Energy Harvesting (EH) plays the main role in sustainable powering low-power application. Wireless sensor network (WSN) is an important topic in developing the applications of the Internet of Things (IoT). The challenge of integrating EH with WSN is efficient power management techniques. In this book, a hybrid energy harvesting system consists of a photovoltaic (PV) system, a Piezoelectric (PIZO) system, and a Fuel cell (FC) system which successfully implemented and connected with the proposed switching technique to achieve the selection of the suitable switch with priority condition for lithium battery charging and discharging. Charging and discharging bi-directional buck-boost DC-DC converter controlled by three Proportional Integral Derivative (PID) controllers.