Dynamic Modelling and Control of a Reciprocating Engine

Nowadays energy systems should be considered as integrated energy systems (IESs), where interactions between different energy vectors affect each other. A good performance of the whole system depends on the adequate behaviour of each individual element as undesired dynamics may propagate from one element to another. Due to the system complexity, a common practice is to employ steady-state models. Although such an approach is valuable as it provides significant insight into the system behaviour, it may hide inherent coupling characteristics as the dynamics are not considered. To ensure the satisfactory performance of each component,dynamic models are not only required, but essential. With a truly dynamic model it is possible to clearly understand how the system is affected by different operating conditions, load variations and disturbances over time, which in turn enables an effective control system design. Following this line, this paper presents a mathematical model, based on the mean value approach, of a reciprocating engine, which is used in combined heat and power units – key component of an IES. Although the system is non-linear, it is shown that a single-input single-output linear system can be derived and, thus, a frequency domain representation suitable for control system design can be obtained. The system has been developed in MATLAB/Simulink. Simulation results show that the designed linear controller is capable of ensuring a good performance of the reciprocating engine non-linear model.