Voltage source inverters transmission does have some disadvantages, which include potentially high power losses and high capital costs when compared with conventional HVDC, but the technology continues to evolve.
Your vote on this answer has already been received
1. relatively poor efficiency , limited switching frequency due to high switching losses
2.current harmonics leading o torque pulsations
3.the maximum speed of operation is limited
4. series,parallel of GTO still poses a problem