Design and optimization of a new control strategy in a parallel hybrid electric vehicle in order to improve fuel economy

In this paper, a new control strategy for the optimization of the fuel consumption of a parallel hybrid electric vehicle (PHEV) is proposed. A continuously variable transmission (CVT) is employed in the PHEV model. CVT gearboxes have a continuum of gear ratios between their upper and lower limits and their proper control can cause the engine to work optimally. The requested power from the driver and the state of charge of the battery are the controller inputs, while the CVT optimal gear ratio is the controller output. This optimal gear ratio helps the engine to work near its optimal operating points, resulting in better fuel economy and reduced emissions. The controller also attempts to enhance the vehicle performance parameters as much as possible. To investigate the effectiveness of the proposed controller, it is implemented in a PHEV simulated model. Initial results are calculated for three different drive cycles. Afterwards, in order to improve outputs, the initial controller parameters are optimized using multiobjective optimization genetic algorithms. Comparison between the initial and the optimized results showed the success of the optimized control strategy in reducing the fuel consumption, while the vehicle performance and emissions remained within their desired limits.