Thermal Balancing Research Articles

Load Management of Modular Battery Using Model Predictive Control: Thermal and State-of-Charge Balancing

Thermal and state-of-charge (SOC) imbalances are well known to cause nonuniform aging in batteries. This paper presents the electrothermal control of a multilevel converter-based modular battery to address this issue. The modular battery provides a large redundancy in synthesizing terminal voltage, which gives extra degrees of freedom in control on cell level. There are multiple tightly coupled control objectives including the simultaneous thermal and SOC balancing as well as battery terminal voltage control. The main purpose of this paper is to devise an electrothermal control scheme for cases where full future driving information is not accessible. The control scheme is based on decomposition of controller into two orthogonal components, one for voltage control and the other for balancing control. This problem decomposition enables the application of constrained linear quadratic model predictive control scheme to solve the balancing problem elegantly. The control scheme is thoroughly evaluated through simulations of a four cell modular battery. The results show that a rather short prediction horizon is sufficient to achieve robust control performance.

Evaluation of Advanced Control for Li-ion Battery Balancing Systems Using Convex Optimization

Typically, the unique objective pursued in either active or passive balancing is equalization of single cell charge. However, a balancing circuit may offer more control features, like virtual equalization of single cell internal resistance or thermal balancing. Such control features for balancing systems are evaluated in this paper by means of convex optimization. More than one hundred cases in a pure EV application are evaluated. Balancing circuits' efficiency models are implemented and realistic cell-to-cell parameter distributions are considered based on experimental data. Different battery sizes and driving cycles are considered. Balancing circuit topology is taken into account by selecting a specific category of energy transfer: cell-to-heat, bypass, cell-to-pack, pack-to-cell, cell-to-cell shared, cell-to-cell distributed or cell-to-pack-to-cell. In general, better results in terms of energy losses, available capacity or temperature are obtained for the last three categories, even for moderate balancing currents. In particular, remarkable improvements are observed under conditions of high power demand with high variability, i.e., smaller battery sizes and more demanding driving cycles.

Evaluation of Combined Active and Passive Thermal Management Strategies for Lithium-Ion Batteries

Lithium-ion batteries are the most commonly used portable energy storage technology due to their relatively high specific energy and power but face thermal issues that raise safety concerns, particularly in automotive and aerospace applications. In these environments, there is zero tolerance for catastrophic failures such as fire or cell rupture, making thermal management a strict requirement to mitigate thermal runaway potential. The optimum configurations for such thermal management systems are dependent on both the thermo-electrochemical properties of the batteries and operating conditions/engineering constraints. The aim of this study is to determine the effect of various combined active (liquid heat exchanger) and passive (phase-change material) thermal management techniques on cell temperatures and thermal balancing. The cell configuration and volume/weight constraints have important roles in optimizing the thermal management technique, particularly when utilizing both active and passive systems together. A computational modeling study including conjugate heat transfer and fluid dynamics coupled with thermo-electrochemical dynamics is performed to investigate design trade-offs in lithium-ion battery thermal management strategies. It was found that phase-change material properties and cell spacing have a significant effect on the maximum and gradient of temperature in a module cooled by combined active and passive thermal management systems.

Gain-Scheduled Control of Modular Battery for Thermal and State-of-Charge Balancing

This paper proposes a simple constrained proportional controller with gain scheduling for simultaneous thermal and state-of-charge (SOC) balancing of a multilevel converter based modular battery. The proposed balancing controller is devised by investigating structural properties of constrained linear quadratic (LQ) model predictive controller (MPC) introduced in our earlier study. This investigation reveals a particular factorization of time-varying control gain matrices, which leads to approximation of matrix gains as scalar gains under the assumption of small parametric variations among battery cells. The gains are scheduled in load current for nominal cells. This special structure enables the identification of two dominant operational modes of the balancing controller: SOC balancing mode in low to medium load current range and thermal balancing mode in high current range. This study also proposes a simple algorithm for control projection on constraint polytope. The proposed balancing controller is tested in simulations for a modular battery with four significantly mismatched cells. The performance is comparable to MPC, which uses true battery parameters. The performance and the simplicity of the controller make it attractive for real-time implementation in large battery packs.

Investigation of effects of hydraulic balance in mechanical system based on energetic and exergetic efficiency in industrial buildings

In the total energy demand and management for heating and cooling systems in industrial processes and commercial buildings for different zones, provision of the appropriate balance flows with hydraulic and thermal balancing of installation lines can generate significant savings in energy consumption and costs. In this study, the effects of energetic and exergetic performance of the hydraulic balance system developed for commercial structures having different zones were examined separately. Despite, the fuel-saving potential of each zone was evaluated for different fuels. According to the results of the analysis, the hydraulic system, which was proposed and implemented, has decreased energy demand of the system approximately 152% compared with the energy efficiency and 82.20% compared with exergy efficiency. At the end of the study, some suggestions to increase energy-saving potential were made by evaluating the potential savings of process.

Integration of Planar Heat Pipes to Solid Oxide Cell Short Stacks

AbstractThis work presents the results of a thermal balancing, heat removal and supply mechanism via high temperature heat spreaders integrated to the solid oxide cell (SOC) stacks. Planar alkali metal heat pipes for almost isothermal two‐directional heat transfer at high power densities are incorporated into the metal interconnector structure of SOC‐short stacks. The objective of this concept is a temperature gradient shrinking within the stacks and a thermal control of SOFC system with a largely reduced additional air cooling. Subsequent to the development of planar heat pipe interconnectors with thickness down to 4 mm and heat transfer rates of up to 150 W per cm2 cross sectional area at isothermal operation, this paper describes their integration into the SOC stack structure. Therefore, short stacks with incorporated planar heat pipes are designed and built up for evaluation. The experimental study focuses on the influence of planar heat pipe interconnectors on temperature distributions within short stacks under various thermal load conditions. The experiments demonstrate the beneficial effects on thermal control of the stack structure and allow a first estimation of their amplitudes.

Thermal Balancing of a Multi-Cylinder Diesel Engine Operating on Diesel, B5 and Palm Biodiesel Blends

Energy crisis and global warming are the two most important issues that threaten the peaceful existence of the human species. More dependency on alternative fuels and energy loss minimization can be an effective solution to this affair. In this regard, thermal balance study of an internal combustion (IC) engine using different biodiesels is worthy of investigation. This manuscript provides an in-depth analysis of the engine heat losses in different subsystems of the engine. Finally, thermal balancing of the engine has been done by showing all energy flows in and out of the engine. The investigation was conducted in a four cylinder diesel engine fuelled with pure diesel, B5 (5% Palm biodiesel + 95% Diesel), 10% (PB10) and 20% (PB20) palm biodiesel blends at full load and in the speed range 1000 to 4000 RPM. The water heat loss and lubricating oil heat loss increased whereas the engine brake power, exhaust heat loss and unaccounted heat loss decreased with the increase of biodiesel percentage in the blends.

Electro-thermal Control of Modular Battery using Model Predictive Control with Control Projections

This paper proposes a novel model predictive control algorithm to achieve voltage regulation and simultaneous thermal and SOC balancing of a modular battery using limited future load information. The modular battery is based on multilevel converter (MLC), which provides a large redundancy in voltage synthesis and extra degree-of-freedom in control. The proposed algorithm is based on orthogonal decomposition of controller into two components, one for voltage control and the other for balancing control. The voltage control decisions are made using a simple minimum norm problem whereas the balancing control decisions are made in two stages. The first stage computes a balancing control policy based on an unconstrained LQ problem and the second stage enforces constraint on control actions via projection on a time-varying control constraint polytope. The control algorithm shows promising performance in a simulation study of a four cell modular battery. The performance and the simplicity of the control algorithm make it attractive for real-time implementation in large battery packs.

A Family of New Multiport Power-Sharing Converter Topologies for Large Grid-Connected Fuel Cells

This paper presents a family of new multiport power-sharing converter (PSC) topologies for utility-scale fuel cell (FC) power generation. The proposed system connects multiple FC sources to a medium-voltage grid via a single multilevel neutral point clamp (NPC) inverter interface with high-frequency isolation. High-voltage series-connected inputs are achieved, despite safely referencing each source to ground. Also, unique power-sharing technology decouples series-connected source currents and enables control of each FCs individual power level. Multidimensional modeling and analysis of the proposed system's PI- and PV-behavior is presented. Then, system topology and design considerations are discussed. Case study simulations show how this topology can operate four 250-kW FCs at separate power levels between 20% and 100%, while connecting to a single three-level NPC utility-interface. Correspondingly, a reduced-scale hardware prototype provides further proof of concept. Altogether, the proposed family of multiport PSC topologies realizes independent power control per source as well as increased output power, operational flexibility, thermal balancing, source availability, and cost effectiveness for utility FC power generation.

On optimizing system energy of voltage–frequency island based 3-D multi-core SoCs under thermal constraints

Three dimensional (3-D) multi-core SoC has been recognized as a promising solution for implementing complex applications with lower system energy. Recently, voltage–frequency island (VFI)-based design paradigm was widely adopted for energy optimization. However, the existing work commonly targeted 2-D platform, which cannot handle the exacerbated thermal issues and the increased solution space from 3-D integration. In this paper, we propose an optimization framework targeting VFI-based 3-D multi-core SoCs to minimize system energy meanwhile still meeting task deadline and thermal constraints. Our framework conducts at an earlier design phase in which designers have the freedom to determine the core stacks and map them into the hardware platform. Besides energy-aware task scheduling, we also conduct core stacking and task adjusting to balance the powers across the chip for thermal optimization. Moreover, by treating each core stack as a unity, the complicated problem of core mapping and VFI partitioning in 3-D platform can be simplified as a 2-D one. Experimental results demonstrate that on average our framework can achieve an energy reduction of 15.8% over the prior thermal balancing algorithm [17] (X. Zhou, J. Yang, Y. Xu, et al. Thermal-aware task scheduling for 3D multicore processors, IEEE Trans. Parallel Distrib. Syst. (TPDS), 21(1) (2010), 60–71.). Moreover, on average a reduction of 4.8°C in peak temperature is achieved by our framework, compared with the state-of-the-art energy optimization scheme [8] (U.Y. Ogras, R. Marculescu, P. Choudhary, et al. Voltage–frequency island partitioning for GALS-based networks-on-chip, in: ACM/IEEE Design Automation Conference (DAC), 2007, pp. 110–115.).

Energetics of single active diffusion trajectories

The fundamental insight into Brownian motion by Einstein is that all substances exhibit continual fluctuations due to thermal agitation balancing with the frictional resistance. However, even at thermal equilibrium, biological activity can give rise to non-equilibrium fluctuations that cause “active diffusion” in living cells. Because of the non-stationary and non-equilibrium nature of such fluctuations, mean square displacement analysis, relevant only to a steady-state ensemble, may not be the most suitable choice as it depends on the choice of the ensemble; hence, a new analytical method for describing active diffusion is desired. Here we discuss the stochastic energetics of a thermally fluctuating single active diffusion trajectory driven by non-thermal random forces. Heat dissipation, usually difficult to measure, can be estimated from the active diffusion trajectory; guidelines on the analysis such as criteria for the time resolution and driving force intensity are shown by a statistical test. This leads to the concept of an “instantaneous diffusion coefficient” connected to heat dissipation that may be used to analyse the activity and molecular transport mechanisms of living systems.

Modeling and control for thermal balancing of multi-core processors

This paper presents an effective thermal balancing policy for multi-core processors thermal management systems. The paper contains two parts. First, a group of one dimensional (1D) partial differential equations (PDEs), which are derived from the normal three dimensional (3D) PDE heat conduction equation, are proposed to describe the thermal behavior of the multi-core processers. Then, an optimal output feedback regulator is designed to manage the power consumption and balance the temperature among the cores. Finally, the performance of the proposed controller is verified via an illustrative example.

Distributed thermal aware load balancing for cooling of modular data centres

Thermal management in data centres requires a complicated trade-off between cooling costs and thermally induced equipment failure rates. Using ideas from cooperative control and distributed rate limiting, in this study the authors describe a distributed architecture that can be used for thermal aware load balancing for a common type of modular data centre; namely an algorithm that, for a given demand D *, distributes load to individual machines such that the temperatures in the individual modules are equalised. The benefit of shifting load based on thermal considerations is that significant gains in cooling cost can be achieved. We evaluate the performance of the algorithm using computational fluid dynamics and Matlab simulations. The results show that significant cost savings can be made by applying such algorithms, and that these can be achieved without the need for detailed modelling and tuning of controllers.

Thermal Management of High Temperature Solid Oxide Electrolyser Cell/Fuel Cell Systems

High temperature solid oxide cells, operated alternately in electrolyser or fuel cell mode, represent an appealing approach for efficient electricity storage via hydrogen production/consumption. This paper analyses the thermal balance of a solid oxide electrolyser cell/fuel cell to enable highly transient operation at high temperaturres and high storage efficiencies. Furthermore, the paper proposes a thermal balancing, heat supply and removal mechanism via high temperature heat pipees integrated into the solid oxide cell stacks. A quasi-2D thermo-electrochemical model of the solid oxide cell system provides numerical results in order to evaluate the benefits of such heat pipe-stack couplings.

Design of Ethernet switch cabinet using MSC.NASTRAN

As microelectronics technology steadily packing more chip power into small packages, where balance is an important element of success in this electronic enclosure packaging. The design challenges include thermal management, vibration reduction and balancing reliability and maintainability. The present work, the objective is to design Ethernet switch cabinet/enclosure and the faceplate on which the Ethernet switch enclosure is mounted. Design considerations are made according to equipment requirement and IEEE and IEC standards. Sheet metal module in PRO-E is used to create 3D CAD models. The improvements are made on the basis of the results, using finite element analysis (FEA).

Design of Ethernet switch cabinet using MSC.NASTRAN

As microelectronics technology steadily packing more chip power into small packages, where balance is an important element of success in this electronic enclosure packaging. The design challenges include thermal management, vibration reduction and balancing reliability and maintainability. The present work, the objective is to design Ethernet switch cabinet/enclosure and the faceplate on which the Ethernet switch enclosure is mounted. Design considerations are made according to equipment requirement and IEEE and IEC standards. Sheet metal module in PRO-E is used to create 3D CAD models. The improvements are made on the basis of the results, using finite element analysis (FEA). Keywords: Microelectronics technology, electronic enclosure packaging, Ethernet switch.

The D&T Report

The D&T Report

Thermal-Aware Compilation for Register Window-Based Embedded Processors

The development of compiler-based mechanisms to optimize the thermal profile of large register files to improve the processor reliability has become an important issue. Thermal hotspots have been known to cause severe reliability issues, while the thermal profile of the devices is also related to the leakage power consumption and the cooling cost. Register window-based architectures provide a relatively large register files. However, such large register files are not designed or utilized for thermal balancing or reliability enhancement. In this letter, we propose a compilation flow that utilizes the register windows to optimize the thermal profile and to reduce the hotspots. As a result, the thermal profile and reliability of the device is clearly improved. Simulation results show that the proposed flow achieves up to 91% reduction of hotspots and 11% reduction of the peak temperature in embedded processors.

ENERGY EFFECTIVENESS OF SIMULTANEOUS HEAT AND MASS EXCHANGE DEVICES

Simultaneous heat and mass exchange devices such as cooling towers, humidifiers and dehumidifiers are widely used in the power generation, desalination, air conditioning, and refrigeration industries. For design and rating of these components it is useful to define their performance by an effectiveness. In this paper, several different effectiveness definitions that have been used in literature are critically reviewed and an energy based effectiveness which can be applied to all types of heat and mass exchangers is defined. The validity and the limitations of the various effectiveness definitions are demonstrated by way of several examples including direct and indirect contact, parallel and counterflow heat and mass exchangers. The limiting case of a simple heat exchanger is also discussed. The importance of thermal balancing in minimizing entropy production and its implications for optimization and design of these devices is dealt with in detail. The application of the energy effectiveness to heat-exchanger-like -NTU correlations is also examined using a detailed numerical model.

Thermal Balancing Policy for Multiprocessor Stream Computing Platforms

Die-temperature control to avoid hotspots is increasingly critical in multiprocessor systems-on-chip (MPSoCs) for stream computing. In this context, thermal balancing policies based on task migration are a promising approach to redistribute power dissipation and even out temperature gradients. Since stream computing applications require strict quality of service and timing constraints, the real-time performance impact of thermal balancing policies must be carefully evaluated. In this paper, we present the design of a lightweight thermal balancing policy MiGra, which bounds on-chip temperature gradients via task migration. The proposed policy exploits run-time temperature as well as workload information of streaming applications to define suitable run-time thermal migration patterns, which minimize the number of deadline misses. Furthermore, we have experimentally assessed the effectiveness of our thermal balancing policy using a complete field-programmable-gate-array-based emulation of an actual three-core MPSoC streaming platform coupled with a thermal simulator. Our results indicate that MiGra achieves significantly better thermal balancing than state-of-the-art thermal management solutions while keeping the number of migrations bounded.