This paper deals with the three-phase current reconstruction method under the low modulation index operation of three-phase three-level PWM inverters by using the single-shunt current signal measurement. The shunt is placed in a DC-link. The proposed reconstruction method is based on the combination of collinear vector injection and shifting of Space Vector Modulation (SVM) signals. The method offers a good solution for the area where the small modulation index appears. In this case, a lack of measurement time exists due to the narrow triggering pulses. This approach was studied theoretically and verified by laboratory experiments.
A new control scheme of the torque trajectory-tracking controller for induction motor is presented in the paper. The proposed approach addresses the problem of torque control of speed sensorless drives at both low and high speed, where rapid speed changes can occur. The scheme allows the precise and quick control of the induction motor flux and torque. A closed-loop rotor flux observer using sliding mode controller and a non-linear stator frequency dependent gain is presented. Sliding mode controllers are used as the stator flux controller and in the rotor flux observer. Non-hear stator frequency dependant gain used in the rotor flux observer enables the operation at low and high speed. Thus at low speed observer turns into the closed-loop observer using stator current, stator voltage and desired rotor flux values as inputs. At high speed the information from desired rotor flux is disconnected and classical voltage model is used.The reference tracking performance of torque and rotor flux is demonstrated in terms of transient and steady-state characteristics by simulation and experimental results.
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