Speed Control of DC and AC Machines - Lab Report Example

6005ELE Lab report: Speed Control of DC and AC Machines Insert Insert Introduction The components that make up the DC motor including the stator and rotor winding which are separately excited, in this case, have independent DC voltage sources. The speed ranges from zero up to motor max speed rating is a feature that requires feeding the armature windings with power through a rectifier. A rectifier made available for such a function is one that allows variations of voltage henceforth leading to variation in motor rotary speed. The use of feedback to obtain speed control of a motor is not a necessity in the case of using the rectifier to feed the armature winding. Speed control of separately excited DC motor by armature voltage variation Steady-state conditions are to be used in the case where the DC motor needs to be excited separately. Loading conditions should be varied and tested. The rectifiers available include the single-phase half controlled bridge rectifier containing a flywheel diode. Cases of firing angle in the setup that is used above ought to be set to a fixed value. Considering the expression that is made use in the control of motor speed as; Where N is the speed V is terminal voltage R is external resistance Is flux per pole Voltage and resistance variation affect characteristics of the armature while flux regarding the pole affects magnetic properties of the motor. It sets the base for the speed control methods as armature control method and the field control methods. Figure 1 Dc motor speed control Resistance variation is achieved via connecting an external resistance with the voltage supply to the motor armature. Losses being negligible are ignored. Alternatively speed control can be achieved by a rheostat resistance in series with the armature of the motor. Magnetic properties of the motor can be varied using a field diverter method. Armature control method has superiority compared to the other methods because it has the abilities to offer fine control of the motor speed, a unified acceleration, and the regulation properties accompanying speed control are superior. On the contrary, the method requires standardized patterns that increases the cost and delivers low efficiency when carrying lighter loads. Operation of a single-phase half controlled bridge rectifier The circuit, as stated above, is made up of controlled and the uncontrolled rectifiers. Diode as components of the design and the freewheeling operations occurs regardless of allowing a negative voltage output. Clamping at zero does not guarantee the rectification of negative voltage hence a half controlled. The positive voltage levels are made use via the rectifier while the negative voltages are cut-off hence unnecessary. Figure 2 Half-controlled rectifier The setup is composed of diodes and the SCRs. With Vin being positive, triggering of SCR S1 occurs at the firing angle determined and denoted as a. current flow will begin from SCR S1 and then flow through D3. Considering the equation above, when SCR1 and the diode D3 will be in the conducting mode when a< wt Read More