Grid Integration at Imperial College

Aim

Photovoltaic(PV) generation presents many grid integration challenges from the generation, transmission and distribution perspectives. However, major growth of PVs is mainly in the distribution networks. This research focuses on distribution connected PV generation systems and the main objective is to specifically study distribution system steady state voltage control in the presence of PV generation.

Research development

Research outcome is to develop an optimal voltage regulation strategy considering the PV inverter reactive power support capabilities. This is due to following reasons :

[1] PV active power injection is causing intermittent overvoltage on distribution feeders. Present day approaches to mitigate this are through active power curtailment of PV generator.

[2] The active power curtailment is not the most effective method to regulate the voltage. Firstly, it leads to a suboptimal clean energy capture. Secondly, it may not consider feeder operational performance.

[3] One of the major steady state voltage control challenges is the impact of PV generation on voltage control mechanisms such as on-load tap changers (OLTCs) and voltage regulators (VRs). The increase in number of tap operations and VR runaway are major challenges reported in the literature. Another research objective is also to use the previous analysis in order to develop a voltage control strategy which mitigates adverse impacts on OLTCs and VRs.

[4] Most of the distribution voltage control strategies reported in the literature are based on the load and generation forecasts and a simulation based set-point calculation. These strategies usually neglect forecast errors. This research work aims at developing a stochastic voltage regulation strategy considering PV generation forecast errors.

 

Main impact

[1] The detailed impact of PV generation on the voltage control devices is not reported in the literature. The challenges such an over voltage, increased tap counts and Voltage Regulator (VR) runaway are analyzed in detail in this research work. A detailed insight is developed into the interaction between the PV generator control settings and the VR control settings while achieving

a steady state voltage control. The distribution reactive power dispatch is proposed to calculate the optimum reactive power set points of devices in order to alleviate steady state voltage control challenges.

[2] The steady state voltage control challenges are aggravated by the PV and load forecast errors. The overvoltage, increased tap counts and VR runaway need to be alleviated in the presence of the forecasting errors. An appropriate stochastic operational strategy is developed to address this. The stochastic indices to model the VR runaway phenomenon are developed. The Chance constraint optimization (CCO) based technique is proposed to alleviate the challenges.

Contact point for further information: Prof. Bikash Pal, Dr.Yashodhan Agalgaonkar