Variable-speed operation of cogeneration plants - a concept with many advantages

Since current CHPs have a fixed speed, the partial load range is achieved by reducing the torque. The modulation capability is only economical up to 50% of the nominal power. The consumption characteristic field of a typical internal combustion engine shows that the specific fuel consumption increases more with the moment than with the engine speed. With generators operated directly on the grid, only a fixed speed, either 1500 min-1 or 3000 min-1, is possible. CHP units equipped with a four-quadrant converter can be operated at variable speeds at any operating point up to the maximum speed of the internal combustion engine. In this way, cheaper operating points with better electrical efficiency can be reached.

The project on which this report is based was funded by the Federal Ministry of Education and Research under grant number 03FH076PX2. The author is responsible for the content of this publication.