  Thermostatically-controlled-loads (TCLs) have been regarded as a good
candidate for maintaining the power system reliability by providing operating
reserve. The short-term reliability evaluation of power systems, which is
essential for power system operators in decision making to secure the system
real time balancing, calls for the accurate modelling of operating reserve
provided by TCLs. However, the particular characteristics of TCLs make their
dynamic response different from the traditional generating units, resulting in
difficulties to accurately represent the reliability of operating reserve
provided by TCLs with conventional reliability model. This paper proposes a
novel multi-state reliability model of operating reserve provided by TCLs
considering their dynamic response during the reserve deployment process. An
analytical model for characterizing dynamics of operating reserve provided by
TCLs is firstly developed based on the migration of TCLs' room temperature
within the temperature hysteresis band. Then, considering the stochastic
consumers' behaviour and ambient temperature, the probability distribution
functions of reserve capacity provided by TCLs are obtained by cumulants. On
this basis, the states of reserve capacity and the corresponding probabilities
at each time instant are obtained for representing the reliability of operating
reserve provided by TCLs in the LZ-transform approach. Case studies are
conducted to validate the proposed technique.
