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Bachelor's Thesis

Maximum Power Point Tracking for Solar-Powered Wireless Sensor Nodes


In the operation of wireless sensor networks, energy is the limiting factor for the lifetime of the sensor nodes. Despite the efforts to decrease the energy consumption, the lifetime of a node is still limited by the capacity of its battery. To create a self-sustaining system, generating energy from the environment using energy harvesters is a suitable solution. One of the most common energy sources is harvesting solar radiation by using photovoltaic cells. Though easy to use, the efficiency can be improved by using a more complex design.

Following Joule’s law P=U·I the maximum power is depending on the characteristic of the cell. The maximum power of a photovoltaik cell is produced at its maximum power point (MPP). This point is not fixed, but depends on the solar radiation, the temperature and the age of the cells. To produce the maximum energy in all situations, the current point of operation needs continuous adjustments to follow the MPP. This is called maximum power point tracking (MPPT).

Work Description

The objective of this thesis is to design, build and test a MPPT energy supply for a wireless sensor node. The MPPT control can be done either in hardware or in software on a microcontroller. The microcontroller platform is based on a wireless sensor node called IRIS from Crossbow Technology.

The main tasks are to design the electric circuit, develop a printed circuit board and implement the control-software on the microcontroller of the IRIS node. The microcontroller is programmed in C. The software measures the environmental parameters to control a DC-DC converter to operate at the MPP.

MPPT is a common business and multiple solutions and detailed information are available. The challenges in this work are the design requirements for a small sensor node. The circuit must be small, cost effective and energy efficient especially for low input power. The harvested energy is stored in a supercapacitor, which shows a different charge characteristic from typical other accumulators. The software controls are integrated in the sensor node software and must not interfere or consume too much computation power for itself.

Start date 20. September 2010
End date 3. January 2011
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Supervisor Jürgen Jessen