A Novel Modulation Strategy for Controllable Current Source Converter

Abstract

Controllable current source converter (CSC) technology is an effective solution in addressing commutation failure issues. Modulation strategy is the fundamental approach for controlling the valve arm of the converter. Higher switching frequencies result in lower AC harmonics but increased losses in the commutation valve. Lower switching frequencies lead to reduced losses but higher harmonics. The major challenge in engineering currently lies in eliminating the direct conduction state of the valve arms in the current source converter and effectively suppressing harmonics. This paper first analyzes the valve arm signal allocation method in the CSC and examines the mechanism and impact of direct conduction. Then, based on double Fourier signal analysis theory, a SPWM modulation method utilizing the odd multiples of "150Hz" is proposed. Modulation range and signal synchronization methods are analyzed. The effectiveness of the method in terms of duty cycle, transmission characteristics, and saturation characteristics is analyzed. Finally, a comparison is made between this method and traditional linear modulation and asymmetric modulation methods.