Page 20 - Mathematical Models and Algorithms for Power System Optimization

10 Chapter 2

2.1 Introduction

2.1.1 Outline of the Problem

The daily economic dispatch problem in this chapter focuses on an actual multiarea system with
many hydrothermal plants and a pumped storage plant. It may be simplified as daily economic
dispatch optimization with pump storage plant. The pumped storage plant normally operates as
a pump on the duration of off-peak load and as a generator on the duration of peak load.

The studied system consists of six areas, including east, west, south, north, and central areas,
along with the power outsourcing purchase area (defined as the purchase area) in a purchase
agreement. The power grids in each area within the province are connected with tie lines,
presenting the problem of joint economic operation and dispatch among multiareas. The
provincial power grid is characterized by a large pumped storage plant in the country, so its
regulation capacity plays an important role in daily economic dispatch.
The generated output plan for the plants in each area needs to be considered, avoiding the
overload on tie lines among the six areas. There are 27 power plants in the provincial system,
among which there are 14 thermal plants, 7 hydroplants, and 1 pumped storage plant. This
system consists of 82 units, of which there are 50 thermal units, 23 hydro units, 2 purchase units,
and 4 pumped storage units. The total installed generation capacity is 13,179MW (refer to
Table 2.1). The property rights vary from different types of power plants. There are Power
Purchase Agreements between the provincial power grid and five purchase power plants, that
is, Tianshengqiao Power Plant, Guangxi Power Purchase, Guizhou Power Purchase, Yunnan
Power Purchase, and Zhongdian Power Purchase. For these power plants to complete their plan
of generated output and energy, the power grid needs to consider the existing agreements with
these power plants.
The basic interconnection relationship of the provincial power grid is shown in Fig. 2.1. Briefly,
there are N areas and M tie lines in the provincial power system, including M 1 hydropower
plants (each plant has N 1i units), M 2 thermal power plants (each plant has N 2j units), and M 3
pumped storage plants (each plant has N 3k units).
The power generation characteristics of thermal and hydropower plants should be considered in
the daily economic dispatch schedule of pumped storage, for example, during 24h in a day, the
hydropower plant may start or stop at any time, the run-of-river hydropower plant could
generate power only in a given period, and the thermal power plant must satisfy the limitations
on interval between startup and shutdown time. The characteristics of the pumped storage plant
should be also fully considered, that is, during 24h in a day, it generates power during the peak
periods and pumps water during the valley periods. There is a large difference between peak
and valley loads in the province (around 4000MW), as shown in Fig. 2.2. If the pumped storage
plant (a total installed capacity of 1200MW) can be fully utilized in peak load shifting, the