AC-AC power processing Cycloconvertors

1. AC to AC Power processing
AC Voltage Controllers

2. AC Voltage Controllers:
ON-OFF control.
Phase-angle control.
Single phase controllers with R and RL loads.
Single phase cyclo-converter
Topics
AC to Ac Power processing

3. Phase-angle control and on-off control
AC to Ac Power processing

4. AC to Ac Power processing
zero-crossing pulse

5. A zero-crossing detector is used to generate a sync pulse as reference related to the AC voltage phase
angle often used in power control circuits.
Figure shows the relationship of a zero-crossing pulse to a sine wave. The pulse occurs at 0, 180, and
360 degrees.
Intro. zero-crossing pulse

6. http://www.bristolwatch.com/ele2/zero_crossing.htmRef:
zero-crossing pulse

7. AC to Ac Power processing
Technical Information- Silicon Carbide Heater Control
Characteristics of Silicon Carbide Heaters
Silicon carbide heaters are normally used in high temperature
furnaces and have a resistance that varies with time and also
with temperature.
Thyristor Firing Mode with Silicon Carbide Heaters

8. Firing circuit based upon Microcontroller

9. Non-Inverting Zero Crossing Detector
Inverting Zero Crossing DetectorInput and Output Waveforms of Schmitt Trigger
Zero Crossing Detector using OP-Am

10. The Schmitt trigger circuit has definite predefined upper
and lower input voltage levels that trigger the output to
switch from one saturation level to the other
Schmitt Trigger Circuit for AC
The input voltage, Vin, is applied to the inverting input
terminal .
voltage is connected as feedback to the non-inverting
input terminal, through a potential divider network.
The input voltage Vin triggers the output voltage Vout to
change from one saturation level to the other, every
time when the input voltage exceeds a certain
predefined voltage levels.
These voltage levels are called as upper threshold
voltage (VUT) and lower threshold voltage (VLT).
Schmitt trigger

11. Phase-angle control
AC to Ac Power processing

12. Triac Conduction Waveform
Triac Phase Control
Watch each rising edge
Ideal Pulse TRIAC
fire at every raising
edge

13. AC-AC Converter: AC Voltage Controller
• ac–ac converters accepts electric power from one AC system and
converts it to another AC system with waveforms of different:
amplitude, frequency, and phase.
• The power may be single-phase or three-phase types depending on
their power ratings.
AC to Ac Power processing

14. Railroad trolleyBicycle
What is common for both of these machines to move ?
Power Electronic
AC-AC convertor
Power Stock
AC to Ac Power processing
Stokes are used to push the load slow/fast

15. AC-AC Power Processing
AC to Ac Power processing

16. Introduction
AC to Ac Power processing
If a thyristor is connected between ac supply and load, the power flow can be controlled by
varying the rms value of ac voltage applied to the load.
 AC voltage controller
Types of control : 1) On-Off control
2) Phase-angle control
Common application : industrial heating, on-load transformer tap changing, light control,
induction motor speed control etc.
Fundamental output frequency remain the same as input
frequency.

17. 17
Principle of On-Off control
Voltage
across
thyristors2 2
1 1
T
T
AC to Ac Power processing
Voltages
across Load
On-Off Control (Integral Cycle
Control)
The load power can be controlled by
connecting the source to the load
for few complete cycles then
disconnecting the source from the
load for another number of cycles,
and repeating the switching cycle.
-Duty cycle, k = n/(m +n)
Average power to the load can be
varied from 0% through 100%

18. General AC Thyristor Power Circuit

19. • In On-Off control technique Thyristors are used as switches to connect the load circuit to
the ac supply (source) for a few cycles of the input ac supply and then to disconnect it for
few input cycles.
• The Thyristors thus act as a high speed contactor (or high speed ac ON-OFF switch).
On-Off CONTROL

20. AC ON-OFF Control OR Burst Control
• For 25% of the power be present at the load, the thyristors should be completely ON for one full cycle and OFF
for three complete cycles.
• To provide 50% power to the load, the thyristor should be ON/OFF for every alternate cycle.
• To provide 75% power to the load, the thyristor should be on three cycle and OFF for one cycle
• To provide 100% power to the load, the thyristor should be ON for all input cycles.
AC Supply

21. PRINCIPLE OF ON-OFF CONTROL TECHNIQUE (INTEGRAL CYCLE
CONTROL)
Reference to the circuit shown below. The thyristor switches T1 and T2
are turned on by applying appropriate gate trigger pulses to connect the
input ac supply to the load for ‘n’ number of input cycles during the time
interval ON t .
The thyristor switches T1 and T2 are turned off by blocking the gate
trigger pulses for ‘m’ number of input cycles during the time interval
tOFF. The ac controller ON time tON usually consists of an integral number
of input cycles.
Waveforms
n = Two input cycles. Thyristors are turned ON during tON for two input cycles4
m =One input cycle. Thyristors are turned OFF during tOFF for one input cycle.

22. vs =Vm sinωt = 2VS sinωt
For a sine wave input supply voltage
V =RMS value of input ac supply = = RMS phase supply voltage
Analysis
Input ac supply is connected to load for ‘n’ number of cycles and
disconnected for ‘m’ number of input cycles
then tOFF = n×T tON = m×T
RMS Output (Load) Voltage
RMS Load Current
Output AC (Load) Power
Input Power Factor
RMS Current of Thyristor T (RMS ) 

23. A single phase full wave ac voltage controller working on ON-
OFF control technique has supply voltage of 230V, RMS 50Hz,
load = 50Ω. The controller is ON for 30 cycles and off for 40
cycles.
Example:
Calculate
• ON & OFF time intervals.
• RMS output voltage.
• Input P.F.
• Average and RMS thyristor currents.

25. PHASE CONTROL
AC-AC Power Processing

26. PHASE CONTROL
• In phase control the Thyristors are used as switches to connect the load circuit to the input ac
supply, for a part of every input cycle.
• That is the ac supply voltage is chopped using Thyristors during a part of each input cycle. The
thyristor switch is turned on for a part of every half cycle, so that input supply voltage
appears across the load and then turned off during the remaining part of input half cycle to
disconnect the ac supply from the load.
• By controlling the phase angle or the trigger angle ‘α’ (delay angle), the output RMS voltage
across the load can be controlled. The trigger delay angle ‘α’ is defined as the phase angle
(the value of ωt) at which
• the thyristor turns on and the load current begins to flow.

27. AC Phase Control
• Phase angle control turns the thyristor on at a variable point in the AC cycle according to the control input of
the thyristor.
• Thyristor fired at 0 angle will let the 100%, AC sine waves of current pass through the load.
• At 50% input only half a sine wave will be seen by the load.
• Phase control thyristors give smooth and constantly variable control of the applied heater voltage and thus are
well suited for use with silicon carbide heaters
AC Supply

28. Single phase full wave ac
voltage controller using TRIAC
Triac Used for Full Wave AC Voltage Phase Control for Resistive Load.
Waveforms of single phase full wave ac voltage controller

29. PERFORMANCE PARAMETERS OF A SINGLE PHASE FULL WAVE
AC VOLTAGE CONTROLLER WITH RESISTIVE LOAD

30. PERFORMANCE PARAMETERS OF A SINGLE PHASE FULL WAVE
AC VOLTAGE CONTROLLER WITH RESISTIVE LOAD
for , α=0

31. A single phase full wave controller has an input voltage of 120 V
(RMS) and a load resistance of 6 ohm. The firing angle of thyristor is.
Find 2π
a. RMS output voltage
b. Power output
c. Input power factor
d. Average and RMS thyristor current.
Example

33. Cycloconverter
AC-AC Power Processing

34. Cycloconverter and Matrix converter
AC to AC Frequency converter

35. Frequency converter
Some load run at low frequency then the AC voltages generated by the Source (1500 KW 0-20HZ motor, 1kw=1.34Hp)
Some load run at low frequency then the AC voltages generated by the Source (400 Hz AC power
Aircraft ground power requirements)
Two method can be utilized to address this need
1. Convert AC source voltage to DC and then converter DC voltages to AC at required frequency
2. Direct conversion of AC source frequency to meet the load frequency requirements
Method one: AC to DC rectifier and Inverter circuits are required to implement.
Method two: Cycloconverter circuits are required for direct frequency conversion.

36. 20,000 HP
Synchronous Stator
Being Cleaned With
Dry Ice
Dry ice pellets are accelerated
through a blast system to the
surface being cleaned and upon
impact dissipate as a moisture free
gas.
The dry ice is non-abrasive and the
contaminate is removed from the
windings through a combination of
kinetic energy and gaseous
expansion.

37. Dry ice pellets are
accelerated through a
blast system

38. WEG’s Net Revenues reached R$ 9.4 billion in 2016
The project scope was to repair the rotor and stator of
the 20,000 HP motor, 10 poles and 13.2 kV.
Scope of Work
Source: https://www.weg.net/institutional/US/en/news/products-and-solutions/weg-repairs-a-
critical-motor-supplying-water-to-sao-paulo

39. Variable Frequency Drives
Variable Frequency Drives (VFDs) control AC motor speed and torque by varying the frequency and
voltage of the motor. Reasons to consider a new VFD or an upgrade to your motor control system:
•Reduce electricity consumption and save on energy costs
• Improve process efficiency
• Provide greater longevity on equipment life
• Reduce maintenance and service costs
USE OF CYCLOCONVERTER
400HZ frequency converters for Aircraft ground power

40. How to make Money

42. Frequency Conversion from 60 Hz to 400 Hz, using
Horlick Motor-Generator Sets
60 Hz to 400 Hz Frequency Conversion
The single-module frequency converters
Cycloconverter inside???

43. • Cycloconverters are direct ac-to-ac. frequency changers
• AC input and AC output.
• The output frequency is lower/higher than the input frequency and is generally an integral
multiple of the input frequency.
Cycloconverters
Frequency converter

44. In simple words Cycloconvertere circuits are used to convert:
High input frequency to its lower integral frequency as output
OR
Low input frequency to its higher integral frequency as output
Two types of AC-AC frequency converters
Cyclo converters
Matrix converters
Frequency converter
(Step-down Cycloconverter)
(Step-up cycloconverter)

45. Frequency converter
High input frequency to its lower integral frequency as output
Step-down frequency cycloconverter

46. Frequency converter
Set of thrystor P1-P3, and P2-P4
as pair are used to develop the
positive half cycle of the out put
frequency
By firing these SCRs number of
time one can increase the width of
the +ve half cycle of output
frequency
Step-down frequency cycloconverter
To create +Ve Half Cycle of the output frequency
First fire P1-P3 for +ve half cycle of the input wave
then fire P2-P4 for +ve half cycle of the input wave
then fire P1-P3 for +ve half cycle of the input wave
That will keep the direction of current same in the Load
Single Phase Natural Commutated Cyclo-converter

47. Frequency converter
Set of thrystor N1-N3, and N2-N4
as pair are used to develop the
negative half cycle of the out put
frequency
By firing these SCRs number of
time one can increase the width of
the -ve half cycle of output
frequency
Step-down frequency cycloconverter
First fire N3-N1- for -ve half cycle of the input wave
then fire N4-N2- for -ve half cycle of the input wave
then fire N3-N1- for -ve half cycle of the input wave
To create -Ve Half Cycle of the output frequency
That will keep the direction of current same in the Load
Single Phase Natural Commutated Cyclo-converter

48. Frequency converter
• Three cycles of input frequency is used to make one cycle of the
output frequency
• Hence output frequency is one third of the input frequency.
• Therefore if input frequency was 60Hz the out frequency that was
created is 20Hz
Input (a) and output (b) voltage waveforms of a cyclo- converter with an
output frequency of 20 Hz for resistive (R) load
Input frequency 60Hz
Output frequency 1/3 of input frequency = 20Hz
Single Phase Natural Commutated Cyclo-converter

49. Frequency converter Single Phase Natural Commutated Cyclo-
converter
Natural Commutation is
used in Step down Cyclo
Converter
Step down for RL load

50. Frequency converter
Single Phase Forced Commutated Cyclo-converter
Step Up
Forced Commutation is
required to step-up the
frequency.

51. Step Up Cycloconverter
Fire P1-P2 at angle α
Forced commutation P1-P2 at wt1
(current direction change in the load)
To create +Ve half cycle of output
wt1

52. • Forced commutation N1-N2 at wt2
• Fire P1, P2 at wt2 (current direction change in
the load)
Repeat this procedure to create
three complete cycle of out put
frequency by using ½ cycle of
the input frequency.
Six complete cycles will be generate
by one full cycle of the input cycle.
Result: Step up 1:6
Step Up Cycloconverter
.
.
.
.
.
.
• Fire P1-P2 at angle α
• Forced commutation P1-P2 at wt1
• Fire N1-N2 angle α + wt1 (current
direction change in the load)
To create -Ve half cycle of the output

53. Thank You