Multi-Receiver GPS-based Direct Time Estimation for PMUs

Modern power distribution systems are incorporating Phasor Measurement Units (PMUs) to measure the instantaneous voltage and current phasors at different nodes in the power grid. These PMU devices depend on GPS for precise time and synchronization. However, GPS L1 C/A signals are vulnerable because of its low power and unencrypted signal structure. Therefore, there is a need for the development of robust time transfer techniques to ensure power grid stability. We propose a novel multi-receiver direct time estimation (MRDTE) algorithm by utilizing the measurements from multiple receivers triggered by a common clock. We first implement a novel signal processing technique known as the Direct Time Estimation (DTE) that directly correlates the received GPS signal with the corresponding signal replica for each of the pre-generated set of clock states. The most optimal set of clock candidates is then estimated based on the principle of maximum likelihood estimation. By leveraging upon the known geographical diversity of multiple receiver positions, we employ a overall Kalman Filter to obtain a robust corrected clock bias and clock drift at any instant. We demonstrate the increased resilience of our MRDTE algorithm against malicious timing attacks that include jamming and meaconing through outdoor field experiments.