ABSTRACT Modern renewable energy systems (RES) require fault ride through (FRT) operation in orde... more ABSTRACT Modern renewable energy systems (RES) require fault ride through (FRT) operation in order to provide voltage and frequency support to the power grid when faults occur. The grid synchronization of a RES could be ensured by the appropriate operation of a phase-locked loop (PLL). A new hybrid PLL (dαβPLL) has recently been suggested by the authors and could operate accurately and faster than the other existing PLLs. The dαβPLL could be a very useful tool in the FRT operation of a RES, since the faster performance of the new PLL could boost the time performance of the FRT algorithm when a disturbance occurs. This paper investigates the performance of the flexible positive and negative sequence control (FPNSC) when the new dαβPLL is used. The paper also deals with the improvement on the FRT operation of the RES that could be obtained from the outstanding performance of the dαβPLL.
ABSTRACT Transmission loss allocation is an important problem in markets where the clearing marke... more ABSTRACT Transmission loss allocation is an important problem in markets where the clearing market procedure neglects transmission losses, such as the majority of European electricity markets. Different allocation methods have been proposed and implemented in different markets, and all these procedures are usually post market actions, which may imply an increase in financial volatility for both generators and consumers. Therefore, a more suitable approach would be to have both market clearing and transmission loss allocation on a real-time base. This paper discusses a simple but effective method for real-time estimation of transmission losses and performs a sensitivity analysis in applying this method in conjunction with different allocation methods according to different market designs.
ABSTRACT The increasing penetration of renewable energy sources in the power grid requires high q... more ABSTRACT The increasing penetration of renewable energy sources in the power grid requires high quality power injection under various grid conditions. The synchronization method, usually a phase-locked loop (PLL) algorithm, is directly affecting the response of the grid side converter of the renewable energy source. This paper proposes a new PLL algorithm that uses an advanced decoupling network implemented in the stationary reference frame with limited requirements for processing time to enable a fast and accurate synchronization even under harmonic distorted voltage and low-voltage grid faults. The robust response of the proposed PLL is validated and the effect of the proposed synchronization on the performance of the grid-connected renewable energy system is investigated. This investigation proves that the robust, accurate and dynamic response of the new PLL can enhance the quality of the injected power from the renewable energy source and can also enable an appropriate fault ride through operation under harmonic distorted voltage and grid faults.
The presence of partial discharges (PD) is one of the most prominent indicators of defects and on... more The presence of partial discharges (PD) is one of the most prominent indicators of defects and ongoing degradation processes of electrical insulation. As a high percentage of failures are associated with PD, the need for the classification, extraction and evaluation of PD signals is essential. Therefore, an electrical model of a breakdown void is more than a necessity. In this paper the classical capacitive network representation of the void (model) and a new capacitive model based on the induced charge concept are presented and discussed.
ABSTRACT Wide area blackouts can be caused by unexpected fault scenarios, in particular protectio... more ABSTRACT Wide area blackouts can be caused by unexpected fault scenarios, in particular protection maloperation, or simultaneous low probability events, which as such might lead to e.g., un-damped electromechanical oscillations. A Spectral Clustering Controlled Islanding (SCCI) method to find a suitable islanding solution for preventing such events was previously proposed and tested using different IEEE test networks. The sole constraint applied to this solution was related to generator coherency. The method demonstrated promising results when it was implemented on these IEEE test networks. The SCCI method was later tested using a simplified Cypriot Network and the Polish Network. The results achieved when implementing the SCCI method on actual power systems highlight practical issues that were not previously considered and require to be addressed when using it. Therefore, this paper presents a robust SCCI method. An outlier problem which affects the quality of clustering and a problem with the computational efficiency of the algorithm (when dealing with systems larger than 500 nodes) are presented and analyzed in this paper. To improve the clustering quality, a more robust clustering algorithm, k-medoids, is used to cluster all nodes in the solution subspace and to find the islanding solution.
ABSTRACT Modern renewable energy systems (RES) require fault ride through (FRT) operation in orde... more ABSTRACT Modern renewable energy systems (RES) require fault ride through (FRT) operation in order to provide voltage and frequency support to the power grid when faults occur. The grid synchronization of a RES could be ensured by the appropriate operation of a phase-locked loop (PLL). A new hybrid PLL (dαβPLL) has recently been suggested by the authors and could operate accurately and faster than the other existing PLLs. The dαβPLL could be a very useful tool in the FRT operation of a RES, since the faster performance of the new PLL could boost the time performance of the FRT algorithm when a disturbance occurs. This paper investigates the performance of the flexible positive and negative sequence control (FPNSC) when the new dαβPLL is used. The paper also deals with the improvement on the FRT operation of the RES that could be obtained from the outstanding performance of the dαβPLL.
ABSTRACT Transmission loss allocation is an important problem in markets where the clearing marke... more ABSTRACT Transmission loss allocation is an important problem in markets where the clearing market procedure neglects transmission losses, such as the majority of European electricity markets. Different allocation methods have been proposed and implemented in different markets, and all these procedures are usually post market actions, which may imply an increase in financial volatility for both generators and consumers. Therefore, a more suitable approach would be to have both market clearing and transmission loss allocation on a real-time base. This paper discusses a simple but effective method for real-time estimation of transmission losses and performs a sensitivity analysis in applying this method in conjunction with different allocation methods according to different market designs.
ABSTRACT The increasing penetration of renewable energy sources in the power grid requires high q... more ABSTRACT The increasing penetration of renewable energy sources in the power grid requires high quality power injection under various grid conditions. The synchronization method, usually a phase-locked loop (PLL) algorithm, is directly affecting the response of the grid side converter of the renewable energy source. This paper proposes a new PLL algorithm that uses an advanced decoupling network implemented in the stationary reference frame with limited requirements for processing time to enable a fast and accurate synchronization even under harmonic distorted voltage and low-voltage grid faults. The robust response of the proposed PLL is validated and the effect of the proposed synchronization on the performance of the grid-connected renewable energy system is investigated. This investigation proves that the robust, accurate and dynamic response of the new PLL can enhance the quality of the injected power from the renewable energy source and can also enable an appropriate fault ride through operation under harmonic distorted voltage and grid faults.
The presence of partial discharges (PD) is one of the most prominent indicators of defects and on... more The presence of partial discharges (PD) is one of the most prominent indicators of defects and ongoing degradation processes of electrical insulation. As a high percentage of failures are associated with PD, the need for the classification, extraction and evaluation of PD signals is essential. Therefore, an electrical model of a breakdown void is more than a necessity. In this paper the classical capacitive network representation of the void (model) and a new capacitive model based on the induced charge concept are presented and discussed.
ABSTRACT Wide area blackouts can be caused by unexpected fault scenarios, in particular protectio... more ABSTRACT Wide area blackouts can be caused by unexpected fault scenarios, in particular protection maloperation, or simultaneous low probability events, which as such might lead to e.g., un-damped electromechanical oscillations. A Spectral Clustering Controlled Islanding (SCCI) method to find a suitable islanding solution for preventing such events was previously proposed and tested using different IEEE test networks. The sole constraint applied to this solution was related to generator coherency. The method demonstrated promising results when it was implemented on these IEEE test networks. The SCCI method was later tested using a simplified Cypriot Network and the Polish Network. The results achieved when implementing the SCCI method on actual power systems highlight practical issues that were not previously considered and require to be addressed when using it. Therefore, this paper presents a robust SCCI method. An outlier problem which affects the quality of clustering and a problem with the computational efficiency of the algorithm (when dealing with systems larger than 500 nodes) are presented and analyzed in this paper. To improve the clustering quality, a more robust clustering algorithm, k-medoids, is used to cluster all nodes in the solution subspace and to find the islanding solution.
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Papers by Elias Kyriakides