ISSN 2319-8885
Vol.04,Issue.06,
March-2015,
Pages:1137-1143
www.ijsetr.com
Design of Phase Shift and Level Shift of a Cascaded H-Bridge Inverter for
Aircraft Electrical Power Systems
G.SRIKAR1, M.SEETARAMA SARMA2
1
PG Scholar, Dept of EEE, CVSR College of Engineering, Hyderabad, Telangana, India.
2
Professor, Dept of EEE, CVSR College of Engineering, Hyderabad, Telangana, India.
Abstract: ―More electrical aircraft‖ introducing active power filter technology. The Multilevel inverters are new engendering
of power inverter choices for high power applications like in aircrafts. In this paper presents a study and analysis of shunt APF
with closed loop control, feed forward compensation path of load current with the Level Shifted PWM Cascaded H – bridge
(CHB) Inverter and Phase Shift PWM CHB-Inverter. The cascade h-bridge inverter is selected as the aeronautical APF (AAPF)
for compensation of reactive power and harmonics. The SAPF helps to improve the power factor and eliminate the Total
Harmonics Distortion (THD) drawn from a Non- Linear Loads. By using a instantaneous PQ theory the compensating currents
are generated. The fast acting dc link voltage controller used to generate the reference compensating currents for cascaded hbridge inverter. Finally a 2-H cascaded bridge of level shifted PWM and phase shifted PWM with PQ controller is adopted to
investigate the performance of CHB Inverter and there THD are also shown by using MATLAB/SIMULINK software.
Keywords: Aeronautical Active Power Filter (AAPF), Cascaded Multi Level Inverter, Closed-Loop Control, THD, PWM
Techniques.
I. INTRODUCTION
The use of the electrical power is demanding more
advanced aircraft power systems in place of hydraulic,
pneumatic, and mechanical power. So ‗More Electric
Aircraft‘(MEA) and ‗All Electric aircraft‘ are introduced to
overcome some of the drawbacks found in conventional
architectures and bring more attractive advantages, such as
improved fuel consumption and lower maintenance and
operation costs. This shows the more increase in demand for
the power electronics equipments, electric loads, and
consumption of electrical energy, more demand for
generated power, power quality, and also stability problems.
MEA shows the significant approach rather than the
conventional architectures. MEA defines about the usage of
the power electronic equipments and also the electrical
power generation and the distribution. Due to the power
electronic devices there is a power quality issues i-e
harmonics, reactive power compensation.
Advantages of the increasing use of electric power in the
aircraft system:
 Optimization of the performance.
 Optimization of the life cycle cost.
 Reduction of weight and size of the equipment.
 Increased reliability.
Harmonic current compensation by means of active
Power filter (APF) is a well-known effective solution for the
reduction of current distortion and for power Quality
improvement in electrical systems. Shunt compensator
behaves as a controlled current Source that can draw any
chosen current references which is usually the harmonic
components of the Load currents. Meanwhile, more and
more APFS are applied not only in harmonic current and
reactive Power compensation but also in the neutral line
Current compensation, harmonic damping Application, and
power flow control. In the aircraft EPS, the APF could be
installed in the source side (such as the aircraft generator) or
near the load side and it could even be integrated into t he
load-front Converter (such as t he input stage converter of
variable-speed drives). Introducing APF technology to
resolve the power quality issues of the aircraft EPS catches
increasing attention.
Fig. 1. Next-generation electrical system of MEA.
Copyright @ 2015 IJSETR. All rights reserved.
G.SRIKAR, M.SEETARAMA SARMA
Fig.1 illustrates the next-generation electrical power
system. To eliminate the harmonics we are connecting an
system (EPS) of MEA. In the variable-speed variableAPF. Here we are mainly sensing the main voltages ( ),
frequency (VSVF)-based EPS, the ―constant speed drive‖ is
Dc-link voltage ( ), and main currents ( ). Mainly due to
moved. Harmonic current compensation by means of active
the non-linear loads the harmonics are producing these
power filter (APF) is a well-known effective solution for the
harmonics will effect mainly on currents but not on
reduction of current distortion and for power quality
voltages. So here both voltage and currents are sensed with
improvement in electrical systems [2]–[4]. The shunt
the DC voltage.
compensator behaves as a controlled current source that can
(1)
draw any chosen current references which is usually the
Where
is DC-link Voltage,
is Current magnitude
harmonic components of the load currents [5]–[7].
Meanwhile, more and more APFs are applied not only in
Main voltage ( ), is to generate reference synchronous
harmonic current and reactive power compensation but also
sine wave which is in amplitude and phase with main
in the neutral line current compensation, harmonic damping
voltage. Multiplier is used to sense the current magnitude
application, and power flow control. As Fig. 1 shows, in the
and shape and the DC bus voltage gives the information of
aircraft EPS, the APF could be installed in the source side
the power balance as shown in Fig.3. The Dc voltage is
(such as the aircraft generator) or near the load side and it
compared with the main voltage and given to the multiplier
could even be integrated into the load-front converter (such
and it generates the practical currents with the desired
as the input stage converter of variable-speed drives).
amplitude and phase. The practical currents are compared
In this paper, a high-performance aircraft APF is proposed.
Differently from traditional open-loop control strategy, the
proposed aeronautical APF (AAPF) works in a close-loop
way. Good power quality of the EPS is achieved by using
the novel AAPF. Furthermore, in order to improve the
dynamic performance of the load response, a feed forward
path of the load current is added. Based on the modelling
and analysis of the close-loop system, the operation
principle of the feed forward compensation path is revealed.
Meanwhile, the control method of the cascaded-inverterbased AAPF is proposed. In, a shunt APF using perfect
harmonic cancellation is studied. The harmonic filtering
performance of the APF using CHB-Inverter with PWM
techniques are presented with Matlab simulation results.
II. SOURCE CURRENT DIRECT CONTROL
The closed-loop system is named as the source current
direct control. This is applied as the main control strategy of
the proposed AAPF. The control diagram of the source
current direct control is shown below. Fig. 2 shows the
configuration and control block diagram of the proposed
active power filter.
Fig. 2. Control diagram of source current direct control.
We are supporting an AC system but also readily DC is also
available which has to be converted to AC and given to the
with the main currents ( ) for the wave shape and the phase
information of the main currents. The generated currents are
in phase with the main voltage. These are given to the PWM
to generate the switching signal. Here in the above figure we
can observe that only one current sensor is used mainly. In
this paper the Voltage Source Inverter (VSI) is used as the
Active Power Filter (APF) have an advantages of:
 Self-Supporting Dc voltage
 Lighter and cheaper
 Expandable to Multi levels(inverters)
A. Multilevel Inverters
The Multi level inverter is like an inverter and it is used
for industrial applications as alternative in high power and
medium voltage situations. General DC-AC Inverter Circuit
the need of multilevel converter is to give a high output
power from medium voltage source. A multilevel converter
has several advantages over a conventional two-level
converter that uses high switching frequency pulse width
modulation (pwm). The attractive features of a multilevel
converter can be briefly summarized as follows.
 Staircase Waveform Quality: multilevel converters
not only can generate the output voltages with very low
distortion, but also can reduce the dv/dt stresses;
therefore electromagnetic compatibility (emc) problems
can be reduced.
 Common-Mode (Cm) Voltage: multilevel converters
produce smaller cm voltage; therefore, the stress in the
bearings of a motor connected to a multilevel motor
drive can be reduced. Furthermore, cm voltage can be
eliminated by using advanced modulation strategies
such as that proposed in.
 Input Current: multilevel converters can draw input
current with low distortion.
 Switching Frequency: multilevel converters can
operate at both fundamental switching frequency and
high switching frequency pwm. It should be noted that
lower switching frequency usually means lower
switching loss and higher efficiency.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.06, March-2015, Pages: 1137-1143
Design of Phase Shift and Level Shift of a Cascaded H-Bridge Inverter for Aircraft Electrical Power Systems
Types of Multilevel Inverters:
 Diode clamped multilevel inverter
 Flying capacitors multilevel inverter
 Cascaded H- bridge multilevel inverter
B. Cascaded H-Bridge Multilevel Inverter
The cascaded H-bride multi level inverter is to use
capacitors and switches and requires less number of
components in each level as shown in Fig.4. This topology
consists of series of power conversion cells and power can
be easily scaled. The combination of capacitors and
switches pair is called an H-bridge and gives the separate
input DC voltage for each H-bridge. It consists of H-bridge
cells and each cell can provide the three different voltages
like zero, positive DC and negative DC voltages. One of the
advantages of this type of multi level inverter is that it needs
less number of components compared with diode clamped
and flying capacitor inverters. The price and weight of the
inverter are less than those of the two inverters. Softswitching is possible by the some of the new switching
methods.
Fig.4. Cascaded H-Bridge Inverter in a Three-Phase
Power System.
The P-Q Theory: "The generalized theory of the
Instantaneous Reactive Power in three-phase circuits" also
known as instantaneous power theory or p-q theory. It is
based on instantaneous values in three-phase power systems
with or without neutral wire, and is valid for steady-state or
transitory operations, as well as for generic voltage and
current waveforms. The p-q theory is one of several
methods that can be used in the control active filters.
Fig.3. Single Phase Structures of Cascaded Inverter (a)
3-Level, (b) 5-Level, (c) 7-Level.
III. APF WITH CONTROLLER BASED ON
INSTANTANEOUS PQ THEORY
Current source nonlinear loads such as a six-pulse rectifier
converter require harmonics current
from the main
supply beside fundamental current . This causes the main
supply to operate at frequencies above the nominal 50Hz or
60Hz and in doing so, also creates a negative phasesequence component which is undesirable. The shunt active
filter is considered a current source because it injects nonsinusoidal current
through the parallel branch of the
network in order to compensate for the current harmonic
demand of the nonlinear load. The role of the cascaded hbridge inverter controller is to sense and monitor the load
current and to appropriately determine the correct reference
harmonic current for the inverter. Once the correct reference
harmonic content is determined; this reference current is fed
through a suitable current controller which then is sent to
the inverter for injection into the network.
Fig.5. Calculations for the Sinusoidal Supply Current
Control Strategy.
In the PQ theory the phase voltages and load currents are
taken as reference from the three phase supply system which
is in the 120˚ angle. These voltages and currents are
converted into two phase by Clarks transformation of 90˚ in
phase as shown in Fig.5. From this we are getting ,
and ,
with zero reference current . Dc voltage is taken
as reference with voltages and currents and calculating
power losses and getting active and reactive power. By
using the Inverse Clark‘s transformation the active and
reactive power will generates the actual currents which are
sinusoidal and in phase with the main voltage and which
are summed with the main currents and given to the PWM
modulation. Here in this paper we are using two PWM
modulation techniques they are:
 Phase Shift Carrier PWM(PSCPWM)
 Level Shift carrier PWM(LSCPWM)
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.06, March-2015, Pages: 1137-1143
G.SRIKAR, M.SEETARAMA SARMA
A. Phase Shift Carrier Pulse Width Modulation
 When the reference signal is greater than both
(PSCPWM)
carrier waveforms then the converter is switched to
The Phase shifted carrier pulse width modulation. In
+Vdc.
general, a multilevel inverter with m voltage levels requires
 When the reference signal is greater than the lower
(m –1) triangular carriers. In the phase shifted multicarrier
carrier waveform but less than the upper carrier
modulation, all the triangular carriers have the same
waveform the converter is switched to zero.
frequency and the same peak -to-peak amplitude, but there
 When the reference is less than both carrier
is a phase shift between any two adjacent carrier waves,
waveforms the converter is switched to 2Vdc.
given by:
(2)
The phase shift multicarrier PWM technique is another
type of multicarrier PWM strategy and has its performance
parameters closest to PDPWM strategy. It uses four carrier
signals of the same amplitude and frequency which are
shifted by 90 degrees to one another as shown in fig.6. The
modulating signal is usually a three - phase sinusoidal wave
with adjustable amplitude and frequency. The gate signals
are generated by comparing the modulating wave with the
carrier waves. It means for the five level inverter, four are
triangular carriers are needed with a 90° phase displacement
between any two adjacent carriers. In this case the phase
displacement of Vcr1=0°, Vcr2=90°, Vcr1- =180° and Vcr2- =
270°.
Fig.7. Carrier Arrangement for PDPWM Strategy.
In this way the both the PWM techniques are used for the
switching operations of the cascaded H-Bridge Inverter as
shown in Fig.7. When the switches operates its generates a
5-level output voltages of
,
0,
,
. The
currents generated from the CHB-Inverter are given to the
three phase supply system. So these currents are called as
the counter harmonics that can reduce the actual harmonics
from the non-linear side that cannot affect the source side.
IV. SIMULATION RESULTS
Simulation results of this paper as shown in Fig.8 to 10.
Fig.6. Carrier Arrangement for PSPWM Strategy.
B. Level Shift Carrier Pulse Width modulation
(LSCPWM)
Total harmonics distortion of phase-shifted modulation
is much higher than level-shifted modulation. Therefore we
have considered level-shifted modulation. An m-level
multilevel inverter using level-shifted multicarrier
modulation scheme requires (m-1) triangular carriers, all
having the same frequency and amplitude. The (m-1)
triangular carriers are vertically disposed such that the bands
they occupy are contiguous. There are three alternative
Pulses with different phase relationships for the level-shifted
multicarrier
modulation
three
alternative
carrier
dispositions. There in, the a-phase modulation signal is
compared with two triangle waveforms. The rules for the in
phase disposition method, when the number of level N = 5,
are
 The N –1 = 5-1= 4 carrier waveforms are arranged
so that every carrier is in phase.
Fig.8. Simulation of the 3-⏀ Supply System with CHBInverter.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.06, March-2015, Pages: 1137-1143
Design of Phase Shift and Level Shift of a Cascaded H-Bridge Inverter for Aircraft Electrical Power Systems
Fig.9. Simulation of the Level Shift PWM Carrier
Signal.
Fig.10. Simulation of the Phase Shift PWM Carrier
Signal.
Fig.12. Simulation Waveforms of the 3-⏀ compensating
current, load Current with CHB-Inverter.
Fig.13. Simulation Waveforms of the 5-level output
voltage of with the CHB-Inverter for both level shift &
phase shift pwm.
The simulated wave forms and THD results for Level
Shift PWM are shown below Figs.11 to 14:
Fig.11. Simulation Waveforms of the 3-⏀ Source
Voltage, Source Current with the CHB-Inverter.
Fig.14. FFT Analysis of the THD of the 3-⏀ Source
Current with the CHB-Inverter using Level Shift PWM.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.06, March-2015, Pages: 1137-1143
G.SRIKAR, M.SEETARAMA SARMA
The simulated waveforms and the THD results of Phase
TABLE I: THD of PSCPWM and LSCPWM schemes
Shift PWM are shown below Figs.15 to 17:
According to the IEEE- Standardisation the THD% with
both control circuits and with PWM techniques are
tabulated in table 2 which are 5%.
Fig.15. Simulation Waveforms of the 3-⏀ Source
Voltage, Source Current and load current with the
CHB-Inverter.
Fig.16. Simulation Waveforms of the Compensating
Currents each Phase with the CHB-Inverter.
Fig.17. FFT Analysis of the THD of the 3-⏀ Source
Current with the CHB-Inverter using Phase Shift PWM.
V. CONCLUSION
In this paper cascaded H-bridge multilevel inverter based
APF is implemented in 3-⏀ AC supply system. Cascade
type inverter has certain advantages as compared with other
types. Instantaneous PQ theory is used to generate reference
currents of CHB-Inverter. The Phase Shifted Carrier PWM
and Level Shift Carrier PWM method reduces individual
device switching frequency despite high frequency output of
the converter. Simulated results validate that the cascaded
multi-level inverter based APF can compensate harmonics
without use of transformer in AC supply system. It can be
concluded that the proposed technique is best suited for load
compensation under non-linear conditions. A Mathematical
model for single H-Bridge inverter is developed which can
be extended to multi H-Bridge. The source voltage, load
current, source current simulation results under non-linear
loads are investigated for both PSCPWM and LSCPWM
with 200v, 400Hz and are tabulated. Finally with the help of
Matlab/Simulink based model simulation we conclude that
LSCPWM is better than PSCPWM techniques and the
results are presented. Total Harmonic Distortion of the
source current has been reduced from a high value to an
allowable limit to meet IEEE 519 and IEC 61000-3
harmonic standard.
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International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.06, March-2015, Pages: 1137-1143