pointer. These solutions are applicable to electronics that are remotely activated or have a fiber optic connection. The first utilizes a cascoded header switch to allow for simultaneous low-voltage harvesting and high-voltage blocking. The second involves the use of a charge pump to boost the harvested voltage to a level appropriate for the gate of a high-voltage switch. Prototypes for each method are developed in order to demonstrate functionality and identify the associated benefits and drawbacks. The results show that combining the two methods allows for optimal activation range (up to 25 m) and component count.

Direct current (DC) power distribution has recently gained traction in buildings research due to the proliferation of on-site electricity generation and battery storage and an increasing prevalence of end uses operating internally on DC. The research discussed in this paper uses Modelica-based simulation to compare the efficiency of DC building power distribution with an equivalent alternating current (AC) distribution. A variety of parametric simulations determine how and when DC distribution proves advantageous. This work shows that using DC distribution can be considerably more efficient than AC: a medium office building using DC distribution has an expected baseline of 11% savings, but may save up to 17%. In these results, the baseline simulation parameters are for a zero net energy (ZNE) building with enough battery storage to act as an islanding microgrid. DC is generally most advantageous in buildings with large solar capacity, large battery capacity, and high voltage DC distribution. In addition, based on the efficiency modeling results, a comparison of the economic performance of DC vs. AC distribution systems in commercial buildings is conducted. The results for the baseline scenario show that DC distribution systems in buildings can be cost effective when PV generation and battery storage are included in the building.

LEDs are rapidly emerging as the dominant light source. As such, the lighting industry values power converters with high efficiency, unity power factor, minimal flicker, dimming, low cost, and small form factor. This paper presents an integrated circuit (IC) LED driver that is designed to achieve these goals. It also introduces multilevel converters with sigma delta modulation to the power IC space. The circuit features a pair of sigma delta controlled multilevel converters. The first is a multilevel rectifier responsible for power factor correction (PFC) and dimming. The second is a multilevel inverter used to cancel AC power ripple from the DC bus. The system also contains an output stage that powers the LEDs with DC and provides for galvanic isolation. The proposed IC LED driver has been simulated and prototyped on a silicon fabrication process. Its functional performance indicates that integrated multilevel converters are a viable topology for lighting and other similar applications.

Despite technical advances in efficiency, devices in standby continue to consume up to 16% of residential electricity. Finding practical, cost-effective reductions is difficult. While the per-unit power consumption has fallen, the number of units continuously drawing power continues to grow. This work reviews a family of technologies that can eliminate standby consumption in many types of electrical plug loads. It also investigates several solutions in detail and develops prototypes. First, burst mode and sleep transistors are established as building blocks for zero-standby solutions. This work then studies the application of two types of wake-up signals. The first is from an optical transmission, and is applicable to remote-controlled devices with a line-of-sight activation, such as set-top boxes, ceiling fans, and motorized curtains. The second is from a wake-up radio, and is applicable to any wireless products. No single technology will address all standby power situations, however, these emerging solutions appear to have broad applicability to save standby energy in miscellaneous plug loads.

The Metacapacitors project aims to improve efficiency, functionality and form factor of offline power converters suitable for LED solid-state lighting, with a view to developing an attractive technology platform for load management and power conversion across a broad range of applications. Based on integrated switched-capacitor (SC) topologies, the project adopts an integrated approach from materials to devices to circuits. We designed capacitors based on high- $\kappa$ dielectric nanocrystals, that can be prepared using high-throughput microfabrication/nanotechnology techniques, ink deposition and multilayering. The capacitor dielectric, a nanocomposite composed of (Ba, Sr)TiO $_{3}$ nanocrystals in polyfurfuryl alcohol (BST/PFA, $\kappa$ $ > 20$ , $100 \text{Hz}$ – $1\ \text{MHz}$ , loss $ , $20\ \text{kHz}$ ), targets a high volumetric capacitance density and ripple current capability. The Dielectric is demonstrated to function in a finished capacitor $ > \! 1000\ \text{h}$ at $125 ^\circ \text{C}$ . The capacitors were board integrated with a custom hybrid-switched-capacitor-resonant dc–dc converter IC. The converter integrates a balanced SC front-end with a series resonant tank, enabling nearly lossless current regulation and tranformerless galvanic isolation. The converter IC can be stacked in the voltage domain to interface a range of inputs. The tested driver delivers about $ 15\;\text{W}$ at $ 470\;\text{mA}$ to a string of $ 12$ LEDs with $ 90\%$ peak efficiency.

A stackable switched-capacitor (SC) converter IC for a hybrid-SC-resonant LED driver using off-chip ceramic capacitors is presented in this paper. The IC can be configured to handle a range of input voltages through chip-stacking in the voltage domain. The tested driver delivers 17.6W at 470mA to the LED load with 90% peak efficiency from a rectified 120VAC line (170VDC) and maintains >85% efficiency over a rectified voltage range from 16VDC to 180VDC.