Abstract
Passing clouds and wind gusts can create unacceptable rapid voltage/power variations in power networks. Simulation results using a real Australian distribution feeder with real load demand and PV output profile show that with a high penetration of PV the voltage variations can increase beyond the allowable limit given by the standards. Similarly, wind gusts can create wind power output variations. This paper addresses the rapid voltage/power variations caused by solar or wind power outputs and presents a control strategy using the energy buffer in energy storage for their impact mitigation. By controlling the discharging/charging operation of the energy storage based on the available energy buffer in the storage unit, not only the rate of power output variations can be maintained at the desired level, but also the voltage variations can be controlled within acceptable limits. An experimental setup, consisting of a PV emulator, inverter, and grid simulator, demonstrates the potential threat of unacceptable voltage variations. The proposed mitigation strategy using energy buffer in the storage for smoothing the power outputs of solar/wind is tested and validated through simulation. Simulation results show that with the proposed control, the fast variations of the voltage/power variations instigated by solar/wind can be maintained within the acceptable limits.
Highlights
The impacts of the steep variations in PV output on electric utility operation due to cloud passing has been reported in previous literature [1], [2]
This paper proposes an additional value-added benefit of the energy buffer available in the energy storage for controlling the rapid voltage/power variations instigated by the PV and the wind output variations, especially in the networks with sensitive installations, where the limits of the rapid voltage/power variation should be strictly adhered to
The key contributions of the paper are as below: (a) This paper has investigated the rapid voltage fluctuations caused by the solar and wind power output variations in the context of IEEE and IEC standards. (b) A strategy to use the rule-based ramp control strategy to charge/discharge the energy storage to compensate for the difference between actual power and desired power has been presented. (c) The use of the energy buffer of the integrated energy storage, as a value-added benefit, for a new control strategy is proposed for the mitigation of unacceptable rapid voltage variations instigated by the PV/wind power
Summary
The impacts of the steep variations in PV output on electric utility operation due to cloud passing has been reported in previous literature [1], [2]. The energy storage devices integrated with PV/wind systems are intelligently controlled using an appropriate control strategy to reduce the rate of the power output variations, and its effect on the voltage smoothing to meet the allowable rapid variation limit is assessed and the results presented. (c) The use of the energy buffer of the integrated energy storage, as a value-added benefit, for a new control strategy is proposed for the mitigation of unacceptable rapid voltage variations instigated by the PV/wind power. As the PV inverters in LV feeders mainly operate at unity power factor and the load demand does not change as abruptly as the steep variations in the PV output caused by the passing clouds, the rapid change in the voltage at the PoC caused by cloud passing can be attributed mainly to the change of PINV for a given network equilibrium. A voltage sensitivity analysis is performed to VOLUME 9, 2021 investigate the potential variation of |V| caused by a given change of PINV ( PINV) due to cloud passing, and taking into account the variation of the line impedance in a weak radial feeder
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