Identification of DC Thermal Steady-State Differential Inductance of Ferrite Power Inductors

In this paper, we propose a method for the identification of the differential inductance of saturable ferrite inductors adopted in DC–DC converters, considering the influence of the operating temperature. The inductor temperature rise is caused mainly by its losses, neglecting the heating contribution by the other components forming the converter layout. When the ohmic losses caused by the average current represent the principal portion of the inductor power losses, the steady-state temperature of the component can be related to the average current value. Under this assumption, usual for saturable inductors in DC–DC converters, the presented experimental setup and characterization method allow identifying a DC thermal steady-state differential inductance profile of a ferrite inductor. The curve is obtained from experimental measurements of the inductor voltage and current waveforms, at different average current values, that lead the component to operate from the linear region of the magnetization curve up to the saturation. The obtained inductance profile can be adopted to simulate the current waveform of a saturable inductor in a DC–DC converter, providing accurate results under a wide range of switching frequency, input voltage, duty cycle, and output current values.

A study of ferroresonance in underground distribution network for 15MVA, 33/11 kV injection substation

This provides an overview of ferroresonance phenomena, modeling aspects and practical experience in recognizing and mitigating the effect of ferroresonance in the power network. In particular, we will present symptoms of ferroresonance. In this study, ferroresonance phenomenon are investigated under the modelling of the underground cable of 15 MVA, 33/11/0.415 kV with four feeders supply over 31 distribution transformers of Garki 1 service unit, Abuja, conducted using MATLAB/SIMSCAPE software package. The network is subjected to switching resulting in the formation of a series LC combination prone to ferroresonance. The waveforms and total harmonic distortion charts obtained are observed, analyzed and then used to design Harmonic filters which have been implemented to mitigate ferroresonance in the network. The simulated ferroresonance phenomenon was suppressed using Shunt Active Harmonic Filter connected in parallel to the network. A reduced harmonic content and dampened event when compared to a non-filtered event was observed. Application of Shunt Active Harmonic filter reduces ferroresonance effect by 67.743%. Keywords: Ferroresonance, Transformer, MATLAB/Simscape, Harmonic Distortion, Power system Modelling, Saturable inductor, Capacitance

Influence of Parasitic Parameters on DC–DC Converters and Their Method of Suppression in High Frequency Link 35 kV PV Systems

Photovoltaic (PV) power generation has shown a trend towards large-scale medium- or high-voltage integration in recent years. The development of high-frequency link PV systems is necessary for the further improvement of system efficiency and the reduction of system cost. In the system, high-frequency high-step-up ratio LLC converters are one of the most important parts. However, the parasitic parameters of devices lead to a loss of zero-voltage switching (ZVS) in the LLC converter, greatly reducing the efficiency of the system, especially in such a high-frequency application. In this paper, a high-frequency link 35 kV PV system is presented. To suppress the influences of parasitic parameters in the LLC converter in the 35 kV PV system, the influence of parasitic parameters on ZVS is analyzed and expounded. Then, a suppression method is proposed to promote the realization of ZVS. This method adds a saturable inductor on the secondary side to achieve ZVS. The saturable inductor can effectively prevent the parasitic elements of the secondary side from participating in the resonance of the primary side. The experimental results show that this method achieves a higher efficiency than the traditional method by reducing the magnetic inductance.