Access Type

Open Access Dissertation

Date of Award

January 2019

Degree Type


Degree Name



Electrical and Computer Engineering

First Advisor

Caisheng Wang



Analysis and Mitigation of the Impacts of Delays in Control of Power Systems

with Renewable Energy Sources


Chang Fu

Apr. 2019

Advisor : Dr. Caisheng Wang

Major : Electrical and Computer Engineering

Degree : Doctor of Philosophy

With the integration of renewable resources, electric vehicles and other uncertain

resources into power grid, varieties of control topology and algorithms have been proposed to

increase the stability and reliability of the operation system. Load modeling is an critical part

in such analysis since it significantly impacts the accuracy of the simulation in power system,

as well as stability and reliability analysis. Traditional power system composite load model

parameter identification problems can be essentially ascribed to optimization problems, and the

identied parameters are point estimations subject to dierent constraints. These conventional

point estimation based composite load modeling approaches suer from disturbances and noises

and provide limited information of the system dynamics. In this thesis, a statistic (Bayesian

Estimation) based distribution estimation approach is proposed for composite load models,

including static (ZIP) and dynamic (Induction Motor) parts, by implementing Gibbs sampling.

The proposed method provides a distribution estimation of coecients for load models and is

robust to measurement errors.

The overvoltage issue is another urgent issues need to be addressed, especially in a

high PV penetration level system. Various approaches including the real power control through

photovoltaic (PV) inverters have been proposed to mitigate such impact, however, most of the

existing methods did not include communication delays in the control loop. Communication delays, short or long, are inevitable in the PV voltage regulation loop and can not only deteriorate

the system performance with undesired voltage quality but also cause system instability. In this

thesis, a method is presented to convert the overvoltage control problem via PV inverters for

multiple PVs into a problem of single-input-single-output (SISO) systems. The method can handle

multiple PVs and dierent communication delays. The impact of communication delays is

also systematically analyzed and the maximum tolerable delay is rigorously obtained. Dierent

from linear matrix inequality (LMI) techniques that have been extensively studied in handling

systems with communication delays, the proposed method gives the necessary and sucient

condition for obtaining a controller and the design procedure is explicitly and constructively

given in the paper. The effectiveness of the proposed method is veried by simulation studies

on a distribution feeder and the widely-used 33-bus distribution test system.

The similar design strategy can be utilized to mitigate delay impacts in Load frequency

control (LFC) as well. LFC has been considered as one of the most important frequency

regulation mechanisms in modern power system. One of the inevitable problems involved in

LFC over a wide area is communication delay. In this thesis, an alternative design method is

proposed to devise delay compensators for LFC in one or multiple control areas. For one-area

LFC, a sucient and necessary condition is given for designing a delay compensator. For multiarea

LFC with area control errors (ACEs), it is demonstrated that each control area can have

its delay controller designed as that in a one-area system if the index of coupling among the

areas is below the threshold value determined by the small gain theorem. Effectiveness of the

proposed method is veried by simulation studies on LFCs with communication delays in one

and multiple interconnected areas with and without time-varying delays, respectively.