A Novel Online Inductance Identification of Traction Network and Adaptive Control Method for Cascaded H-Bridge Converter

The grid-tied cascaded H-bridge (CHB) converter may become unstable, especially for the traction onboard application where the grid impedance may gradually vary as the train moves. In order to overcome this weakness, a small-signal stability-based adaptive control strategy is proposed in this article, where the parameter of the current-inner-loop controller is adaptively regulated according to the online grid inductance identification (GII) result. In the proposed control structure, there is only one control parameter needed to be regulated online, which is based on the estimated value of the grid inductance. In this article, the grid inductance is estimated by injecting the specific harmonic current. With the corresponding harmonic current regulator, stable and sustained harmonic current can be injected, which is beneficial to mitigate the fierce fluctuation of the GII result. The GII algorithm is made up of three parts, including the analog low-pass filter, the sliding discrete Fourier transform, and the digital composite filter, which can suppress the switching noise, the low-frequency grid harmonics, and the grid frequency deviation. With the proposed adaptive control strategy, the CHB can ensure small-signal stability wherever it is connected. All these theoretical analyses are verified by the experiment.