Implementation of Multilevel DC-Link Inverter for Standalone Application

 

ABSTRACT:

In this paper, the details of the implementation of a multilevel dc-link inverter (MLDCLI), suitable for standalone application is presented. The first stage of the MLDCLI is a multilevel dc-link to provide a stepped dc voltage waveform approximating the shape of a rectified sine wave. This rectified sine wave is then inverted after every alternate cycle by a conventional single phase full bridge inverter. MLDCLI requires lesser number of switches thus reducing the number of gate drive circuits and switching complexities as compared to the conventional multilevel inverters (MLI). Hence MLDCLI is chosen for this work. The simulation of nine level cascaded half bridge MLDCLI in closed loop is carried out and results are presented. The hardware implementation of the MLDCLI in square wave staircase operation mode and in-phase level shifted multicarrier sine triangular pulse width modulation mode (IPD-SPWM) is carried out and results are presented. DSP TMS320F28069 is used for the implementation of MLDCLI.

KEYWORDS:

  1. MLI
  2. MLDCLI
  3. Cascaded half bridge MLDCLI
  4. DSP
  5. PI compensator

 

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

 Fig. 1 Generalized block diagram of MLDCLI

 EXPECTED SIMULATION RESULTS:

 Fig. 2. Simulation waveforms for closed loop system with kp=19.163 and

ki=22552 (a) Entire waveform (b) Enlarged view

Fig. 3. Harmonic profile of load voltage

Fig. 4. Simulation waveforms for closed loop system

CONCLUSION:

The advantages of a nine level cascaded half bridge MLDCLI is studied, verified by a detailed simulation study and validated experimentally. The substantial reduction in number of components and associated advantages as compared to the conventional MLI makes cascaded half bridge MLDCLI a good choice for high power, medium voltage applications. The closed loop simulation results proved the tracking efficiency of the PI compensator. Square wave and IPDSPWM are the switching schemes selected for the implementation. It is verified from the results of the experimental prototype, that square wave switching scheme requires lower switching frequency and produces lower EMI than IPD-SPWM, but IPD-SPWM scheme has lower voltage THD. The experimental results of a scaled down laboratory prototype of a nine level cascaded half bridge MLDCLI using DSP TMS320F28069 is presented in this paper. The results obtained are in congruence with the theoretical claims and the simulation study.

REFERENCES:

[1] Samir Kouro, Mariusz Malinowski, K. Gopakumar, Josep Pou, Leopoldo G. Franquelo, Bin Wu, Marcelo A. Pérez, “Recent Advances and Industrial Applications of Multilevel Converters,” IEEE Transactions On Industrial Electronics, vol. 57, no. 8, pp. 2553- 2577, Aug. 2010.

[2] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilvel converters arrives,” IEEE Ind.Electron. Mag., vol. 2, no. 2, pp. 28–39, Jun. 2008.

[3] J. Rodriguez, L. G. Franquelo, S. Kouro, J. I. Leon, R. C. Portillo, M. A. M. Prats, and M. A. Perez, “Multilevel converters: An enabling technology for high-power applications,” Proc. IEEE, vol. 97, no. 11, pp. 1786–1817, Nov. 2009.

[4] Gui-Jia Su, “Multilevel DC-Link Inverter”, IEEE Transactions On Industry Applications, vol. 41, no. 3, pp.848 – 854, May/June 2005.

[5] H. Abu-Rub, J. Holtz, J. Rodriguez, and G. Baoming, “Medium voltage multilevel converters—State of the art, challenges, and requirements in industrial applications,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2581– 2596, Aug. 2010.

Cascaded Multilevel Inverter Based Electric Spring for Smart Grid Applications

 

ABSTRACT:

This paper proposes “Electric Spring” (ES) based on Single Phase three-level Cascaded H-Bridge Inverter to achieve effective demand side management for stabilizing smart grid fed by substantial intermittent renewable energy sources (RES). Considering the most attractive features of multilevel inverter (MLI), an effective structure of Electric Spring is proposed for suppressing voltage fluctuation in power distribution network arising due to RES and maintaining the critical load voltage. Also, the operation of ES in capacitive as well as inductive mode is discussed. Further, the paper describes droop control method for parallel operation of distributed electric spring for stabilization the power grid. An exclusive dynamic performance of the system using electric spring has been tested and demonstrated through detailed MATLAB simulation.

KEYWORDS:

  1. Critical load
  2. Cascaded H-Bridge Inverter
  3. Droop control
  4. Electric Spring
  5. MLI
  6. RES
  7. Smart load

 SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Fig. 1. Schematic of Electric Spring.

EXPECTED SIMULATION RESULTS:

Fig. 2. Observed RMS value of (a) Source voltage (Vs), (b) Non–critical voltage (Vnc), (c) Electric spring voltage (Va) & current (Ia), (d) Critical voltage (Vc) in capacitive mode.

Fig. 3. Observed Instantaneous value of (a) Source voltage (Vs), (b) Non–critical voltage (Vnc), (c) Electric spring voltage (Va) & current (Ia), (d) Critical voltage (Vc) in capacitive mode.

Fig. 4. Observed RMS value of (a) Source voltage (Vs), (b) Non–critical voltage (Vnc), (c) Electric spring voltage (Va) & current (Ia), (d) Critical voltage (Vc) in inductive mode.

Fig. 5. Observed Instantaneous value of (a) Source voltage (Vs), (b) Non– critical voltage (Vnc), (c) Electric spring voltage (Va) & current (Ia), (d) Critical voltage (Vc) in inductive mode.

Fig. 6. THD analysis of (a) Two-level and (b) Three-level CHMLI based ES.

CONCLUSION:

The paper proposes new approach for regulating the mains voltage using MLI based ES for smart grid applications. The implemented Three-level CHMLI based ES for smart grid application effectively regulates the ac mains voltage and reduces the THD content as compared with Two-level VSI based ES. The effectiveness of ES is validated through digital simulation in terms of THD. Lastly simulation results of droop control for Four Electric springs have been implemented in a large-scale distributed pattern in order to make multiple ES act in coordinating manner so as to have robust stabilizing effect.

REFERENCES:

[1] Edward J.Coster, Johanna M.A.Myrzik, BAS Kruimer, “Integration Issues of Distributed Generation Distribution Grids,” Proceedings of the IEEE, vol.99, no.1, pp.28-39, January, 2011.

[2] Koutsopoulos and L. Tassiulas, “Challenges in demand load control for the smart grid,” IEEE Netw., vol. 25, no. 5, pp. 16–21, 2011.

[3] M.H.J.Bollen, “Understanding Power Quality Problems: Voltage Sags and Interruptions,” IEEE Press, 2000.

[4] N. Hingorani and L. Gyugyi, Understanding FACTS, Concepts and Technology of Flexible AC Transmission Systems. New York: IEEE Press, 2000.

[5] M. Parvania and M. Fotuhi-Firuzabad, “Demand response scheduling by stochastic SCUC,” IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 89–98, Jun. 2010