ABSTRACT:
The high-frequency
magnetic link is gaining popularity due to its light weight, small volume, and
inherent voltage balancing capability. Those features can simplify the
utilization of multilevel converter (MLC) for the integration of renewable
energy sources to the grid with compact size and exert economic feasibility.
The modulation and control of MLC are crucial issues especially for grid
connected applications. To support the grid, the converter may need to operate
in over-modulation (OVM) region for short periods depending upon the loading
conditions. This OVM operation of the converter causes increased harmonic
losses and adverse effects on overall system efficiency. On top of that, the
size and cost of filtering circuitry become critical to eliminate the unwanted
harmonics. In this regard, a modified OVM scheme with phase disposed carriers
for grid connected high frequency magnetic link-based cascaded H-bridge (CHB)
MLC is proposed for the suppression of harmonics and the reduction of converter
loss. Furthermore, with the proposed OVM technique, the voltage gain with
modulation index can be increased up to the range which is unlikely to be
achieved using the classical ones. Extensive simulations are carried out with a
2.24 MVA permanent magnet synchronous generator-based wind energy conversion
system which is connected to the 11 kV ac grid through a high-frequency
magnetic link and a 5-level CHB MLC. A scaled down laboratory prototype is
implemented to validate the performance of the converter.
KEYWORDS:
1. Multilevel converter
2. Over modulation
3. Grid connection
4. High-frequency magnetic link
5. Wind energy
SOFTWARE: MATLAB/SIMULINK
CONCLUSION:
To improve the system performance, a
modified OVM technique is presented in this paper with grid connected and
islanded operation. With the proposed modified carrier signal based BCPWM
techniques, the overall loss and THD are decreased for both the islanded and
grid connected modes compared with the traditional OVM techniques. Moreover,
the voltage gain can be increased and remains approximately constant in the
proposed method, which may not be possible to obtain using the traditional OVM
methods. In this paper, a high-frequency magnetic link-based fully-rated CHB
converter is developed for wind energy applications and the behavior of the
system under rated and overrated load conditions are investigated.The use of
magnetic link for the generation of isolated and balanced dc sources of the MLC
inherently overcomes the voltage imbalance problem of CHB MLC and hence
effectively simplifies the system control complexities. The core loss of
high-frequency magnetic link is also measured to identify the overall loss of
the system. The effectiveness of the proposed technology is confirmed by the
simulation and experimental results.
REFERENCES:
[1] M. R. Islam, Y. G. Guo, J. G. Zhu, H. Lu, and J. X. Jin, “High-frequency magnetic-link medium-voltage converter for superconducting generator-based high-power density wind generation systems,” IEEE Trans. Appl. Supercond., vol. 24, no. 5, pp. 1–5, Oct. 2014.
[2] N. Mendis, K. M. Muttaqi, S. Perera, and S. Kamalasadan, “An effective power management strategy for a wind–diesel–hydrogen-based remote area power Supply System to meet fluctuating demands under generation uncertainty,” IEEE Trans. Ind. Appl., vol. 51, no. 2, pp. 1228–1238, Mar.–Apr. 2015.
[3] B. Jain, S. Jain, and R. K. Nema, “Control strategies of grid interfaced wind energy conversion system: An overview,” Renew. Sustain. Energy Rev., vol. 47, pp. 983–996, Apr. 2015.
[4] Y. Tan, K. M. Muttaqi, P. Ciufo, and L. Meegahapola, “Enhanced frequency response strategy for a PMSG-based wind energy conversion system using ultracapacitor in remote area power supply systems,” IEEE Trans. Ind. Appl., vol. 53, no. 1, pp. 549–558, Jan.–Feb. 2017.
[5] M. R. Islam, Y. G. Guo, and J. G. Zhu, “A multilevel medium-voltage inverter for step-up-transformer-less grid connection of photovoltaic power plants,” IEEE J. Photovolt., vol. 4, no. 3, pp. 881‒889, May 2014.
