Anna Kulmala

Coordinated Voltage Control in Distribution Networks Including Several Distributed Energy Resources

Connecting distributed generation (DG) to weak distribution networks can often cause voltage rise problems. Traditionally, these voltage rise problems have been mitigated by passive methods such as reinforcing the network. This can, however, lead to high connection costs of DG. The connection costs can in many cases be lowered if active voltage control methods are used instead of the passive approach. In this paper, two coordinated voltage control algorithms suitable for usage in distribution networks including several distributed energy resources are proposed and studied. The first algorithm uses control rules to determine its control actions and the second algorithm utilizes optimization. The operation of the implemented algorithms is, at first, studied using time domain simulations. Thereafter, the network effects and costs of both algorithms are compared using statistical distribution network planning and also practical implementation issues are discussed.

RTDS verification of a coordinated voltage control implementation for distribution networks with distributed generation

In weak distribution networks the amount of distributed generation (DG) is usually limited by the voltage rise effect. The voltage rise can be mitigated using passive methods such as increasing the conductor size which can, however, be quite expensive. Also active voltage control methods can be used to reduce the maximum voltage in the network. In many cases active voltage control can increase the capacity of connectable DG substantially which can lead to significantly lower connection costs. In this paper, operation of an active voltage control algorithm is viewed. The algorithm controls the substation voltage and DG reactive power and determines its control actions based on the state of the whole network. The algorithm is implemented as a Matlab program and communication between Matlab and SCADA is realized using OPC Data Access. Correct operation of the algorithm is verified using Real Time Digital Simulator (RTDS). The same algorithm could also be implemented as a part of the distribution management system (DMS).

Problems related to Islanding Protection of Distributed Generation in Distribution Network

In this paper, the problems related to islanding detection in distribution network with distributed generation are described. Typical methods for islanding detection and needs for protection coordination are discussed. Example simulations are performed in a PSCAD environment. The results for the simulations reveal certain problems. As expected, the theoretical case with power balance results in sensitivity problems. The possibility of nuisance trippings is also observed. Some novel methods are also ideated during the simulations.

Active Voltage Level Management of Distribution Networks with Distributed Generation using On Load Tap Changing Transformers

In this paper, time domain performance of active voltage level management based on co-ordinated control of substation voltage is studied. A control algorithm that controls the set point of the automatic voltage control (AVC) relay at the substation is proposed and its operation in an example network is tested using PSCAD simulations. The study network is a real distribution network located in south-west Finland which will experience voltage rise problems if a planned wind park is constructed.

Including active voltage level management in planning of distribution networks with distributed generation

The existing distribution networks are designed based on the assumption of unidirectional power flows. The amount of distributed generation (DG) is, however, constantly increasing which creates a need to revise the current network operation and planning principles. This paper focuses on voltage level management issues related to DG. The effect of different kinds of voltage level management strategies on distribution network planning is discussed and a planning procedure regarding voltage issues when a new DG unit is interconnected to an existing distribution network is proposed.

Managing cascade transformers equipped with on-load tap changers in bidirectional power flow environment

Existing voltage control schemes of cascade on-load tap changers (OLTCs) have been developed considering unidirectional power flow. However, in recent years, integration of distributed generation such as solar and wind power to the grid has created possibility for bidirectional power flow resulting in inefficiency of previous voltage control methods of cascade OLTCs. In this paper, an effective method for managing cascade OLTCs in bidirectional power flow environment is presented. Tracking the active and reactive power changes in both MV and LV networks, the developed method is able to detect the cause of voltage variation i.e. MV or LV network. Accordingly, it enables the system operator to order tap actions at accurate voltage level which decreases unnecessary tap actions and improves the voltage quality at costumer points. The proposed voltage control method is tested in different network scenarios.

Plug-in vehicle ancillary services for a distribution network

In this paper, we have investigated the possibilities of plug-in vehicles to produce ancillary services for distribution networks. First, special features of plug-in vehicles as controllable resources are discussed and then motivation and methods of four different types of ancillary services are discussed. These services are peak load management, network power flow management, customer back-up power and power quality improvement. Finally some conclusions are made and future work is proposed.

Demonstrating coordinated voltage control in a real distribution network

The connection of distributed generation (DG) to weak distribution networks is likely to cause voltage rise problems. At present, the voltage rise is usually mitigated by reinforcing the network but as the penetration level of DG increases also active voltage control methods need to be taken into use. Active voltage control has been a subject of extensive research in the past decade but the number of real implementations is still very low. One reason for this is that only few demonstrations have been conducted in real distribution networks. In this paper, the operation of one coordinated voltage control (CVC) algorithm is successfully demonstrated in a real Finnish distribution network. The main objective of the paper is to identify the problems that may arise when academic smart grid methods are implemented in real electricity networks. The second objective is to verify the operation of the studied CVC algorithm.

The IDE4L Project: Defining, Designing, and Demonstrating the Ideal Grid for All

The Purpose of the IDE4L project was to define, design, and demonstrate the ideal grid for all, with an active distribution network that integrates renewable energy sources (RESs) and new loads and guarantees the reliability of classical distribution networks. The active distribution network consists of the infrastructure of power delivery, active resources, and active network management (ANM) and combines passive infrastructure with active resources, ANM functionalities, and distribution automation information and communication technology infrastructure. Active distributed energy resources (DERs) include distributed generation (DG), demand, response, and storage. The concept of a commercial aggregator offering flexibility services is also integrated in an ANM.

Avoiding adverse interactions between transformer tap changer control and local reactive power control of distributed generators

Local reactive power control of distributed generators (DG) can be used to mitigate the voltage rise effect caused by themselves. In this paper, dynamic interactions between local voltage controllers of the DG units and transformer on load tap changers (OLTCs) are studied using time domain simulations. Studies are conducted with different control modes of DG unit and OLTC control and also secondary substation tap changers are considered. Several types of adverse interactions are identified in the simulations: unnecessary OLTC operations can occur, reactive power transfers can unnecessarily increase and consecutive tap changer operations can occur in case of cascaded OLTCs. The paper gives also some general planning guidelines to avoid the adverse interactions identified in the simulations.