Abstract
For synchronization between the grid voltage and generator voltage, we propose a phase-locked loop (PLL) algorithm with virtual rotational reference frame and feed-forward compensation. It is possible to accurately estimate the phase angle through a virtual coordinate system that uses the phase angle information of the grid instead of the phase angle information of the generator. In addition, to eliminate the effect of harmonic components, which make it difficult to calculate the exact phase angle and to alleviate the very sensitive problem to external noise, a feed-forward compensation algorithm is applied. To verify the feasibility of the proposed approach, PSIM simulations and experiments are performed on prototypes. In particular, in order to utilize the emergency generator as a demand resource, the existing stand-alone emergency generator system is changed to a grid-tied uninterruptible power supply structure and verified through a 280kW actual load test for four operating modes. With the proposed virtual coordinates and feed-forward compensation, fast and stable transfer switching is possible. The error of the phase angle estimation is excellent as 0.02°, and it has a 20% lower time-constant for phase angle estimation compared to the conventional method at the moment of phase transfer when 5% of the 5th harmonic component is included in the grid voltage. Consequently, it can be confirmed that inrush current do not occur in all operating modes.
Highlights
Various research on Uninterruptible Power Supply (UPS) system using ESS (Energy Storage System) were conducted for the stable supply of energy generated by renewable power sources [1]-[16]
General closed transition transfer switch (CTTS) can change over without interruption, but since it is impossible to change in zero power state, there is a problem that stress occurs on peripheral devices due to inrush current during transfer switching and may adversely affect the stability of the grid
Closed-loop synchronization methods are based on non-linear negative feedback control systems: phase-locked loop (PLL) [52], [53] or frequency locked loop (FLL) [54]-[56]
Summary
Various research on UPS (uninterruptible power supply) system using ESS (Energy Storage System) were conducted for the stable supply of energy generated by renewable power sources [1]-[16]. The synchronization time between the two power sources is very slow and inaccurate, and in severe cases, it may lead to a transfer switching failure To solve this problem, one of the most important work is to apply a fast phase angle estimation technique [37]-[47]. It is necessary to analyze whether the PLL-based synchronization algorithm shows stable and fast response characteristics by directly applying it to a large power capacity system. We propose a PLL algorithm that applies feed-forward compensation enabling fast and reliable synchronization between the grid and the generator It is based on the proposed virtual coordinates, which uses the phase angle information of the grid instead of that of the generator. To verify the feasibility of the proposed method, PSIM simulation was conducted, and a 280kW uninterruptible power supply system employing an emergency generator was designed, manufactured, and tested through actual load operation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
