The combined frequency modulation of thermal power and energy storage is an important method to improve the AGC regulation performance of coal-fired power units

and the frequency modulation performance can be significantly enhanced through optimized control strategies. Existing strategies mainly focus on energy storage systems

while failing to emphasize the impact of unit load variation on the economy and environmental friendliness of frequency modulation. To address this issue

this paper proposes a control strategy considering the flexible load variation of thermal power units. First

to measure the impact of unit load variation

this paper establishes a frequency modulation economic model and a frequency modulation quality model. Next

a multi-objective optimization problem is constructed with the frequency modulation cost and frequency modulation rate as the bi-level objective functions

and with historical operation data and frequency modulation stability constraints. Then

the improved NSGA-Ⅱ algorithm is used to solve this problem

obtaining the optimal output coefficients of each frequency modulation subsystem. Finally

a model is built for simulation verification. The results show that within the 300-second adjustment period

compared with other strategies

the frequency modulation cost is reduced by 3.1% and 2.9% respectively

and the NOx emissions are decreased by 4.5% and 4.9%

respectively.