I. INTRODUCTION

II. SYSTEM DESCRIPTION

III. THE SMOOTHING STRATEGY AND DEFINITION OF PV POWER FLUCTUATIONS

IV. ROLLING OPTIMIZATION FOR BASE POWER OF VSPSS

V. EXPERIMENTS AND RESULTS

VI. CONCLUSION

REFERENCES

Due to strong volatility and intermittent characteristics, the fluctuations of the photovoltaic (PV) output is inevitable which cause negative impacts on power system operation. However, such an issue can be resolved in a combined cascade hydro-PV-pumped storage (CH-PV-PS) generation system through an appropriate control. Based on the optimal base power of variable-speed pumped storage station (VSPSS), a smoothing method of fuzzy complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) is proposed in this paper. To prevent smoothing insufficient and excessive, the fuzzy CEEMDAN algorithm is used to obtain the target power of the photovoltaic-pumped storage (PV-PS) generation system and the control signal of cascade hydro stations (CHSs) for eliminating large amplitude fluctuations of the PV output. Furthermore, in order to overcome the drawback that too frequent conversion of unit operating mode would reduce the service life and smoothing effect of the VSPSS unit, the optimization model of the base power of the VSPSS is established and solved by the grid adaptive direct search method (MADS) to obtain the control signal of the VSPSS for suppressing the short-term fluctuations of the PV output. Finally, the performance of the method is evaluated through using the PV station data in Xiaojin County, Sichuan province, China. The simulation results reveal that compared with the fixed base power smoothing method, this method can effectively suppress the PV power fluctuations and improve the smoothing effect and energy efficiency.

INTRODUCTION

In order to build a sustainable energy system, solar energy as a low-carbon and friendly renewable energy form has attracted worldwide attention. However, output power of the PV systems, which is strong volatility and intermittent characteristics, due to frequent change solar radiation and temperature [1], [2], may induce voltage fluctuations, voltage flicker, grid side power fluctuations, and frequency fluctuations [3]. Therefore, PV energy sources cause grid power instability and poor power quality when large quantities of PV energy penetrate the power grid [4]. In order to increase the permeability of PV generation and reduce the impact of power fluctuations, the Puerto Rico Electric Power Authority (PREPA) and State Grid Corporation of China requires that the maximum power fluctuations range of a PV plant should be less than 10%/min of its installed capacity [5]. In some regions where water resources and solar energy are abundant, many small and medium-sized PV power stations and hydro stations have been built. Therefore, we should rationally combine these two energy sources to build a hydro-PV complementary generation system which can effectively suppress PV power fluctuations and fully improve the PV and hydro economic benefits [18]. It is well known that pumped storage is a kind of more mature and economically efficient storage technology, which can store high quantities of unpredictable energy for avoiding grid stability problems [6].