Abstract
This study presents a novel switching scheme for three-level neutral point clamped (NPC) inverters. The proposed switching method independently drives the upper- and lower-arm elements of the inverter based on the polarity information of the reference current. The proposed switching scheme does not require the inclusion of dead-time for each switching, except when the current polarity changes. Therefore, unlike the conventional inverter switching method, dead-time compensation is not needed, and the possibility of an arm-short accident is prevented. In this study, a switching procedure is detailed, and the operation mode analysis of the proposed switching scheme is presented. The effectiveness of the proposed switching method is verified experimentally by application to a grid-connected inverter that requires inverter current control.
Highlights
Three-level inverters are widely used for medium- and large-capacity inverters
Since the three-level inverter has a smaller current ripple than the two-level inverter, it is advantageous as a grid-connected inverter, where the problem of harmonics included in the output current is important
We present a novel switching method of three-phase neutral point clamped (NPC) three-level inverters that selects a switching device using the polarity information of the reference inverters that selects a switching device using the polarity information of the reference current
Summary
Three-level inverters are widely used for medium- and large-capacity inverters. As three-level inverters have good performance and efficiency, they have complex circuits and controls. In the case of a three-level NPC inverter, a study that eliminates the dead-time by dividing the switching modes according to the polarity of the voltage reference and the polarity of the actual current has been proposed [15,16]. 8; the proposed shorter than the determined dead-time, is applied just onceswitching when the method polarityisofnot the recommended for systems where the output current is not significant compared to the reference current is changed. If the polarity of the reference current is changed before the polarity of the actual current, the current discontinuity may occur near-zero current in the proposed switching scheme, as depicted in Figure 8; the proposed switching method is not recommended for systems where the output current is not significant compared to the ripple current caused by switching
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