Abstract
Implementation of a smart power conditioning system with a novel seamless transfer method for an energy storage system (ESS) was proposed in this paper. The power conditioning system is to control the power quality or protect the grid system. Therefore, it requires various functions. One of the these functions, the uninterruptible power supply (UPS) function, was applied to proposed power conditioning system. In order for the grid-interactive power conditioning system to continuously supply power to the load, two operation modes are required depending on the grid state. One is the grid connected (GC) mode and the other is the stand-alone (SA) mode. Under normal grid condition, the power conditioning system is operated in GC mode and controls the current. On the other hand, under abnormal grid conditions such as grid outage, the power conditioning system operates in SA mode and supplies power to the load. Unintentional sudden changes in operating mode cause unwanted phenomena (e.g., voltage/current spike, inrush current) which can make system degradation or failure. To improve this situation, the seamless transfer function became necessary. In this paper, by adding seamless function to power conditioning system, it is possible to supply power to the load stably regardless of grid state. In addition, it is possible to prevent secondary accident and to operate stably even if non-detection zone condition occurs by using an active frequency method. The proposed control algorithm was verified through field experiments.
Highlights
Fossil fuels, which have been used as resources for electricity generation for centuries, are reaching their limits
The block diagram is composed of a phase-locked loop (PLL) part for phase detection and axis transformation, a part for converting the sensed 3-phase voltages and currents to the dq-axis, current control part for grid connected (GC) mode, voltage control part for SA mode, an active damping part for inhibiting the resonance phenomenon of the system to improve the stability, and a part that can avoid the non-detection zone (NDZ), which can occur under a specific load condition
It was confirmed that the proposed algorithm operates without any abnormality through various experimental conditions
Summary
Fossil fuels, which have been used as resources for electricity generation for centuries, are reaching their limits. The seamless transfer function was focused that enables the PCS to supply power to the load stably, in normal grid and in abnormal grid conditions in this paper. Indirect current method-based seamless transfer control was examined [18,19] This method, requires a long clearing time to change the operation mode. When the difference between the power consumption of the load and the power supplied by the PCS is small, the PCS cannot accurately recognize the grid state (i.e., NDZ condition) In this case, a control algorithm is required to escape this range because it cannot transmit the information to the ESS despite the occurrence of a system anomaly, which can cause secondary accidents in the system operation [26,27,28].
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