Wind Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 55

Main: 25 k 50 s/div

2.14 V

With MPPT Control

0.66 V

Without MPPT Control

0 50 100 150 200 250 300 350 400

Time (sec)

FIGURE 2.18
Performance of the WEH system with MPPT and without MPPT for charging a supercapacitor.

with MPPT is much higher than its counterpart without the MPPT scheme.
This is because more electrical power is transferred from the wind turbine
through the boost converter with the resistor emulation MPPT scheme to the
supercapacitor. Under a dynamic load condition, changing R load , the closed-
loop resistance emulator is still able to manipulate the duty cycle D of the
boost converter given by Equation 2.6 to maintain R em always at the optimal
resistance value, so that MPPT operation takes place. When the WEH system
is operating with the MPPT scheme, the amount of energy accumulated in the
supercapacitor after 500 s is 3.43 J, which is 10 times more than its counterpart
of 0.33 J; hence, this exhibits the superior performance of the WEH system
with the MPPT scheme over its counterpart under a dynamic load condition.
The charging process seen in Figure 2.19 , is divided into two regions: un-
controllable and controllable. Initially, the supercapacitor is fully discharged,

4000 mV WINDOW1 4000 mV WINDOW2

Uncontrollable
Region

Controllable Region

0 mV
0 mV

0 mV
0 mEU

4000 mV 1000 mEU

Load/Supercapacitor Voltage (V) Duty Cycle

FIGURE 2.19
Illustration of the supercapacitor's charging process using the WEH system with MPPT.