• 제목/요약/키워드: Neutral point potential balance

검색결과 9건 처리시간 0.018초

A Hybrid Modulation Strategy with Reduced Switching Losses and Neutral Point Potential Balance for Three-Level NPC Inverter

  • Jiang, Weidong;Gao, Yan;Wang, Jinping;Wang, Lei
    • Journal of Electrical Engineering and Technology
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    • 제12권2호
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    • pp.738-750
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    • 2017
  • In this paper, carrier-based pulse width modulation (CBPWM), space vector PWM (SVPWM) and reduced switching losses PWM (RSLPWM) for the three-level neutral point clamped (NPC) inverter are introduced. In the case of the neutral point (NP) potential (NPP) offset, an asymmetric disposition PWM (ASPDPWM) strategy is proposed, which can output PWM sequences correctly and suppress the lower order harmonics of the inverter effectively. An NPP balance strategy based on carrier based PWM (CBPWM) is analyzed. A hybrid modulation strategy combining RSLPWM and the NPP balance based on CBPWM is proposed, and hysteresis control is adopted to switch between the two modulation strategies. An experimental prototype of the three-level NPC inverter is built. The effectiveness of the hybrid modulation is verified with a resistance-inductance load and a permanent magnetic synchronous motor (PMSM) load, respectively. The experimental results show that reduced switching losses and an acceptable NPP can be effectively achieved in the hybrid modulation strategy.

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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    • 제12권3호
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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.

Optimized Low-Switching-Loss PWM and Neutral-Point Balance Control Strategy of Three-Level NPC Inverters

  • Xu, Shi-Zhou;Wang, Chun-Jie;Han, Tian-Cheng;Li, Xue-Ping;Zhu, Xiang-Yu
    • Journal of Power Electronics
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    • 제18권3호
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    • pp.702-713
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    • 2018
  • Power loss reduction and total harmonic distortion(THD) minimization are two important goals of improving three-level inverters. In this paper, an optimized pulse width modulation (PWM) strategy that can reduce switching losses and balance the neutral point with an optional THD of three-level neutral-point-clamped inverters is proposed. An analysis of the two-level discontinuous PWM (DPWM) strategy indicates that the optimal goal of the proposed PWM strategy is to reduce switching losses to a minimum without increasing the THD compared to that of traditional SVPWMs. Thus, the analysis of the two-level DPWM strategy is introduced. Through the rational allocation of the zero vector, only two-phase switching devices are active in each sector, and their switching losses can be reduced by one-third compared with those of traditional PWM strategies. A detailed analysis of the impact of small vectors, which correspond to different zero vectors, on the neutral-point potential is conducted, and a hysteresis control method is proposed to balance the neutral point. This method is simple, does not judge the direction of midpoint currents, and can adjust the switching times of devices and the fluctuation of the neutral-point potential by changing the hysteresis loop width. Simulation and experimental results prove the effectiveness and feasibility of the proposed strategy.

A Novel Virtual Space Vector Modulation Strategy for the Neutral-Point Potential Comprehensive Balance of Neutral-Point-Clamped Converters

  • Zhang, Chuan-Jin;Tang, Yi;Han, Dong;Zhang, Hui;Zhang, Xiao;Wang, Ke
    • Journal of Power Electronics
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    • 제16권3호
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    • pp.946-959
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    • 2016
  • A novel Virtual Space Vector (VSV) modulation strategy for complete control of potential neutral point (NP) issues is proposed in this paper. The neutral point potential balancing problems of multi-level converters, which include elimination of low frequency oscillations and self-balancing for NP dc unbalance, are investigated first. Then a set of improved virtual space vectors with dynamic adjustment factors are introduced and a multi-objective optimization algorithm which aims to optimize these adjustment factors is presented in this paper. The improved virtual space vectors and the multi-objective optimization algorithm constitute the novel Virtual Space Vector modulation. The proposed novel Virtual Space Vector modulation can simultaneously recover NP dc unbalance and eliminate low frequency oscillations of the neutral point. Experiment results show that the proposed strategy has excellent performance, and that both of the neutral point potential issues can be solved.

Simplified PWM Strategy for Neutral-Point-Clamped (NPC) Three-Level Converter

  • Ye, Zongbin;Xu, Yiming;Li, Fei;Deng, Xianming;Zhang, Yuanzheng
    • Journal of Power Electronics
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    • 제14권3호
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    • pp.519-530
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    • 2014
  • A novel simplified pulse width modulation(PWM) strategy for neutral point clamped (NPC) three-level converter is proposed in this paper.The direct output voltage modulation is applied to reduce the calculation time. Based on this strategy, several optimized control methods are proposed. The neutral point potential balancing algorithm is discussed and a fine neutral point potential balancing scheme is introduced. Moreover, the minimum pulse width compensation and switching losses reduction can be easily achieved using this modulation strategy. This strategy also gains good results even with the unequal DC link capacitor. The modulation principle is studied in detail and the validity of this simplified PWM strategy is experimentally verified in this paper. The experiment results indicated that the proposed PWM strategy has excellent performance, and the neutral point potential can be balanced well with unequal DC link captaincies.

An Optimized Control Method Based on Dual Three-Level Inverters for Open-end Winding Induction Motor Drives

  • Wu, Di;Su, Liang-Cheng;Wu, Xiao-Jie;Zhao, Guo-Dong
    • Journal of Power Electronics
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    • 제14권2호
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    • pp.315-323
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    • 2014
  • An optimized space vector pulse width modulation (SVPWM) method with common mode voltage elimination and neutral point potential balancing is proposed for an open-end winding induction motor. The motor is fed from both of the ends with two neutral point clamped (NPC) three-level inverters. In order to eliminate the common mode voltage of the motor ends and balance the neutral point potential of the DC link, only zero common mode voltage vectors are used and a balancing control factor is gained from calculation in the strategy. In order to improve the harmonic characteristics of the output voltages and currents, the balancing control factor is regulated properly and the theoretical analysis is provided. Simulation and experimental results show that by adopting the proposed method, the common mode voltage can be completely eliminated, the neutral point potential can be accurately balanced and the harmonic performance for the output voltages and currents can be effectively improved.

Torque Ripple Reduction in Three-Level Inverter-Fed Permanent Magnet Synchronous Motor Drives by Duty-Cycle Direct Torque Control Using an Evaluation Table

  • Chen, Wei;Zhao, Ying-Ying;Zhou, Zhan-Qing;Yan, Yan;Xia, Chang-Liang
    • Journal of Power Electronics
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    • 제17권2호
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    • pp.368-379
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    • 2017
  • In this paper, a direct torque control algorithm with novel duty cycle-based modulation is proposed for permanent magnet synchronous motor drives fed by neutral-point clamped three-level inverters. Compared with the standard DTC, the proposed algorithm can suppress steady-state torque ripples as well as ensure neutral-point potential balance and smooth vector switching. A unified torque/flux evaluation table with multiple voltage vectors and precise control levels is established and used in this method. This table can be used to evaluate the effects of duty-cycle vectors on torque and flux directly, and the elements of the table are independent of the motor parameters. Consequently, a high number of appropriate voltage vectors and their corresponding duty cycles can be selected as candidate vectors to reduce torque ripples by looking up the table. Furthermore, small vectors are incorporated into the table to ensure the neutral-point potential balance with the numerous candidate vectors. The feasibility and effectiveness of the proposed algorithm are verified by both simulations and experiments.

Neutral-point Voltage Balancing Strategy for Three-level Converter based on Disassembly of Zero Level

  • Wang, Chenchen;Li, Zhitong;Xin, Hongliang
    • Journal of Power Electronics
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    • 제19권1호
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    • pp.79-88
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    • 2019
  • The neutral-point (NP) voltage of three-phase three-level NP-clamped converters is needed for balance. To maintain NP potential and suppress ripple, a novel NP voltage balancing strategy is proposed in this work. The mechanism of NP voltage variation is studied first. Then, the relationship between the disassembly of zero level (O level) and NP current is studied comprehensively. On these bases, two methods for selecting one of three output phases for the disassembly of its O level are presented. Finally, simulation and experimental results verify the validity and practicability of the proposed algorithms.

A Study on the Characteristics of Knitwear Fashion Design: With a focus on Missoni, Sonia Rykiel, Azzedine Alaia

  • Chun, Hei Jung;Park, Jae Min
    • International Journal of Costume and Fashion
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    • 제13권1호
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    • pp.23-34
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    • 2013
  • The purpose of this study is to better understand the development and characteristics of knitwear fashion design by examining the transformation process of the modern knits. The subjects of the study are Missoni, Sonia Rykiel, and Azzedine Alaia, designers who are world-renowned knit designers, and the expressive techniques in their designs will be evaluated. The study also intends to analyze the aesthetic value of each designer's style through their product's silhouette, colors, and knitting techniques. On the basis of the analysis, we hope to research the factors in the designing process that will allow knits, which were made for practical purposes, to be valued as a luxury fashion item, and with the results, show the potential for knits in expanding its domain in fashion to become a more luxurious, creative fashion item. The characteristic comparison of the designers is as follows: First, in the case of colors, Missoni shows its distinct identity through a balance of splashy colors as well as nature-inspired color composition and balance. And, only with color use, is also able to express perspective, form composition, and rhythm. Sonia Rykiel designs are composed of black backgrounds with strong primary colors that are contrasted with one-point or stripes to express a light, urban image. Alaia emphasizes femininity by the use of black and white colors, which show modernity, in combination with neutral skin-toned colors, such as beige and gray. So, in other words, Missoni and Sonia Rykiel mixed colors for visual interconnectivity, while Alaia expressed femininity through the use of an achromatic color. Second, in the case of knitting techniques, Missoni uses the jacquard technique to make complex patterns that show balance of colors and patterns such as zigzag, stripe, geometries, and titan check, which are geometric, abstract, and symmetric. Sonia Rykiel who uses stripes as her trademark, most often utilizes the intarsia technique, which is expressed through one-point. Alaia combines diverse techniques, such as the Skashi weaving, by using computerized knitting. Third, as for silhouettes, Missoni eliminated exaggerated details in order to emphasize the flashy colors and delicate patterns and weavings of its designs, and this resulted in simplistic and relaxed silhouettes. Sonia Rykiel took advantage of the elasticity that the knit offers to get a tight silhouette, and in turn, emphasized the female sensuality. Alaia used curvilinear cuts that emphasized the womanly curves and gained an image considered soft and feminine.