Wassif Shabbir

Voltage Control for Enhanced Power Electronic Efficiency in Series Hybrid Electric Vehicles

The paper presents a dc-link voltage control scheme by which the power losses associated with the power electronic converters of a series hybrid electric vehicle (HEV) powertrain are reduced substantially. A dc-link commonly connects the three powertrain branches associated with series HEVs, presently interfaced by a three-phase rectifier, a three-phase inverter, and a dual-active bridge (DAB) dc–dc converter. Dynamic efficiency models of the converters are developed, and a methodology is proposed by which the dc-link voltage is varied with respect to its default value, based on the ratio between the battery and dc-link voltages. The voltage control scheme introduced varies the phase shift between the gating signals of the two DAB converter bridges, proportionally to the ratio of converter input voltage to output voltage referred to the transformer primary. This level of instantaneous control forces the converter to operate in boost mode when the battery charges and buck mode when the battery discharges, allowing the converter to persistently avoid hard switching losses over its entire operating range. The control scheme is tested in simulations with a full HEV model by comparing its performance with constant voltage and unity voltage conversion ratio PI control schemes. The scheme proves most effective for vehicles with high hybridization factor driving in an urban environment.

Efficiency analysis of a continuously variable transmission with linear control for a series hybrid electric vehicle

Abstract This paper investigates the performance of a continuously variable transmission (CVT) using an intuitive control in a hybrid electric vehicle (HEV) of a series architecture under varying driving conditions. The detailed dynamic vehicle simulation model employed in this study enables an in-depth evaluation of the CVT as compared to a fixed transmission (FT) that utilises a fixed final drive ratio between the motor and wheels. The investigation uses three distinct driving cycles to show that the CVT offers reduction in motor energy consumption of up to 9.38%. Also, the particular impacts of the transmission systems are understood by analysing the energy flows from the Permanent Magnet Synchronous Motor (PMSM).

Series hybrid electric vehicle supervisory control based on off-line efficiency optimization

A supervisory control system (SCS) is developed for a dynamic model of a series hybrid electric vehicle. The powertrain steady-state behavior is analyzed to produce a control map offline which maximizes the vehicle energy efficiency for any driving condition. This map can be accessed on a real-time basis during driving at low computational cost to locally optimize efficiency. The vehicle transient response is considered to ensure efficient, stable and healthy operation. Simulations using standard drive cycles verify that the designed Efficiency Maximizing Map (EMM) control allows smoother operation of the powertrain and it brings reductions in fuel consumption as compared to a Thermostat control scheme.

Exclusive Operation Strategy for the Supervisory Control of Series Hybrid Electric Vehicles

Supervisory control systems (SCSs) are used to manage the powertrain of hybrid electric vehicles (HEVs). This brief presents a novel SCS called exclusive operation strategy (XOS) that applies simple rules based on the idea that batteries are efficient at lower loads while engines and generators are efficient at higher loads. The XOS is developed based on insights gained from three conventional SCSs for series HEVs: 1) thermostat control strategy (TCS); 2) power follower control strategy (PFCS); and 3) global equivalent consumption minimization strategy. Also, recent technological developments have been considered to make the XOS more suited to modern HEVs than conventional SCSs. The resulting control decisions are shown to emulate the operation of approximate global optimal solutions and thus achieve significant improvement in fuel economy compared with TCS and PFCS. In addition, the generally linear relationship between required power and engine power for the XOS provides auditory cues to the driver that are comparable to conventional vehicles, thus reducing barriers to adopting HEVs. The simplicity and the effectiveness of the XOS make it a practical SCS.

A Practical Control Methodology for Parallel Plug-In Hybrid Electric Vehicle Powertrains

This paper presents an original control algorithm for a parallel plug-in hybrid-electric vehicle powertrain. Two operational strategies using this algorithm are designated as EV/CS (battery-only operation followed by charge sustaining operation) and CD/CS (charge depleting blended operation followed by charge sustaining operation) with the same control algorithm used throughout both. An algebraic mapping of three observable variables outputs a single motor torque-command that can either propel or regeneratively brake the vehicle. This mapping is on-line feasible in real time, avoiding the use of look-up tables or some computationally complex optimization approach involving searches over an admissible control space. Another important feature of this methodology is that the highly developed engine and transmission controls of non-hybrid powertrains are essentially maintained. Using a Simulink model, the fuel economy and SOC (state-of-charge) as a function of driving distance for both strategies are presented. Most importantly, results of recorded on-road SOC data are included that shows practicality on a real vehicle in a real driving situation over 96 miles. Also presented are simulated and real driving acceleration results.

Evaluation of the Through-the-Road Architecture for Plug-In Hybrid Electric Vehicle Powertrains

This paper investigates the through-the-road (TTR) powertrain architecture and its suitability for plug-in hybrid-electric vehicles (PHEVs) in the passenger vehicle category. The advantages and disadvantages of this architecture with respect to cost, sizing, control and manufacturability are contrasted against those of conventional architectures. The comparison extends into powertrain configurations used in recent commercial vehicles, such as the Toyota Prius and the Chevrolet Volt. The research includes the characterization of the mechanical dynamics and constraint equations of each architecture to quantify the control requirements. It is found that the TTR architecture excels in terms of manufacturability, and its ability to blend the motor and engine torques independently.

Efficiency maximizing and charge sustaining supervisory control for series hybrid electric vehicles

A supervisory control system (SCS) that maximizes the overall powertrain efficiency of a series hybrid electric vehicle (HEV) is developed. A novel approach of formulating the overall power efficiency which considers the idling losses of the engine and also characterizes separately the charging and discharging efficiencies of the battery, is proposed. These features allow the mode of direct power transfer from engine to battery to be included in the optimization. In turn, this enables the formulation of an optimization problem with a charge-sustaining scheme for improved control. A dynamic model of a series HEV is used in the development and testing of the SCS. Simulations with standard driving cycles demonstrate the significant improvement in fuel economy and battery charge sustaining of the designed Efficiency Maximizing and Charge Sustaining Map (EMCSM) over a Thermostat control scheme.