Research Of DSP Based Direct Torque Control On Induction Motor Fed By Three Level Inverter

Direct torque control (DTC) is a new type frequency control technology and has many issues that need our study. This paper focuses on the three-level inverter direct torque control and has received good purposes, which has effective reference function in multilevel inverter direct torque control (DTC) system.Firstly, the paper analyses the work principle, work progress and switch model of diode-clamped three-level inverter, then it builds mathematics models between three-level inverter and asynchronous motor. On the basis of these investigation, the basic principle and configuration of the direct torque control of asynchronous motor which is supplied by three-level inverter. It gives the control way used by magnetism chain and torque, analyses the reasons of neutral-point potential fluctuation and then analyses the problems lies in direct torque control supplied by three-level inverter, which includes the voltage swing, switch frequency, switch frequency and the balance of neutral-point voltage. In order to settle the problems in direct torque control supplied by three-level inverter, we analyses several improveed arithmetic and gives a new three-level inverter direct torque control way based on fixation complex vector. The simulation research was done and it showed that the new way has good effects in balancing neutral-point potential fluctuation and reducing voltage swing.The paper also introduces the desien of three-level inverter, which includes the main circuit, switch device driving circuit, current and voltage detecting circuit and protect circuit. Considering that the main circuit of three-level inverter have many switches and the driving signal can't be connected to the same ground, the paper introduces a drving circuit based on the optocoupler isolation driving device (HCPL316J) for power device IGBT to reduce the electromagnetic interference and protect the power device real-time when abnormity phenomenon such as excessive currents appears. Lastly, this paper implements a three-level inverter tester which uses TMS320F2812 as control center. Correlative experimental researches are implemented by this prototype, and the tester can work reliably in the whole experimental process. The simulation and experimental results show that the research method and the control strategies are right and effective.