【作者】 陈权；

【导师】 王群京；

【作者基本信息】 合肥工业大学 ， 电力电子与电力传动， 2007， 博士

【摘要】 多电平变换器由于在输出功率、谐波、功率因数、负载共模电压等方面具有显著优势，从而得到了广泛关注。然而经过二十多年的研究，多电平变换器在理论与实践中仍有许多方面研究得不太成熟，以致限制了它向更广领域应用。本文着重对目前尚未解决或解决得不够完善的一些问题进行研究，并提出相应解决方案，主要内容包括以下几个方面：1．对多电平变换器在调制方式、谐波抑制、能量损耗和系统控制策略等方面作了回顾，主要从拓扑结构方面介绍了多电平变换器的基本理论，并着重介绍了三电平变换器原理。2．在分析多电平变换器最优开关序列及常用调制策略原理的基础上，提出应充分挖掘多电平变换器的特点，对其调制应多考虑与其他系统性能要求相结合。在此指导思想下，提出一种针对不同负载降低系统损耗的PWM调制方法。3．针对传统方法求解消谐方程组的不足，深入分析消谐方程组的特点，提出应用多元多项式理论求解中点箝位式变换器消谐方程组。以中点箝位式三电平变换器中求解4个开关角为例，说明了如何应用对称多项式降幂和结式理论消元。这种方法不仅克服了迭代法求解需给定初值的弊端，而且可求得全局解。对所求得的开关角作了实验验证。4．提供研究多电平变换器通态损耗的方案。根据电流、电压关系确定器件导通规律，以此为基础计算器件导通占空比和推导用于计算通态损耗的表达式。作为该方案的应用，对正弦调制和三次谐波注入法调制下的中点箝位式三电平变换器通态损耗进行了分析与比较。5．对多电平变换器开关损耗研究。根据电压、电流波形理论上是电压、电流前期与后期函数的事实，通过表征开关电量波形的几个特性参数，由波形产生的内在机理，精确拟合逼近实际波形。根据波形表达式，结合多电平变换器的工作原理，建立多电平变换器开关损耗模型。作为方法的应用，研究了三电平中点箝位式变换器开关损耗，研究的器件为主流功率器件IGBT和快恢复二极管。对三电平变换器开关损耗计算方法和结果进行了实验验证。6．理论研究三电平变换器在直接转矩控制系统中的应用。研究直接转矩控制的退磁现象及解决方法；研究电压矢量对转矩脉动的影响，并根据多电平变换器的特点，给出开关状态选择方案，并作了仿真比较。7．完成了基于SVPWM的一台箝位式三电平变频器的设计。以TMS320LF2407A DSP为控制核心，进行了速度开环、恒压频比控制的交流电机调速实验。实验结果验证了软件、硬件设计的有效性和正确性。更多还原

【Abstract】 Multilevel inverters have drawn tremendous interest recently due to their advantages regarding power export, harmonics, power factor, and common-mode voltage. However, the present research on its theories and applications have not matured enough and suffer from restrict of application in wider area. This dissertation will stress on those unsolved or imperfect solved problems. The main contents of this paper are as follows:1. This dissertation presents a review of multilevel inverter modulation methods, harmonic suppression, losses, and control strategy. The basic multilevel theory is introduced from the point of topology structure, and the three-level one is stated explicitly.2. By analysis of the principle of the optimal space vector sequence and the relevant modulation methods, the viewpoint of the novel modulation method produced for multilevel inverter should consider more system performances is proposed. Under this guidance of this idea, a PWM strategy for the three-level inverter with an ability to reduce losses according to different load is established.3. The nonlinear, harmonic elimination equations solved by traditional iterative algorithm exists some weaknesses. After analyzing the equations deeply, this dissertation presents an approach to eliminate harmonics in neutral-point-clamped inverter using the theory of multivariable polynomial. Taking computing 4 switching angles for instance, the results show that the elementary symmetric polynomials can be exploited to reduce the degree of the polynomials and the resultant theory can be utilized to eliminate variables. The research indicates the method has many merits, such as hurdling the difficulty of determining the initial values when solving the selective harmonic elimination nonlinear equations, obtaining all solutions accurately. Experimental and simulation results of two groups of solutions are presented to confirm the validity of the technique.4. The scheme of study on multilevel inverter conduction losses is provided. Conduction loss expressions are derived based on the knowledge of conduction devices, which are determined by the working condition, and the conduction duty cycle. The loss model is used to analysis and comparison on two different modulation strategies, sinusoidal PWM (SPWM) and third harmonic injection PWM (THIPWM), for neutral-point-clamped three-level inverter.5. The multilevel inverter switching losses is studied. The algebraic equations that represent the voltage and current waveforms during the switching event are developed based on the fact that the current and voltage waveforms during switching are principally a function of the pre- and post-switching voltage and current, the character parameters, and the physics of the switching process. The switching losses model of neutral-point-clamped three-level inverter with widely used IGBT and fast recovery diode is developed. The simulation and experimental results demonstrated the validities of turn-on and -off models and switching losses models of the semiconductor devices.6. Direct torque control (DTC) for induction motor-fed by three-level inverter is studied theoretically. Especially, the demagnetization phenomenon of stator flux and the torque pulsations caused by space vector voltage are analyzed. This paper also lays out an improved switching lookup table and compares with simulation results.7. The design of a three-phase three-level NPC inverter based on SVPWM is accomplished in this paper. A speed-loop-open, constant ratio of voltage and frequency controlled AC motor drive is fulfilled, which employs TMS320LF2407A DSP as control core. The experimental results testify the correctness and validity of the designed software and hardware.更多还原