Voltage Sourced Converters are being increasingly used in High-Voltage Direct Current Transmission Systems. They offer the advantage of asynchronous transfer between ac power networks and precise control of real and reactive power. There is a somewhat erroneous understanding amongst the electrical engineering community that they are a perfect solution. However, the talk will show that there are some limits to the operation of VSC converters. Like their LCC counterparts, they too cannot operate satisfactorily if the short circuit ratio is too low. Also, due to their finite MVA rating, they may also require reactive power support at the converter busbar. These results will be demonstrated using a power-voltage stability analysis. Using linearized small signal analysis, the presentation will also demonstrate that the phase-locked loop plays an important role in the behavior of VSC grid converters connected to weak ac systems. Using small-signal analysis, it can be shown that the theoretically calculated power transfer capability can only be approached when the VSC converter's PLL has low gains. All analysis results above are validated using electromagnetic transients simulation on a detailed converter-ac network model.
Prof. Ani Gole is Distinguished Professor and NSERC Industrial Chair in Power Systems Simulation at the Department of Electrical and Computer Engineering, at the University of Manitoba. He has over 30 years experience in the development of modelling tools for power networks incorporating power-electronic equipment. He is one of the original developers of the PSCAD/EMTDC simulation program. Dr. Gole has also made important contributions to the development of, the RTDS real-time simulator . Earlier, Dr. Gole worked with Hydro Quebec and Manitoba Hydro as an HVDC Studies Engineer. For his contributions to the modelling of Flexible Ac Transmission System (FACTS) devices , Dr. Gole was named the year 2007 recipient of the IEEE PES Nari Hingorani FACTS Award. Dr. Gole is a Fellow of the IEEE, a Fellow of the Canadian Academy of Engineering and is a Registered Professional Engineer in the Province of Manitoba, Canada