Novel Cascaded Seven-Level Inverter With Embedded Voltage Boosting for Renewable Energy Applications

 Abstract

This paper proposes a novel seven-level inverter for renewable energy applications with voltage boosting capability. The proposed inverter is based on a full-bridge (FB) inverter, whose two half-bridge legs are cascaded with a three-level T-type (3LTT) inverter, respectively. It is supplied by a single dc source in series with an input inductor. The inductor is charged by the dc source internally through the FB inverter without using extra switches. It then transfers energy to capacitors that directly supply the 3LTT inverters. Auxiliary circuits for balancing the voltages of capacitors are not required, since each capacitor can be charged by the inductive dc-link with the same step-up average voltage. Carrier-based phase-shift pulse-width modulation (PWM) scheme is applied to the FB inverter to produce an inductive- charge duty ratio and generate suitable voltage gain. Theoperating principles of the proposed inverter are described. Key inverter parameters including voltage gain and voltage stresses on devices are analyzed and compared with those of the prior-art solutions. Simulations and experimental results verify the feasibility of the proposed single-stage dc-to-ac power conversion for producing a boosted seven-level output voltage with relatively high efficiency.

Index Terms

Cascaded multilevel inverter, full-bridge inverter, phase-shift PWM scheme, three-level T-type inverter, voltage boosting.

Block Diagram:

Fig. 1. Proposed C7L inverter based on one full-bridge (FB) and two 3LTT (#1 and #2) inverters supplied by Vin in series with Lin.

Expected Simulation Results:

Fig. 2. Simulated (a) steady-state inductor current (ILin), output voltage (vAB),

capacitors voltages (VCA1,2, VCB1,2), and (b) dynamic waveforms including PV

voltage, current, power (VPV, IPV, PPV,) and grid voltage and current (vg, ig).

Fig. 3. Simulated (a) junction temperatures of the switches SA1-SA6 (top to

bottom) and (b) their power losses, respectively.

Conclusion

A novel CMI based on FB and 3LTT inverters has been presented in this paper. The proposed C7L inverter features an embedded voltage-boosting capability realized by the input inductor cooperating with the FB switches. The voltages of capacitors for the two 3LTT inverters are stepped up without using extra switches. Their voltages can also be self-balanced at the same average value and of the same ripple, which simplifies the design and selection of the devices. A customized phase-shift PWM scheme using ac and dc modulation signals has been proposed to control the voltage gain while achieving multilevel synthesis. Theoretical analysis of the proposed C7L inverter has been given and verified by simulations and experimental results obtained under both steady-state operation and dynamic transients. The overall dc-to-ac voltage gain is more than 4 times and the power conversion efficiency obtained by the proposed C7L inverter is larger than 95% over a wide range of output power. Together, they proved that the proposed inverter is a suitable candidate for applications such as renewable power generations, where the step-up output voltage is expected through a single-stage dc-to-ac power conversion.

References

[1] S. Daher, J. Schmid, and F. L. M. Antunes, “Multilevel inverter topologies for stand-alone PV systems,” in IEEE Transactions on Industrial Electronics, vol. 55, no. 7, pp. 2703–2712, Jul. 2008.

[2] L. Zhang, K. Sun, Y. Xing, and J. Zhao, “A family of five-level dual-buck full-bridge inverters for grid-tied applications,” in IEEE Transactions on Power Electronics, vol. 31, no. 10, pp. 7029–7042, Oct. 2016.

[3] J. A. Anderson, E. J. Hanak, L. Schrittwieser, M. Guacci, J. W. Kolar, and G. Deboy, “All-silicon 99.35% efficient three-phase seven-level hybrid neutral point clamped/flying capacitor inverter,” in CPSS Transactions on Power Electronics and Applications, vol. 4, no. 1, pp. 50–61, Mar. 2019.

[4] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inverter,” in IEEE Transactions on Industry Applications, vol. IA-17, no. 5, pp. 518–523, Sept. 1981.

[5] T. Meynard, H. Foch, P. Thomas, J. Courault, R. Jakob, and M. Nahrstaedt, “Multicell converters: Basic concepts and industry applications,” in IEEE Transactions on Industrial Electronics, vol. 49, no. 5, pp. 955–964, Oct. 2002.