What is the instantaneous optimization-based energy management strategy for hybrid electric vehicles?

The energy management strategy based on instantaneous optimization is also called real-time optimization energy management strategy. This strategy converts the energy consumption of the motor into the equivalent fuel consumption. The sum of the equivalent fuel consumption of the motor and the engine fuel consumption is called the nominal fuel consumption, and the torque distribution is performed with the minimum nominal fuel consumption at each moment as the control goal. Real-time optimal energy management strategy can realize real-time optimal control, but instantaneous optimality is not equal to global optimality. Moreover, this strategy has a relatively large amount of calculation and a relatively high application cost.

Some scholars integrate the obtained driving road condition information into the optimal control strategy with the minimum equivalent fuel consumption, adjust the control parameters in real time, use the battery power evenly throughout the driving conditions, and reduce the process of the engine charging the battery and discharging the battery again. , reduce the energy loss of secondary energy conversion, and some researchers have proposed an instantaneous optimal control strategy with the goal of minimizing equivalent fuel consumption, comparing energy as an equivalent factor, and battery power as a state variable, which is updated in real time with the operation of the vehicle, etc. The efficiency factor is used to correct the power of the motor and the power of the engine in real time to achieve the goal of saving fuel.

Further in-depth research is to propose an adaptive equivalent fuel consumption minimum control strategy. The core of the control strategy is to periodically update the equivalent factor of the control strategy according to changes in the current driving conditions, adjust the torque distribution between the engine and the motor, and ensure that the fuel The consumption is minimal and the battery power is maintained within a certain range.

What is the instantaneous optimization-based energy management strategy for hybrid electric vehicles?
equivalent fuel consumption minimum control strategy

The basic control idea of ​​the rule-based logic threshold control strategy is to use the electric drive system composed of the motor and the battery as a buffer for driving power output from the perspective of optimal engine efficiency to adjust the power output of the engine to adjust the operating range of the engine. , so that the engine always runs in the high-efficiency area, in order to obtain higher fuel economy of the whole vehicle.

The instantaneous optimal control strategy based on the instantaneous equivalent consumption minization strategies (ECMS) is from the perspective of the entire drive system of the hybrid vehicle, comprehensively considering the energy consumption of the drive system when it meets the driving power demand, and the system’s energy consumption Instantaneous fuel consumption is expressed as the sum of engine fuel consumption and equivalent fuel consumption of electricity consumption, so as to minimize the equivalent fuel consumption of each moment to obtain higher fuel economy of the whole vehicle.

The research on the control law of the instantaneous optimal control strategy can provide a certain reference for the design of the real-time control strategy of the hybrid electric vehicle.

When distributing the driving power, the instantaneous optimal control strategy of hybrid electric vehicle based on the minimum instantaneous equivalent fuel consumption control strategy comprehensively considers the SOC correction coefficient of the battery equivalent fuel consumption to ensure the battery power maintenance strategy and the “recovery by regenerative braking”. The average expected regenerative braking power corrected by “Free Energy”, as well as the equivalent fuel consumption conversion factor of the future battery power consumption condition and the equivalent fuel consumption conversion factor of the battery power future compensation condition obtained through the optimization calculation under the target driving condition .

When extracting the control rule for the real-time control strategy of HEV, since the deviation of the battery SOC relative to the target SOC and the average expected regenerative braking power value when the real-time control strategy uses this control rule is not known, the instantaneous optimization When the control rules of the control strategy are used, the influence of the battery power maintenance strategy and the “free energy” factor recovered by regenerative braking on the driving power distribution will no longer be considered.

For the established real-time control strategy, in order to ensure the battery’s power maintenance strategy, the deviation of the battery SOC relative to the target SOC is corrected. The battery power maintenance strategy is realized by adjusting the output power of the motor.

For the influence of the “free energy” factor recovered by regenerative braking on the driving power distribution, the influence of the regenerative braking recovery energy on the driving power distribution is indirectly corrected by the correction control of the battery SOC relative to the target SOC.

Figure 1 shows the relationship between the instantaneous equivalent fuel consumption rate of the drive system and the engine output torque when the required rotational speed at the input shaft end of the transmission is 160 rad/s and the required driving torque is 120 N m. The instantaneous optimization algorithm determines the optimal engine and motor output torque distribution scheme according to the instantaneous equivalent fuel consumption rate of the engine and motor output torque distribution schemes. At this operating point of the vehicle, the optimal output torque distribution scheme is as follows: the output torque of the engine is 169.2N·m, the output torque of the motor is -24.6N·m, and the energy of the fuel is converted into electric energy for the battery. When charging, the instantaneous equivalent fuel consumption rate at this time is 1.431g/s.

What is the instantaneous optimization-based energy management strategy for hybrid electric vehicles?
Figure 1 The relationship between the engine output torque and the instantaneous equivalent fuel consumption rate

Under the assumption that the battery SOC is always at the target SOC, the instantaneous optimization algorithm is used to calculate the torque distribution between the engine and the motor under different driving power requirements at each speed (the speed of the engine and the motor has a fixed proportional relationship, so the The distribution of the driving power of the engine and the motor can be regarded as the distribution of its driving torque), and the optimal torque distribution map of the engine under each possible speed-torque demand as shown in Figure 2 is obtained.

What is the instantaneous optimization-based energy management strategy for hybrid electric vehicles?
Figure 2 MAP map of engine optimal torque distribution of instantaneous optimization control strategy

The extraction process of the above instantaneous optimal control strategy control rules is carried out under the assumption that the battery SOC is always at the target SOC. In fact, under the same driving conditions, when the battery SOC is different, the distribution of the required power is different, as Keeping the battery in power balance also requires adjusting the distribution of the drive torque demand between the engine and the electric machine based on the degree to which the battery SOC deviates from the target SOC based on the optimal engine torque distribution shown in Figure 2.

When the battery SOC changes slightly relative to the target SOC, the control algorithm adjusts the engine output torque so that the actual output torque distribution between the engine and the motor often deviates from the obtained optimal torque distribution control rule. Therefore, a SOC penalty function is introduced to adjust the engine output torque adjustment amount according to the degree to which the battery SOC deviates from the target SOC.

The basic method is that when the battery SOC is close to the target SOC, the value of the SOC penalty function is basically 0, that is, when the battery SOC is close to the target SOC, the engine output torque is basically not adjusted, so as to adjust the engine and motor according to the optimal control rules. The output torque is distributed. Moreover, the change of the value of the SOC penalty function near the target SOC should be relatively gentle, so that the actual driving torque distribution is as close to the optimal torque distribution as possible. When the battery SOC deviates from the target SOC, the value of the penalty function changes in two directions, the SOC is greater than the target SOC and the SOC is less than the target SOC. When the battery SOC is close to the upper and lower limits of the SOC working range, the value of the SOC penalty function rapidly increases the adjustment of the engine output torque adjustment torque T, so that the battery SOC returns to the target SOC as soon as possible.