Date: Wednesday 26 March 2014
Time: 11:00 - 12:30
Location / Room: Konferenz 1

Chair:
Geoff Merrett, University of Southampton, UK

Co-Chair:
Davide Brunelli, University of Trento, IT

Modern energy storage systems affect all areas of power electronics, from micro-power energy harvesting systems to mega-watt Smart Grid systems. Papers in this session address novel approaches for on-chip power electronics operating under variable Vdd, and optimisation approaches to efficient design of smart grid energy storage.

Time	Label	Presentation Title Authors
11:00	6.3.1	(Best Paper Award Candidate) ASYNCHRONOUS DESIGN FOR NEW ON-CHIP WIDE DYNAMIC RANGE POWER ELECTRONICS Speakers: Delong Shang1, Xuefu Zhang2, Fei Xia3 and Alex Yakovlev2 1School of EEE,Newcastle University, GB; 2School of EEE, Newcastle University, GB; 3School of EEE, GB Abstract Asynchronous circuits will play an important role in microelectronic systems in the future, especially in energy harvesting and autonomous (EHA) systems where such circuits will be able to offer robustness and deliver high efficiency in a wide range of power-energy conditions. The concept of Capacitor Bank Block (CBB) mechanisms was proposed to form the basis of electronics for powering asynchronous loads. These mechanisms will benefit EHA systems by enabling effective co-scheduling of computational tasks and energy supply. This paper demonstrates how the CBB mechanisms can themselves be controlled by asynchronous circuits, thereby forming a new type of power delivery units (PDU) that will be able to deliver power to intelligent digital logic in future EHA systems. These PDUs are superior to traditional power converters largely because the latter can only regulate sufficiently high power and energy levels (regular and periodic) as well as their controllers require stable power levels themselves. This makes them unsuitable for intermittent and sporadic conditions inherent to EHA systems. In this paper, a novel asynchronous control for the CBB is described. Experiments and analysis of the new PDUs, comprising CBBs and asynchronous control, are presented and discussed in detail.
11:30	6.3.2	REAL-TIME OPTIMIZATION OF THE BATTERY BANKS LIFETIME IN HYBRID RESIDENTIAL ELECTRICAL SYSTEMS Speakers: Maurizio Rossi, Alessandro Toppano and Davide Brunelli, University of Trento, IT Abstract We present a real-time optimization framework to manage Hybrid Residential Electrical Systems (HRES) with multiple Energy sources and heterogeneous storage units. HRES represents urban buildings where photovoltaic (PV) or other renewable sources are installed along with the traditional connection to the main grid. In this paper heterogeneous storage units are used to realize energy buffers for the exceeding energy produced by the renewable when buildings and the grid are not available to accept it. We considered two different battery banks as electric energy storage, in particular lead-acid as the primary one for its low price and low self-discharge rate; while the lithium-ion chemistry is used as secondary bank because of the higher energy density and higher number of cycles. The proposed optimization strategy aims at maximizing the lifetime of the battery banks and to reduce the energy bill by managing the variability of the PV source, in price-varying scenarios. We used a Dynamic-Programming (DP) algorithm to schedule off-line the use of the lead-acid bank minimizing the number of cycles and the Depth-of-Discharge (DoD) under given irradiance forecasts and user load profiles. Forecasts of the user loads and of the renewable energy intake are introduced in the optimization. Moreover a Real-Time scheme is introduced to manage the lithium bank and to minimize the need and the purchase of energy from the Grid when the actual demand does not fit the forecast. Our simulation results outperform the state of the art where the efficiency of both banks is not taken into consideration, even if complex approaches based on DP are used.
12:00	6.3.3	OPTIMAL DIMENSIONING OF ACTIVE CELL BALANCING ARCHITECTURES Speakers: Swaminathan Narayanaswamy1, Sebastian Steinhorst1, Martin Lukasiewycz2, Matthias Kauer3 and Samarjit Chakraborty4 1TUM CREATE, SG; 2TUM CREATE Singapore, SG; 3TUM CREATE Ltd,, SG; 4TU Munich, DE Abstract This paper presents an approach to optimal dimensioning of active cell balancing architectures, which are of increasing relevance in EES for EV or stationary applications such as smart grids. Active cell balancing equalizes the state of charge of cells within a battery pack via charge transfers, increasing the effective capacity and lifetime. While optimization approaches have been introduced into the design process of several aspects of EES, active cell balancing architectures have, until now, not been systematically optimized in terms of their components. Therefore, this paper analyzes existing architectures to develop design metrics for energy dissipation, installation volume, and balancing current. Based on these design metrics, a methodology to efficiently obtain Pareto-optimal configurations for a wide range of inductors and transistors at different balancing currents is developed. Our methodology is then applied to a case study, optimizing two state-of-the-art architectures using realistic balancing algorithms. The results give evidence of the applicability of systematic optimization in the domain of cell balancing, leading to higher energy efficiencies with minimized installation space.
12:15	6.3.4	OPTIMAL DESIGN AND MANAGEMENT OF A SMART RESIDENTIAL PV AND ENERGY STORAGE SYSTEM Speakers: Di Zhu1, Yanzhi Wang1, Naehyuck Chang2 and Massoud Pedram1 1Univ. of Southern California, US; 2Seoul National University, KR Abstract Solar photovoltaic (PV) technology has been widely deployed in large power plants operated by utility companies. However, the home owners are not yet convinced of the saving cost benefits of this technology, and consequently, in spite of government subsidies, they have been reluctant to install PV systems in their homes. The main reason for this is the absence of a complete and truthful analysis which could explain to home owners under what conditions spending money on a PV system can actually save them money over a long-term, but known, time horizon. This paper thus presents a design and management mechanism for a smart residential energy system comprising PV modules, electrical energy storage banks, and conversion circuits connected to the power grid. First, we figure out how much savings can be achieved by a system with given PV modules and EES bank capacities by optimally solving the daily energy flow control problem of such a system. Based on the daily optimization results, we come up with the optimal system specifications with a fixed budget. Experiments are conducted for various electricity prices and different profiles of PV output power and load demand. Re-sults show that the designed system breaks even in 6 years and in the system lifetime achieves up to 8% annual profit besides paying back the budget.
12:30	IP3-1, 939	DESIGN AND FABRICATION OF A 315 μH BONDWIRE MICRO-TRANSFORMER FOR ULTRA-LOW VOLTAGE ENERGY HARVESTING Speakers: Enrico Macrelli1, Ningning Wang2, Saibal Roy2, Michael Hayes2, Rudi Paolo Paganelli3, Marco Tartagni1 and Aldo Romani1 1DEI, University of Bologna, IT; 2Tyndall National Institute, UCC, IE; 3CNR-IEIIT, University of Bologna, IT Abstract This paper presents a design study of a new topology for miniaturized bondwire transformers fabricated and assembled with standard IC bonding wires and toroidal ferrite (Fair-Rite 5975000801) as a magnetic core. The micro-transformer realized on a PCB substrate, enables the build of magnetics on-top-of-chip, thus leading to the design of high power density components. Impedance measurements in a frequency range between 100 kHz to 5 MHz, show that the secondary self-inductance is enhanced from 0.3 μH with an epoxy core to 315 μH with the ferrite core. Moreover, the micro-machined ferrite improves the coupling coefficient from 0.1 to 0.9 and increases the effective turns ratio from 0.5 to 35. Finally, a low-voltage IC DC-DC converter solution, with the transformer mounted on-top, is proposed for energy harvesting applications.
12:31	IP3-2, 85	PROVIDING REGULATION SERVICES AND MANAGING DATA CENTER PEAK POWER BUDGETS Speakers: Baris Aksanli and Tajana Rosing, University of California San Diego, US Abstract Data centers are good candidates for providing regulation services in the power markets due to their large power consumption and flexibility. In this paper, we develop a framework that explores the feasibility of data center participation in these markets. We use a battery-based design that can not only help with providing ancillary services, but can also limit peak power costs without any workload performance degradation. The results of our study using data for a 21MW data center show up to $480,000/year savings can be obtained, corresponding to 1280 more servers providing services.
12:32	IP3-3, 812	THE ENERGY BENEFIT OF LEVEL-CROSSING SAMPLING INCLUDING THE ACTUATOR'S ENERGY CONSUMPTION Speakers: Burkhard Hensel and Klaus Kabitzsch, Dresden University of Technology, DE Abstract When using level-crossing (also called send-on-delta) sampling in control loops, messages can be saved compared to periodic sampling without degrading control performance. While it is clear that reducing messages improves also the energy efficiency of battery-powered sensor devices, this can be disadvantageous for the energy efficiency the actuator device. This paper addresses the question, under which conditions level-crossing sampling is also for the actuator device more energy-efficient than periodic sampling. It is shown that there is an optimum inter-sample interval. Methods for reaching this optimum by appropriate controller and transmission settings are given. The theory is demonstrated using several known, standardized wireless network protocols.
12:30		End of session Lunch Break in Exhibition Area Sandwich lunch