Active Vibration Cancellation of a Free-Piston Linear Generator Engine

A free-piston linear generator engine (LG) is a device that couples a free-piston combustion engine with a linear electric generator. The engine is consisted with a part called piston-rod assembly (PRA), where two pistons are connected by a rod attached with permanent magnet. During the operation of LG, PRA will linearly reciprocate between two internal combustion chambers on the opposite sides. However, when the PRA is on one side of the engine, an unbalanced impact force is created. The unbalanced forces provide an undesirable impact force acting on the engine block, causing the engine to vibrate. The control of vibration for the LG becomes crucial, because proper vibration controls maintain a consistent electricity output and maximize the efficiency of the engine. Current work proposed using a linear motor (LM) to create an anti-phase momentum into the system to counter the impact forces created by PRA. The works are based on analytical modeling with MATLAB used for simulation. Simulation shows the system instability characteristics, the time and frequency responses for LG. The results showed the existence of a real pole at the right hand side of complex plane which contribute to the system instability. The non-proportional damped time response obtained using state-space approach shows the overall interaction between mass forcer and PRA decreased with respect to time. The frequency responses showed that with the application of active vibration cancellation, the resonance can be delayed and the magnitude of the resonance can be reduced. A lumped-mass quarter car suspension model is used for validation. Case study is carried out to decide the best available driven forces that drive the LG. The conclusion of current study showed that with proper vibration control for the LG, the vibration level of LG can be reduced to a desirable level while maintaining the optimum operating conditions.