Novel adaptive tolerance band based PWM for field-oriented control of induction machines

Two levels of an innovative adaptive switching pattern (ASP) for use in the control of induction machines are described. The ASP is based on a tolerance band control strategy resulting in nearly sinusoidal stator currents. The first level (ASP1) significantly increases the switching time thereby eliminating the very fast switching sometimes experienced. The second level (ASP2) reduces the number of double commutations by one or two orders of magnitude. The price for applying ASP is only a small, irregular, consequential increase in the current error. A rotating reference frame fixed to the rotor flux is applied. This makes ASP especially suitable for application in the field-oriented control of current controlled voltage source inverter (CC-VSI) fed induction motor drives. The theoretical background supported by conclusive simulation results illustrates clearly the significant benefits of ASP over the regular switching pattern often used. To complete the picture a short survey of the various techniques used in the speed control of induction machines is presented in the introduction