A Digital Computer Transient Model of a Three-Phase Naturally-Commutated Inverter Including Line and Inverter Faults

Using a digital computer, a naturally commutnted three-phase Inverter was simulated to study both voltage fed and current fed inverters. The "real" characteristics of the thyristors were also simulated. The interaction between the load and the inverter circuit was investigated. The ratio between the dc voltage and the amplitude of the ac voltage (Vs/Vm), the ratio between smoothing inductance and load inductance (Ldc/LS) and the variation of firing angle α were included. The program could also allow for three phase currents with adjustable frequency to be used in adjustable speed drives. The normal operation of the naturally commutated inverter and its operation during faults occurring both on the line and in the inverter circuit were" also investigated. These faults included three-phase ehort-circu its, thyristor failures, line-to-line faults, false triggering and open-circuit faults.