Smart transmission with large renewable energy

  • Zhibo Ma

Student thesis: Doctoral ThesisPhD


Renewable energy connection to power systems has been growing worldwide, which brings more challenges to power systems than ever before and correspondingly, the investment in wind farms is increasing rapidly. Instead of connecting single wind turbines or small wind farms to the distribution network, energy companies and manufactures tend to connect large wind farms to the transmission network. These wind farms can contain 200 plus turbines and have a rated capacity of 100 MW up to several GW. Consequently, significant new challenges appeared in the transmission system.

Wind intermittency is one of the biggest issues in power systems in that it affects both frequency and system power flow. This project has focused on the transmission system power flow issue that was caused by wind intermittency, and defined it as Wind Intermittency Constraint (WIC). To avoid studying the whole system, WIC was used as a new method in this project to calculate and identify the problematic circuits that were caused by wind intermittency only. These circuits will be calculated in the Power Transfer Distribution Factor (PTDF) method, which is the key part of WIC calculation, and will be defined as WIC. WIC for each circuit in transmission system will be ranked, and circuits with higher WIC ranking over 20% are wind intermittency circuits and will be closely monitored.

Smart grid technology has been considered as an effective way to improve system visibility and controllability when attempting to overcome difficulties caused by renewable energy. There are three major parts for this project, which are flexible demand mechanism, generator participation and Flexible AC Transmission (FACTs) equipments. To have a more accurate FACTs control and calculation for wind intermittency only, this project uses a new concept of DI (Dynamic Impedance) to contribute to the controller algorithm. A novel algorithm has been introduced to build three controllers of demand, generation and impedance. To achieve different goals, these three controllers will take instruction from the central selector. The three goals identified in this project are economical, green and secure functions, where economical function is to minimise system cost during different wind scenarios, green function is to maximise system renewable energy output, and security function is to make sure the system is secure when it minimizes cost and maximizes renewable energy.

The algorithm will also calculate different wind scenarios and produce a 24 hour profile for system demand, generation and impedance. This profile will be achieved by the three controllers (Demand, generation and impedance controller)

A new model for wind scenarios is also used in this project which is called A to B model. It calculates a continuous 24 hour wind profile and find out the system stress points. These points are define as A and B. The controller algorithm will download wind scenario and calculate the best strategy to move from period A to period B. During the A to B process, cost, green and security factors are considered and the best strategy will be presented.

6-node, 9 nodes and 39 nodes IEEE standard models are used across the project to prove the concept of WIC (Wind Intermittency Constraint), DI (Dynamic Impedance), A to B wind profiles and controller algorithm. A simplified UK model has also been used to test real weather data and produce the best strategy to achieve economical, green and security goal. For thermal and voltage study, standard IEEE models are used. For stability study, a dynamic model is used to monitor rotor angle.
Date of Award27 Jun 2017
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorMiles Redfern (Supervisor) & Roderick Dunn (Supervisor)

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