SECURITY ASPECTS OF MULTI AREA ECONOMIC DISPATCH WITH RENEWABLE ENERGY AND HVDC TIE LINES.

Transcription

1 SECURITY ASPECTS OF MULTI AREA ECONOMIC DISPATCH WITH RENEWABLE ENERGY AND HVDC TIE LINES. PROJECT INDEX: 134. PRESENTED BY KIPKOECH C. JOHN. SUPERVISOR: MR. PETER MOSES MUSAU. EXAMINER: DR. CYRUS WEKESA.

2 Introduction. Modern power systems are large, with multiple control areas interconnected through tie-lines. Each control area has its own load and generation. Areas of individual utility are interconnected through tie-lines to operate with maximum reliability, reserve sharing, improved security, and less production cost than when operated as an isolated area [7]. The rapid growth of cross-border trading (energy and reserve) among electricity markets between nations, system of an interconnected multi-area system calls for the development of a market-clearing model to ensure a secure and economically efficient operation of each national/regional system and the interconnected system as a whole [3].

3 Definition of terms. Economic dispatch (ED). Economic dispatch is the short term determination of the optimal output of a number of electricity generating facilities to meet system demand/load at lowest possible cost subject to transmission and operational constraints. Multi-Area economic Dispatch (MAED). It is the short term determination of optimal output of a number of electricity generating facilities to meet the system demand while allowing cross-border power sharing at lowest possible cost subject to transmission, Tie-line and operational constraints.

4 Definition of terms cont d Tie-line. Connection point between two or more power plants or power grids. Power flow in tie line will flow in both directions since either ends (or both power grids) are synchronized. Renewable Energy (RE). Energy resources that are naturally replenishing but flow limited. They include wind, solar, tides, geothermal heat etc. they cannot be exhausted and is constantly renewed. Power system Security. It s the ability of the system to withstand credible contingencies without violating normal operating limits.

5 Problem statement. There has been a great improvement in the electricity market with recent entry of renewable energy, this has led to reduction in the emission of greenhouse gases in to the atmosphere by the thermal sources. Although these sources offer great benefits, they come with security challenges. This project tries to address these security issues in a multi area system with HVDC tie lines.

6 Project objectives The main purpose of this project is to introduce renewable energy (wind and solar) into a classical multi area economic dispatch problem while addressing security aspects related to bus voltage limit violation and the transmission and tie lines power flow limit violation of the system. Sub objectives. Security analysis of multi area economic dispatch with renewable energy. Security aspects addressed by HVDC tie lines in multi area power interconnection. Formulation of power output from solar and wind energy.

7 Project questions. What is the optimal allocation of generation units to the available thermal generating units, wind generating units and solar generating units so as to meet the system load demand in a multi area environment at the lowest possible cost and within generation, tie line, and area power balance and area import/export constraints? What are the effects of introducing renewable energy to the classical multi area economic dispatch problem? What are the effects of introducing security treatment to the classical MAED problem total cost?

8 Effects of RES on power system security. Voltage stability. Due to the distinct characteristics of Renewable Power Plants (the controllers involved) and current grid regulation, the voltage stability of the system can be significantly affected by high Renewable energy penetration. The effect of high RPPs penetration on the voltage magnitude and stability of the transmission and sub- transmission systems has been studied in the literature by using both deterministic and time series analyses [33]. Rotor angle stability. A number of researches have devoted to revealing the impact of Renewable Power Plants (i.e., large-scale wind and solar on power plants) on power system large-disturbance rotor angle stability. Many of the works have revealed that the reduction of system inertia due to the displacement of conventional generators by RPPs is the main reason for reduction of system rotor angle stability margins. The authors of [34] have analyzed the impact of reactive power control methodology on converter based RPPs and revealed that the reactive power control employed in converter control of RPPs can directly influence the large-disturbance rotor angle stability of the system.

9 Effects of RES on power system security. Cnt d Frequency stability. With the high penetration of RPPs, a significant number of synchronous generators in the system would be replaced by RPPs and resulting in the reduction system inertia. As the high penetration of zero inertia generators such as PV and full converter wind turbines, the conventional generators that are co-existing with these generators will be forced to provide torque and inertia to mitigate any instability events, which could lead to the frequency instability problem. The incident in Electricity Reliability Council of Texas (ERCOT) system on Feb. 26, 2008 is an excellent example of such a situation [35], where the unexpected loss of some synchronous generators with wind generator ramp down and load ramp-up led to a decline in system frequency. It is believed that high penetration of zero inertia generators such as PV with a higher ramp rate could adversely affect the frequency stability of the system

10 Effects of RES on power system security. Cnt d Critical Ancillary Service Planning. The power system relies on primary, secondary and tertiary responses to regulate the imbalance between generation and loads when sudden contingencies occur in the system. Traditionally, synchronous generators associated controls are used to provide such regulation. Over the years synchronous generator inertial response has been used to limit the rate of change of frequency. However, RPPs have very limited inertial regulation capability. Moreover, RPPs that are operating at their maximum available power do not participate in frequency regulation. Due to current grid practice in Europe, most of the wind turbine manufacturers have added frequency response capabilities in their designed systems [36], which make the wind turbine to operate below their maximum loading level. However, the recent offshore grid development (wind turbines are mostly connected by HVDC links) makes the frequency response planning more difficult.

11 Power system security advantages of HVDC links Because HVDC allows power transmission between unsynchronized AC systems, it can help increase the system stability. It does so by preventing cascading failures from propagating from one part of a wider power transmission grid to another, while still allowing power to be imported or exported in the case of small failures

12 Problem formulation.

13 Problem formulation cnt d

14 Problem formulation cnt d

15 Problem formulation cnt d The same was done for PV power plant and the constants were then mapped as follows, Thermal power plants Wind power plant PV power plant A 0 0 B C

16 Problem formulation cnt d

17 Problem formulation cnt d

18 Problem formulation cnt d

19 Problem formulation cnt d

20 PROPOSED METHODOLOGY Area1-IEEE 14 bus system Area2-IEEE 5 bus system. Area3-IEEE 30 bus system. Area4-IEEE 30 bus system. Area5-IEEE 6 bus system. First, 5 area problem without security aspects considerations was solved using particle swarm optimization. The problem was simulated using MATLAB R2013a. Secondly, optimal power flow was performed on the above system to address security issue of bus voltage limit violation and transmission lines limit violation. Particle swarm optimization was also used to solve the optimal power flow problem.

21 PROPOSED METHODOLOGY. One renewable energy plant in area1 (P5-wind generator). Two renewable energy power plants in area3 (P13-PV power plant and P14-wind generation power plant). Two renewable energy power plants in area4 (P19-PV power plant and P20-wind generation power plant)

22 Flowchart

23 Results, Analysis and Discussion area demand. Area Demand (MW) Area1 259 Area Area Area Area

24 Results, Analysis and Discussion cont d

25 Results, Analysis and Discussion cont d

26 Results, Analysis and Discussion cont d

27 Results, Analysis and Discussion cont d RESULTS WITH SECURITY CONSIDERATION.

28 Results, Analysis and Discussion cont d

29 Results, Analysis and Discussion cont d

30 Conclusion and recommendation for further work. The project successfully applied PSO for the solution of classical MAED problem with security consideration and without security consideration. The aims of the project were to introduce renewable energy to a classical MAED problem and minimize the production costs while taking into consideration the transmission lines, tie lines and bus voltage constraints. The proposed algorithm was successfully tested on a five-area system. Introduction of security aspects to the classical MAED problem resulted in an increase in the total production cost of power.

31 Recommendations Proposed algorithm was found to take a considerable amount of time. The total computation time can be reduced by using Hybrid PSO or Improved PSO. The Five-area system was considered as one system with same marginal cost. Future work could be extended to include areas with different marginal costs. Renewable energy output were modelled as static system with stable outputs, future work could therefore be extend to include time varying renewable energy generation power output. This project considered only security aspects related to transmission lines, tie lines flow and bus voltage stability, future work could be improved to include contingency analysis like, generator or transmission line outage.

32 THANK YOU