The Asynchronous Motor Direct Torque System Based On Svpwm

With the beginning of asynchronous motor occupying position in inductionmotor drive field, studies on high-performance of AC motors attractedattentions of many researchers. Especially in the1980s, direct torque controlfurther improve the performance of AC motors, for its simple and efficientcontrol. Because of torque and flux hysteresis width, the conventional DTChas torque ripples even in steady state. Superior motor performance isachieved by narrower hysteresis bands which in turn are achieved by highswitching frequency. The high-power occasions require good torque controlperformance at low switching losses, the traditional DTC is hard to meet themboth at the same time.First, Basic principles of conventional DTC based on AC motor areintroduced, then the space voltage modulation is presented for DTC strategy,and finally The traditional DTC strategy and the SVM-DTC strategy areestablished. This paper mainly describes AC motor on the basis of a spacevoltage modulation scheme. This method uses only one output of PI controllerand is based on control of separation between amplitude and angle of referencestator flux for determining reference stator voltage vector in generating PWMoutput voltage for AC motors. In addition, the proposed technique is based onthe relationship between instantaneous slip angular frequency and rotor angularfrequency in adjustment of the reference stator flux angle. As torque responsedepends on instantaneous slip angular frequency, the torque can be directlycontrolled. Comparative analysis verify the scheme is effective.However, there is two PI regulators adding to AC motor system based onSVM-DTC, which increase the complexity for debugging. To solve the problem,sliding mode variable structure control has been applied to speed regulator instead of the speed PI regulator. Such scheme can not only bring convenience toadjust PI parameters, but make full use of the fast, robust advantages of thesliding mode control. Simulation results show that speed is robust to load and fast dynamic responses are achieved.