Renewable energy (RESs) such as wind power and photovoltaic (PV) power have experienced rapid development in recent years in an attempt to reduce reliance on fossil fuels and associated pollution. However, fault characteristics of RESs are significantly different from those of from those of synchronous generators (SGs) and mainly represent the limited amplitude, the controlled phase angle, frequency offset and rich harmonics, so the traditional protection principles face operational challenge.

The main improved methods in the field of protection and control are to introduce some new mathematical theories to measure fault signatures of RESs. However, the fault current of RESs is sometimes very small and even is difficult to be measured accurately by current transformers (CTs). In addition, it may be expensive to update all protection devices deployed on the transmission line. These problems can be solved when RESs can provide some special signal or behave like SGs by improving the control system of RESs.

The key motivation of this project is to solve protection problems in perspective of the control system of RESs. Based on the study of response of the RES control system in different reference values or control typologies, some effective protection and control method are projected to be formed to reliably recognize the internal fault and trip the line with a high speed.

The significance of this project is represented by providing new schemes in coordination between protection and control system and relieving the effect of RESs on the traditional protection principles. The protection methods will involve new directional relay, distance protection and differential protection that are often deployed on the transmission line in AC system. These improved protection methods can avoid malfunction and failure that has a severe threat for the security and safety of the system. In addition, it is cost-effective because the protection devices are not necessary to be updated or the protection algorithm is easy to be achieved with a common sampling value. Furthermore, this project is a useful attempt to solve protection problems in terms of the control system not just improving protection algorithm. Therefore, this research is important for the system operation in a reliable and efficient way.

In order to solve these problems, some coordination methods between protection and control system are proposed in this project. The specific research objectives are as follows:

Building a simulation model for a system with RES power plant, which can be used to analyze fault behaviours and protection adaptability under different fault types and control strategies.
Searching for the key reason that can influence protection operation and altering these fundamental frequency fault characteristics by optimizing the control system to improve protection performance.
Designing a new control typology to inject a special signal such as a harmonic, which make it easy for the protection device to recognize the internal fault.
Developing a hardware-in-the-loop system based on real-time digital simulator (RTDS) in the laboratory. The online experiment and offline simulation will be combined to verify the proposed coordination methods.
The main outcomes of this project not only provide some new knowledge in the protection field and promote coordination between protection and control, but also contribute to the safe and stable and efficient operation of the power system with minimal power loss.

Funding: China Scholarship Council (CSC)
Effektiv start/slut dato01/11/202031/10/2023


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