Optimized low switching frequency modulation with neutral point voltage control for three‐level converters

Bo Guan,Chuanchuan Luo,Xiaoliang Zhen 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.7

The use of three-level converters with low switching frequency (SF) modulation is urgently needed for medium voltage high power applications. However, since it is not possible to frequently adjust the injected zero-sequence voltage and duty time of redundant vectors, the neutral point (NP) voltage problem of three-level converters becomes a tricky issue under low SFs. In this paper, an optimized low SF modulation with NP voltage control is proposed, which is based on half-wave symmetry selective harmonic elimination pulse width modulation. The proposed modulation specifically addresses the low-frequency NP voltage fluctuation of three-level converters, using the amplitude and phase of the 3n-order harmonics as degrees of freedoms (DOFs). In addition, it actively optimizes the control problem into constraint equations. By revealing the relationship between these new DOFs and low-frequency NP voltage fluctuation, and obtaining the optimum settings for the new DOFs, the newly established constraint equations can naturally suppress the low-frequency NP voltage fluctuation, without the need for real-time switching angle adjustments. It fits very well with the feature that switching angles can only be calculated offline and used via a table online. Experimental results show the validity and feasibility of the proposed modulation strategy.

Capacitance Effect on Microwave Power Spectra of Spin-Torque Oscillator with Thermal Noise

Bo Guan,Yan Zhou,Franklin G. Shin,Johan Akerman 한국자기학회 2008 한국자기학회 학술연구발표회 논문개요집 Vol.- No.-

Effect of Quantum Barrier Thickness in the Multiple-Quantum-Well Active Region of GaInN/GaN Light-Emitting Diodes

Guan-Bo Lin,Dong-Yeong Kim,Qifeng Shan,Jaehee Cho,Schubert, E. Fred,Hyunwook Shim,Cheolsoo Sone,Jong Kyu Kim IEEE 2013 IEEE photonics journal Vol.5 No.4

<P>The dependence of the polarization-induced electric field in GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) on the GaN quantum barrier (QB) thickness is investigated. Electrostatic arguments and simulations predict that a thin QB thickness reduces the electric field in the quantum wells (QWs) and also improves the LED efficiency. We experimentally demonstrate that the QW electric field decreases with decreasing QB thickness. The lower electric field results in a better overlap of electron and hole wave functions and better carrier confinement in the QWs. A reduced efficiency droop and enhanced internal quantum efficiency is demonstrated for GaInN/GaN LEDs when the QB thickness is reduced from 24.5 to 9.1 nm.</P>

Optimal Two Degrees-of-Freedom Based Neutral Point Potential Control for Three-Level Neutral Point Clamped Converters

Guan, Bo,Doki, Shinji The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

Although the dual modulation wave method can solve the low-frequency neutral point potential (NPP) fluctuation problem for three-level neutral point clamped converters, it also increases the switching frequency and limits the zero-sequence voltage. That makes it harmful when dealing with the NPP drift problem if the converter suffers from a long dead time or asymmetric loads. By introducing two degrees of freedom (2-DOF), an NPP control based on a search optimization method can demonstrate its ability to cope with the above mentioned two types of NPP problems. However, the amount of calculations for obtaining an optimal 2-DOF is so large that the method cannot be applied to certain industrial applications with an inexpensive digital signal processor. In this paper, a novel optimal 2-DOF-based NPP control is proposed. The relationships between the NPP and the 2-DOF are analyzed and a method for directly determining the optimal 2-DOF is also discussed. Using a direct calculation method, the amount of calculations is significantly reduced. In addition, the proposed method is able to maintain the strongest control ability for the two types of NPP problems. Finally, some experimental results are given to confirm the validity and feasibility of the proposed method.

Optimal Two Degrees-of-Freedom Based Neutral Point Potential Control for Three-Level Neutral Point Clamped Converters

Bo Guan,Shinji Doki 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

Although the dual modulation wave method can solve the low-frequency neutral point potential (NPP) fluctuation problem forthree-level neutral point clamped converters, it also increases the switching frequency and limits the zero-sequence voltage. Thatmakes it harmful when dealing with the NPP drift problem if the converter suffers from a long dead time or asymmetric loads. By introducing two degrees of freedom (2-DOF), an NPP control based on a search optimization method can demonstrate itsability to cope with the above mentioned two types of NPP problems. However, the amount of calculations for obtaining anoptimal 2-DOF is so large that the method cannot be applied to certain industrial applications with an inexpensive digital signalprocessor. In this paper, a novel optimal 2-DOF-based NPP control is proposed. The relationships between the NPP and the2-DOF are analyzed and a method for directly determining the optimal 2-DOF is also discussed. Using a direct calculationmethod, the amount of calculations is significantly reduced. In addition, the proposed method is able to maintain the strongestcontrol ability for the two types of NPP problems. Finally, some experimental results are given to confirm the validity andfeasibility of the proposed method.

A study on the influence of graduation internship on employment anxiety among college students in Tianjin, China

Bo Guan KOREA INSTITUTE FOR HUMANITIES AND SOCIAL SCIENCES 2023 Journal of Arts and Cultural Studies(ACS) Vol.2 No.2

Background: The employment rate of university students in Tianjin has decreased due to the epidemic and economic downturn. Many graduates have experienced negative emotional problems such as employment anxiety. Objectives: To explore the main factors affecting employment anxiety among college students in the current social development, analyze the relationship between the internship and the anxiety related to employment, and find feasible measures to eliminate employment anxiety. Methods: The test subjects for this research were 179 fresh graduates from universities in Tianjin. They were evaluated against the Employment Anxiety Scale before and after the three-month internship. Relevant influencing factors were collected for statistical analysis. Content: Through investigations to explore the source of employment pressure and relieve stress, analyze the relationship between internship behavior and employment anxiety, and suggest relevant suggestions for optimizing internship behavior. Conclusions: Internships can make most fresh graduates from Tianjin universities acquire certain knowledge about employment, accumulate employment experience, and reduce employment anxiety.

A Narrow Pulse Compensation Method for Neutral-Point-Clamped Three-Level Converters Considering Neutral-Point Balance

Bo Guan,Chenchen Wang 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

For medium/high voltage high-power neutral-point-clamped (NPC) three-level converters, narrow pulses appear usually when modulation waves are close to ±1 and 0. To ensure reliable switching and the safety, a long narrow pulse limit time needs to be set. Narrow pulse problems will become prominent. Meantime, neutral-point voltage balance problem of three-level NPC converters is a key issue that should be seriously considered. The strong coupling effects between narrow pulse problem and neutral-point voltage balance problem is also worth attention. Ignoring the strong coupling effects, traditional narrow pulse methods realize narrow pulse compensation and neutral-point voltage balance separately. Considering the two problems and the coupling effects, a novel narrow pulse compensation method is proposed. By analyzing the limits of modulation waves caused by narrow pulses, narrow pulses are eliminated completely in this paper. Simulation and experimental results show that it has a good performance for narrow pulse compensation and has few adverse effects on neutral-point voltage balance. The overall performance is better than traditional narrow pulse compensation methods.

The beneficial effects of a p-type GaInN spacer layer on the efficiency of GaInN/GaN light-emitting diodes

Guan-Bo Lin,Xiaoguang Zhang,이수민,George Papasouliotis,김종규,E. Fred Schubert,조제희 한국물리학회 2015 Current Applied Physics Vol.15 No.10

Light-emitting diodes (LEDs) with a Mg-doped p-type Ga1-xInxN (0 ≤ x ≤ 0.07) spacer layer located between an undoped GaN spacer layer and the electron blocking layer are investigated. The LEDs are found to have comparable peak efficiency but less efficiency droop when the crystal quality of the p-type Ga1-xInxN spacer layer is well-controlled by lowering the growth temperature and by using a suitable In composition and Mg doping concentration. All LED samples with the p-type spacer layer show a smaller efficiency droop compared to a reference LED having an undoped GaN spacer. Among the sample sets investigated, an optical power enhancement of 12% at 111 A/cm2 is obtained when inserting a 5 nm-thick p-type Ga0.97In0.03N spacer layer. The results support that carrier transport is the key factor in the efficiency droop observed in GaN-based LEDs.

A complementary matching technique to reduce the variance of optical and electrical properties of light-emitting diodes

Lin, Guan-Bo,Schubert, Martin F.,Cho, Jaehee,Schubert, E. Fred,Kim, Hyungkun Wiley Blackwell (John Wiley Sons) 2011 Journal of the Society for Information Display Vol.19 No.6

최적화된 신경망 기반 무선 센서 노드위치 알고리즘 제안

관보(Bo Guan),쥐훙샹(Hongxiang Qu),양펑지옌(Fengjian Yang),리홍량(Hongliang Li),정양권(Yang-Kwon Jeong) 한국전자통신학회 2022 한국전자통신학회 논문지 Vol.17 No.6

본 연구는 RSSI의 거리측정 방법이 외부 환경에 의해 쉽게 영향을 받아 위치 오차가 크다는 결점을 도출하였고 이 3차원 배치 환경에서 RSSI의 거리측정 노드에서 측정한 거리값을 최적화하는 문제에 대해 향상된 CA-PSO 알고리즘을 개선한 CA-PSO-BP 알고리즘을 제안하였다. 제안된 알고리즘은 3차원 무선센서네트워크(WSN) 공간에서 인식할 수 없는 노드를 설정할 수 있도록 하였다. 또한, CA-PSO를 BP 신경망에 응용하므로, 학습을 통해 BP 네트워크의 학습시간 단축과 알고리즘의 수렴 속도를 제고 할 수 있었다. 본 연구에서 제안한 알고리즘을 통해 네트워크의 위치의 정밀도를 현저(15%)하게 높일 수 있다는 것을 증명하였고 유의미한 결과를 얻을 수 있었다. This study leads to the shortcoming that the RSSI distance measurement method is easily affected by the external environment and the position error is large, leading to the problem of optimizing the distance values measured by the RSSI distance measurement nodes in this three-dimensional configuration environment. We proposed the CA-PSO-BP algorithm, which is an improved version of the CA-PSO algorithm. The proposed algorithm allows setting unknown nodes in WSN 3D space. In addition, since CA-PSO was applied to the BP neural network, it was possible to shorten the learning time of the BP network and improve the convergence speed of the algorithm through learning.Through the algorithm proposed in this study, it was proved that the precision of the network location can be increased significantly (15%), and significant results were obtained.