Performance Test of 2.5 kW DC Boost Converter for Nanogrid System Applications

The development of power electronics continues to grow rapidly. One type of power electronics is the DC boost converter, which steps up DC voltage to another level. DC boost converters are widely used in many applications; for renewable energy, DC boost converters are very useful for stepping up DC voltage levels from nonconventional energy resources, such as photovoltaics, wind turbines, and fuel cells, to the main system. In this study, we tested a DC boost converter that has been developed to step up 48 V_DC from energy storage to 235 V_DC in the main bus. The DC boost converter will be used in the nanogrids system, developed by TREC and will supply household appliances such as televisions, lamps, laptops, and mobile phones. The performance tests showed between +3% and -1.2% of voltage deviation and 66–98% efficiency.

DC boost; Efficiency; Nanogrids; Performance test

A DC-DC converter converts directly from DC voltage to another level of DC voltage. DC-DC converters are widely used for many applications, such as traction motor control in automobiles, trolley cars, marine hoists, forklift trucks, and mine haulers, to provide smooth acceleration control, high efficiency, and fast dynamic response (Rashid, 2004). DC-DC converters are divided into two main types: hard-switching pulse width modulated (PWM) converters and resonant, soft-switching converters. PWM converters are currently more commonly used because they have high efficiency, simple operational control, and a simple topology that uses fewer components. However, PWM converters experience significant losses at high switching.

PWM converter topology is generally divided into four types: buck converters (step down), boost converters (step-up), buck-boost converters (step-up/step-down), and ?uk converters. These four converter topologies are non-isolated DC-DC converter types, where the input voltage has the same grounding as the output voltage. Non-isolated DC-DC converters, with high static gain, have received the focus of research attention as there is a need for this technology in many applications, such as nonconventional energy sources like photovoltaic (PV) modules, small wind turbines, and fuel cells (Blaabjerg & Ma, 2013; Ajami et al., 2015), which generate low DC voltages and need to be stepped up. Low voltages normally range from 12 to 125 V and must be boosted to AC grid requirement voltage (Silveira et al., 2014).

This paper examines a DC boost converter used for nanogrids systems that is being developed by TREC, a research center at the University of Indonesia. Based on previous nanogrids research, there is more than one type of converter that can adjust the energy resource voltage into the voltage required for household appliances, such as 24 V_DC or 48 V_DC. However, the proposed converter will boost 48 V_DC from energy storage into 235 V_DC for the main bus as the reference voltage, and then supply household appliances. Performance tests were conducted on this converter to determine its reliability and stability and, therefore, whether it would work well when applied to the nanogrids system. The nanogrids system is a power distribution system, as are microgrids (Adda et al., 2012b; Dong et al., 2013), but are different in capacity and topology. Nanogrids can operate in either off-grid or on-grid systems (Sivarasu et al., 2015) and have the ability to operate as AC, DC, or hybrid AC-DC. Nanogrids generally consist of a renewable energy source (Cvetkovic et al., 2012; Schönberger et al., 2006) and some sort of load that is based on the voltage rating (Adda et al., 2012a).

The basic components of nanogrids are:

1. Local power production derived from renewable energy, such as solar and wind, or fossil energy such as diesel generators or fuel cells.
2. Local loads are electrical household appliances in a house, such as televisions, lamps, and water heaters, which are supplied by local power.
3. A gateway that consists of a charge controller and power converter to convert DC voltage to AC or to DC voltage at another voltage level, to allow it to be distributed to the load.
4. A nanogrid control device, consisting of protection systems and component connections. Nanogrid control devices have the ability to transmit/receive electricity to/from the utility grid.
5. Energy storage, which stores and distributes the energy for balancing the system between supply and demand in the nanogrid.

Nanogrid topology can be divided into three types:

1.     DC nanogrids. Generally, these systems use a DC voltage of 380 V_DC on the main bus and convert the voltage, using a converter, to 24 or 48 V_DC to meet the load requirement. The main bus voltage can be supplied by renewable energy, such as PV systems, or a utility grid converted to DC voltage.

2.    AC nanogrids. These systems use AC voltage of 100–230 V_AC on the main bus, depending on technical regulations. The energy source used in this technology is AC but can also use DC sources, such as PV, which is converted to AC voltage. This system can also use DC load supplied by power adapters or AC-DC converters with switch mode power supply (SMPS) technology (Setiawan et al., 2017).

3.    Hybrid AC-DC nanogrids, a combination of the two previous systems. There are two main buses in such systems, for AC and DC voltages. Load separation is carried on these systems according to the main bus.

The performance test of this converter achieved very stable output with +3% and -1.2% voltage deviation. The average output voltage was 235.15 V, with a difference of 0.15 V or 0.06% from the setting value, meaning that the output voltage of the converter was quite stable. The converter efficiency in this test was 66–98%. The low efficiency was affected by significant standby losses to the load supplied, while at high loads – above 930 watts – the converter efficiency was stable at 93–98%. This indicates that the converter already has good efficiency for use in Dual Power, a new concept for nanogrid systems.

This paper was supported and funded by the Hibah Program Pengembangan Teknologi Industri of the Ministry of Research, Technology, and Higher Education of the Republic of Indonesia, grant number 03/II/PPK/E/E4/2018.

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