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SUKIČ, P., RODIČ, M., ŠTUMBERGER, G.
ADAPTING CAR CHARGING STATION TO PV PLANT OUTPUT POWER
KOMUNALNA ENERGETIKA / POWER ENGINERING, 31
The increasing number of PV systems increases also their influence on the electricity network in which they are connected. The PV systems operation has often a negative impact on the network voltage profile. Fluctuation of clouds causes a step decrease of a solar irradiation and subsequently leads to drastically changes in PV system’s output power in a very short period of time. In areas with a high concentration of PV systems it is to expect the drop of network voltage or even frequency. Problems related to step changes in output power of PV systems are usually solved by using energy storage devices, which are capable to compensate the output power changes. Simultaneously with PV systems charging stations for electrical vehicle appeared in electricity networks. The most powerful chargers achieve a power up to 120 kW per installed unit and represent a heavy load in comparison to other loads connected to the network in vicinity. In case of a step reduction in PV system’s output power it is possible to lower the charging of electrical vehicles during the transient behaviour in order reduce the overall impact on the electricity network. The paper presents simulation of the PV system disturbance compensation with the temporary decrease in charging power of vehicle connected to the charging station. The results presented show that the proposed compensation can improve voltage profile in the electricity network.

BELIČ, E., VOH, J., SUKIČ, P., ŠTUMBERGER, G.
IMPACT OF PHOTOVOLTAIC SYSTEMS’ REACTIVE POWER GENERATION ON ACTIVE POWER GENERATION AND TRANSMISSION LOSSES IN THE LOW VOLTAGE DISTRIBUTION NETWORK
KOMUNALNA ENERGETIKA / POWER ENGINERING, 33
This paper evaluates the impact of photovoltaic systems’ reactive power generation on active power generation and transmission losses in the low voltage distribution network. The introduced experimental system consists of two major parts. The photovoltaic system represents the first part, in which every photovoltaic module is connected to the low voltage network by the individual microinverter. Two way communication is established to each microinverter by the communication gateway. The second part consists of a control system with data acquisition system. The flexible experimental system offers a possibility to add and establish different network connections of the single-phase or three-phase smart grids. Within the scope of this work, additional cable was installed to establish one phase low voltage network with the photovoltaic system on one side and network on the other. The results of the analysis and measurements performed for operation of experimental low voltage network show that the reactive power generation in photovoltaic systems increases the amount of active power that can be generated in photovoltaic systems without to violate voltage profile. However, with both of these actions transmission losses in the low voltage network increase.

SUKIČ, P., ŠTUMBERGER, G.
ELECTRICAL ENERGY STORAGE AND CURRENT SITUATION OF ELECTRICAL ENERGY STORAGE IN GERMANY
KOMUNALNA ENERGETIKA / POWER ENGINERING, 23
New era of investment in renewables began in the last year. Due to technical needs for energy storage and network regulation, as well as government grants, Germany began developing energy storage systems for personal use and commercial purposes. Current battery storage systems based on lithium cells have efficiency of ~ 86%, with price per unit of installed power capacity ~1 €/W/Wh, and dropping. Year 2016 is expected to be a landmark year for electrical energy storage systems, as it is assumed that prices of electricity from solar power and energy storage system (with grant included) will reach the price of electricity from the electric grid. This paper presents current technical and economic state of energy storage systems for various needs.

SUKIČ, P., ŠTUMBERGER, G.
GENERATION OF REACTIVE POWER WITH SOLAR POWER PLANTS AND EXAMPLES OF IMPROPER OPERATION OF SOLAR POWER
KOMUNALNA ENERGETIKA / POWER ENGINERING, 30
The article discusses the generation of reactive power with solar power plants. Discussed is the impact of reactive power generation on the efficiency of solar inverter. Throughout the year solar power plants operate with maximum power only in short time intervals. Therefore it is possible to generate large amounts of reactive power with solar power inverters, if needed. Due to improper operation of solar power plants, anomalies in the distribution network occur. This paper presents some of these anomalies.

SUKIČ, P., DREVENŠEK, D., BELIČ, E., ŠTUMBERGER, G.
EFFICIENCY OF INVERTERS IN SOLAR POWER PLANTS WITH REACTIVE POWER GENERATION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 14
The paper discusses possibilities for reactive power generation using inverters for solar power plants. Measurements performed on an inverter for solar systems were performed for different values of generated active and reactive power in order to determine the efficiency characteristic. The obtained characteristic is approximated with a surface. It is applied to evaluate increase of inverter losses due to reactive power generation as well as to evaluate the potential of inverters in solar power plants for reactive power generation.

BELIČ, E., SUKIČ, P., DEŽELAK, K., ŠTUMBERGER, G.
DYNAMICAL MODEL OF DISTRIBUTION NETWORK WITH DISTRIBUTED GENERATION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 18
In this paper a dynamical model of distribution network with distributed generation is presented. Model of distribution network was developed using software package Matlab/Simulink with its blockset SymPowerSystems. Elements of utility network like supply network, power lines, load, and distribution transformer were modeled with elements which are already included in this blockset, but the distributed generator model was developed based on the current injection to the grid, considering references of active and reactive power. The aim of network modeling was to analyze the voltage profiles and transmission loses before and after connection of the distributed generation to the grid. Presented are the results of performed analysis.

SUKIČ, P.
MAKING OF AN ELECTRIC BICYCLE FOR 2012 STUDENT COMPETITION
KOMUNALNA ENERGETIKA / POWER ENGINERING, 28
The team of three students decided to participate in the student competition in making of an electric bicycle in year 2012. This paper describes the whole process of making an electric bicycle, from the idea, market review, buying components, bicycle building, testing and at the end competition. The team had a lot of problems with some components, with setup and testing. It was decided to give priority to the developed torque of the whole system, which was proven as a good decision. An older bicycle Pony 20'' was equipped with 1000W Brushless DC motor and LiPo battery package which can store 720 Wh of energy. The team finished the competition at the second place.

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