# A Novel Energy Optimization Control Strategy for Electric Drive System Based on Current Angle
## 4 Steady State and Transient State Simulation Validation
### Steady State Simulation Validation  
The target working conditions of the two controlled EDS were first set at 4000 rpm/40 Nm and then simulation was done in MATLAB/Simulink in this paper. When the EDS reached the target operating conditions and remained stable, the three-phase current \(i_{d}/i_{b}/i_{c}\) and the dq-axis current \(i_{d}/i_{q}\) of the two control strategies could be obtained under this steady state, as shown in Figure 12. The amplitude of \(i_{a}/i_{b}/i_{c}\) before optimization was 97.6 A, which was 58.96% larger than 61.4 A after optimization. Furthermore, the \(i_{d}/i_{q}\) before and after optimization was \(-\)79.8 A/52.3 A and \(-\)29.4 A/52.3 A, respectively, and at this time, \(\beta\) was 0.1847\(\pi\) and 0.3370\(\pi\), respectively. It can be seen that the proposed control strategy in this paper can reduce \(i_{d}/i_{q}\) of the motor by changing \(\beta\). Consequently, it can reduce the power of EDS and improve the overall efficiency of EDS. Figure 11: Schematic diagram of proposed control in this paper. In addition, the constant speed-variable torque and constant torque-variable speed performance of the EDS are very important. Therefore, the working condition at 4000 rpm and variable torques and working condition at 40 Nm and variable speeds were simulated in this paper, in which the EDS efficiency, copper loss, iron loss, inverter loss, and overall loss of EDS controlled by traditional control and proposed control were studied respectively. The results are shown in Figures 13 and 14. Figure 13 shows the comparison of EDS before and after optimization at 400 rpm and variable torques while Figure 14 shows the comparison of EDS before and after optimization at 40 Nm and variable speeds. Figure 14: Comparison of EDS efficiency (**a**) and various losses (**b**) between traditional control and proposed control at 40 Nm and variable speeds. Figure 12: Current comparison between traditional control and proposed control at 4000 rpm/40 Nm: Traditional control current diagram (**a**); proposed control current diagram (**b**). Figure 13: Comparison of EDS efficiency (**a**) and various losses (**b**) between traditional control and proposed control at 400 rpm and variable torques. In order to verify the superiority of the proposed control strategy in this paper compared with the traditional control strategy in the full working range, simulation of different steady-state conditions was carried out, and the results are shown in the Table 2. It can be seen that the inverter efficiency was always maintained at a high level, and its change contributed less to the change of EDS efficiency than that of the motor. However, it can be seen from the table that the optimization of overall EDS efficiency will be more accurate only when considering the inverter efficiency and motor efficiency together. As shown in Table 2, 2880 rpm was the base speed of the motor. Before this, the optimized value of EDS efficiency by the control strategy proposed in this paper was not high compared with the traditional MTPA control. This is because the traditional MTPA control has minimized the copper loss in the motor, which improves EDS efficiency to some extent. Despite all this, the control strategy proposed in this paper still improved the EDS efficiency by as much as 0.6% compared with the traditional control. When the motor enters into the flux weakening region, the optimized value becomes obvious. For instance, compared with the traditional control, the highest improvement of EDS efficiency by the proposed control occurred at 5000 rpm/40 Nm, reaching 5.9%. Through the above results of steady state analysis, it can be concluded that the proposed control strategy can effectively improve the overall efficiency of EDS compared with the traditional control strategy.