Cycloconverters

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1. Cycloconverters Zeeshan Ahmed Abdul Aleem Faiz Q amar Aziz ullah mamon Abdul Rehman Group Member's

2. Basically, cyclo -converters are AC to AC converters and are used to vary the frequency of a supply to a desired load frequency. These are naturally commutated, direct frequency converters that use naturally commutated thyristors . These are mainly used in high power applications up to tens of megawatts for frequency reduction. Introduction

3. DC link AC - ac converters

4. Due to the DC-link storage element, there is the advantage that both converter stages are to a large extent decoupled for control purposes. Furthermore, a constant, AC line independent input quantity exists for the PWM inverter stage, which results in high utilization of the converter’s power capability. On the other hand, the DC-link energy storage element has a relatively large physical volume, and when electrolytic capacitors are used, in the case of a voltage DC-link, there is potentially a reduced system lifetime DC link converters

5. converter  uses an induction generator motor, in that it rotates to transform single- phase  utility power into  three - phase  electricity. A  rotary phase converter  generates one line of power from the induction generator motor and merges that with two single- phase  lines converters

6. There are mainly two types of cycloconverters blocking mode type and circulating mode type. When the load current is positive, the positive converter supplies the required voltage, and the negative converter is blocked. Suppose if the load current is negative, then the negative converter supplies the voltage and the positive converter is blocked. This operation is called blocking mode operation. The cycloconverters which are using this method are called blocking mode cycloconverters . application cyloconverters

7. Blocking Mode  Cyclocornverters : Circulating Current  Cycloconverters : Single-Phase to Single-Phase  Cycloconverter : Single-Phase to T hree-Phase   Cycloconverter : Three-Phase to Three-Phase  Cycloconverter : Controlling the Speed of the Single Phase Induction Motor. Type of cyloconvertrs

8. Blocking mode cycloconverters don’t need any intergroup reactor (IGR). Depends on the polarity, one of the converters is enabled. The blocking mode operation has some advantages and disadvantages over circulating mode operation. They don’t need any reactors hence size and cost is less. Only one converter is in conduction at all times rather than two. During delay time current stays at zero distorting the voltage and current waveforms. This distortion means complex harmonic patterns. Blocking mode cyloconvertrs

9. Both the converters operate at all times in this case. The big disadvantage is an IGR is needed. The number of devices connecting to this is twice than of blocking current cycloconverter . circulating current cyloconvertrs

10. The operation principles of cyclo converters can be classified into the following three types based on the type of input AC supply applied to the circuit. Principles of cycloconverters

11. Understanding of operation principles of cyclo converters should begin with single-phase to single-phase cycloconverter. This converter is having back to back connection of two full-wave rectifiers. Suppose for getting one-fourth of input voltage at the output, for the first two cycles of Vs the positive converter operates supplying current to the load and it rectifies the input voltage. Single-Phase to Single-Phase  Cycloconverter:

12. In the next two cycles, the negative converter operates supplying current in the reverse direction. When one of the converters operates the other one is disabled so that there is no current circulating between rectifiers. In the below figure Vs represents input supply voltage and Vo is the required output voltage which is one-fourth of the supply voltage . Image for One-fourth of input voltage at the output using 1-phase to 1-phase Cycloconverte.

13. Like as above converters, three-phase to single-phase cycloconverter applies rectified voltage to the load. Positive Cycloconverters will supply positive current only while negative converters will supply negative current only. The cyclo converters can operate in four quadrants as (+v, + i ), (+v, - i ) rectification modes and (-v, + i ), (-v, - i ) inverting modes. The polarity of the current determines if the positive or negative converter should be supplying power to the load. When there is a change in current polarity, the converter previously supplying current is disabled and the other one is enabled. During the current polarity reversal, the average voltage supplied by both the converters should be equal Single-Phase to three-Phase   Cycloconverter:

14. Two basic configurations are available for three-phase cyclo converters such as delta and wye. If the outputs of the above converter are connected in wye or delta and if the output voltages are 120º phase-shifted the resulting converter is three-phase to the three-phase converter. The three-phase converters are mainly used in machine drive systems running three-phase synchronous and induction machines. three-Phase to three-Phase  Cycloconverter:

15. ingle-phase induction motors are widely used in many applications. Improvements in its performance mean a great saving in electrical energy consumption. A speed controller based on cycloconverter is proposed . The above circuit diagram can be used to control the speed of a single-phase induction motor in three steps by using cyclo converters and thyristors . The circuit uses a thyristor controlled cycloconverter which enabling the control of speed in steps of an induction motor. Controlling the Speed of the Single Phase Induction Motor .

16. For the 8051 series of microcontrollers, a pair of slide switches are provided to select the required speed range of operation of induction motor. These switches are interfacing with the microcontroller to deliver the pulses to trigger the SCRs in a dual bridge. Thus the speed of the motor can be achieved in three steps. Some other applications where Cycloconverters can be used are cement mill drives, ship propulsion drives, Rolling mills, and mine winders, washing machines, water pumps, and used in industries as well. If any further more queries on this topic or on the electrical and electronic projects leave the comments section below.

17. AC Motor Speed Controller Circuit.

18. ADVANTAGES Efficiency is very high compared to other converters AC power at one frequency is directly converted to a lower frequency in a single conversion If one of the SCR fails, the cyclo -converter operates with a distorted output In this converter, power transfer is possible from supply load and vice versa at any power factor Dynamic response is good  Smooth low-speed operation Advantages and disadvantages of cycloconverter

19. DISADVANTEGES Control circuit become complex so difficult to design The output frequency of the cycloconverter is 1/3th or 1/2th for responsible power output and efficiency Power factor is too much poor at large values of α More distortion at low frequencies

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