INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
INTERNATIONAL CONFERENCE ON MODELLING AND SIMULATION IN ENGINEERING AND TECHNOLOGY ICMSET-2014, 15-16 FEBRUARY,
2014
An Unity PF Controlled Rectifier Driving a Shunt
DC Motor for Power Quality application
1
1
Dipali V.Patil, 2Madhuri S.Chaudhari
M.E(E&P), V.B.K.C.O.E Malkapur Dist-Buldhana,
2
M.E(EPS),S.S.B.T.C.O.E.T Bambhori,Jalgaon
Emails: patildipa1691@gmail.com ,cmadhu20@gmail.com
Abstract— This paper describes a technique to achieve low
harmonic and unity power factor for a three-phase controlled
rectifier. The proposed controlled rectifier consists of a
thyristor bridge, three bi-directional switches, and a current
shaping network. The bi-directional switch is switched at
double the line frequency. The current shaping network
consists of two capacitor and three resistors. The scheme
provides a simple upgrading to controlled rectifier hased DC
drives. THD and power factor improvements are acceptable.
The output DC voltage characteristic is similar with capacitor
smoothing rectifier. This scheme is suitable for application at
medium to high power level DC motor or a front end to AC
motor drive.
Keywords-AC-DC power conversion, converters, harmonic
distortion, controlled rectifier, power factor.
I. INTRODUCTION
Linear load torque is a common load in industrial
applications. Torque for this type of loads will be in the
category of weight lifting such as, conveyor belt, hoist, and
winch roller. These load torques are directly proportionate to
speed. Even the proliferation of AC variable speed drives is
increasing in this area, DC motor driven by a three phase
controlled rectifier is still an attractive option. The later
option still provides a mature, low-cost, reliable and robust
solution for industrial needs.
However, it is commonly known that the application of a
three phase controlled rectifier affects the power quality.
Input current of a phase-controlled rectifier is highly
distorted especially at higher delay angles. Its current
contains 5th, 7th, 11th, etc harmonics.
Significant effort is required to reduce the harmonics to
cope with the IEEE 519 standard Installing a bulky passive
or active filter, modifying the controlled rectifier to be a 12pulses controlled rectifier and applying the current injection
method are some of the methods used to reduce the input
current harmonics of a controlled rectifier.
This paper focus on reducing the input current harmonics
of the DC motor driven by a three phase controlled rectifier
by applying the current injection method. The method is
chosen as it offers several advantages like lightweight,
cheap, robust, and it is only a minor retrofit to existing
system. With a proper parameter calculation, input current
THD as low as 5% can be achieved in a wide enough
operating area. Displacement factor is another factor that
affects the input power quality. This factor with nonsinusoidal input current affect the power factor as described
in equation (1) below:
Theoretically, power factor of about 0.9549 (nearly ideal)
can be reached when firing angle (α) is zero [11].However,
as output voltage depends on the firing angle, it is not
possible for the rectifier to operate at zero firing angle all the
time.
II. CURRENT INJECTION METHOD
For three-phase rectifiers, a promising approach is to
reduce the input current harmonics by injecting triplen
harmonic to input side of the rectifier. It was investigated by
Ametani [4]. Low power processing, no resonance problem,
and simple upgrade to current existing three phase rectifier
is several factor that led to further investigation on the
current injection technique.
Fig. 1
Typical Current Injection Circuit
The current injection technique consists of two main part,
current injector and current injection network. The current
injector can be implemented using zigzag connected
transformer [2,6], inductor-capacitor injector, special
magnetic device injector, delta-star transformer, and bidirectional switches [4,5]. It functions is to inject the current
generated by the current injection network to the input side
of the controlled rectifier. The current injection network is
responsible for generating the third harmonic current. It can
ISSUE 3 VOL 3 JUNE-JULY ICMSET 2014 PROCEEDINGS
INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
INTERNATIONAL CONFERENCE ON MODELLING AND SIMULATION IN ENGINEERING AND TECHNOLOGY ICMSET-2014, 15-16 FEBRUARY, 2014
be implemented using passive or active [5,7] approach.
Pejovic [12] stated that in the case of optimal power
injection, the power taken by current injection circuit is
8.571% resulting in THD equal to 5.125%. Further
enhancement in this method will be around current shape
and current injector circuit to gain a lightweight, simple and
robust method while maintaining optimal power processing
and THD. Figure 1 shows typical circuit configuration of the
current injection method.
III. IMPROVED 3-PHASE CONTROLLED RECTIFIER WITH HIGH POWER
FACTOR
Lightweight, low cost, and high performance are basic
criteria for the proposed topology. Among third harmonic
current injection technique, Maswood et all [7] indicated a
mean to eliminate the injection transformer and replace it
with three bi-directional switches. Pegovic [12] proposed a
simple current shaping network that consists of three
resistors and two capacitors. The absence of inductor in this
current shaping network makes this topology simple, cheap,
and lightweight. Since all requirements have been satisfied
by Pejovics’ method, the proposed method for input power
quality improvement for three-phase controlled rectifier with
current injection is based on its scheme. Fig. 2 describe the
complete circuit of the proposed method.
From figure 4, iC can be found as:
Through substitution one can get the following
equation:
Hence, it can be found that
With Rodd=3Re it can be calculated that:
In a similar
way, the even component of the injection current is found
as:
Based the above derivations, the following improved
current injection network is suggested in Fig.3.
Fig. 2 Proposed transformer less three-phase
controlled rectifier circuit
From current shaping equations above, it can generally be
observed that load should be highly inductive and it should
only experience DC component. As injection circuit only
contains AC component, a series capacitor is needed to
block DC current in the three-phase controlled rectifier DC
bus. It is assumed that the series capacitance is high enough
to provide low capacitive reactance for all AC component
frequency.
In the circuit of Fig.4, if VAC and VBC is defined as
Fig. 3 Adopted Improved current shaping network
1. Control Scheme for Bidirectional Switch
After passing series capacitor with negligible voltage drop,
VAC and VBC will only contain AC component
In three-phase controlled rectifier, at any given time, there
are two phases in conduction state and one in nonconduction state. With this proposed method, line that is in
ISSUE 3 VOL 3 JUNE-JULY ICMSET 2014 PROCEEDINGS
INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
INTERNATIONAL CONFERENCE ON MODELLING AND SIMULATION IN ENGINEERING AND TECHNOLOGY ICMSET-2014, 15-16 FEBRUARY, 2014
un-conducted state will be connected to the injection circuit
by means of a bi-directional switch. As there are three lines
utilized, it should be determined which line is to be
connected. To determine which line that should be
connected to current shaping network, can be done by
analyzing the thyristor gating timing table illustrated in table
I below where switch S1-S6 are replaced by thyristors T1T6:
Table 1. Thyristor Decoding
Gating in
T1
T2
T3
T4
T5
T6
SR
OFF
OFF
ON
OFF
OFF
ON
Bi-directional switch state
SS
OFF
ON
OFF
OFF
ON
OFF
ST
ON
OFF
OFF
ON
OFF
OFF
Fig. 4. Bi-
demonstrate the effectiveness of the current injection
method, it is important to understand the correlation of the
dc motor input voltage and input current in conjunction with
controlled rectifier delay angle. It is so because voltage and
current parameters determine the resistive equivalent load
(Re) value. These voltage and current values determine the
resistors value of the current shaping circuit in the scheme.
Correlation between Re, dc motor input voltage, and its
input current is described in the equation below:
It has been conducted to verify the Re value resulted from
the above figure 4.2 It stated the Re in percentage of its
rated value. From the figure 4.2, it can be seen that the Re
value varies linearly in a narrow band of about 5% if the
controlled rectifier works in the range of 0 up to 50 degree
delay angle.
Since the network in the current injection circuit utilizes
fixed value resistors, controlled rectifier operations in the
range of 0 to 50 degree delay angle can be employed. In that
range, the resistive equivalent load only changes slightly and
in a linear fashion. Hence, effectiveness of this scheme is
limited up to 50 degrees delay angle.
directional switches control scheme
If T1 or T4 are triggered (see Fig.2), than phase R will
enter into conduction state. It will leave the conduction state
while phase S is activated by triggering T3 or T6. Phase S
will leave it conduction state while phase T is activated by
triggering T2 or T5. It can be shown from table I that if T1
or T4 are triggered, phase T should be connected to current
shaping network. This is because when T1 or T4 are
triggered phase R and phase S are in conduction state while
phase T are left un-conducted. In other word, switch on
phase T are controlled by trigger on T1 or T4, respectively
switch on phase S are controlled by trigger on T2 or T5, and
switch on phase R are controlled by trigger on T3 or T6.
IV. LINEAR LOAD TORQUE DC SHUNT MOTOR DRIVEN BY
THREE-PHASE CONTROLLED RECTIFIER
Fig.5. DC shunt motor driven by a controlled rectifier
This model was developed to investigate the voltage and
current of a shunt dc motor with linear load torque when
supplied by a three-phase controlled rectifier. The model is
shown in figure 4.1. As the aims of this research is to
Fig.6. Resistive equivalent load value as delay angle change
V. APPLICATION OF THE CURRENT INJECTION SCHEME TO
THE DC MOTOR DRIVE
Fig.7. DC shunt motor driven by a controlled rectifier with the proposed
current injection scheme.
To reduce the input current THD of the controlled, rectifier the
proposed current injection scheme is applied. Two capacitors, three
resistors, and three bi-directional switches form the current
injection circuit. The current injection circuit is shown in the
ISSUE 3 VOL 3 JUNE-JULY ICMSET 2014 PROCEEDINGS
INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
INTERNATIONAL CONFERENCE ON MODELLING AND SIMULATION IN ENGINEERING AND TECHNOLOGY ICMSET-2014, 15-16 FEBRUARY, 2014
dashed box of figure 4.3. The resistor (R) value is determined by
the equation below:
R = 3Re
VI. RESULT
Several models have been developed to investigate the
proposed circuit. Performance are measured based on the
following three parameters.
1.Input current total harmonic distortion (THD)
2. Rectifier efficiency (
Fig. Voltage and Current shape of a thyristor rectifier at α=40 without the
)
proposed current injection scheme.
3.Power factor (Cos φ)
I1 is defined as fundamental frequency current.
Two variables that are used to investigate the converter
performance are
1. Delay angle (α)
2. Variation of input line inductance (Lin)
By varying these two variables, performance of the
modified controlled rectifiers is analyzed. Table 4 and figure
Fig. Current spectra at α=40 without current injection
5.1 to 5.7 show the results.
Table 2. Performance Parameters with The Proposed Technique
Without Input Inductance (Lin)
THD
η
COSφ
α=0
4.797%
91.001%
0.999
THD
η
COSφ
13.502%
85.523%
0.991
α=20
α=40
α=60
5.1158%
7.585% 18.739%
78.7938% 52.868% 33.199%
0.9928
0.997
0.983
2 mH Input Inductance (Lin)
11.8529% 11.792% 15.629%
86.8790% 68.914% 45.492%
0.9928
0.993
0.998
Fig. 5.1 and 5.6 show input voltages and currents at the
controlled rectifier at delay angle (a) 40'. Fig. 5.3 shows
voltage and current waveform without input line inductance
whereas figure. shows voltage and current with 2 mH input
line inductance. Fig. 5.5 and 5.7 show the input current
spectra. Fig. 5.1 and 5.2 shows voltage-current and current
spectra of common controlled rectifier without It can be
seen in fig. 5.3 that at some point, there are some glitches in
the current wave shape. The glitches occur while rectifier
leave conduction region and enter current injection scheme.
into nonconductive region. This is due to thyristor
commutation process. Comparing fig. 5.3 through 5.6 with
those in fig. 5.1 and 5.2 for a normal thyristor rectifier, one
can see the significant improvement in the current waveform
with the proposed scheme.
Fig. Voltage and Current shape at a=40 without line inductance
Fig. Current spectra at α=40 without line inductance
ISSUE 3 VOL 3 JUNE-JULY ICMSET 2014 PROCEEDINGS
INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
INTERNATIONAL CONFERENCE ON MODELLING AND SIMULATION IN ENGINEERING AND TECHNOLOGY ICMSET-2014, 15-16 FEBRUARY, 2014
near unity power factor converter with retrofitting potential
for existing thyristor based drives. The interface draws input
currents with a harmonic distortion of less than 5% and
provides a regulated dc voltage at the output. This approach
can be applied to provide a three-phase utility interface for
most of the power electronics equipment
VIII. REFERENCES
[1]
[2]
Fig. Voltage and Current shape at α=40 with 2mH line inductance
[3]
[4]
[5]
[6]
Fig. Current spectra at α=40 with 2mH line inductance
[7]
[8]
[9]
[10]
[11]
Fig .5.7 Load voltage
The load voltage is DC with some ripple as evident in
fig.5.7 With a highly inductive load such as DC motor
armature circuit, the load current is expected to be a smooth
DC.
VII. CONCLUSION
A linear torque loaded DC motor supplied by a three
phase controlled rectifier. It is already discussed in above fig
4.1 From this model, the resistive equivalent load value is
determined under various operating point. Re value is used
to determine the individual resistor value of the current
injection circuit. It can be found that in a narrow band,
resistive equivalent load value changes linearly if the
controlled rectifier operates within 0 to 50 degree delay
angle. The proposed current injection technique maintains
AC mains current harmonics low and can be considered a
[12]
[13]
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