Control of AC-DC converters under unbalanced operating conditions using the DC space vector control concept

AC-DC power converters within an unbalanced system experience abnormal harmonics on both AC and DC sides. In particular, a 2^nd harmonic power ripple appears across the converter, which can have negative consequences on the converter and the load. A passive alternative to decrease these detrimental effects is to increase input and output filters of the converter, which increases cost and size while tending to decrease converter lifetime. Due to these reasons, development of control methods to mitigate the low order harmonics has received much attention. Recently, this research has been focused on control methods using feedforward schemes to nullify the ripple power. The lack of robustness in feedforward schemes, combined with the complexity of associated filters needed for sequence component extraction have been factors against their widespread deployment. This paper introduces a new controller that addresses ripple power via DC voltage feedback. A new DC space vector controller is proposed that operates together with a stationary frame AC current controller to eliminate 2^nd harmonic DC ripple and mitigate the propagation of associated 3^rd harmonic AC line currents. The efficacy of the controller is proven by experimental results.