Cyclo Converter using Thyristors

Cyclo Converter using Thyristors Isometric

Cyclo converter using thyristors can be used to control the speed of Induction motor. This system is a very complicated solution to control the induction motor’s speed particularly for single or 3-phase ac motors. In our daily life, AC motors are mostly used in various applications like domestic as well as industrial level. The applications of these motors mainly include water pumps, vacuum cleaners, and washing machines. The speed control of these motors is difficult due to invariable.

Here, we are going to discuss a cyclo converter using thyristors for driving the single-phase induction motor, whose cost would less be as compared the other motor drivers. Through by using this system, the motor speed could be controlled. This system would be made with the help of microcontroller AT89S51/52, LM358, optocouplers, SCR, and semiconductor switches such as thyristors.

Cyclo Converter using Thyristors

A.C. motors have the great advantages of being relatively inexpensive and very reliable. Induction motors, in particular, are very robust and therefore used in many domestic appliances such as washing machines, vacuum cleaners, water pumps, and others.

The induction motor may be regarded as practically a constant-speed machine, the difficulty of varying its speed economically constitutes one of its main disadvantages. This drawback is overcome by using a thyristor controlled cyclo converter that enables the speed to be lowered in steps by Microcontroller triggering an SCR bank of 8nos in F/2 & F/3.

The hardware requirements of this cyclo converter using thyristors mainly include power supply block, the microcontroller (AT89S52/AT89C51), Opt isolator (MOC3021), single phase induction motor, pushbutton, SCR, LM358, LED, Diode (IN4007), Resistors, and Capacitors.

Cyclo Converter using Thyristors Block Diagram

Software Requirements

• Keil, ARM Company makes C compilers, macro assemblers, real-time kernels, debuggers, simulators, integrated environments, evaluation boards, and emulators for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and 8051 MCU families.
• Compilers are programs used to convert a High-Level Language to object code. Desktop compilers produce an output object code for the underlying microprocessor, but not for other microprocessors.
  i.e the programs written in one of the HLL like ‘C’ will compile the code to run on the system for a particular processor like x86 (underlying microprocessor in the computer).
• For example compilers for Dos platform is different from the Compilers for Unix platform So if one wants to define a compiler then the compiler is a program that translates source code into object code.

Microcontroller AT89S51/52

It is a smaller computer and it has on-chip RAM, ROM, I/O ports…

Features of AT89S51/52

• Compatible with MCS®-51 Products
• 8K Bytes of In-System Programmable (ISP) Flash Memory
• Endurance: 10,000 Write/Erase Cycles
• 4.0V to 5.5V Operating Range
• Fully Static Operation: 0 Hz to 33 MHz
• 256 x 8-bit Internal RAM
• 32 Programmable I/O Lines
• Three 16-bit Timer/Counters
• Eight Interrupt Sources
• Full Duplex UART Serial Channel
• Interrupt Recovery from Power-down Mode
• Watchdog Timer
• Dual Data Pointer

8051 Microcontroller

Optocoupler

Optocoupler is a 6 pin IC. It is a combination of 1 LED and a DIAC. Pin 5 is not generally used and when light falls on the DIAC then it switches ON the DIAC.

Opto Coupler MOC3021

When a logic zero is given as input to the LED then the light doesn’t fall on DIAC so the DIAC is off meant the current does not flow through the DIAC.

When logic 1 is given as input to the LED then light emitted by LED falls on DIAC so it starts conducting i.e., now there will be current flowing through the DIAC.

Three Phase Induction Motor

• It consists of the fixed stator or frame, a three-phase winding supplied from the three-phase mains and a turning rotor
• There is no electrical connection between the stator and the rotor
• Stator and rotor are made of highly magnetizable core sheet providing low eddy current and hysteresis losses

Three Phase Induction Motor

Stator & Rotor

The stator winding consists of three individual windings which overlap one another and are offset by an electrical angle of 120°

Synchronous Speed (Ns)= 60*f/p

Ns= Synchronous Speed/ minute;
F= frequency;
P=Pole pair Number;

Rotor in induction machines with squirrel-cage rotors consists of a slotted cylindrical rotor core sheet package with aluminum bars which are joined at the front by rings to form a closed cage

Stator & Rotor

SCR

A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four-layer solid state device that controls current flow
An SCR can be seen as a conventional rectifier controlled by a gate signal.

SCR

• It is a 4-layered 3-terminal device
• When the gate to cathode voltage exceeds a certain threshold, the device turns ‘on’ and conducts current
• The operation of an SCR can be understood in terms of a pair of tightly coupled Bipolar Junction Transistors
• SCR has three states: Reverse blocking mode, forward blocking mode, and forward conducting mode

Silicon Controlled Rectifier

LM358

• The LM358 series consists of two independent, high gain; internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages.
• The operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.

LM358

Features

• Available in 8-Bump micro SMD chip sized package.
• Large dc voltage gain: 100 Db.
• Wide power supply range:
• Single supply: 3V to 32V
• or dual supplies: ±1.5V to ±16V
• Very low supply current drain (500 µA)-essentially independent of supply voltage.

Working of Project

The project uses zero voltage reference, 8 Optoisolators (MOC3021) are used for driving 8 SCR’s. Triggering pulses so generated by the MC as per the program written provides input condition to the Optoisolator that drives the respective SCR to get conducting for 20ms from the 1st bridge and next 20ms from the 2nd bridge to get the output, total time period of one AC cycle of 40ms which is 25 Hz.

Thus F/2 is delivered to the load while switch 1 is closed. Similarly, for F/3, the conduction takes place for 30ms in the 1st bridge and next 30ms from the next bridge, such that a total time period of 1 cycle comes to 60ms which in turn in F/3 while switch -2 is operated.

The fundamental frequency of 50Hz is available by triggering on a pair from the 1st bridge for 1st 10ms and for the next 10ms from the next bridge while both the switches are kept in “OFF” condition. The reverse current flowing through the gates of the SCR’s are Opto – isolator output.

I hope you have clearly understood the topic of cyclo converter using thyristors. If any furthermore queries on this topic or on the electrical and electronic projects leave the comments section below.