Torque-oscillations damping in micro-cogeneration units with high brake mean pressure engines and PM-brushless generators

The paper discusses the concept and the overall performance of a 20 kW micro-cogeneration unit, suitable for distributed energy conversion and based on a 4-cylinder, supercharged methane fuelled, spark ignited, internal combustion engine (ICE). The latter is coupled to a three-phase PM-brushless electric generator, whose armature is controlled by an active front-end [12,14]. The ICE is derived from a widespread Diesel unit, which has been properly modified; it is chosen among many other engines as a reliable, very high efficiency, cost effective unit [6], suitable for energy conversion systems (such as residential or commercial applications). The paper starts by defining the criterion which led to the adoption of a high brake mean pressure, in order to produce the above mentioned electric power. After the description of the solutions adopted to optimize the ICE operation performance, a very simple and efficacious control strategy of the generator+converter set is presented. This technique is able to conveniently reduce the magnitude of shaft-torque ripple produced by a high brake mean pressure (and consequently cycle peak pressure), in order to reduce vibrations, noise and rotating speed oscillations. The control is based on assigned curves of ICE torque vs. shaft angular position. Some considerations are also made to define the right generator sizing, in order to allow an efficacious damping action, maintaining good efficiency levels of the generator+converter set. The effectiveness of the control is validated by a series of numerical results in significant operating conditions.