Introduction

                     Introduction

Advancement of inverter technique has made available the ac power supply, whose output voltage and current can be controlled as vector quantities of variable amplitude and frequency. Controllability of ac motors are now invading into application areas where dc motor control have been predominantly used. However it seems that ac motor control technique has not been well grounded on a sound theoretical base. The problem is that transient phenomena of ac motors have not been well analyzed. The conventional ac motor theories have not been well analyzed.                          The conventional ac motor theories have been lacking in their ability to analyze electromagnetic transient phenomena of ac motors. Most control theories of ac motors have been based on the equivalent two phase machine theory, which is sometimes called d,q axes theory. Its characteristic equation is of 4^th degree and thus the theory is unwieldy. It is being tried to replace the two phase theory with the space vector method. But it relies too much on physical pictures and is not mathematically rigorous in derivation of circuit equations of ac motors. The spiral vector method will simplify analysis of electro magnetic transient phenomena ac circuits and ac machines, just as the phasor notation simplified analysis of steady states of ac circuits and machines. Analytical results obtained by the spiral vector have revealed superior control features of ac motors. The spiral vector method will also bring about a new development in the ac circuit theory, where steady state and transient state are separately treated by the separately treated by the separate two theories, the ac circuit which uses the phasor notation, and the transient theory, which uses instantaneous real values. The spiral vector will unify the two theories into the spiral vector theory of ac circuit and machine.          

                           In industry application the variable speed drive use often a vector control of induction machine. The field orientation defines conditions for decoupling the field from the toque control the field oriented induction motor emulates separately exited DC motor in two aspects

·         Both the magnetic field and the torque developed in the motor can be controlled independently

·         Optimal conditions for torque production, resulting in the maximum torque per Unit samplers, occur in the motor both in steady state conditions and transient   Conditions of an operation.

A vector control is obtained by the conventional theories which are based on two axis method, they involve complicated variable transformations, which are not so successful in analyzing the machine. In this work we propose a vector control of induction machine by a spiral vector theory. The application of this theory conduct to eliminate the Park’s Transformation to make the regulation and to obtain a good decoupling between the air gap flux and electromagnetic torque