Abstract
High voltage direct current voltage source converter (HVDC-VSC) technology is one of most important solutions for transmission of large-scale renewable sources. Modular multilevel converter (MMC) is one of the most popular topologies for HVDC-VSC system. The extreme faults affect the safety and reliability of MMC greatly. This paper gives comprehensive analysis and experiment of extreme faults in MMC based on integrated gate commutated thyristor (IGCT). Causes and characterization of the extreme faults are analyzed in detail. A new protection solution based on IGCT with controlled punch-through design (CP-IGCT) and fast recovery diode with high surge current capability (HS-FRD) is proposed. The surge current capability of HS-FRD is validated via experiment successfully. Theoretical calculation shows that the protection solution based on CP-IGCT and HS-FRD can help reduce the maximum fault current below 50% when the anode inductor is 0.8 μH in the extreme shoot-through fault. Test results show that the protection solution can realize the discharge of the DC capacitor below 4.5 kV in the extreme shoot-through fault. The maximum fault current in MMC based on IGCT is only about 600 kA while the maximum fault current in MMC based on insulated gate bipolar transistor (IGBT) is over 1100 kA. Explosion proof of CP-IGCT is validated during the tests, which is similar to that of the protection thyristor. However, IGBT can't guarantee the stability of the package and may cause severe safety problem. The failed CP-IGCT has the short circuit failure mode (SCFM) and can be used for bypass of the faulty MMC sub-module (MMC-SM). Via comparison, the proposed protection solution has lowest cost and complexity, as well as the highest safety.
Published Version
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