This paper proposes a new five-level voltage source
inverter for medium-voltage high-power applications. The proposed inverter is
based on the upgrade of a four-level nested neutral-point clamped converter.
This inverter can operate over a wide range of voltages without the need for
connecting power semiconductor in series, has high-quality output voltage and
fewer components compared to other classic five-level topologies. The features
and operation of the proposed converter are studied and a simple sinusoidal PWM
scheme is developed to control and balance the flying capacitors to their
desired values. The performance of the proposed converter is evaluated by
simulation and experimental results.
KEYWORDS:
1.
Multilevel
converter
2.
Dc–ac power
conversion
3.
Sinusoidal
pulse width modulation (SPWM)
Fig.
1. New five-level three-phase inverter.
EXPECTED SIMULATION RESULTS:
Fig.
2. Simulation waveforms in steady-state condition (a) inverter voltage, (b)
output currents, and (c) voltages of flying capacitors (m = 0.95).
Fig.
3. Simulation waveforms in steady-state condition (a) inverter voltage,
(b)
output currents, and (c) voltages of flying capacitors (m = 0.65).
Fig.
4. Simulation waveforms in steady-state condition (inductive load) (a)
inverter
voltage, (b) output currents, and (c) voltages of flying capacitors (m =
0.95,
PF = 0.7).
Fig.
5. Simulation waveforms in steady-state condition (capacitive load)
(a)
inverter voltage, (b) output currents, and (c) voltages of flying capacitors
(m
= 0.9, PF = −0.7).
Fig.
6. Simulation waveforms in transient-state condition; load changes from
half-load
to full-load (a) inverter voltage, (b) output currents, and (c) voltages
of
flying capacitors (m = 0.95).
Fig.
7. Simulation waveforms; voltage of flying capacitors with and without
the
controller
CONCLUSION:
This
paper introduces a new five-level voltage source inverter for medium-voltage
applications. The proposed topology is the upgrade of the four-level NNPC
converter that can operate over a wide range of input voltage without any power
semiconductor in series. The proposed converter has fewer components as com- pared
with classic multilevel converters and the voltage across the power
semiconductors is only one-fourth of the dc-link. A SPWM strategy is developed
to control the output voltage and regulate the voltage of the flying
capacitors. The proposed strategy is very intuitive and simple to implement in
a digital system. The performance of the proposed converter is confirmed by
simulation in MATLAB/Simulink environment and the feasibility of the proposed
converter is evaluated experimentally and results are presented.
[1]
B. Wu, High-Power Converters and AC Drives. Piscataway, NJ, USA: IEEE
Press, 2006.
[2]
J. Rodriguez, S. Bernet, B. Wu, J. Pontt, and S. Kouro, “Multilevel voltagesource-
converter topologies for industrial medium-voltage drives,” IEEE Trans. Ind.
Electron., vol. 54, no. 6, pp. 2930–2945, Dec. 2007.
[3]
S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B.Wu, J.
Rodriguez, M. A. Perez, and J. I. Leon, “Recent advances and industrial applications
of multilevel converters,” IEEE Trans. Ind. Electron., vol. 57, no. 8,
pp. 2553–2580, Aug. 2010.
[4]
Y. Zhang, G. Adam, T. Lim, S. Finney, andB.Williams, “Hybrid multilevel converter:
Capacitor voltage balancing limits and its extension,” IEEE Trans. Ind.
Informat., vol. 9, no. 4, pp. 2063–2073, Aug. 2013.
[5]
M. Saeedifard, R. Iravani, and J. Pou, “Analysis and control of DCcapacitor- voltage-drift
phenomenon of a passive front-end five-level converter,” IEEE Trans. Ind.
Electron., vol. 54, no. 6, pp. 3255–3266, Dec. 2007.
