Chapter 4
ECONOMIC DISPATCH AND UNIT COMMITMENT
,1 INTRODUCTION
A power system has several power plants. Each power plant has several
generating units. At any point of time, the total load in the system is met by
the generating units in different power plants. Economic dispatch control
determines the power output of each power plant, and power output of
each generating unit within a power plant , which will minimize the overall
cost of fuel needed to serve the system load.
• We study first the most economical distribution of the output of a
power plant between the generating units in that plant. The method
we develop also applies to economic scheduling of plant outputs for
a given system load without considering the transmission loss.
• Next, we express the transmission loss as a function of output of the
various plants.
• Then, we determine how the output of each of the plants of a system
is scheduled to achieve the total cost of generation minimum,
simultaneously meeting the load on the system.
,2 INPUT – OUTPUT CURVE OF GENERATING UNIT
Power plants consisting of several generating units are constructed
investing huge amount of money. Fuel cost, staff salary, interest and
depreciation charges and maintenance cost are some of the components
of operating cost. Fuel cost is the major portion of operating cost and it
can be controlled. Therefore, we shall consider the fuel cost alone for
further consideration.
, To get different output power, we need to vary the fuel input. Fuel input can
be measured in Tonnes / hour or Millions of Btu / hour. Knowing the cost of
the fuel, in terms of Rs. / Tonne or Rs. / Millions of Btu, input to the
generating unit can be expressed as Rs / hour. Let Ci Rs / h be the input
cost to generate a power of Pi MW in unit i. Fig.1 shows a typical input –
output curve of a generating unit. For each generating unit there shall be a
minimum and a maximum power generated as Pi min and Pi max.
Ci
in Rs / h
Pi in MW
Pi min Pi max
Fig.1 Input-Output curve of a generating unit
ECONOMIC DISPATCH AND UNIT COMMITMENT
,1 INTRODUCTION
A power system has several power plants. Each power plant has several
generating units. At any point of time, the total load in the system is met by
the generating units in different power plants. Economic dispatch control
determines the power output of each power plant, and power output of
each generating unit within a power plant , which will minimize the overall
cost of fuel needed to serve the system load.
• We study first the most economical distribution of the output of a
power plant between the generating units in that plant. The method
we develop also applies to economic scheduling of plant outputs for
a given system load without considering the transmission loss.
• Next, we express the transmission loss as a function of output of the
various plants.
• Then, we determine how the output of each of the plants of a system
is scheduled to achieve the total cost of generation minimum,
simultaneously meeting the load on the system.
,2 INPUT – OUTPUT CURVE OF GENERATING UNIT
Power plants consisting of several generating units are constructed
investing huge amount of money. Fuel cost, staff salary, interest and
depreciation charges and maintenance cost are some of the components
of operating cost. Fuel cost is the major portion of operating cost and it
can be controlled. Therefore, we shall consider the fuel cost alone for
further consideration.
, To get different output power, we need to vary the fuel input. Fuel input can
be measured in Tonnes / hour or Millions of Btu / hour. Knowing the cost of
the fuel, in terms of Rs. / Tonne or Rs. / Millions of Btu, input to the
generating unit can be expressed as Rs / hour. Let Ci Rs / h be the input
cost to generate a power of Pi MW in unit i. Fig.1 shows a typical input –
output curve of a generating unit. For each generating unit there shall be a
minimum and a maximum power generated as Pi min and Pi max.
Ci
in Rs / h
Pi in MW
Pi min Pi max
Fig.1 Input-Output curve of a generating unit
