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

Abstract

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.

A high efficiency 20kWe microcogeneration unit based on a turbocharged automotive gas engine

“…As regards compatibility with the specific grid needs, it should be remembered that some active power factor control systems and line filters [5,6] could be required, because each different phase could serve three different 230 VAC utilities. Moreover, during self-starting a high over-current could occur, this aspect making require some device to be adopted (like the insertion of specific electric resistances).…”

“…However the author considers that some diminution in the generation efficiency of the machine should be expected when coupled to an I.C.E. when running at high loads, this because of torque and speed fluctuation deriving from pressure peaks [6].…”

“…In the following Table 4 the gaseous emissions (after catalyst) have been reported at different loads, resulting well below the ½ Luft regulation limits which are considered the reference values for European Union. As regards the electric efficiency and power quality, it can be observed that generator seems to be just slightly affected by torque variability caused by the internal combustion engine, also thanks to a high inertia flywheel and an elastic coupling placed between the engine and generator [6]. The system also showed that the power regulation performed by varying turbo-charging pressure and EGR rate is very attractive, because it can give an adequate power regulation in most of real cases without important efficiency drop caused by throttling [7], while limiting gaseous emissions and keeping the system very simple and cost effective.…”

A single input dual buck-boost output reconfigurable converter for distributed generation

“…market and the growing concerns about environmental gas emission have been key factors for the diffusion of local distributed energy sources (DES) [1]. Typical DES are photovoltaic arrays [2,4], fuel cells [5,6], variable speed wind turbines [7], and high efficiency cogenerator systems [8,9].…”