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Analysis of Effective Three-Level Neutral Point Clamped Converter System for the Bipolar LVDC Distribution

1
Smart Power Distribution Lab, Power Distribution ICT Group, KEPCO, Daejeon 34056, Korea
2
Power Conversion Research Center, Smart Grid Research Division, KERI, Changwon 51543, Korea
*
Author to whom correspondence should be addressed.
Electronics 2019, 8(6), 691; https://doi.org/10.3390/electronics8060691
Received: 12 May 2019 / Revised: 14 June 2019 / Accepted: 15 June 2019 / Published: 19 June 2019
(This article belongs to the Section Power Electronics)
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Abstract

Low-voltage direct current (LVDC) distribution has attracted attention due to increased DC loads, the popularization of electric vehicles, energy storage systems (ESS), and renewable energy sources such as photovoltaic (PV). This paper studies a ±750 V bipolar DC distribution system and applies a 3-level neutral-point clamped (NPC) AC/DC converter for LVDC distribution. However, the 3-level NPC converter is fundamental in the neutral-point (NP) imbalance problem. This paper discusses the NP balance control method using zero-sequence voltage among various solutions to solve NP imbalance. However, since the zero-sequence voltage for NP balance control is limited, the NP voltage cannot be controlled to be balanced when extreme load differences occur. To maintain microgrid stability with bipolar LVDC distribution, it is necessary to control the NP voltage balance, even in an imbalance of extreme load. In addition, due to the bipolar LVDC distribution, the pole where a short-circuit condition occurs limits the short current until the circuit breaker operates, and a pole without a short-circuit condition must supply a stable voltage. Since the conventional 3-level NPC AC/DC converter alone cannot satisfy both functions, an additional DC/DC converter is proposed, analyzed, and verified. This paper is about a 3-level NPC AC/DC converter system for LVDC distribution. It can be used for the imbalance and short-circuit condition in bipolar LVDC distribution through the prototype of the 300 kW 3-level NPC AC/DC converter system and experimented and verified in various conditions. View Full-Text
Keywords: bipolar LVDC distribution; 3-level NPC AC/DC converter; zero-sequence voltage; DC/DC converter bipolar LVDC distribution; 3-level NPC AC/DC converter; zero-sequence voltage; DC/DC converter
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kim, J.-Y.; Kim, H.-S.; Baek, J.-W.; Jeong, D.-K. Analysis of Effective Three-Level Neutral Point Clamped Converter System for the Bipolar LVDC Distribution. Electronics 2019, 8, 691.

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