Final Thoughts

The distribution grid of the future is already here in many places around the world. The high penetration of distributed rooftop photovoltaic panels equipped with inverters with power and voltage control capabilities is proving that it is not that simple anymore.

Gone are the good times when voltage control was pure and simple in a passive distribution network. You could easily calculate the voltage drop along the distribution feeder based on its loading and then regulate the voltage within the required range using the transformer tap changer or capacitor banks. 
Today we have in some areas a very high penetration of rooftop solar generators connected to the network with smart inverters that have voltage control capabilities. The system operator can take advantage from the autonomous control capabilities of the inverters.

A couple of these voltage control related capabilities are:

  • Reactive Power Control which sets the level of reactive power (kVAR) generation or consumption, and operates within the constraints of the inverter’s power envelope and current irradiance conditions
  • Reactive Power Ramp Rate that defines the rate at which the reactive power production by the inverter transitions between set points

These functions operate based on the monitoring of local parameters and predefined set points.  However, if these actions by numerous distributed and autonomous devices are also not coordinated with the conventional voltage control functionality in the substation, it may lead to voltage variations in the distribution system that may result in damages of sensitive equipment.

This brings us to the generic issue of the controllability of distributed energy resources of any kind. DERs are here to stay, but with their growing numbers if they are not possible to control by the system operator or protection and control systems we will be in for a lot of trouble.

This means that the protection, automation and control industry needs to work with the DER industry to ensure that Internet of Things (IoT) technology can be integrated in the DERs and hierarchical control systems can be designed and implemented in order to allow the energy management systems to maintain the secure and reliable operation of the Smart Grid.





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