Parallel converter can significantly increase the capacity of the converter and improve the power quality of AC side, but the circulation which can lead to high switching loss and even damage the devices will easily e...Parallel converter can significantly increase the capacity of the converter and improve the power quality of AC side, but the circulation which can lead to high switching loss and even damage the devices will easily exist in the direct parallel converters. In this paper, the average model of parallel interleaved inverters system to analyze the circulation current is shown, and the cross current is relevant to DC-bus voltage and the overlap time of zero vectors in the switching period. Based on this observation, a discontinuous space vector modulation without using zero vectors (000) is eliminate and suppress the zero-sequence current to entire system. Finally, the effectiveness of modulation strategy is verified by the simulations in this paper.展开更多
When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse wi...When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation(GSDPWM) method of threephase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method,which can equally derive the minimized total harmonic distortion(THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.展开更多
This paper proposes a dual-frequency discontinuous space vector pulse width modulation(DFDSVPWM)for a five-phase voltage source inverter with harmonic injection.In this modulation,for dual-frequency voltage output and...This paper proposes a dual-frequency discontinuous space vector pulse width modulation(DFDSVPWM)for a five-phase voltage source inverter with harmonic injection.In this modulation,for dual-frequency voltage output and reduction of switching losses,two different zero-vector-inserted modes are flexibly employed by alternatively using two types of zero vectors.Based on the comparison with continuous SVPWM,the idea and principle of the proposed DFDSVPWM are analyzed and an example of PWM signals for one bridge is also presented.For switching losses analysis,the impact factors and the calculation method are investigated and the corresponding implementation is given as well.The simulation and experimental results from a prototype verify the correctness and effectiveness of the proposed modulation and it has the advantages of outputting dual-frequency voltage and reducing switching losses.展开更多
Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this resear...Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this research was to determine the impacts of PWM duty cycle and frequency on spray drift characteristic.Spray tests were conducted in a wind tunnel with a PWM variable-rate spraying system.The airborne drift and sediment drift were determined with tracer method,and the drift potential reduction(DPR)compared with reference condition of 100%duty cycle at vertical profile and horizontal planes were calculated,respectively.The results show that,at a given frequency,droplet size decreases with the increase of duty cycle,the main reason is that the liquid does not reach full pattern development at lower duty cycle.Duty cycle has a greater impact than the frequency on spray drift,the influence weights of duty cycle on airborne drift and sediment drift were 88.32%and 77.89%,respectively.At a lower PWM frequency,in addition to the droplet size,the spray drift may be affected by the pulsed spray pattern.From the perspective of reducing spray drift,it is recommended that the PWM duty cycle should be set in the range of 20%-70%to reduce the potential drift in PWM sprays.This research provides a pesticide drift reduction scheme for variable spraying technology,which can serve as a theoretical basis for PWM parameter selection.展开更多
Space-vector modulation (SVM) is widely used in multilevel inverters because of its ability to improve DC bus utilization, reduce harmonic distortion, and enhance operational flexibility. However, the increasing compl...Space-vector modulation (SVM) is widely used in multilevel inverters because of its ability to improve DC bus utilization, reduce harmonic distortion, and enhance operational flexibility. However, the increasing complexity of multilevel inverter topologies, such as neutral-point clamped, cascaded H-bridge, and modular multilevel converters, presents challenges in terms of computational efficiency, neutral-point voltage balancing, and common-mode voltage suppression. A detailed review of SVM techniques is provided, including traditional methods and advanced variants such as carrier-based SVM, selective harmonic elimination SVM, and virtual SVM. Additionally, recent hybrid approaches that combine multiple strategies to address specific performance requirements are discussed. The findings highlight advancements in improving the modulation performance, reducing switching losses, and achieving better harmonic attenuation. A discussion of the future challenges and opportunities for multilevel inverter modulation strategies is concluded.展开更多
文摘Parallel converter can significantly increase the capacity of the converter and improve the power quality of AC side, but the circulation which can lead to high switching loss and even damage the devices will easily exist in the direct parallel converters. In this paper, the average model of parallel interleaved inverters system to analyze the circulation current is shown, and the cross current is relevant to DC-bus voltage and the overlap time of zero vectors in the switching period. Based on this observation, a discontinuous space vector modulation without using zero vectors (000) is eliminate and suppress the zero-sequence current to entire system. Finally, the effectiveness of modulation strategy is verified by the simulations in this paper.
文摘When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling(PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation(GSDPWM) method of threephase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method,which can equally derive the minimized total harmonic distortion(THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.
基金This work was supported in part by the National Natural Science Foundation of China(51507079)the China Postdoctoral Science Foundation Funded Project(2014M560421,2016T90454)the Fundamental Research Funds for the Central Universities(NJ20160046,NS2018025).
文摘This paper proposes a dual-frequency discontinuous space vector pulse width modulation(DFDSVPWM)for a five-phase voltage source inverter with harmonic injection.In this modulation,for dual-frequency voltage output and reduction of switching losses,two different zero-vector-inserted modes are flexibly employed by alternatively using two types of zero vectors.Based on the comparison with continuous SVPWM,the idea and principle of the proposed DFDSVPWM are analyzed and an example of PWM signals for one bridge is also presented.For switching losses analysis,the impact factors and the calculation method are investigated and the corresponding implementation is given as well.The simulation and experimental results from a prototype verify the correctness and effectiveness of the proposed modulation and it has the advantages of outputting dual-frequency voltage and reducing switching losses.
基金The authors acknowledge that this research was financially supported by National Key R&D Program of China(2019YFD1101102-3)National Natural Science Foundation of China(32071907)+1 种基金Outstanding Scientist Cultivation Project of Beijing Academy of Agriculture and Forestry Sciences(JKZX202205)Qingyuan Smart Agriculture Research Institute+New R&D Institutions Construction in North and West Guangdong(2019B090905006).
文摘Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this research was to determine the impacts of PWM duty cycle and frequency on spray drift characteristic.Spray tests were conducted in a wind tunnel with a PWM variable-rate spraying system.The airborne drift and sediment drift were determined with tracer method,and the drift potential reduction(DPR)compared with reference condition of 100%duty cycle at vertical profile and horizontal planes were calculated,respectively.The results show that,at a given frequency,droplet size decreases with the increase of duty cycle,the main reason is that the liquid does not reach full pattern development at lower duty cycle.Duty cycle has a greater impact than the frequency on spray drift,the influence weights of duty cycle on airborne drift and sediment drift were 88.32%and 77.89%,respectively.At a lower PWM frequency,in addition to the droplet size,the spray drift may be affected by the pulsed spray pattern.From the perspective of reducing spray drift,it is recommended that the PWM duty cycle should be set in the range of 20%-70%to reduce the potential drift in PWM sprays.This research provides a pesticide drift reduction scheme for variable spraying technology,which can serve as a theoretical basis for PWM parameter selection.
文摘Space-vector modulation (SVM) is widely used in multilevel inverters because of its ability to improve DC bus utilization, reduce harmonic distortion, and enhance operational flexibility. However, the increasing complexity of multilevel inverter topologies, such as neutral-point clamped, cascaded H-bridge, and modular multilevel converters, presents challenges in terms of computational efficiency, neutral-point voltage balancing, and common-mode voltage suppression. A detailed review of SVM techniques is provided, including traditional methods and advanced variants such as carrier-based SVM, selective harmonic elimination SVM, and virtual SVM. Additionally, recent hybrid approaches that combine multiple strategies to address specific performance requirements are discussed. The findings highlight advancements in improving the modulation performance, reducing switching losses, and achieving better harmonic attenuation. A discussion of the future challenges and opportunities for multilevel inverter modulation strategies is concluded.
文摘在中压大功率并网逆变器中,存在开关频率低、输出滤波器设计困难等问题。采用断续脉宽调制策略(discontinuous pulse-width modulation,DPWM)能在保证开关损耗不变的前提下,有效提高逆变器等效开关频率、降低滤波器设计难度。首先,对6种三电平DPWM(DPWM0、DPWM1、DPWM2、DPWM3、DPWMA、DPWMB)的各自优缺点进行比较分析,结果表明在单位功率因数及较高调制度下,DPWMA兼具开关损耗小、共模电压与谐波畸变低的优点;其次,针对DPWMA调制策略输出谐波相对集中于第一载波带的特性,引入LLCL滤波器拓扑,并基于选频思想提出一种改进阻尼方案,在有效提高载波频率处谐波衰减能力的同时,确保谐振抑制能力且显著降低阻尼电阻损耗;随后,给出了所提滤波器的参数设计原则及其详细流程。对30 k W样机进行实验,实验结果表明,采用该文所提调制策略和滤波器设计方法,逆变器的输出共模电压和并网电流谐波含量能够得到有效降低,同时阻尼电阻损耗较小,有利于减小中压大功率逆变器的网侧滤波器体积与成本,提高系统效率。
