Voltage imbalance of power units is the key problem degrading the operating stability of STATCOM

which so far has not been solved with satisfaction. This paper proposes a voltage balancing method based on the real-time allocation of PWMs

and describes its principle and implementation. It is validated by simulations under several scenarios including full power

low power

step power and low-voltage-riding-through. According to field application experiences

it is known that all the STATCOMs adopting this method are capable of operating stably in a long term.