Climatic ramifications as a consequence of global pollution have tilted the scale in favor of renewable energy resources. Consequently, it is anticipated that high penetration of renewable distributed generation in medium voltage distribution network will bring challenges in power system operation due to the uncertainty and variability of renewable energy. Additionally, the intermittent nature of renewable energy can potentially intensify the volatility of power flow. To date, numerous studies have assessed the mathematical description of the uncertainty characteristics of renewable distributed generation and the corresponding models of distribution networks management, some of which are optimization-based. In addition, published literature shows that active power management is mainly considered when dealing with the uncertainty in renewable-rich active distribution networks, while reactive power control is commonly applied in the voltage regulation schemes. However, in distribution networks where the R/X ration is relatively high, the active and reactive power are highly coupled in the power flow and network operation.
To this end, researchers from the College of Energy and Electrical Engineering at Hohai University in China: Dr. Junpeng Zhu and Professor Yue Yuan together with Professor Weisheng Wang at the China Electric Power Research Institute developed new active distribution network management scheme coordinating active/reactive power dispatch and network reconfiguration in a multi-stage framework, integrated with centralized and local control methodologies considering the different timescales and communication limits in each management stage. Their goal was to promote the renewable energy consumption and mitigate the system uncertainty through the development of a multi-stage management scheme for renewable-rich medium voltage distribution network. Their work is currently published in International Journal of Electrical Power and Energy Systems.
In the first stage of their approach, a day-ahead dispatch model was developed to promote the renewable distributed generation consumption and decrease the power loss. In the second stage, a model predictive control based rolling optimization model for intra-day operation was proposed to minimize the mismatch of the interactive power at the upstream Grid Supply Point between the day-ahead schedule and intra-day operation. Multiple active management elements such as network reconfiguration and soft open point were then integrated and a novel second order cone programming model for the centralized optimal power flow in the day-ahead and intra-day stages was presented. In the third stage, a decentralized P/Q(V) control strategy of renewable distributed generation inverter for real-time voltage regulation was proposed to ensure system safety and mitigate the fast voltage fluctuation.
Simulation results demonstrated that the proposed management scheme could simultaneously promote the renewable energy consumption and mitigate the system uncertainty. Specifically, it was noted that the power deviation of grid supply point could be decreased notably with a very small sacrifice of renewable distributed generation consumption. Further, the results also showed that network reconfiguration and soft open point had a notable effect in the renewable-rich active distribution network optimization, and that proposed real-time control strategy could avoid the over-limit and fast fluctuation of voltage magnitude through power regulation of RDGs and static var compensators.
In summary, the study justified the idea that in the near future, given any renewable-rich power system, the distribution feeder has the responsibility of local uncertainty management in the power interaction with upstream system. Remarkably, the effectiveness of the proposed management scheme was demonstrated in a test system integrating a standard network and real-world data of load and renewable distributed generation output profiles. In a statement to Advances in Engineering, Dr. Junpeng Zhu, first author highlighted that their work put forth invaluable contributions that will facilitate further exploration of distributed communication and control frameworks and strategies.
Junpeng Zhu, Yue Yuan, Weisheng Wang. Multi-stage active management of renewable-rich power distribution network to promote the renewable energy consumption and mitigate the system uncertainty. International Journal of Electrical Power and Energy Systems, volume 111 (2019) page 436–446.