Per Lund

The Danish Cell Project - Part 1: Background and General Approach

The paper presents the current situation in the Danish power system, which is unique as more than 50% of the total production capacity is dispersed throughout local distribution grids of 60 kV voltages and below. This characteristic has lead to the cell controller pilot project which aims at developing a new solution for optimal management and active grid utilisation of the large amount of distributed generation present in Western Denmark.

A Systematic Approach for Dynamic Security Assessment and the Corresponding Preventive Control Scheme Based on Decision Trees

This paper proposes a decision tree (DT)-based systematic approach for cooperative online power system dynamic security assessment (DSA) and preventive control. This approach adopts a new methodology that trains two contingency-oriented DTs on a daily basis by the databases generated from power system simulations. Fed with real-time wide-area measurements, one DT of measurable variables is employed for online DSA to identify potential security issues, and the other DT of controllable variables provides online decision support on preventive control strategies against those issues. A cost-effective algorithm is adopted in this proposed approach to optimize the trajectory of preventive control. The paper also proposes an importance sampling algorithm on database preparation for efficient DT training for power systems with high penetration of wind power and distributed generation. The performance of the approach is demonstrated on a 400-bus, 200-line operational model of western Danish power system.

Dynamic Reactive Power Compensation of Large-Scale Wind Integrated Power System

Due to progressive displacement of conventional power plants by wind turbines, dynamic security of large-scale wind integrated power systems is significantly compromised. In this paper we first highlight the importance of dynamic reactive power support/voltage security in large-scale wind integrated power systems with least presence of conventional power plants. Then we propose a mixed integer dynamic optimization based method for optimal dynamic reactive power allocation in large-scale wind integrated power systems. One of the important aspect of the proposed methodology is that unlike static optimal power flow based approaches, the proposed method considers detailed system dynamics and wind turbine grid code compliance while optimizing the allocation of dynamic reactive power sources. We also advocate that in large-scale wind integrated power systems, 1) better utilization of existing wind turbines especially wind farms with additional grid support functionalities like dynamic support (e.g., dynamic reactive power support, etc.) and 2) refurbishment of existing conventional central power plants to synchronous condensers could be one of the efficient, reliable and cost-effective option to address not only the issue of dynamic voltage security but also to strengthen other dynamic capabilities of the system including system inertia, etc. that are also significant challenges in large-scale wind penetrated power system. The proposed methodology is applied to the detailed model of the western Danish power system which is characterized by large-scale wind integration and least presence of central power plants.

Transient stability assessment of power system with large amount of wind power penetration: The Danish case study

Recently, the security and stability of power system with large amount of wind power are the concerned issues, especially the transient stability. In Denmark, the onshore and offshore wind farms are connected to distribution system and transmission system respectively. The control and protection methodologies of onshore and offshore wind farms definitely affect the transient stability of power system. In this paper, the onshore and offshore wind farms are modeled in detail in order to assess the transient stability of western Danish power system. Further, the computation of critical clearing time (CCT) in different scenarios is proposed to evaluate the vulnerable areas in western Danish power system. The result of CCTs in different scenarios can evaluate the impact of wind power on power system transient stability. Besides, some other influencing factors such as the load level of generators in central power plants, load consumption level and high voltage direct current (HVDC) transmission links are taken into account. The results presented in this paper are able to provide an early awareness of power system security condition of the western Danish power system.

Power System Structural Vulnerability Assessment Based on an Improved Maximum Flow Approach

With the increasing complexity of the power grid and the concerns on major blackouts, there is an urgent need for an efficient and effective tool to assess the power system structural vulnerability. To tackle this challenge, this paper proposes a maximum flow-based complex network approach to identify the critical lines in a system. The proposed method consists of two major steps. First, the power network is modeled as a graph with edges (transmission lines, transformers, etc.) and nodes (buses, substations, etc.). The critical scenarios are identified by using the principal component analysis and convex hull. Then the second step is to use an improved maximum flow-based complex network approach for topology analysis. Weighted vertices in the network are considered, enabling taking the selected operating conditions into consideration when identifying the vulnerable lines. The proposed method is validated using the western Danish power system. The vulnerable lines in the network are ranked. Simulation results demonstrate the effectiveness of the method by intentional attacks and comparison with the planning strategy from the system operator.

Realistic Approach for Phasor Measurement Unit Placement: Consideration of Practical Hidden Costs

This paper presents a realistic cost-effective model for optimal placement of phasor measurement units (PMUs) for complete observability of a power system considering practical cost implications. The proposed model considers hidden or otherwise unaccounted practical costs involved in PMU installation. Consideration of these hidden but significant and integral part of total PMU installation costs was inspired from practical experience on a real-life project. The proposed model focuses on the minimization of total realistic costs instead of a widely used theoretical concept of a minimal number of PMUs. The proposed model has been applied to IEEE 14-bus, IEEE 24-bus, IEEE 30-bus, New England 39-bus, and large power system of 300 buses and real life Danish grid. A comparison of the presented results with those reported by traditional methods has also been shown to justify the effectiveness of the proposed model with regard to its realistic and practical nature.

Real-time reduced steady state model synthesis of active distribution networks using PMU measurements

Due to the increase of generation sources in distribution networks, it is becoming very complex to develop and maintain models of these networks. Network operators need to determine reduced models of distribution networks to be used in grid management functions. This paper presents a novel method that synthesizes steady-state models of unbalanced active distribution networks with the use of dynamic measurements (time series) from phasor measurement units (PMUs). Since phasor measurement unit (PMU) measurements may contain errors and bad data, this paper presents the application of a Kalman filter technique for real-time data processing. In addition, PMU data capture the power systems response at different time-scales, which are generated by different types of power system events; the presented Kalman filter has been improved to extract the steady-state component of the PMU measurements to be fed to the steady-state model synthesis application. Performance of the proposed methods has been assessed by real-time hardware-in-the-loop simulations on a sample distribution network.

Robust fallback sheme for the Danish automatic voltage control system

This paper proposes a fallback scheme for the Danish automatic voltage control system. It will be activated in case of the local station loses telecommunication to the control center and/or the local station voltage violates the acceptable operational limits. It cuts in/out switchable and tap-able shunts to maintain the voltage locally. The fallback scheme is fully self-regulated according to the predefined triggering logic. In order to keep the robustness and avoid many shunts are being triggered in a short term, the inverse time characteristic is used to trigger switching one by one. This scheme allows for fast triggering when the voltage violation is large, and enlarges the response time when the voltage violation is small. The functioning of the fallback scheme is investigated via time domain simulations, where case studies are carried out in a benchmark model and a model of the western Danish power system.

Assessing the impact of multi-terminal HVDC grids for wind integration on future scenarios of a real-world AC power system using grid code compliant open models

The exploitation of multi-terminal (MT) HVDC (High Voltage Direct Current) grids for offshore wind farm integration into continental bulk AC system raises several technical issues, in particular the verification of the compliance of MTDC grids and offshore wind parks to the performance requirements (in terms of frequency, voltage support and fault ride through) which are being established by the grid codes, and the availability of general and customizable models to simulate their response. The goal of this work is to provide a set of “open” general models, able to fulfill the grid code requirements if suitably tuned, enabling the TSOs to perform their analyses without relying exclusively on vendor-specific models. In order to verify the realistic response of these models, an example of MTDC grid is simulated, connecting it to several plausible operating scenarios of a real world AC system (the West Denmark grid) in target year 2020: after a preliminary N-1 static security assessment study on the integrated AC/DC system, some simulations are performed to check the fulfillment of grid code requirements in case of typical contingencies.

Realistic Approach for Phasor Measurement Unit Placement: Consideration of Hidden Practical Costs

This paper presents a realistic cost-effective model for optimal placement of phasor measurement units (PMUs) for complete observability of a power system considering practical cost implications. The proposed model considers hidden or otherwise unaccounted practical costs involved in PMU installation. Consideration of these hidden but significant and integral part of total PMU installation costs was inspired from practical experience on a real-life project. The proposed model focuses on the minimization of total realistic costs instead of a widely used theoretical concept of a minimal number of PMUs. The proposed model has been applied to IEEE 14-bus, IEEE 24-bus, IEEE 30-bus, New England 39-bus, and large power system of 300 buses and real life Danish grid. A comparison of the presented results with those reported by traditional methods has also been shown to justify the effectiveness of the proposed model with regard to its realistic and practical nature.