Text/Civil
Everyone knows that hybrid models are through the switching of various modes to ensure the efficiency and fuel economy of the power system, perhaps our own cognition is that the engine, generator back and forth or work together, is nothing more than the control of two or three modes.
But in fact, the control strategy of hybrid vehicles can be said to be one of the most complex problems in new energy models, involving mechanical, electrical, hydraulic, electronic control and other fields. It is the biggest test for car companies. Hybrid vehicle control strategies can be divided into four levels and one restriction: mode control, SOC balance control, torque distribution, and component control. And a system capability limit (in addition to the mode control, the upper limit of the other three is determined by it).
First, the mode control
The main task of mode control is to keep the vehicle in the most suitable mode at all times, so as to have better economy and power. The hybrid vehicle configuration is different, and the types of modes included are also very different, mainly including pure electric mode, series mode, parallel mode and so on. Complex DHT hybrid systems also involve multiple gears and also require mode control.
But the ever-changing is inseparable, in most cases: the battery SOC is used when the pure electric mode is high; the battery SOC is low, and the series mode is generally used when the speed is low; the battery SOC is lower, and the parallel mode is used when the speed is higher; and the division of the mode is generally referred to: speed, acceleration pedal opening, soc, battery charge and discharge capability, etc. Mode control is currently the highest request for vehicles, so it determines the subsequent levels of regulation.
Second, the battery SOC balance control
Battery SOC balance control is done by calculating the target power of the engine and then keeping the battery SOC in the healthy range. Sufficient backup power must be guaranteed at the same time as fuel economy. In general, when the battery SOC is higher than the target range, it is necessary to let the battery discharge, and the engine can reduce the output; when the battery SOC is lower than the target range, the battery needs to be charged, and the engine increases the output; the battery SOC needs to maintain a balanced power within the target range, and the engine is also in a stable output state. The battery SOC balance control determines the subsequent torque distribution.
Third, torque distribution
When the vehicle is on the move, the system needs to ensure that the wheel end torque is in line with the driver's requirements. The engine outputs according to the request after the power balance, and the rest of the requirements are completed by the motor. However, the demand after the power balance may not be in the most economical area of the engine, so the test of the car company is the balance between the power balance strategy and the optimal working range of the engine.
At the same time, when switching modes, in order to ensure smoothness, it is also necessary to adjust the speed or twist of the power components to ensure the smoothness of the transition, if there is a clutch, it is also necessary to consider sliding to ensure smoothness. Therefore, torque distribution is the torque request of each component, including the control of the pressure of the engine, motor, generator, and clutch.
Fourth, component control
Each component responds to the requested instructions in accordance with the working conditions. Component control is the VCU (vehicle controller) instructions to each component to carry out specific actions, in which the engine start-stop state, the actual engagement state of the clutch determines the mode switching.
Fifth, the system capacity limitations
System capability limitation is the physical limit of each component, the charge and discharge power of the battery and other conditions on the power, torque, speed of the entire system components of the limit. The limitation of system capability is related to the entire hybrid control strategy, which has a greater impact on system protection and torque distribution, and needs to be considered.
Most of the hybrid vehicle control strategies are inseparable from the above four levels and a restriction, and then car companies calibrate and adjust specific parameters according to their own product characteristics.
summary:
The control strategy of hybrid models is very complex, but as long as you understand the above four levels and one restriction, then you can understand most of the hybrid model control strategies. When you are driving, you can also imagine that your car is constantly thinking and responding to your needs, which is considered to be a good effort.