Cascaded H-bridge converter has been widely used and researched in industry, since it is suitable for the operation under both normal and fault conditions. This paper proposes a novel PWM strategy based on state transition for cascaded H-Bridge inverter with unbalanced DC sources to achieve high quality line-to-line output voltages and maximize the linear modulation range. In this modulation strategy, the duration time of each switching state will be modified directly through the correction value. Ranges of correction value are derived by analyzing the modulation index limitation. Then, proper correction value is added into duration times to transform the switching states and extend modulation index to the maximum value. Meanwhile, balanced AC currents can be obtained under unbalanced DC sources condition, even under larger unbalanced coefficients. Furthermore, a three-phase power control algorithm (PCA) is introduced to achieve the balanced distribution of three-phase power. Compared with the traditional zero-sequence voltage injection method, the proposed strategy is more convenient and effective theoretically, and it can be applied to the higher-level cascaded H-bridge converter. The advantage and effectiveness of the proposed strategy are verified by simulation and experiment results.

1. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
A PWM Strategy Based on State Transition for Cascaded H-
Bridge Inverter under Unbalanced DC Sources
ABSTRACT:
Cascaded H-bridge converter has been widely used and researched in industry, since it is
suitable for the operation under both normal and fault conditions. This paper proposes a novel
PWM strategy based on state transition for cascaded H-Bridge inverter with unbalanced DC
sources to achieve high quality line-to-line output voltages and maximize the linear modulation
range. In this modulation strategy, the duration time of each switching state will be modified
directly through the correction value. Ranges of correction value are derived by analyzing the
modulation index limitation. Then, proper correction value is added into duration times to
transform the switching states and extend modulation index to the maximum value. Meanwhile,
balanced AC currents can be obtained under unbalanced DC sources condition, even under larger
unbalanced coefficients. Furthermore, a three-phase power control algorithm (PCA) is
introduced to achieve the balanced distribution of three-phase power. Compared with the
traditional zero-sequence voltage injection method, the proposed strategy is more convenient and
effective theoretically, and it can be applied to the higher-level cascaded H-bridge converter. The
advantage and effectiveness of the proposed strategy are verified by simulation and experiment
results.
KEYWORDS:
1. State transition
2. Linear modulation range

2. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
3. Unbalanced DC sources
4. Power control algorithm
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
A novel PWM strategy based on state transition for CHBI with unbalanced DC sources has been
proposed in this paper. Compared with ZSVIM and NVM, the duration times of each switch
states can be modified directly by correction value and the gate signals can be acquired easily
through ST-PWM. To acquire the maximum linear modulation index, the reason of the
modulation index limitation and the novel modulation strategy based on the state transition are
studied. The proposed strategy can achieve high quality line-to-line output voltages and extend
the modulation range as high as possible. Besides, the three-phase power control algorithm is
introduced to acquire balanced power distribution. The effectiveness has been verified by
simulation and experiment results.
In our current work, we incorporate PCA into the ST-PWM strategy, which is a prototype of
multi-objective control. Since both modulation index extension and power control are achieved
by adjusting ΔT, there is a conflict on the control objectives. That is to say, the control ability of
PCA will decrease when the modulation index is extended. However, we have not yet found a
strict mathematical relationship between them due to time constraints. And we will do a further

3. ELECTRICAL PROJECTS USING MATLAB/SIMULINK
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
For Simulation Results of the project Contact Us
Gmail: asokatechnologies@gmail.com, Website: http://www.asokatechnologies.in
0-9347143789/9949240245
research on multi-objective optimal PWM strategy and multi-objective control boundaries under
unbalanced dc sources in the future.
REFERENCES:
[1] A. Marzoughi, R. Burgos, D. Boroyevich, and Y. Xue, "Investigation and comparison of
cascaded H-bridge and modular multilevel converter topologies for medium-voltage drive
application," in Industrial Electronics Society, IECON 2014 - 40th Annual Conference of the
IEEE, 2014, pp. 1562-1568.
[2] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, et al., "Recent
Advances and Industrial Applications of Multilevel Converters," IEEE Trans. Ind. Electron., vol.
57, no. 8, pp. 2553-2580, Aug. 2010.
[3] X. Zha, L. Xiong, J. Gong and F. Liu, "Cascaded multilevel converter for medium-voltage
motor drive capable of regenerating with part of cells," IET Power Electronics, vol. 7, no. 5, pp.
1313-1320, May. 2014.
[4] G. Farivar, C. D. Townsend, B. Hredzak, J. Pou, and V. G. Agelidis, "Low-capacitance
cascaded H-bridge multilevel StatCom," IEEE Trans. Power Electron., vol. 32, no. 3, pp. 744-
1754, Mar. 2017.
[5] K. D. Teryima, G. Y. Nentawe, and A. O. David, "A Overlapping Carrier Based SPWM for a
5-Level Cascaded H-bridge Multilevel Inverter," International Journal of Power Electronics and
Drive Systems (IJPEDS), vol. 7, no. 2, pp. 349-357, 2016.