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    PE Lecture 1

    Uploaded by

    Ahmed Kamran
    Power electronics deals with using power semiconductor devices like thyristors and transistors to efficiently convert and control electrical power at high levels. These devices can be used as switches to precisely control voltage, current, and frequency. When used as switches operating at high frequencies, power loss is minimized as the devices are either fully on with near-zero voltage or fully off with near-zero current. Common power electronics circuits include rectifiers, choppers, inverters, and static switches.

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    PE Lecture 1

    Uploaded by

    Ahmed Kamran
    149 views20 pages
    Power electronics deals with using power semiconductor devices like thyristors and transistors to efficiently convert and control electrical power at high levels. These devices can be used as switches to precisely control voltage, current, and frequency. When used as switches operating at high frequencies, power loss is minimized as the devices are either fully on with near-zero voltage or fully off with near-zero current. Common power electronics circuits include rectifiers, choppers, inverters, and static switches.

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    PE Lecture 1 (1)

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    Power electronics deals with using power semiconductor devices like thyristors and transistors to efficiently convert and control electrical power at high levels. These devices can be used as switches to precisely control voltage, current, and frequency. When used as switches operating at high frequencies, power loss is minimized as the devices are either fully on with near-zero voltage or fully off with near-zero current. Common power electronics circuits include rectifiers, choppers, inverters, and static switches.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    149 views20 pages

    PE Lecture 1

    Uploaded by

    Ahmed Kamran
    Power electronics deals with using power semiconductor devices like thyristors and transistors to efficiently convert and control electrical power at high levels. These devices can be used as switches to precisely control voltage, current, and frequency. When used as switches operating at high frequencies, power loss is minimized as the devices are either fully on with near-zero voltage or fully off with near-zero current. Common power electronics circuits include rectifiers, choppers, inverters, and static switches.

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    © All Rights Reserved
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    Download as pptx, pdf, or txt
    of 20

    MtE-313

    Power Electronics
    Lecture No. 1
    Electric Power, Electronics and Control
    • Power Electronics deals with the application
    of power semiconductor devices, thyristors
    and transistors, for the conversion and control
    of electrical energy at high power levels.
    • Controlled parameters:
    • Voltage, current, frequency
    • Simple Rectification
    • Rectification with voltage level adjustment
    Why Power Electronics?
    • Transfer of Electrical power from source to
    load
    – Varying supply voltage (Variable Transformer)
    – Inserting a regulator (Variable resistor)
    • Semiconductor devices used as switches:
    • Small, inexpensive and efficient
    • Control power automatically
    A Rheostat as a Control Device
    • From maximum Power Transfer Theorem
    – Conversion is only 50%
    • Overheating
    – Rheostat must be physically larger to dissipate
    additional heat
    • Poor efficiency means large losses
    A switch as a control Device
    • Efficiency is 100%
    – No power loss
    • Switch can not be set to intermediate
    positions to vary power
    • Same effect can be created by periodically
    turning the switch on and off.
    Power Semiconductor switches
    • Diodes
    • Bipolar junction transistors (BJT)
    • Metal-oxide semiconductor field-effect
    transistors (MOSFET)
    • Insulated-gate bipolar transistor (IGBT)
    • Silicon Controlled Rectifiers (SCR)
    • Triacs
    • Gate-turnoff thyristors (GTO)
    • MOS-controlled thyristors (MCT)
    Power Semiconductor Devices
    • Operated in switching mode
    • Operated at high frequencies
    • Power loss in the switch is small
    – Either voltage is nearly zero (switch ON)
    – Or current is nearly zero (switch OFF)
    Ideal Switch
    • It turns on and turns off in zero time
    • When the switch is on, the voltage drop across
    it is zero
    • When the switch is off, the current through it
    is zero
    • It dissipates zero power
    Other desirable characteristics
    • When on, it can carry a large current
    • When off, it can withstand high voltage
    • It uses little power to control its operation
    • It is highly reliable
    • It is small in size and weight
    • It is low in cost
    • It needs no maintenance
    Power Losses in Real Switches
    • Bipolar junction transistor
    • Two major sources of power loss
    – Conduction loss
    – Switching loss
    Conduction losses in BJT

    • POFF = VS * ILEAK
    • PON = VCE(sat) * IC
    • where IC = VS - VCE(sat) /RL ≈ VS/RL
    Switching losses in BJT
    Power Losses
    t(OFF )
    • POFF = VS * ILEAK *
    t

    • PON = VCE(sat) * IC * d
    1
    • PSW = *VCE (max) * IC (max) *[tSW (ON )  tSW (OFF ) ]* f
    6
    • where IC = VS - VCE(sat) /RL ≈ VS/RL
    Example
    • VS is 50V, RL is 5Ω, and the switch is ideal with
    no switching loss. If on-state voltage drop is
    1.5V and the leakage current is 1.5mA,
    calculate the power loss in the switch when it
    is:
    • A)on
    • B) off
    Example
    • Calculate the maximum and average power
    loss for the switch in the previous example, if
    the switching frequency is 500Hz with a duty
    cycle of 50%.
    • Pavg(ON) = PON * tON/T
    • Pavg(OFF) = POFF * tOFF/T
    • Average power loss for one cycle
    • Maximum power dissipation (PON) (last
    example)
    Example
    • VS is 120V, RL is 6Ω and the transistor is ideal
    with no conduction loss. If tSW(ON) = tSW(OFF) =
    1.5μs, calculate the average switching power
    loss at a switching frequency of 1kHz.
    1
    • PSW(avg) = *VCE (max) * I C (max)
    6
    Example
    • The transistor switch with the following characteristics controls power to a 25kW
    load,
    • IRATED = 50A, VRATED = 500V, ILEAKAGE = 1mA
    • VCE(sat) = 1.5V
    • Turn-on time tSW(ON) = 1.5μs
    • Turn-off time tSW(OFF) = 3.0μs
    • VS is 500V and RL is 10Ω. If the switching frequency is 100Hz with a duty cycle of
    50%, find:
    • On-state power loss
    • Off-state power loss
    • Maximum power loss during turn-on
    • Energy loss during turn-on
    • Energy loss during turn-off
    • On-state energy loss
    • Off-state energy loss
    • Total energy loss
    • Average power loss
    Example
    • In previous example, if switching frequency is
    increased to 100kHz with duty cycle of 50% find:
    • Energy loss during turn-on
    • Energy loss during turn-off
    • On-state energy loss
    • Off-state energy loss
    • Total energy loss
    • Average power loss
    Types of Power Electronics Circuits
    • Uncontrolled Rectifiers (AC voltage to fixed
    DC voltage)
    • Controlled Rectifiers (fixed AC voltage to
    variable DC voltage)
    • DC choppers (fixed DC voltage to variable DC
    voltage)
    • AC voltage controllers (fixed AC to a variable
    AC at the same frequency)
    Types of Power Electronics Circuits
    • Inverters (fixed DC voltage to fixed/variable AC
    voltage and frequency)
    • Cycloconverters (fixed voltage and frequency
    to variable voltage and frequency)
    • Static switches (replacing traditional
    mechanical and electromagnetic switches)

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