EL - 324 Power Electronics – Lab Manual
Lab No. 03
PE – Lab #
03
To Execute a 1 – φ Half-wave
Controlled Rectifier using RL Load
(α = 0 ~ 180°)
Power Electronics Lab
OBJECTIVES:
The aim in this lab exercise is to determine:1.
2.
3.
4.
Control characteristic Udα with resistive load.
Effect of the type of load on the d.c. voltage formation
Effect of the type of load on the direct current formation.
Valve stress with α > 0°.
CIRCUIT DIAGRAM:
COMPONENTS LAYOUT:
APPARATUS / NECESSARY EQUIPMENT:
1.
2.
3.
4.
1 Load resistor 100Ω, 2.5A
1 Load inductance 50-200mH, 5A
1 Oscilloscope
1 multimeter
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EL - 324 Power Electronics – Lab Manual
Lab No. 03
5. Probe & Connecting wires
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EL - 324 Power Electronics – Lab Manual
Lab No. 03
DESCRIPTION OF CIRCUIT:
In previous labs, only diodes are used in power converter circuits that have no possibility of influencing
the output voltage with the converter. In this lab, the uncontrolled valves are replaced by thyristors so
that a d.c. output voltage dependent on the respective triggering can be set. This can also be called as
“Controllable converters”.
The Triggering delay of thyristor is described by triggering delay angle α.
The Arithmetical mean value of d.c. output voltage is represented by “Udα” and the voltage at α = 0° is
referred to as “Udo”.
If the thyristors are triggered later (α > 0°), the d.c. output voltage Udα of the converter concerned can be
reduced. Since a thyristor only drops back into a non-conducting state at values below the holding
current, the type of load of the controlled converter also has an influence on the value of d.c. output
voltage Udα.
In this circuit, thyristor triggering is only possible in the positive half-wave of the d.c. voltage, so
a positive voltage must also occur across the load. In the ideal case, voltage/angle area can be
adjusted from zero at α = 180° to a full positive half-wave at α = 0°.
For the consideration of voltage, with the half-wave power converter, the d.c voltage Udα is a function of
control angle “α”, so the d.c. voltage can be varied between zero and the maximum value Udo = 0.45 U.
Under the condition of a purely resistive load, the mathematical relationship is:
1 + cos α
Udα = Udo ×
(for control angle, range is 0° ≤ α ≤ 180°)
2
For the range of possibly delays, the cases of α = 45°& α = 135° have been presented below.
Figure 3.1: a) Sinusoidal input AC voltage U.
b) DC output voltage Udα for α = 45°& α = 135°.
c) Characteristic of associated voltage uAK for voltage at thyristor V1.
If a triggering angle α = 180°, the power converter cannot be triggered because the instantaneous value
of a.c. voltage is zero. If α > 180°, it cannot be triggered, since the anode of the thyristor is more
negative than the cathode during the negative half-wave so that blocking operation therefore exists for
the thyristor.
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EL - 324 Power Electronics – Lab Manual
Lab No. 03
For the consideration of current, considering the basis of a purely resistive load, once the thyristor has
triggered, the voltage and current at the load are always in phase. Since the greatest current flows
when α = 0°, the valve can be designed on the basis of formula:
Udα
The Graphical representation of the voltage ratio Udo as a function of control angle α is referred as
“Control characteristics” which are shown in the following figure:
Figure 3.2: Control characteristic of half-wave power controller with resistive load.
On one side, inductive loads store electrical energy (Wmagn=1/2 Li2), while on other side, they give this
energy up again. This means that the thyristor continues to conduct, even after polarity reversed and
the driving voltage becoming negative. The stored energy produces such a high self-induced voltage in
the coil that the current continues to be driven in the previous direction of flow at the expense of the
magnetic energy. Since an ideal coil is discharged for just as long as it was charged previously, then,
with α = 0°, there is a flow of direct current during the entire period T. The valve remains in a conductive
state and, there is, across the load, an a.c. voltage Udα whose mean value is always zero in this case.
Figure 3.3: Basic circuit of half-wave power converter with inductive load.
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EL - 324 Power Electronics – Lab Manual
Lab No. 03
Figure 3.4: Voltage and current characteristics for half-wave power converter with inductive load for α = 0°& α = 90°.
a) AC input voltage
c) Load currents
b) DC output voltages
d) Valve voltages
Energy received from the applied a.c. voltage during the positive half-wave must therefore be returned
to the system during the negative half-wave. This mode of operation is referred to as “the transition
from rectifier mode (energy import) to inverter mode (energy export)”. Since Udα = 0 V for this particular
mode, the d.c. power Pd is also 0 W.
Now, the resistive-inductive (mixed) load occurs very frequently with power converters. i.e. 0 < L/R < ∞
In respect of its behaviour as a function of τ = L/R, it lies between the two types of load. In contrast to
the current in the case of a purely resistive load ( τ = L/R = 0) an abrupt characteristic of the load
current id is not possible because of the inductive component. Similarly, larger or smaller positive and
negative voltage/angle areas occur as a function of the triggering delay angle α. Two characteristic
cases are presented in the following figure for α = 45° and α = 90°.
Figure 3.5: Voltages and Currents for half-wave power converter with resistive-inductive load.
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EL - 324 Power Electronics – Lab Manual
1.
Lab No. 03
Control characteristic Udα = f(α):
Rload =____________Ω .
1.1
Connect the output of converter to a purely resistive load.
1.2
Adjust the control angle in steps of ∆α = 36° from α = 0° to α = 180°. Observe / Check the trigger
delay of Udα for each control angle with the oscilloscope. Measure the corresponding values of Udα
with the multimeter and enter in table.
α
deg
Udα
V
Udα
Udo
1 + cos α
2
0
36
72
108
144
180
1.0
1.0
1.3
Calculate the normalized values of Udα/Udo with calculator and check with the given relationship
(1 + cos α)/2.
1.4
Transfer the values of row Udα/Udo of the table point by point to the diagram and join them up to
form control characteristic.
Udα
Udo
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
α
0
36
72
108
144
180
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deg
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EL - 324 Power Electronics – Lab Manual
2.
Lab No. 03
Effect of the type of load on the DC voltage formation:
Rload =____________Ω
Lload =___________mH
2.1
Measure voltage Udα for α = 108° for resistive load
with the oscilloscope. Transfer the voltage curve to
the grid.
2.2
Disconnect bridge at position “b” & “c”. Repeat the
voltage measurement as in 2.1 without changing
the control angle. Draw the characteristic in phase
with 2.1 on the grid.
Ud = _______________V ;
uRRM = _____________V ;
uRRM
= _______________.
Ud
2.3
Set a control angle α = 108°. Measure voltage
ud(108) with inductive load (bridge position “a” & “b”)
using the oscilloscope. Transfer the curve in
phase with 2.1 and 2.2 to the grid.
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EL - 324 Power Electronics – Lab Manual
3.
Lab No. 03
Effect of the type of load on the direct-current formation:
Rload =____________Ω
Lload =___________mH
3.1
Measure the load current id for α = 108° for
resistive load (bridge at positon “b” & “c”) indirectly
across Rmeas. Transfer the voltage characteristic
across Rmeas to the grid.
3.2
Disconnect bridge at position “b” & “c” and Repeat
the measurement as in 3.1 with a constant control
angle. Transfer the curve of the measuring voltage
in phase with 3.1 to the grid.
Transfer the curve in phase with 2.1
and 2.2 to the grid.
Ud = _______________V ;
uRRM = _____________V ;
uRRM
= _______________.
Ud
3.3
Bridge the measuring points “a” and “b” and repeat
the measurement as in 3.1 without changing the
control angle. Transfer the characteristic of the
measuring voltage with correct phasing to 3.1
& 3.2 using oscilloscope.
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EL - 324 Power Electronics – Lab Manual
4.
Lab No. 03
Valve stress with α > 0°:
Rload =____________Ω
Lload =___________mH
4.1
Set a control angle α = 108° with resistive-inductive load. Check the voltage Ud108 using the
oscilloscope.
4.2
Determine the characteristic of the valve current
by measuring voltage Ucd proportional to the valve
current using the oscilloscope. Draw the signal
curve on the grid.
Ө = ______________°.
4.3
Determine the current-flow angle of V1 from 4.2.
4.4
Measure the anode-cathode voltage of thyristor V1
(uAK) in phase with 4.2 and transfer the voltage
curve to the grid.
4.5
Determine the reverse voltags uRRM across V1 for
α = 108° from the diagram of 4.4. (using
oscilloscope).
uRRM = ______________V.
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EL - 324 Power Electronics – Lab Manual
Lab No. 03
PSPICE SIMULATION:
(Simulate the circuit provided for this lab & find the output voltages for α = 45°
α = 90° & α = 135°).
Marks Awarded: _________________ Lab Supervisor Signature/Date: ________________________
Comments: ________________________________________________________________________
__________________________________________________________________________________
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