Three-level Inverter Induction Motor Direct Torque Control Study

In recent years, with multi-level technology, high-performance high-power medium voltage speed control system become one of the current research keystone. Diode-clamped three-level inverter has been widely used in the medium voltage variable frequency speed regulation system due to it's mature topology. The main contents of this paper is three-level induction motor direct torque control based on the single-vector, and the development of general-purpose inverter.Paper introduces the topology and the basic principles of three-level inverter. As a result of a three-level inverter the mid-point is floating, three-level inverter circuit and the load which is induction motor should be study as a whole, with a fifth-order differential equations to describe its behavior. In this paper, the mathematical model of three-level inverter speed regulation system was built.In this paper, three-level realization of direct torque control principle was introduced, and discussed the problem of how to choice the vector and balance the mid-point, which should solve in three-level inverter circuit of direct torque vector control. Then a choice scheme based single vector was given. The scheme has high use rate of voltage, and avoid the amplitude's hopping of the outrageous output voltage, and it can solve the issue of the mid-point voltage deviation.This paper developed a high-power three-level general-purpose inverter which capacity is 690V/600kW. The design of control software has modular structure. This paper introduces the basic idea of software programming, and describes the principle of the main function modules. Paper introduced the acting time's calculation of space vector modulation and the switching order. High-performance V/f control scheme was realized through the stator voltage compensation, slip compensation and maximum current restriction. Main circuit of system using diode-clamped three-level topology. Paper introduced the master chip, the control circuit and driver circuit, and gave the main circuit parameters.Finally, the test results of three-level high-power general-purpose inverter was given. The result indicates that the inverter can achieve a good waveform and performance.