近年来，多电平逆变器在高压大容量电能变换中得到广泛应用，而其控制策略和电路拓扑等已成为了研究热点。相对传统的两电平逆变器，它具有效率高动态性能好，对电动机产生的谐波少，适合高压大容量等优点。但随着电平数的增加，基本控制算法越来越复杂，同时还存在中点电压不平衡等问题。将DSP数字控制技术应用于多电平逆变器不仅简化了系统的硬件控制电路，提高了系统性能，还可以实现系统的优化控制。 本文以二极管箝位式三电平逆变器为研究对象，首先介绍了三电平逆变器的拓扑结构和工作原理，对三电平逆变器的电路方程进行了深入的分析，在开关函数的基础上建立了三电平逆变器的数学模型。在此基础上，对空间电压矢量脉宽调制（SVPWM）算法进行了改进，并详细推导了该调制算法的计算公式，结合中点电位控制来确定开关矢量的作用顺序，使仿真和实现都比较容易。然后重点分析了三电平逆变器直流侧电容电压不平衡问题产生的原因，提出了一种能控制逆变器直流侧电容中点电位平衡的电压空间矢量脉宽调制方法。最后采用MATLAB仿真软件对所推导的三电平逆变器SVPWM调制算法和中点电位平衡控制方法进行了仿真分析，证明了该调制算法的正确性和可行性。

Recently, multi-level inverter has been widely applied in power electronics, and its control strategies and topologies of power circuits are become the research focuses. Comparing with the two-level inverter, it has many advantages, such as high efficiency and good dynamic performance, making less harmonic waves and suiting for high voltage large capacity applications. However, its basic control strategies are much more complicated than that of a two-level inverter, and the unbalance problem of the neutral-point may appear with the increase of the level order. If DSP digital control technique is applied to multi-level inverter, its control strategy can be optimized and system performance is advanced, while the control circuits are simplified. The topology of diode-clamped three-level inverter is studied in this paper. Firstly, the topology and principle of three-level inverter are introduced, its circuit equations are deeply analyzed, and the mathematical model of three-level inverter are established based on the switch function. On this basis, mathematical formula for the improved SVPWM is deduced in detail. To make simulation and realization much easier, the operating order of switching vector is determined by controlling the midpoint voltage. Then, the reason for unbalance of the capacitor voltage in three-level inverter is analyzed. A SVPWM method is also proposed, which can balance the midpoint voltage of the DC capacitor. Finally, simulation is carried out on the SVPWM method and control strategy of neutral point balance for three-level inverters with MATLAB. Simulation results prove the feasibility of the proposed method.