Active Control and Power Flow Routing in the Smart Grid
- Written by Faycal Bouhafs and Michael Mackay
In the last few years, novel control concepts have been proposed with the goal of making distribution networks more flexible by introducing active control mechanisms. Active control is expected to help with maintaining the health and stability of the power grid even after disturbances, loss of equipment or other unforeseen situations, by undertaking proactive actions to preserve the stability of the power network.
A major benefit of the smart grid will be the introduction of Distributed Energy Resources (DERs) into the electricity grid on a large scale. DERs will be able to supply areas with electricity when isolated from the main power grid due to failure conditions or system/equipment failures. Currently, the supply of isolated locations with electricity comes with an increased cost to the distribution network operators (DNOs), as the majority of the energy that is meant for customers is wasted in the form of heat before delivering any useful energy to the consumer. In this case, DER represents a cheaper and more efficient solution to deliver energy closer to the consumer than the centralized power grid.
Although the integration of DER into power grids will make energy supplies more reliable and affordable, it will bring with it many new design issues. The low transmission capacity of the distribution network imposes certain limitations on the amount of energy that could be carried over it, making the connection of distributed renewable energy generators at residential and tertiary buildings very difficult.
Moreover, the variation of load demand, and the unpredictable nature of distributed generation will create instability within distribution networks, making them prone to faults and congestion. Perhaps the most pressing problem is that the legacy control systems that currently govern the power grid were designed decades ago around the centralized and vertical architecture of the power grid. This centralized control approach is not suitable for a modern smart power grid that has been built to effectively integrate distributed generation. In traditional grids, electricity usually flows from large central power stations to consumers. In a modern power grid enhanced with DER, electricity follows in two directions as new sources of energy are introduced at a lower voltage.
To introduce DER technology, operators will be faced with the challenge of making their power distribution networks more flexible and dynamic. While distribution networks were considered as static with no major control operation or re-configuration requirements in the past, in the smart grid, distribution networks will be in constant change according to the direction and amount of power flow at a given time. Distribution network control systems will therefore need to move from passive control to a more active control approach wherein the distribution network can be dynamically modified and re-configured according to changes in the power flow.
Over the last few years, novel control concepts have been proposed with the aim of making distribution networks more flexible by introducing active control mechanisms. Active control is expected to help with maintaining the health and stability of the power grid even after disturbances, loss of equipment or other unforeseen situations, by undertaking proactive actions to preserve the stability of the power network.
Current active control contributions focus only on addressing the issues created by the introduction of DER at a large scale, such as: voltage variations, fault level increases, protection selectivity, power quality and stability. Active control systems try to prevent problems by planning the most optimal configuration of the power distribution network. However, future control systems should not only be limited to re-dispatching pre-planned power generation, but should also be able to physically manage power flows in a more reactive and interactive manner.
Power routing is a new active control paradigm that aims to address the management of multiple power flows by replacing central control sites with intelligent power routers. These power routers will use local information and collaboration to improve the distribution network reliability, and avoid or relieve network congestion. Like routing in communication networks, power routers will be installed at critical points in the power network to facilitate the control of power flows.
Power routing, however, will add new communication requirements on the power grid. Collaboration between power routers will necessitate horizontal communication links and more transmission bandwidth. Power routers are also expected to communicate with generators, power lines, and customers. Therefore, new communication protocols should be designed to provide functionalities that do not exist in the current communication infrastructures, such as: secure data routing, broadcasting, multicasting and so on.
The first steps towards the introduction of power routing are being taken through the development of Virtual Power Plants (VPPs), which allow DERs to be grouped together, either logically or geographically, to present one unified energy resource. This will allow distribution network operators to interact with a single entity with responsibility for a range of DERs, which can provide fine-grained energy prediction and information availability and carry out highly localized actuation commands in response. By integrating VPPs with next- generation power routed networks, the smart grid will be able to effectively integrate DERs and capitalise on the efficiency and robustness capabilities they offer. Research into the feasibility of VPPs and standardised management models is already underway in Europe and the United States. For example, models based on IEC 61850 have been proposed in the literature.