# An Inverter Topology for Wireless Power Transfer System with Multiple Transmitter Coils
## 4 Proposed Controller
### Primary-Side Controller  
The proposed control block diagram of the primary-side controller is shown in Figure 14. First, the controller operates in the transmitter coil selection mode, as shown in Figure 14a. Each transmitter coil is energized, one at a time. The current in each transmitter coil is obtained through the measured total primary current, \(I_{PT}\), and sent to the current sensor. A signal conditioner consisting of a rectifier and low-pass filter circuit is included in the current sensor module. The DC signal representing the magnitude of the total primary current, \(|I_{PT}|\), is obtained. The MCU reads the \(|I_{PT}|\) signal through the analog to digital (A2D) converter function. Then, the controller starts the coil selection process. All the \(|I_{PT}|\) signals collected from each transmitter coil are compared with \(|I_{PT}^{limit}|\), as described in Section 3.2. Then, the switching pattern of the inverter circuit is obtained for a proper transmitter coil pattern corresponding to the receiver coil position. After the selected coil pattern is energized, the controller operates in the output voltage regulation mode, as shown in Figure 14b.  
This mode is based on the relationship between the output voltage and angle \(\alpha\) of the inverter voltage in Equation (7). The output voltage signal, \(V_{out}\), is wirelessly fed back from the secondary side, and compared with the reference value (\(V_{out}^{*}\)). The resulting error (e) is sent to the PI controller, and the adjusting angle \(\alpha\) is obtained.  
Figure 13: Program flowchart of the secondary-side controller.  
The program flowchart of the primary-side controller is shown in Figure 15. At the beginning, the controller operates in the transmitter coil selection process. To prevent excessive current in each transmitter coil, the angle \(\alpha\) of 126 degrees is assigned to the upper switch \(\mathsf{S_{U}}\). The current limit, \(\left|I_{PT}^{limit}\right|\), is set to 1.5 A. Initially, the transmitter coil number 1 (i = 1) is energized by turning the switch \(\mathsf{S_{1}}\) on. Then, the current signal \(\left|I_{PT}^{(1)}\right|\) is read. If \(\left|I_{PT}^{(1)}\right|>\left|I_{PT}^{limit}\right|\), the switching function of the excitation switch (\(S^{(1)}\)) is set to \"0\"; otherwise, it is set to \"1\". As the value of \"1\" is increasing, transmitter coils 2, 3, and 4 take turns energizing. The signals \(\left|I_{PT}^{(2)}\right|\), \(\left|I_{PT}^{(3)}\right|\), and \(\left|I_{PT}^{(4)}\right|\) are read and compared with the \(\left|I_{PT}^{limit}\right|\). The switching pattern of the inverter circuit is obtained. The pattern 0 is obtained when the receiver coil is placed outside the designated area. That is, the magnetic coupling is too weak, and the system will be turned off. The proper transmitter coil pattern is formed if the switching pattern 1 to 15 is presented. Next, the controller operates in the output voltage regulation process. The output voltage data \(V_{out}\) is read. If \(V_{out}=0\), the detection switches are still on, and the system is in the detection mode. The controller will wait until the system is in normal operation mode, where \(V_{out}\) is not equal to zero. Then, the feedback signal \(V_{out}\) is compared with the reference signal, \(V_{out}^{*}\). With the PI controller, the angle \(\alpha\) of an inverter voltage is adjusted. The actual output voltage follows the reference value.  
Figure 14: Proposed control block diagram of the primary-side controller: (**a**) Transmitter coil pattern selection mode; (**b**) Output voltage regulation mode.  
Figure 15: Program flowchart of the primary-side controller.