Abstract
Variable over voltage, excessive tap counts, and voltage regulator (VR) runaway condition are major operational challenges in distribution network while accommodating generation from photovoltaics (PVs). The conventional approach to achieve voltage control based on offline simulation for voltage set point calculation does not consider forecast errors. In this work, a stochastic optimal voltage control strategy is proposed while considering load and irradiance forecast errors. Stochastic operational risks such as overvoltage and VR runaway are defined through a chance constrained optimization (CCO) problem. This classical formulation to mitigate runaway is further improved by introducing a stochastic index called the Tap Tail Expectation . Operational objectives such as power losses and excessive tap count minimization are considered in the formulation. A sampling approach is proposed to solve the CCO. Along with other voltage control devices, the PV inverter voltage support features are coordinated. The simulation study is performed using a realistic distribution system model and practically measured irradiance to demonstrate the effectiveness of the proposed technique. The proposed approach is a useful operational procedure for distribution system operators. The approach can minimize feeder power losses, avoid voltage violations, and alleviate VR runaway.
Highlights
T HE RENEWABLE portfolio initiatives in various countries are acting as a stimulus for the growth of grid connected renewable generation sources such as photovoltaics (PVs)
Two variants of chance constrained optimization (CCO) are proposed to minimize the risk of voltage regulator (VR) runaway
A classical CCO considers the runaway phenomenon by modeling the violation probability and by defining T ap nonpreferred zones
Summary
T HE RENEWABLE portfolio initiatives in various countries are acting as a stimulus for the growth of grid connected renewable generation sources such as photovoltaics (PVs). Runaway happens due to the interaction between VR control settings and PV reactive power support It depends upon several other factors such as PV capacity, load and irradiance values, voltage setpoints of devices, and distribution feeder topology. The stochastic predictions of the power flows and voltage levels in distribution systems having renewable energy generation is carried out in [21]. The available literature does not, consider the VR runaway in system operation, including the forecast errors This motivated us to pursue our research effort to propose a stochastic framework that minimizes the risk of VR runaway. A stochastic distribution voltage control strategy is proposed.
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