A comparison of micro gas turbine operation modes for optimal efficiency based on a nonlinear model

The novel contribution of this paper is that Micro gas turbine (MGT) operation modes for optimal efficiency are compared based on a nonlinear model, and the variable-speed control is proposed for optimal efficiency. The nonlinear mathematical MGT model is established based on thermodynamic analysis, which can completely reflect the MGT operational characteristics. When the air flow rate is fixed, the rotational speed of the rotor greatly influences the MGT efficiency. At a certain value of speed, the system efficiency reaches its maximum. On this basis, the efficiency of four MGT operation modes are studied: 1. constant speed of a simple cycle, 2. variable speed of a simple cycle, 3. constant speed of a regenerative cycle, and 4. variable speed of a regenerative cycle. In this paper, the relationship between optimal efficiency and the corresponding rotational speed of different output powers formulated using a numerical calculation method is studied. The optimal efficiency formula can be used to generate the given speed of the MGT speed controller for optimally efficient operation. The results show that the variable-speed operation mode of the regenerative cycle exhibited the highest system efficiency and has an evident efficiency optimization effect under a small load. - Highlights: • The efficiency optimal control method of micro gas turbine(MGT) is proposed. • The MGT efficiency of four operation modes is studied. • The existence of the efficiency optimal operation point by changing speed is verified. • Efficiency of the efficiency optimal mode and the constant speed mode is compared. • The variable speed mode of regenerative cycle is optimal and more obvious effect with light load.