Abstract
In the power electronic equipment, the uninterruptible power supply (UPS) systems are widely used whose core is a CVCF SVPWM voltage source converter. The technical characters of the output voltage waveform consist of low total harmonic distortion (THD) at steady state, and mitigate the unbalanced voltage caused by unbalanced load and the rapid transient response. In this thesis, the dual-loop control of the VSC is studied. Not only using the repetitive control to imply the outer loop voltage controller to reduce the low harmonic of the voltage, but also using the double decoupled synchronous frame (DDSRF) to be the inner loop current controller to efficiently control the positive- and negative-sequence component of the voltage at the PCC to improve the voltage unbalanced situation, beside the repetitive control principle, stability and the eroor convergence rate are also studied. The proposed control strategy has been validated through PSCAD simulations, and implemented as a laboratory-scale VSC system providing a 1KVA power to a three-phase 220V AC voltage with a fundamental frequency of 60 Hz.