Inner current loop for large voltage low switching frequency

In high power applications, i.e. HVDC and SVC, the coupling between rating, performance and utilization is of highest interest. Therefore, the performance of inner current loop control for large voltage source power converters is studied with respect to the ability to limit the power converter current during unsymmetrical conditions in the supplying AC network. A comparison is made between if the inner current loop is implemented in either the αβ-plane or the rotating dq-plane. The influence of an extra time delay using digital control and the pulse number (sample period) are also evaluated. Results are presented from dynamical studies, carried out with both computer simulations and real time analog simulations with a digital control system. The simulations verifies the implemented inner current loop ability to limit the power converter current during load changes and disturbances in the feeding AC network