Bài giảng Tối ưu hóa vận hành hệ thống điện - Chapter 6: Hydrothermal Coordination - Võ Ngọc Điều

2/16/2014
1
1
Dr. Vo Ngoc Dieu
Department of Power Systems
Ho Chi Minh City University of Technology
Email: vndieu@gmail.com
Chapter 6:
HYDROTHERMAL COORDINATION
TỐI ƯU HÓA VẬN HÀNH 
HỆ THỐNG ĐIỆN
2
Introduction
• Optimal scheduling of power plant generation is the 
determination of the generation for every generating 
unit such that the total system generation cost is 
minimum while satisfying the system constraints.
• The objective of the hydrothermal scheduling
problem is to determine the water releases from each 
reservoir of the hydro system at each stage such that 
the operation cost is minimized along the planning 
period.
• The operation cost includes fuel costs for the thermal 
units, import costs from neighbouring systems and 
penalties for load shedding.
2/16/2014
2
3
Introduction
• The basic question in hydro thermal coordination is to 
find a trade-off between a relative gain associated with 
immediate hydro generation and the expectation of 
future benefits coming from storage.
• Two aspects make the hydrothermal scheduling a 
complex problem:
- The uncertainty of inflows.
- The hydraulic coupling between hydro plants.
• The operation planning of hydrothermal systems is 
called Hydrothermal Coordination (HTC) problem.
• Hydrothermal coordination (HTC) problem requires 
solving for the thermal unit commitments and 
generation dispatch as well as the hydro schedules.
4
Introduction
• The objective is to minimize thermal production cost 
subject to meeting the forecasted demand and other 
operating constraints.
• The HTC problem is usually solved by decomposition of 
the original problem into long, medium and short term 
problems each one considering the appropriate aspects 
for its time step and horizon of study.
• It is also essential to take into consideration two basic 
aspects of the hydro system:
- The available water quantity (water inflows) is 
stochastic in nature.
- The decision for the energy allocated to hydro units is 
deterministic.
2/16/2014
3
5
Need of Hydrothermal Scheduling
• The operating cost of thermal plant is very high, though 
their capital cost is low.
• On the other hand the operating cost of hydroelectric 
plant is low, though their capital cost is high.
• So it has become economical as well convenient to have 
both thermal and hydro plants in the same grid.
• The hydroelectric plant can be started quickly and it 
has higher reliability and greater speed of response.
• The starting of thermal plants is slow and their speed of 
response is slow.
6
Classification of Hydro Plants
• Classification on the basis of type
- Conventional plants
+ Storage plants
+ Run-of-river plants
- Pumped storage plants
• Classification on the Basis of Location
- Hydro plants on different streams
- Hydro plants on the same stream
- Multi-chain hydro plants
2/16/2014
4
7
Classification of Hydro Plants
8
Classification of Hydro Plants
2/16/2014
5
9
Classification of Hydro Plants
10
Classification of Hydro Plants
• Classification According to Quantity of Water Available
- Run-off- River Plants without Pondage
- Run-off River Plants with Pondage
- Reservoir Plants
• Classification of Hydrothermal Scheduling Problems
- Long range problem
- Short range problem
2/16/2014
6
11
Classification of Hydro Plants
• Long range problem
- Long range problem includes the yearly cyclic nature 
of reservoir water inflows and seasonal load demand 
and correspondingly a scheduling period of one year is 
used.
- The long-range hydro-scheduling problem involves 
the long-range forecasting of water availability and the 
scheduling of reservoir water releases (i.e., 
“drawdown”) for an interval of time that depends on 
the reservoir capacities.
- Typical long-range scheduling goes anywhere from 1 
week to 1 year or several years.
12
Classification of Hydro Plants
• Short range problem
- The load demand on the power system exhibits cyclic 
variation over a day or a week and the scheduling 
interval is either a day or a week.
- The amount of water to be utilized for the short-range 
scheduling problem is known from the solution of the 
long-range scheduling problem.
- Short-range hydro-scheduling (1 day to 1 week) 
involves the hour-by-hour scheduling of all generation 
on a system to achieve minimum production cost for the 
given time period.
2/16/2014
7
13
Classification of Hydro Plants
• The short term hydrothermal scheduling problem is 
classified in to two groups
- Fixed head hydro thermal scheduling
- Variable head hydro thermal scheduling
14
Scheduling Problems
• In the operation of a hydroelectric power system, three 
general categories of problems depending on the 
balance between the hydroelectric generation, the 
thermal generation, and the load. 
• Systems without any thermal generation are fairly rare. 
- The economic scheduling of these systems is really a 
problem in scheduling water releases to satisfy all the 
hydraulic constraints and meet the demand for 
electrical energy.
- Techniques developed for scheduling hydrothermal 
systems may be used in some systems by assigning a 
pseudo-fuel cost to some hydroelectric plant and then 
the schedule is developed by minimizing the production 
“cost” as in a conventional hydrothermal system.
2/16/2014
8
15
Scheduling Problems
• The largest category of hydrothermal systems includes
- Those where there is a closer balance between the 
hydroelectric and thermal generation resources and
- Those where the hydroelectric system is a small 
fraction of the total capacity.
• In these systems, the schedules are usually developed 
to minimize thermal generation production costs, 
recognizing all the diverse hydraulic constraints that 
may exist.
• Scheduling problem consists of
- Problem characteristics
- Problem formulation
- Solution approach
16
Scheduling Energy
• Suppose we have two sources of electrical energy to 
supply a load, one hydro and another steam. The hydro 
plant can supply the load by itself for a limited time.
2/16/2014
9
17
Scheduling Energy
18
Scheduling Energy
2/16/2014
10
19
Scheduling Energy
20
Scheduling Energy
2/16/2014
11
21
Scheduling Energy
22
Scheduling Energy
2/16/2014
12
23
Scheduling Energy
24
Scheduling Energy
2/16/2014
13
25
Short Term Hydrothermal Scheduling
26
2/16/2014
14
27
28
2/16/2014
15
29
30
2/16/2014
16
31
32
2/16/2014
17
33
34
2/16/2014
18
35
36
2/16/2014
19
37
38
2/16/2014
20
39