ISSN 2319-8885
Vol.04,Issue.13,
May-2015,
Pages:2394-2400
www.ijsetr.com
A Novel Unique 5-Level Cascaded Multilevel Inverter based Active Power
Filter for Power Quality Enhancement
R. PRAMOTH KUMAR1, T. SRINIVASA RAO2
1
PG Scholar, Dept of EEE, Avanthi Institute of Engineering & Technology, Narasipatnam, AP, India,
E-mail: htomarp5035@gmail.com.
2
Assoc Prof, Dept of EEE, Avanthi Institute of Engineering & Technology, Narasipatnam, AP, India,
E-mail: srinivasarao.tegala@gmail.com.
Abstract: Implementation of intelligence controller by using voltage as feedback for significantly improving the dynamic
performance of advanced compensator, the comparative analysis of several control strategies fed APF for power quality
improvement features is presented. Fuzzy control has emerged as one of the most active and fruitful areas for research in the
applications of fuzzy set theory, especially in the realm of industrial process, which do not lend of quantities data regarding the
input-output relations. Due to nonlinear loads, current harmonics, unbalanced voltages and current and reactive power problems
will be created in the network. The Instantaneous real power theory (IRPT) provides the real power calculation with PI controller
will not provide accurate result and good performance under both steady state and transient state. The APF system is validated
through extensive simulation under steady state and transient condition with different non-linear loads. The cascaded
multilevel inverter switching signals are derivates from triangular-sampling current controller; it gives a good dynamic
performance under steady state and transient operations. The cascaded active filter system is validated through extensive
simulation under steady state and transient conditions with PI/Fuzzy control schemes. The simulation results are obtained using
MATLAB/SIMULTION software.
Keywords: Shunt Active Filter, Instantaneous Power Theory (IRP), Power Quality, Triangular-Sampling Current Modulator.
I. INTRODUCTION
Fuzzy control is based on fuzzy logic; it is much closer in
spirit to human thinking and natural language than traditional
logical systems application to many industries and residential
usages. The increased use of nonlinear devices in industry
has resulted in direct increase of harmonic distortion in
the industrial power system in recent years. Conventionally,
this problem can be solved by using passive filters whose
main components are inductors and capacitors. Although
this kind of filter has the advantage of low hardware
cost, the performance of this configuration is often
significantly affected by system impedance and load
characteristics. With the emergence of power electronics, an
active power filter that helps to suppress the harmonics and
improves the power quality. This proposal was mainly based
on the theory of harmonic current injection. In the circuit
operation. The current-controlled power converter generates
the harmonic current that is opposite to the load
harmonic current injecting into the power feeders. Hence,
the current harmonics can be effectively suppressed and only
the fundamental component of load current is extracted. In
other words, the active power filter can also be regarded
as a harmonic current source that is allocated in parallel
with the power system. Therefore the notorious resonance
problems can be easily avoided. However, because the
switching frequency of the power ratings, the design of active
power filters power converter is inversely proportional to for
high-power applications should be made carefully.
Recently Active Power Line Conditioners (APLC) or
Active Power Filters (APF) overcome these problems and are
designed for compensating the harmonics and suppressing
the reactive power simultaneously [4]. Since basic principles
of active filter compensation were proposed by Gyugyi and
Strycula in 1976[5]. In 1984, Hirofumi Akagi introduced a
new concept of instantaneous reactive power (p-q theory)
compensators [6],[7]. The generalized instantaneous reactive
power theory which is valid for sinusoidal or nonsinusoidal and balanced or unbalanced three-phase power
systems with or without zero-sequence currents was later
proposed [8]. The active filter can be connected in series or
in parallel with the supply network. The series active power
filter is suitable for voltage harmonic compensation. Most of
the industrial applications need current harmonic
compensation, so the shunt active filter is popular than
series active filter [9]. Currently, remarkable progress in the
capacity and switching speed of power semiconductor
devices such as insulated -gate bipolar transistors (IGBTs)
has spurred interest in APF [10]. Due to these reasons,
multilevel inverter based active power filters, which have the
ability to synthesize high voltage with low voltage
components, have been designed to compensate harmonics
Copyright @ 2015 IJSETR. All rights reserved.
R. PRAMOTH KUMAR, T. SRINIVASA RAO
and suppress reactive power simultaneously and numerous
Similarly, the instantaneous source current isa, isb, isc also
control techniques have been proposed by many researchers
transformed into the α− β coordinate‟s current iα, iβ by
Clarke transformation that is given as
[1-8].
According to the current reference‟s generation methods,
these control methods of multilevel inverter based APFs can
be categorized into ABC frame current reference generation
[1], [6], DQ-frame current reference generation [2], [4], [7]
and prediction based current reference generation [8]. While
these control techniques can compensate harmonics and
reactive power to some extent, they suffer from several
drawbacks. The first one is they can only reduce overall
harmonics and reactive power, but have no control on
specific order of harmonics. The second one is only at high
switching frequency, can the performance of these control
methods be ensured. However, a high switching frequency
will increase switching loss and complicate thermal
management of the system, especially in high voltage and
high power density applications. Additionally, while most of
these techniques can compensate harmonics and reactive
power simultaneously, few of them can also balance
unbalanced loads at the same time.
II. PROPOSED INSTANTANEOUS POWER THEORY
The proposed instantaneous real-power (p) theory derives
from the conventional p-q theory or instantaneous power
theory concept and uses simple algebraic calculations. It
operates in steady-state or transient as well as for generic
voltage and current power systems that allowing to control
the active power filters in real-time. The active filter should
supply the oscillating portion of the instantaneous active
current of the load and hence makes source current
sinusoidal.
Fig.1. α-β coordinates transformation.
The p-q theory performs a Clarke transformation of a
stationary system of coordinates a-b-c to an orthogonal
reference system of coordinates α− β . In a-b-c coordinates
axes are fixed on the same plane, apart from each other by
120o that as shown in Fig 1. The instantaneous space vectors
voltage and current Va,ia are set on the a-axis Vb,ib are on the
b axis, and Vc,ic are on the c-axis. These space vectors are
easily transformed into α− β coordinates. The instantaneous
source voltages vsa , vsb, vsc are transformed into the α− β
coordinate‟s voltage vα, vβ by Clarke transformation as
follows:
(2)
Where α and β axes are the orthogonal coordinates. They V α,
iα are on the α-axis, and Vβ, iβ are on the β-axis. Real-Power
(p) calculation: The orthogonal coordinates of voltage and
current vα , iα are on the α-axis and vβ , iβ are on the β-axis.
Let the instantaneous real-power calculated from the α-axis
and β-axis of the current and voltage respectively. These are
given by the conventional definition of real-power as
(3)
This instantaneous real-power (pac) is passed to first order
Butterworth design based 50 Hz low pass filter (LPF) for
eliminating the higher order components; it allows the
fundamental component only. These LPF indicates ac
components of the real-power losses and it‟s denoted as
.
The DC power loss is calculated from the comparison of the
dc-bus capacitor voltage of the cascaded inverter and desired
reference voltage. The proportional and integral gains (PI
Controller) are determining the dynamic response and
settling time of the dc-bus capacitor voltage. The DC
component power losses can be written as
(4)
The instantaneous real-power (p) is calculated from the
AC component of the real-power loss
and the DC power
loss
; it can be defined as follows
(5)
The instantaneous current on the α− β coordinates of i cα
and icβ are divided into two kinds of instantaneous current
components; first is real-power losses and second is reactive
power losses, but this proposed controller computes only the
real-power losses. So the α− β coordinate currents icα, icβ are
calculated from the Vα, vβ voltages with instantaneous real
power p only and the reactive power q is assumed to be zero.
This approach reduces the calculations and shows better
performance than the conventional methods. The α− β
coordinate currents can be calculated as
(6)
From this equation, we can calculate the orthogonal
coordinate‟s active-power current. The α-axis of the
instantaneous active current is written as
(7)
Similarly, the β-axis of the instantaneous active current is
written as
(1)
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400
(8)
A Novel Unique 5-Level Cascaded Multilevel Inverter based Active Power Filter for Power Quality Enhancement
Let the instantaneous powers p(t) in the α-axis and the β-axis
phase consists of two-H-bridges in cascaded method for 5is represented as pα and pβ respectively. They are given by
level output voltage, shown in Fig 3. Each H-bridge is
the definition of real-power as follows
connected a separate dc-bus capacitor and it serves as an
energy storage elements to supply a real-power difference
(9)
between load and source during the transient period. The
From this equation (9), substitute the orthogonal coordinates
capacitor voltage is maintained constant using PI-controller.
α-axis active power (7) and β-axis active power (8); we can
The 24-power transistors switching operations are performed
calculate the real-power ( pt) as follows
using triangular-sampling current controller and harmonics is
achieved by injecting equal but opposite current harmonic
components at Point of Common Coupling (PCC).
(10)
The AC and DC component of the instantaneous power
(pt) is related to the harmonics currents. The instantaneous
real power generates the reference currents required to
compensate the distorted line current harmonics and reactive
power.
III. SHUNT ACTIVE POWER FILTER SYSTEM
Instantaneous real-power theory based cascaded active
filter for power line conditioning system is connected in the
distribution network at the PCC through filter inductances
and operates in a closed loop. The shunt active filter system
contains a cascaded inverter, RL-filters, a compensation
controller (instantaneous real-power theory) and switching
signal generator (proposed triangular-sampling current
modulator) as shown in the Fig 2. The three-phase supply
source connected with non-linear load and these nonlinear
loads currents contains fundamental and harmonic
components. If the active power filter provides the total
reactive and harmonic power,
will be in phase with the
utility voltage and would be sinusoidal. At this time, the
active filter must provide the compensation current;
therefore, active power filter estimates
the fundamental components and compensating the harmonic
current and reactive power.
Fig.3. Design of cascaded multilevel active power filter.
B. Reference Current Control Strategy
The control scheme of the shunt active power filter must
calculate the current reference signals from each phase of the
inverter using instantaneous real-power compensator. The
block diagram as shown in Fig.4, that control scheme
generates the reference current required to compensate the
load current harmonics and reactive power. The PI-controller
is tried to maintain the dc-bus voltage across the capacitor
constant of the cascaded inverter. This instantaneous real
power compensator with PI-controller is used to extracts
reference value of current to be compensated.
Fig.2. Shunt active power line conditioners system.
Fig.4. Reference current generator using instantaneous
real-power theory.
A. Power Converter
A cascaded multilevel active power inverter is constructed
by the conventional of H-bridges. The three-phase active
filter comprises of 24-power transistors with diodes and each
These reference currents
,
are calculated
instantaneously without any time delay by using the
instantaneous α−β coordinate currents. The required
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400
R. PRAMOTH KUMAR, T. SRINIVASA RAO
references current derivate from the inverse Clarke
the suppression of the harmonics, average switching
transformation and it can be written as
frequency of each inverter is equality and unconditioned
stability. The reference currents ,
(extracted by
instantaneous real-power compensator) compared with actual
source current
to generate cascaded inverter
switching signals using the triangular-sampling current
modulator. The five-level voltage source inverter systems of
the current controller are utilized independently for each
(11)
phase. Each current controller directly generates the
The reference currents ( ,
are compared with
switching signal of the three A, B and C phases. The A-phase
actual source current
) that facilitates generating
actual source current represented as isa and reference current
cascaded multilevel inverter switching signals using the
represent as
as shown in Fig 5, similarly represented the B
proposed triangular-sampling current modulator. The small
and C phase currents.
amount of real-power is adjusted by changing the amplitude
of fundamental component of reference currents and the
To determine the switching frequency by means the error
objective of this algorithm is to compensate all undesirable
current [desired reference current compare with the actual
components. When the power system voltages are balanced
source current] multiplied with proportional gain (Kp) and
and sinusoidal, it leads to constant power at the dc bus
compared with triangular-carrier signals. The four triangular
capacitor and balanced sinusoidal currents at AC mains
signals are generated; that is same frequency with different
simultaneously.
amplitude for cascaded multilevel inverter. Thus the
switching frequency of the power transistor is equal to the
C. Control Loop Design using PI Controller
frequency of the triangular-carrier signals. Then, the output
Voltage control of the dc-bus capacitor is performed by
signal of the comparator is sampled and held D-Latch at a
adjusting the small power flowing in to DC components, thus
regular interval Ts synchronized with the clock of frequency
compensating conduction losses and switching losses.
equal to Ts / 1. Note that 4-external clock applied to each
Proportional Integral controller is used in order to eliminate
converter and Ts is set as 30 ns, because each phase in one
the steady state error and reduce the ripple voltage of the
converter does not overlap other phase. Therefore the
cascaded inverter. The transfer function is defined as
harmonic currents are reduced as if the switching frequency
were increased. The interface inductor between cascaded
voltage source inverter and PCC suppresses the harmonics
caused by the switching operation of the inverter.
(12)
The proportional and integral gains [
are set
such way that actual Vdc across capacitor is equal to the
reference value of Vdc voltage.
Fig.5. Proposed triangular-sampling current controller.
D. Proposed Triangular-Sampling Current Modulator
The proposed triangular-sampling current modulator for
active power filter line currents can be executed to generate
the switching pattern of the cascaded multilevel voltage
source inverter. There are various current control methods
proposed; but the triangular-sampling current control method
has the highest rate for cascaded active power filter
applications. These current controller based inverter features
are quick current controllability, switching operation induced
III. INTRODUCTION TO FUZZY LOGIC
CONTROLLER
Fig.6 shows the internal structure of the control circuit.
The control scheme consists of Fuzzy controller, limiter, and
three phase sine wave generator for reference current
generation and generation of switching signals. The peak
value of reference currents is estimated by regulating the DC
link voltage. The actual capacitor voltage is compared with a
set reference value. The error signal is then processed
through a Fuzzy controller, which contributes to zero steady
error in tracking the reference current signal. A fuzzy
controller converts a linguistic control strategy into an
automatic control strategy, and fuzzy rules are constructed by
expert experience or knowledge database. Firstly, input
voltage Vdc and the input reference voltage Vdc-ref have been
placed of the angular velocity to be the input variables of the
fuzzy logic controller. Then the output variable of the fuzzy
logic controller is presented by the control Current Imax. To
convert these numerical variables into linguistic variables,
the following seven fuzzy levels or sets are chosen as: NB
(negative big), NM (negative medium), NS (negative small),
ZE (zero), PS (positive small), PM (positive medium), and
PB (positive big) as shown in Fig.7. The fuzzy controller is
characterized as follows:
 Seven fuzzy sets for each input and output;
 Fuzzification using continuous universe of discourse;
 Implication using Mamdani's „min‟ operator;
 De-fuzzification using the „centroid‟ method.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400
A Novel Unique 5-Level Cascaded Multilevel Inverter based Active Power Filter for Power Quality Enhancement
IV. MATLAB MODELING AND SIMULATION
RESULTS
The APF model is established based on Matlab/Simulink
Platform. Here simulation is carried out in different cases
such as 1) Implementation of 5-Level APF using IRP Based
Controller. 2) Implementation of 5-Level APF using Fuzzy
Controller.
Case 1: Implementation of 5-Level APF using IRP Based
Controller
Fig.6.Conventional fuzzy controller.
Fig.7. Membership functions for Input, Change in input,
Output.
Fuzzification: the process of converting a numerical variable
(real number) convert to a linguistic variable (fuzzy number)
is called fuzzification.
De-fuzzification: the rules of FLC generate required output
in a linguistic variable (Fuzzy Number), according to real
world requirements, linguistic variables have to be
transformed to crisp output (Real number).
Fig.8. Matlab/Simulink Model of proposed 5-Level APF
using IRP Based Controller.
Fig.8 shows the Matlab/Simulink Model of proposed 5Level APF using IRP Based Controller using Matlab/
Simulink Platform.
Database: the Database stores the definition of the
membership Function required by fuzzifier and defuzzifier.
Rule Base: the elements of this rule base table are
determined based on the theory that in the transient state,
large errors need coarse control, which requires coarse in-put/
output variables; in the steady state, small errors need fine
control, which requires fine input/output variables. Based on
this the elements of the rule table are obtained as shown in
Table 1, with „Vdc‟ and „Vdc-ref‟ as inputs.
TABLE I: Fuzzy Rules
Fig.9.Source Voltage, Source Current, Load Current with
5-Level APF.
Fig.9 shows the Source Voltage, Source Current, Load
Current with 5-Level Compensator, due to non-linear diode
rectifier pollutes source side current, with Conventional
Controller based compensator we get source current is
sinusoidal.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400
R. PRAMOTH KUMAR, T. SRINIVASA RAO
Case 2: Implementation of 5-Level APF using Fuzzy
Controller.
Fig.10. Source Side Power Factor with IRP Controller
based APF.
Fig.10 shows the Source side Power Factor, both voltage &
current are maintained sinusoidal and in phase condition.
Fig. 13. Source Voltage, Source Current, Load Current
with Intelligence Controller based Compensator.
Fig.13 shows the Source Voltage, Source Current, Load
Current with 5-Level Compensator, due to non-linear diode
rectifier pollutes source side current, with compensator we
get source current is sinusoidal.
Fig.11. FFT Analysis of source current with compensator
using IRP Controller with 5-Level APF.
Fig.11 shows the FFT Analysis of source current with
compensator using IRP Controller with 5-Level APF, here
we get 4.83%.
Fig.14. Five Level Output Voltage.
Fig.15.Source Side Power Factor with Intelligence
Controller.
Fig.12. Five Level Output Voltage.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400
A Novel Unique 5-Level Cascaded Multilevel Inverter based Active Power Filter for Power Quality Enhancement
Fig.15 shows the Source side Power Factor, both voltage
proc. of India International Conference on Power Electronics
& current are maintained sinusoidal and in phase condition.
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[4] B.Geethalakshmi, M.Kavitha, and K.Delhibabu,
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[5] K.N.V Prasad, G.Ranjith Kumar, T. Vamsee Kiran,
G.Satyanarayana., "Comparison of different topologies of
cascaded
H-Bridge
multilevel
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[6] Crosier, R., Shuo Wang and Jamshidi, M., “A 4800-V
grid-connected electric vehicle charging station that provides
STACOM-APF functions with a bi-directional, multi-level,
cascaded converter ”, in proc. of Applied Power Electronics
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[7] K.N.V. Prasad, G.Ranjith Kumar, Y.S. Anil Kumar, G.
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Fig.16. FFT Analysis of source current with compensator
multilevel inverter as Dynamic Voltage Restorer," Computer
Communication and Informatics (ICCCI), 2013 International
using Intelligence Controller.
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Fig.16 shows the FFT Analysis of source current with
[8] Fang Zheng Peng & Jih-Sheng Lai, “Generalized
compensator using Intelligence Controller, we get THD is
Instantaneous Reactive Power Theory for Three-Phase Power
0.78%.
Systems”, IEEE Trans. on Inst. and Meast, Vol.45, No.1,
V. CONCLUSION
pp.293-297, 1996
A five-level cascaded multilevel voltage source inverter
[9] Joao Afonso, Carlos Couto, Julio Martins “Active Filters
based active filter using instantaneous real-power controller
with Control Based on the p-q Theory”- IEEE Industrial
is found to be an effective solution for power line
Elects Society Nletter-2000
conditioning. Shunt active filter with the proposed controller
[10] E. H. Watanabe, H. Akagi, M. Aredes “Instantaneous preduces harmonics and provides reactive power
q Power Theory for Compensating Non sinusoidal Systems”compensation due to non-linear load currents; as a result
International School on Nonsinllsoidal Currents and
source current(s) become sinusoidal and unity power factor is
Compensation Lagow, Poland-2008
also achieved under both transient and steady state
[11] Leszek S. Czarnecki “Instantaneous Reactive Power p-q
conditions. The proposed instantaneous real-power controller
Theory and Power Properties of Three-Phase Systems”uses reduced computation for reference current calculations
IEEE Trans on Power, VOL. 21, NO. 1, pp 362-367, 2006.
compared to conventional approach. The cascaded inverter
switching signals are generated using triangular-sampling
current controller; it provides a dynamic performance under
transient and steady state conditions. As evident from the
simulation studies, dc bus capacitor voltage settles early and
has minimal ripple because of the presence of Fuzzycontroller. The THD of the source current after compensation
for 5-level 4.83% and with fuzzy 0.78% which is less than
5%, the harmonic limit imposed by the IEEE-519 standard.
VI. REFERENCES
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International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.13, May-2015, Pages: 2394-2400