ISSN 2319-8885
Vol.04,Issue.52,
December-2015,
Pages:11159-11168
www.ijsetr.com
A High Voltage Gain Modular Multilevel DC/DC Converter and Inverter
Fed Induction Motor
RAFI MOHAMMAD1, O. RANJIT KUMAR2
1
PG Scholar, Dept of EEE, QIS Institute of Technology, Ongole, Prakasam (Dt), AP, India.
Assistant Professor, Dept of EEE, QIS Institute of Technology, Ongole, Prakasam (Dt), AP, India.
2
Abstract: In this paper a high voltage gain modular multilevel dc/dc converter is derived by integrating the full bridge converter
and three level flying capacitor for high voltage and high step down applications. The high switch voltage stress on the primary
side is effectively reduced full bridge modules in series and zero voltage switching performance for all the active switches due to
phase shift control scheme. Therefore low rated power devices can be employed to obtain the benefits of low conduction loss.
More importantly the voltage auto balance ability among cascaded full bridge modules is achieved by inherent small flying
capacitor, which removes additional active components or control loops. By using this modular multilevel dc/dc converter the
performance of induction motor is checking with Matlab/Simulink software.
Keywords: Input Voltage Auto Balance, Modular Multilevel Dc/Dc Converter, Phase-Shift Control Scheme, Zero-Voltage
Switching (ZVS), Induction Motor.
I. INTRODUCTION
Electric power conversion can be met in various modern
applications. Starting from household appliances, for example
computers, mobile phone chargers, and white appliances, up
to industrial applications, such as traction motors, steel mills,
and even up to the electrical network level, when transferring
vast amounts of power. As a consequence of such a wide
application range, power conversion is required to be as
efficient as possible, in order not to overuse valuable
resources, and to reduce the environmental impact of human
activities. A lot of progress has been made during recent years
towards higher efficiency of power electronic conversion
systems, such as new topologies, control methods, and even
new materials are investigated. High-voltage AC-AC power
converters have been widely used in industry, because of the
wide speed range, quick response and good performances. In
the field of high-voltage AC-AC power conversion,
traditional ―high-low high‖ two-level AC-AC converters with
introduction of transformers have the disadvantages of large
volume, high cost and low efficiency, and high-voltage ACAC converters based on power electronic devices in series are
hard to achieve. Contrast to the drawbacks of traditional ACAC converters mentioned above, the multilevel converter
technology has the advantages of low harmonic component,
small dV/dt, high power factor, and it has developed rapidly
in the last few years [1]-[3].
However, the AC-AC converters using neutral-pointclamped multilevel converters and flying-capacitor multilevel
converters have the disadvantages such as the complex
topology structure and the identical specification. The
cascaded H-bridge multilevel converter is widely used
recently because it is easy to install and to develop to higher
voltage. Induction motors have been available for nearly 100
years. In fact the first electric motors were designed and built
for operation using direct current power. Although AC motors
are mainly used in industry for high speed operation because
they are smaller, lighter, less expensive, require virtually no
maintenance comparing to their DC counter parts, the latter
are still used. The reasons for this are that they exhibit wide
speed range, good speed regulation, starting and accelerating
torques in excess of 400% of rated, less complex control and
usually less expensive drive. Today, induction motors are still
used in several applications as in industrial production and
processing of paper pulp, textile industries, in electric vehicle
(EV) propulsion and in public transport such as TRAM
(trolley) and METRO. The control of these motors is usually
made of power electronics devices, such as modular
multilevel inverter fed AC drives or chopper-fed AC drives
and because of their simplicity, ease of application, reliability
and favorable cost have been a backbone of industrial
applications.
Another way to classify AC motor drives is according to
the type of the converter which is utilized in order to control
the speed and the torque of the AC motor ([2]-[4]). When a
modular multi level inverter (one or three phase) is used the
respective category is called: Controlled inverter-Fed
induction Motor Drive. In case that a DC to DC converter is
used the respective category is called: Chopper Fed Induction
Motor Drive. Both of these categories can further subdivided
into non-generative and generative drives based on what was
mentioned earlier. Induction motors are used extensively in
adjustable-speed drives and position control applications.
Copyright @ 2015 IJSETR. All rights reserved.
RAFI MOHAMMAD, O. RANJIT KUMAR
Their speeds below the base speed can be controlled by
current-type rectifiers can be employed. In this section, the
armature-current control. Speeds above the base speed are
widely adopted current-type full-wave rectifier is applied as
obtained by field-flux control. As speed control method for
an example to explore the circuit performance of the proposed
induction motors are simpler and less expensive than those for
modular multilevel configuration, which is illustrated in Fig.
the AC motors, DC motors are preferred where wide speed
1. In the primary side, the capacitors C1and C2are used to split
range control is required. DC choppers also provide variable
the high input voltage, S11−S14are the power switches of the
top full-bridge module, S21−S24form the bottom full-bridge
dc output voltage from a fixed dc input voltage.
module,Cs11−Cs24are the parasitic capacitors of the power
II. DERIVATION LAW OF MODULAR MULTILEVEL
switches, and Llk1and Llk2 are the leakage inductors of the
CONVERTERS
transformersT1andT2, respectively. In the secondary side,
The derivation process of the proposed modular
Do11, Do12, Lf1, and Co1 are for the top full-bridge module and
multilevel dc/dc converters is discussed in this section. It is
Do21, Do22, Lf2, and Co2 are for the bottom full-bridge module.
well known that the neutral-point-clamped (NPC) converters
ip1, ip2, iDo11, iDo12, iDo21, and iDo22are the primary and
and flying capacitor-based converters are the major multilevel
secondary currents through the windings of the transformers
topologies for the high-voltage and high-power applications.
with the defined direction in Fig. 1. And is1and is2 are the filter
For the conventional NPC converters with pulse width
inductors currents.
modulation control, the abnormal operation condition, such as
the mismatch in the gate signals, may cause the voltage
imbalance of the input capacitors. Therefore, the converter
reliability is impacted. Furthermore, the phase-shift control
scheme is not suitable for the conventional NPC converters,
which leads to large switching losses. Fortunately, by
inserting a small flying capacitor parallel connected with the
clamping diodes, the input capacitor voltages are
automatically shared because the flying capacitor can be
directly parallel with the series input capacitors alternatively.
Based on the previously summarized combined multilevel
derivation principle, the cascaded full bridge converter and
three level flying capacitor are integrated to derive the
advanced modular multilevel dc/dc converter, which is
illustrated in Fig.1.
Fig.2. Proposed Modular Multilevel Dc/Dc Converter with
Input Voltage Auto Balance Ability.
Fig.1. Derivation of the proposed modular multilevel dc/dc
converter: (a) cascaded full-bridge converter, (b) flying
capacitor-based TLC, and (c) proposed modular
multilevel dc/dc topology.
III. OPERATION PRINCIPLE AND INPUT VOLTAGE
AUTOBALANCE MECHANISM
For the secondary side of the derived modular multilevel
dc/dc converters, the current-type full-wave rectifier, fullbridge rectifier, current doubler rectifier, and other advanced
A. Operation Analysis
The phase-shift control scheme is employed in the proposed
converter to realize the ZVS performance of all the power
switches, where S11, S13, S21, and S23 are the leading-leg
switches and S12, S14, S22, and S24 are the lagging-leg
switches. The key waveforms of the proposed converter are
shown in Fig. 2. For the top full-bridge module, S11 and S13
act with 0.5 duty cycle complementarily with proper dead
time td, so as for the switches S12 and S14. The phase-shift
angle between the leading and lagging switch pairs is defined
as ϕ1. The gate signal pattern of the bottom full-bridge
module is similar to that of the top full-bridge module with
the phase-shift angle ϕ2. Meanwhile, the leading switches pair
S11 andS13 turns ON and OFF simultaneously with the switch
pair S21 and S23, while the phase-shift angles ϕ1 and ϕ2 are
decoupled control freedoms for the output voltage regulation.
The mode 0 <ϕ1−ϕ2 <td is taken into consideration when
analyzing the operation of the converter, and the equivalent
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
A High Voltage Gain Modular Multilevel DC/DC Converter and Inverter Fed Induction Motor
operation circuits are depicted in Fig. 3. In order to simplify
the analysis, the following assumptions are made:
 all the power switches and diodes are ideal;
 the parasitic capacitorsCs11−Cs24of the switches have the
same value as Cs;
 the voltage ripples on the divided input capacitorsC1,C2
and flying capacitors Cf are small due to their large
capacitance;
 the turns ratio of both transformers is N= n2:n1; and
 the input voltage is balanced and the auto balance
mechanism will be depicted later. There are 15 operation
stages in one switching period. Due to the symmetrical
circuit structure and operation, only the first eight stages
are analyzed as follows.
Fig.4. Stage 1.
Stage 2 [t1,t2]: At t1, the turn-off signals of the switches
S11and S21are given. ZVS turn off for these two switches are
achieved due to the capacitors Cs11 and Cs21. Cs11 andCs21 are
charged andCs13 andCs23 are discharged by the primary
currents as shown in Fig.5.
Fig.3. Key waveforms of the proposed converter.
Fig.5. Stage 2.
Stage 1 [t0,t1]: Before t1, the switches S11,S14,S21, and S24are
in the turn-on state to deliver the power to the secondary side.
The output diodes Do11 and Do21 are conducted and the output
diodes Do12 and Do22 are reverse biased as shown in Fig.4. The
flying capacitor Cf is in parallel with the input divided
capacitor C1 to make VCf equal toVC1.
Stage3 [t2,t3]: At t2, the voltages of Cs13 andCs23 reach 0 and
the body diodes of S13 and S23 are conducted, providing the
ZVS turn-on condition for S13 and S23 as shown in Fig.6. The
flying capacitor Cf is changed to be in parallel with the input
divided capacitor C2. The primary currents are derived by
(1)
(3)
(2)
(4)
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
RAFI MOHAMMAD, O. RANJIT KUMAR
Fig.8. Stage 5.
Fig.6. Stage 3.
Stage 4[t3,t4]: At t3,S14turns off with ZVS as shown in Fig.7.
Cs14 is charged andCs12 is discharged, leading to the forward
bias of Do12; hence, the secondary currentis1 circulates freely
through both Do11andDo12. ip1is regulated by
Stage 6 [t5,t6]: At t5,Cs12is discharged completely and the anti
parallel diode of S12 conducts, getting ready for the ZVS
Turn-on ofS12 as shown in Fig.9. During this time interval, ip1
declines steeply duo to half-input voltage across the leakage
inductorLlk1. ip1 is given by
(5)
(7)
Fig.7. Stage 4.
Stage 5 [t4,t5]: At t4, the turn-off signal of S24comes. ZVS
turn-off performance is achieved forS24 as shown in Fig.8.
Similar to the previous time interval, Do21 and Do22 conduct
simultaneously, thus leading to the transformer T 2 shortcircuit.ip2is regulated by
(6)
Fig.9. Stage 6.
Stage 7 [t6, t7]: At t6,ip1 decreases to 0 and increases reversely
with the same slope throughS12 andS13 as shown in Fig.10.
Cs22 is discharged completely and the anti parallel diode of S22
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
A High Voltage Gain Modular Multilevel DC/DC Converter and Inverter Fed Induction Motor
conducts. ip2 declines rapidly duo to half-input voltage across
B. Input Voltage Auto balance Mechanism
the leakage inductor Llk2.ip2is given by
The input voltage imbalance is one of the major
drawbacks for most multilevel converters and ISOP
converters, which is mainly caused by the asymmetry of the
(8)
component parameter difference and the mismatch of control
signals. It has been carried out that the transformer turns ratio
difference (N), leakage inductance distinction (Llk), and
phase-shift angle mismatch (ϕ) are the main reasons for the
input voltage imbalance in the steady state for the ISOP
phase-shift-controlled converters. The effect of these factors
is summarized in Table I, which shows that N1 >N2 or Llk1
>Llk2 or ϕ1 >ϕ2 leads to the voltage VC1on the top input
capacitor C1higher than the voltageVC2on the bottom
capacitor C2 and vice versa. As the parameter difference
increases, the voltage gap betweenVC1and VC2 increases
correspondingly. The input voltage auto balance mechanism
of the proposed modular multilevel dc/dc converter is
displayed in Fig. 12 and detailed elaborated as follows.
Fig.10. Stage 7.
Stage 8 [t7, t8]: At t7, ip2 decreases to 0 and increases
reversely through S22 and S23. The current through the output
diodeDo11 decreases to 0 and turns off. The output diode D o21
turns off after t8, and then a similar operation works in the rest
stages as shown in Fig.11.
Fig.11. Stage 8.
Fig.12. Input voltage auto balance mechanism: (a)C f in
parallel withC1 and(b)Cf in parallel withC2.
According to the steady operation of the proposed
converter,
for
the
leading-leg
switches,
the
switchesS11andS21have the same time sequence and the
switchesS13 andS23 are operated synchronously. WhenS11
andS21 are turned ON, S13 and S23 are turned OFF
accordingly, and the flying capacitor Cf is connected in
parallel with the top input capacitor C1 as plotted in Fig.
12(a). This makes VCf equal toVc1. In the same way, as given
in Fig. 12(b), the flying capacitor Cf is in parallel with the
bottom input capacitor C2, whenS13and S23are in turn-on state.
This denotes that VCf andVc2 are the same. The connection of
Cf with C1 or C2 alternates with high switching frequency,
which leads to the voltages on both the input capacitors
automatically shared and balanced. It is important to point out
that the flying capacitor does not connect with the lagging-leg
switches directly. As a result, the operation of Cf hardly
affects the states of the lagging-leg switches. Then, both the
two phase-shift anglesϕ1 and ϕ2 can be taken as control
freedoms to regulate the output voltage.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
RAFI MOHAMMAD, O. RANJIT KUMAR
IV. DYNAMIC MODELLING OF INDUCTION
MOTOR
In a conventional four pole induction motor, there are two
(14)
sets of identical voltage profile windings will be present in the
Voltage equations in dq0 frame can be solved from the
total phase winding. These two windings are connected in
basic equations of induction motor
series as shown in fig. 13(a). For the proposed inverter these
two identical voltage profile winding coils are disconnected,
and the available four terminals are taken out, like shown in
the fig13 (b). Since these two windings are separated equally,
stator resistance, Stator leakage inductance and the
magnetizing inductance of each identical voltage profile
windings are equal to the half of the normal induction motor
shown in fig.13(a). The voltage equitation for the stator
winding is given by common dc link.
(9)
Flux linkages are as follows
(10)
The effective voltage across the stator winding is the sum
of the voltages across the two individual windings.
(11)
The expression for the electromagnetic torque in terms
of dq0 axis currents is
(15)
Rotor speed in terms of Torque is
(16)
Fig. 13. Induction Motor stator winding: (a) General
arrangement (b) Arrangement for the proposed inverter.
The motor phase voltage can be achieved by substituting
equations (9) and (10) in (11)
(12)
Similarly voltage equitation for the remaining phases are
(13)
Where
d: direct axis,
q: quadrature axis,
s: stator variable,
r: rotor variable,
, ,: q and d–axis stator voltages,
, ,: q and d–axis rotor voltages,
: Rotor resistance,
: Stator resistance,
L1s: stator leakage inductance,
L1r : rotor leakage inductance,
iqs ,ids: q and d–axis stator currents,
iqr, idr: q and d–axis rotor currents,
p: number of poles,
J: moment of inertia,
Te: electrical output torque,
TL: load torque.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
A High Voltage Gain Modular Multilevel DC/DC Converter and Inverter Fed Induction Motor
From the equations (9), (10),(11) it can be observed that
there is no difference between the normal induction motor.
V. SIMULATION RESULTS
Simulation results of this paper is shown in bellow Figs.14
to 26.
Fig.16. Simulation Waveform of Proposed System Output
Voltage without Flying Capacitor.
Fig.14. Matlab/Simulink Circuit of Proposed System
without Flying Capacitor.
Fig.17.Matlab/Simulink Circuit of Proposed System with
Flying Capacitor.
Fig.15.Simulation Waveform of Proposed System Input
Voltage Without Flying Capacitor.
Fig.18.Primary Voltage and Current of converter.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
RAFI MOHAMMAD, O. RANJIT KUMAR
(a)
(b)
Fig.19. Simulation Results Of ZVS Operation: (A) ZVS
Operation For S11 And (B) ZVS Operation For S14.
Fig.22.Matlab/Simulink Circuit with Flying Capacitor fed
Induction Motor.
Fig.23. Inverter Input Voltage.
Fig.20.Simulation Waveform Of Proposed System Input
Voltage With Flying Capacitor.
Fig.21. Simulation Waveform of Proposed System Output
Voltage with Flying Capacitor.
Fig.24.Inverter Output Phase To Neutral Voltage.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168
A High Voltage Gain Modular Multilevel DC/DC Converter and Inverter Fed Induction Motor
modular multilevel dc/dc converter concept can be easily
extended to N-stage converter with stacked full-bridge
modules to satisfy extremely high-voltage applications with
low-voltage-rated power switches. The simulation results
show that the proposed system effectively controls the motor
speed and enhances the drive performance.
Fig.25. Inverter Output Line to Line Voltage.
Fig.26.Simulation Waveform of Armature Current, Speed
and Torque for Induction Motor.
VI. CONCLUSION
In this paper, a novel phase-shift-controlled modular
multilevel dc/dc converter is proposed and analyzed for the
high input voltage dc-based systems. Due to the inherent
flying capacitor, which connects the input divided capacitors
alternatively, the input voltage is automatically shared and
balanced without any additional power components and
control loops. Consequently, the switch voltage stress is
reduced and the circuit reliability is enhanced. By adopting
the phase-shift control scheme, ZVS soft-switching
performance is ensured to reduce the switching losses. The
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International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.52, December-2015, Pages: 11159-11168