【作者】 袁庆庆；

【导师】 伍小杰；

【作者基本信息】 中国矿业大学 ， 电力电子与电力传动， 2014， 博士

【摘要】 中压大功率变频器的环保节能主要体现为对负载及电网的谐波污染小，能量变换效率高。当功率器件工作电压升高、功率增大，其开关损耗大幅增加，且成为变频装置主要损耗来源。为降低开关损耗，需降低功率器件开关频率(≤500Hz)，但会对变频器控制系统、调制算法等造成影响。本文以二极管钳位型双三电平大功率PWM变频器为例，对其展开在低开关频率下的系统建模、调制算法及控制系统设计等方面的研究。对低开关频率下的三电平PWM电压源型整流器进行复矢量建模，理论分析低开关频率影响整流器性能的本质原因；设计复矢量电流调节器，基于现代控制理论工具验证其稳定性及有效性。首次对三电平PWM环节输出谐波进行二重傅里叶解析分析，为改善低开关频率下PWM环节的输出性能提供理论基础；在此基础上研究将不对称规则采样与空间矢量脉宽调制相结合的不对称空间矢量脉宽调制算法(asymmetric space vector modulation,ASVM)及其改进方案。为使低开关频率下的并网电流满足入网标准，研究一种模型预测控制(modelpredictive control, MPC)与滑动傅里叶(sliding discrete fourier transform, sDFT)相结合的三电平PWM脉冲模式。首先，采用sDFT提取网侧电流的基波和各谐波幅值，并将其作为MPC目标函数的一部分，同时考虑尽量降低开关频率和减少中点电位偏差；然后通过滚动时域优化实现谐波降低、器件开关频率较低和中点电位平衡。该脉冲模式控制方式具有类似特定谐波消除(selective harmonicelimination, SHE)特性，但能实现在线动态调节。为进一步简化算法，基于参考坐标系将三电平矢量调制降阶至两电平，更易于数字实现。考虑三电平逆变器带电励磁同步电机负载，首先为简化凸极电励磁同步电机模型、考虑转子不对称性，提出基于复矢量与矩阵相结合的复矩阵建模方法。针对低开关频率造成的电机定子侧电流谐波成分大，常规滤波器在提取基波分量易造成相位滞后、幅值衰减等问题，从经典控制理论入手、结合电机复矩阵模型，提出电机电流内环的基波观测器及复矢量调节的控制策略，实现低开关频率下定子电流磁化分量与转矩分量的有效控制。本文针对低开关频率下的分段调制方法，首次根据PWM谐波输出的二重傅里叶解析结果推导其分段调制分界点。针对常规同步对称优化PWM算法只能离线计算、动态性能不佳的缺陷，将滚动时域优化与SHEPWM相结合的模型预测控制优化PWM脉冲模式移植至电励磁同步电机。在研究SHEPWM稳态开关角规律基础上，以定子磁链为跟踪目标，将磁链跟踪误差转化为滚动时域内的伏-秒值以实现对开关角的动态调整，解决优化PWM算法在动态调用时可能会引起的开关角错乱、装置过流以致无法正常运行等问题。为进一步提高双三电平PWM变频器系统运行性能，针对低调制度区采用的SVPWM调制算法，研究一种基于桥臂优化选取的中点电位控制方法，只需判断中点电位差、无需引入输出侧电流，从而避免低开关频率下电流畸变严重对中点电流极性判断的影响。针对非理想电网环境，研究一种能同时适用于单相和三相并网系统的基于SHE鉴相的新型锁相环(SHE-phase locked loop, SHE-PLL)技术；与常规PLL相比，该SHE-PLL具有良好跟踪性能的同时较易数字化实现。文末简单给出电网不平衡下三电平整流器在低开关频率下的控制策略。最后，搭建相应实验平台，完成本文研究内容的相关实验验证。更多还原

【Abstract】 Medium voltage high-power converters have advantages in environmentalprotection and energy savings considering their small harmonic pollution for the loadand the grid, and the high efficiency in energy conversion. The switching frequency ofthe power semiconductors is usually limited to below500Hz to reduce the switchlosses and to improve the output power of the converters. However, a low switchingfrequency affects the control system and the modulation algorithm. Some detailedresearch mainly focusing on system modeling, modulation algorithm and controlstrategy, have been carried out in this dissertation by taking the diode clamped doubleback to back three-level high-power PWM converter as an example.Firstly, a complex model is established for the three-level PWM voltage sourcerectifier (VSR) considering the influence from low switching frequency. And then, anovel current controller with complex state variables is proposed to solve thecross-coupling between the idand iq, whose stability and effectiveness are bothverified by the modern control theory. Also, a new modulation strategy combined withasymmetric regular sampling and the space vector PWM (SVPWM) is studied as wellas its improvement, which ia called asymmetric space vector modulation (ASVM),after the first using of a novel double fourier analytic approach to deeply analyze theharmonic output performance of the three-level PWM topology.In order to make the output current of high-power grid-connecting convertersmeet the grid standards with a low switching frequency, a novel pulse pattern basedon the combination of model predictive control (MPC) and sliding discrete fouriertransform (sDFT) has been presented. Firstly, extract the current fundamentalamplitude as well as the harmonic components’, and which will be taken as a part ofthe cost function for MPC besides the consideration of switching frequency andneutral point potential balancing issues. This kind of pulse pattern not only has acharacteristic similar with the selective harmonic elimination (SHE), also can realize adynamic regulation. For the further algorithm simplification, a reduced-ordermodulation from three-level to two-level is adopted here by the reference coordinatestheory to realize a simple digital implementation.Taking an electrically excited synchronous machine (EESM) as a load ofthree-level converter, a novel complex matrix model based on the combination of thematrix and complex vector methods is proposed considering the rotor asymmetry of an EESM. Owing to the low switching frequency, the harmonic current componentsof the stator are increased and extracting the fundamental content by low-pass filtersproduces a signal delay and amplitude reducing, which can not meet systemrequirements of high dynamic control. To overcome these problems, a novel hybridfundamental current observer at different coordinates for EESMs is designed based onthe observer theory and the complex matrix model. The stability of the fundamentalobserver at different speed or with a parameters mismatch has been analyzed using theclassic control method. Then, a complex current controller is applied to realize thedecoupling between imand it.For the subsection modulation with a low switching frequency, the demarcationpoint is firstly given based on the analytical results from double Fourier approach. Forthe disadvantages that the conventional synchronous symmetry optimal PWMalgorithm only being calculated off-line, a novel dynamic performance schemecombining the receding horizon policy and SHEPWM is firstly rolled in the controlstrategy for EESMs. By taking stator flux as the tracking trajectory, the flux trackingerror can be converted to volt-second value in the receding horizon, and the switchangles calculated from SHEPWM can be modified dynamically to meet the suddenchanged conditions.In order to make a further performance improvement for the back to backthree-level PWM converters, an approach controlling the neutral point potential isresearched based on the optimal selection of the sub-bridges for low modulation index.This method doesn’t need the output current as a feedback signal, which avoids theeffect from the severe distortion of the output current at low switching frequency. Fornon-ideal grid environment, a new kind of phase locked loop (PLL) both suitable forthe single and three phases is studied. With the characteristics of SHE, the SHE theorycombined with square wave has been adopted to form the novel phase detector, andwhose feasibility is proved by the fourier analysis. Lastly, a control strategy to be usedunder non-deal grid environment is also given.Finally, an experimental platform has been set up to complete the verification ofthe cooresponding research contents in this dissertation.更多还原