Closed loop control of converter fed motor
- 1. Submitted By – Rishabh Dutt Shukla University Roll No – 1805420909 Branch (Electrical Engineering) Submitted To – Prof Sahab Ahmad
- 2. INTRODUCTI ON Closed loop control is a technique used to control the speed of the motor by reducing that is by chopping the fixed DC voltage to variable DC voltage. Here the four quadrant chopper method is used that is four switching devices are used to control the speed of the motor. The motor speed can be controlled by controlling the duty cycle applied to the switching devices. The output voltage totally depends on the ON time of the device if the on time of the switching frequency increases then the output voltage is also increased.
- 3. CLOSED LOOP SPEED CONTROL OF DC DRIVE ■ To avoid the disadvantage that is caused due to open loop speed control closed loop speed control technique is implemented. ■ Here the output speed measured is feed back to the speed controller.
- 4. CLOSED LOOP FIELD CONTROL This method is used for varying speed of DC shunt motor above the rated speed. The armature voltage is kept constant and field current is varied. The reference voltage is passed through the ramp unit to provide soft starting of the motor. The o/p of ramps unit acts as the speed reference, this reference signal is compared with the speed feedback signal obtained from tachogenerator. ■ The o/p of comparator is called as speed error signal. ■ The speed controller will produce a control voltage from error signal i/p and this control signal changes the firing angle α in such a way that thefield voltage is automatically increased or decreased.
- 5. CLOSED LOOP ARMATURE CONTROL ■ In this method the field winding is excited by a constant D.C. voltage and the armature voltage is varied in order to vary the speed of the motor. ■ The working of armature control scheme is basically same as the field control scheme. ■ The control signal changes the firing angle α in such a way that the armature voltage is automatically increased or decreased so that the speed error gets reduced and the armature voltage is varied to vary the speed of a DC shunt motor.
- 6. FEEDBACK LOOP IN A CLOSED LOOP CONTROL SYSTEM • Feedback is a common and powerful tool when designing a control system. • The feedback loop is the tool that takes the system output into consideration and enables the system to adjust its performance to meet the desired result of the system. • In any control system, the output is affected due to a change in environmental conditions or any kind of disturbance. So one signal is taken from the output and is fed back to the input. • This signal is compared with a reference input and the error signal is generated. This error signal is applied to the controller and the output is corrected. Such a system is called a feedback system. The figure below shows the block diagram of a feedback system.
- 7. OPEN LOOP VS CLOSED LOOP CONTROL SYSTEMS Sr. No. Open Loop Control System Closed Loop Control System 1 The feedback element is absent. The feedback element is always present. 2 An error detector is not present. An error detector is always present. 3 It is a stable one. It may become unstable. 4 Easy to construct. Complicated construction. 5 It is economical. It is costly. 6 Having a small bandwidth. Having a large bandwidth. 7 It is inaccurate. It is accurate. 8 Less maintenance. More maintenance. 9 It is unreliable. It is reliable. 10 Examples: Hand drier, tea maker Examples: Servo voltage stabilizer, Thermostat Heater.
- 8. ADVANTAGES & DISADVANTAGES Advantages: • Closed loop control systems are more accurate even in the presence of non- linearities • The sensitivity of the system may be made small to make the system more stable • The closed loop systems are less affected by noise. Disadvantages: • Closed loop control systems are costlier and complex • The feedback in the closed loop system may lead to oscillatory response • The feedback reduces the overall gain of the system • Stability is the major problem in the closed loop system and more care is needed to design a stable closed loop system
- 9. APPLICATIO NS • Disk drive system • Guided missiles • Automatic gain control in radio receivers, satellite tracking antenna, etc • Electric traction
- 10. CONCLUSIO N As we have seen that control systems are used in almost every domain of our life and it is a developing concept which will play crucial role in the future of automated and smart society. There is a lot of scope for research and development in the feedback loop system so the study of the control systems is essential in terms of technological growth.
- 11. REFERENCE S ■ International Conference on Science, Technology, Engineering & Management ■ M.Nedeljkovic and Z.Stojiljkovic, Fast current control for thyristor rectifiers, IEE Proceeding. Electr. Power Appl, 150(6), 2003, 636- 628. ■ Wikipedia -- https://en.wikipedia.org/wiki/Pulse- width_modulation#Principle ■ D.A. Staton, M.I.McGilp and T.J.E.Miller, DC machine teaching experiment, in proceedings of the European Power Electronics Association EPE, Brighton, 1993, 35-40.