Multi-level medium voltage inverters for reactive power and harmonic compensation

With the promotion of decreasing prices for inverter modules many drive applications are equipped with active front ends instead of rectifier or thyristor bridges. With today's IGBTs powerful medium voltage inverters with a quite high switching frequency in multilevel technology (typically three level NPC or four level floating capacitor designs) are available for metal and many other applications. Active front ends can be utilised to reduce or compensate harmonics produced by other loads or supply reactive power into the grid. Different methods of harmonic compensation and possible applications are discussed. Benefits of a Kalman filter approach are shown