Drive Circuit For Electrical Load

[0016]Referring to FIG. 1, a drive of a three phase motor comprises a non-phase shifting transformer 10 having a secondary with outputs at various tappings A-N corresponding to the voltage ratios required. The output of the tappings are each three phase voltages supplied to power cells A1, B1, C1-AN, BN, CN. The power cells provide the supply voltages A, B and C to the electrical load 12 which may be, for example, a 10 kV 3-phase induction motor as illustrated. Any other suitable AC electrical load can be driven by the same drive circuit. In the following the rating of the circuit components is assumed to be suitable for the power handling capability of the circuit and the application to which it is put. For example, some of the switches are power switching devices and the accompanying components have power handling characteristics as appropriate.

[0017]FIG. 2 illustrates the circuit of each power cell depicted in FIG. 1. It comprises phase inputs a, b and c corresponding to the outputs