Transcript File - Go ELECTRONICS

Application of power
electronics
CONTENT:
APPLICATIONS OF POWER
ELECTRONICS
SMPS-(Switch mode power supply)
UPS-(Uninterrupted power supply)
SINGLE PHASE CYCLOCONVERTERS
SMPS-[switch mode power supply]
 DIAGRAM
WORKING:
INPUT RECTIFIER AND FILTER STAGE The function of rectifier is to convert AC voltage into
unregulated DC voltage.
 Which is then sent to the filter capacitor.
 If the SMPS has AC input, then its first job is to convert the input
to DC.
INVERTER CHOPPER STAGE It converts DC,whether directly from input or from rectifier and filter
stage to AC running through power oscillator.
 The output voltage is optically coupled to the input and thus very
tightly controlled.
OUTPUT TRANSFORMER This converts the voltage up or down to the required
output level on its secondary winding.
 The output transformer in the block diagram serves
this purpose.
OUTPUT RECTIFIER AND FILTER The rectified output is then smootched by a filter
consisting of inducters and capacitors.
 For higher switching frequencies, components with
lower capacitnce and inductance are needed.

CHOPPER CONTROLLER-
Feedback circuit monitors the output voltage and
compares it with a referance voltage , which is set
manually or electronically to the desired output.
 The chopper controller is used as switching regulator
to generates accurate output DC voltages.
TYPES OF SMPS:
1. Fly-back SMPS
2. Feed forward SMPS
3. Push pull SMPS
4. Full bridge SMPS
1) Fly-back SMPS:
 Fly-back SMPS is the most commonly used SMPS circuit for
low output power applications where the output voltage
needs to be isolated from the input main supply.
 Input to the circuit is generally unregulated dc voltage
obtained by rectifying the utility ac voltage followed by a
simple capacitor filter.
Circuit diagram of Fly-back SMPS
Fly-back SMPS:
 The circuit can offer single or multiple isolated output voltages and
can operate over wide range of input voltage variation.
 In respect of energy-efficiency, fly-back power supplies are inferior to
many other SMPS circuits but its simple topology and low cost makes
it popular in low output power range.
Output waveforms of Fly back SMPS
OUTPUT EQUATION IS GIVEN AS;
Vout=Vin x (n2/n1) x (Ton x f) x (1/(1(Ton x f)))
where:
n2 = secondary turns on T1
n1 = primary turns on T1
Ton = conduction time of Q1
The control circuit monitors Vout and
controls the duty cycle of the drive
waveform to Q1
2) Feed forward SMPS:
 The 'extra' winding of a forward converter's transformer
ensures that at the start of a switch conduction, the net
magnetisation of the transformer core is zero.
 If there were no extra winding, then after a few cycles the
transformer core would magnetically saturate, causing the
primary current to rise excesively, so destroying the switch
(ie transistor).
Circuit diagram of feed
forward/forward SMPS
FORWARD SMPS
 The diode on the secondary that is connected between the 0V line
and the junction of the inductor and rectifiying diode is often
called the 'flywheel diode‘.
 The diode on the secondary that is connected between the 0V line
and the junction of the inductor and rectifiying diode is often
called the 'flywheel diode'.
Output waveform of feed forward SMPS
Output equation is given As:
 The output voltage of a forward converter is equal to the
average of the waveform applied to the LC filter and is given
by:
 Vout = Vin x (n2/n1) x (Ton x f)
 n2 = secondary turns on T1
 n1 = primary turns on T1
 Ton = conduction time of switch
 f = frequency of operation
3) Push pull smps
Circuit diagram of push pull smps
Push pull smps:
 The push pull converter belongs to the feed forward converter
family.
 With reference to the diagram above, when Q1 switches on,
current flows through the 'upper' half of T1's primary and the
magnetic field in T1 expands.
 The expanding magnetic field in T1 induces a voltage across T1
secondary, the polarity is such that D2 is forward biased and D1
reverse biased. D2 conducts and charges the output capacitor
C2 via L1. L1 and C2 form an LC filter network

When Q1 turns off, the magnetic field in T1 collapses, and after a
period of dead time (dependent on the duty cycle rough the 'lower'
half of T1's primary and the magnetic field in T1 expands. Now the
direction of the magnetic flux is opposite to that produced when
Q1 conducted.
 The expanding magnetic field induces a voltage across T1 secondary,
the polarity is such that D1 is forward biased and D2 reverse biased.
D1 conducts and charges the output capacitor C2 via L1.
waveforms:
OUTPUT EUATION IS GIVEN AS:
 These criteria must be satisfied by the control and drive
circuit and the transformer.
 The output voltage Vout equals the average of the waveform
applied to the LC filter:
 Vout = Vin x (n2/n1) x f x (Ton,q1 + Ton,q2)
Where;
 Vout=Average output voltage –Volts
 Vin=Supply Voltage –Volts
 n2=half of total number of secondary turns
 n1=half of total number of primary turns
 f = frequency of operation – Hertz
 Ton,q1 = time period of Q1 conduction – Seconds
 Ton,q2 = time period of Q2 conduction – Seconds
 The control circuit monitors Vout and controls the duty
cycle of the drive waveforms to Q1 and Q2.
 If Vin increases, the control circuit will reduce the duty cycle
accordingly, so as to maintain a constant output.
 Likewise if the load is reduced and Vout rises the control
circuit will act in the same way.
 Conversely, a decrease in Vin or increase in load, will cause
the duty cycle to be increased. The diagram below shows
associated waveforms from the push pull converter.
4) Full bridge smps:
Circuit diagram of full bridge smps
Full bridge SMPS:
 The full bridge converter is similar to the push pull converter, but
a centre tapped primary is not required.
 The reversal of the magnetic field is achieved by reversing the
direction of the primary winding current flow. This type of
converter is found in high power applications.
 For the full bridge converter, the output voltage Vout equals the
average of the waveform applied to the LC filter
 The full bridge converter is similar to the push pull
converter, but a centre tapped primary is not required.
 The reversal of the magnetic field is achieved by reversing
the direction of the primary winding current flow. This
type of converter is found in high power applications.
 For the full bridge converter, the output voltage Vout equals
the average of the waveform applied to the LC filter
Output euation is given as:
 Vout = Vin x (n2/n1) x f x (Ton,q1 + Ton,q2)
 Vout=Output Voltage –Volts
 Vin=Input Voltage – Volts
 n2=0.5 x secondary turns
 n1=primary turns
 f = operating frequency – Hertz
 Ton,q1 = Q1 conduction time – Seconds
 Ton,q2 = Q2 conduction time – Seconds
 Diagonal pairs of transistors will alternately conduct, thus
achieving current reversal in the transformer primary. This can
be illustrated as follows - with Q1 and Q4 conducting, current
flow will be 'downwards' through the transformer primary, and
with Q2 and Q3 conducting, current flow will be 'upwards'
through the transformer primary.
 The control circuit monitors Vout and controls the duty cycle
of the drive waveform to Q1, Q2, Q3 and Q4.
 The control circuit operates in the same manner as for the
push-pull converter and half-bridge converter, except that
four transistors are being driven rather than two.
UPS-(unregulated power supply)
WORKING
AC MAINS SECTION It receives AC supply, filters it and rectifies it to desired level.
INVERTER AND FILTER When power is given there,this delivers constant 230volt
AC,50Hz.o/p to load.
 When power is lost or off, this takes 12v DC from battery and
converts it into 230v and given to output load.
BATTERY AND BATTERY CHARGER When AC supply is available this section charges the battery
through battery charger circuit.
 This circuit converts input AC to desired DC and charges the
battery.
STATIC SWITCH/CONTACTOR In event of power failure the inverter is connected to the load with
the help of static contactor switches.
TYPES OF UPS:
1)OFF-LINE UPS:
2)ON-LINE UPS:
OFF-LINE UPS:
WORKING:
 Transfer switch is set to choose filtered AC i/p as the primary
power source and switches to battery as backup source.
 When that happens, transfer switch must oparates the switch the
load over to the battery/inverter backup power source.
 This circuit also provides adequate noise filtration and surge
suppretion.
The off-line UPS runs the computers of the normal utilities power
until detects the problems. At that point, it very quickly turn on
power inverter an runs the computers of the UPS’s battery.
In this type of UPS , the battery is charged when AC mains are on
and as soon as AC mains are off,the battery discharges and supplies
power to the PC as shown in figure.
High switching is involved in off-line UPS.
ADVANTAGES1.
Lower in cost compared to on-line UPS.
 DISADVANTAGES1.
High switching is required otherwise there is possibility that cut in
power and reboot the system.
ON-LINE UPS:
WORKING:
 In the on line UPS the primary power source is UPS’s battery and
utility power is the secondary power source.
 The on –line type of UPS, in addition to providing protection
against complete failure of the utility supply.
 In online UPS,the power for the system supplied by the batteries
continuousely,i.e., battery charged continuosely.
 Then battery provides DC voltage to inverter. Here inverter convert
DC to 230v, 50Hzs AC voltage and given to computer system.
 Thus in this type of UPS the switching is not involved spikes are not
generated.
 Under normal opertion the on-line UPS is always uses the battery as
its main source of power and the line power is the secondary source of
power
ADVANTAGES1.
2.
The switching is not involved,thus avoids reseting of PC and spikes
generation.
These UPS provides large protection by breaking down and
reasserting the power.
 DISADVATAGES1.
2.
It generates more heat.
UPS batteries require more frequent replacement since they run
constantly.
SINGLE PHASE CYCLO CONVERTER:
Circuit diagram of single phase cycloconverter
SINGLE PHASE
CYCLOCONVERTER:
 The cyclo-converter generally consists of two converter
group one of which is called the positive converter and
another one is negative converter.
 Generally the switching device of positive converter group
goes in conduction during positive half cycle whereas the
negative converter group goes in conduction during negative
half cycle of the input wave shape.
 The control circuit controls the operation of each converter
group and provides synchronization of the output signal with
the input signal.
 The basic circuit diagram of a single phase cyclo-converter is
shown in the fig.
 The single phase cycloconverter is a 2 pulse cyclo-converter
because there are two phase controlled pulses per cycle of the
output phase .
waveforms:
 The positive converter operates whenever the load current
is positive with the negative converter remaining idle
during this period.
 In a similar manner, the negative load current is supplied
by the negative converter with the positive converter
remaining idle during this period .
 A cycloconverter circuit is comprised of power, control
and filter sections