Module 3 : Frequency Control in a Power System
Lecture 16 : Automatic Generation Control (AGC)
Objectives
In this lecture you will learn the following
What is automatic generation control ?
In what way is it different from governor action ?
Automatic Generation Control (AGC)
We saw in the previous example how load sharing in a multi-generator power system can be
achieved using droop characteristics of governors. The sharing according to droop is irrespective of
load location.
However if non-zero governor droops are used (which is necessary for appropriate sharing), a
steady state frequency error will remain which needs to be corrected. Moreover, since all the
governors respond to the load change irrespective of load location, there may be undesirable
exchange of power between different areas of the grid. This is manifested as a change in the flows
of lines interconnecting these areas.
To ensure that frequency steady state error is corrected and generators in a particular area take on
the burden of their own load, the load reference ( Pm0 ) of governors is adjusted slowly. This control
is also called "secondary control". This correction may be done over several minutes as opposed to
5-10 seconds for initial or "primary" control action of governors.
Thus, while primary control (governor action) ensures that a large and sudden frequency fall or rise
is prevented, secondary control or Automatic Generation Control ensures that frequency is brought
back to the nominal value and inter-area power flow is regulated.
Automatic Generation Control (AGC) (Con td..)
Any change of reference value will lead to a change in sharing among the generators. Thus by
slowly changing the reference of speed governors we can over-ride the sharing which is imposed by
the droop characteristics.
The question then arises: which generators should change their governor references and what the
exact value of these changes ?
In a 2 - area system, if governors are present on some machines in both
areas
and
a) power flow in certain ac line, which connects 2 areas is to be
regulated.
Lecture 16 : Automatic Generation Control (AGC)
Objectives
In this lecture you will learn the following
What is automatic generation control ?
In what way is it different from governor action ?
Automatic Generation Control (AGC)
We saw in the previous example how load sharing in a multi-generator power system can be
achieved using droop characteristics of governors. The sharing according to droop is irrespective of
load location.
However if non-zero governor droops are used (which is necessary for appropriate sharing), a
steady state frequency error will remain which needs to be corrected. Moreover, since all the
governors respond to the load change irrespective of load location, there may be undesirable
exchange of power between different areas of the grid. This is manifested as a change in the flows
of lines interconnecting these areas.
To ensure that frequency steady state error is corrected and generators in a particular area take on
the burden of their own load, the load reference ( Pm0 ) of governors is adjusted slowly. This control
is also called "secondary control". This correction may be done over several minutes as opposed to
5-10 seconds for initial or "primary" control action of governors.
Thus, while primary control (governor action) ensures that a large and sudden frequency fall or rise
is prevented, secondary control or Automatic Generation Control ensures that frequency is brought
back to the nominal value and inter-area power flow is regulated.
Automatic Generation Control (AGC) (Con td..)
Any change of reference value will lead to a change in sharing among the generators. Thus by
slowly changing the reference of speed governors we can over-ride the sharing which is imposed by
the droop characteristics.
The question then arises: which generators should change their governor references and what the
exact value of these changes ?
In a 2 - area system, if governors are present on some machines in both
areas
and
a) power flow in certain ac line, which connects 2 areas is to be
regulated.
