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Fuzzy Load-Shedding Strategy Considering Photovoltaic Output Fluctuation Characteristics and Static Voltage Stability

1,2,*, 1 and 2
1
College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China
2
School of Electric Power Engineering, Nanjing Institute of Technology, Nanjing 211167, China
*
Author to whom correspondence should be addressed.
Energies 2018, 11(4), 779; https://doi.org/10.3390/en11040779
Received: 12 February 2018 / Revised: 22 March 2018 / Accepted: 27 March 2018 / Published: 28 March 2018
(This article belongs to the Section Electrical Power and Energy System)
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Abstract

Based on the equilibrium point equations of a classic three-node system integrated with a large-scale photovoltaic cell (PV) power plant, the impact of PV output fluctuation on the saddle-node bifurcation (SNB) was derived and analyzed. When PV runs in a unity power factor and the PV output active power Ppv is not too large (several hundred MW and below), the PV output fluctuation has little effect on the SNB point position and load margin index, so that the load margin index can be calculated online using the SNB point at Ppv = 0 pu. On the other hand, the local reactive power compensation in the load center can effectively raise the load bus voltage and make the voltage stability problem become more concealed; the traditional under-voltage load-shedding (UVLS) strategy only carries out load shedding when the bus voltage amplitude is below the specified value and cannot effectively maintain the system static voltage stability in some occasions. In this paper, a fuzzy load-shedding strategy considering the impact of PV output fluctuations for the large-scale PV grid-connected system was designed, taking the load bus voltage amplitude and load margin index as fuzzy input variables, and the load-shedding command as a fuzzy output variable. Nine fuzzy IF-THEN rules were extracted for the fuzzy controller and the corresponding practical calculation method of load-shedding quantity was put forward. The simulation results of the classic three-node system and IEEE 14-bus system, both with a 100 MW PV power plant, verified the effectiveness of the fuzzy load-shedding controller whose input variable load margin index was calculated using the SNB point when the PV active power output was 0. The designed fuzzy load-shedding strategy can compensate for the defect—that the traditional UVLS strategy cannot effectively guarantee the system static voltage stability—and it can be widely used in power grids integrated with PV power plants whose scales are at a level of several hundred MW and below. View Full-Text
Keywords: photovoltaic power plant; photovoltaic output fluctuation; saddle-node bifurcation (SNB); load margin index; fuzzy load-shedding; load-shedding quantity photovoltaic power plant; photovoltaic output fluctuation; saddle-node bifurcation (SNB); load margin index; fuzzy load-shedding; load-shedding quantity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Li, S.; Wei, Z.; Ma, Y. Fuzzy Load-Shedding Strategy Considering Photovoltaic Output Fluctuation Characteristics and Static Voltage Stability. Energies 2018, 11, 779.

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