Effects of Time Delays on the Behavior of a Centralized Control System for Providing System Ancillary Services in an Active Distribution Network

Abstract

An electrical distribution system with several

dispersed generation (DG) units interconnected to the AC

grid through PWM static converters is considered. The DG

units can provide both energy and system ancillary services

(e.g. voltage regulation, voltage harmonic distortion and

unbalance compensation).

The DG unit converters are coordinated through a

centralized control system that provides in real time the

reference signals to the control systems of the DG static

converters allowing them to provide the aforementioned

services. The centralized control system calculates the

reference signals using an optimization procedure whose

inputs are measurements from the distribution network

busbars and whose outputs are the reference signals; thus,

the compensation action is depending on the unavoidable

time delays introduced in the whole process by data

acquisition, digital processing and data communication.

With particular reference to the waveform distortion

compensation, the paper proposes a new procedure to

compensate them. Time domain simulations on an actual

distribution system are reported in order to analyze the

delay effects and show the effectiveness of the proposed

compensation procedure.