This paper presents an optimal placement and sizing of distribution static compensator (DSTATCOM) in radial distribution networks as multi-objective optimization with the objective of power loss reduction, voltage profile improvement and network reliability considering different variable demands using whale optimization algorithm (WOA). The WOA is inspired by the hunting behavior of humpback whales. The optimal location and size of DSTATCOM are considered as decision variables that are determined using the WOA. Network reliability is defined as energy not supplied (ENS) of the customers caused by line outages. The proposed method is implemented on IEEE 33-bus and Ahvaz 59-bus distribution networks. The optimal placement and sizing of DSTATCOM are investigated considering different residential, commercial and industrial loads, and also the effect of incorporating reliability is evaluated on power loss, minimum voltage and ENS. The simulation results show that the power loss and ENS are declined and also voltage profile is improved by determining the location and size of DSTATCOM in the networks in different loading conditions using the WOA. The obtained results demonstrate that considering reliability further reduces the ENS and more customer demand is met. The power loss decreases 21.60%, 30.71%, and 22.03% for residential, commercial and industrial loads in the 33-bus network and 26.86%, 31.94%, and 24.39% for the 69-bus network, respectively compared to base networks. Moreover, the performance of the WOA is compared with previous studies and the results indicate the superiority of the proposed method.

The high operating voltage and switching speed of silicon carbide (SiC) MOSFETs have significant impacts on parasitic elements. This leads to a limitation in the performance of the devices. Especially in the bridge-leg configuration, the coupling of the parasitic elements, in the upper and lower bridge-legs, produces knock-on effects, which complicates the modeling development to reveal the underlying mechanisms. This paper presents a detailed piecewise linear analytical model for bridge-leg configured SiC MOSFETs, which takes into account their characteristics and all parasitic elements. The novelty of the proposed model lies in the fact that the critical parameters in each stage are distinguished flexibly and emphatically according to their influence weights to the corresponding main variables. Therefore, the complexity of the model which considers all parasitic elements is reduced but the critical impacts on the switching processes are carefully kept. The turn-on and turn-off processes are analyzed stage-by-stage in detail with the derived critical parameters equivalent circuits, and the mechanism underlying how each critical parameter influences the model is revealed individually. Furthermore, based on this model, the impact mechanisms and trends of the switching rate variation, the power loop attenuation oscillation, and the driver loop crosstalk phenomenon for different critical parameters are analyzed emphatically. Double pulse measurements with a 600 V/20A SiC MOSFETs based bridge-leg test circuit are used for the experimental verification of the accuracy of the model and the trends of the critical parameters' impacts.

SiC MOSFETs have an excellent characteristic of high switching speed, which can improve the efficiency and power density of converters significantly. However, the fast switching processes of SiC MOSFETs cause serious crosstalk problems in bridge-arm configurations, which restricts the devices’ performances. This paper presents a detailed and accurate improved crosstalk analytical model, which takes into account the nonlinear capacitances, the parasitic inductances, the reverse recovery characteristics of the anti-parallel diodes, and the nonlinear voltage switching and damping oscillation process. The novelty of the proposed model lies in the fact that under the condition of comprehensively considering all these non-ideal factors of the bridge-arm, the effects of multi-parasitic elements and multi-variables coupling to the crosstalk are hierarchically divided. The parasitic elements and their correlations are described in detail and the direct and indirect variables’ impacts are clearly traced. Thus, according to the different variables switching stages, the influence processes of these parasitic elements and variables can be integrated and a complete equivalent analytical model of the crosstalk process can be derived. The simulation and experiment platforms are established and a series of experimental verifications and comparisons prove that the model can replicate experimental measurements of crosstalk with good accuracy and detail.

This paper presents the common methods and corresponding drawbacks concerning nonlinear analysis of fluxgate excitation circuits and emphasizes the importance of nonlinear analysis for these circuits. With regard to the nonlinearity of the excitation circuit, this paper proposes the use of the core-measured hysteresis curve for mathematical analysis and the use of a nonlinear model that considers the coupling effect of the core and winding and influence of the historical magnetic field on the core for simulation analysis. The feasibility of mathematical calculations and simulation for the nonlinear study of fluxgate excitation circuit is verified via experiments. The results demonstrate that, in this regard, the simulation is four times better than a mathematical calculation. The simulation and experimental results of the excitation current and voltage waveforms under different excitation circuit parameters and structures are essentially consistent, with a difference in current of no more than 1 mA, thereby verifying the effectiveness of the nonlinear excitation analysis method.

Fluxgate sensors are key devices for magnetic field surveys in geophysics. In areas such as deep drilling, fluxgate sensors may have to operate steadily at high temperatures for a prolonged period of time. We present an accordant ring-core type fluxgate sensor that is stable up to $220$°C. The high temperature consistency is achieved by using an Fe-based nanocrystalline magnetic core, PEEK structural components, an epoxy resin wrapping, as well as a broadband short-circuited working mode. The sensor was characterized at various temperatures up to $220$°C by evaluating impedance, hysteresis, permeability and sensitivity. We found a sensitivity of approximately 24 kV/T at $25$°C with an acceptable temperature coefficient of 742 ppm/°C throughout the range. The variation law of magnetic characteristics and their influence mechanism on output amplitude and phase are discussed.

The instantaneous output power of a two-stage single-phase inverter pulsates at twice the output voltage frequency (2f_o), which results in a large amount of second harmonic current (SHC) in the front-end dc–dc converter. This article proposes a novel dual-loop control strategy based on the parallel output impedance model of the front-end dc–dc converter, in order to reduce the SHC and improve the dynamic performance. The proportional–integral–resonant controller (PIRC) is used in the current-loop, and the SHC can be further suppressed under the limited loop bandwidth condition. In the voltage-loop, a notch filter is inserted into the forward path of the active disturbance rejection controller (ADRC). It allows the voltage-loop cutoff frequency to become greater than 2f_o, which significantly improves the load transient response. Furthermore, a step-by-step closed-loop parameters design method considering the SHC reduction, phase margin, and dynamic performance is proposed. Finally, a 1.8 kW two-stage single-phase inverter prototype is built and tested. The experimental results demonstrate the high effectiveness of the proposed dual-loop control strategy.