Module 5 : Real and Reactive Power Scheduling
Lecture 21 : Introduction
Objectives
In this lecture you will learn the following
What is scheduling?
Examples of control variables and constraints
Objective functions
Control and Scheduling
In previous lectures, we have seen how various quantities like voltage, frequency and power flow are controlled.
Speed governors, AGC, voltage and power flow regulators are essentially automatic feedback controllers which
work without manual intervention and ensure that these quantities are maintained within acceptable ranges.
Most automatic controllers ensure that these quantities are regulated, i.e., their values are maintained at a
certain set-point. A set-point is a reference value which is given to these controllers by an operator. There
exists some flexibility in deciding the exact value of the set point.
Consider the following examples:
A plant operator may increase the value of the voltage setting of a automatic voltage regulator from 1.0
pu to,say, 1.02 pu. This will increase the reactive power output of the generator. Note that while 1.0 pu is
1. the nominal value of terminal voltage, it is not sacrosanct and an operator may change it to a value near-
about it as long as it does not violate any limit (see capability of a generator).
Following a sudden load increase, governors respond and try to restore frequency by increasing generated
power. Subsequently AGC ensures that tie line power flow and frequency is brought back to the nominal
2. value. However, a system operator may wish to alter the sharing among various generators (say, to
decrease overall cost of generation).
If due to line tripping, a system is in the alert or insecure state, then a system operator may reduce
3. power flow through certain lines by changing the power output of different generators.
Manual control actions by a system or plant operator which essentially change the set point of various automatic
controllers is termed as "scheduling". Scheduling may be done in order to achieve a certain economic objective
or may supplement the existing automatic controller action in ensuring secure system operation.
Control Variables
A system or a plant operator has the flexibility to set several variables (not only the generator power) in order
to meet certain objective(s).
A tentative listing of such variables are:
Lecture 21 : Introduction
Objectives
In this lecture you will learn the following
What is scheduling?
Examples of control variables and constraints
Objective functions
Control and Scheduling
In previous lectures, we have seen how various quantities like voltage, frequency and power flow are controlled.
Speed governors, AGC, voltage and power flow regulators are essentially automatic feedback controllers which
work without manual intervention and ensure that these quantities are maintained within acceptable ranges.
Most automatic controllers ensure that these quantities are regulated, i.e., their values are maintained at a
certain set-point. A set-point is a reference value which is given to these controllers by an operator. There
exists some flexibility in deciding the exact value of the set point.
Consider the following examples:
A plant operator may increase the value of the voltage setting of a automatic voltage regulator from 1.0
pu to,say, 1.02 pu. This will increase the reactive power output of the generator. Note that while 1.0 pu is
1. the nominal value of terminal voltage, it is not sacrosanct and an operator may change it to a value near-
about it as long as it does not violate any limit (see capability of a generator).
Following a sudden load increase, governors respond and try to restore frequency by increasing generated
power. Subsequently AGC ensures that tie line power flow and frequency is brought back to the nominal
2. value. However, a system operator may wish to alter the sharing among various generators (say, to
decrease overall cost of generation).
If due to line tripping, a system is in the alert or insecure state, then a system operator may reduce
3. power flow through certain lines by changing the power output of different generators.
Manual control actions by a system or plant operator which essentially change the set point of various automatic
controllers is termed as "scheduling". Scheduling may be done in order to achieve a certain economic objective
or may supplement the existing automatic controller action in ensuring secure system operation.
Control Variables
A system or a plant operator has the flexibility to set several variables (not only the generator power) in order
to meet certain objective(s).
A tentative listing of such variables are:
