*3.3. Equivalent Consumption Minimization Strategy*

ECMS is one of the best optimization control strategies, and ECMS treats the energy storage system, battery pack/supercapacitor as a buffered energy source. The loss of battery power during travel must be recovered from the brake regeneration or the generator driven by the ICE. The cost function of ECMS is shown in Equation (31), which contains the fuel consumption of the ICE and the electricity energy consumption. Since the electricity power consumption and fuel consumption could not be directly compared, electricity power consumption should be converted into the equivalent fuel consumption by Equations (32) and (33).

$$J(t) = \dot{m}\_{fc, \text{eqv}} = \dot{m}\_{fc}(P\_e(t)) + \dot{m}\_{\text{eqv}}(P\_{\text{em}}(t)),\tag{31}$$

$$\begin{array}{ll}\dot{m}\_{\text{cylv}}(t) = & \mathcal{Y} \cdot \mathbf{s}\_{\text{dis}} \frac{\mathrm{BSFC}(t) \cdot \mathcal{P}\_{\text{cyl}}(t)}{\eta\_{\text{ultt}t}(P\_{\text{cylv}}) \eta\_{\text{lvv}}(P\_{\text{cyl}})} \\ & + (1 - \mathcal{Y}) \cdot \mathbf{s}\_{\text{clg}} \cdot \eta\_{\text{batt}}(P\_{\text{cyl}}) \eta\_{\text{lvm}}(P\_{\text{cyl}}) \cdot \mathrm{BSFC}(t) \cdot \mathcal{P}\_{\text{cyl}}(t), \end{array} \tag{32}$$

$$\gamma = \frac{1 + \text{sign}(P\_{\text{em}}(t))}{2},\tag{33}$$

where *mfc, eqv* is the summation of instant fuel consumption, *meqv(t)* is the equivalent fuel consumption of electricity power, *Pem* is the output power of the motor, and *sdis* and *schg* are the equivalent factors of discharging and charging, respectively. *BSFC* is the fuel consumption per unit ICE output energy. η*batt* and η*em* are the working efficiency of battery pack and motor, respectively.
