Hybrid Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 150

harvested without MPPT. This proves that MPPT is beneficial in maximizing
the amount of energy that can be harvested from the solar panel.

5.2.3 Hybrid Solar and Wind Energy Harvesting System

In this HEH research, the outputs of the WEH and SEH subsystems were
connected in parallel so that more power could be delivered to the electri-
cal load. The expected outcome of this hybrid topology is the summation of
the harvested powers of the WEH and SEH subsystems as shown in Figure
5.3 . The two diodes as shown in Figure 5.3 connect the outputs of the WEH
and SEH subsystems together, and they play a critical role in their successful
combination. The role of the diode is to prevent any current flow from the
output of either boost converter to the other subsystem as shown in Figure
5.10 . As such, simultaneous charging from both energy sources is accom-
plished. In addition, with these blocking diodes, the proposed HEH topology
is able to carry out MPPT operations in the WEH and SEH subsystems. The
WEH subsystem uses the resistor emulation (RE) technique, while the SEH
subsystem uses the CV technique.
Referring to Figure 5.10a , when the WEH subsystem is operating in MPPT
mode, it is observed that the SEH subsystem appears as an infinite resistance
to the WEH subsystem. The effective load experienced by the WEH subsys-
tem is just simply the energy storage device. Similarly, for the SEH subsystem
seen in Figure 5.10b , it sees the WEH subsystem as an infinite resistance,

Wind Energy Harvesting Subsystem

V wind

V cap

AC-DC
Active
MOSFET
Rectifier

Wind
Tu r b ine-
Generator

Wireless
Sensor
Node

Boost
Converter
with MPPT

Energy
Storage

∞Ω

(a) Wind energy harvesting subsystem in MPPT operation

V cap

Wireless
Sensor
Node

Energy
Storage

∞Ω

Solar Energy Harvesting Subsystem

V solar

Boost
Converter
with MPPT

Solar
Panel

(b) Solar energy harvesting subsystem in MPPT operation

FIGURE 5.10
Efficiency plot of a diode block under varying solar irradiance and resistance loadings.