Simulation Analysis & Hardware Design of Sensor-less Vector Control of Induction Motor

Abstract

Since its development the induction motor is widely used for constant speed applications. Three-phase squirrel cage induction motors mainly have advantage like, simple construction, robustness and maintenance free operation, because of lack of brushes and commutators. But in case of variable speed applications, usually DC motors are preferred. The main reason for using this separately excited DC motor is the high torque, easy speed and torque control because the field (If) and the armature currents(Ia) are decoupled from each other. But DC motors are expensive to produce, physically larger, high time to time maintenance of commutators & brushes. The recent developments in power electronics and digital signal processors (DSPs) have made the implementation of new control schemes possible to realize, so that induction motors can be used for variable speed application. Different control techniques such as scalar (V/f) control, vector control, sensor-less vector control and direct torque control (DTC) etc., have used to realize variable speed drives through variable frequency control of squirrel cage induction motors. In case of scalar control technique, they are simple, cheap and well implementable method; so many applications have this control technique in industries. The main drawback of scalar control drive is the poor dynamic response. This is because; in scalar method magnitude of voltage and frequency is varied instead of controlling phase and magnitude of currents. In case of vector control, the decoupled control of flux and torque makes its behavior similar to a separately excited dc motor. Vector control satisfies the requirements of dynamic drives, where fast dynamic response is necessary. It is high-performance control technique. However, the vector control technique can be further classified into two methods (i) Direct vector control and (ii) indirect vector control differing in their method of implementation. In the present report, the Model Reference Adaptive System technique for speed estimation is used to actualize sensor-less vector control induction motor drive. Through the application of sensor-less vector control techniques, the performance is enhanced, reduce the power consumption of motor systems and increase energy efficiency. This motor control schemes enabled by next generation digital signal processing technology, promises to accelerate the adoption of advanced control schemes. This report includes simulation of the conventional method of three fundamental tests in motor parameter identification, which are DC test to determine stator resistance (Rs) of induction motor, No-load test to determine mutual inductance (Lm), and Blocked rotor test to determine rotor resistance (Rr), stator self-inductance (Lls), rotor self-inductance (Llr). This section also describe methods to determine Torque (T) & Inertia (J). In the present report, hardware design procedure is also discussed in brief for LV drive, which includes Power Card, Control Card & HMI.