# An EV SRM Drive and Its Interconnected Operations Integrated into Grid, Microgrid, and Vehicle
## 3 EV SRM Drive
### DC Source-Povered Fixed DC-Link Voltage SRM Drive
#### 3.1.2 Control Scheme  
The proposed control scheme of the SRM drive is shown in Figure 4. It consists of an outer speed loop, inner current loop, commutation scheme, and PWM switching scheme. In driving mode, the dynamic commutation tuning (DCT) scheme generates the advanced shift angle \(\beta_{d}\) to improve the current tracking response. The back-EMF current feedforward controller (CFFC) yields the control voltage according to the motor speed, observed inductance slope, rotor position, and current command to compensate the effects of back-EMF under high speed and heavier load. As the DC-link voltage exceeds the preset value (570V), the dynamic braking leg chopped operation will be activated. To let the EV SRM drive successfully perform regenerative braking in deceleration, when the current command \(I_{c}^{*}\) becomes negative, the commutation angle will be shifted backward \(\beta_{g}=21.24^{\circ}\) to let SRM operate as an SRG. The relationship between \(\beta_{d}\), \(\beta_{g}\), and dwell angle (\(\theta_{d}\)) is shown in Figure 5.  
Figure 4: Control scheme of SRM drive. Figure 5: Relationship between \(\beta_{d}\), \(\beta_{g}\) and \(\theta_{d}\) in commutation mechanism. Dynamic commutation tuning scheme  
As shown in Figure 5, the DCT scheme is proposed to shift the commutation angle forward automatically, which excites the stator winding at the small inductance slope region (\(\partial L(i,\theta_{r})/\partial\theta_{r}\approx\ 0\)). By neglecting the winding resistance and back-EMF, and assuming the constant winding inductance (\(L(i,\theta_{r})=L_{\text{min}}\)), the advanced shifted time interval \(\Delta T_{d}\) and angle \(\beta_{d}\) can be estimated to let the winding current be raised to the command \(I_{c}^{*}\) as follows:  
\[\Delta T_{d}=\frac{L_{\text{min}}}{v_{dc}}I_{c}^{*},\ \beta_{d}=\Delta T_{d} \omega_{r}=\frac{L_{\text{min}}}{v_{dc}}I_{c}^{*}\omega_{r} \tag{1}\]  
In the proposed current control scheme of each phase shown in Figure 4, the PWM control force \(v_{c}\) is composed of the following: (i) the feedback control voltage \(v_{cb}\) by the current controller \(G_{ci}(s)\); (ii) the back-EMF feedforward term \(v_{cd}\); and (iii) the current command feedforward term \(v_{cf}\). The sensing factor for the winding current is \(K_{i}=0.03\) V/A, the DC-link voltage sensing factor is \(K_{v}=0.00145\) V/V, and the motor speed sensing factor is \(K_{av}=0.0001\) V/ rpm. Back-EMF current feedforward controller (CFFC)  
Based on the estimated SRM inductance slope, the back-EMF feedforward control terms can be determined as:  
\[v_{cd}=\theta_{i}=\frac{\omega^{\prime}r}{K_{av}}\frac{i_{i}^{*}}{K_{i}}K_{Li} \frac{K_{v}}{v^{\prime}_{dc}}=\frac{K_{Li}K_{v}}{v^{\prime}_{dc}K_{i}K_{av}}i _{i}^{*}\omega^{\prime}r,\ i=1,2,3 \tag{2}\]  
where  
\[K_{L1}\underline{\Delta}\ \frac{\partial L_{1}(i_{1},\theta_{r})}{\partial \theta_{r}}=0.00373,\ K_{L2}\underline{\Delta}\ \frac{\partial L_{2}(i_{2},\theta_{r})}{\partial \theta_{r}}=0.00437,\ K_{L3}\underline{\Delta}\ \frac{\partial L_{3}(i_{3},\theta_{r})}{ \partial\theta_{r}}=0.00369 \tag{3}\]  
Current feedback controller  
The current controller is set to PI type as:  
\[G_{ci}(s)=K_{pi}+\frac{K_{ii}}{s} \tag{4}\]  
Due to the DCT scheme, it is assumed that the winding inductance is the smallest at the beginning of the commutation and there is no back-EMF effect.