Daming Zhang

Differential Evolution Based Parameter Identification of Static and Dynamic J-A Models and Its Application to Inrush Current Study in Power Converters

The Jiles-Atherton (J-A) model is very suitable for modeling ferrite-core based inductors and transformers. In this paper the differential evolution (DE) method was applied to extract five parameters in static J-A model first. Then it was applied to extract another two parameters in dynamic J-A model with five parameters in static J-A model as inputs. It is found that extracting five parameters in static J-A model is relatively easy but extracting another two parameters in dynamic J-A model needs extra effort, especially specifying their ranges. After obtaining all seven parameters, we applied dynamic J-A model to predict the current behavior of a practical switching circuit and successfully obtained the inrush current phenomenon as experimentally observed and reported in literature. We conclude that application of DE method to extract seven parameters in dynamic J-A model for ferrite is feasible.

Determination of Dimension-Independent Magnetic and Dielectric Properties for Mn–Zn Ferrite Cores and Its EMI Applications

Simultaneously high permeability and permittivity results in a pronounced dimensional effect in Mn-Zn ferrite cores, which makes the measured complex permeability differ for cores with different dimensions. This paper provides a succinct method to solve an inverse problem of tracing dimension-independent or intrinsic complex permeability and permittivity for Mn-Zn ferrites using two toroidal and rectangular-cross-sectioned cores with different dimensions. The apparent complex permeability of ferrite cores with other dimensions can then be predicted from the traced intrinsic values, so will the effective impedance of common-mode chokes made of such cores. The traced intrinsic permeability is in good agreement with the measured apparent complex permeability of a very small toroidal ferrite core, in which dimensional effect can be ignored. The apparent complex permeabilities of ferrite cores with other dimensions are measured experimentally, and are also calculated from the determined intrinsic values. A very good agreement between the measured and calculated values is found.

An efficient finite-difference-based Newton-Raphson method to determine intrinsic complex permeabilities and permittivities for Mn-Zn ferrites

This paper presents a fast and efficient algorithm, based on the finite-difference method, to extract intrinsic complex permeability and permittivity from measured values for Mn-Zn ferrite cores. Our algorithm is considerably more efficient than the analytical solution-based Newton-Raphson method and reduces computing time from hours to tens of seconds

Autonomous micro-grid operation by employing weak droop control and PQ control

This paper presents an autonomous operation of a micro-grid by employing a droop control and PQ control strategy. The local distributed generation (DG) is modeled by a grid-tied inverter with LCL filter. A proportional-resonant controller is adopted to control the inverter. A new control scheme based on a combination of weak droop control and PQ control is proposed in this paper. Droop control aims to share the load change after islanding occurs. Meanwhile, weak droop control equations with a small power-dependent variation are used for generating the reference signal for PQ control after islanding has occurred. These are implemented using code in the Simulink environment. The simulations show that the proposed scheme which combines droop control with PQ control could operates well in both grid-connected and islanded conditions. By employing such a scheme the transition of the micro-grid from grid-connected operation to autonomous operation or vice versa is smooth.

Detection of High Impedance Faults using wavelet transform

High Impedance Fault (HIF) has long been a challenging problem in network protection. This is because of its difficulty to be detected and discriminated accurately and reliably. In real cases, arcing is usually associated with HIFs. In this paper, arcing currents are produced by setting up a HV experiment. Normal switching transients are also produced by simulation or experiment. They are then analysed based on wavelet transform. It was found by previous researches that db4 is sensitive in detecting high frequency transient. Different features for the fault currents are found and a detection criterion is developed. The simple detection criterion is used to discriminate the high impedance fault from switching transients and normal load current.

Application of partial direct-pole-placement and differential evolution algorithm to optimize controller and LCL filter design for grid-tied inverter

In this paper differential evolution algorithm has been adopted to identify a suitable set of values of L-C-L filter used in a grid-tied voltage source inverter to meet total harmonic distortion (THD) requirement. A single-phase circuit model with virtual equivalent impedance of inverter output power was used to analyze total harmonic distortion. This paper also adopted a combination of partial direct-pole-placement and differential evolution algorithm to determine basic parameters of the proportional resonant controller for the inverter. To have effective damping, the real part of the complex pole of the closed-loop transfer function closest to imaginary axis is pre-set as one of objectives for differential evolution algorithm to identify. The validity of the optimized L-C-L and controller parameters and effectiveness of one-phase equivalent circuit for THD analysis have been verified by Matlab Simulink based platform.

A universal controller for grid-tied DC/AC converters for harnessing PV panel based solar energy and PMSG based wind energy

This paper proposes a universal converter topology and its controller for harnessing both PV panel based solar energy and permanent magnet synchronous generator (PMSG) based wind energy. Such controller has the function of maximum power point tracking. For the same level of power harnessing, the same controllers parameters can be used for both wind energy and solar energy harnessing. LCL filter used to contain current THD into grid set by standard has been optimized by zeros-poles cancellation and differential evolution based methods. Overall system works according to the design target.

Erratum to: Benzylammonium Thermometer Ions: Internal Energies of Ions Formed by Low Temperature Plasma and Atmospheric Pressure Chemical Ionization

The extent of internal energy deposition upon ion formation by low temperature plasma and atmospheric pressure chemical ionization was investigated using novel benzylammonium thermometer ions. C-N heterolytic bond dissociation enthalpies of nine 4-substituted benzylammoniums were calculated using CAM-B3LYP/6-311++G(d,p), which was significantly more accurate than B3LYP/6-311++G(d,p), MP2/6-311++G(d,p), and CBS-QB3 for calculating the enthalpies of 20 heterolytic dissociation reactions that were used to benchmark theory. All 4-substituted benzylammonium thermometer ions fragmented by a single pathway with comparable dissociation entropies, except 4-nitrobenzylammonium. Overall, the extent of energy deposition into ions formed by low temperature plasma was significantly lower than those formed by atmospheric pressure chemical ionization under these conditions. Because benzylamines are volatile, this new suite of thermometer ions should be useful for investigating the extent of internal energy deposition during ion formation for a wide range of ionization methods, including plasma, spray and laser desorption-based techniques. Graphical Abstract ᅟ.

Study on high impedance fault arcing current characteristics

The high impedance fault (HIF) is still one of most challenging problem for electrical engineers for its difficulty to be detected and discriminated accurately and reliably. There is a need for accurate and reliable modeling of arcing since arcing is usually associated with HIFs. In this paper, the HIF detection methods and arc modeling development are reviewed. HIF arcing experiments are also set up to investigate the features of HIF arcing in time domain preliminarily.

Arcing current features extraction using wavelet transform

High Impedance Fault (HIF) has long been a challenging problem in network protection. This is because of its difficulty to be detected and discriminated accurately and reliably. In real cases, arcing is usually associated with HIFs. In this paper, arcing currents produced by using different metals are analysed based on wavelet transform. The wavelet db4 is used and found to be sensitive in detecting high frequency transient. Test results show that the features for different current magnitudes are different. These features are studied to develop a simple detection criterion to distinguish arcing fault currents from the normal load.