SMPS-(Switch mode power supply) UPS-(Uninterrupted power
supply) SINGLE PHASE CYCLOCONVERTERS APPLICATIONS OF POWER
ELECTRONICS CONTENT:
Slide 3
SMPS-[switch mode power supply] DIAGRAM
Slide 4
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.
Slide 5
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.
Slide 6
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.
Slide 7
TYPES OF SMPS: 1. Fly-back SMPS 2. Feed forward SMPS 3. Push
pull SMPS 4. Full bridge SMPS
Slide 8
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.
Slide 9
Circuit diagram of Fly-back SMPS
Slide 10
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.
Slide 11
Output waveforms of Fly back SMPS
Slide 12
V out =V in 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 V out and
controls the duty cycle of the drive waveform to Q1 OUTPUT EQUATION
IS GIVEN AS;
Slide 13
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).
Slide 14
Circuit diagram of feed forward/forward SMPS
Slide 15
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'.
Slide 16
Output waveform of feed forward SMPS
Slide 17
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: V out = V in 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
Slide 18
3) Push pull smps Circuit diagram of push pull smps
Slide 19
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
Slide 20
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.
Slide 21
waveforms:
Slide 22
These criteria must be satisfied by the control and drive
circuit and the transformer. The output voltage V out equals the
average of the waveform applied to the LC filter: V out = V in x
(n2/n1) x f x (Ton,q1 + Ton,q2) OUTPUT EUATION IS GIVEN AS:
Slide 23
Where; V out =Average output voltage Volts V in =Supply Voltage
Volts n2=half of total number of secondary turns n1=half of total
number of primary turns
Slide 24
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 V out and controls the duty cycle of
the drive waveforms to Q1 and Q2.
Slide 25
If V in increases, the control circuit will reduce the duty
cycle accordingly, so as to maintain a constant output. Likewise if
the load is reduced and V out rises the control circuit will act in
the same way. Conversely, a decrease in V in or increase in load,
will cause the duty cycle to be increased. The diagram below shows
associated waveforms from the push pull converter.
Slide 26
4) Full bridge smps: Circuit diagram of full bridge smps
Slide 27
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 V out equals the average of the
waveform applied to the LC filter
Slide 28
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 V out equals the average of the
waveform applied to the LC filter
Slide 29
Output euation is given as: V out = V in x (n2/n1) x f x
(Ton,q1 + Ton,q2) V out =Output Voltage Volts V in =Input Voltage
Volts n2=0.5 x secondary turns n1=primary turns
Slide 30
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.
Slide 31
The control circuit monitors V out 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.
Slide 32
UPS-(unregulated power supply)
Slide 33
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.
Slide 34
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.
Slide 35
TYPES OF UPS: 1)OFF-LINE UPS: 2)ON-LINE UPS:
Slide 36
OFF-LINE UPS:
Slide 37
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.
Slide 38
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 UPSs 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.
Slide 39
ADVANTAGES- 1. Lower in cost compared to on-line UPS.
DISADVANTAGES- 1. High switching is required otherwise there is
possibility that cut in power and reboot the system.
Slide 40
ON-LINE UPS:
Slide 41
WORKING: In the on line UPS the primary power source is UPSs
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.
Slide 42
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
Slide 43
ADVANTAGES- 1. The switching is not involved,thus avoids
reseting of PC and spikes generation. 2. These UPS provides large
protection by breaking down and reasserting the power.
DISADVATAGES- 1. It generates more heat. 2. UPS batteries require
more frequent replacement since they run constantly.
Slide 44
SINGLE PHASE CYCLO CONVERTER: Circuit diagram of single phase
cycloconverter
Slide 45
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.
Slide 46
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.
Slide 47
waveforms:
Slide 48
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
