Fundamental Research on Multilevel Current-Source and Voltage-Source Inverters by using PWM Control Method and Multiple Connection

在本研究中，我们工作的目的之一是提出一种考虑直流电容电压平衡问题的三相五电平二极管箝位脉宽调制（PWM）变换器的控制方法。该控制电路采用多频带迟滞比较器（MHC’s）来简化主电路的控制。通过改变MHC的形状，解决了直流电容电压平衡问题。该方法可以克服直流电容处的电压不平衡；2)实现了统一的功率因数；3)产生近似正弦的输入电流；4)将电能再生回电力系统。本研究的下一个结果是提出一种五电平双变换器系统的控制策略，该系统通过将整流器连接到五电平逆变器来构建，用于大型交流电机驱动。除了以往的优点外，该方法还可以实现调速驱动。本研究包括以下内容：1)五电平二极管箝位逆变器分析；主电路结构，电路分析，器件损耗特性，五电平双变换器系统控制策略电流控制策略，五电平电压控制方法，3)仿真结果4)实验结果；实验设置，实验结果。仿真和实验结果验证了该控制策略的有效性。然而，在实验结果中观察到较大的电压波动。需要进一步研究开发一种控制方法，以减少直流链路电容器的电压纹波以及输入和输出波形的谐波畸变。

In this research, one of the purpose of our works is to presents a control method for a three-phase five-level diode-clamp pulse width modulation (PWM) converter considering dc-link capacitor voltage balancing problem. The proposed control circuit uses multiband hysteresis comparators (MHC's) to simplify the control of the main circuit. The dc-link capacitor voltage balancing problem is solved by changing the shape of the MHC.The proposed method can 1) overcome voltage imbalance at the dc-link capacitors ; 2) achieve a unity power factor ; 3) generate nearly sinusoidal input currents ; 4) regenerate electric power back to the power system.The next result of this research is to present a control strategy for a five-level double converter system constructed by connecting the rectifier to a five-level inverter for large ac motor drives. In addition to previous advanteges, the method can achieve adustable-speed drive. This research includes the following contents 1) Analysis of Five-Level Diode Clamped Inverter ; Main circuit Configuration, Circuit Analysis, Device Loss Characteristics, 2) Proposed Control Strategy for Five-Level Double Converter System ; Current Control Strategy, Control Method of the Five-Level Voltages, 3) Simulation Results ; 4) Experimental Results ; Experimental Setup, Experimental Results. Simulation and experimental results verified the validity of the control strategy. However, large voltage ripples were observed in the experimental results. Further study is needed to develop a control method that can reduce voltage ripples at the dc link capacitors as well as the harmonic distortions of the input and output waveforms.