【作者】 赵菁；

【导师】 何湘宁；

【作者基本信息】 浙江大学 ， 电力电子与电力传动， 2012， 博士

【摘要】 混合箝位多电平逆变器除了具有输出THD值小、器件电压应力低和EMI低等优点,还实现了器件可靠箝位,直流母线电压自平衡等功能。它采用两种及以上的箝位器件混合在一起共同实现箝位功能,拓扑结构和控制更复杂,因而拓扑分析难度增加,系统可靠性下降,三电平以上的拓扑更是如此。论文的工作,就是基于以上几点,对混合箝位多电平逆变器分析和测试方法、载波PWM控制技术及器件的故障诊断等方面进行了研究。首先,论文提出了拓扑分解和开关模态组合的思想,为复杂多电平逆变器新拓扑的分析和构造提供了一条新的思路。论文运用拓扑分解的思想,构造了一个将开关电容电路和悬浮电容四电平逆变器相结合的新拓扑。该拓扑无需设计复杂的冗余开关模态组合来解决电容电压的平衡问题,不受负载性质的限制,可应用于有功和无功变换的场合。初步的仿真研究表明了该拓扑的有效性和合理性。论文还结合多电平逆变器基本单元的概念,提出了将开关电容电路与逆变器基本单元组合构造新拓扑的方法,并初步讨论了其合理性。论文又对电容电压自平衡混合箝位多电平逆变器开关电容电路部分进行改造,得到一种改进拓扑——基于开关电容变换器和二极管箝位变换器的多电平电路(MCT-BSD),并通过仿真和实验验证了该拓扑的有效性和合理性。MCT-BSD拓扑保留了电容电压自动平衡的优点,又减少了开关器件及母线电容的数量,还实现了升压的功能。其次,论文提出了多电平逆变器开关模态切换分析的方法,并运用该方法完成了电容电压自平衡混合箝位多电平逆变器开关模态的分析和拓扑建模。论文还提出“准在线测试”的概念,在电容电压自平衡混合箝位多电平逆变器实验样机的基础上设计和搭建了准在线测试平台,对开关模态切换分析的结果进行了实验验证。然后,论文提出了载波单元和载波子单元的概念,以此为基础构造出几种新的载波波形排列,从而得到几种新的PWM控制方法,从不同方面改善了逆变器的性能。基于“载波单元”的概念,将电容电压自平衡混合箝位多电平逆变器中各个开关管的载波波形用“载波单元”重新排列组合,得到一种高低载波带交替反向PWM(HLCCAPO PWM)控制方法,并通过仿真和实验验证了其有效性和通用性。该方法除了能减少开关次数,还能使谐波能量从低频带向高频带转移,这一特性可简化输出滤波器的设计。针对因死区的存在而导致输出相电压波形中出现意外电平的现象,论文提出了通过改造载波波形来有效消除输出波形中意外电平的PWM控制方法,并进行了仿真和实验,结果表明了该方法在不同调制度下的有效性。最后,论文提出了基于开关模态分析和测试的多电平逆变器故障诊断方法。该方法从逆变器输出的故障波形中提取故障特征,结合开关模态分析和测试方法,通过相关模态下特定电压或电流量的测量,完成器件故障的诊断和定位。论文以电容电压自平衡混合箝位五电平逆变器为对象,对各种器件故障情况下的故障特征进行了分析和归纳,总结出一套故障诊断规则,具有一定的实用性。更多还原

【Abstract】 Hybrid clamped multilevel inverters have the advantages of low THD, low voltage stress on power switches and low system EMI, and they can also implement the functions of reliable clamping on power devices and self-voltage balancing on DC link capacitors. Two or more kinds of clamping components are used together in hybrid clamped multilevel inverters, thus leading to more complicated topology structure and control method, so topology analyses become more difficult and system reliability are decreased, especially for n (n>3) level inverters. The analysis and testing method, the carriers PWM control techniques and the devices fault diagnosis methods for hybrid clamped multilevel inverters are studied in this dissertation.Firstly, the ideas of topology decomposition and switching modes combination are proposed in this dissertation, which offer a new way of constructing new multilevel inverters topologies. Based on the idea of topology decomposition, a new topology combining a switched-capacitor circuit with a flying-capacitor four-level inverter is constructed. It can balance the capacitor voltages inherently without designing the redundant switching states, and can be applied to real power or reactive power conversions regardless of load characteristics. Preliminary simulation result shows the validity and rationality of this new topology. Integrating the basic constructing units of multilevel inverters with switched-capacitor circuits, a new method of constructing new multilevel inverter topology is proposed, and its rationality is also discussed. By altering the structure of switched-capacitor circuit of the hybrid clamped multilevel inverter with self-voltage balancing, an improved topology named MCT-BSD (Multilevel Circuit Topologies Based on the Switched-capacitor Converter and Diode-clamped Converter) is attained, and its generality and feasibility under three-phase operation are discussed. Simulated and experimental results show its validity and rationality. The MCT-BSD topology remains the advantage of self-voltage balancing, and the number of power switches and DC link capacitors are decreased. Moreover, stepping up output voltage can be realized in MCT-BSD, which can reduced the step-up ratio of the input transformer, thus reducing the cost of transformer.Then, the analysis methods of switching modes transitions for multilevel inverters are proposed in this dissertation. The analyzing and modeling of hybrid clamped multilevel inverters with self-voltage balancing are completed based on analysis methods of switching modes transitions. On the other hand, the concept of quasi on-line testing is proposed in this dissertation. Based on the experimental prototype of hybrid clamped multilevel inverters with self-voltage balancing, a quasi on-line testing platform is built in order to verify the analysis on the switching modes transitions.Furthermore, the concepts of carrier cells and carrier sub cells are proposed in this dissertation. By constructing some kinds of new carrier wave arrangements with carrier cells and sub cells, some new kinds of carrier PWM methods are put forward so as to improve the performance of multilevel inverters from the different aspects. The carrier waveforms of each switching device in hybrid clamped multilevel inverters with self-voltage balancing were rearranged with carrier cells, and then a new carrier PWM control method--HLCCAPO PWM (Higher and Lower Carrier Cells Alternative Phase Opposition PWM) is attained. Simulated and experimental results show that comparing with the carrier PD PWM method, HLCCAPO PWM method can effectively reduce the number of devices switching on or off within broad modulation index range, consequently reducing switching losses. Also, the energy of lower harmonics transfers to higher harmonics band with the HLCCAPO PWM method. The reduction of the energy of lower harmonics can simplify the design of output filter and reduce its size. Setting the reasonable dead time between the complementary switching devices of hybrid clamped multilevel inverters is necessary in order to ensure the reliable operation of multilevel inverters. However, the existing of dead time brings about the unexpected level on the output voltage waveform. Based on the carrier cells, a method of effectively eliminating the unexpected output levels by improving the carrier waveform is proposed in this dissertation. Simulations and experiments show the unexpected output levels, which are caused by the dead time, can be effectively eliminated by applying the improved PWM method to the hybrid clamped multilevel inverter within broad modulation index range.Last, the devices fault diagnosis method for hybrid clamped multilevel inverters based on the analysis and testing on switching modes transitions is proposed in this dissertation. The fault features are extracted from the output voltage waveform of inverters, and then devices diagnosis can be preliminarily classified and sifted according to the fault features. Devices fault diagnosis and fault location are finally completed by measuring the specific voltages or currents under the certain switching modes. Taking a hybrid clamped five-level inverter with self-voltage balancing as instance, devices fault features under all kinds of fault conditions are analyzed and generalized in detail, and the rules of devices fault diagnosis are given, which has practicality.更多还原