A Unit Commitment Model Considering the Flexibility Retrofit of Combined Heat and Power Units for Wind Integration

In northern China, the combined heat and power (CHP) units account for a large proportion of the local generation capacity. However, the inherent heat-power coupling of CHP units poses a large barrier for wind power accommodation. To facilitate the local wind integration, the key is to improve the flexibility of the CHP system, and there are two types of feasible methods. One is the addition of heat storage tanks and electric boilers into the CHP system, and this method has been considered in the scheduling of the CHP system, such as the unit commitment (UC) optimization. The other type of method is the flexibility retrofit of CHP units, including the two-stage bypass modification and low-pressure cylinder removal (LPCR). However, prior research has not attempted to integrate the flexibility retrofit into the UC scheduling. To fill this gap, this paper proposes a novel UC model incorporating the bypass and LPCR retrofit of CHP units. In this model, the constraints on the safe operation region, fuel cost, reserve provision, ramping and mode switching of different types of CHP units are thoroughly described. Cases studies are conducted on a test system. Simulation results show that the proposed UC model is capable of utilizing the bypass and LPCR retrofit to facilitate wind accommodation, with the wind curtailment reduced by 81.94% and 20.45% under the bypass and LPCR retrofit, respectively.