A Selective Order Voltage Ripple Suppression Control Strategy for DC-DC Converter

Two-stage AC/DC converters are widely used as the battery charger for locomotives. Typically, a DC-link capacitor is used to compensate for the instantaneous power difference between the front-end unidirectional rectifier and the back-end DC/DC converter. Due to the pulsating output power of the rectifiers, there is a sixth-order harmonic ripple across the dc bus voltage. This ripple will penetrate to the dc-dc converter, leading to the same voltage ripples at the final output, which will damage the battery and reduce charging efficiency. Firstly, this paper analyzes the propagation mechanism of the sixth-order harmonic ripple. Secondly, a novel voltage controller, which employs a second-order generalized integrator (SOGI) to create a virtual resistor at the selective frequency, is proposed to suppress the dc-dc converter output voltage ripples. Simulation results are provided to verify the effectiveness of the proposed control scheme.