Modified Phase-Shifted PWM for Cascaded Half-Bridges of Photovoltaic Application

Xiaoguang Diao,Fei Liu,Yuan Song,Mengyue Xu,Xiaoming Zha,Yizhan Zhuang

doi:10.1109/access.2020.2977351

Xiaoguang Diao, Fei Liu + Show 4 more

Open Access

https://doi.org/10.1109/access.2020.2977351

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Abstract

Photovoltaic power plants are generally far away from loads such as cities and industrial zones. Moreover, long-distance power transmission for renewable energy will become an inevitable trend in the future. Cascaded dc-dc converters can reach a high voltage to collect and transport photovoltaic energy, with advantages such as lower costs and larger capacities. However, the input power mismatch may cause a large amount of switching harmonic components, resulting in dc-link voltage fluctuations, which will not only increase the volume of filter components, but also cause unreliable circuit breaker actions. To solve the aforementioned problems, a hierarchical phase-shifted pulse width modulation (HPS-PWM) is proposed. By rationally grouping and layering the modules, low-order harmonics generated by the switching process of the dc-dc converter can be eliminated. The fluctuation of dc-link voltage can be suppressed by HPS-PWM, according to simulation results. When the number of modules is 27 and 81, the weighted total harmonic distortion (WTHD) of the HPS-PWM method can be reduced by more than 60% compared to the phase-shifted tracking pulse width modulation (PST-PWM) and fault tolerant adaptive phase-shifted pulse width modulation (FTA-PS-PWM). Finally, experiments verify the performance of HPS-PWM, agreeing with the simulation results.

Highlights

The gradual depletion of fossil energy and the increasingly prominent environmental issues will result in renewable energy sources constituting an increasing proportion of future power systems [1]
In comparison with phaseshifted tracking pulse width modulation (PST-PWM) and FTA-Phase-shifted pulse width modulation (PS-PWM), the weighted total harmonic distortion (WTHD) of hierarchical phase-shifted pulse width modulation (HPS-PWM) declined by 77.77% and 68.55%, respectively, and THD declined by 49.11% and 33.33%, respectively
In comparison with PST-PWM, WTHD is reduced by 86.30% and THD is reduced by 60.57% using HPS-PWM

Summary

INTRODUCTION

The gradual depletion of fossil energy and the increasingly prominent environmental issues will result in renewable energy sources constituting an increasing proportion of future power systems [1]. Phase-shifted pulse width modulation (PS-PWM) has been the most attractive method owing to its simplicity and outstanding ability regarding harmonic elimination. It can prolong the converter’s service life by equalizing the power losses of switches [6]–[9], [23]. Phase-shifted tracking pulse width modulation (PST-PWM), proposed in [5], expands the cascaded number from three to infinity (theoretically), but only the first harmonic is cancelled using this method. If there is no power loss in the system, the state average model can be obtained as iG

Dk can be solved as

Vn n

CONCLUSION

According to the rules for vectors