Power electronics overview

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“IN THE NAME OF ALLAH THE MOST MERCIFUL AND

THE MOST BENEFICIAL”

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POWER ELECTRONICS

Presented By:

Engr.Tafseer AhmedBS in Electrical (Electronics) Engineering

CIIT, Abbottabad

a.tafseer@gmail.com

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What is Power Electronics

Power electronics deals with the applications of power semiconductor devices such as Thyristor and transistors for the conversion and control of electrical energy at high power levels.

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Relationship of Power Electronics

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Elements of Power Electronics

• Analogue circuits

• Control Systems

• Power Systems

• Electronics Devices

• Electric Machines

• Numerical Simulation

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POWER ELECTRONICS MAIN AREAS

• As the technology for the power semiconductor devices and integrated

circuit develops, the potential for applications of power electronics become

wider. The power semiconductor devices or power electronic converter fall

generally into four categories :

• Thyristor Devices

• AC to DC Converter (Controlled Rectifier)

• DC to DC Converter (DC Chopper)

• AC to AC Converter (AC voltage regulator)

• DC to AC Converter (Inverter)

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Diagram Block of Converters

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• AC to DC Converters: An AC to DC converter circuit can convert AC

voltage into a DC voltage. The DC output voltage can be controlled by varying the firing angle of the thyristors. The AC input voltage could be a single phase or three phase.

• AC to AC Converters: This converters can convert from a fixed ac input voltage into variable AC output voltage. The output voltage is controlled by varying firing angle of TRIAC. These type converters are known as AC voltage regulators.

• DC to DC Converters : These converters can converte a fixed DC input voltage into variable DC voltage or vice versa. The DC output voltage is controlled by varying of duty cycle.

• DC to AC Converters: These converters can convert a constant DC input voltage into a variable AC voltage with variable frequency.

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1.Uncontrolled turn on and off (Power Diode)

2.Controlled turn on uncontrolled turn off (Thyristors)

3.Controlled turn on and off characteristic (Power Transistor, BJT, MOSFET, GTO, IGBT)

4.Continuous gate signal requirement (BJT, MOSFET, IGBT)

5.Pulse gate requirement (SCR(Silicon-Controlled Rectifier) , GTO)

6.Bidirectional current capability (TRIAC)

7.Undirectionalcurrent capability (SCR, GTO, BJT, MOSFET, IGBT)

POWER ELECTRONIC SWITCHING DEVICES

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COMMONLY USED DEVICES

• Power Diodes• Power Transistors• Thyristor Family• SCR( Silicon Controlled Rectifier)• SCS( Silicon controlled Switch)• GTO( Gate Turnoff Thyristor )• The DIAC• The TRIAC• MCT( The MOS-Controlled Thyristor)

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Devices Along with Symbols & Characteristics

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Power Ratings of Devices

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Ratings of Power Devices

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Applications of Power Devices

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Control Characteristics of Devices

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Control Characteristics of Devices

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Uncontrolled Rectifiers (AC to DC)

( )

2 mo average

VV

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Controlled Rectifier( AC to DC)• AC to DC Converters -Single phase, half wave AC to DC converter

Input voltage

Output average voltage :

rms value of Output voltage :

Waveform of single-phase, half wave AC to DC converter α

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AC-DC Rectifier( Full Wave)

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( ) (1 cos )mo

VV average

1 sin 2(( ) )

22m

rms

VV

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AC-AC (Voltage Regulator)

1/ 2

( )

1 sin 2

22m

o rms

VV

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AC to DC Converters

Single phase, Full wave AC to DC converter

The average output voltage can be found from :

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AC to DC Converters Three-phase, Half wave AC to DC converter

If the phase voltage is : van= Vm Sin(wt). Theaverage output voltage for a continuous load current is :

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AC to DC Converters Three-phase, Full Wave AC to DC converter

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DC-DC CONVERTER (DC Chopper)

• In many industrial application , DC-DC converter is required to convert a fixed-voltage DC source into a variable-voltage DC source. Like a transformer, DC-DC converter can be used to step down or step up a DC voltage source.

• Application :

Traction motor control in electric automobiles, trolley cars, marine hoists, forklift trucks, mine haulers, etc

• Advantages :

High Efficiency and fast dynamic response

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DC-DC CONVERTER (DC Chopper)Principle Of Step-Down Operation

When the switch SW is closed for a time t1, the input voltage Vs appears across the load Vo = Vs. If the switch remains off a time t2, the voltage across the load is zero, Vo= 0.

The converter switch SW can be implemented by using Transistor, MOSFET, GTO, IGBT, BJT, etc.

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The average output voltage is given by :

The average output current is given by :

The rms output voltage is given by :

=

Where : T is the chopping period

k = t1/T is the duty cycle

f = 1/T is chopping frequency

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STEP UP DC to DC CONVERTER

When switch SW is closed for t1, the inductor current rises and energy is stored in the inductor L. If the switch SW is opened for time t2, the energy stored in the inductor is transferred to load through diode D1and the inductor current falls.

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When this DC to DC converter is turned on “switch SW is closed, the voltage across the inductor L is :

And this gives the peak-to-peak ripple current in inductor as

The average output voltage is :

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Buck – Boost Regulators

• A buck – boost Regulator provides an output voltage that may be less than or greater than the input voltage- hence the name "buck-boost"; the output voltage polarity is opposite to that of the input voltage. this regulator is also known as an inverting regulator.

• The circuit operation can be divided into two modes. during mode 1, transistor Q1 is turned on and diode Dm is reversed biased. the input current, which rises flows through inductor L and transistor Q1. During mode 2, transistor Q1 is switched off and the current, which was flowing through inductor L, would flow through L, C, Dm, and the load. The energy stored in inductor L would be transferred to the load and the inductor current would fall until transistor Q1 is switched on again in the next cycle. The equivalent circuit for the modes are shown in the next slide.

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DC-AC Converter (Inverter)

1( )

40.90

2s

o rms fundamental S

VV V

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Examples of Some

Applications

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