SNG5100 series high-voltage variable frequency speed regulation system is composed of multiple identical and independent IGBT power units. After power units are divided into three phas es, star connection is applied for high voltage output. The power unit is the PWM modulation voltage source inverter that is featured by the AC/DC/AC structure. Unit schematic diagram 3.

Composition of power units: With three-phase full-bridge rectification of diodes, the input three-phrase AC power is converted to DC power through a capacitor filter. After SPWM modulat ion of IGBT inverter bridge s, the DC power is output as single phase AC power. After the output voltage of multiple power units at each phaseare overlaid, multiplexed phase voltage waveforms are produced. Phrase and line voltage waveforms are respectively featured by 2N+1 voltage steps and 4N+1 voltage steps, as shown in Figure 4 oscillogram. Power units have a wide operating voltage rage and operate normally in the fluctuation range of (30%/-30%) power-line voltage. Fiber communication is applied for power units and master control system, thus overcoming electrical isolation and electromagnetic interference between high voltage and low voltage. All power units have the same structure and electrical performance, and is changeable, which guarantees system safety and reliability.