Controllable line-commutated converter (CLCC) topology realizes reliable recovery of thyristor valve from main branch and controllable shutdown of bridge arm by adopting main and auxiliary branch structure based on hybrid coupling of full controlled and half controlled components. In this way

the problem of commutation failure of line commutated converter (LCC) can be fundamentally solved. Based on the renovation of ±500 kV converter in Nanqiao Station

the design and prototype development of the ±500 kV CLCC are described from four aspects as follows: elec-trical design

structural design

valve control design

and test verification. Firstly

the selection principle of power electronic device is described. Then

the coupling mechanism of the series number

resistance-capacitance parameters and arrester parameters on the stress is analyzed

and the influence of thyristor resistance-capacitance parameter on valve stress and loss is achieved. Consequently

the whole electrical parameter configuration of ±500 kV CLCC is completed. A compact modular valve tower prototype and a double-layer digital-analog mixed valve control system of ±500 kV CLCC are developed

which passes all the operation and insulation type tests. The controllable turn-off test results show that the ±500 kV CLCC can actively turn off the fault current of 2.4 kA or above for 5 consecutive times and provide enough back pressure to the main branch thyristor to ensure its reliable turn-off

which verifies its ability to resist commutation failure.