In this paper the need for a better design of the galvanic isolation and the output filter inductor in the customer-end inverter (CEI) of the low voltage DC (LVDC) network is discussed. The galvanic ...isolation can be implemented either with a 50 Hz transformer after the CEI or with an isolated DC-DC converter between the DC network and the CEI. However, the 50 Hz transformer solution adds a significant amount of volume and mass to the system. Based on calorimetric measurements conducted with the current system in which the galvanic isolation is implemented with the former method, the minimum requirements for the isolated DC-DC converter are presented and a comparison is carried out. For the system to be cost efficient the DC-DC converter should result in reduced lifetime cost compared with the transformer solution. In the output filter part a design method for an amorphous core filter inductor based on minimization of the lifetime cost is presented.
The paper focuses on developing the control for directly connected battery energy storage system (BESS) in low voltage direct current (LVDC) distribution systems. The main purpose of the control is ...to provide essential connection/disconnection and charge/discharge functions. Additionally, due to direct connection, it is necessary to implement control functions for management of the power flows in the distribution network. Furthermore, the control system is capable of running the system as island and seamlessly disconnecting and reconnecting to the feeding medium voltage (MV) network. Control system enables implementation of the Smart Grid (SG) functionalities and practically eliminates the interruptions seen by the electricity end-users.
This paper concentrates on the effects of d.c. mains voltage level selection on earthing and protection of the low voltage direct current (LVDC) distribution systems. Among the low voltage range the ...possibilities are to go up to 1500 VDC in unipolar and ±750 VDC in bipolar LVDC system. Voltage level selection is one of the main tasks in LVDC system design process as it directly affects the electric safety, structure and life-cycle costs of the system. The main outcome of the paper is on presenting the essential design aspects from earthing system and protection setup perspective, by utilizing case examples.
In Finland, new reliability criteria for electricity distribution companies have been analysed, and now, the implementation of the criteria is being discussed. The criteria cover the customer-based ...cumulative sum of durations of long interruptions and the cumulative number of short interruptions. The criteria are established by the Finnish Energy Industries (ET) together with electricity distribution companies and technical universities.
Summary form only given. The role of electricity has become more significant in today's society; electricity distribution has to be reliable and there should be no outages. Incentives from economic ...regulation support this direction of development. Therefore, there is a demand for development of distribution networks. The key question is, from which viewpoint the issue of reliability is addressed in the network renovation process? Are we optimizing the number of faults (SAIFI), the duration of faults (SAIDI), the outage costs (CENS), or some other reliability index? If the target is to minimize CENS, can this be done by evaluating the basic reliability indices? These questions have to be answered when considering the placement of a network automation device. Network automation such as circuit reclosers or switchgear with breaker functions and remote-controlled disconnectors belong to the basic structures in distribution technology, and they play a significant role in the improvement of reliability. A recloser installed into the network may have a great impact on reliability, by which the outage costs can be reduced even by 30 %. Hence, a study, which approaches the reliability indices as a decisive factor in the placement of network automation devices, is needed.
The reliability requirements and the role of the supervisory authority in the electricity distribution business have grown strongly in the past few years. Electricity distribution companies are ...forced to consider new investment strategies to meet the challenges arising from the new operational environment. Aged electricity networks are subject to the more challenging weather conditions. To meet the new requirements, the traditional line extension approach is no longer an acceptable and sustainable planning method. There are various new technical solutions and methods to develop electricity networks. In this paper, different kinds of electricity distribution investment strategies in the modern business environment are studied. Strategies are based on several new technical innovations successfully implemented in Finnish electricity distribution companies. Methods such as roadside networks, 1000 V low voltage system, underground cables and low-cost primary substations are exploited successfully in the long-term planning process.
In paper, a solution for the integration of a home energy management system (HEMS) to be a part of an utility LVDC distribution system is introduced. The considered LVDC network comprise ...network-level battery energy storage system (BESS), public DC distribution system with a single connection point to medium-voltage AC network and multiple prosumer customers. The usage of the BESS is multi-objective. It could be a part of large-scale virtual power plant, or a part of frequency containment reserve (FCR), and simultaneously operate as a backup power source. In such, part of the storage capacity could considered to be shared between the customers, electricity traders, distribution network company and the transmission system operator. In order to increase efficiency of the BESS operation and capacity allocation, information from the energy end-users could be used. Similarly, the energy resources in end-users' homes can be used to provide flexibility. Control of loads, such as heating, cooling and ventilation within the boundary conditions of the in-house climate can be used simultaneously with the energy storage resources for similar purposes or to support the BESS functionalities. The household digital HEMS is not yet common, especially those that integrate BESS. Therefore, solution is not restricted to interface design and considers also sensor networks that are installed at customer premises, to provide fully integrated solution.
This paper presents an approach to power electronic converter design in which the objective is to minimize the life cycle cost when the converter is used to supply a residential customer. In the ...paper, the life cycle cost is defined as the sum of the cost of the main components of the power stage and the cost of the losses during the utilization period. The semiconductor switches, output filtering, heat sink, gate drivers, and DC link capacitance are included in the analysis, whereas their parameters are freed in the optimization process. The behavior of the load of an average residential customer is taken as one of the inputs in the calculation. It is shown that parameters such as the optimal silicon area, filter inductance, and switching frequency can differ significantly from the industry norm in which a high weight factor is given to the performance near the nominal power.
Energy storage system technologies have been developed within the recent years. The energy capacity of the storages has been increased and also more power can be discharged from the storages. The ...development has opened new possibilities to utilise energy storages. The technical success has been the key factor but also falling prices of energy storages increase interest in storage applications. Thus, there is a demand to develop methodology to assess benefits of energy storages. This paper presents a method to analyse the benefits of energy storages in reduction of interruptions experienced by electricity end-users. The methodology is based on Monte Carlo simulation modelling reliability of distribution system. (4 pages)
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