# Motor Vector Control Based on Speed-Torque-Current Map
## 4 Verification of the Proposed Vector Control Strategy
### Simulation Analyses
#### 4.2.2 Torque Coupling Mode Performance Simulation  
According to the flow shown in Figure 15, the designed simulation condition of the torque coupling mode is as follows: during the period from 0 to 0.05 s, the vehicle speed is adjusted to 18 km/h. In this process, the torque is adjusted to the required torque. After 0.05 s, the vehicle accelerates to 19.7 km/h with 1.8889 m/s\({}^{2}\) acceleration during 0.25 s. When the vehicle speed is 18 km/h and the acceleration is 1.8891 m/s\({}^{2}\), the required torque and speed of the main reducer are 224 Nm and 720 rpm, respectively. According to the dynamic equation of the torque couple mode, the speeds of MG1 and MG2 are 1494 rpm and 2237 rpm, respectively. Under the corresponding speed constraint, the maximum electromagnetic torques of MG1 and MG2 can achieve 153 Nm and 75 Nm, respectively. The torque intervals of MG1 and MG2 are [-153 Nm, 153 Nm] and [-75 Nm, 75 Nm], respectively. Moreover, the torques of MG1 and MG2 (i.e., \(\rm T_{m1}\) and \(\rm T_{m2}\)) are also limited by the demand torque \(\rm T_{o}\) of the main reducer, namely:  
\[\rm T_{o}=T_{m2}\cdot(k+1)\cdot i_{2}\cdot\eta_{2}\cdot\eta_{p}+T_{m1}\cdot i_ {1}\cdot\eta_{1}. \tag{17}\]  
The motor electromagnetic torque is the sum of the load torque and the speed regulating torque. If the load torque is too large, the motor will lose the ability to regulate the speed. In order to meet the requirements of the output characteristics of the main reducer, the initial and target torques of MG1 are limited in the range of [-2 Nm, 148 Nm] based on Equation (17). Under the same working condition, the torque of MG1 is 88 Nm according to the motor static model control strategy, which is set as the initial MG1 torque. That is, T1 = 88 Nm. In this section, the MG1 target load torque value (T1* = -2 Nm) is taken as an example to analyze the speed-torque characteristics during the transition process of two motor working points under this working condition. The dynamic response process of the two motors is shown in Figure 18.  
Figure 18 demonstrates the change of the two motor speeds, as the vehicle speed is adjusted to 18 km/hat, no load condition during the period of 0-0.045 s. In the period of 0.045-0.05 s, the torques of the two motors are adjusted to the demand torque corresponding to the condition (i.e., 18 km/h vehicle speed and 1.8991 m/s2 acceleration. At the moment of 0.05 s, the motor MG1 is loaded by the target  
Figure 18: Changes of speed and torque of MG1 and MG2. torque of \(-2\) Nm, and the torque of MG2 is calculated from the real-time load torque and the load torque of MG1. In the torque coupling mode, the torques of MG1 and MG2 can be coupled arbitrarily, as long as the output torque of the vehicle meets requirements. This means that countless combinations of the torques of MG1 and MG2 exist. The economy of each combination can be measured by the demand power of the electric drive system. According to the flow shown in Figure 16, the MG1 target torque is traversed to obtain the corresponding demand power of the electric drive, as shown in Figure 19.  
When the demand torque is constant in the torque coupling mode, the torque of MG1 is 88 Nm on the point of the allocated power obtained from the static model. In the dynamic model, the demand power of the electric drive system first decreases and then increases with the increase of the MG1 target torque, as shown in Figure 19. Note that the starting point \(T_{1}{}^{*}=-2\) Nm, the final point \(T_{1}{}^{*}=148\) Nm, and the trough point \(T_{1}{}^{*}=68\) Nm are employed in the simulation studies, as shown in Table 4.  
The motor static model cannot reflect the loss during the transition process of the motor working point, so the optimal power distribution scheme of the two motors cannot be obtained when the power demand of the system is fixed. If the vehicle demand torque is constant, MG1's target torque is too high, which results in MG1 working near the peak torque.