This paper introduces a phase change material (PCM) based heat sink (PCMHS) to reduce the idle and operating temperature of a direct current (DC)/DC converter in an underwater battery power system. The developed macro-encapsulated PCM enclosure features a dampening assembly that maximizes thermal contact and eliminates void space catered for volumetric expansion of the PCM during melting. The operating temperature of the DC/DC converter at steady-state (both idle and full-load cycle condition) is estimated via a validated thermal model. A percentage improvement of at least 27% can be achieved by PCMHS at different load cycle conditions tested. The PCM's volume expansion of approximately 6.4% corresponds to the measured cover movement of around 3 mm. The relationship between the state of expansion (or melt state) to solid-state of the PCM is also established.

Application of battery power systems increases in the marine and offshore industry. Most applications target to reduce the energy consumptions when the battery power system is wholly or partially used. The hardware and software of the battery power system design for underwater application are described. The testing of the battery power system is successfully performed in a water tank at low temperature of 4 degrees C that mimics subsea operating condition where most remotely-operated vehicle (ROV) operates. The average variation of state-of-charge for the 12-cell is approximately 5 percent after active cell balancing. The battery management system is capable of estimating the state-of-charge and using the data to perform the active cell balancing on each cell with different imbalanced state-of-charge values of at least 30 percent.

This paper introduces a pseudo three-dimensional electrochemical-thermal coupled battery model for a cylindrical Lithium Iron Phosphate battery. The model comprises a pseudo two-dimensional electrochemical cell model coupled with three-dimensional lumped thermal model. The cell is disassembled to obtain the physical dimensions of the cell components. The thermal characteristics of the cell are studied during the discharge process over a range of temperatures and discharge rates. The validity of the numerical model is demonstrated experimentally via a 26,650 cylindrical Lithium Iron Phosphate/graphite battery cylindrical cell. Instead of infrared thermal images, series of regression models are utilized to quantify the thermal behavior at various depth of discharge under various discharge rates. The results demonstrated that the battery cell performs differently at a lower ambient temperature and lower discharge rate where the exothermic reactions are milder.

A robust macro-encapsulation design of a low-temperature phase change material based thermal energy storage unit is presented. The developed macro-encapsulation container eliminates the need for the 20% air void space catered for the volumetric expansion of the phase change material during melting in conventional designs. A study was conducted to validate the effectiveness of the design on thermal conductivity with volumetric expansion on a 2-dimensional axis symmetrical model. The results from the numerical and experimental approaches came to a good agreement that heat transfer has improved. The thermal robustness of the proposed design was successfully demonstrated after multiple thermal cycles on the design.

Ambient temperature affects the performance of a battery power system and its accuracy in state-of-charge (SOC) estimation for electric vehicles and smart grid systems. This paper proposes a battery model that considered ambient temperature, cell temperature, hysteresis voltage and thermal aging on capacity due to multiple charging and discharging. The SOC is then estimated using an extended Kalman filter. Several forms of validation were tested on an actual cell battery under specific ambient temperatures to verify the battery cell model, terminal voltage and SOC estimation performance. The SOC estimation results show an improvement in root-mean-squared error as compared to Extended Kalman Filter (EKF) without considering the temperature dependency. The proposed battery temperature-dependent model gave a smaller root-mean square error in SOC and terminal voltage at 5 °C, 15 °C and 45 °C.

Lithium-ion battery (LIB) power systems have been commonly used for energy storage in electric vehicles. However, it is quite challenging to implement a robust real-time fault diagnosis and protection scheme to ensure battery safety and performance. This paper presents a resilient framework for real-time fault diagnosis and protection in a battery-power system. Based on the proposed system structure, the self-initialization scheme for state-of-charge (SOC) estimation and the fault-diagnosis scheme were tested and implemented in an actual 12-cell series battery-pack prototype. The experimental results validated that the proposed system can estimate the SOC, diagnose the fault and provide necessary protection and self-recovery actions under the load profile for an electric vehicle.

This paper presents an integrated state-of-charge (SOC) estimation model and active cell balancing of a 12-cell lithium iron phosphate (LiFePO4) battery power system. The strong tracking cubature extended Kalman filter (STCEKF) gave an accurate SOC prediction compared to other Kalman-based filter algorithms. The proposed groupwise balancing of the multiple SOC exhibited a higher balancing speed and lower balancing loss than other cell balancing designs. The experimental results demonstrated the robustness and performance of the battery when subjected to current load profile of an electric vehicle under varying ambient temperature.

A study is conducted to examine the effects of void spaces of air in phase change material based thermal energy storage (PCM-TES) system. A thermal simulation and analysis on a 2d axis symmetrical model is performed to simulate the effect of phase change, buoyancy driven convection and heat transfer. Two models are compared, one with a 20% air space and the other without. Both models are consistent in PCM volume. Results obtained from the simulation are validated by experimental results and showed good agreement. The model with the void space demonstrated characteristics which resembles a sensible heat storage system rather than the constant temperature characteristics of a latent heat storage system. The significant volume taken up by the void space could be reduced and replaced with more phase change material (PCM); which will increase the heat storage capacity of the system. Hence, understanding the effects of void spaces will be paramount in the development of future PCM-TES system designs.

Unmanned underwater vehicles (UUV) are widely used for survey and mining of natural resources in the region of underwater and seabed in the last two decades. In underwater, vision and depth perception will be poor, thus navigating and maneuvering a remotely operated vehicles (ROVs) will not be an easy task. The umbilical cable might get entangled. In the event that the ROV loses power from its umbilical cord or an autonomous underwater vehicle (AUV) power failure, an emergency power system will be needed to power the critical equipment on the ROV or AUV to facilitate its recovery and to limit the loss of data. In this paper, a large format 2 KWh lithium iron phosphate (LiFePO4) battery stack power system is proposed for the emergency power system of the UUV. The LiFePO4 stacks are chosen due to their high energy density, modularity and ready availability. The proposed LiFePO4 battery system includes the design and development of a smart battery management system (BMS) with high efficiency active cell balancing technology and intelligent self-learning battery state of charge (SOC) estimation for the LiFePO4 battery. The proposed BMS will lead to better utilization of battery's potential capacity and maximize the cycle life of the battery. The battery system has a pressure-resistance enclosure to eliminate extra battery pressure chamber and associated risks, therefore increase the reliability of the power system amidst high pressures down to 3km of deep-water. (C) 2017 The Authors. Published by Elsevier Ltd.

This paper details the thermal study of a battery power system within a sealed enclosure via software modeling and simulation. The model has been developed as a tool to study the thermal effects of the battery system within the watertight enclosure in order to implement sufficient thermal management solutions to ensure the reliable and safe operation of the entire battery power system. The proposed method is based on thermal simulation using Computation Fluid Dynamics (CFD) program. The results determined from the simulations are compared with results based on an experiment. The error is deemed to be minor and acceptable.