MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
69
Performance Investigation of SVPWM
Controlled Diode Clamped and Flying
Capacitor Multilevel Converters
Vikas Shukla
Member, IEEE
Dept of EE, KNIT, Sultanpur
vikas@gmail.com
S. P. Singh
Member, IEEE
Dept of EE, KNIT, Sultanpur
singhsurya12@gmail.com
A. K. Gautam
Student Member, IEEE
Dept of EE, KNIT, Sultanpur
abhinavgautam97@gmail.com
Vipul Agarwal
Dept of EE,
MIT Moradabad
vipul.agarwal85@gmail.com
ABSTRACT
load, increase in load and decrease in load. The analysis is also performed for source perturbation like Increase & decrease
up in output voltage without use of transformer. Due to power electronic switches used in conversion process vulnerability
of power system is increased and results in different power quality issues power factor, Harmonics injection in supply and
this paper perform transformer less boosting, conversion and less vulnerability to power quality.
Index Terms:
INTRODUCTION
The era of high power converters and Medium voltage (MV)
drives evolved in mid 1980s when 4500 volt Gate Turn off
Thyristor (GTO) became commercially available.
They have the drawback of poor power quality in terms of injection of current harmonics, resultant voltage waveform distortion
and poor power factor at input ac supply. Also slowly varying
: Multilevel converters present great advantages compared with conventional and
very well-known two-level converters. These advantages are
fundamentally focused on improvements in the output signal
quality and a nominal power increase in the converter. The power
converter output voltage improves its quality as the number of
levels increases reducing the total harmonic distortion (THD)
of the output waveforms.
These properties make multilevel converters very attractive and
researchers are spending great efforts trying to improve multiand the performance of different optimization algorithms in
order to enhance the THD of the output signals, and the ripple
of the currents. For instance, nowadays researchers are focused
on the harmonic elimination using pre-calculated switching
the development of new multilevel converter topologies (hybrid
or new ones), and new control strategies. Also conversion of
3 phase ac to dc, line side voltage and current waveforms are
getting polluted with conventional pulses schemes like 12,
24, 48..... Pulse convertors as shown in Fig. 1. So multilevel
converters are showing much effectiveness in this area with
new control technique.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
70
Fig. 1: Block diagram representation of a multilevel converter
DIODE CLAMPED AND FLYING CAPACITOR
MULTILEVEL CONVERTERS
Fig.3: A 4-Level Flying Capacitor Multilevel Converter
The drawbacks of the two-level converters are the high voltage stress
across the devices, large passive components and hence due to the
inherent advantages of the three-level Diode Clamped converters
were proposed to draw the sinusoidal line currents in phase with
mains voltage. And improving the waveform quality and reducing voltage stress on the power devices. The voltage stress on
the open power devices is constrained by clamping capacitors.
SVPWM CONTROL TECHNIQUE FOR DIODE
CLAMPED AND FLYING CAPACITOR
A standard Space vector PWM has been used for three-phase
Diode clamped and Flying capacitor multilevel converters. The
basic principle of operation of a Converter employing SVPWM
technique block diagram is shown below.
Fig. 4: Control Scheme of Multilevel converter in two-frame of
references
Fig. 2: A 4-level Diode Clamped Multilevel Converter
this topology capacitor are not shared among different legs of the
converter; each phase has its own set of capacitors. Regulation
of capacitor voltages is possible without using an external circuit
regardless of the number of levels of the converter. This is one
of the advantages of this topology. Because the voltage of the
outer capacitors is higher than the inner ones, several capacitors
need to be connected in a series to reach to the required voltage
(the tolerable voltage for each capacitor bank). Therefore, the
number of capacitors drastically increases when the number of
voltage levels increases. Furthermore, the number of capacitors
is proportional to the number of phases of the converter. This is
one of the primary drawbacks of this topology.
This scheme involves 3-basic actions performed by system as
for switching operation and ride through from any abnormal
operation.
Transformation Stage
minals of three phase ac supply through source inductance. The
input three phase supply voltage can be written as,
Va =
Vb =
Vb =
…(1)
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
Where Vm is peak phase voltage of supply and
frequency of source.
is angular
For the diode clamped three level converters, line to ground
voltages can be derived from switching states Sa , Sb, Sc. If the
converter is connected to a balanced three phase source, corresponding phase voltages can be derived from line to ground
voltages using (2). Then these phase voltages are transformed
into the
reference frame by (3) and the resultant coordinates
for the vectors in sector can be computed. This can implemented
using Clarke’s function and easily applied using MATLAB em-
=
...(2)
=
…(3)
.
71
. .
…(5)
.
. .
Where is angular frequency of three - phase voltage and vd, v´d
, id and vq, v´q , iq are components of v, v´ , id and is is in d and q
axis respectively. Here both equations depict behavior of id and iq
can be controlled using voltages vd and vq
0
Concept of Space vector calculation
The space vector diagram with equivalent circuit representation
Fig.6: Space vector diagram for all switching states in three phase
converters
…(4)
This equation can be expressed in a rotating reference frame
(d-q), with the d-axis oriented in the direction of source voltage
vector v as shown in Fig. 5.
Fig.7: One sector of space vectors representation with time of
switching
It is to be emphasized that this method only controls the total DC
bus voltage. The current controllers deliver the reference values
for voltages in d and q frame of reference. By using coordinates
frame transformation, we obtain v* and v* in stationary frame
of reference. The voltages v* and v* are used to derive the
reference command input v* and its angle . These are now fed
to space vector modulator and used for generation of control
pulses for 12 semiconductor switches.
Fig. 5: Vector diagram of multilevel converter in two frame of
references
The equation can be written as below
All 27 possible conduction states of NPC or Flying capacitor
multilevel converter produce 19 different space vectors. The
complex plane can be subdivision of 6 sectors and 24 triangles
triangle can be formed using voltage components v0 , v7 and v9.
Also it is assumed command voltage vector v* will reside in
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
region R1 when following equations of (4.6) and (4.7).
V1 Ta
Ta
8
72
For comparison of two dif-
Tb + V2 Tc = V* Tsamp/2
…(6)
+ Tc = Tsamp/2
b
…(7)
Where V1, V2 and V8 are corner voltage triangles of selected
region. Respective time intervals are represented as Ta , Tb and
Tc whether Tsamp is sampling time of these vectors.
parameter which helps at time of different cases as preset indicators and responses in a manner of ease in comparison. So for this
objective few parameters named as Source side and Load side
in disturbed and without any disturbance.
Table I System Parameters
region one as a reference then we can obtain analytical time
expression for time intervals Ta, Tb and Tc.
System Parameters
Input Side Parameters
mH
DC Bus capacitors C1 = C2 = 4700 F
…(8)
Region 1:
mH
Chopping Frequency of Switches=5000 Hz
DC Bus voltage (Reference)=3000 volts
SIMULATION RESULTS OF DIODE CLAMPED
MULTILEVEL CONVERTER
…(9)
Region 2:
load
5mH and 1000 volt ac (rms). Also no variation is applied in
source voltage. Then the performance evaluation of Diode
clamped converter is performed.
Region 3:
…(10)
Fig. 8: Output voltage waveform
Region 4:
…(11)
As shown in Fig.8.The peak overshoot is 320 volts and start to
settle after peak value. At time t=0.6 sec it completely settled
down to reference.
Where is command vector angle, modulation index m = 2/ ,
(V*/V0), V* command voltage vector and V0 is dc bus voltage
of converter. In similar fashion two other region time vectors
can be calculated.
SIMULATION RESULTS AND DISCUSSIONS
A MATLAB/SIMULINK model is developed to investigate the
performance comparison of PI based SVPWM controlled Flying capacitor and Diode clamped converters. The performance
is analyzed for different cases in which changes in load done.
Fig. 9: Waveform of source voltage and current
As shown in Fig. 9. Waveforms are depicted from source side
current and phase angle no lagging operation is visualized. And
waveform is having little distortion.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
73
As shown in Fig.15 load is suddenly increased at t=1 sec. The
dip in output supply voltage of 240 volt and settled down at
time t = 1.8 sec
Fig.10: Voltage across upper capacitor
As shown in the Fig.10. Vc1 Is crossing and swinging over 1500
volts. The same property is showing by Fig.11.
Fig. 16: Waveforms of source voltage and current for sudden
Increase in Load
As shown in Fig.16 source voltage and current Waveforms are
depicted from source side current and phase angle no lagging
operation is visualized.
Fig.11: Voltage across lower capacitor
Fig. 17: Voltage across upper capacitor
which crossing and swinging over 1500 volts are. The same
property is showing by Fig.18.
Fig.12: Voltage difference across capacitors,
Vc = Vc1 – Vc2
Fig. 18: Voltage across lower capacitor
Fig. 13: Harmonic spectrum of source current
:
denly increased at t=1 sec. In this condition the performance
and behavior of Diode Clamped Converter is analyzed with
such change in load.
Fig. 15: Output Voltage waveform for Sudden Increase in Load
Fig. 19: Voltage difference across capacitors,
Vc = Vc1 – Vc2
Fig.19 shows Voltage difference across capacitors, which is
range of 8 volts.
Fig. 20 shows the power factor of supply which is approximate
to unity.
Fig. 20: Power Factor of source
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
denly decreased at t=1 sec. In this condition the performance
and behaviour of Diode Clamped Converter is analyzed with
such change in load.
74
Vc = Vc1 – Vc2
Fig. 25 shows Voltage difference across capacitor which are of
range 7 volts.
Fig. 26: Power Factor of system
Fig.21: Output Voltage Waveform during Sudden Decrease in Load
Fig. 26 shows the power factor of supply which is approximate
to unity.
As shown in Fig.21. Load is suddenly decreased at (t=1) sec.
The rise in output supply voltage of 220 volt and settled down
at time (t = 1.5) sec.
Fig. 27: Harmonic analysis of source current
Fig. 22: Waveform of source voltage and current for sudden Load
Decrease
voltage
The analysis is performed with three phase ac source on line side
of rating 1100 volt (rms) value on frequency of 50 Hz. In this
no transient condition is examined. The increase in voltage is of
10% and for this case the analysis is carried out.
Fig. 23: Voltage across upper capacitor
Fig. 28: Output voltage waveform for increase in Source Voltage
Fig. 24: Voltage across lower capacitor
As shown in Fig. 28 the output waveform of DC supply is with
which is crossing and swinging over 1500 volts. The same property is showing by Fig. 24.
voltage is done. The peak overshoot is 250 volts and start to
settle after peak value. At time t = 2.4 sec it completely settled
down to reference.
Fig. 25: Voltage difference across capacitors,
Fig. 29: Waveform of source voltage and current for increase in
source voltage
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
75
As shown in Fig. 29 Waveform are depicted from source side
current and phase angle no lagging operation is visualized. Also
waveform is having little distortion.
Fig. 35: Waveform of source voltage and current for Decrease in
source voltage
Fig. 30: Voltage across upper capacitor
As shown in Fig. 34 the output waveform of DC supply is with
overshoot is 400 volts and start to settle after peak value. At time
t = 0.9 sec it completely settled down to reference.
Fig. 31: Voltage across lower capacitor
As shown in the Fig. 30 voltage across upper capacitor is shown
which is crossing and swinging over 1500 volts. The same property is showing by Fig. 31.
Fig. 32: Voltage difference across capacitors,
Fig. 32 shows Voltage difference across capacitors, which are
of range 10 volts.
Fig. 36: Voltage across upper capacitor
Fig. 37: Voltage across lower capacitor
As shown in the Fig. 36 voltage across upper capacitor is shown
which is crossing and swinging over 1500 volts. The same property is showing by Fig. 37.
Fig. 33: Power Factor of source
Fig. 33 shows the power factor of supply which is approximate
to unity.
Fig. 38: Voltage difference across capacitors,
Supply voltage is decreased to 900 volt and in this condition the
performance and behaviour of controller is analyzed with such
reduction in source voltage.
Fig. 38 shows Voltage difference across capacitors, which are
of range 7 volts.
Fig. 39: Power Factor of source
Fig. 34: Output voltage waveform for decrease in Source Voltage
Fig. 39 shows the power factor of supply which is approximate
to unity.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
76
Fig. 40: Harmonic analysis of source current during load disturbance
Fig. 44: Voltage across upper capacitor
Fig. 41: Switching stress across a switch
Fig. 41 shows the switching stress across a switch during its
operation and showing peak value of voltage across it as 1600
volts. This voltage is of intermittent nature because of switch
getting regularly turning On and Off.
SIMULATION RESULT OF FLYING CAPACITOR
MULTILEVEL CONVERTER
load
Fig. 45: Voltage across lower capacitor
As shown in the Fig. 44 voltage across capacitor one Vc1 is
shown which is crossing and swinging over 1500 volts. The
same property is showing by Fig.45
Fig. 46 shows Voltage difference across capacitors which are
of range 7 volts
variation is applied in source voltage. Then the performance
Fig. 42: Output voltage waveform
As shown in Fig.42. The peak overshoot is not found and start to
settle after peak value. At time t = 0.4 sec it completely settled
down to reference.
Fig. 46: Voltage difference across capacitors
Fig. 43: Waveform of source voltage and current
As shown in Fig. 43, Waveform are depicted from source side
current and phase angle no lagging operation is visualized. Also
waveform is having little distortion.
Fig. 47: Power Factor of Source.
Fig. 47: shows the power factor of supply which is
approximate to unity.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
Fig. 48 Harmonic analysis of source current
77
Fig. 51: Voltage across lower capacitor
Fig. 50 and Fig. 51 shows the balancing of capacitor voltage
which is of variable in nature. Whenever a capacitor voltage is
increasing other voltage is getting decreased.
suddenly increased at t=1 sec. In this condition the performance
and behaviour of Flying Capacitor Converter is analyzed with
such change in load.
Fig. 52: Voltage difference across capacitors,
Fig. 52 shows Voltage difference across capacitors which are
of range 8 volts.
Fig. 48: Output Voltage waveform for Sudden increase in Load
Fig. 53: Power Factor of source
Fig. 49: Waveform of source voltage and current for sudden increase
in Load
As shown in Fig. 48. The dip in output supply voltage of 200
volt and settled down at time (t = 1.8) sec. As shown in Fig. 48,
Waveforms are depicted from source side current and phase angle
no lagging operation is visualized.
Fig. 50: Voltage across upper capacitor
Fig. 53 shows the power factor of supply which is approximate
to unity.
:
is suddenly decreased at t=1 sec. In this condition performance
and behaviour of Flying Capacitor Converter is analyzed with
such change in load.
Fig. 54: Output Voltage Waveform during Sudden decrease in Load
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
78
As shown in Fig. 54. Load is suddenly decreased at t = 1 sec.
The rise in output supply voltage of 210 volt and settled down
at time t=1.3sec.
Due to sudden drop of load the output voltage is getting increased at time t=1sec. This supply current is suddenly sensed
performed at time t=1.3 seconds and output supply is maintained
at 3000 volts reference.
Fig. 59: Power Factor of system
Fig. 59 shows the power factor of supply which is approximate
to unity.
Fig. 55: Waveform of source voltage and current for sudden
Decrease in Load
Fig. 60: Harmonic analysis of source current during load disturbance
voltage
Fig. 56: Voltage across upper capacitor
and no transient condition is examined.
Fig. 61: Output voltage waveform for Increase in Source Voltage
Fig. 57: Voltage across lower capacitor
Fig. 62: Waveform of source voltage and current for increase in
source voltage
Fig. 58: Voltage difference across capacitors
Fig. 58 shows Voltage difference across capacitors which are
of range 15 volts.
done. At time (t=0.3) sec it completely settled down to reference.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
Fig. 63: Voltage across upper capacitor
Fig. 64: Voltage across lower capacitor
As shown in the Fig. 63 voltage across capacitor one Vc1 is
shown which is crossing and swinging over 1500 volts. The
same property is showing by Fig. 64.
79
Fig. 67: Output voltage waveform for decrease in Source Voltage
Fig. 68: Waveform of source voltage and current for decrease in
source voltage
As shown in Fig. 67 the output waveform of DC supply is with
t =0.3 sec it completely settled down to reference.
Fig. 69: Voltage across upper capacitor
Fig.65: Voltage difference across capacitors,
Fig. 65 shows Voltage difference across capacitors which are
of range 10 volts.
Fig. 70: Voltage across lower capacitor
As shown in the Fig. 69 voltage across capacitor one Vc1 is
shown which is crossing and swinging over 1500 volts. The
same property is showing by Fig. 70.
Fig. 66: Power Factor of source
Fig.66 shows the power factor of supply which is approximate
to unity.
Supply voltage is decreased to 900 volt and in this condition the
performance and behaviour of controller is analyzed with such
reduction in source voltage.
Fig. 71: Voltage difference across capacitors,
MIT International Journal of Electrical and Instrumentation Engineering Vol. 4, No. 2, August 2014, pp. 69-80
ISSN 2230-7656 ©MIT Publications
Fig.71 shows Voltage difference across capacitors which are of
range 10 volts.
3.
0.15
0.4
4.
Settling time (sec)
0.7
0.4
5.
DC bus voltage
Overshoot (%)
11.33
0
6.
DC bus voltage
Undershoot (%)
Nature of Response
10
10.1
Under damped
Over damped
7.
Peak Time (sec)
80
CONCLUSIONS
Fig. 72: Power Factor of source
Fig. 72 shows the power factor of supply which is approximate
to unity.
The main conclusions drawn from work which is carried out in
this paper are summarizes for saliency of work:
different kind of problems as reduction of life of equipment; heat up of windings, distorted waveform of source
current etc. THD of line side current should also be within
prescribed limit IEC standard and is about 5%-10% for
both of converters. But Diode clamped converter is working in limit of 6% THD.
converters are able to operate without transformer at source
side for step up of voltage and then conversion to DC.
Fig. 73: Harmonic analysis of source current during load disturbance
in case of supply voltage variation.
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Fig. 74: Switching stress across a switch
Fig. 74 show the switching stress across a switch during its
operation and showing peak value of voltage across it as 2600
volts. This voltage is of intermittent nature because of switch
getting regularly turning ON and Off of switch.
PERFORMANCE COMPARISON OF DIODE
CLAMPED AND FLYING CAPACITOR
MULTILEVEL CONVERTERS
Performance comparison of SVPWM controlled Diode clamped
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S.
No.
Performance
Parameters
1.
2.
Diode Clamped
Multilevel Converter
Flying Capacitor
Multilevel Converter
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, vol. 148, pp. 35-43, Jan. 2001.
Delay time (sec)
0.01
0.1
Rise Time (sec)
0.1
0.26
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