A modified control strategy for LCC with IGCT‐based full‐bridge submodules to solve the commutation failure issues

Abstract

AbstractTo solve the commutation failure (CF) issues in high voltage direct current (HVDC) transmission systems based on line commutated converter (LCC), this paper proposes a hybrid solution combining the LCC inverter with the continuously controlled IGCT‐based full‐bridge submodules (FBSMs). The scheme can provide the LCC inverter with an additional commutation area, and compensate for the phase‐shift of the grid voltage under faults. Therefore, it shows better CF resistance than the existing scheme. The characteristics of the proposed hybrid converter are modelled and analyzed in both normal and fault conditions. Then a decoupling control strategy is presented for it. With the ability to counteract negative‐sequence grid voltage, the strategy brings good voltage stability to the dc transmission. And when the grid fault occurs, it can switch to suppress CF by rapidly increasing the output voltage of the FBSMs and applying commutation failure prevention (CFPREV) control to the LCC. As a result, the CF issues can be maximally solved with a smaller number of FBSMs than the existing scheme. Simulations in PSCAD verify the effectiveness of the strategy. Furtherly, an experimental platform is built to show the capacity of the proposed scheme to solve the CF issues.