Christopher R. Lashway

Advanced Battery Management and Diagnostic System for Smart Grid Infrastructure

This paper presents the design and implementation of an advanced battery management system (BMS). The basic concept is to divide each series battery array into sub-arrays where each battery is individually monitored and managed. The proposed BMS continuously monitors the voltage, current, and energy of each battery. Based on these measurements, the BMS can calculate individual state of charge (SoC) levels and C-rates. Furthermore, the system has the capability to isolate each individual battery to apply different charging profiles and advanced diagnostics to detect the correct problems. Pulsed charging is deployed using different duty cycles for SoC balancing. The isolated battery is bypassed to maintain uninterrupted supply to the load despite reduced series array voltage. An unidirectional dc-dc boost converter maintains a constant output voltage level to the load, regardless of the number of batteries connected, until the problem is corrected. A hardware implementation of the proposed BMS is explained in detail. The performance of the system is tested experimentally under different loading conditions, including heavy pulsed loads.

Modeling and Feasibility Analysis of Quasi-Dynamic WPT System for EV Applications

In this paper, a new bidirectional wireless power transfer (WPT) charging and discharging concept is analyzed for its feasibility in integration at traffic signals. Classified as quasi-dynamic WPT (QDWPT), a string of coils are proposed to be installed beneath the road surface to provide grid-to-vehicle and vehicle-to-grid (V2G) services to battery electric vehicles (BEVs) while stopped. An experimentally verified lithium-ion battery array and Bidirectional Wireless Power Transfer system are combined to provide a comprehensive simulation under three proposed scenarios. First, four fixed standardized WPT charging levels are evaluated under a Federal Test Procedure-72 city driving profile. Second, a variable charging scenario autonomously adjusts the charging level based on the BEV state of charge. Third, an algorithm is proposed to toggle between charging and discharging based on the BEV psychological and grid retail price to evaluate V2G service viability. For each scenario, a comparison over the maximum driving range per drive cycle and range gained for each consumed kWh is quantified. Moreover, the effect of WPT coil misalignment over the driving performance is investigated and evaluated. This paper concludes that QDWPT at traffic signals is a promising solution to substantially extend the driving range and operating time for city driving especially at high charging levels.

Optimal renewable energy farm and energy storage sizing method for future hybrid power system

This paper proposes a novel optimization method for sizing a renewable energy farm consisting of batteries and ultra-capacitors in a hybrid power system. The combination of ultra-capacitors with batteries is an emerging practice in advanced power electronic systems and a superior configuration scheme is crucial to deploy them effectively with the high penetration of renewable energy sources and critical loads in future power systems. The proposed sizing method fully utilizes the energy generated from the renewable energy farm and limits power fluctuation within the utility grid, improving grid stability and reducing construction and maintenance costs. This two-step optimization process appropriately sizes the renewable energy farm and the energy storage system by using a genetic algorithm (GA). Regional historical data of the solar irradiance, wind speed, and local load profile of Key West, Florida is used to establish the first cost function for optimizing the combination of PV and wind power based on the entire years daily energy difference between the renewable energy farm and twenty percent of the local load. With the optimized renewable energy farm size, a second cost function is designed to get the optimal combination of battery and ultra-capacitor sizes to smooth the impact caused by the renewable energy farm. A case study of a hybrid power system located in Key West, Florida is presented to verify the advantages of the proposed optimal sizing method.

Adaptive Battery Management and Parameter Estimation Through Physics-Based Modeling and Experimental Verification

In this paper, adaptive battery monitoring, health, and performance analysis techniques are proposed and implemented for use in a hybrid energy storage management system. Developed through physics-based models of a lead acid and lithium ion battery cell, a chemistry detection and equivalent circuit estimation technique was accomplished using a low-frequency C/10 pulsed load. Once in operation, an adaptive coulomb counting algorithm accounts for shifts in the state of health from cycle-to-cycle using two assessment methods: estimating equivalent circuit parameters and updating the usable capacity represented by a capacitive energy model. The proposed system has the following novelties: 1) determination of the battery chemistry type and cell configuration through the use of a single standardized pulse; 2) the use of a fixed C-rate pulsed load in order to obtain a basic set of equivalent circuit parameters; 3) new voltage and temperature-based initial state of charge mechanisms for both a lead acid and a lithium ion battery; and 4) the implementation of a final control platform with chemistry detection, cell configuration, refined initial state of charge estimation, and production of a Randles equivalent circuit, regardless of the battery state of health.

DC voltage ripple quantification for a flywheel-battery based Hybrid Energy Storage System

Flywheel energy storage has started attracting more attention as an energy storage means, but certain impediments face their deployment such as a high self-discharging rate and power quality issues. A potential solution is to combine flywheels with another energy storage types to form a Hybrid Energy Storage System (HESS). In this paper, a new method is established to perform power quality analysis and DC voltage ripple quantification in an HESS connected solely to a DC bus. Previous efforts have analyzed voltage and current ripple using an AC frequency reference, but these techniques are ineffective when the system does not contain an AC connection. Extensive laboratory testing and verification is conducted to characterize a flywheel-battery based HESS with different battery contribution levels. A correlation is made between the required battery support and resulting DC voltage ripple. Due to the nature of a flywheel operating at various speeds, a new Machine Speed Multiple (MSM) frequency reference is used as a profiling tool corresponding to the harmonic number in AC systems. Using the MSM in conjunction with the Discrete Fourier Transform, a voltage ripple frequency table is produced to highlight the target frequencies which must be reduced. A quantitative analysis identifies an overall reduction of voltage ripple magnitudes as a result of current injection from the battery.

Breakdown voltage assessment of GaN HEMT devices through physics-based modeling

An extensive study is conducted to evaluate breakdown mechanisms in gallium nitride (GaN) high electron mobility transistors (HEMT). A comprehensive physics-based model of a common HEMT provides the base comparison to conduct different material and geometric investigations. The variations are evaluated in a progression toward the optimal configuration: 1) varying the passivation material, 2) replacing the substrate material, 3) reducing the doping profile along the GaN and aluminum nitride (AlGaN) layers and 4) a field plate (FP) addition. The electric field distribution across the source, gate, and drain is analyzed for each case as well as their I-V curves until the breakdown voltage (BV). The best results are revealed under the FP case.

Optimal sizing of inverters and energy storage for power oscillation limiting in grid connected large scale Electric Vehicle park with renewable energy

Power oscillations can result from the expansion of large-scale grid-connected Electric Vehicles (EV) parks fed from photovoltaic (PV) arrays which raising concerns about grid stability. This paper addresses the optimal sizing for the energy storage battery, its corresponding DC-DC power converter and the grid tie inverter to satisfy grid requirements and maximize the profit of a EV park owner under the utility constraints. This was achieved through two stages: probabilistic forecasting of the EV load pattern and optimal sizing of the battery and power converters by the aid of linear programming (LP). Three types of batteries were studied to support the EV park: Sodium Sulfur (NaS), Lead Acid (LA) and Vanadium-Redox (VR). Moreover, a sensitivity analysis was done by investigating the effect of changing the number of grid tie inverters. Results showed the effectiveness of the proposed solution in limiting the power oscillations at the point of common coupling with the grid and maximizing the EV parks owner profit. Results also revealed the superiority of the VR battery for a low number of grid tie inverters while LA was preferable for implementing higher numbers of grid tie inverters on the host grid while limiting the power fluctuations at the grid side.

A multi-level bi-directional buck-boost converter using GaN devices for electric vehicle applications

A modular multi-level bi-directional diode-clamped DC-DC converter based on enhancement Gallium Nitride (eGaN) High Electron Mobility Transistor (HEMT) is proposed as a plugin charger for electric vehicles (EVs). The eGaN HEMT can switch efficiently even in hard switching, but their problem is that they cannot tolerate voltage stresses higher than 650V. The proposed multilevel topology reduces the voltage stress across the switches which enables utilizing eGaN HEMT technology in the powertrain of the EVs. Simulations were carried out in PSpice environment using the eGaN equivalent circuit provided by the manufacturer. The simulation results prove that the performance of the proposed converter complies with the theoretical analysis.

On the adaptive protection of microgrids: A review on how to mitigate cyber attacks and communication failures

One main challenge in the practical implementation of a microgrid is the design of an adequate protection scheme in both grid connected and islanded modes. Conventional overcurrent protection schemes face selectivity and sensitivity issues during grid and microgrid faults since the fault current level is different in both cases for the same relay. Various approaches have been implemented in the past to deal with this problem, yet the most promising ones are the implementation of adaptive protection techniques abiding by the IEC 61850 communication standard. This paper presents a critical review of existing adaptive protection schemes, the technical challenges for the use of classical protection techniques and the need for an adaptive, smart protection system. However, the risk of communication link failures and cyber security threats still remain a challenge in implementing a reliable adaptive protection scheme. A contingency is needed where a communication issue prevents the relay from adjusting to a lower current level during islanded mode. An adaptive protection scheme is proposed that utilizes energy storage (ES) and hybrid ES (HESS) already available in the network as a mechanism to source the higher fault current. Four common grid ES and HESS are reviewed for their suitability in feeding the fault while some solutions are proposed.

Modeling and energy management of modern shipboard power systems

• An exhaustive overview of the shipboard power system types, architectures, and load analysis • Various bus configurations, distribution schemes, and notable standards were discussed • Various energy storage devices and hybrid energy storage systems were introduced for their strengths in supporting shipboard power system load profiles • 4 unique control schemes to support a hybrid DC microgrid while a number of different case studies were carried out for experimental verification • Hybrid energy storage containing a flywheel was evaluated for both its strengths and weaknesses in supporting shipboard loads from both a general and power quality perspective • Comprehensive hybrid energy storage systems were tested on ship power profiles with both single and multiple pulsed loads applying new dynamic operation tactics to extend shipboard operating durations.