*2.4. Model of Diesel Engine*

Considering the unpredictability and uncontrollability of wind turbines and photovoltaic power generation in the microgrid system, in order to meet the reliability of the power supply of the microgrid system, it is usually necessary to configure a backup power supply for the microgrid system in case of emergency [25]. The backup power source configured in this study is a diesel generator.

However, diesel generators will cause environmental pollution and increase the operating cost of the system. Therefore, it is usually only put into use when renewable energy generation is insufficient to meet the power demand of the load. Moreover, diesel generators cannot run at lower operating power levels. Operating power levels that are too low not only increase fuel consumption, but also affect the operation of diesel generators, and reduce their service life. The minimum operating power level of the generator is 30% in this paper.

In addition, diesel generators should be able to operate at a power level of 75%. At this time, it is not only the most economical in terms of fuel consumption and output power, but also the spinning reserve of the unit, which is the best operating power for diesel generators.

In summary, in the range of 30–100% of diesel generator operating power, the relationship between its fuel consumption *F* and its output power can be expressed as follows [25],

$$F = F\_0 \cdot P\_{dc-rate} + F\_1 \cdot P\_{dc} \tag{8}$$

where *Pde*−*rate* and *Pde* represent the rated power value and actual output power value of the diesel engine, respectively, *F*0 and *F*1 represent the two fitting coefficients of the fuel-power curve of the diesel generator, which can generally be measured according to the actual measurement of the diesel generator.
