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45 results on '"Qin, Changwei"'

12. Novel Space Vector Modulation Method for the Quasi-Z-Source Asymmetrical Three-Level Inverter

Author

Li, Xiaoyan, Qin, Changwei, and Chu, Zhiyuan

Abstract

The quasi-Z-source (QZS) asymmetrical three-level inverter (ATLI) can be regarded a post-fault topology of the QZS T-type three-level inverter. Due to the inherent limitation of this topology, the output states are restricted, and the conventional modulation methods are not applicable any more. This brief presents a novel space vector modulation (SVM) for the normal operation of the QZS ATLI. Depending on whether the medium vector is included, the sectors of the space vector diagram (SVD) are categorized into two types. According to the sector type, different combinations of basic vectors are selected to generate the correct ac output voltage, and the appropriate shoot-through states are properly adopted to implement the dc voltage boosting. Additionally, to guarantee the neutral-point voltage (NPV) balance, the effective small vectors are selected, whose duty cycles are adjusted in different sectors. The detailed calculating process of duty cycles and arrangement of switching sequences are provided. The effectiveness of the proposed method is verified by experimental results.

Published
2024
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16. Improved Particle Swarm Optimization Based Selective Harmonic Elimination and Neutral Point Balance Control for Three-Level Inverter in Low-Voltage Ride-Through Operation

Author

Xiaoyan Li, Qin Changwei, Ying Jiang, Xiangyang Xing, and Zhiyuan Chen

Subjects
Computer science, Particle swarm optimization, Computer Science Applications, Power (physics), Harmonic analysis, Nonlinear system, Local optimum, Control and Systems Engineering, Control theory, Harmonics, Inverter, Electrical and Electronic Engineering, Low voltage ride through, Information Systems
Abstract

In high-power applications, selective harmonic elimination pulsewidth modulation (SHEPWM) method is widely used to eliminate low-order harmonics in three-level inverters with low power losses. However, it faces the challenges that the conventional optimization methods for solving harmonic elimination equations in SHEPWM are easy to be trapped in local optimum. Moreover, the neutral point (NP) voltage of three-level inverter cannot be balanced under low-voltage ride-through (LVRT) condition with conventional SHEPWM method. To address these problems, a SHEPWM scheme is proposed, which is on the basis of an improved particle swarm optimization (IPSO) algorithm to solve the harmonic elimination equations and an enhanced NP balance control method in LVRT operation. First, an IPSO algorithm is proposed to calculate the switching angles of the transcendental equations for harmonic elimination. The IPSO algorithm defines a nonlinear negative exponential inertia weight considering the current and optimal fitness value, which can dynamically adjust the local and global searching speed and step size according to the actual situation, greatly improving the convergence speed and solution accuracy and avoiding falling into the local optimum. Then, by increasing the degree of freedom of the output current direction and combining with the NP voltage deviation, an enhanced NP voltage balance control method of SHEPWM in LVRT operation is proposed. The validity of the proposed method is proved by simulation and experimental results.

Published
2022

23. Generalised model predictive control scheme for three‐level converter under unbalanced grid voltage considering full power factor operation

Author

Xiangyang Xing, Duan Bin, Xiaoyan Li, Qin Changwei, Guangxian Zhang, and Chenghui Zhang

Subjects
Renewable Energy, Sustainability and the Environment, Computer science, 020209 energy, 020208 electrical & electronic engineering, 02 engineering and technology, Power factor, AC power, Grid, law.invention, Power (physics), Capacitor, Model predictive control, law, Control theory, 0202 electrical engineering, electronic engineering, information engineering, Grid code, Voltage
Abstract

With the increase of grid-connected renewable power generation units, the three-level converter (TLC) is widely utilized. However, when unbalanced grid voltage occurs, the converter should provide a certain of reactive power to satisfy the grid code, which decreases the power factor and degrades neutral-point (NP) voltage balance. The existing model predictive control methods for NP voltage balance in TLC mainly focus on high power factor operation, which are not applicable to low power factor operation. To solve this problem, this study proposes a generalized model predictive control (GMPC) scheme for the TLC. By analyzing the influence of P-type and N-type small vectors on NP voltage, it is indicated that the charging and discharging operation of the dc-link capacitors are determined by the grid currents directions with the defined small vectors. Since the directions of grid currents are changed with different power factors, the effect of one small vector on NP voltage is change. In the proposed GMPC scheme, the direction of grid currents and the capacitor voltage difference are simultaneously used to select the appropriate small vector to mitigate the NP voltage unbalance effectively in the full power factor range. The validity is verified by simulation and experimental results.

Published
2020

24. Improved Virtual Space Vector Modulation Scheme for the Reduced Switch Count Three-Level Inverter With Balanced and Unbalanced Neutral-Point Voltage Conditions.

Author

Qin, Changwei and Li, Xiaoyan

Abstract

This article presents an improved virtual space vector modulation scheme for the reduced switch count three-level inverter with balanced and unbalanced neutral-point voltage (NPV) conditions. By analyzing the effects of unbalanced NPV conditions on basic voltage vectors, the new virtual vectors are constructed by considering the dc unbalancing coefficient and distribution factor for small vectors simultaneously. To facilitate the calculation of duty cycles, the nonorthogonal coordinate system is employed. In addition, an optimized control scheme is developed to obtain the optimized distribution factor, and the relative durations of P-type and N-type small vectors are adjusted to control the voltages across two dc-link capacitors separately. The satisfactory quality of output currents is maintained with both balanced and unbalanced NPV conditions. The feasibility of the proposed scheme is verified by simulated and experimental results. [ABSTRACT FROM AUTHOR]

Published
2023
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29. An Adaptive Model Predictive Control for Reduced Switch Count Three-Level Inverter

Author

Xing, Xiangyang, Jing, Mengmeng, Du, Chunshui, Qin, Changwei, Liu, Chang, and Chen, Zhiyuan

Abstract

The reduced switch count three-level neutral-point-clamped (RSC-3LNPC) inverter is becoming popular due to the advantage of cost reduction. However, maintaining the lower current ripple and balancing the dc-link voltage is always a challenging task, especially when the medium vector is missing. To overcome this limitation, this article proposes an adaptive model predictive control (MPC) with optimized vector and duty cycle to guarantee the lower current ripple and achieve the dc-link voltage balancing. First, the voltage vector reference is derived based on the mathematic model of RSC-3LNPC inverter. Then, the virtual medium vectors are constructed with two adjacent large vectors, which increases the voltage vectors from 21 to 27. On the basis of voltage vectors, two or three vectors are optimally selected to synthesize the voltage reference. Finally, the capacitor voltage balance is achieved by selecting redundant small vectors to avoid the weighting factor tuning process. The proposed MPC features a lower current ripple and improves the dynamic-state performance while guaranteeing the dc-link voltage balancing. With the proposed method, the performance of the system is improved, which is verified by simulation and experimental results.

Published
2023
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30. Optimal Current Ripple PWM for Three-Level Inverter With Common Mode Voltage Reduction.

Author

Liu, Xi, Xing, Xiangyang, Chen, Jie, Qin, Changwei, Li, Xiaoyan, Zhang, Chenghui, and Chen, Alian

Subjects
PULSE width modulation transformers, PULSE width modulation inverters, VOLTAGE, ROOT-mean-squares, ELECTRIC drives, VECTOR spaces
Abstract

Three-level inverter has been widely used in electric drives and renewable power generation system. However, the common mode voltage (CMV) and output current ripple reduction of a three-level inverter should be carefully regulated for the appropriate operation. As these two targets are mutually interrelated, the conventional space vector modulation (SVM) scheme cannot cope with them decently. To overcome this drawback, this article proposes a novel modified SVM scheme to realize CMV and current ripple reduction simultaneously. The generating mechanism of output current ripple is analyzed, and the relationship between current ripple and utilized vectors is quantitatively described. Based on the analyses, the proposed optimal current ripple and CMV reduction pulsewidth modulation (OCR-CMVRPWM) method adopts four voltage vectors (large, medium, small, and zero vectors) to reduce the root mean square value of current ripple by allocating the sequence and dwell times of utilized vectors. Compared to the existing PWM methods, the proposed OCR-CMVRPWM scheme can reduce the peak of CMV to half of the value using the conventional SVM, and obtain a significant reduction of output current total harmonic distortion. The effectiveness of the proposed method is validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Published
2022
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