Voltage fluctuations caused by rapid reactive power consumption of loads and photovoltaic or wind generator output variations may produce flickers and cause undesired effects on electric power components and human eyes. This paper presents a hybrid approach for voltage fluctuations assessment by using a synchrosqueezing transform-based algorithm. The proposed method first gives characterization of voltage fluctuations through accurate extraction of the measured voltage envelope by the Hilbert transform. The synchrosqueezing transform and an unsupervised clustering method called mean shift are then applied to determine the number of frequency components and corresponding frequencies. It is followed by the implementation of the bandpass filters to detect the magnitude of each frequency component. The proposed hybrid method is tested by both simulations and field measurements. Results compared with other commonly seen methods show that the proposed method provides a more accurate assessment.

This paper presents an improved dynamic voltage-current model of an ac electric arc furnace (EAF) for multiple operation stages and for the study of propagations of voltage fluctuations in a power network associated with the EAF in operating stages. The EAF model is developed based on wavelet-transform and neural-network-based methods by training actual measured EAF current and voltage data. The proposed EAF model is then implemented in an actual 161-kV power system for simulations. The voltage fluctuations at other buses due to the EAF in operation are then assessed. Simulation and measured results show that the improved hybrid EAF model is accurate and is suitable for voltage fluctuation assessment when the actual measurements in the power network are limited or not available while the EAF is in operation or before the similar types of EAFs are to be installed in the system.

This paper proposes a discrete wavelet transform (DWT) and radial basis function neural network (RBFNN)-based method for modeling the dynamic voltage-current (v-i)characteristics of the ac electric arc furnace (EAF). The objective of the study is to develop a complete model of the EAF including different operation stages, and the model can be used as a harmonics and flicker source in its connected power system for the power-quality penetration or mitigation study, where the developed model can be embedded in the power system implemented by a commonly seen simulation tool, such as Matlab/Simulink. In the study, a combination of the DWT and the sequential RBFNN with parameters initialization algorithm is proposed to build the EAF v-i characteristics with enhanced lookup tables for different operation stages, where the field measurements of the EAF voltage and current are used to train the RBFNN for modeling the EAF load. Simulation results obtained by using the proposed model are compared with different measured data. It shows that the solution procedure accurately models the EAF dynamic v-i behavior. The proposed method also can be applied to model other highly nonlinear loads to assess the effectiveness of compensation devices or to perform relative penetration studies.

This paper presents power compensation based on digital predictive current controlled three-phase bi-directional inverter with wide inductance variation. The three-phase bidirectional inverter can fulfill both real power and reactive power compensation for ac grid. With the proposed control, the inverter can track sinusoidal reference currents precisely with unity power factor or power factors -0.5 ~ +0.5, and it is allowed to have wide inductance variation, reducing core size significantly. In the design and implementation, the inductances corresponding to various inductor currents are measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. Moreover, a one-phase shift detection method for anti-islanding operation based on the proposed control is also presented. Measured results from a 10 kVA 3ø bi-directional inverter have confirmed the feasibility of the discussed control approach and detection method.