MIDC can realize large-capacity power transmission and flexible operation,but it also increases the complexity of the system and brings more problems.As a common fault,commutation failure can cause the increase of DC current and overvoltage of converter busbar.It will cause both local commutation failure and concurrent commutation failure.Therefore,the recovery problem has been generally concerned.How to control the time and range of commutation failure to the minimum can affect the entire system.The paper proposes that Statcom can add strength of AC system and expand the stable operating area so as to improve the recovery process after the commutation failure.