MDSRC - 2017 Proceedings, 27-28 December, 2017 …MDSRC - 2017 Proceedings, 27-28 December, 2017...

MDSRC - 2017 Proceedings, 27-28 December, 2017 Wah/Pakistan

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Three Phase Frequency Converter Quratulain Jamil1, Hafiz Muhammad Ashraf Hayat2, Haris Masood3

1Department of Electrical Engineering Wah Engineering College, University of Wah

[email protected]


[email protected]


[email protected]

ABSTRACT

The radar operates at a frequency of 400Hz but the frequency coming from main is 50Hz. So the project is devised to carter this problem. Secondly, the power supply units that are used to convert three- phase AC voltage from 50Hz to 400Hz are too big in size and are difficult to be carried to far-off places. It is designed to carter this drawback and is made compact yet cost effective. The project includes an AC to DC (converter) circuit and then DC to AC (inverter) circuit by switching DC voltage using MOSFETs or IGBT, to achieve 400Hz.The work cycle begins as the 3 phase AC is converted to DC using rectifier circuit and then capacitor is used to smooth the voltage. This DC voltage is then converted into 400Hz by using a 3 phase inverter circuit. The output of 3 different phases is then supplied to the radar.

Keywords: IGBT’s, Pulse Generation, Rotary converters, Six-pulse inverter circuit, Three-

phase inversion.

1. INTRODUCTION

A radar operation requires an input of 3

phase AC voltage of 200 Volts 400 Hz

rating. The desired rating of the

frequency is obtained by power supply

units that are attached to the radars.

These power supply units work on

rotatory converter principles to convert

the frequency of the AC voltage coming

from main grid (220 V 50 Hz).It consists

of large generators and transformers

which generates the voltage and

frequency and then step down it to the

desired level. The basic discrepancy of

these power units was their size. The

power units are of large sizes due to

which they cannot be carried to distant

areas of war or abandoned areas.

Secondly, the power units used for

operating radars are imported from

foreign countries. This reason makes the

power units highly expensive. Also the

manufacturing of the power units is not

common in our country and the spare

parts are also not easily available and are

needed to be imported from other

countries in case of faults. Lastly their

transport was a big issue because of their

size. This need developed the desire of a

compact yet efficient frequency

converter. By understanding the

problems of the prior technology, the

three phase frequency converter was

devised to be cost effective, compact

and efficient.

2. METHODOLOGY

The working of three phase frequency

converter can be divided into 3 phases:


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1) Rectification.

2) Three Phase Inverter.

3) Pulse Generation through Arduino.

In the first phase of the project the

incoming single phase AC voltage (220V

50Hz) from the grid is rectified using a

simple bridge rectifier which is based on

simple rectification techniques. The AC

220V is converted into 310V DC.

Second phase of the project includes

arduino, pulses are generated through

arduino and is fed to the driver IC which

controls the switching of IGBT’s.

Third phase involves design of a 3 phase

inverter that converts single phase into

three phases. This is done cascading

three legs or 6 MOSFETs/IGBTs in series

to obtain the following 3 phase output.

The frequency of this output is set by

changing the frequency of the

MOSFETS/IGBTs. For this purpose arduino

is used which controls the input to the

driver IC hence controlling the switching

of the MOSFETs/IGBTs. The three phases

for the working of three phase frequency

converter are illustrated in figure 1.

Figure 1: Block Diagram

Block diagram illustrates that:

Firstly three phase AC supply of

220V is supplied as input to a

rectifier.

Secondly rectifier converts an

input of 3-phase 220V 50Hz AC

into 310V DC.

Next this DC voltage is fed to a

MOSFET/IGBT driver circuit that

steps up frequency up to 400Hz

using arduino or microcontroller,

and desired frequency is

achieved.

This DC voltage is fed to an

inverter that converts the DC

voltages in AC voltages of

required frequency and ratings.

And lastly, this frequency is used

for operating radars.

The main drawback of these power

supply units is their size. These units are

too big in size, as shown in figure 1 due

to which they cannot be carried to far-off

places especially war zones, deserts and

abandoned areas. Hence the desire for a

portable frequency converter emerges.

2.1 Rectification

Rectification is a process in which

alternating current is converted into

direct current (unidirectional). The

rectification process is a simple process

in which AC is converted into pulsating

DC using diodes as illustrated in figure 2.

Figure 2: Simple rectifier circuit

In the positive cycle, the diode is forward

biased i.e. positive voltage occurs across

its positive end that allows the current to

pass through it. And in negative cycle,

current is not allowed to pass as it is

reverse biased. The rectification method

used is three phase rectification

technique.

Three-phase diode rectification converts

a three-phase AC voltage input into a DC

voltage as the output. It is called three

phase rectification as it converts Three

phase input into three phase output. The

circuit and the waveforms at output of

three phase rectification as illustrated in

figure 3.


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Figure 3: Three Phase

Rectification

2.2 Three Phase Inverter

A three phase inverter is a device that

converts a single phase DC voltage into a

three phase AC voltage. The circuit

topology for a three phase inverter is

cascading three legs of single phase

inverters in series with the phase

difference of 120 degrees between them.

A three phase output can be obtained by

a configuration of six transistors and six

diodes as illustrated in figure 4 [1]. The

type of three-phase inverter used in this

frequency converter project is 6-pulse

inverter, and will be explained in detail

later.

Figure 4: Three Phase Inverter

Two types of control signals can be

applied to transistors 180 degree

conduction and 120 degree condition that

are [2]:

1. 180 degree conduction

2. 120 degree conduction

In the project, 180 conduction mode is

used for obtaining three phase output. In

180 degree conduction mode, each

transistor conducts for 180 degree [3].

Three transistors in the circuit remain on

at any instant of time. The switches

cannot be switched on concurrently in

any leg of the inverter circuit. This can

cause short circuit across the dc link of

the voltage supply in the circuit [4]. In

this mode of operation three out of six

switches are conducting at one time.

Each switch (MOSFET/IGBT) is operated

with an angle delay of 60 degree. Using

this method of conduction we can easily

obtain a pure sine wave. The output

voltages are illustrated in figure 5 and 6.

Figure 5: Phase Voltages

Figure 6: Line Voltages

2.2.1 Six pulse inverter circuit

The purpose of inverter in our project is

to convert the DC 220 volts into a three

phase AC voltage signal with the

frequency of 400 Hz. The inverter

topology used in the project is three

phase square wave inverter or 6 pulse

inverter circuit as illustrated in figure 7.


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Figure 7: Six Pulse Inverter Circuitry

There are six MOSFETs/IGBTs used in the

circuit as switches. The three phase

output is obtained by controlling the

switching pattern of these switches. The

basic catch in this circuit is that the

switches are driven in such a way that

the switches of same column are not

turned on at the same time. The Proteus

simulation of six pulse inverter is

illustrated in figure 8.

Figure 8: Proteus Simulation of six

pulse inverter

Components used in Six pulse inverter

circuit are:

MOSFETs/IGBTs as switches.

IR2130 Driver IC.

Arduino.

Optocoupler (6N137)

2.2.1.1 IGBT’s

IGBT are fast switching devices. They

have both the characteristics of BJT’s

and MOSFET’s. The IGBT’s like MOSFET’s

have relatively high input impedance.

And like BJT’s have low on-state losses,

in case of conduction [5].

The IGBT used in the project is

(FGA25NI20ANTD). The reason to use this

IGBT among many IGBT’s is:

IGBT deals with superior

conduction properties.

It has better switching

performance.

It has high avalanche ruggedness

and has stress-free parallel

operation.

The IGBT is appropriate for the

resonant applications.

It offers soft switching

applications.

2.2.1.2 Optocouplers

The name indicates that this device is

used to couple isolated circuits. It is

made of light sensing components. It is

used to interconnect two isolated circuits

by optical interfacing, using light.

The optocoupler 6N137 is used to couple

the isolated circuits of 6 pulse inverter

and arduino.

The main features are:

It has very high speed.

The working voltages are double

up to -480V.

It has logic gate output.

Output is strobable because of

very high speed photo detector.

It has an open collector.

Temperature ranges between -40°C to

+85.

2.3 Pulse Generation through Arduino

The microcontroller board is based on ATmega2560. The arduino ATmega2560 has 54 input and output pins, out of which 14 can be used as PWM. 16 pins are


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analog input pins. It has four hardware serial ports. It has everything that needs to support the microcontroller. It only needs a PC with a USB cable, and also can be powered by an AC to DC adapter as illustrated in figure 9. A battery can also be needed to get it started.

Figure 9: Arduino ATmega 2560

Features of the arduino ATmega 2560

are:

It compromises microcontroller

ATmega2560

Operating Voltages are 5V.

Recommended input Voltage are

between 7-12V.

Input Voltage limits between 6-

20V.

It consists of 54 pins.

It has 16 analog pins.

DC Current per I/O Pin is 40 mA

DC Current is 50 mA for 3.3V Pin.

Flash Memory is 256 KB out of

which 8 KB is used by the boot

loader

16 MHz is the clock speed.

2.3.1 Advantages of arduino

Arduino ATmega 2560 is used to generate

pulses that are then fed to the driver IC

which is IR2130, which controls the

switching of IGBT’s. The IGBT’s used for

switching are FGA25NI20ANTD. Instead of

arduino microcontrollers can also be used

but there are some advantages of arduino

over microcontroller stated as below:

Arduino’s main advantage is that

it is is very easy to code and

interface with other sensors, and

LCD etc

It is open source which makes it

better than microcontrollers.

It’s easily programmable and has

many libraries, drivers and

examples available for easy

learning, while microcontrollers

need complete hardware and

software knowledge for making

project.

3. DESIGN

To make a three phase frequency

converter an additional keypad and a LCD

has been used along with the arduino.

There is a switch button that is used for

switching on and off of the whole three-

phase frequency converter. The required

frequency is then entered via

keypad and is displayed on the LCD. The

value of frequency is then fed to the

controller (Arduino and six pulse inverter)

which changes the switching frequency of

transistor according to our desired

frequency.

For the controller we set the frequency

of 400Hz as reference and all of the other

frequencies are first compared with this

reference frequency and then we get the

desired switching time for the transistor,

resulting in our required

output frequency.

For example, let the time for 400Hz was

2303 milliseconds. We multiplied the

2302 ms with 400 and then divided it with

the required frequency entered via

keypad e.g. the time for 50Hz is 19708

milliseconds for Arduino controller. So we

divided the product of 400 and 2303 with

50 it result it approx. 19708 millisecond

.hence through this way we achieved our

task and made the VFD.


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4. RESULTS AND DISCUSSIONS

The project’s main goal is to convert

conventional frequency of 50 Hz into

desirable frequency of 400 Hz, as many

machines and devices operate on this

frequency like radars. For calculation of

results a digital oscilloscope is used. The

digital oscilloscope shows the desired

waveforms of line to line and line to

neutral voltages of a three-phase 6 pulse

inverter circuit. Frequency and other

parameters like time period, rise time,

fall time and RMS voltages are also

determined.

The project is capable of obtaining

desired frequencies other than only the

reference frequency i.e. is 400Hz. We

will obtain calculations for different

frequencies for verifying our results

accuracy.

4.1 CASE 1 (50 Hz)

The desired frequency is fed to the

arduino through the keypad feature and

the oscilloscope displays the required

frequency that is converted with help of

6 pulse driver circuitry and VFD together.

In case 1, the desired frequency is50 Hz

and the oscilloscope shows the required

line voltage waveform and measures

parameters for e.g. 49.26 Hz.

Formula can be used to calculate the

time period of the desired frequency by

general formula: T=1/f

Input=50Hz

Full time=1/50= 0.02sec.

Conversion in micro second:

0.02*1000*1000= 20,000 µs.

Output= 49.26Hz

Full time=1/49.26=0.0203

Conversion in micro second:

0.0203*1000*1000= 20,300 µs.

Now the difference between input full

time and output full time is due to the

delay added by the arduino [4]. Figure 10

(a) and (b) illustrate the line voltages and

phase voltages respectively, while (c)

shows the measured parameters, with

help of a digital oscilloscope.

Figure 10 (a): Line voltages

Figure 10 (b): Phase voltages

Figure 10 (c): Measured Parameters


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4.2 CASE 2 (400 Hz)

The desired frequency is fed to the

arduino through the keypad feature and

the oscilloscope displays the required

frequency that is converted with help of

6 pulse driver circuitry and VFD together.

In case 1, the desired frequency is50 Hz

and the oscilloscope shows the required

line voltage waveform and measures

parameters for e.g. 362.32 Hz.

Formula can be used to calculate the

time period of the desired frequency by

general formula: T=1/f

Input=400Hz

Full time=1/400= 0.0025sec.

Conversion in micro second: 0.0025

*1000*1000 = 2500µs.

Output=362.32 Hz

Full time=1/362.32= 0.002759sec.

Conversion in micro second: 0.002759

*1000*1000 = 2760µs.

Now the difference between input full

time and output full time is due to the

delay added by the arduino. Figure 11(a)

and (b) illustrate the line voltages and

phase voltages respectively, while (c)

shows the measured parameters, with

help of a digital oscilloscope.

Figure 11 (a): Line voltages

Figure 11 (b): Phase Voltages

Figure 11 (c): Measured Parameters

5. FUTURE RECOMMENDATIONS

The Project has a tendency to be

upgraded in near future by integrating it

with any Renewable energy resources i.e.

Solar, Wind etc. Moreover, portability of

project can also be improved and more

work can also be done to make it a more

marketable and standalone product in

foreseeable future.

6. CONCLUSION

This project was chosen to solve the

problem of rotary converters, are used to

convert frequency for radars, induction

motors and in aircrafts. The main goal of

the project was to design and fabricate a

frequency converter that could convert

frequency from 50 Hz to 400 Hz and is


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feasible, cost effective and most

importantly concise and compact so that

it can be easily carried to places of need.

As the rotary converters are of very large

size the repair, maintenance and

transport of it was a major issue. The

frequency converter in the project was

designed to achieve frequency of 400 Hz

AC three-phase. As for the milestones

achieved at the end of the project, not

only all the goals set in the start were

achieved successfully but some additional

tasks were also performed and tested

successfully. The additional tasks

included installation of LCD and keypad

with arduino. As for the learning process,

a lot was learnt during the course of the

project. The project helped have a

clearer concept of some major

phenomenon in the field of electronics. It

also helped in building a more practical

approach and the problems relating to

implementations of different circuit

elements and topologies like transistor

switching, DC-DC converters, gate

drivers, Microcontrollers and high power

MOSFETs, and frequency drives. Lastly,

the project helped us in developing skills

on working on our own and in establishing

technical skills in field of engineering and

technology.

REFERENCES

[1] Bose, Upama, K. Divya, Vallathur

Jyothi, and Sreejith S. 2014.

Performance analysis of four

switch three-phase inverter-fed

induction motor drive, Power and

Energy Systems Conference:

Towards Sustainable Energy, 2(1)

, pp.1-6.

[2] S Satar, Mohamad Nasrul Abdul,

and Dahaman Ishak. 2011.

Application of Proteus VSM in

modeling brushless DC motor

drives, 4th International

Conference on Mechatronics,

4(11), pp. 3-7.

[3] Muhammad H. Rashid. 2003. Power Electronics Handbook, 3rd Edition, Pearson.

[4] Saied, Mohamed H., M. Z. Mostafa, T. M.Abdel- Moneim, and H. A. Yousef. 2012. New 13-space vector diagram for the three-phase six switches voltage source inverter, IEEE International Symposium on Industrial Electronics, 9(12), pp. 402-407

[5] Robert W. Erickson, Dragan Maksimovic. 2001. Fundamentals of Power Electronics, 2nd edition, Kluwer Academic Publishers.

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MDSRC - 2017 Proceedings, 27-28 December, 2017 …MDSRC - 2017 Proceedings, 27-28 December, 2017...

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