Three-phase voltage source inverter system

A three-phase voltage source inverter system comprising:

• a direct-current power source;
• a three-phase voltage source inverter apparatus including:
• a three-phase inverter unit in which ON-periods are respectively set to 120° for upper side switching elements in each of three phases with a 120° delay, and ON-periods are respectively set to 120° for lower side switching elements in each of the three phases with a 180° delay from the upper side switching elements and with a 120° delay between each phase;
• and a three-phase output transformer with a primary side Y winding connected to an output end in each of three phases of the three-phase inverter and a secondary side Δ winding;
• and
• an auxiliary circuit inserted between the direct-current power source and the three-phase voltage source inverter apparatus, including:
• a dividing capacitor, dividing a direct-current voltage of the direct-current power source;
• a single-phase inverter unit in which ON-periods are respectively set to 60° for upper side switching elements in each phase of single-phase with an 80° delay, and ON-periods are respectively set to 60° for lower side switching elements in each phase of single-phase with a 60° delay from the upper side switching elements and with an 80° delay between each phase;
• and an auxiliary transformer in which a primary side winding is connected to a connection midpoint between upper and lower switching elements in each phase of the single-phase inverter unit, and a secondary side winding is connected between a connection midpoint of the dividing capacitor and a connection midpoint of a primary Y winding in the three-phase transformer.