We've updated our privacy policy. Click here to review the details. Tap here to review the details.

Successfully reported this slideshow.

Your SlideShare is downloading.
×

Activate your 30 day free trial to unlock unlimited reading.

Activate your 30 day free trial to continue reading.

Top clipped slide

1 of 21
Ad

controller

controller

- 1. LECTURE 28 AC Voltage Controllers Dr. Rostamkolai ECE 452 Power Electronics 1
- 2. Introduction The power flow into a load can be controlled by varying the rms value of the load voltage This can be accomplished by thyristors, and this type of power circuit is known as ac voltage controllers 2
- 3. The most application of ac voltage controllers are: Industrial heating On-load transformer tap changing Light controls Speed control of induction motors AC magnet controls 3
- 4. For power transfer, two types of control are normally used: On-off Control Phase angle control In on-off control, thyristor switches connect the load to the ac source for a few cycles of the input voltage and then disconnected for a few cycles In phase control, thyristor switches connect the load to the ac source for a portion of each cycle 4
- 5. The ac voltage controllers can be classified into two types: Single-Phase Controllers Three-Phase Controllers Each type can be subdivided into: Unidirectional or Half-Wave Control Bidirectional or Full-Wave Control 5
- 6. Since the input voltage is ac, thyristors are line commutated Typically phase control thyristors which are cheaper are used For applications up to 400 Hz, TRIACs are used 6
- 7. Performance Parameters An ac voltage controller produces a variable ac voltage at a fixed or variable frequency Input source is a fixed voltage and frequency ac supply 120 or 240 V 50 or 60 Hz The output should ideally be a pure sine-wave 7
- 8. 8
- 9. From the input side, the performance parameters are similar to those of diode rectifiers Input power, Pi Rms input current, Is Total harmonic distortion of the input current, THDi Crest factor of the input current, CFi Harmonic factor of the input current, HFi Form factor of the input current, FFi Input transformer utilization factor, TUFi Ripple factor of the input current, RFi 9
- 10. From the output side, the performance parameters are similar to those of inverters Output power, Po Rms output current, Io Output frequency, fo Total harmonic distortion of the output voltage, THDv Crest factor of the output voltage, CFv Harmonic factor of the output voltage, HFv Form factor of the output voltage, FFv Ripple factor of the output voltage, RFv 10
- 11. Principle of On-Off Control The principle of on-off control can be explained with the following single-phase full-wave controller 11
- 12. 12
- 13. This type of control is applied in applications which have high mechanical inertia and high thermal time constant Typical examples are industrial heating and speed control of large motors If the input voltage is connected to load for n cycles and is disconnected for m cycles, the output load voltage is found from: 13
- 14. Note that k is called the duty cycle, and the power factor and output voltage vary with the square root of k k V n m n V V t d t V m n n V s s rms o s rms o 2 / 1 2 0 2 2 ) ( sin 2 ) ( 2 14
- 15. Principle of Phase Control The principle of phase control can be explained with the following circuit 15
- 16. Due to the presence of diode D1, the control range is limited The rms output voltage can only be varied between 70.7 to 100% The output voltage and input current are asymmetrical and contain a dc component 16
- 17. This circuit is a single-phase half-wave controller and is suitable only for low power resistive loads, such as heating and lighting Since the power flow is controlled during the positive half-cycle of input voltage, this type of controller is also known as unidirectional controller 17
- 18. The rms value of the output voltage is found from: The average value of the output voltage is: 2 / 1 2 / 1 2 2 2 2 2 )] 2 2 sin 2 ( 2 1 [ )]} ( sin 2 ) ( sin 2 [ 2 1 { s o s s o V V t d t V t d t V V ) 1 (cos 2 2 )] ( sin 2 ) ( sin 2 [ 2 1 2 s dc s s dc V V t d t V t d t V V 18
- 19. Single-Phase Full-Wave Controllers with Resistive Loads The problem of dc input current can be prevented by using bidirectional or full-wave controller 19
- 20. 20
- 21. The firing pulse of T1 and T2 are 180 degrees apart The rms value of the output voltage is: By varying α from 0 to π, Vo can be varied from Vs to 0 2 / 1 2 / 1 2 2 2 2 sin ( 1 ) ( sin 2 2 2 s o s o V V t d t V V 21

No public clipboards found for this slide

You just clipped your first slide!

Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips.Hate ads?

Enjoy access to millions of presentations, documents, ebooks, audiobooks, magazines, and more **ad-free.**

The SlideShare family just got bigger. Enjoy access to millions of ebooks, audiobooks, magazines, and more from Scribd.

Cancel anytime.
Be the first to like this

Total views

3

On SlideShare

0

From Embeds

0

Number of Embeds

1

Unlimited Reading

Learn faster and smarter from top experts

Unlimited Downloading

Download to take your learnings offline and on the go

You also get free access to Scribd!

Instant access to millions of ebooks, audiobooks, magazines, podcasts and more.

Read and listen offline with any device.

Free access to premium services like Tuneln, Mubi and more.

We’ve updated our privacy policy so that we are compliant with changing global privacy regulations and to provide you with insight into the limited ways in which we use your data.

You can read the details below. By accepting, you agree to the updated privacy policy.

Thank you!

We've encountered a problem, please try again.