Real Time Evaluation of Wavelet Transform for Fast and Efficient HVDC Grid Non-Unit Protection

Abstract

This paper presents a real-time evaluation of a Wavelet Transform (WT) for HVDC grid non-unit protection. Due to its time and frequency localisation capability, WT can successfully extract the necessary information present in the voltage transients following a DC fault. This capability is exploited to achieve fast and selective HVDC grid protection. A Digital Signal Processor (DSP) is employed to execute real-time Stationary Wavelet Transform (SWT) on voltage signals using discrete convolution to efficiently compute the WT coefficients. Hardware-in-the loop (HIL) simulation is performed to test a WT-based hardware module using a Digital Real-Time Simulator (DRTS), in which a meshed HVDC grid is modelled. The closed-loop interaction enables the hardware device to emulate a protection relay that can generate trip commands for the HVDC breakers integrated within the HVDC grid model. The real-time simulations demonstrate the technical feasibility, speed and robust performance of the SWT implementation.