Browsing by Keyword "three-level modulation"
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Item Analysis of the Average Neutral-Point Current Limits of the Neutral-Point-Clamped Converter under Three-Level Modulation(IEEE Computer Society, 2020-10-18) Jiang, Zhuolin; Beniwal, Neha; Ceballos, Salvador; Pou, Josep; Tafti, Hossein Dehghani; Farivar, Glen G.; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe neutral-point-clamped (NPC) converter employed in applications like bipolar dc-bus, back-to-back converters, power compensator, etc., requires a nonzero average neutral-point (NP) current injection under certain operating conditions. In order to better implement the average NP current injection, this paper studies the maximum and minimum average NP current that can be injected with an NPC converter. For this study, a three-level modulation technique is employed in which one of the three phases is selected to switch between the positive dc-rail and the negative dc-rail while the other two phases switch in two consecutive voltage levels. The maximum and minimum average NP current injection limits are analyzed under different loading conditions. The presented study also evaluates the effects of modulation index and operating power factor on the limits.Item Enhancing the Natural Voltage Balancing Capability of Neutral-Point-Clamped Converters under Carrier-Based Pulsewidth Modulation(Institute of Electrical and Electronics Engineers Inc., 2018-07-02) Beniwal, Neha; Pou, Josep; Townsend, Christopher D.; Ceballos, Salvador; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn this paper, a new modulation technique is presented which aims to enhance the natural voltage balancing capability of neutral-point-clamped converters. The traditional carrier-based pulsewidth modulation technique with zero-sequence injection faces some drawbacks, namely, its inability to balance initial capacitor voltage imbalances quickly and the divergence of the capacitor voltages in the presence of nonlinear loads with even harmonics. This paper aims to find a trade-off between voltage balance performance and switching losses by reducing the difference between the average capacitor voltages without incorporating any external circuitry. A reference neutral-point (NP) current is generated using the average difference between the capacitor voltages. Depending on the reference NP current and predicted NP current, appropriate duty cycles are applied to switch the three phases. These duty cycles are directly linked to the voltage unbalance between the capacitor voltages and thus provides the necessary 'push' to mitigate deviations in natural balancing characteristics. To validate the proposed modulation technique, simulation results are presented for linear loads as well as for nonlinear loads with even harmonics.