• Title, Summary, Keyword: Neutral-point clamped

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Neutral Point Voltage Control for Grid-Connected Three-Phase Three-Level Photovoltaic Inverter (계통연계형 3상 3레벨 태양광 인버터의 중성점 전압제어)

  • Park, Woonho;Yang, Oh
    • Journal of the Semiconductor & Display Technology
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    • v.14 no.4
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    • pp.72-77
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    • 2015
  • Three-level diode clamped multilevel inverter, generally known as neutral point clamped (NPC) inverter, has an inherent problem causing neutral point (NP) potential variation. Until now, the NP potential problem of variation has been investigated and lots of solutions have also been proposed. This paper presents a neutral point voltage control technology using the anti-windup PI controller and offset technology of PWM (Pulse Width Modulation) to control the variation of NPC 3-phase three-level inverter neutral point voltage. And the proposed algorithm is tested and verified using a PLL (Phase Locked Loop) in order to synchronize the phase voltage from the line voltage of grid. It significantly improves the voltage balancing under a solar fluctuation conditions of the inverter. Experimental results show the good performance and effectiveness of the proposed method.

Performance Analysis of Active Neutral-Point-Clamped Inverter Systems (Active NPC 인버터의 모델링 및 성능 분석)

  • Park, Heung-Seok;Lee, Kyo-Beum
    • Proceedings of the KIPE Conference
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    • pp.171-172
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    • 2018
  • 본 논문에서는 NPC (Neutral-Point-Clamped) 인버터와 ANPC (Active Neutral-Point-Clamped) 인버터의 특성과 성능을 비교 분석한다. ANPC 인버터는 기존의 NPC 인버터와 비교하여 스위칭 부하를 분산시켜 발열의 불균형을 해소하고 소자 수명을 증가시킨다. 기존의 NPC 인버터 시스템과 ANPC 인버터에 대하여 이론적인 특징과 성능을 분석하고 모델링과 시뮬레이션을 통하여 비교 분석한다.

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A Simple Control Strategy for Balancing the DC-link Voltage of Neutral-Point-Clamped Inverters at low modulation index (Neutral-Point-Clamped 인버터의 저 변조지수에서 DC 링크 전압 균형을 위한 간단한 컨트롤 기법)

  • Ma C.S.;Kim T.J.;Kang D.W.;Hyun D.S.
    • Proceedings of the KIPE Conference
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    • pp.560-564
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    • 2003
  • This paper proposes a simple control strategy based on the discontinuous PWM(DPWM) to balance the DC-link voltage of three-level Neutral-Point-Clamped(WPC) inverters at low modulation index. New DPWM methods in multi-level inverter are also introduced. The proposed DPWM method changes the path and duration to flow the neutral point current out of or into neutral point of the DC-link and it makes the overall fluctuation of the DC-link voltage zero during a sampling time of reference voltage vector. Therefore, the voltage of the DC-link can be balanced fairly well and also the voltage ripple of the DC-link is reduced significantly. Moreover, comparing with conventional methods, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by experiment

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Active Voltage-balancing Control Methods for the Floating Capacitors and DC-link Capacitors of Five-level Active Neutral-Point-Clamped Converter

  • Li, Junjie;Jiang, Jianguo
    • Journal of Power Electronics
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    • v.17 no.3
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    • pp.653-663
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    • 2017
  • Multilevel active neutral-point-clamped (ANPC) converter combines the advantages of three-level ANPC converter and multilevel flying capacitor (FC) converter. However, multilevel ANPC converter often suffers from capacitor voltage balancing problems. In order to solve the capacitor voltage balancing problems for five-level ANPC converter, phase-shifted pulse width modulation (PS-PWM) is used, which generally provides natural voltage balancing ability. However, the natural voltage balancing ability depends on the load conditions and converter parameters. In order to eliminate voltage deviations under steady-state and dynamic conditions, the active voltage-balancing control (AVBC) methods of floating capacitors and dc-link capacitors based on PS-PWM are proposed. First, the neutral-point current is regulated to balance the neutral-point voltage by injecting zero-sequence voltage. After that, the duty cycles of the redundant switch combinations are adjusted to balance the floating-capacitor voltages by introducing moderating variables for each of the phases. Finally, the effectiveness of the proposed AVBC methods is verified by experimental results.

A Small Signal Modeling of Three-level Neutral-Point-Clamped Inverter and Neutral-Point Voltage Oscillation Reduction (3레벨 NPC인버터의 소신호 모델링과 중성점 전압 진동 저감)

  • Cho, Ja-Hwi;Ku, Nam-Joon;Joung, Seok-Eon;Hyun, Dong-Seok
    • The Transactions of the Korean Institute of Power Electronics
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    • v.19 no.5
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    • pp.407-414
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    • 2014
  • This study proposes a control design for the grid output current and for reducing the neutral-point voltage oscillation through the small-signal modeling of the three-phase grid connected with a three-level neutral-point-clamped (NPC) inverter with LCL filter. The three-level NPC inverter presents an inherent problem: the neutral-point voltage fluctuation caused by the neutral-point current flowing in or out from the neutral point. The small signal modeling consists of averaging, dq0 transformation, perturbing, and linearizing steps performed on a three-phase grid connected to a three-level NPC inverter with LCL filter. The proposed method controls both the grid output and neutral-point currents at every switching period and reduces the neutral-point voltage oscillation. The validity of the proposed method is verified through simulation and experiment.

A Study on the Neutral Point Potential Variation under Open-Circuit Fault of Three-Level NPC Inverter (3레벨 NPC 인버터 개방성 고장 시 중성점 전압변동에 관한 연구)

  • Park, Jong-Je;Park, Byoung-Gun;Ha, Dong-Hyun;Hyun, Dong-Seok
    • The Transactions of the Korean Institute of Power Electronics
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    • v.14 no.4
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    • pp.333-342
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    • 2009
  • Three-level Diode Clamped Multilevel Inverter, generally known as Neutral-Point-Clamped (NPC) Inverter, has an inherent problem causing Neutral Point (NP) potential variation. Until now, in many literatures NP potential problem has been investigated and lots of solutions have also been proposed. However, under fault and fault tolerant control, distinctive feature for NP potential variation problem was rarely published from the standpoint of reliability. In this paper, NP potential is analytically investigated both normal and faulty conditions under carrier based PWM. Subsequently, relation between fault detection time and size of capacitor is analyzed. This information is explored by simulation and experiment results, which contribute to enhance the reliability of inverter system.

Neutral-point Potential Balancing Method for Switched-Inductor Z-Source Three-level Inverter

  • Wang, Xiaogang;Zhang, Jie
    • Journal of Electrical Engineering and Technology
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    • v.12 no.3
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    • pp.1203-1210
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    • 2017
  • Switched-inductor (SL) Z-source three-level inverter is a novel high power topology. The SL based impedance network can boost the input dc voltage to a higher value than the single LC impedance network. However, as all the neutral-point-clamped (NPC) inverters, the SL Z-source three-level inverter has to balance the neutral-point (NP) potential too. The principle of the inverter is introduced and then the effects of NP potential unbalance are analyzed. A NP balancing method is proposed. Other than the methods for conventional NPC inverter without Z-source impedance network, the upper and lower shoot-through durations are corrected by the feedforward compensation factors. With the proposed method, the NP potential is balanced and the voltage boosting ability of the Z-source network is not affected obviously. Simulations are conducted to verify the proposed method.

A Novel Modulation Method for Three-Level Inverter Neutral Point Potential Oscillation Elimination

  • Yao, Yuan;Kang, Longyun;Zhang, Zhi
    • Journal of Power Electronics
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    • v.18 no.2
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    • pp.445-455
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    • 2018
  • A novel algorithm is proposed to regulate the neutral point potential in neutral point clamped three-level inverters. Oscillations of the neutral point potential and an unbalanced dc-link voltage cause distortions of the output voltage. Large capacitors, which make the application costly and bulky, are needed to eliminate oscillations. Thus, the algorithm proposed in this paper utilizes the finite-control-set model predictive control and the multistage medium vector to solve these issues. The proposed strategy consists of a two-step prediction and a cost function to evaluate the selected multistage medium vector. Unlike the virtual vector method, the multistage medium vector is a mixture of the virtual vector and the original vector. In addition, its amplitude is variable. The neutral point current generated by it can be used to adjust the neutral point potential. When compared with the virtual vector method, the multistage medium vector contributes to decreasing the regulation time when the modulation index is high. The vectors are rearranged to cope with the variable switching frequency of the model predictive control. Simulation and experimental results verify the validity of the proposed strategy.

DC-Link Capacitor Voltage Balanced Modulation Strategy Based on Three-Level Neutral-Point-Clamped Cascaded Rectifiers

  • Han, Pengcheng;He, Xiaoqiong;Zhao, Zhiqin;Yu, Haolun;Wang, Yi;Peng, Xu;Shu, Zeliang
    • Journal of Power Electronics
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    • v.19 no.1
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    • pp.99-107
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    • 2019
  • This study proposes a new modulation strategy to deal with unbalanced output voltage that is based on three-level neutral-point-clamped cascaded rectifiers. The fundament idea is to reallocate the value of the voltage levels generated by each of the modules on the basis of space vector pulse width modulation. This proposed modulation strategy can reduce the switching frequency while maintaining the mutual-module voltage balance. First, an analysis of unbalanced output voltage is reflected. Then a new modulation strategy is introduced in detail. Internal module capacitor voltages are balanced by the selection of redundant vectors. Moreover, the voltage balance ability is calculated. Finally, the feasibility of this modulation strategy is verified through experimental results.

Carrier Based Common Mode Voltage Reduction Techniques in Neutral Point Clamped Inverter Based AC-DC-AC Drive System

  • Ojha, Amit;Chaturvedi, Pradyumn;Mittal, Arvind;Jain, Shailendra
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.142-152
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    • 2016
  • Common mode voltage (CMV) generation is a major problem in switching power converter fed induction motor drive systems. CMV is the zero sequence voltage generated due to the switching action of power converters. Even a small magnitude of CMV with a high rate of change may circulate large bearing currents which may damage a machine's bearings and shorten its life. There are several methods of controlling CMV. This paper presents 3-level sinusoidal pulse width modulation based techniques to control the magnitude and rate of change of CMV in multilevel AC-DC-AC drive systems. Simulation and experimental investigations have been presented to validate the performance of proposed technique to control CMV in 3-level neutral point clamped inverter based AC-DC-AC system.