Abstract
The SOGI-FLL (Second-Order Generalized Integrator–Frequency-Locked Loop) is a well-known and simple adaptive filter that allows for estimating the parameters of grid voltage with a small computational burden. However, the SOGI-FLL has been shown to be especially sensitive to voltage sags and voltage swells, which deeply distort the estimated parameters, especially the frequency. This problem can be alleviated by simply using a saturation block at the Frequency-Locked Loop (FLL) output to limit the impact of distortion on the estimated frequency. Improving upon this straightforward approach, in this paper we propose the use of a finite state machine (FSM) for the definition of the different states of the SOGI-FLL frequency response during a voltage sag or swell fault. The FSM approach allows for applying different gains during the fault, enhancing the SOGI-FLL transient response. The performance of the FSM-based SOGI-FLL is evaluated by using simulation results, which show a better and faster response to these kinds of faults.
Highlights
The phase, amplitude, and frequency of utility voltage are critical information for the operation of inverter-based distributed generators
The synchronization block of power converters should be able to quickly detect fault events in the grid, like voltage sags, to avoid the deep impact that they have on the estimated parameters of the grid voltage, which is especially strong for the case of the estimated frequency [1]
In this paper we aimed to improve the response of the SOGI-Frequency-Locked Loop (FLL) to voltage sags since it is highly
Summary
The phase, amplitude, and frequency of utility voltage are critical information for the operation of inverter-based distributed generators. As seen in (3), the transient response of the estimated frequency to a change in the grid frequency is determined by the system parameters, i.e., the SOGI filter damping factor ξ and the FLL gain λ. These same parameters are responsible for the estimated frequency behavior under whatever input voltage condition, either nominal or perturbed. For SOGI-FLL normal operation, these parameters are designed according to an inherent trade-off between the rejection of harmonic distortion at the SOGI outputs (1)–(2) and the transient response to frequency step perturbation in the grid voltage (3). Type-a sags happen at 0.195 s, when b sags happen at 0.2 s, when theingrid voltage is atestimated zerofrequency crossing
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