Andrey Lana

Research Site for Low-Voltage Direct Current Distribution in a Utility Network—Structure, Functions, and Operation

This paper introduces a research site for a low-voltage direct current (LVDC) distribution system. The research site was established to enable practical studies concerning different areas of the LVDC distribution. Because the LVDC distribution is a novel approach to public electricity distribution, the objective is to combine a fully functional LVDC system and a flexible research platform, where various measurements and tests can be conducted. The scope of this paper is to discuss the design, structure, functionalities, and operation of the site. Experiences of use and measurement results are provided to demonstrate the major functionalities and other important system properties. Finally, future research tasks and the development of the site towards the LVDC μGrid are presented.

Galvanic Isolation and Output LC Filter Design for the Low-Voltage DC Customer-End Inverter

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.

On Low-Voltage DC Network Customer-End Inverter Energy Efficiency

In this paper, the results of the energy efficiency and power loss measurements of a 16 kVA customer-end inverter (CEI) unit are analyzed. The CEI is part of the low-voltage dc (LVDC) distribution network. The efficiency of the CEI power conversion significantly affects the energy efficiency of the LVDC distribution network and the electricity supply chain. The efficiency of the CEI and its components is measured by applying calorimetric and electrical input-output methods. The power loss measurement results are analyzed, and the power loss mechanisms are described. The efficiency optimization goals are discussed and set.

Control and monitoring solution for the LVDC power distribution network research site

This paper introduces and describes a control and condition monitoring system of a low-voltage DC (LVDC) public electricity distribution network. To enable practical studies concerning the LVDC distribution system, a research site was built by Lappeenranta University of Technology (LUT) and a Finnish distribution system operator Suur-Savon Sähkö Oy. To enable secure operation of the research site, a condition monitoring system was developed. It comprises system supervision and control for both normal operation and emergency situations. Moreover, network power quality monitoring functions are implemented to monitor the quality of supply and system reliability in general. In the paper, the condition monitoring, information, control, and diagnostic functions of the developed management system are described.

Implementation design of the converter-based galvanic isolation for low voltage DC distribution

In this paper the implementation of the galvanic isolation in the low voltage direct current (LVDC) network is discussed. The galvanic isolation can be implemented either with a 50 Hz transformer located at the customer AC output of the customer-end inverter (CEI) or with an isolated DC-DC converter at the input DC network side of the CEI. However, the former solution results in a significant increase of the volume and mass of the system and has a high amount of no-load losses. Therefore, an isolated DC-DC converter is studied in this paper. Based on calorimetric measurements conducted for the passive 50 Hz transformer, the requirements for the DC-DC converter are set. Selection of the converter topology is carried out and the selected topology is studied by simulations and calculations. The results are compared with the 50 Hz transformer.

Control of directly connected energy storage in diesel electric vessel drives

This paper focuses on the control developing for directly connected energy storage (ES) in diesel electric vessel drives and on analysis of the application benefits. The energy storage reduces load variations of diesel and generator. This can lead to fuel consumption savings, especially during dynamic positioning mode of offshore supply vessel. Energy storage can be connected to vessel AC power network by power electronics, which means additional losses on energy transfer upon charging and discharging. The other more effective way is to connect energy storage directly to the DC link of the propulsion drives. In this case, the DC link voltage level must be controlled to charge and discharge ES according to generator power and drive load. The aim of the control is to keep generation output in optimal fuel consumption range of the prime mover with keeping up the energy storage state of charge. The control is developed using power distribution network model of the offshore support vessel in MATLAB/Simulink environment. DC and AC power distribution network concepts with directly connected ES are evaluated. Gains and benefits of controlled and directly connected ES on variation of generation and diesel fuel consumption is discussed in the paper.

Power electronic losses of a customer-end inverter in low-voltage direct current distribution

A low-voltage direct current (LVDC) distribution system comprises a rectifier, a DC network, and customer-end inverters (CEI) responsible for the AC supply to the electricity end-users. The CEIs can be implemented as single-phase or three-phase ones; in this paper, feasible single- and three-phase topologies are introduced and their losses are calculated using nine different power switches. Three commercially available IGBT, MOSFET, and SiC MOSFET power switches are selected for comparison. In this application, a galvanic isolation between the DC network and the customer is required. The isolation is implemented by using an isolating DC/DC converter at the CEI supply, and therefore, the input voltage of the CEI can be different from the DC network voltage. In this paper, the effect of the supply voltage level on the losses of the CEI is calculated for the nine power transistors in single- and three-phase topologies.