ABSTRACT:
This paper proposes a high-efficiency two stage three-level
grid-connected photovoltaic inverter. The proposed two-stage inverter comprises
a three-level step up converter and a three-level inverter. The three-level
step up converter not only improves the
power-conversion efficiency by lowering the voltage stress but also guarantees the
balancing of the dc-link capacitor voltages using a simple control algorithm;
it also enables the proposed inverter to satisfy the VDE 0126-1-1 standard of
leakage current. The three-level inverter minimizes the overall power losses with
zero reverse-recovery loss. Furthermore, it reduces harmonic distortion, the
voltage ratings of the semiconductor device, and the electromagnetic
interference by using a three-level circuit configuration; it also enables the
use of small and low cost filters. To control the grid current effectively, we
have used a feed-forward nominal voltage compensator with a mode selector; this
compensator improves the control environment by presetting the operating point.
The proposed high-efficiency two-stage three-level grid-connected photovoltaic
inverter overcomes the low efficiency
problem of conventional two-stage inverters, and it provides high power quality
with maximum efficiency of 97.4%. Using a 3-kW prototype of the inverter, we
have evaluated the performance of the model and proved its feasibility.
KEYWORDS:
1.
Transformerless
2.
Multilevel
3.
Dc-ac power
conversion
4.
Single-phase
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
Fig.
1. Proposed high-efficiency two-stage three-level grid-connected PV inverter
circuit diagram.
EXPECTED SIMULATION RESULTS:
Fig.2.
Simulation results for the leakage current of the proposed twostage
inverter.
Fig.3.
Simulation results for the leakage current using a conventional three-level
step-up converter of Fig. 2(b) as dc-dc power conversion stage of two-stage
inverter.
CONCLUSION:
A
high-efficiency two-stage three-level grid-connected PV inverter and control
system are introduced. Also, a theoretical analysis is provided along with the
experimental results. By using the novel circuit configuration, the proposed
two-stage inverter performs power conversion with low leakage current and high
efficiency; in dc-dc power conversion stage, the connection of midpoints of
capacitors enables the proposed two-stage inverter to limit the leakage current
below 300mA; in dc-ac power conversion stage, the overall power losses are
minimized by eliminating the reverse-recovery problems of the MOSFET body
diodes. Besides, the proposed inverter with three voltage levels reduces the
power losses, harmonic components, voltage ratings, and EMI; it also enables
using small and low cost filters. For the control system, the feedforward nominal
voltage compensator also improves the control environment by presetting the
operating point. This developed control algorithm makes the proposed inverter
feasible. Thus, the proposed high-efficiency two-stage three-level grid connected
PV inverter provides high power quality with high power-conversion efficiency.
By using a 3-kW prototype, this experiment has verified that the proposed inverter
has high efficiency, and the developed control system is suitable for the
proposed inverter.
REFERENCES:
[1]
B.K. Bose, “Global energy acenario and impact of power electronics in 21st
century,” IEEE Transactions on Industrial Electronics, vol. 60, no. 7, pp.
2638-2651, July. 2013.
[2]
Y. Zhou, D. C. Gong, B. Huang, and B. A. Peters, “The impacts of carbon tariff
on green supply chain design,” IEEE Transactions on Automation Science and
Engineering, July. 2015. Available: DOI: 10.1109/TASE.2015.2445316
[3]
Y. Wang, X. Lin, and M. Pedram, “A near-optimal model-based control algorithm
for households equipped with residential photovoltaic power generation and
energy storage systems,” IEEE Transactions on Sustainable Energy, vol. 7, no.
1, pp. 77-86, Jan. 2016.
[4]
Y. W. Cho, W. J. Cha, J. M. Kwon, and B. H. Kwon, “Improved single-phase transformerless inverter with
high power density and high efficiency for grid-connected photovoltaic
systems,” IET Renewable Power Generation, vol. 10, no. 2, pp. 166-174, Feb.
2016.
[5]
A. Shayestehfard, S. Mekhilef, and H. Mokhlis, “IZDPWMBased feedforward
controller for grid-connected inverters under unbalanced and distorted
conditions,” IEEE Trans. Ind. Electron., vol. 64, no. 1, pp. 14-21, Jan. 2017.
