Analysis of a Commercial Biogas Generation System Using a Gas Engine–Induction Generator Set

This paper presents both field-measured results and dynamic stability analysis of a commercial 100-kW biogas generation system (BGS). The studied BGS consists of a gas engine (GE) and an induction generator (IG) whose mechanical shaft is directly coupled to the crank of the GE. The stator windings of the IG are directly connected to a three-phase, three-wire 380 V, 60 Hz distribution system through a connection cable and an electromagnetic switch. To start up the BGS, the IG is first operated as both an induction motor (IM) and a GE starter to generate sufficient starting torque to start up the GE. The purified biogas mixed with air of proper proportion inside the combustion chamber of the GE is ignited by spark plugs at correct instants to make GE generate sufficient mechanical torque to drive the IG. When the speed of the IG is higher than its synchronous speed, the IG can deliver electrical power to the distribution system. The employed parameters of the studied IG are calculated by using the manufacturer's certification data and comparing both field-test data and simulated results under two specified operating rotational speeds. Dynamic stability analyses of the studied BGS using eigenvalue analysis and nonlinear model simulations under various values of rotational speed and grid voltage are investigated. It can be concluded from the field- measured data and the simulated results of the studied BGS that the studied GE-IG set has a fast response and exhibits stable and easy grid-connection characteristics for converting biogas energy to electrical energy.