Estimation of Load Inertia using Ambient Measurements from Synchrophasor Technology

The number of non-synchronous renewables and dynamic loads is rapidly increasing, which results in a variable system inertia. Thus, accurately quantifying the contribution of the demand side to the system inertia is becoming an important aspect and can help operators to maintain the system stability. This paper proposes an online estimation method to monitor the time-varying inertia of the loads under normal operating conditions. The widely used composite load model (CLM) of Western Electricity Coordinating Council (WECC) is employed, capable of representing diverse composition and dynamic characteristics of loads, in an aggregate manner. A measurement-oriented approach is proposed to estimate the load inertia considering only ambient measurements provided by Phasor Measurement Units (PMUs) during normal grid operation. The inertia estimation of load buses at the transmission level is performed using the Least Squares (LS) method. The proposed method is validated under various case studies using the 39-bus test system, where the CLM is integrated. The case studies consider scenarios with different load composition and time varying load inertia, demonstrating that the proposed method can accurately and dynamically estimate the load inertia by using only ambient PMU measurements.