## 4 Simulation and Experiment Results
### Experiment Result  
In order to verify the communication hardware proposed in this paper, the system was constructed and the experiments were performed in the same way as the simulation.  
Figure 11 shows a system with three-level communication hardware that can transmit and receive simultaneously in two-wire communication. The system consisted of three 500 W class power converters in parallel. The communication was conducted by constructing a protocol with 19,200 bps, 2-byte data, and 2-byte CRC as in the simulation.  
Figure 12 shows the result waveform of communication hardware proposed in this paper. As for the order of the result waveform from the top, transmit data TX1 and TX2, communication line three-level voltage \(V_{L}\), and received data RX are listed. As shown in the figure, the two transmitters transmit data, but the synchronization is different, so the three-level voltage appearing on the communication line voltage \(V_{L}\) is different. However, in the case of the received data, it can be confirmed that the data of the sender is correctly received. When parallel operation is performed using the three-level communication, as described above, it is two times faster than the conventional communication method. In order to verify this, the parallel operation experiment was conducted compared to the existing serial communication method. At this time, the controller characteristics of each power converter were set the same to check the control characteristics according to the load variation.  
Figure 10: Parallel operation simulation circuit diagram. (**a**) Resulting waveform using the existing communication method; (**b**) resulting waveform using the proposed communication method.  
Figure 11: Power converter system with three-level communication hardware.  
Figure 12: Simultaneous bidirectional communication experiment results.  
Figure 13 shows the resulting waveforms, when parallel operation is performed using the existing serial communication method and the three-level communication. The experiment proceeds under parallel operation by changing the load conditions (50%\(\rightarrow\)100%\(\rightarrow\)50%). The blue portion of the waveform indicates 50% load condition, and the red portion indicates a 100% load condition. The experiment compared the difference according to the communication method by checking the output voltage, the current waveform of the master converter, and the current waveform of the slave converter. The experiment was difficult to measure, clearly due to the current delay according to the communication method, if the communication speed is too fast. Thus, the experiment was conducted by constructing the protocol with 19,200 bps, 2-byte data, and 2-byte CRC.  
Figure 13: Parallel operation experiment waveform. (**a**) Parallel operation result waveforms applied to existing serial communication; (**b**) parallel operation result waveforms applied to three-level communication.  
Figure 13a shows the resulting waveform when parallel operation is performed by applying the existing serial communication method. As can be seen from the result waveform, the variation of the output voltage is large due to the delay of the current command value according to the communication speed when the load variation occurs. Figure 13b shows the result waveform when parallel operation is performed using the communication method proposed in this paper. As can be seen from the result waveform, the delay of the current command value is reduced and the variation of the output voltage is relatively stable compared to the conventional serial communication method.