## 3 Integrated Cooling System  
Figure 4 shows the TMS topology. This system employs liquid cooling, with the battery, inverter, and motor being considered as thermal loads. Prioritising battery cooling, the coolant flows successively through the battery, inverter, and motor and then returns to a radiator for thermal recovery. The switching control of the cooling system is regulated by a rule-based hysteresis control strategy taking battery temperature and inverter temperature as inputs, as shown in Figure 5. To ensure that the battery temperature is <60 \({}^{\circ}\)C while the motor and inverter temperatures are each <150 \({}^{\circ}\)C, the switch-on thresholds in Figure 5 are far below these temperatures. Either battery temperature or inverter temperature can trigger the activation or deactivation of the cooling system, but the former holds an overriding position. When activated, the pump provides a flow rate for the coolant, and the fan will provide an air speed through the radiator [25]. For component thermal modelling, the motor and inverter are each considered as a lumped mass, and their heat generation \(Q_{gm}\) (W) is equal to their efficiency loss, as (2), where \(P\) (W) is the power of the motor or inverter and \(\eta\) is the efficiency of the motor or inverter. The heat dissipation \(Q_{dis}\) (W) of the motor or inverter is calculated based on the heat transfer to the coolant, as (3) [26], where \(T\) (\({}^{\circ}\)C) is the temperature of the motor or inverter, \(T_{lib,in}\) (\({}^{\circ}\)C) is the inlet coolant temperature of the motor or inverter, and \(r\) (K/W) is the thermal resistance of motor-to-coolant or inverter-to-coolant, which is measured from experiments and collected as an LUT based on the coolant flow rate. The updated temperature of the motor or inverter after cooling, \(T^{\prime}\) (\({}^{\circ}\)C), can then be obtained as (4) [27],  
Figure 4: Topology of the integrated liquid-cooling system. Blue and green arrows represent coolant and air flows, respectively. Figure 5: Switching control of the cooling system—hysteresis control strategy based on temperatures of the battery and inverter [25]. where \(\tau\) is the thermal time constant of the motor or inverter and \(dt\) (s) is the time step. The outlet coolant temperature of the motor or inverter, \(T_{\mathit{Iliq,out}}\) (\"C), can be acquired by (5) [28], where \(C_{\mathit{Iliq}}\) (\(\mathrm{J/K/kg}\)) is the heat capacity of the coolant, which is measured from experiments and collected as an LUT based on the inlet coolant temperature; \(\rho\) (\(\mathrm{kg/m^{3}}\)) is the density of the coolant, which is measured from experiments and collected as an LUT based on the inlet coolant temperature; and \(q\) (\(\mathrm{L/min}\)) is the coolant flow rate. Battery thermal modelling will be described in Section 4. \[Q_{\mathit{gen}}=\frac{P}{\eta}\times(1-\eta) \tag{2}\]  
\[Q_{\mathit{dis}}=\frac{T-T_{\mathit{Iliq,\ in}}}{r} \tag{3}\]  
\[T^{\prime}=T+\frac{(Q_{\mathit{gen}}-Q_{\mathit{dis}})\times r}{\tau}dt \tag{4}\]  
\[T_{\mathit{Iliq,out}}=T_{\mathit{Iliq,in}}+\frac{Q_{\mathit{dis}}}{C_{\mathit{ liq}}\times\rho\times q/60,000} \tag{5}\]  
The pump and fan models are used to control the coolant flow rate and the radiator air intake speed, respectively. The radiator is modelled by dividing it into the coolant side and the air side, as Figure 6. The heat transfer coefficients for each side are calculated based on the radiator's core, tube, and fin parameters as well as the properties of the coolant and air, including density, heat capacity, dynamic viscosity, and thermal conductivity. The two heat transfer coefficients are then weighted according to the coolant flow rate, air intake speed, and the inlet temperatures of the coolant and air to obtain an overall equivalent heat transfer coefficient. This is used to determine the outlet temperatures of the coolant and air. The formulas for the above-mentioned calculations can be found in [29].