Investigation into the control methods to reduce the DC-link capacitor ripple current in a back-to-back converter

Three-phase back-to-back converters have a wide range of applications (e.g. wind turbines) in which the reliability and cost-effectiveness are of great concern. Among other components and interconnections, DC-link capacitors are one of the weak links influenced by environmental stresses (e.g. ambient temperature, humidity, etc.) and operating stresses (e.g. voltage, ripple current). This paper serves to investigate the ways of reducing ripple current stresses of DC-link capacitors in back-to-back converters. The outcome could benefit to achieve either an extended lifetime for a designed DC-link or a reduced DC-link size for fulfilling a specified lifetime target. The proposed control strategies have been demonstrated on a study case of a 1.5 kW converter prototype. The experimental verifications are in well agreement with the theoretical analyses.