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

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.

Single-Switch Bipolar Output DC-DC Converter for Photovoltaic Application

“…This work proposes the use of a bipolar DC bus instead of the monopolar DC bus, for which a new DC-DC converter topology is proposed, which allows the connection of each photovoltaic string to this bus [12,13]. The connection of a distributed generation system with DC output to a bipolar network can be done in different ways.…”

“…However, in this paper, a design procedure is established for the use of these converters in the connection of photovoltaic systems to bipolar DC networks. The operation of the converter is analyzed for a system This work proposes the use of a bipolar DC bus instead of the monopolar DC bus, for which a new DC-DC converter topology is proposed, which allows the connection of each photovoltaic string to this bus [12,13].…”

Energy Efficiency Based Control Strategy of a Three-Level Interleaved DC-DC Buck Converter Supplying a Proton Exchange Membrane Electrolyzer

“…Currently, multi-source systems based on a DC configuration suffer from their use to low power applications because of the use of basic DC-DC converters (boost converter for fuel cells, and buck converter for electrolyzers (ELs)) [1][2][3]. These topologies present limited voltage conversion ability and are not fit for medium and high power applications [4].…”

Soft-Switching Bidirectional Three-Level DC–DC Converter with Simple Auxiliary Circuit

“…The non-isolated bidirectional three-level DC-DC converter has been widely used for energy storage systems [1][2][3]. As shown in Figure 1, it uses four series-connected power switches and two series-connected capacitors [1].…”

“…Switch voltage stresses are reduced by half as power switches are stressed on half of the full DC-link voltage [2]. It can use lower voltage-rated power switches, which have better switching performance than the power switches in the two-level converters [3]. Aside from energy storage systems [4], the bidirectional three-level DC-DC converter has been utilized for ultra-capacitor applications [5] and various electric vehicle charging applications [6,7].…”