Modeling and flexible load control of combined heat and power units

The electric load change of a power unit must be regulated rapidly to achieve power system stability, and it is increasingly becoming urgent especially that large-scale renewable energies are connected to power grids. Combined heat and power units hardly improve their power ramp rate because they commonly operate in heatled mode. This paper presents a coordinated boiler-turbine heating model, describes the dynamics between the heat source mass flowrate and electric power output, and furthermore provides a strategy for heat and power control. Simulation results show that with the heat and power control strategy, the change of electric power can instantly respond, the power ramp rate can reach 2.9% of the rated power per minute, and the stable controls of the main steam pressure and heat supply can remain unaffected. The findings demonstrate the effectiveness of the proposed strategy for flexible heat and power load control.