Woongchul Choi

Development of an 85-kW Bidirectional Quasi-Z-Source Inverter With DC-Link Feed-Forward Compensation for Electric Vehicle Applications

This paper presents a detailed operation analysis, controller design, and realization of a high-power, bidirectional quasi-Z-source inverter (BQ-ZSI) for electric vehicle applications. The circuit analysis shows that with a bidirectional switch in the quasi-Z-source network, the performance of the inverter under small inductance and low power factor can be improved. Based on the circuit analysis, a small signal model of the BQ-ZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the dc input voltage. Therefore, a dedicated voltage controller with feed-forward compensation is designed to reject the disturbance and stabilize the dc-link voltage during a non-shoot-through state. An 85-kW prototype has been built. Both simulation and experimental results are presented to prove the functionality of the circuit and the effectiveness of the proposed control strategy.

A full study of a PHEV charging facility based on global optimization and real-time simulation

This paper provides insight into two important issues arising in scenarios with high level of penetration of photovoltaic (PVs) based Plug-In Hybrid Vehicles (PHEVs) charging stations. Namely, the paper proposes a method to determine the optimal size of the local energy storage (LES) for a charging facility and also develops the control strategy for the proper integration of these LES and PVs with the PHEV charging stations. The proposed LES sizing method, which is based on optimal control theory, minimizes a cost function based on the average value of kWh price, irradiance and PHEVs usage patterns. A power-loss/temperature model and a temperature based charging strategy, previously developed by the authors, are utilized in determine the optimized LES sizing. Then, with the optimized facility parameters, a detailed circuit model of a charging facility is built. Control strategies of the power electronics networks in this charging facility is proposed and tested with real time simulations.

Biomechanical analysis of biphasic distribution of skull injury in falls from height.

Fall from height is one of the most common ways of suicide in Korea. Skull fractures are typically accompanied with these cases, but several autopsy cases show absence of skull fracture even with serious body injuries including sternal and vertebral fracture. The mechanism of this pattern of injury can be explained by impact of facial part on chest or abdomen when the back of the body touches the ground first. We tried to figure out the relevance of this pattern of injury to the height of fall using a computer simulation tool (MADYMO 7.5). For this experiment, a condition of initial pose was limited to leaning forward. The simulation showed that when the body rotated forward, the body parts which got injured by the ground depended on the height of fall. For relatively lower height, head got injured, but as the height was set higher, the point of first impact area changed to the back, hip and then legs. When the body struck first around hip area on supine position, the impact made forceful flexion of lumbar, thoracic and cervical vertebrae, leading to folding the body in two, which resulted in collision between the part of face and the anterior part of body. Through the current investigation, it was explained that the biphasic distribution of the number of head injury cases versus the height distribution was attributed to the forward rotation of the body during the fall.

Electrification of Public Transportation: Battery Swappable Smart Electric Bus with Battery Swapping Station

As an effort to reduce greenhouse gas and save fossil fuels, electrification of public transportation system, namely a battery swappable smart electric bus system has been developed and is currently in pilot operation. The system consists of a battery swappable smart electrified bus, a battery swapping station and a smart bus information service. With this battery swapping strategy and solution approach, efficient and economical operation of the public transportation system can be tried out and evaluated for its usefulness. Furthermore, as the independent ownership of the battery can be readily exercised, a new business model for the battery swapping and charging station can be developed independently from the ownership of the bus. Detailed description of the overall architecture of the system is provided in the current paper.

Optimal design of synchronous reluctance machine : A feasible solution to eliminating rare earth permanent magnets for vehicle traction applications

Purpose – The purpose of this paper is to present optimally designed synchronous reluctance machine (SynRM) to demonstrate the feasibility of eliminating the use of rare earth permanent magnet (PM) in electric machine for vehicle traction applications. Design/methodology/approach – A typical rare earth interior permanent magnet (IPM) machine is used as the benchmark to conduct the optimal design study. Based on the flux distribution, major changes are made to the rotor lamination design. Enhanced torque production and lower torque ripple are specifically targeted as the two main objectives of the proposed design approach. Findings – As a result, the optimally designed SynRM can achieve performance very close to that of the benchmark PM machine with a potential for further improvement. Originality/value – Discussions of IPM replacement by optimally designed SynRM in electrical and hybrid electrical vehicles are given in terms of performance and cost.

Experimental study for the reproduction of sudden unintended acceleration incidents.

A few cases of the sudden unintended acceleration have been reported over the last few years [1-11] and some of them seemed to be somewhat related to an electronic throttle control (ETC) system [11,12]. In this experimental study, efforts were made to reproduce the cases of sudden unintended acceleration possibly related to the ETC. Typically, an ETC of the engine is managed based on signals from airflow sensor, throttle position sensor and acceleration pedal sensor. With this typical sensor configuration in mind, these sensor signals were checked for noise levels. However, none of them showed any clear relationship with the sudden unintended acceleration mainly due to the robustness of the ETC logic software. As an alternative approach, supply voltage to an engine control unit (ECU) was tempered intentionally to observe any clues for the incidents. The observed results with the supply voltage drop and fluctuation tests were rather astonishing. The throttle valve position went all the way up to 100% for around one second when the battery voltage plunged down to 7V periodically despite that the acceleration pedal position was kept steady. As an effort to confirm the case, multiple tries were made systematically on a chassis dynamometer as well as on the test road. In this paper, detailed procedures and findings are reported accordingly.