Neutral Point Voltage Controller For Diode Clamped Three Level Inverter Based Statcom And Grid Connected Inverter Applications

Abstract: When the STATCOM is designed based on diode clamped three level converter, to compensate unbalanced loads, the problem of neutral point voltage deviation has to be addressed to avoid unequal distribution of dc link voltage between top and bottom links. The present invention mitigates the neutral point voltage deviation using a novel method. In this technique the direction of neutral point current is estimated by using the data of actual line currents and previous switching states of IGBTs of inverter. By using the estimated direction of neutral point current and level of neutral point voltage deviation, the dwell times of small P and small N vectors of Space Vector Pulse Width Modulation (SVPWM) are modified suitably without fully elimination, to mitigate the voltage deviation in each switching period. Thus the developed technique mitigates the neutral point voltage deviation without introduction of additional switching and harmonics. Fig. 1

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