Page 132 - Mathematical Models and Algorithms for Power System Optimization

Load Optimization for Power Network 123

LSC of a power grid. The LSC index is initially used as a reliability index to determine the event
of load supply shortage. LSC can be used to determine system load level. When the system load
exceeds this level, a failure occurs somewhere in the system. LSC helps to indicate the load that
cannot be supplied by a system.

The power grid is a complex structure involving multiple aspects, such as power
generation, transmission, transformation, distribution, and consumption, all of which should
be considered in determining the grid’s LSC. In the past, the LSC of a power grid was
often assessed by using the simple capacity-load ratio method or a trial-and-error method.
The capacity-load ratio is a single macroindex used to assess the grid’s LSC. This index
is applied to examine the grid’s LSC from the grid’s transformation aspect but not applied to
the mutual relationship between the grid’s power generation, transmission, distribution,
and consumption. The trial-and-error method continues to increase system load, distribute
load to each load point by a certain load distribution coefficient, and execute the power
flow calculation until a very small increase in load would cause power over branch. In
this method, the load distribution coefficient is the key issue to the accuracy of the final
assessment result.
The LSC model based on linear programming can be applied to scientifically and accurately
assess the maximum LSC of the urban power grid.

5.1.3 Overview of This Chapter

This chapter discusses the bus load optimization problem under fault and normal conditions. It
also introduces bus load as a variable to formulate a simple linear programming model based on
a DC power flow model. The model is used to determine the basic expressions of objective
function and constraints. The different weights, assigned to each load bus based on different
load properties, are considered in the cost coefficient, so the total curtailed load is minimized
under fault condition, whereas the load is maximized under normal condition, which meets
the reliability requirements for different loads. The bus load variable is added to the power
balance constraint (grid power balance, bus power balance, and branch power balance) in
equality constraints. The bus load constraint is added to inequality constraints (grid branch
power constraint and generation bus output constraint).
Section 5.2 specifically gives basic ideas of formulating an optimization model; Section 5.3
provides a load optimization mathematical model; Section 5.4 introduces the algorithm and
calculation process of LC optimization (LCO); Section 5.5 first uses a small-scale case study to
verify the proposed LCO model and algorithm, and then gives detailed results of an actual case
study for analysis to confirm the effectiveness of the proposed LCO model and algorithm;
Section 5.6 gives the calculation process of maximizing LSC; and Section 5.7 uses a case study
to verify the proposed optimization model and algorithm for maximizing LSC.