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
随机开关频率调制策略通过将开关频率在扩频范围内随机变化抑制高频谐波。虽然过宽的扩频范围能更有效地抑制高频谐波,但同时会带来严重的电流畸变和较大的转矩脉动。为此,该文提出在窄扩频范围下考虑随机数变化的随机开关频率空间矢量...随机开关频率调制策略通过将开关频率在扩频范围内随机变化抑制高频谐波。虽然过宽的扩频范围能更有效地抑制高频谐波,但同时会带来严重的电流畸变和较大的转矩脉动。为此,该文提出在窄扩频范围下考虑随机数变化的随机开关频率空间矢量脉宽调制(random switching frequency space vector pulse width modulation,RSF-SVPWM)。与传统的RSF-SVPWM相比,提出的方法通过限制相邻随机数变化的最大值,减小了相邻随机数的相对变化,使高频谐波由三角形分布变为梯形分布,从而降低了高频谐波幅值,实现窄扩频范围内对高频谐波的有效抑制。实验结果表明,在相同的扩频范围内,该方法更有效地降低了开关频率及其整数倍处谐波的峰值。展开更多
在三相两电平逆变器中,虚拟空间矢量调制(virtual space vector modulation,VSVM)因其能降低共模电压的幅值和三次谐波而受到广泛关注,但还存在共模电压的谐波成分丰富,且幅值变化和方向变化的发生率较高的问题,为此提出一种改进型VSVM...在三相两电平逆变器中,虚拟空间矢量调制(virtual space vector modulation,VSVM)因其能降低共模电压的幅值和三次谐波而受到广泛关注,但还存在共模电压的谐波成分丰富,且幅值变化和方向变化的发生率较高的问题,为此提出一种改进型VSVM方法。该方法通过分析经典VSVM的矢量合成和共模电压特点,对虚拟矢量和虚拟零矢量所对应的基本矢量进行优化排序,使每个开关周期的共模电压波形相同,均为单个矩形波。进一步分析了所提方法的共模谐波、死区补偿和开关损耗。在逆变器-永磁同步电机系统中进行仿真和实验。结果表明:与经典VSVM相比,所提方法在保持共模电压低幅值的同时,使幅值变化和方向变化的发生率都降低3倍,完全消除基带谐波和边带谐波分量,并使共模电压的高频段峰值平均减小6 dB,且线电流、线电压、转矩和转速等性能依然良好。该方法在不增加系统体积和成本的情况下,能更有效抑制共模干扰,有利于共模滤波器的设计,并为其他共模抑制脉冲宽度调制(pulse width modulation,PWM)方法的研究提供了借鉴。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.
文摘光伏等新能源及储能系统基于电力电子接口融入微电网,其低惯量问题显著,面临严峻的频率稳定风险。为了改善微电网频率动态特性,利用模型预测控制(model predictive control,MPC)协同优化外环与内环,提出了一种基于级联模型预测(cascaded model predictive control,CMPC)的虚拟同步机(virtual synchronous generator,VSG)控制策略。在外环,利用MPC的滚动优化,对输入VSG的有功功率参考值进行实时修正。在内环,优化通过两个阶段寻找最优电压矢量(voltage vector,VV)的离散空间矢量模型预测控制(discrete space vector model predictive control,DSVM-MPC)方法,减少跟踪外环输出误差,使频率控制更为精确。仿真结果表明,所提策略能够提升频率响应和限流效果,避免频率过冲。
文摘随机开关频率调制策略通过将开关频率在扩频范围内随机变化抑制高频谐波。虽然过宽的扩频范围能更有效地抑制高频谐波,但同时会带来严重的电流畸变和较大的转矩脉动。为此,该文提出在窄扩频范围下考虑随机数变化的随机开关频率空间矢量脉宽调制(random switching frequency space vector pulse width modulation,RSF-SVPWM)。与传统的RSF-SVPWM相比,提出的方法通过限制相邻随机数变化的最大值,减小了相邻随机数的相对变化,使高频谐波由三角形分布变为梯形分布,从而降低了高频谐波幅值,实现窄扩频范围内对高频谐波的有效抑制。实验结果表明,在相同的扩频范围内,该方法更有效地降低了开关频率及其整数倍处谐波的峰值。
文摘有源中点钳位型ANPC(active neutral-point-clamped)三电平结构可以优化开关器件的损耗分布,在大功率电机驱动系统应用中更具优势。为提高低开关频率运行条件下驱动系统的性能,研究了多模式同步空间矢量脉宽调制SSVPWM(synchronous space vector PWM)切换策略,针对不同同步空间脉宽调制模式之间切换时产生的电流与转矩冲击问题,提出1种基于脉冲插入的ANPC三电平逆变器的多模式SSVPWM切换策略。通过对电机输出的定子磁链进行重构,在线计算切换处的定子磁链偏差,并在切换时刻结合ANPC冗余零状态选择,以插入电压脉冲方式对其进行补偿,实现了不同模式之间的平稳过渡。仿真和实验验证了所提策略的正确性和有效性。
