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Standalone Power Systems and Power Converters

A stand-alone power system (SAPS) is an off-grid electricity system typically implemented in locations that are not connected to the grid [1]. An example of SAPS is the photovoltaic SAPS [1]. This kind of electrical power systems is popular in rural areas because it is more efficient due to its ability of storing electricity, also it is cost effective [1]. SAPS generate electricity using many methods such as solar panels, wind turbine, diesel and other burnable fuels; the power then gets stored within battery banks or fuel cells [1]. There are two types of standalone systems, a direct-coupled system and a standalone system with batteries [1]. In a direct coupled system no power that gets produced is stored as the generator is connected directly to the load, in the standalone system excess energy is stored in battery banks [1]. The batteries allow the system to store and provide energy, produce more stable current and voltages and can provide surge currents if necessary [1]. The downsides of a SAPS is that some loads cannot be used with a SAPS, some loads may have low efficiency and some non-linear loads may create distortion of the inverter waveform [1]. System monitoring must be implemented so that the status of the system can be monitored to help detect the need to replace batteries before system failure occurs and improve overall system improvements [1]. An SAPS that our team could attempt to implement can be mapped out in [2, Fig. 1].

Fig. 1. Standalone power system

A power converter is an electrical device that converts electrical energy from alternating current (AC) to direct current (DC) or to increase or decrease the voltage or changing the frequency, phase, and other electrical characteristics or characteristics of a power supply system [3]. In stand-alone power systems we need AC-DC converters in order to change the generated AC power from wind turbines and solar panels into DC so that the generated power can be stored in batteries [2]. This DC power then needs to be converted back to AC power so that it can meet the needs of the households we hope to service. Many forms of power converters exist such as current source inverters, voltage source inverters, line commutated converters and multilevel inverters [3]. Some SAPS utilize the three phase rectifier, a power converter that converts AC to DC, an example of this circuit is seen in [4, Fig. 2]. The SAPS as illustrated in [2, Fig. 1] used four converters: Two DC-DC converters, one rectifier (AC-DC converter) and one inverter (DC-AC converter).

 

 

References

[1] “Stand-alone power system,” Wikipedia, 06-Oct-2017. [Online]. Available: https://en.wikipedia.org/wiki/Stand-alone_power_system. [Accessed: 17-Sept-2017].

[2] M. Ramalakshmi.T and M. J. G. S, “Grid Connected PV/Wind (GCPW) Hybrid System with Improved Power Quality,” International Journal of Advanced Research in Electrical, Electronics and Instrumentation Energy, 01-Jan-1970. [Online]. Available: https://www.rroij.com/open-access/grid-connected-pvwind-gcpw-hybrid-system-with-improved-power-quality.php?aid=43798. [Accessed: 6-Oct-2017].

[3] J. Rodriguez and P. Cortes, Predictive control of power converters and electrical drives. New York: John Wiley & Sons Inc, 2012.

[4] OPERATION OF A 3-PHASE FULLY-CONTROLLED RECTIFIER. [Online]. Available: http://www.technik-emden.de/~elmalab/projekte/ws9899/pe_html/ch05s1/ch05s1p1.htm. [Accessed: 06-Oct-2017].