Microgrids

3

Intelligent Local Controllers

Thomas Degner, Nikos Soultanis, Alfred Engler and Asier Gil de Muro

3.1 Introduction

The development and use of the intelligent local controllers for microgenerators and controllable loads enables stable microgrid operation. These controllers provide efficient voltage and frequency control in case of islanded operation, ancillary services in interconnected mode, and deal efficiently with frequency and voltage variations during transitions from interconnected to islanded operation and vice versa.

The main tasks of microsource controllers are to allow power sharing between the different sources at different locations, acting on the electronic converters that interface them to the network. As communication lines, especially for long distances and control purposes are expensive and vulnerable, at least fast communication should be avoided. This can be achieved by using local controllers, which are based on frequency and voltage droops. This way, the locally available information – frequency and voltage – is used for power sharing. Normally, the frequency is linked to the active power, and voltage is linked to the reactive power.

Standard rotating generator systems inherently support these droops. Sometimes, for improving performance, additional controllers are applied. Therefore it is possible to operate large numbers of such generators in a single network. However, with standard static inverters, characterized by fixed frequency and voltage, such an ...