The effect of AC system frequency spectrum on commutation failure in HVDC inverters

Previous studies have shown that many types of system disturbances will lead to commutation failure at HVDC inverter stations. The problem is further aggravated if the inverter is connected to a weak (low short-circuit ratio) AC system. The authors analyze the problem in terms of the frequency spectrum of the AC network and its relation to the transient disturbance which causes the failure. Methods are discussed for modifying the frequency spectrum in order to decrease the probability of commutation failure. A sample simulation study was performed to illustrate the effectiveness of one particular type of filter. Results indicate that in some cases the probability of failure can be reduced dramatically