The Design and Development of Multivariable Controls with the Application for Energy Management of Hybrid Electric Vehicles.

Lead Research Organisation: Cranfield University
Department Name: Sch of Engineering


In recent years, a lot of research has been carried out in the field of energy management for full HEVs and EVs. Strategies that are based on heuristics can be easily implemented in a real vehicle by using a rule-based strategy or by using fuzzy logic. To find the global optimal solution, control techniques such as linear programming, quadratic programming, optimal control, especially dynamic programming have been studied. A different approach has been proposed in some recent work. In this approach instead of considering one particular driving cycle for calculating an optimal control law, a set of driving cycles is considered, resulting in a stochastic optimization approach. After considering the optimisation based methods described above, the following observation is made. The principal common drawback of all the aforementioned strategies is consideration of drivability as an afterthought. The drivability is considered in an ad hoc fashion as these approaches are not dynamic model based. At best, techniques such as game-theoretic optimisation utilises quasi-static models which are not sufficient to address drivability requirements. Another important drawback of these strategies is robustness. Theses strategies do not include a feedback control block, so the robust performance of the strategy is not guaranteed as the vehicle parameters deviated from their nominal conditions. Ad hoc adaptation of these strategies for drivability does impact their optimality and therefore a negative impact on the emissions and fuel consumption. The robust multivariable control has extensively been used in the aerospace industry, process control and chemical and petrochemical plants. However, the application of the multivariable control in the automotive industry is scarce and when it comes to the energy management development, there is no application. There exists multivariable based method such as Model Predictive Controls, however, these techniques are mainly time domain based, which has its drawbacks and they have the limitations such as on-line implementation is not possible. The multivariable control design has been used by this author for integration of active chassis systems (Active Roll Control and Active Limited Slip Differential). There is a tremendous opportunity for reducing fuel consumption, emissions, and calibration effort to production utilising this methodology. The user fuel economy data obtained from Toyota Prius has shown that there is approximately 10-15% difference between the average real world and driving cycle fuel economy. This difference is mainly due to the drivability impact. Our conservative projection of fuel savings and CO2 reduction of this proposal is 5-7%. An approximate annual savings of 400 Million, due to reduction in calibration effort, based on a volume projection of 50,000 hybrid vehicles after the end of this project. Furthermore, additional possible benefits and savings are foreseeable due to transferability between platform variants. The aim of this work is to design and develop a multivariable feedback controller to replace the ad hoc design currently used to address robustness and vehicle drivability issues as stated above. The robust feedback multivariable is derived based on the dynamic models of the plant so the drivability requirements are addressed as a part of the design and development of the controller and it is not an afterthought. Furthermore, the lack of robustness is not an issue with the Multivariable controls as they are inherently derived from feedback policies.

Planned Impact

In recent years, there has been tremendous progress in the theoretical development of the advanced control techniques, e.g. multivariable robust controls, soft constrained fuzzy logics, switching hybrid controls, and model predictive controls. However, the story is very different between theoretical development and pragmatic implementation in the automotive domain. What are still being implemented are many feedforward strategies and the limited feedback controls utilises the traditional approaches such as Proportional and PID controllers. The automotive industry as whole is still very mechanically oriented and the benefits of feedback controls are not very well understood. In addition, the automotive mechatronics, which combines the electro-mechanical systems and digital controls in a nicely packaged field, has not well developed and taught in our academic institution. Therefore, there is an ever increasing gap between theoretical work in the area of controls and its practical implementation. This gap results in tremendous missed opportunities in terms of making a positive impact on the environment, quality product and economic growth for automotive industry, and end-user perception of technology. It is our plan to try to close this gap through this project and similar future projects. 1- Environment: the fuel economy and emission reduction prediction of 5 to 7%. 2- Automotive industry: the estimated worldwide revenue for torque manager software changes and calibration for automotive industry in 2009 is US$5 billion. In Europe the predicted revenue is around US$1.25 billion. The UK is one of the stronger European contributors in terms of alternative powertrain revenue generation in the region. It is foreseeable that the large portion of this revenue. The proposed work will further enhance this leading position as it is foreseeable that the UK will benefit the large portion of the predicted European revenue. 3- End-user perception of technology: The enhancement of vehicle drivability through this proposed work will have a significant impact on the sale of the future hybrid powertrain technology and this will in turn have a positive impact on the UK economic growth. 4- Academic Institutions: As a result of collaboration with industrial collaborators, the research will develop technical skills which are transferrable and valuable for both employments in academia as well as in industry.


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