scholarly journals Voltage Jump Suppression and Capacitor Voltage Fluctuation Analysis for a Four-Level Hybrid Flying Capacitor T-Type Converter

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 698 ◽  
Author(s):  
Chen Wei ◽  
Xibo Yuan ◽  
Juan Zhou ◽  
Kangan Wang ◽  
Yonglei Zhang ◽  
...  
Keyword(s):  
Dead Time ◽  
Fluctuation Analysis ◽  
Voltage Fluctuation ◽  
Multilevel Converters ◽  
Medium Voltage ◽  
Time Period ◽  
Capacitor Voltage ◽  
And Control ◽  
Laboratory Prototype ◽  
Voltage Jump

In low and medium voltage power conversion systems, multilevel converters are becoming more and more attractive due to improved power density. However, the complexity of topology and control is a big challenge for the application of multilevel converters. In this paper, a four-level (4L) hybrid flying capacitor (FC) T-type converter has been researched in detail. The topological advantage of the converter is displayed in comparison to existing four-level converters. According to the feature of the topology, the operating status has been analyzed and the reason for the voltage jump is researched in detail during the dead-time period. A strategy to reduce voltage jump by adjusting the switching states has be presented. The FC voltages can be balanced by selecting the appropriate switching states. The relationships between the fluctuations of FC voltages and the modulation index and power factor (PF) have been analyzed by simulation results. The performance of the 4L converter has been investigated in MATLAB/Simulink as well as on a down-scaled laboratory prototype.

scholarly journals Operation and Control of a Seven-Level V-Clamp Multilevel Converter

Energies ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4761
Author(s):  
Yao Xue ◽  
Xiaofeng Yang ◽  
Lutian Yuan ◽  
Trillion Q. Zheng
Keyword(s):  
Power Conversion ◽  
Modulation Method ◽  
Multilevel Converter ◽  
Multilevel Converters ◽  
Output Performance ◽  
Flying Capacitors ◽  
Dynamic Voltage ◽  
Set Up ◽  
And Control ◽  
Laboratory Prototype

Multilevel converters are well suited for high-power and high-quality power conversion. This paper presents a new seven-level V-clamp multilevel converter (VMC) with reduced clamping devices. All phases of the VMC share common DC-link capacitors and realize bidirectional power conversion without flying capacitors. Each branch of the VMC sustains only a single-level voltage of the DC-link capacitors during its commutation process. Hence, the series switches can be controlled as simple as one switch and the dynamic voltage unbalancing issue is avoided. In this paper, the operation principle and the modulation method of the VMC are analyzed in detail. In addition, compensation control for non-ideal factors is designed to improve the output performance. The output fundamental distortion is compensated and the harmonics are reduced. Finally, a laboratory prototype of the seven-level VMC is set up to verify the feasibility of the presented topology and analysis.

scholarly journals Modeling Dynamic Multifractal Efficiency of US Electricity Market

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6145
Author(s):  
Haider Ali ◽  
Faheem Aslam ◽  
Paulo Ferreira
Keyword(s):  
Electricity Markets ◽  
Electricity Market ◽  
Fluctuation Analysis ◽  
The Novel ◽  
Market Returns ◽  
Multifractal Detrended Fluctuation Analysis ◽  
Daily Data ◽  
Time Period ◽  
Rolling Window ◽  
And Control

The dramatic deregulatory reforms in US electricity markets increased competition, resulting in more complex prices compared to other commodities. This paper aims to investigate and compare the overall and time-varying multifractality and efficiency of four major US electricity regions: Mass Hub, Mid C, Palo Verde, and PJM West. Multifractal detrended fluctuation analysis (MFDFA) is employed to better quantify the intensity of self-similarity. Large daily data from 2001 to 2021 are taken in order to make a more conclusive analysis. The four electricity market returns showed strong multifractal features with PJM West having the highest multifractality (corresponding to lowest efficiency) and Mass Hub having the lowest multifractality (i.e., highest efficiency). Moreover, all series exhibited mean reverting (anti-persistent) behavior in the overall time period. The findings of MFDFA rolling window suggest Palo Verde as the most volatile index, while a significant upward trend in the efficiency of Mass Hub and PJM West is observed after the first quarter of 2014. The novel findings have important implications for policymakers, regulatory authorities, and decision makers to forecast electricity prices better and control efficiency.

Hybrid modular multilevel converter with cascaded full bridges for medium-voltage motor drives

2019 ◽  
Vol 41 (12) ◽  
pp. 3279-3291 ◽  
Author(s):  
Yu Jiali ◽  
Xia Chaoying
Keyword(s):  
High Frequency ◽  
Stable State ◽  
High Amplitude ◽  
Motor Drives ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Voltage Fluctuation ◽  
Constant Frequency ◽  
Medium Voltage ◽  
Capacitor Voltage

Modular multilevel converter (MMC) is especially appropriate in high-voltage constant-frequency systems due to its modularity and scalability. But, so far MMC has not been widely used in motor drives applications. Since the capacitor voltage fluctuation is proportional to the output current amplitude and inversely proportional to the output frequency under constant torque load, at the low-speed, the excessive sub-module (SM) capacitor voltage fluctuation is one of the major obstacles for MMC applied in motor drives. To suppress the SM capacitor voltage fluctuation, an effective solution is to inject a high frequency zero sequence voltage to the three-phase output voltages of MMC and control the circulating current per phase reasonably. However, the introduced high frequency and high amplitude common voltage at the motor side is harmful. In this paper, a hybrid MMC with cascaded full-bridge SMs (HMMC-CFB) topology is used in the medium-voltage motor drives. The high frequency and high amplitude common mode voltage is absorbed by the cascaded full-bridge SMs. Besides, the capacitor voltage fluctuations of each arm and the cascaded full-bridge SMs is easily limited within a reasonable range. Finally, the state space model of HMMC-CFB system is established and a stable state-error feedback control law is given. By the passive theory, the necessary and sufficient condition for the globally uniformly asymptotical stability of the HMMC-CFB closed-loop system is deduced. Simulation results confirm the superiority of this novel topology and the validity of the proposed control strategy.

scholarly journals Fault Simulations in a Multiterminal High Voltage DC Network with Modular Multilevel Converters Using Full-Bridge Submodules

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1653
Author(s):  
Ioan-Cătălin Damian ◽  
Mircea Eremia ◽  
Lucian Toma
Keyword(s):  
High Voltage ◽  
Energy Resource ◽  
Fault Analysis ◽  
Renewable Energy Resource ◽  
Dynamic Simulations ◽  
Multilevel Converters ◽  
Strong Focus ◽  
Modular Multilevel Converters ◽  
Overhead Power Lines ◽  
And Control

The concept of high-voltage DC transmission using a multiterminal configuration is presently a central topic of research and investment due to rekindled interest in renewable energy resource integration. Moreover, great attention is given to fault analysis, which leads to the necessity of developing proper tools that enable proficient dynamic simulations. This paper leverages models and control system design techniques and demonstrates their appropriateness for scenarios in which faults are applied. Furthermore, this paper relies on full-bridge submodule topologies in order to underline the increase in resilience that such a configuration brings to the multiterminal DC network, after an unexpected disturbance. Therefore, strong focus is given to fault response, considering that converters use a full-bridge topology and that overhead power lines connect the terminals.

scholarly journals Lifetime and reliability improvements in modular multilevel converters using controlled circulating current

2021 ◽  
Author(s):  
Nasiru B. Kadandani ◽  
Mohamed Dahidah ◽  
Salaheddine Ethni ◽  
Musbahu Muhammad
Keyword(s):  
Control Method ◽  
Semiconductor Devices ◽  
Junction Temperature ◽  
Multilevel Converters ◽  
Control Approach ◽  
Circulating Current ◽  
Inherent Feature ◽  
Modular Multilevel Converters ◽  
Current Loading ◽  
Laboratory Prototype

AbstractCirculating current has been an inherent feature of modular multilevel converters (MMC), which results in second-order harmonics on the arms currents. If not properly controlled, the circulating current can affect the lifetime and reliability of a converter by increasing the current loading, loss distribution, and junction temperature of its semiconductor devices. This paper proposes controlled circulating current injection as a means of improving the lifetime and reliability of an MMC. The proposed method involves modifying the reference modulating signals of the converter arms to include the controlled differential voltage as an offset. The junction temperature of the semiconductor devices obtained from an electro-thermal simulation is processed to deduce the lifetime and reliability of the converter. The obtained results are benchmarked against a case where the control method is not incorporated. The incorporation of the proposed control method results in a 68.25% increase in the expected lifetime of the converter and a 3.06% increase on its reliability index. Experimental results of a scaled down laboratory prototype validate the effectiveness of the proposed control approach.

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