The work done in this thesis can be divided into two areas: development and testing of active voltage control methods and development of distribution network planning. The scientific contribution of the thesis can be concluded as follows:
· Various voltage control methods (rule based and optimizing) for different kinds of situations have been developed and tested using time domain simulations.
· Operation of one developed coordinated voltage control method has been verified using real time simulations and also a real distribution network demonstration is conducted.
· The development process of active voltage control methods has been defined.
· Statistical distribution network planning is developed to take active voltage control into account.
· Issues that affect selection of voltage control method for a particular case are discussed.
The developed voltage control methods are relatively simple and their operation can be quite easily understood. Moreover, the developed methods can be implemented as a part of the already existing distribution management system which could encourage DNOs to take the methods into use because active voltage control would only be a new feature of the DMS and not a completely new system. Hence, the developed methods are such that taking them into use would be relatively easy to the DNOs.
The complete development process of active voltage control methods is defined in the thesis and also gone through using one of the developed voltage control methods. Most publications on active voltage control concentrate only on determining the control principles of the control algorithm and time domain operation and practical implementation issues are omitted. This is not, however, adequate to make the proposed method a real alternative in DNOs’ network planning procedure but the methods should be commercialized or, at least, their operation in real distribution networks needs to be demonstrated before the DNOs will consider taking the methods into real distribution network use.
Development and commercialization of active voltage control methods do not alone guarantee that the methods will be taken into real distribution network use. Also planning methods need to be developed in order to be able to show the possible benefits of utilizing active voltage control. In this thesis, a planning procedure that utilizes statistical distribution network planning is used to compare different voltage control strategies. Also other issues that affect the selection of the voltage control method for a particular case are discussed.
In conclusion, the studies of this thesis aim at making the introduction of active voltage control as easy as possible to the DNO. This is achieved by developing voltage control methods that are easily implementable in real distribution networks and by developing the distribution network planning procedure to enable comparison of alternative voltage control methods. First three of the barriers introduced in 1.1.1 are, hence, dealt with. In addition to these studies, also the network business regulation model needs to be modified and acquisition of adequate input data for active voltage control needs to be arranged to enable large-scale utilization of active voltage control.
The results of this thesis can be directly utilized by companies that produce network information systems and distribution management systems. Also distribution network
operators can utilize the results of this thesis in distribution network planning and operation.
At present, the network business regulation model does not encourage usage of active voltage control but this might change in the future if the regulators decide to change the model to incentivize towards minimizing the network’s total costs instead of the current practice of favouring investment costs over operating costs. Also the regulators can exploit the results of this thesis when the regulation model is contemplated. Active voltage control can also indirectly affect the business of companies that manufacture small generation units because high connection costs can make otherwise profitable DG projects uneconomical.
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