Achievement of a 10 kV IMD system by 6 kV three-level NPC inverter with IGCTs in series connection applied in water works

A high power 10 kV IMD (induction motor drives) system supplied by a 6 kV three-level NPC (neutral point clamped) inverter with IGCTs (integrated gate commutated thyristors) in series connection, which applied in water works has been developed and achieved. The designed three-level inverter system includes a 24 pulses rectifier, a diode NPC three-level medium voltage VSI (voltage source inverter). The three-level inverter operates with 2 IGCTs in series connection in each cell with an output LC filter in order to obtain a 6 kV high voltage output. Because of the high power IMDS has 10 kV line voltage input, which must be changed from a star connection to a delta connection to fit the 6 kV output inverter. According to the PUMP load, a DSP (data signal processor) with FPGA (field programming gate array) controller is adopted to fulfill an optimized constant V/Hz control strategy. The PWM-SHE (pulse width modulation-special harmonic elimination) pattern is presented to keep the inverter has sinusoidal output with minimal harmonics and minimal torque ripple. Achievement and control strategy of the designed system have been presented and discussed.