As the core of hybrid electric vehicle, the main function of energy management is to meet the basic technical performance (such as power, driving stability, etc.) and cost requirements of the vehicle, according to the characteristics of each component and the operating conditions of the vehicle, Realize the flow of energy between energy conversion devices (such as engine, motor, energy storage device, power conversion module, power transmission device, generator and fuel cell) according to the best route, so as to maximize the energy utilization efficiency of the whole vehicle and improve the economy of electric vehicles. Therefore, energy management is one of the important links in the design of hybrid electric vehicles.
- Energy transmission route
The energy conversion device of hybrid electric vehicle is usually composed of power generation device (engine / generator), energy storage device (battery, supercapacitor, etc.), power conversion module, power transmission device, charge and discharge device, etc. Its energy transmission routes can be divided into four: one is the power transmission route from the power generation device to the wheel; The second is from the energy storage device to the wheel; Third, from power generation device to energy storage device; The fourth is the energy flow route from the wheel to the energy storage device (energy recovery). In order to make electric vehicles have good mechanical properties, electric driving performance and reasonable energy distribution, the energy management of electric vehicles must effectively monitor and control the work of energy transmission route.
According to the energy supply mode, the basic working modes of hybrid power system can be divided into pure electric driving mode, pure engine driving mode, hybrid driving mode, driving charging mode, deceleration / braking energy feedback mode, idle / parking mode and other working modes corresponding to different stages of driving cycle.
- Energy control strategy
Energy control strategy is not only the core of hybrid electric vehicle control strategy, but also determines the energy transmission route. At present, hybrid electric vehicles researched and developed all over the world have different structural forms. There are three kinds of drive modes, i.e. parallel drive mode and hybrid drive mode. Different combination methods have different energy management and control strategies.
2.1. Energy management and control strategy of series hybrid electric vehicle
Because the engine of series hybrid electric vehicle is not directly related to the vehicle driving conditions, the main goal of energy management control strategy is that the engine works in the optimal efficiency zone and emission zone. Static logic threshold control strategy is mainly adopted. At present, two typical control strategies are max. SOC of PPS (peaking power source) and constant temperature control strategy (engine switch control strategy).
2.2. Energy management control strategy of parallel hybrid electric vehicle
The control of parallel hybrid electric vehicle energy management is essentially an optimal control problem of fuel and emission under certain constraints. On the one hand, due to the randomness of driving conditions and driver’s operation, the optimal control of parallel hybrid electric vehicle is an optimal control problem of stochastic dynamic system; On the other hand, the parallel hybrid system includes many different types of components, and there is a complex coordinated working relationship between the components. When the system works, the running state of each component is constantly changing, so the dynamic equation of the system is very complex.
At the same time, the control strategy of parallel hybrid electric vehicle is different from that of series hybrid electric vehicle. It usually needs to be controlled according to the SOC of battery, the position of driver’s accelerator pedal, the average power of vehicle and driving wheel and other parameters. The engine and motor output the corresponding torque to meet the requirements of driving torque of driving wheel. Therefore, parallel hybrid electric vehicles often adopt dynamic optimization control strategy and intelligent control strategy based on fuzzy logic or neural network in energy control strategy.
2.3. Energy management and control strategy of hybrid electric vehicle
The energy management and control strategy of hybrid electric vehicle is: when the vehicle is running at low speed, the drive system mainly manages the energy with the energy management and control strategy of series hybrid electric vehicle; When the vehicle runs stably at high speed, the energy management control strategy of parallel hybrid electric vehicle is used to manage the energy. Such an energy management control strategy can better achieve various performance indicators of the vehicle, so that the engine will not be affected by the driving conditions of the vehicle, and will always work or automatically shut down in the highest efficiency state, so that the vehicle can achieve low emission and ultra-low emission at any time. However, the technology to realize the control strategy is complex, and the structural design and manufacturing requirements of energy management controller are high.