# A Novel Energy Optimization Control Strategy for Electric Drive System Based on Current Angle
## 4 Steady State and Transient State Simulation Validation
### Transient State Simulation Validation  
In reality, the working condition of EDS is complex and changeable and works in transient state at most times, so it is necessary to verify the transient performance of EDS. In order to verify the excellent performance of the proposed control strategy in the transient state, the transient simulation of EDS controlled by the proposed control strategy and EDS controlled by the traditional control strategy was carried out, respectively. The simulation time was 0.5 s and the time interval was 0.000001 s. In addition, the SVPWM modulation frequency \(f_{prem}\) (inverter switching frequency) was 20 kHz in the two EDS models. The target speed in 0 s-0.1 s, 0.1 s-0.2 s, 0.2 s-0.3 s, 0.3 s-0.4 s, and 0.4 s-0.5 s was set as 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm, and 6000 rpm, respectively, and the load before 0.25 s was set as 60 Nm while the load after 0.25 s was set as 40 Nm. The simulation results of EDS controlled by the traditional control strategy and EDS controlled by the proposed control strategy are shown in Figure 15, including torque, speed, dq-axis current \(i_{d}\) /\(i_{q}\) various losses, and EDS efficiency. In Figure 15a, the simulation results of the proposed control and the traditional control were almost the same, and the torque and speed curves of EDS before and after optimization almost overlapped, which showed that the proposed control strategy can ensure the power performance of EDS to achieve the same control effect as the traditional control strategy. In addition, when the EDS speed exceeded the base speed 2880 rpm, which meant the EDS entered into the flux weakening region, the optimized torque was slightly lower than the traditional control strategy in accelerating process, as shown in the last three torque peaks in Figure 15a. That is because traditional control only considered the limit of voltage limit circle and current limit circle, but ignored the limit of motor power, whereas proposed control in this paper considered the power limit of EDS, so its torque was slightly smaller than that of traditional control, which was more reasonable. Figure 15b showed the difference between the proposed control strategy and the traditional control. The control strategy in this paper increased the negative value of \(i_{d}\) by changing the value of \(\beta\) and \(i_{s}\) before base speed region. For example, \(i_{d}\) was \(-17.6\) A and \(-24.5\) A at 2000 rpm/40 Nm and 3000 rpm/40 Nm, respectively, while those in traditional control were 0 A. On the other hand, after base speed region, namely in the flux weakening region, it not only met the driving demand, but also made the amplitude of \(i_{d}\) smaller and the loss of the EDS lower than the traditional one. In the case of 4000 rpm/60 Nm, 4000 rpm/40 Nm, 5000 rpm/40 Nm, and 6000 rpm/40 Nm steady states, \(i_{d}\) in proposed control were \(-29.5\) A, \(-28.7\) A, \(-37.2\) A, and \(-41\) A, respectively, while those in traditional control were \(-82.3\) A, \(-83.5\) A, \(-108.7\) A, and \(-121.5\) A, respectively. Figure 15: _Cont._Figure 15: Comparison of transient state performance between proposed control and traditional control: The comparison of torque and speed between two controls (**a**); the comparison of \(i_{d}\) and \(i_{q}\) between two controls (**b**); the comparison of different loss between two controls (**c**); the comparison of efficiency of EDS between two controls (**d**). As shown in Figure 15c-d, copper loss accounts for most of the EDS loss, so the EDS efficiency was more affected by the change of copper loss. Before 0.2 s, the optimization of current vector traditional MTPA and FW control was enough, and the optimization of the control strategy proposed in this paper mainly came from iron loss and inverter loss. At this time, the efficiency optimization of EDS was from 86.2% of the traditional control efficiency to 86.6% at 2000 rpm/60 Nm, and from 88.6% to 89.2% at 3000 rpm/60 Nm. After 0.2 s, the control strategy proposed in this paper obviously changed the current vector.