The operation and performances of an innovative small scale polygeneration system (BIO_MGT), which combines biomass and natural gas in a micro gas turbine, has been simulated in the present work by means of a thermodynamic matching analysis. The BIO_MGT unit matches an externally fired cycle with a commercial Micro Gas Turbine (MGT, 100 kWe). A significant share of the total energy input (similar to 70%) is supplied by solid biomass: the remaining is provided by natural gas. The system is therefore characterised by a dual combustion system. The configuration of the plant has been conceived so to require only minor modifications to conventional MGTs and biomass furnaces available on the market. This paper describes the design of the proposed bioenergy plant as well as the structure and the application of the in-house developed simulation model AMOS which has been used as computer-aid design tool. The design activity compared various plant schemes available from literature or past research works. The thermodynamic matching analysis of the selected configuration was then carried out, with the aim to verify compressor and turbine working points and to compare these with those typical of the MGT working under standard natural gas conditions. The steady-state matching analysis was based on the performance maps (i.e. characteristic lines) of each component. The design specifications and operating range for main and sub-components were defined, and the BIO_MGT performance maps were computed. Results showed that both the turbine as well as the compressor will work within the acceptable limits, and plant performances have also been calculated at part load conditions. (C) 2009 Elsevier Ltd. All rights reserved.