5. Simulation verification and results
5.1. Simulation set-up
In order to verify the proposed control scheme and converters, simulations were carried out on a high-voltage system using MATLAB/Simulink software. The parameters of the system are shown in Table 2. The performances of the proposed converters are also compared with that of the four-switch converter introduced in literature [18]. The value of the dc inductor Ldc is selected such that the converter operates in continuous conduction mode with 5% ripple in the inductor current. The value of the output filter capacitor Co is chosen such that the output voltage contains 10% ripple under the rated operating conditions of the converter. The transmission line model parameters line resistance RTand line inductance LT are also considered in the simulation tests. A 200 km transmission line is chosen with a line inductance value of 0.11155 mH/km and line resistance value of 0.014 Ω/km [21]. The values of RT and LT used in the simulation tests are 3 Ω and 20 mH, respectively. In the dc system, the line resistance is the main factor of line losses when it operates in normal condition. When the fault occurs, the line inductance prevents the rate of change of fault current. In all the tests, the converter is assumed to be operating in steady-state before the occurrence of short-circuit fault.
Table 2.
Parameters used in the simulation and experimental tests.