Multiple harmonic current injection system for AC filter capacitors in HVDC converter stations considering grid frequency fluctuation

With the development of the High Voltage Direct Current (HVDC) technology, the audible sharp noise originated by the AC filter capacitors has become a serious noise pollution problem in HVDC converter stations. However, the harsh and complex operating conditions of power capacitors in converter stations make on-site noise analysis and testing extremely challenging. Therefore, this strategy focuses on three key aspects: (1) accurately simulating real operating conditions, (2) synchronizing fundamental and harmonic currents, and (3) fast and precise harmonic current detection and control. In this paper, a Multiple Harmonic Current Injection System (MHCIS) is proposed to simulate the actual working conditions of power capacitors in HVDC converter stations. Accurate and fast harmonic current detection, along with fundamental-harmonic synchronization, are critical for MHCIS. First, a comparative survey about the performance among Single-Phase Locked Loops based on the Orthogonal Signal Generation (OSG-SPLL) is presented, then a new SPLL strategy based on the Arbitrary Phase Delay (APD-SPLL) is proposed. A Multiple Synchronous Reference Frame (MSRF) combined with the Moving Average Filter (MAF) is applied to detect and control the selective harmonic current in MHCIS. Finally, both simulations and experiments demonstrate the effectiveness of the MHCIS introduced in this paper.