Multilevel inverter neutral-point voltage sensor diagnostic based on the Extended Kalman Filter

A new algorithm for neutral point voltage imbalance estimation in DC link of the three-level (3L) neutral point clamped (NPC) voltage source inverter (VSI) is proposed. Application of the proposed algorithm does not require any additional sensors. The unbalanced voltage calculation is based on the information derived from the inverter output measured currents and from the knowledge of the load model parameters. In order to estimate the unbalanced voltage Extended Kalman Filter is used to model non-stationary object. Proposed algorithm can be used for sensorless operation without voltage sensor at the neutral point and can be used also for the voltage sensor diagnostic purposes by comparison of the estimated and measured values. Proposed algorithm implementation provides redundancy and improved reliability of the inverter.