三相SPWM逆变器的谐波分析及其抑制策略

对三相电压型SPWM逆变器输出电压和电流谐波及其产生规律进行了讨论。并提出了一种新的易于工程实现的谐波抑制策略,该方法通过正确选择载波频率和在正弦调制波上叠加一个三次波使之成为鞍形波,产生相应的SPWM波形来控制逆变器开关器件的通断从而改善输出波形。数学分析表明有利于降低输出电压波形畸变系数（THD）、改善谐波电流损耗和转矩特性,仿真结果证明了这些措施的有效性和实用性。     

特殊逆变器调制技术研究

特殊逆变器工作频率为数kHz,通常采用脉冲法控制策略,输出波形特性差。针对传统特殊逆变器缺点,提出阶梯波调制方法。介绍特殊逆变器的拓扑结构,分析了基于阶梯波调制的特殊逆变器的基本原理,研究了阶梯调制算法。该特殊逆变器拓扑结构简单、开关器件开断损耗小、整机效率高,具有良好的谐波抑制能力。建立仿真模型,并进行分析,得出仿真结果。从仿真结果可以看出,采用阶梯波调制算法的特殊逆变器输出波形特性好,谐波含量低。     

基于神经网络的多电平逆变电路故障诊断

因含有大量的开关器件,多电平逆变器难以用基于模型的方法进行故障诊断。针对这一问题,提出了一种基于神经网络的故障识别和分类方法。采用载波相移脉冲宽度调制（PWM）策略搭建级联五电平逆变电路,对逆变器的输出电压信号进行快速傅里叶变换,获取其频谱并以此作为特征信息。利用反向传播算法（BP）神经网络对输出电压模式进行分类。Matlab仿真结果表明,本文设计的 BP神经网络有效地实现了对逆变器的故障诊断。     

无三次谐波电压输出的空间矢量脉冲宽度调制技术

本文针对空间矢量脉冲宽度调制(SVPWM)技术使得电压源型逆变器(VSI)输出电压中含有三次谐波的问题,提出一种新的方法,使得输出电压中不再含有三次谐波。首先分析了SVPWM存在三次谐波的原因是每个载波周期中三个输出端电压的平均值不为零。在此基础上,本文提出一种新的开关管开通和关断时间的计算方法,使得每个载波周期三个输出端电压的平均值为零,从而确保输出电压中没有三次谐波。最后通过仿真,验证了本文所提方法的有效性。     

基波电压线性输出的两相SVPWM算法

本文提出了一种基于基波电压幅值线性输出控制的两相SVPWM过调制算法,该算法不需要存储数据.能够使逆变器平滑的从线性调制工作状态过渡到方波工作状态,非常适合数字化应用。文中分析了应用该算法以后,逆变器输出相电压的谐波畸变（THD）情况,以及主要谐波成分百分含量的变化情况,并和传统两相SVPWM控制算法进行了技术指标对比。分析及仿真证明,该算法具有输出基波电压增益线形和实现简单的优点,非常适合电机实际应用。     

混合型级联多电平逆变器的PAM调制和PWM调制

介绍了混合型级联多电平逆变器的PAM和PWM调制方法,在Matlab7．0中构建了基于这两种调制方法的多电平逆变器的仿真模型。仿真结果表明,混合型级联多电平逆变器能够有效减小谐波畸变率,改善输出电压波形。     

谐波补偿正弦波逆变器研究

针对平均值反馈型正弦波逆变器存在的问题，提出利用高频谐波补偿方法改善输出波形的质量，减小输出滤波器设计压力，提高逆变器负载适应能力。实验表明，这个方法对逆变器输出谐波有很好的抑制效果，对非线性负载也完全适用。     

闭环光纤陀螺方波调制失真的影响与消除

数字闭环光纤陀螺仪测量角速度时,采用方波调制引起的各种失真会对输出结果产生影响。基于傅里叶级数建立包含失真噪声的闭环光纤陀螺方波调制、解调信号模型,对各种调制失真引起的输出误差进行了仿真分析,并提出一种双极型归零脉冲方波解调方法,用于消除方波调制闭环光纤陀螺仪的输出信号误差。仿真结果表明:采用常规方波解调时,调制信号的相位失真、方波脉宽失真、谐波失真以及梳状噪声脉冲对光纤陀螺仪输出有很大影响,测量角速度相对误差可达1%量级。采用双极型归零脉冲方波解调时,上述调制失真的影响都得到有效的减小,陀螺仪测量角速度相对误差只有0.1%量级,降低了一个数量级,说明文中提出的双极型归零脉冲方波解调方法对提高闭环陀螺的测量精度和稳定性有重要意义。     

基于FPGA与谐波合成信号发生器的实现

提出一种结合傅里叶级数展开和DDS原理产生任意波形信号发生器的实现方法。利用FPGA设计了15个DDS模块,将一周期正弦波的样值写入DDS模块的ROM表。对目标信号进行傅里叶变换得到信号各次谐波的频率和幅值,取其1~15次谐波的频率作为每个DDS模块的频率控制字,将各个DDS模块输出的样值与输入该模块的频率对应谐波幅值的乘积进行累加,经低通滤波器输出最终所需波形。测试表明,利用该实现方法得到的信号发生器输出波形稳定、频率转换速度快、精度在0.002 79 Hz以内。     

六相全桥逆变器驱动PMSM的简化模型预测电流控制

全桥逆变器电机驱动或称开绕组结构虽然兼具相间电气隔离、容错性能好及器件开关频率低等优点,但存在逆变器输出电压矢量多、冗余严重且控制约束等问题。文中以共直流母线供电的六相全桥逆变器驱动六相永磁同步电机为研究对象,提出了一种基于二级矢量优化的简化模型预测电流控制算法,在实现电机定子基波电流有效跟踪控制的同时有效抑制了定子电流的谐波及零序分量。文中基于矢量空间解耦理论对六相全桥逆变器的输出电压矢量进行了分层分析,以定子基波电流控制、谐波及零序电流抑制为准则对逆变器输出的729个电压矢量进行二级优化,得到候选的12个电压矢量,以此为基础设计了模型预测电流控制算法。实验结果表明,该简化模型预测电流控制方法具有良好的动静态性能,能在基波电流控制的同时有效抑制谐波及零序电流分量,可为多相电机驱动系统研究提供一定的理论支撑。     

Temperature dependent current-voltage characteristics of n-MgxZn1−xO/p-GaN junction diodes

This study investigates the temperature dependence of the current-voltage (I-V) characteristics of n-Mg_xZn_1−xO/p-GaN junction diodes. The n-Mg_xZn_1−xO films were deposited on p-GaN using a radio-frequency (rf) magnetron sputtering system followed by annealing at 500, 600, 700, and 800 °C in nitrogen ambient for 60 s, respectively. The n-Mg_xZn_1−xO/p-GaN diode at a substrate temperature of 25 °C had the lowest leakage current in reverse bias. However, the leakage current of the diodes increased with an increase in annealing temperatures. The temperature sensitivity coefficients of the I-V characterizations were obtained at different substrate temperatures (25, 50, 75 100, and 125 °C) providing extracted values of 26.4, 27.2, 17.9, and 0.0 mV/°C in forward bias and 168.8, 143.4, 84.6, and 6.4 mV/°C in reverse bias, respectively. The n-Mg_xZn_1−xO/p-GaN junction diode fabricated with Mg_xZn_1−xO annealed at 800 °C demonstrated the lowest temperature dependence. Based on these findings, the n-Mg_xZn_1−xO/p-GaN junction diode is feasible for GaN-based heterojunction bipolar transistors (HBTs).     

Effects of high doping on the bandgap bowing for AlxGa1−xN

This paper gives the composition dependence of the bandgap energy for highly doped n-type Al_xGa_1−xN. We report results of the bowing parameter obtained using a random simulation. Three groups of Al_xGa_1−xN semiconductors were considered and which are distinguishable by their non degenerate or degenerate character in the doping density (10¹⁷?N_D?10²⁰ cm⁻³). A striking feature is the large discrepancy of the bandgap bowing (−2.02?b?2.94 eV), as was demonstrated from our calculations. This suggests that high doping may be a possible cause able to induce the large range of bowing parameters reported for Al_xGa_1−xN alloys.     

Interfacial reactions and electrical properties of Hf/p-Si0.85Ge0.15

Interfacial reactions and electrical properties of Hf/p-Si_0.85Ge_0.15 as a function of the annealing temperature were studied. Hf₃(Si_1−xGe)₂ and Hf(Si_1−xGe)₂ were initially formed at 500°C and 600°C, respectively. At temperatures above 400°C, Ge segregation out of the reacted layers associated with strain relaxation of the unreacted Si_0.85Ge_0.15 films appeared. At 780°C, agglomeration occurred in the Hf(Si_1−xGe_x)₂ films. All the as-deposited and annealed Hf/p-Si_0.85Ge_0.15 samples showed the formation of an ohmic contact. The lowest specific contact resistance around 10⁻⁵ ω cm² could be obtained for the Hf₃ (Si_1−xGe_x)₂ contacts to p-Si_0.85Ge_0.15 formed at 500°C. Below 500°C, the decrease of specific contact resistance with the annealing temperature is mainly caused by the formation of Hf₃(Si_1−xGe_x)₂ and an interfacial Ge-rich layer between the Hf₃(Si_1−xGe_x)₂ and unreacted Si_0.85Ge_0.15 films, while above 600°C, the increase of specific contact resistance may be due to the formation of Hf(Si_1−xGe_x)₂ and SiC as well as the roughness of the Hf(Si_1−xGe_x)₂ films.     

Formation of Ni(Ge1−xSnx) layers with solid-phase reaction in Ni/Ge1−xSnx/Ge systems

We have demonstrated the formation of Ni(Ge_1−ySn_y) layers on Ge_1−xSn_x layers by using solid-phase reaction for samples with Sn contents ranging from 2.0% to 6.5%. We have also investigated solid-phase reaction products in Ni/Ge_1−xSn_x/Ge samples after annealing and the crystalline properties of nickel-tin-germanide layer/Ge_1−xSn_x contact structures. After annealing at temperatures ranging from 350 to 550 °C, the formation of polycrystalline Ni(Ge_1−ySn_y) layers has been observed on epitaxial Ge_1−xSn_x layers with Sn contents ranging from 2.0% to 6.5%. We also observed anisotropic crystal deformation of NiGe with the incorporation of Sn atoms into substitutional sites in NiGe. In the case of the Ni/Ge_1−xSn_x/Ge sample with a Sn content of 3.6%, the formation of an epitaxial Ni₂(Ge_1−zSn_z) layer on the Ge_1−xSn_x layer was found. The formation of β-Sn crystallites was observed after annealing at above 450 °C in samples with a high Sn content of 6.5%. This β-Sn formation is due to the precipitation of Sn atoms. In all samples annealed at 350 °C, the morphology of Ni-Ge-Sn layers is smooth and uniform. However, the surface roughness and interface roughness increase for an annealing temperature of 550 °C. In particular, in the sample with a Sn content of 6.5%, the temperature at which agglomeration noticeably occurs is as low as 450 °C.     

An Initial Investigation of Nitrogen Doping of Wide-Bandgap HgCdTe During Molecular-Beam Epitaxy Using Ar/N Plasmas

An initial investigation of the use of atomic nitrogen for controlled p-type doping of wide-bandgap Hg_0.3Cd_0.7Te (x = 0.7) is reported. Mixtures of argon and nitrogen, ranging in nitrogen concentration from 0.1% to 100%, have been utilized to demonstrate well-controlled nitrogen incorporation in the 10¹⁶ cm⁻³ to 10²⁰ cm⁻³ range using total gas flow rates of 0.3 sccm to 4.0 sccm and radiofrequency (RF) powers of 100 W to 400 W. Nitrogen doping exhibits several desirable attributes including abrupt turn-on and turn-off and minimal sensitivity to variations in growth temperature and HgCdTe composition, with no negative effects on HgCdTe dislocation density and morphology. Preliminary electrical measurements indicate primarily n-type behavior in the 10¹⁴ cm⁻³ to 10¹⁵ cm⁻³ range in as-grown x = 0.7 HgCdTe and CdTe films doped with nitrogen at 10¹⁸ cm⁻³ to 10²⁰ cm⁻³ concentrations, while ZnTe films have exhibited p-type electrical activity with hole concentrations approaching 10²⁰ cm⁻³.