WaFFLe

Managing thermal imbalance in contemporary chip multi-processors (CMPs) is crucial in assuring functional correctness of modern mobile as well as server systems. Localized regions with high activity, e.g., register files, ALUs, FPUs, and so on, experience higher temperatures than the average across the chip and are commonly referred to as hotspots. Hotspots affect functional correctness of the underlying circuitry and a noticeable increase in leakage power, which in turn generates heat in a self-reinforced cycle. Techniques that reduce the severity of or completely eliminate hotspots can maintain functional correctness along with improving performance of CMPs. Conventional dynamic thermal management targets the cores to reduce hotspots but often ignores caches, which are known for their high leakage power consumption. This article presents WaFFLe , an approach that targets the leakage power of the last-level cache (LLC) and hotspots occurring at the cores. WaFFLe turns off LLC-ways to reduce leakage power and to generate on-chip thermal buffers. In addition, fine-grained DVFS is applied during long LLC miss induced stalls to reduce core temperature. Our results show that WaFFLe reduces peak and average temperature of a 16-core based homogeneous tiled CMP with up to 8.4 ֯ C and 6.2 ֯ C, respectively, with an average performance degradation of only 2.5 %. We also show that WaFFLe outperforms a state-of-the-art cache-based technique and a greedy DVFS policy.

Effect of Phase Change Material On Dynamic Thermal Management Performance for Power Electronics Packages

High temperature silicon carbide (SiC) die are the most critical and expensive component in electric vehicle (EV) power electronic packages and require both active and passive methods to dissipate heat during transient operation. The use of phase change materials (PCMs) to control the peak junction temperature of the SiC die and to buffer the temperature fluctuations in the package during simulated operation is modeled here. The latent heat storage potential of multiple PCM and PCM composites are explored in both single-sided and dual-sided package configurations. The results of this study show that the addition of phase change material (PCM) into two different styles of power electronics (PE) packages is an effective method for controlling the transient junction temperatures experienced during two different drive cycles. The addition of PCM in a single-sided package also serves to decrease temperature fluctuations experienced and may be used to reduce the necessary number of SiC die required for EVs, lowering the overall material cost and volume of the package by over 50%. PCM in a single-sided package may be nearly as effective as the double-sided cooling approach of a dual-sided package in the reduction of both peak junction temperature of SiC as well as controlling temperature variations between package layers.

Wide range continuously tunable and fast thermal switching based on compressible graphene composite foams

Thermal switches have gained intense interest recently for enabling dynamic thermal management of electronic devices and batteries that need to function at dramatically varied ambient or operating conditions. However, current approaches have limitations such as the lack of continuous tunability, low switching ratio, low speed, and not being scalable. Here, a continuously tunable, wide-range, and fast thermal switching approach is proposed and demonstrated using compressible graphene composite foams. Large (~8x) continuous tuning of the thermal resistance is achieved from the uncompressed to the fully compressed state. Environmental chamber experiments show that our variable thermal resistor can precisely stabilize the operating temperature of a heat generating device while the ambient temperature varies continuously by ~10 °C or the heat generation rate varies by a factor of 2.7. This thermal device is promising for dynamic control of operating temperatures in battery thermal management, space conditioning, vehicle thermal comfort, and thermal energy storage.

Application of Digital Twin in Smart Battery Management Systems

Lithium-ion batteries have always been a focus of research on new energy vehicles, however, their internal reactions are complex, and problems such as battery aging and safety have not been fully understood. In view of the research and preliminary application of the digital twin in complex systems such as aerospace, we will have the opportunity to use the digital twin to solve the bottleneck of current battery research. Firstly, this paper arranges the development history, basic concepts and key technologies of the digital twin, and summarizes current research methods and challenges in battery modeling, state estimation, remaining useful life prediction, battery safety and control. Furthermore, based on digital twin we describe the solutions for battery digital modeling, real-time state estimation, dynamic charging control, dynamic thermal management, and dynamic equalization control in the intelligent battery management system. We also give development opportunities for digital twin in the battery field. Finally we summarize the development trends and challenges of smart battery management.

Power Management to Meet Thermal Safe Power in Fault-Tolerant Embedded Systems

Thermal Design Power (TDP) as the chip-level power constraint for a specific chip has been exploited in fault-tolerant embedded systems. TDP, as the chip-level power constraint of the system, could be either pessimistic or thermally unsafe. Employing TDP as a pessimistic constraint can increase the rate of missing real-time constraints because of triggering Dynamic Thermal Management (DTM) more frequently. If TDP as a chip-level power constraint is not a pessimistic constraint, TDP can be thermally unsafe and can lead to thermal violations. Employing Thermal Safe Power (TSP) as the core-level power constraint, which is defined as a function of the number of simultaneously operating cores, can result in improving the efficiency and the schedulability. This comment improves the efficiency and the schedulability rate of one of the proposed methods in the literature by employing TSP.

Power Management to Meet Thermal Safe Power in Fault-Tolerant Embedded Systems

Thermal Design Power (TDP) as the chip-level power constraint for a specific chip has been exploited in fault-tolerant embedded systems. TDP, as the chip-level power constraint of the system, could be either pessimistic or thermally unsafe. Employing TDP as a pessimistic constraint can increase the rate of missing real-time constraints because of triggering Dynamic Thermal Management (DTM) more frequently. If TDP as a chip-level power constraint is not a pessimistic constraint, TDP can be thermally unsafe and can lead to thermal violations. Employing Thermal Safe Power (TSP) as the core-level power constraint, which is defined as a function of the number of simultaneously operating cores, can result in improving the efficiency and the schedulability. This comment improves the efficiency and the schedulability rate of one of the proposed methods in the literature by employing TSP.

Flow-Controlled Spray Cooling Approaches for Dynamic Thermal Management

Two-phase spray cooling is considered as one of the most promising thermal management techniques characterized by high heat transfer coefficient (HTC) and critical heat flux (CHF), as well as near-uniform temperatures on target surface. Normally, spray cooling systems feature steady flow rate and continuous spray, and are designed to satisfy the maximum expected heat load. However, if the heat load varies due to operating conditions, such as cold starts and pulsing power cycles, a spray cooling system uses excessive coolant most of the time, and causes low cooling efficiencies because of lower utilization of phase-change heat transfer and higher pumping power. This study aimed to investigate variable and intermittent flow spray cooling characteristics for dynamic thermal management. Variable flow spray cooling scheme requires control of pump input voltage (or speed), and intermittent flow spray cooling scheme requires control of solenoid valve duty cycle and frequency. Tests were conducted on a closed-cycle system with HFE-7100 dielectric coolant at varying liquid flow rate and subcooling conditions, and using smooth and enhanced heat transfer surfaces. Results, compared to a baseline performance from steady flow case, indicated that the variable flow spray cooling conditions achieve similar cooling performance at low and moderate heat fluxes, while the intermittent flow spray conditions result in high temperature penalty and much lower CHF.