This paper proposes a novel modulation technique and
a new balancing control strategy for a single-phase five-level flying-capacitor
(FC)-based active-neutral-point-clamped (ANPC) converter. The proposed
modulator can control the FC voltage to follow the requested reference value
and simultaneously generate the required ac output voltage regardless of the
values of the dc capacitor voltages of the converter. By implementing this
method, smaller values of the dc-link capacitor and FC can be used even in
applications that could experience ripple or transient in the capacitor
voltage. In a single-phase five-level ANPC converter applications, where the
capacitors can experience pulsation power and dc-link balancing issues, such as
grid-connected photovoltaic system, the selection of the reference voltage
value for the FC can play an important role to balance the average values of
the dc-link capacitor voltage. The
proposed new control strategy uses a new reference voltage for the FC to be
applied by the new modulator to have an average balanced dc-link voltages as
well as an ac output voltage with good power quality. Simulation studies and experimental
results demonstrate the effectiveness of the proposed modulation technique and
control strategy even with relatively small dc capacitors to produce
high-quality output voltage and current waveforms while maintaining an average
balanced dc-link voltages.
KEYWORDS:
1.
Active-neutral-point-clamped
(ANPC) converter
2.
Flying
capacitor (FC)
3.
Multilevel converters
4.
Photovoltaic
(PV) power system
5.
Pulse width
modulation
6.
Voltage
balancing
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Single-phase 5L-ANPC converter.
Fig.
2. Results of applying conventional modulation technique with dc-link capacitors
equal to 300 μF. (a) DC-link voltage, dc-link capacitor voltages, and FC
voltage. (b) Inverter output voltage. (c) Inverter output and ac grid current. (d)
Magnitude of current harmonics (p.u.).
Fig.
3. Results of applying conventional modulation technique with dc-link
capacitors
equal to 3 mF. (a) DC-link voltage, DC-link capacitor voltages, and
FC
voltage. (b) Inverter output voltage. (c) Inverter output and ac grid current.
(d)
Magnitude of current harmonics (p.u.).
Fig.
4. Results of applying proposed modulation technique with dc-link
capacitors
equal to 300 μF and FC reference voltage equal to Vdc/4.
(a) DClink
voltage,
dc-link capacitor voltages, and FC voltage. (b) Inverter output
voltage.
(c) Inverter output and ac grid current. (d) Magnitude of current
harmonics
(p.u.).
Fig.
5. Results of applying proposed modulation technique with dc-link
capacitors
equal to 300 μF and FC reference voltage equal to half of the engaged
dc-link
capacitor in each output half-cycle. (a) DC-link voltage, dc-link
capacitors
voltages, and FC voltage. (b) Inverter output voltage. (c) Inverter
output
and ac grid current. (d) Magnitude of current harmonics (p.u.).
Fig.
6. Results of applying the proposed modulation technique with the proposed
FC
reference voltage with having step power in the PV and transmission
power
to the grid at t = 37 ms: (a) DC-link voltage, dc-link capacitors
voltage,
and
FC voltage. (b) Inverter output and grid current.
CONCLUSION:
A
novel modulation and control strategy for a five-level FC based ANPC converter
has been presented. A theoretical framework of a novel extended modulation
technique for unsymmetrical and symmetrical voltage conditions of a 5L-ANPC
converter has been proposed. The application of the proposed modulation and
control strategy, for a single phase grid-connected PV system using a
five-level FC-based ANPC converter to produce ac output voltages with good
power quality under both symmetrical and unsymmetrical conditions, has been
investigated. Issues related to the balancing of dc-link voltages and its
associated problems are discussed, and a new control strategy has been
introduced to solve the dc-link voltage divergence problem. The proposed
strategy is applicable for other applications of the five-level FC-based ANPC
converter. The effectiveness of the
proposed modulation technique and control strategy was demonstrated by the
simulation and experimental results in the laboratory, demonstrating the
ability of the system to operate properly using smaller size dc-link capacitors
to produce ac output voltage and current waveforms with good power quality
while maintaining dc-link average voltage balancing.
REFERENCES:
[1]
J. I. Leon, L. G. Franquelo, S. Kouro, B. Wu, and S. Vazquez, “Simple modulator
with voltage balancing control for the hybrid five-level flying-capacitor based
ANPC converter,” in Proc. IEEE ISIE, 2011, pp. 1887–1892.
[2]
P. Barbosa et al., “Active neutral-point-clamped multilevel converters,”
in Proc. 36th IEEE PESC, 2005, pp. 2296–2301.
[3]
F. Kieferndorf et al., “ANPC-5L technology applied to medium voltage variable
speed drives applications,” in Proc. Int. SPEEDAM, 2010, pp. 1718–1725.
[4]
S. A. Gonzalez, M. I. Valla, and C. F. Christiansen, “Five-level cascade asymmetric
multilevel converter,” IET Power Electron., vol. 3, no. 1, pp. 120–128, Jan. 2010.
[5]
Y. Kashihara and J. Itoh, “Parameter design of a five-level inverter for PV systems,”
in Proc. 8th IEEE ICPE ECCE, 2011, pp. 1886–1893.
