A 13-levels Module (K-Type) with two DC sources for Multilevel Inverters

 Abstract

This paper presents a new reconfiguration module for asymmetrical multilevel inverters in which the capacitors are used as the DC links to creates the levels for staircase waveforms. This configuration of multilevel converter makes a reduction in DC sources. On the other hand, it is possible to generate 13 levels with lower DC sources. The proposed module of multilevel inverter generates 13 levels with two unequal DC sources (2VDC and 1VDC). It also involves two chargeable capacitors and 14 semiconductor switches. The capacitors are self-charging without any extra circuit. The lower number of components makes it desirable to use in wide range of applications. The module is schematized as two back-to-back T-type inverters and some other switches around it. Also, it can be connected as cascade modular which lead to a modular topology with more voltage levels at higher voltages. The proposed module makes the inherent creation of the negative voltage levels without any additional circuit (such as H-bridge circuit). Nearest level control switching modulation (NLC) scheme is applied to achieve high quality sinusoidal output voltage. Simulations are executed in MATLAB/Simulink and a prototype is implemented in the power electronics laboratory which the simulation and experimental results show a good performance.

Index Terms

1.      Asymmetric

2.      Capacitors

3.      Multilevel inverter

4.      Power electronics

5.      Self-charging

6.      Nearest level control switching

Block Diagram:

Fig.1 The general conceptual asymmetric MLIs with capacitors

Expected Simulation Results:

Fig.2 The waveform of output Voltage (simulation) for the proposed module: (a) Waveform (b) Harmonics spectrums.

Fig.3 The waveform of output Voltage (simulation) for the first cascade topology (25 Levels): (a) Waveform (b) Harmonics spectrums.

Fig.4 The waveform of output Voltage (simulation) for the second cascade topology (169 Levels): (a) Waveform (b) Harmonics spectrums.

Conclusion

This paper introduced one module for asymmetrical multilevel inverter to produce 13 levels by two DC sources. The proposed multilevel is designed based on two back to back TType modules with some switches around them. The proposed module is named K-Type. The configuration of K-type provides two extra DC links by capacitors (as the virtual DC supply) to achieve more levels to create staircase waveform. The module needs lower components including two DC sources, two capacitors, 14 semiconductors. It can be used in power applications with unequal DC sources (with ratio 1:2). It can also be easily modularized in two strategies in cascade arrangements to form high voltage outputs with low stress on semiconductors and lowering the number of devices. This ability can be used in some special applications such as solar farm along with a lot of DC sources. DC sources can also have different voltage amplitudes. In the conventional methods, it should be considered one inverter for each DC resources and fix the output voltage the same amplitude. It increases complexity and losses from this aspect, but in asymmetrical multilevel converters, it is possible to combine some DC resources together and generate a unique AC output. It reduces the number of separated inverter, components, losses and etc. The other advantage of K-Type module is its capability to generate both positive and negative output voltage without any additional circuit. Module is tested and it shows a good performance. THD% for one module is obtained 3.87% and 4.07% in simulation and experimental results, respectively that satisfy harmonics standard (IEEE519). THD% for cascade connection (two module) is calculated 1.99% in simulation and 2.26% in experimental results.

References

[1]Essakiappan, S.; Krishnamoorthy, H.S.; Enjeti, P.; Balog, R.S.; Ahmed, S., "Multilevel Medium-Frequency Link Inverter for Utility Scale Photovoltaic Integration," in Power Electronics, IEEE Transactions on , vol.30, no.7, pp.3674-3684, July 2015

[2]A. Nami, J. Liang, F. Dijkhuizen and G. D. Demetriades, "Modular Multilevel Converters for HVDC Applications: Review on Converter Cells and Functionalities," in IEEE Transactions on Power Electronics, vol. 30, no. 1, pp. 18-36, Jan. 2015.

[3]I. A. Gowaid, G. P. Adam, A. M. Massoud, S. Ahmed and B. W. Williams, "Hybrid and Modular Multilevel Converter Designs for Isolated HVDC–DC Converters," in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 6, no. 1, pp. 188-202, March 2018.

 [4] Xibo Yuan, "A Set of Multilevel Modular Medium-Voltage High Power Converters for 10-MW Wind Turbines," in Sustainable Energy, IEEE Transactions on , vol.5, no.2, pp.524-534, April 2014

 [5] Ahmadi, D.; Jin Wang, "Online Selective Harmonic Compensation and Power Generation With Distributed Energy Resources," in Power Electronics, IEEE Transactions on , vol.29, no.7, pp.3738-3747, July 2014