Design and implementation of a real-time power management strategy for a parallel hybrid electric bus

A real-time energy management strategy derived from an equivalent consumption minimization strategy for a parallel hybrid electric bus is introduced. Although an equivalent consumption minimization strategy is a near-optimal control strategy for the power management problems of hybrid electric vehicles, the computation cost and the driveability requirements are still barriers for it to be directly implemented on real-time controllers. This paper analyses the controller characteristics of the equivalent consumption minimization strategy based on the Willans line model for an internal-combustion engine and an electric motor. A two-step method is proposed to simplify and approximate the standard equivalent consumption minimization strategy controller. The strategy for the proposed controller, which is called the Willans line-equivalent consumption minimization strategy, can reduce the computation cost of optimization and can guarantee near-optimum fuel economy, while improving the vehicle driveability. The proposed controller is then validated by offline simulation and an onboard bench test. A backward simulation is conducted to test the fuel economy performance of the controller simplified from the two steps, together with dynamic programming and an equivalent consumption minimization strategy based on look-up tables. Then the controller is tuned by a high-fidelity forward simulation to explore the trade-off between the fuel economy and the driveability. Finally, a bench test with real powertrain components is presented to illustrate the effectiveness of the proposed methodology.