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MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICALTURE RURAL DEVELOPMENT THUY LOI UNIVERSITY LE QUOC HUNG RESEARCH ON THE SCIENTIFIC BASIS TO IMPROVE THE EFFICIENCY OF ELECTRICITY

MINISTRY OF EDUCATION

AND TRAINING

MINISTRY OF AGRICALTURE RURAL DEVELOPMENT THUY LOI UNIVERSITY

LE QUOC HUNG

RESEARCH ON THE SCIENTIFIC BASIS TO IMPROVE THE EFFICIENCY OF ELECTRICITY GENERATION FOR CASCADE RESERVOIRS IN COMPETITIVE POWER

GENERATION MARKET, APPLIED FOR THE CHU RIVER BASIN

Specialty: Hydraulic Engineering Code: 9580202

DISSERTATION ABSTRACT

HANOI, 2019

This dissertation is completed at Thuyloi University

Advisor 1: Assoc Prof Dr Phan Ky Nam

Advisor 2: Assoc Prof Dr Le Van Nghi

Reviewer 1: Prof Dr Ha Van Khoi – Vietnam Water Resources Development

INTRODUCTION

1 Statement of the problem

In recent years, hydropower has been developing strongly in our country and is constantly increasing in the following years Apart from the development of power sources from wind, coal, solar energy, gas, etc., it is necessary to study and exploit effectively the constructed hydropower plants (HPPs) to reduce the difficulty of supplying electricity for production Along with that, the process of reservoir operation, flood discharge of reservoirs to optimize the operation of the reservoirs to ensure the harmony of the benefits of water use and the maximum use of hydropower, flood and drought mitigation at the downstream is a matter of social concern and is always current At present, the Government has issued a joint operating procedure for all reservoir system in Vietnam's large basins, including the Ma River basin However, reservoir system operating, especially in the dry season, only regulates safe operation and minimum flow for downstream areas, but not to mention operational efficiency and competitive entry into the electricity market With the practical requirements as stated, the topic of "Research on the scientific basis to improve the efficiency of electricity generation for staged reservoirs in competitive power generation market, applied for the Chu River basin " is extremely necessary to meet the current practical requirements in Vietnam

2 Objective of the study

To study the scientific basis to build the optimal calculation model of electricity sales for the system of staged reservoirs under competitive power generation conditions in order to provide operational instructions in combination with the coordination chart deliver the full annual output contract and drive to the largest revenue

To analyze and build the relationship between the decrease and the distribution of the hourly electricity price, according to the accumulated time of each month with the monthly electricity output and the number of monthly trading hours, then to calculate annual adjustment to improve the efficiency of electricity generation, bringing the biggest revenue to the investors

3 Subject and scopes of the study

Objectives of the study: The research subject of the project is a system of reservoirs

regulating the combined electricity generation in the Chu River basin in the context of competitive power generation in Vietnam

Scope of the study: The scope of applied research is to improve the efficiency of the

operation of the Hua Na and Cua Dat reservoirs combined with electricity generation in competitive power generation conditions in Vietnam

4 Study methodology

(1) Inherited method; (2) Mathematical simulation method; (3) Analytical methods

5 Scientific and practical contributions

(1) The dissertation has improved some of the best operating models for coordinated or separate operation purposes, with the objective of generating the largest revenue for the combined generation, in the market conditions competitive electricity in Vietnam

(2) The results of calculating the regulation scheme and the instructions for the monthly electricity generation of each reservoir and inter-reservoir are referenced by reservoir owners in the operation of the reservoir system with the constraints of flood water level, the water supply flow and the target is the maximum revenue benefit

6 New contribution

(1) The dissertation has developed the problem and the program to coordinate the reservoir to achieve the largest revenue, improve the efficiency of power generation when entering the competitive electricity market

(2) Adopt a program of calculations for reservoirs in the Chu River basin to re-examine the program under constrained conditions of multi-objective operation Propose a chart

to coordinate the operation of electricity generation to ensure energy security as required by the moderation mechanism of the power system

7 Structure of the dissertation

Besides Introduction and Conclusion sections, the dissertation consists of 03 chapters as follows:

Chapter 1 Overview of cascade reservoir operational research and competitive electricity markets

Chapter 2 Research on scientific and practical basis to improve the efficiency of cascade reservoirs in the competitive power generation market

Chapter 3 Apply calculation and analysis results to determine the operating trend for the cascade reservoir in the Chu River

CHAPTER 1 OVERVIEW OF CASCADE RESERVOIR OPERATIONAL RESEARCH AND COMPETITIVE ELECTRICITY MARKETS

1.1 Studies on reservoir operation in the world

Afzali et al (2008) studied the combined operation of Khersan hydropower system, Iran by combining simulation and optimization algorithms with the objective of generating a total of four reservoirs The authors have applied the masterpiece to each

of the reservoirs and to all four reservoirs for comparison The results show that the combination of 4 reservoirs with the objective function will produce about 7.9% higher electricity output than the total power of 4 reservoirs operating separately

Daniel De Ladurantaye et al (2009) studied the optimization of profitability from hydropower The study presents a coherent, randomized mathematical model to maximize the return earned by selling electricity through dams and reservoirs in a spot

market (immediate payment) The first model is based on the specified electricity price while the other model integrates randomly through the management of a tree of potential price scenarios Numerical results based on historical data demonstrate the superiority of the random model on the deterministic model It also shows that price fluctuations affect the profitability of the random model

Le Ngoc Son (2017) studied the establishment of a scientific basis combining the model

of simulation - optimization - artificial intelligence, building the optimal model of dynamic programming (DP) to propose the transport plan Optimal access to the reservoir system includes the actual alteration of the water source and the need for water use to improve the efficiency of electricity generation, meeting the downstream water supply requirements for the Ba River basin Simulation results verified with the actual performance of Song Hinh hydropower station showed that the model proposed

by the author brings more efficiency However, the period of calculation in the model does not subdivide the difficult period corresponding to the short-term hydrological forecast period of 10 days The study also fails to take into account the randomness of

water demand and electrical systems that only incorporate constraints Operational constraints on water use and electricity systems in the competitive electricity market need to be further researched in order to make the model more adaptable when water demand for the economy- society and market conditions change

1.3 General introduction of competitive electricity market

Competitive power markets have been established and are operating effectively in a number of European, American and Australian countries According to the electricity market plan in Vietnam will develop through three levels and continue to be completed after each test When entering the competitive electricity market, long-term regulated reservoirs will have the advantage of offering prices as well as flexible operation in order to sell electricity at high price frames Therefore, this is an advantage and also a complex problem that requires the owners to take into account when planning power generation as well as regulating the power generation reservoir, in order to bring about high efficiency in the conditions of the hydrographic regime change

1.4 Research orientation of the dissertation

The researches on reservoir operation in Vietnam and in the world show that the authors focus on solving optimal problems of power generation, water supply as well as flood control when applying different calculation methods Some authors have also examined the location of HPP in the national grid However, there are currently no studies that consider entering the competitive electricity market when looking for optimal operating options for power generation reservoirs

Based on a review of studies on the Chu River basin system, there is no specific study

on the combination of the Hua Na - Cua Dat system during power generation operations This is a gap, it should be studied because each system has its own characteristics, and there is not any single algorithm or model as general to resolve completely the reservoir system operating problem

In terms of research methods, an overview shows that the DP method or DP improvements are often used in the study of reservoir operation and are effective in conducting a global optimization In terms of optimal computation of revenue for two

cascade reservoirs, the dissertation selects a top-down recalculation method to compute boundaries, and applies the bottom-up approach in Build a computational model that matches the processing capabilities of the programming language From the analysis of the competitive electricity market, the model selection dissertation is the optimal maximum revenue for the staged reservoir when entering the electricity market

Figure 1.10 The diagram shows the research steps

1.5 Conclusion of chapter 1

At present, in the Ma River basin in particular and the big river basins in Vietnam in general, the Government has issued the inter-reservoir operating procedure which sets out the operating rules However, the owners still have the right to actively operate and coordinate operations within the scope or binding permissions

The operation, according to the new process, is currently halting the introduction of water or discharge constraints, to ensure minimum facility safety and water supply, without optimizing it In addition, the operation is in the "equivalent to the design and

construction process", that is the operating instructions on the coordination chart remain relatively fixed; update the data over time to adjust On the other hand, every year, participating factories in the competitive electricity market are assigned different outputs Distributions in the months of the year also change between years As a result, more appropriate modes of operation for the cascade reservoir system are needed to improve the efficiency of power generation combined with flood prevention and water supply and overcome other bottlenecks in the operation of the hydro power system

Analysis of the unresolved aspects of the previous studies in Chapter 1, which is the basis for calculating and solving the problem of the operation of the reservoir generation of the dissertation Consequently, the approach and approach is the optimal combination of power generation in the competitive market and the reservoir steps that will be addressed in the next two chapters

CHAPTER 2 RESEARCH ON SCIENTIFIC AND PRACTICAL BASIS TO IMPROVE THE EFFICIENCY OF CASCADE RESERVOIR IN THE COMPETITIVE ELECTRICITY MARKET

2.1 The optimal solution for inter-reservoir operation

The dissertation calculates inter-reservoir operation using the DP method, seeks to optimize the target on the basis of historical flow and historical electricity purchase data From there, it is possible to determine the optimal positions in the operation and to produce actual operating directions on time, following the water level of the reservoirs

at each operating point for the reservoir owners, The reservoirs can operate singly or in combination to increase total revenue for the system

2.2 Solution for DP methodology

DP usually use following approaches:

 top-down: The problem is divided into sub-problems Sub-problems solved and

solutions can be memorized in case of re-use This is recursive and archives are combined together

 bottom-up: All problems that may be needed are solved first, and then used to

construct solutions for larger problems This approach is better for the memory space used for the stack and the number of function calls

To avoid having to solve multiple sub-problem problems (DP top-down), the dissertation uses the DP bottom-up method to calculate and define the maximum revenue function; In order to construct the water margin to ensure energy security, the dissertation utilizes a top-down approach with a set of starting points reversing from the last dead water level complex of reservoirs

The transition period (for the next period) needs to record the path values that make up the target function in all meshes (which are in the calculation period) In each pair of divided lattices (two reservoirs), it is necessary to determine the appropriate path from the starting point (first pair of meshes) to the meshes in question

2.3 Calculate optimal regulation of reservoir of hydropower station by DP

Figure 2.2 Describe the optimal path directions in reservoir regulation

Step 1: Divide calculation cycle T into n period ΔT

Step 2: Then carry out iterations to narrow down the dividing net of ΔZ = 0.1m

Step 3: Number the corresponding meshes Zi,k with i is the period in the calculation cycle T and k is the mesh position

Step 4: Let the comparison algorithm be implemented and assign a new value (greater than the old value) found in the meshes: In the case of finding the largest value, with the incremental values being positive, the initial value at the grid points needs to be assigned to a value less than 0 Assign revenue value at all points on the mesh Bj,k = –1

Step 5: Select the starting point and assign the revenue value at the starting point Bo = 0

Step 6: Link point Zo to all points: Z1,1; Z1,2; to Z1,m-3; Z1,m-2; Z1,m-1; Z1,m determine the difference of the head capacity and the end of the period for each point ΔV1,1; ΔV1,2;

to ΔV1,m-3; ΔV1,m-2; ΔV1,m-1; ΔV 1,m

∆𝑉1,𝑘 = 𝑉 𝑍1,𝑘 − 𝑉 𝑍𝑜 (mil m3/s) (2-6) With V(Z) is the value of the reservoir capacity corresponding to the upstream water level Z, interpolation according to the relationship between water level and reservoir volume Use this volume difference; The program calculates the flow out of the reservoir If the flow-rate is negative, Search values at that point are assigned value -1

If the flow out of the reservoir ensures the minimum flow of the corresponding period, The values for water head, capacity, power and revenue at that point will be saved

Step 7: Determine the flow out of the reservoir in the mesh according to the following general formula:

Step 9: Determine the corresponding revenue, by calculating the contract output for period 1; contract prices; the level of distribution of electricity generation hours in the history of electricity trading; ceiling price of period 1 Values will be assigned B1,k at the meshes Z1,k If there is a reasonable path from Zo to Z1,k In case, there is no reasonable path in the mesh Z1,k, value of B1,k still equals –1

Step 10: Determine the average price of the period, based on the amount of electricity generated (KB1) or the number of hours taking advantage of the available capacity of the period (KB2)

Step 13: Repeat steps 6 through 12, for the third time With the determination, see which path brings the largest revenue B2,k at Z2,k In this step, if B2,k > 0, path to Z2,k, will be saved as a line derived from one of the meshes Z1,j through comparison

Step 14: Repeat steps 6 through 13, until the end of the calculation cycle is Bn,k

Knowing the water level to reach at the end; from the chain equation system will find the previous values From there, determine the optimal single-track operation line to obtain the largest revenue for the calculation cycle of T

At each calculation step (the calculation period is between two consecutive calculation periods), for example if there are two terraced reservoirs, the program considers the pair