ABSTRACT:
In this paper, a new topology of two-stage cascaded switched-diode
(CSD) multilevel inverter is proposed for medium voltage renewable energy
integration. First, it aims to reduce the number of switches along with its
gate drivers. Thus, the installation space and cost of a multilevel inverter
are reduced. The spike removal switch added in the first stage of the inverter
provides a flowing path for the reverse load current, and as a result, high
voltage spikes occurring at the base of the stepped output voltage based upon
conventional CSD multilevel inverter topologies are removed. Moreover, to
resolve the problems related to dc source fluctuations of multilevel inverter
used for renewable energy integration, the clock phase-shifting (CPS) one-cycle
control (OCC) is developed to control the two-stage CSD multilevel inverter. By
shifting the clock pulse phase of every cascaded unit, the staircase-like
output voltage waveforms are obtained and a strong suppression ability against fluctuations
in dc sources is achieved. Simulation and experimental results are discussed to
verify the feasibility and performances of the two-stage CSD multilevel
inverter controlled by the CPS OCC method.
KEYWORDS:
1.
Novel cascaded
multilevel inverter
2.
Two-stage
3. One-cycle control
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.
1. Renewable energy generation system with multilevel inverter.
EXPECTED SIMULATION RESULTS:
Fig.
2. The output voltage and current of the first stage converter of the 5-level
simulation
prototype. (a) Output voltage ug ;
(b) Output current ig .
Fig.
3. The output voltage and inductor current of the 5-level simulation
prototype.
(a) Output voltage uCD ; (b) Output
voltage after filter uo ;
(c) Inductor current il
Fig.
4. The output voltage and current of the first stage converter of the
9-level
simulation prototype. (a) Output voltage ug ;
(b) Output current ig .
Fig.
5. The output voltage and inductor current of the 9-level simulation
prototype.
(a) Output voltage uCD ;
(b) Output voltage after filter uo ;
(c) Inductor current il .
Fig.
6. The simulation results of the 5-level prototype: DC source with basic
unit
1 contains a 10 Hz ripple with amplitude 16 V.
(a) uo using CPS OCC; (b)
uo using CPS SPWM.
Fig.
7. The simulation results of the 5-level prototype: DC source with each
basic
unit contains a 10 Hz ripple with amplitude 8 V.
(a) uo using CPS OCC; (b)
uo using CPS SPWM.
CONCLUSION:
A
new topology of two-stage CSD multilevel inverter has been proposed in this
paper. n cascaded basic units and one spike removal switch form the
first stage. Then by adding a full-bridge inverter as the second-stage
converter, both of the positive and negative output voltage levels are
generated. Since the one full-bridge converter in the output side leads to the
restriction on high-voltage applications, the proposed topology is suitable for
medium-voltage renewable energy integration. The comparisons with the CHB and
cascaded half-bridge topologies show that the CSD topology requires less
switches and related gate drivers for realizing Nlevel output voltage. As a
result, the installation space and cost of the multilevel inverter are reduced.
Meanwhile, the spike removal switch added in the first stage provides a flowing
path for the reverse load current under R-L loads, thus, the high voltage
spikes, due to the collapsing magnetic field in a very short time interval, are
removed. The CPS OCC method, which is composed by n similar but dependent
OCC controllers, has been designed and implemented to control the CSD
multilevel inverter. Simulation and experimental results demonstrate that, by
shifting the clock pulse phase of each cascaded unit, the staircase-like
voltage waveforms are obtained. Moreover, to evaluate the performance of CPS
OCC, in both the simulation and experiment, the DC sources mixed with low
frequency ripples are implemented to simulate the DC supply from renewable
energy generations, and the comparative results between CPS OCC and CPS SPWM
reveal that CPS OCC possesses a superior ability in suppressing the unbalance
or low frequency ripples in DC sources. These results demonstrate that the CPS
OCC method can be a substitute for conventional controllers to control
multilevel inverters for renewable energy integration with improved control
performances.
[1]
M. S. B. Ranjiana, P. S. Wankhade, and N. D. Gondhalekar, “A modified cascaded
H-bridge multilevel inverter for solar applications,” in Proc. 2014 Int.
Conf. Green Comput. Commun. Elect. Eng., 2014, pp. 1–7.
[2]
F. S. Kang, S. J. Park, S. E. Cho, C. U. Kim, and T. Ise, “Mutilevel PWM
inverters suitable for the use of stand-alone photovoltaic power systems,” IEEE
Trans. Energy Convers., vol. 20, no. 4, pp. 906–915, Dec. 2005.
[3]
L. V. Nguyen, H.-D. Tran, and T. T. Johnson, “Virtual prototyping for distributed
control of a fault-tolerant modular multilevel inverter for photovoltaics,” IEEE
Trans. Energy Convers., vol. 29, no. 4, pp. 841–850, Dec. 2014.
[4]
J. Rodriguez, J. S. Lai, and F. Z. Peng, “Mutilevel inverters: A survey of topologies,
controls, and application,” IEEE Trans. Ind. Electron., vol. 49, no. 4,
pp. 724–738, Aug. 2002.
[5]
F. Z. Peng and J. S. Lai, “Mutilevel converters—A new breed of power
converters,” IEEE Trans. Ind. Appl., vol. 32, no. 3, pp. 509–517, May/Jun.
1996.