Multiple Harmonic Current Injection System for Audible Noise Analysis of AC Filter Capacitors in Converter Stations

The audible noise of AC filter capacitors is one of the major noise sources in High Voltage Direct Current (HVDC) converter stations. In order to avoid the sharp noise of AC filter capacitors, it is necessary to design a Multiple Harmonic Current Injection System (MHCIS) for power capacitors to analyze their audible noise characteristics. Simulating effectively the noise of AC filter capacitors under their actual working conditions in converter stations is the primary target of this proposed MHCIS. To ensure the accuracy of the harmonic currents injected into the power capacitors, each harmonic current is detected and controlled separately. On the basis of the instantaneous reactive power theory, a selective harmonic current detection algorithm is proposed in this paper for the single-phase MHCIS. The amplitude of the selected harmonic current can be tracked timely and exactly in d-q synchronous rotational coordinate system, such that a Proportional Integral (PI) controller can be directly operated to eliminate the steady-state errors. The experimental parameters are usually invariable in this system, the phase deviation of the selected harmonic current is also fixed. Thus the phase angle offset of the corresponding harmonic current can be detected and calculated to compensate the system inherent delay. Owing to the accurate detection and control of multiple harmonic currents, the actual working conditions of AC filter capacitors can be accurately simulated, and the reliable noise analysis results of power capacitors can be obtained. Finally, the proposed selective harmonic current detection and control algorithm is verified by the theoretical analysis, simulation and experimental results.