01-09-2014, 12:43 PM
- PHASE INDUCTION MOTOR SPEED CONTROL USING V/F CONTROL
PHASE INDUCTION.docx (Size: 29.33 KB / Downloads: 12)
ABSTRACT:
An important factor in industrial progress during the past five decades has been the increasing sophistication of factory automation which has improved productivity many-fold. Manufacturing lines typically involve a variety of variable speed motor drives which serve to power conveyor belts, robot arms, overhead cranes, steel process lines, paper mills, and plastic and fiber processing lines to name only a few. Prior to the 1950s all such applications required the use of a DC motor drive since AC motors were not capable of smoothly varying speed since they inherently operated synchronously or nearly synchronously with the frequency of electrical input. To a large extent, these applications are now serviced by what can be called general-purpose AC drives. In general, such AC drives often feature a cost advantage over their DC counterparts and, in addition, offer lower maintenance, smaller motor size, and improved reliability. However, the control flexibility available with these drives is limited and their application is, in the main, restricted to fan, pump, and compressor types of applications where the speed need be regulated only roughly and where transient response and low-speed performance are not critical.
More demanding drives used in machine tools, spindles, high-speed elevators, dynamometers, mine winders, rolling mills, glass float lines, and the like have much more sophisticated requirements and must afford the flexibility to allow for regulation of a number of variables, such as speed, position, acceleration, and torque. Such high-performance applications typically require a high-speed holding accuracy better than 0.25%, a wide speed range of at least 20:1, and fast transient response, typically better than 50 rad / s, for the speed loop.
Until recently, such drives were almost exclusively the domain of DC motors combined with various configurations of AC-to-DC converters depending upon the application. With suitable control, however, induction motor drives have been shown to be more than a match for DC drives in high-performance applications. While control of the induction machine is considerably more complicated than its DC motor counterpart, with continual advancement of microelectronics, these control complexities have essentially been overcome. Although induction motors drives have already overtaken DC drives during the next decade it is still too early to determine if DC drives will eventually be relegated to the history book. However, the future decade will surely witness a continued increase in the use of AC motor drives for all variable speed applications.
Unfortunately, the induction motor and reluctance motor are both inflexible in speed when operated on a standard constant-frequency a.c supply. The reluctance motor operates synchronously at a speed which is determined by the supply frequency and the number of poles for which the stator is wound. The induction motor runs slightly below synchronous speed. For intermittent operation at reduced speeds, stator voltage control of the induction motor is satisfactory. Sub-synchronous speed control of a wound-rotor induction motor is obtained by means of a converter cascade for slip-energy recovery. However, efficient wide-range speed control of the reluctance motor or cage-rotor induction motor is only possible when a variable-frequency a.c. supply is available. Consequently, in the project a variable frequency method of obtaining variable-speed a.c. motor operation is implemented.
In a static frequency converter, the fixed-frequency a.c.supply voltage is transformed to a variable-frequency output, which is used to power conventional a.c. motors. In the present project a variable voltage, variable frequency inverter is designed and implemented to drive an induction motor. The inverter is built around the efficient power devices, i.e. IGBTs, and the inverter elements are driven by a micro controller to obtain a sinusoidal output waveform, from the inverter.