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

Electronics ◽  
2019 ◽  
Vol 8 (6) ◽  
pp. 691 ◽  
Author(s):  
Ju-Yong Kim ◽  
Ho-Sung Kim ◽  
Ju-Won Baek ◽  
Dong-Keun Jeong
Keyword(s):  
Distribution System ◽  
Low Voltage ◽  
Balance Control ◽  
Short Circuit ◽  
Renewable Energy Sources ◽  
Neutral Point ◽  
Extreme Load ◽  
Zero Sequence ◽  
Zero Sequence Voltage ◽  
Short Circuit Condition

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.

scholarly journals A Novel Neutral-Point Potential Balance Strategy for Three-Level NPC Back-to-Back Converter Based on the Neutral-Point Current Injection Model

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Yingjie Wang ◽  
Haiyuan Liu ◽  
Wenchao Wang ◽  
Kangan Wang
Keyword(s):  
Balance Control ◽  
Neutral Point ◽  
Control Algorithms ◽  
Model Based ◽  
Point Potential ◽  
Injection Model ◽  
Zero Sequence ◽  
Flow Through ◽  
Dc Bus ◽  
Zero Sequence Voltage

The neutral-point (NP) potential balance control in three-level neutral-point-clamped (NPC) back-to-back converter is a research nodus. Its current strategies are the same as the strategies of a single three-level NPC converter. But the strategies do not give full play to its advantages that the neutral-point current can only flow through the connected midlines in both sides of the converter but does not flow through the DC-bus capacitors. In this paper, firstly the NP potential model based on the NP current injected is proposed. It overcomes numerous variable constraints and mutual coupling in the conventional model based on the zero-sequence voltage injected. And then on this basis, three NP-potential balance control algorithms, unilateral control, bilateral independent control, and bilateral coordinated control, are proposed according to difference requirements. All of these algorithms use the midlines rather than the DC-bus capacitors to flow the NP current as much as possible. Their control abilities are further quantitatively analyzed and compared. Finally, simulation results verify the validity and effectiveness of these algorithms.

scholarly journals A Carrier-Based Discontinuous PWM Strategy of NPC Three-Level Inverter for Common-Mode Voltage and Switching Loss Reduction

Electronics ◽  
2021 ◽  
Vol 10 (23) ◽  
pp. 3041
Author(s):  
Guozheng Zhang ◽  
Yingjie Su ◽  
Zhanqing Zhou ◽  
Qiang Geng
Keyword(s):  
Pulse Width Modulation ◽  
Control Method ◽  
Balance Control ◽  
Neutral Point ◽  
Switching Loss ◽  
Major Drawback ◽  
Common Mode ◽  
Common Mode Voltage ◽  
Zero Sequence ◽  
Zero Sequence Voltage

For the conventional carrier-based pulse width modulation (CBPWM) strategies of neutral point clamped (NPC) three-level inverters, the higher common-mode voltage (CMV) is a major drawback. However, with CMV suppression strategies, the switching loss is relatively high. In order to solve the above issue, a carrier-based discontinuous PWM (DPWM) strategy for NPC three-level inverter is proposed in this paper. Firstly, the reference voltage is modified by the twice injection of zero-sequence voltage. Switching states of the three-phase are clamped alternatively to reduce both the CMV and the switching loss. Secondly, the carriers are also modified by the phase opposite disposition of the upper and lower carriers. The extra switching at the border of two adjacent regions in the space vector diagram is reduced. Meanwhile, a neutral-point voltage (NPV) control method is also presented. The duty cycle of the switching state that affects the NPV is adjusted to obtain the balance control of the NPV. Still, the switching sequence in each carrier period remains the same. Finally, the feasibility and effectiveness of the proposed DPWM strategy are tested on a rapid control prototype platform based on RT-Lab.

scholarly journals Novel Earth Fault Protection Algorithm Based on MV Cable Screen Zero Sequence Current Filter

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3190 ◽  
Author(s):  
Krzysztof Lowczowski ◽  
Jozef Lorenc ◽  
Jerzy Andruszkiewicz ◽  
Zbigniew Nadolny ◽  
Jozef Zawodniak
Keyword(s):  
Distribution System ◽  
Low Voltage ◽  
Renewable Energy Sources ◽  
Simulation Software ◽  
Protection Relay ◽  
Medium Voltage ◽  
Earth Fault ◽  
Fault Protection ◽  
Zero Sequence ◽  
Cable Lines

This paper presents novel zero sequence current filter and earth fault protection relay, which utilize cable screens earthing current in protection algorithm. Different problems connected with state of the art of zero sequence current filters and protection relays are presented and compared with the proposed solution. The presented concept is verified in PowerFactory simulation software, experiment concerning modeling the earth fault current flow in medium voltage (MV) cable supplied from the low voltage (LV) network and measurements in the MV network in the Polish distribution system. The proposed solution is characterized by higher sensitivity and reduced number of erroneous trips. The presented solution is suitable for any MV cable lines. Biggest advantages are observed in power output lines from renewable energy sources, which are often operated under no-load conditions.

scholarly journals Neutral-Point Voltage Balance Control of Three-Level Converter Based on Selection Method of Dynamical Adjustment for Small Voltage Vector

2021 ◽  
Vol 11 (11) ◽  
pp. 5076
Author(s):  
Hongyan Zhao ◽  
Yan Li ◽  
Fei Lin ◽  
Yian Yan
Keyword(s):  
Balance Control ◽  
Harmonic Distortion ◽  
Selection Method ◽  
Neutral Point ◽  
Voltage Vector ◽  
Unbalanced Voltage ◽  
Zero Sequence ◽  
Ac Current ◽  
Level Converter ◽  
Small Voltage

The balance control of neutral-point voltage (NPV) is important in the three-level converter. In this paper, this problem is studied by taking the VIENNA circuit as an example. The deviation of NPV is essentially caused by mismatch between the charging and discharging time of two series capacitors by the neutral-point current flowing into or out of the DC side. The unbalanced NPV will lead to unbalanced voltage stress of two capacitors and power switches and may cause overvoltage damage to both and also increase the total harmonic distortion (THD) and harmonic components in the AC current. In this paper, by analyzing the role and effect of a small-voltage vector on NPV, a control strategy based on the selection method of dynamical adjustment for a small vector is proposed. By judging the fluctuation of NPV, different small vectors are dynamically selected to act to adjust the NPV. For verification, the proposed strategy is compared with the traditional zero-sequence voltage injection (ZSV-J) method through simulation and experiment. Compared with ZSV-J, the THD of AC current is decreased by about 27.2%, the efficiency is increased by about 1.66%, and the adjustment speed of NPV is increased by about 50%. Therefore, the feasibility and advantages of the strategy are verified.

Short-Circuit Fault Protection of a Low Voltage DC Distribution System using Superimposed Current Components

2017 ◽  
Vol 31 (10) ◽  
pp. 86-94
Author(s):  
Saeed Zaman Jamali ◽  
Muhammad Omer Khan ◽  
Syed Basit Ali Bukhari ◽  
Muhammad Mehdi ◽  
Gi-Hyeon Gwon ◽  
...  
Keyword(s):  
Distribution System ◽  
Low Voltage ◽  
Short Circuit ◽  
Fault Protection ◽  
Dc Distribution ◽  
Short Circuit Fault

scholarly journals Identifying Faulty Feeder for Single-Phase High Impedance Fault in Resonant Grounding Distribution System

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 598
Author(s):  
Tao Tang ◽  
Chun Huang ◽  
Zhenxing Li ◽  
Xiuguang Yuan
Keyword(s):  
Distribution System ◽  
Single Phase ◽  
Fault Resistance ◽  
High Impedance ◽  
Significant Difference ◽  
High Impedance Fault ◽  
Transition Resistance ◽  
Zero Sequence ◽  
High Impedance Faults ◽  
Zero Sequence Voltage

The identification of faulty feeder for single-phase high impedance faults (HIFs), especially in resonant grounding distribution system (RGDS), has always been a challenge, and existing faulty feeder identification techniques for HIFs suffer from some drawbacks. For this problem, the fault transient characteristic of single-phase HIF is analyzed and a faulty feeder identification method for HIF is proposed. The analysis shows that the transient zero-sequence current of each feeder is seen as a linear relationship between bus transient zero-sequence voltage and bus transient zero-sequence voltage derivative, and the coefficients are the reciprocal of transition resistance and feeder own capacitance, respectively, in both the over-damping state and the under-damping state. In order to estimate transition resistance and capacitance of each feeder, a least squares algorithm is utilized. The estimated transition resistance of a healthy feeder is infinite theoretically, and is a huge value practically. However, the estimated transition resistance of faulty feeder is approximately equal to actual fault resistance value, and it is far less than the set threshold. According to the above significant difference, the faulty feeder can be identified. The efficiency of the proposed method for the single-phase HIF in RGDS is verified by simulation results and experimental results that are based on RTDS.

A Carrier-Based PWM Strategy With Zero-Sequence Voltage Injection for a Three-Level Neutral-Point-Clamped Converter

2012 ◽  
Vol 27 (2) ◽  
pp. 642-651 ◽  
Author(s):  
Josep Pou ◽  
Jordi Zaragoza ◽  
Salvador Ceballos ◽  
Maryam Saeedifard ◽  
Dushan Boroyevich
Keyword(s):  
Neutral Point ◽  
Zero Sequence ◽  
Clamped Converter ◽  
Zero Sequence Voltage
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