Int. J. of Recent Trends in Engineering & Technology, Vol. 11, June 2014
Simulation of Cascaded and Modified Cascaded
H-Bridge Multilevel Inverter for 3-Phase
Asynchronous Motor
Tejas M. Panchal1, Rakesh A. Patel2, and Hiren S. Darji3
1
U V Patel College of Engineering/ Electrical Engg. Department, Mehsana, India
Email: tejaspanchal4@gmail.com
2
U V Patel College of Engineering/ Electrical Engg. Department, Mehsana, India
Email: rap01@ganpatuniversity.ac.in2, hsp04@ganpatuniversity.ac.in3
Abstract— This paper proposed three phase five level cascaded and modified cascade multilevel inverter for
asynchronous motor drive. The multilevel inverters have drawn a tremendous interest in the power industry now
a day. A Multilevel inverter is a converter used to obtain an ac voltage at desired magnitude and frequency
waveform from separate dc sources. In recent decade multilevel inverters have been used for high-power and
medium-voltage energy control applications. Out of different types of multilevel inverter topologies, cascaded
multilevel inverter requires least number of components, circuit flexibility and simple circuit layout and also there
are no extra clamping diodes or voltage balancing capacitor required. Here, Sinusoidal Pulse Width Modulation
techniques are adopted to obtain a distortion less output for asynchronous motor drives.
Index Terms — Multilevel Inverter (MLI), Sinusoidal Pulse Width Modulation (SPWM), Constant Switching
Frequency Multi-Carrier Pulse Width Modulation (CSFMCPWM)
I. INTRODUCTION
The concept of multilevel inverters (MLI) has been introduced since 1975. The name of multilevel can start
with the three-level inverter. From that, we can develop the several multilevel converter topologies.
Nowadays, multilevel inverter is to use in the most of industries for the medium voltage high power
application. PV Cells, capacitors, batteries, etc. voltage sources can be used as the multiple dc voltage
sources in the multilevel voltage source inverter [1].
Now, inverters are static power electronics device which is converts dc input voltage to ac output voltage
with the desired magnitude and frequency. The output voltage waveforms of ideal inverters should be
sinusoidal. But in practically it is square-wave or quasi-square-wave. The multilevel voltage source inverters
unique structure allows them to reach medium voltages and high power levels without use of transformers.
They are especially suited to high voltage vehicle drives where low output voltage total harmonic distortion
(THD) and electromagnetic interference (EMI) are needed. The general function of multilevel inverter is to
synthesize a desired voltage from several levels of dc voltages [10].
Basically, there are three types of multilevel inverter topologies i. e. Diode clamped, Flying capacitor and
cascaded h-bridge MLI. Out of that, the cascaded h-bridge MLI topology is beneficial because in that
topology the circuit complexity and layout is simple also there are no extra components are required like
clamping diode or flying capacitor compare to diode clamped and flying capacitor MLI topology [3].
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So, Cascaded H-bridge MLI using reduced switch topology is chosen. Here, asynchronous motor is used as a
non-linear load. The three phase AC signals gives to the rectifier circuit than it is converted into the DC.
After that, these DC signal gives to the cascaded H-bridge MLI. Then the signals connect with to the load.
For the MLI, the gating signals are provided through the PWM controller. The basic block diagram of the
cascaded h-bridge multilevel inverter as shown in figure 1 [4].
Fig. 1. Basic Block Diagram of Multilevel Inverter
In multilevel inverter, the number of levels increases, the output waveform have more steps and we can
obtain nearly the sinusoidal wave output, which contains the lower harmonics distortion [5].
II. CASCADED H-BRIDGE MULTILEVEL INVERTER
The multilevel inverter using with the Separate DC Sources (SDCSs), that DC sources may be obtained from
batteries, fuel cells, PV cells or solar cells. Nowadays this topology becomes very popular in high power ac
power supply and adjustable speed drive applications. A single-phase two-cell series configuration of the five
level cascaded H-bridge multilevel inverter is shown in figure 2 and also the output voltage waveform as
shown in figure 3 [6].
Fig. 2. Cascaded H-Bridge Multilevel Inverter
Fig. 3. Output voltage oh 5-level Inverter
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Each SDCS is associated with a single-phase full-bridge inverter. For the five level there are 8 switches used.
The switching pattern for the different voltage level is shown in the table I. Output of the five level inverters
are 0, +Vdc, +2Vdc, -Vdc, -2Vdc as shown in figure 3 (assuming that Vdc is the supply voltage).
Table I. Switch combinations of the voltage levels and switch states
Output Voltage VAO
S1
S2
S3
S4
S5
S6
S7
S8
V5=2Vdc
1
0
0
1
1
0
0
1
V4=Vdc
1
0
0
1
1
1
0
0
V3=0
1
1
0
0
1
1
0
0
V2=-Vdc
1
1
0
0
0
1
1
0
V1=-2Vdc
0
1
1
0
0
1
1
0
III. MODIFIED CASCADED H-BRIDGE MLI USING ONE H-BRIDGE & ONE POWER
SEMICONDUCTOR SWITCH
A PWM control scheme is introduced to generate switching signals for the switches and to produce five
output-voltage levels: zero, +1/2Vdc, Vdc, −1/2Vdc, and −Vdc (here also assuming that Vdc is the supply
voltage). Here, the modified five level cascaded h-bridge MLI using one h-bridge & one power
semiconductor switch as shown in figure 4. The voltage can divided using capacitor. The switching pattern
for that five level inverter is as shown in table II [11].
Fig. 4. five-level multilevel inverter (5 switches)
Table II. Switching Logic for 5-level Inverter (5 switch)
Vinv
S4
S5
S6
S7
S8
+Vdc/2
1
0
0
0
1
+Vdc
0
1
0
0
1
0
0
1 or 0
0 or 1
1 or 0
0 or 1
-Vdc/2
1
0
0
1
0
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-Vdc
0
0
1
1
0
IV. SINUSOIDAL-PULSE WIDTH MODULATION TECHNIQUE
In Sinusoidal Pulse Width Modulation (SPWM) technique the signal is generated by comparing a sinusoidal
reference signal with a triangular carrier wave of frequency fc. The frequency of the reference signal is fr
determines the output frequency fo and its peak amplitude is Ar controls the modulation index M. The gating
signal for SPWM technique is shown in figure 5. The output waveforms are given in pulses by comparing the
reference and carrier signals.
Fig. 5. Principle of PWM generation
Fig. 6. Constant switching frequency multicarrier Pulse width modulation (CSFMC-PWM)
Figure 6 shows Constant switching frequency multicarrier Pulse width modulation (CSFMCPWM)
technique. In this technique four triangular carrier signals are comparing with the one sinusoidal reference
signal and the output waveforms are in the form of pulses and that pulses signals given to the switches of the
multilevel inverter. The m-level inverter, m-1 carriers with the same frequency fc and the same amplitude Ac
are disposed. The reference waveform has peak to peak amplitude Am, the frequency fm, and its zero cantered
in the middle of the carrier set. The reference signal is continuously compared with each of the carrier
signals. If the Reference is greater than the carrier signal, then they active device corresponding to that carrier
is switched off [8].
V. SIMULATION OF 3-PHASE, 5-LEVEL CASCADED H-BRIDGE MLI OF CSFMCPWM
TECHNIQUE USING 8 SWITCHES AND 5 SWITCHES
A.
Using 8 switches
The model for three-phase 5-level cascaded h-bridge multilevel inverter of asynchronous motor using
Constant Switching Frequency Multi-Carrier PWM Technique is simulating using MATLAB/SIMULINK. In
this technique single sinusoidal reference signal is compared with four triangle carrier signal and from the
logical operation generated the pulse for the 8-switches of MLI. The switching sequence for that 5-level
inverter is shown in table I. The two h-bridge configuration is shown in figure 8. From that sine and
triangular signal generate the 5-level output voltage as shown in figure 9. The model is simulated using two
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DC source each of 140 V. The 5- level output is 560V (peak to peak) of single sine and four triangle
comparison, Generated CSFMCPWM and Output voltage waveform of three phase 5-level cascaded h-bridge
multilevel inverter. The output voltages are: 0, +140, +280, -140, -280 Volts. Now the model for five-level
each can connected in 3-phase in 120 degree apart from each other and connected to the 3-phase
asynchronous motor. The model for three-phase 5 level cascaded h-bridge MLI of Asynchronous motor using
8 switches shown in the figure 7.
Fig. 7. three-phase 5 level cascaded H-bridge MLI of Asynchronous motor using 8 switches
Fig. 8. Cascaded H-bridge 5-level multilevel Inverter
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Fig. 9. four carrier and one reference signal of 5 level Inverter
The stator current with respect to 3-phase waveform for asynchronous motor is as shown in figure 10. The
phase to ground and phase to phase voltage of the 5-level MLI of asynchronous motor is shown in figure 11
and 12 respectively. After simulating this model, motor speed is increase and settled at nearly 1406 rpm
while the rated speed of the motor is 1430 rpm. The output waveform of the motor speed is shown in figure
13.
Fig. 10. Three-phase stator current of asynchronous machines
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Fig. 11. Three-phase 5 level phase to ground Voltage of asynchronous machines
Fig. 12. Three-phase 5 level phase to phase Voltage of asynchronous machines
Fig. 13. Speed of asynchronous machines for MLI using 8 switches
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Fig. 14. FFT analysis of 5 level voltage waveform of Constant switching frequency multi-carrier PWM Technique
Fig. 15. FFT analysis of 5 level current waveform of Constant switching frequency multi-carrier PWM Technique
The FFT analysis of 5-level voltage waveform using CSFMCPWM is shown in figure 14. It can be seen that
the magnitude of fundamental voltage for five-level inverter fed asynchronous motor drive is 278.4 Volts.
The Total Harmonics Distortion of the voltage is nearly 27.29%. The FFT analysis of 5-level current
waveform using CSFMCPWM is shown in figure 15. For that the magnitude of fundamental current for fivelevel inverter fed asynchronous motor drive is 60.11 Amps. The Total Harmonics Distortion of the current is
nearly 15.57%.
Using 5 switches
The model for three-phase 5-level modified cascaded h-bridge multilevel inverter of asynchronous motor
using Constant Switching Frequency Multi-Carrier PWM Technique is simulating using
MATLAB/SIMULINK. In the modified cascaded MLI there are one h-bridge and 1 power semi-conductor
switch is use for generate 5-level output as shown in figure 16. The switching sequence for the five switches
is shown in table II. Here also the model is simulated using one DC source of 280V. The 5-level output is
560V (peak to peak) for single sine and four triangle comparison, Generated CSFMCPWM and Output
voltage waveform of three-phase 5-level modified cascaded H-bridge Multilevel Inverter. The output
voltages are: 0, +140, +280, -140, -280 Volts. Now the model for five-level each can connected in 3-phase in
120 degree apart from each other and connected to the 3-phase asynchronous motor..
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Fig. 16. MATLAB/SIMULINK models of single phase 5-level cascaded H-bridge Multilevel Inverter using 5 switches
Fig. 17. 3 phase stator current of asynchronous machine
Fig. 18. 3 phase 5 level phase to ground Voltage of asynchronous machines
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Fig. 19. Speed of asynchronous machines for MLI using 5 switches
Fig. 20. FFT analysis of 5 level voltage waveform of Constant switching frequency multi-carrier PWM Techniques
Fig. 21. FFT analysis of 5 level current waveform of Constant switching frequency multi-carrier PWM Techniques
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The phase to ground voltage of the 5-level MLI for asynchronous motor is shown in figure 19. After
simulating this model, motor speed is increase and settled at nearly 1396 rpm while the rated speed of the
motor is 1430 rpm. The FFT analysis of 5-level voltage waveform using CSFMCPWM is shown in figure 20.
It can be seen that the magnitude of fundamental voltage for five-level inverter fed asynchronous motor drive
is 249.4 Volts. The Total Harmonics Distortion of the voltage is nearly 29.42%. The FFT analysis of 5-level
current waveform using CSFMCPWM is shown in figure 21. For that the magnitude of fundamental current
for five-level inverter fed asynchronous motor drive is 51.75 Amps. The Total Harmonics Distortion of the
current is nearly 6.38%.
CONCLUSION
In this paper, cascaded h-bridge and modified cascaded h-bridge 5-level multilevel inverter of asynchronous
motor drive is simulate using Matlab simulation. For that simulation, Constant Switching Frequency Multi
Carrier PWM Techniques are used from that the THD is comparatively reduced in modified cascaded
multilevel inverter. From this technique, we can obtain the desired output for the asynchronous motor drive.
There are also in modified cascaded multilevel inverter requires only five switches and one DC source. So,
the cost is comparatively reduces for the five level and also that there are circuit flexibility, simple circuit
layout and there are no extra clamping diodes or voltage balancing capacitor required. Thus, the modified
cascaded h-bridge MLI is very beneficial over the cascaded MLI and other convectional MLI topologies.
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