本文以三电平二极管中点钳位型（NPC）逆变器馈电的异步电动机直接转矩控制系统为课题展开研究。文章开始部分描述了多电平逆变器的拓扑结构和异步电动机调速控制的几种方法。文章的前半部分是系统研究的理论部分，先以二极管中点钳位型三电平逆变器为核心，讲述了多电平逆变器的几种模型，并对各个模型加以说明，同时详细介绍了三电平NPC型逆变器的工作原理，推导出了其数学模型并对其所存在的相关问题作以分析。然后对三电平NPC型逆变器馈电的异步电动机直接转矩控制（DTC）系统的原理进行分析，从矢量坐标变换、DTC原理、滞环比较控制、电压空间矢量选择等诸多方面详细分析了研究课题的理论部分，为后期研究做好基础。 本文的后半部分在文章前半部分理论研究的基础上，对课题进行了更加深入的研究。首先借助于计算机仿真软件MATLAB/Simulink工具包，对三电平逆变器馈电的异步电动机直接转矩控制算法、静止坐标系的3/2变换、磁链观测模型、矢量合成方法等原理进行仿真验证。仿真结果验证了系统设计思路的可行性，然后在现有实验条件的基础上对相关电路进行硬件电路设计和调试。在电路调试时，以TI公司高性能DSP控制器TMS320F2812为主控制器，结合软件调试CCS环境，设计相关程序，实现系统调试。 最后，利用实验室现有条件，选择一台1.1kW的异步电动机作为实验对象，进行直接转矩控制实验，在文章的最后给出了相关实验结果。

This paper disscusses and researches the diode Neutral Point Clamped (NPC) three-level inverter-fed induction motor direct torque control system. At the beginning of this article describes a multi-level inverter topology and asynchronous motor speed control method. The first part of the article is the theoretical research, describes several models of multi-level inverter, and explained each model. At the same time it introduces the NPC three-level inverter working principle, deduced the mathematical model of the inverter and related issues. Then analysis the principle of NPC three-level inverter-fed induction motor direct torque control (DTC) system. From the vector coordinate transformation, DTC principle, hysteresis comparative control, voltage space vector selection, and many other aspects of a detailed analysis of the theoretical part of the research project, prepare the ground for the later study. The latter part of this article based on the theory studied in greater depth. First, utilize computer simulation software MATLAB / Simulink tool kit, include direct torque control algorithm, 3/2 coordinate transformation, flux observer, vector synthesis method principle simulation. Simulation results verify the feasibility of the system design ideas, and then basis on the existing experimental conditions debugging and design the relevant circuit hardware. Using the TI company DSP controller TMS320F2812 as the based controller, combined with CCS software debugging environment, design-related procedures, realize system debugging. Finally, by using the existing laboratory conditions, select a 1.1kW induction motor as subjects for direct torque control experiment. In the last article we give the results of experiments.