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4.6 NUETRAL POINT CLAMPED (NPC) INVERTERS


Known as three-level inverters

Problem of 2-level inverter in high-power applications
High DC page link voltage requires series connection of devices  difficulty in dynamic voltage sharing during switching

Solved using NPC inverter or multilevel inverter

NPC inverter circuit


NPC (3)

DC page link capacitor split to create neutral point 0

Q11, Q14 : main devices (2-level inverter)

Q12, Q13 : auxiliary devices – clamp output potential to neutral point with help of clamping diodes D10 D10’

All PWM techniques apply

NPC inverter operation
Consider HEPWM technique to eliminate 2 lowest significant harmonics (5th and 7th) and control fundamental voltage