A line commutated converter comprising: a plurality of converter limbs (12A, 12B, 12C) extending between first and second DC terminals (14, 16) connected in-use to a DC network, each converter limb (12A, 12B, 12C) including first and second limb portions (20A, 20B, 20C, 22A, 22B, 22C) separated by an AC terminal (24A, 24B, 24C) connected in-use to a respective phase (A, B, C) of an AC network, and each limb portion (20A, 20B, 20C, 22A, 22B, 22C) having a switching element connected between a respective AC terminal (24A, 24B, 24C) and a corresponding one of the first or the second DC terminal (14, 16); and a controller programmed to in-use control operation of the converter and to monitor during operation of the converter a DC converter current (I dc) flowing between the first and second DC terminals (14, 16) and an AC converter current (I ac) flowing between respective pairs of AC terminals (24A, 24B, 24C), the controller, while the DC converter and AC converter currents (I dc, I ac) are equal to one another, operating the converter in a normal mode during which the controller is configured to set a first firing angle for each switching element, the first firing angle being greater than ninety degrees to operate the converter as an inverter, the controller, when a fault occurs temporarily causing the DC converter current (I dc) to exceed the AC converter current (I ac), operating the converter in a fault detection and mitigation mode during which the controller is configured to: set a second firing angle for each switching element, the second firing angle being less than ninety degrees to operate the converter as a rectifier; check whether operating the converter as a rectifier causes the AC converter current (I ac) to exceed the DC converter current (I dc); and (i) to bypass the converter if the AC converter current (I ac) exceeds the DC converter current (I dc), or (ii) to set a third firing angle for each switching element, the third firing angle being greater than ninety degrees but reduced relative to the first firing angle to operate the converter as an inverter with a reduced power transfer capability, if the AC converter current (I ac) does not exceed the DC converter current (I dc). a plurality of converter limbs (12A, 12B, 12C) extending between first and second DC terminals (14, 16) connected in-use to a DC network, each converter limb (12A, 12B, 12C) including first and second limb portions (20A, 20B, 20C, 22A, 22B, 22C) separated by an AC terminal (24A, 24B, 24C) connected in-use to a respective phase (A, B, C) of an AC network, and each limb portion (20A, 20B, 20C, 22A, 22B, 22C) having a switching element connected between a respective AC terminal (24A, 24B, 24C) and a corresponding one of the first or the second DC terminal (14, 16); and a controller programmed to in-use control operation of the converter and to monitor during operation of the converter a DC converter current (I dc) flowing between the first and second DC terminals (14, 16) and an AC converter current (I ac) flowing between respective pairs of AC terminals (24A, 24B, 24C), the controller, while the DC converter and AC converter currents (I dc, I ac) are equal to one another, operating the converter in a normal mode during which the controller is configured to set a first firing angle for each switching element, the first firing angle being greater than ninety degrees to operate the converter as an inverter, the controller, when a fault occurs temporarily causing the DC converter current (I dc) to exceed the AC converter current (I ac), operating the converter in a fault detection and mitigation mode during which the controller is configured to: set a second firing angle for each switching element, the second firing angle being less than ninety degrees to operate the converter as a rectifier; check whether operating the converter as a rectifier causes the AC converter current (I ac) to exceed the DC converter current (I dc); and (i) to bypass the converter if the AC converter current (I ac) exceeds the DC converter current (I dc), or (ii) to set a third firing angle for each switching element, the third firing angle being greater than ninety degrees but reduced relative to the first firing angle to operate the converter as an inverter with a reduced power transfer capability, if the AC converter current (I ac) does not exceed the DC converter current (I dc). set a second firing angle for each switching element, the second firing angle being less than ninety degrees to operate the converter as a rectifier; check whether operating the converter as a rectifier causes the AC converter current (I ac) to exceed the DC converter current (I dc); and (i) to bypass the converter if the AC converter current (I ac) exceeds the DC converter current (I dc), or (ii) to set a third firing angle for each switching element, the third firing angle being greater than ninety degrees but reduced relative to the first firing angle to operate the converter as an inverter with a reduced power transfer capability, if the AC converter current (I ac) does not exceed the DC converter current (I dc). (i) to bypass the converter if the AC converter current (I ac) exceeds the DC converter current (I dc), or (ii) to set a third firing angle for each switching element, the third firing angle being greater than ninety degrees but reduced relative to the first firing angle to operate the converter as an inverter with a reduced power transfer capability, if the AC converter current (I ac) does not exceed the DC converter current (I dc).