**4. Conclusions**

g

Herein, a controller design method that reflects the small-signal voltage and current characteristics of a laser PV module for a wireless power system using a laser beam was presented. The laser PV module was fabricated to generate the maximum energy from a laser light source of a specific wavelength (1080 nm in the case of the module used in this study). From the PV module experiment, it was confirmed that the voltage and current characteristics were similar to those of the solar cell module. First, the power generated by the laser PV module varies according to the power of the laser beam. Therefore, to control the operating point to the maximum power generation point that varies

according to the power of the laser beam, the power conversion unit must have an MPPT control function. Secondly, the laser PV module has a characteristic of a small-signal resistance having a negative value similar to that of a solar cell module, and the small-signal resistance value increases as the operating point go to the current source region. Therefore, when designing the controller for controlling the operating point of the laser PV module, the small-signal resistance characteristics of the laser PV module must be reflected. Third, although not described in this paper, the temperature of the PV module increases when a laser beam is irradiated with the laser PV module. As the temperature of the laser PV module increases, the open-circuit voltage of the laser PV module tends to decrease rather than the magnitude of the short circuit current. Therefore, electrical characteristics analysis and control studies according to the temperature rise of the laser PV module are required as future research.

Accordingly, in this paper, a controller design method that can stably control the input voltage in the MPPT mode by inducing the transfer function of the boost converter, reflecting the small-signal characteristics of the laser PV module, was systematically presented. The method proposed herein was verified through simulation results based on Matlab/Simulink and an experiment involving a 25-W-class prototype boost converter.

**Author Contributions:** S.L. contributed to the main idea of this study and wrote the paper. S.L., N.L., and W.C. performed the experiments. J.B., Y.L., and J.P. revised the paper comprehensively. All authors have read and agreed to the published version of the manuscript.

**Funding:** This paper was supported by a Korea Institute for Advancement of Technology (KIAT) gran<sup>t</sup> funded by the Korea Government (MOTIE) (P0002092, The Competency Development Program for Industry Specialist). This work was supported the Korea Institute of Energy Technology Evaluation and Planning (KETEP) gran<sup>t</sup> funded by the Korea governmen<sup>t</sup> (MOTIE) (20182410105280).

**Conflicts of Interest:** The authors declare no conflict of interest.
