Introduction
The Philips woodstove is a high tech cooking device for cooking in communities currently relying on less efficient means. It is designed for burning wood very efficiently and for reducing the smoke and toxic emissions to very low levels. When properly used the woodstove typically reduces fuel consumption up to 80% compared with traditional, three stone fires. Apart from faster and more convenient cooking, this energy efficiency means the stove can save the cost of the time needed to gather fuel, and should also slow deforestation. The Philips woodstove reduces pollution due to smoke up to 90%, and organic volatile emissions up to 99% of the level of traditional cooking fires.

Requirements
To reach such efficient burning an electronically controlled fan forces air through the stove, leading to higher temperatures and a better fuel to air ratio. The problem is that there is normally no electricity available in the neighbourhood. To cope with this a thermoelectric generator (TEG) is used that generates electricity out of the heat from the burning wood. For the cold start a small, rechargeable battery is used which will be recharged once there is sufficient power from the TEG. The electronics needed for the woodstove has to convert the low voltage from the battery and TEG to the higher voltage needed for the fan. This conversion should be done at the highest possible efficiency both in power conversion as in load matching because the energy from the TEG is limited. It also has to control the battery recharging process and the regulation of excess energy to e.g. an external LED light. It’s a kind of an intelligent energy balancer.

Design phase
After some initial experiments it became clear that for intelligent, flexible functioning of the electronics a microcontroller is needed. MiPlaza started the design of the electronics. To reach a high efficiency of the power converter the choice of components should be done very carefully. Clever selection of components in relation to the characteristics of the TEG resulted in a power conversion efficiency of over 90%. After the hardware was fixed most of the design is pure embedded software.

Realisation
MiPlaza was also responsible for the manufacturing of the prototypes. The first (hand wired) prototype was used externally from the woodstove. After some extensive tests by the customer the design and software was further optimised for a second prototype. This prototype was smaller and is built into the woodstove casing. Two of those second prototypes were used extensively for demonstrations. The second prototype is also used as base for the pilot production version. MiPlaza gave extensive support to the department responsible for the pilot production.