scholarly journals A Harmonic Voltage Injection Based DC-Link Imbalance Compensation Technique for Single-Phase Three-Level Neutral-Point-Clamped (NPC) Inverters

Energies ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1886 ◽  
Author(s):  
Kyoung-Pil Kang ◽  
Younghoon Cho ◽  
Myung-Hyo Ryu ◽  
Ju-Won Baek
Keyword(s):  
Second Order ◽  
Neutral Point ◽  
Voltage Difference ◽  
Imbalance Problem ◽  
Offset Voltage ◽  
Half Wave ◽  
Unbalanced Voltage ◽  
Compensation Technique ◽  
Harmonic Voltage ◽  
Harmonic Components

In three-level neutral-point-clamped (NPC) inverters, the voltage imbalance problem between the upper and lower dc-link capacitors is one of the major concerns. This paper proposed a dc-link capacitor voltage balancing method where a common offset voltage was injected. The offset voltage consists of harmonic components and a voltage difference between the upper and the lower capacitors. Here, both the second-order harmonics and the half-wave of the second-order component were injected to compensate for the unbalanced voltage between the capacitors. In order to show the effectiveness of the proposed voltage injection, the theoretical analyses, simulations, and experimental results are provided. Since the proposed method does not require any hardware modifications, it can be easily adapted. Both the simulations and the experiments validated that the voltage difference of the dc-link could be effectively reduced with the proposed method.

scholarly journals DC-Link Capacitor Voltage Imbalance Compensation Method Based Injecting Harmonic Voltage for Cascaded Multi-Module Neutral Point Clamped Inverter

Electronics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 155 ◽  
Author(s):  
Kyoung-Pil Kang ◽  
Younghoon Cho ◽  
Ho-Sung Kim ◽  
Ju-won Baek
Keyword(s):  
Theoretical Analysis ◽  
Compensation Method ◽  
Neutral Point ◽  
Voltage Difference ◽  
Imbalance Problem ◽  
Offset Voltage ◽  
Capacitor Voltage ◽  
Harmonic Voltage

In a three-level (NPC) converter, the voltage imbalance problem in the DC-link capacitors is major issue. This paper proposes the DC-link capacitor voltage imbalance compensation method, where a common offset voltage is injected for a multi-module NPC inverter. The offset voltage consists of a harmonic voltage and a voltage difference between the upper and lower capacitors. The proposed method does not require any hardware modification, so that it is easily implemented. In order to show the effectiveness of the proposed balancing method, theoretical analysis is provided to balance the voltages, and both the simulations and the experiments were carried out to show that the voltage difference of the DC-link was decreased by the proposed method.

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.

scholarly journals Effect of the Harmonic Voltage Distortion on the Efficiency of a Compact Fluorescent Lamp

2020 ◽  
Vol 29 (54) ◽  
pp. e11604
Author(s):  
Esteban Rojas-Osorio ◽  
Andrés Julián Saavedra-Montes ◽  
Carlos Andrés Ramos-Paja
Keyword(s):  
Mathematical Model ◽  
Test Bench ◽  
Harmonic Distortion ◽  
Fluorescent Lamp ◽  
Constant Frequency ◽  
Voltage Distortion ◽  
Variable Voltage ◽  
Harmonic Voltage ◽  
Compact Fluorescent Lamp ◽  
Harmonic Components

This paper evaluates the effect of the voltage harmonic distortion over the efficiency of a compact fluorescent lamp that is fed with a constant RMS voltage and constant frequency. Several works have been published about the assessment of compact fluorescent lamps, but the effect of the voltage distortion over the efficiency is still an open topic. This work focuses on designing an experiment to estimate the efficiency of a compact fluorescent lamp while changing the voltage harmonic distortion of the power supply. First, a mathematical model that represents a bus susceptible to harmonic distortion (high impedance) that feeds the compact fluorescent lamp is analyzed. Then the mathematical model is reproduced through a test bench in a laboratory of rotating electrical machines. The test bench produces a three-phase bus with constant voltage and frequency, and variable voltage harmonic distortion. The compact fluorescent lamp is subjected to varying harmonic voltage distortion while recording its electrical variables and the produced lumens to estimate its efficiency. That is a practical approach to calculate the lamp efficiency while several works limit their scope measuring only the efficiency of the input converter. The experimental results show that a variation of the voltage harmonic distortion of 8 % on a compact fluorescent lamp reduces its efficiency. Those results put into evidence the importance of regulating harmonic distortion limits to reduce or prevent the increment of power losses caused by harmonic components.

scholarly journals The Virtual Harmonic Power Droop Strategy to Mitigate the Output Harmonic Voltage of the Inverter

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2196 ◽  
Author(s):  
Yuan Yao ◽  
Longyun Kang
Keyword(s):  
Distributed Generation ◽  
Second Order ◽  
Droop Control ◽  
Virtual Power ◽  
Generation System ◽  
System A ◽  
Common Control ◽  
Harmonic Voltage ◽  
The Mathematical Model ◽  
Harmonic Power

The harmonic voltage issue becomes a challenge for a distributed generation system. Considering that droop control is the most common control algorithm used in the distributed system, a virtual harmonic power droop strategy which aims to mitigate the harmonic voltage is proposed in this paper. First, the conventional droop control is analyzed. Based on that concept, the virtual power algorithm is introduced. Second, the output harmonic voltage issue and the mathematical model of the inverter are presented. In addition, the second-order generalized integrator is briefly discussed. Third, taking into consideration the algorithms and models presented, a virtual harmonic power droop strategy is proposed to implement the harmonic voltage mitigation. In this algorithm, signals in fundamental frequency and harmonic frequency are separated with the help of second-order generalized integrators. Unlike the conventional voltage–current dual loop structure which is used to mitigate system harmonics, this method only needs the virtual power feedback to mitigate the harmonic voltage. Based on these features, the system’s control structure is simplified. Simulation and experimental results verified the harmonic voltage mitigation ability of the proposed strategy.

scholarly journals Thermal Analysis of a Directly Grid-Fed Induction Machine With Floating Neutral Point, Operating Under Unbalanced Voltage Conditions

2019 ◽  
Vol 47 (11-12) ◽  
pp. 1060-1076 ◽  
Author(s):  
Fabio Santiago ◽  
Fernando Bento ◽  
Antonio J. Marques Cardoso ◽  
Konstantinos N. Gyftakis
Keyword(s):  
Thermal Analysis ◽  
Induction Machine ◽  
Neutral Point ◽  
Unbalanced Voltage

Second-order relativistic corrections for the S(L=0) states in one- and two-electron atomic systems

2005 ◽  
Vol 83 (1) ◽  
pp. 1-21
Author(s):  
Alexei M Frolov ◽  
Catalin C Mitelut ◽  
Zheng Zhong
Keyword(s):  
Second Order ◽  
Electron Systems ◽  
Specific Interest ◽  
Atomic Systems ◽  
Expectation Value ◽  
Relativistic Corrections ◽  
Alternative Approach ◽  
Compensation Technique ◽  
Three Body ◽  
Regular Operators

An analytical approach is developed to compute the first- (~α2) and second-order (~α4) relativistic corrections in one- and two-electron atomic systems. The approach is based on the reduction of all operators to divergent (singular) and nondivergent (regular) parts. Then, we show that all the divergent parts from the differentmatrix elements cancel each other. The remaining expression contains only regular operators and its expectation value can be easily computed. Analysis of the S(L = 0) states in such systems is of specific interest since the corresponding operators for these states contain a large number of singularities. For one-electron systems the computed relativistic corrections coincide exactly with the appropriate result that follows from the Taylor expansion of the relativistic (i.e., Dirac) energy. We also discuss an alternative approach that allows one to cancel all singularities by using the so-called operator-compensation technique. This second approach is found to be very effective in applications of more complex systems, such as helium-like atoms and ions, H+2-like ions, and some exotic three-body systems.

Study on the Methodology of Detection for Transformer Winding Insulation Defects Based on Impulse Test

2013 ◽  
Vol 805-806 ◽  
pp. 863-866
Author(s):  
Yu Sheng Quan ◽  
Dai Juan Wang ◽  
Hua Gui Chen ◽  
Zong Cheng Zhang
Keyword(s):  
Ratio Method ◽  
Half Wave ◽  
Insulation Defect ◽  
Impulse Voltage ◽  
Transformer Winding ◽  
Lightning Impulse ◽  
Harmonic Voltage ◽  
Transient Voltage ◽  
The Moment ◽  
Winding Insulation

A methodology of diagnosing the winding insulation defect according to data of transient voltage and current from the impulse voltage test is put forward in this paper. Lightning impulse test for transformer is divided into half-wave and full-wave at the moment. According to the full voltage and reduced voltage at two pressure processes. The transient voltage and current from the impulse voltage test can be divided into Series of harmonics. The insulation defect is diagnosed by dividing impulse voltage and current into series of harmonic and structuring discriminant function according to the longitudinal ratio method and cross ratio method for the corresponding period of harmonic voltage and current. The methodology is also applicable to diagnose whether there are insulation damage in the windings those have passed the lightning impulse test.

scholarly journals Power Quality Improvement with a Pulse Width Modulation Control Method in Modular Multilevel Converters under Varying Nonlinear Loads

2020 ◽  
Vol 10 (9) ◽  
pp. 3292 ◽  
Author(s):  
Majid Mehrasa ◽  
Radu Godina ◽  
Edris Pouresmaeil ◽  
Eduardo M. G. Rodrigues ◽  
João P. S. Catalão
Keyword(s):  
Pulse Width ◽  
Pulse Width Modulation ◽  
Second Order ◽  
Control Law ◽  
Nonlinear Load ◽  
Control Laws ◽  
The Third ◽  
Circulating Current ◽  
Harmonic Components ◽  
Circulating Currents

In order to reach better results for pulse width modulation (PWM)-based methods, the reference waveforms known as control laws have to be achieved with good accuracy. In this paper, three control laws are created by considering the harmonic components of modular multilevel converter (MMC) state variables to suppress the circulating currents under nonlinear load variation. The first control law consists of only the harmonic components of the MMC’s output currents and voltages. Then, the second-order harmonic of circulating currents is also involved with both upper and lower arm currents in order to attain the second control law. Since circulating current suppression is the main aim of this work, the third control law is formed by measuring all harmonic components of circulating currents which impact on the arm currents as well. By making a comparison between the switching signals generated by the three proposed control laws, it is verified that the second-order harmonic of circulating currents can increase the switching losses. In addition, the existence of all circulating current harmonics causes distributed switching patterns, which is not suitable for the switches’ lifetime. Each upper and lower arm has changeable capacitors, named “equivalent submodule (SM) capacitors” in this paper. To further assess these capacitors, eliminating the harmonic components of circulating currents provides fluctuations with smaller magnitudes, as well as a smaller average value for the equivalent capacitors. Moreover, the second-order harmonic has a dominant role that leads to values higher than 3 F for equivalent capacitors. In comparison with the first and second control laws, the use of the third control-law-based method will result in very small circulating currents, since it is trying to control and eliminate all harmonic components of the circulating currents. This result leads to very small magnitudes for both the upper and lower arm currents, noticeably decreasing the total MMC losses. All simulation results are verified using MATLAB software in the SIMULINK environment.

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