Differential Mode Currents Research Articles

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Internal Short-Circuit Fault Location of Rail Transit Auxiliary Inverter Based on Voltage Deviation

In order to improve the ability of locating and detecting the internal short-circuit fault of rail transit auxiliary inverter, a method of locating the internal short-circuit fault of rail transit auxiliary inverter based on voltage deviation is proposed. The fault sensing information acquisition module of rail transit auxiliary inverter is constructed by using the detection method of fundamental frequency characteristics of differential mode current of excitation winding, and the voltage deviation analysis of rail transit auxiliary inverter under internal short-circuit fault state is realized by using the methods of MVCR excitation winding control and output reactive power adjustment. Combined with the dynamic distribution characteristics of output harmonics and initial phase of rail transit auxiliary inverter, the equivalent compensation and capacity expansion methods of excitation winding circuit are adopted. The signal test model of fault location is established, and the spectral characteristics of the internal short-circuit fault signal of rail transit auxiliary inverter are extracted. A fault joint feature location and monitoring model is established by using the data clustering analysis method of fusion difference, and the internal short-circuit fault location detection of inverter is realized according to the voltage deviation distribution characteristics of inverter in short-circuit state. The test results show that the accuracy of short-circuit fault location in rail transit auxiliary inverter is high, and the dynamic estimation ability of inverter output voltage deviation is strong.

Analysis and Design Guidelines of the Isolated Modular Multilevel DC–DC Converter With the Impact of Magnetizing Inductance

The Isolated Modular Multilevel DC-DC (IMM DC-DC) converter is one of the potential candidates for interconnection of medium and high voltage DC grids. One of the key components for realization of the IMM DC-DC converter is its transformer whose magnetizing inductance depends on the core material, dimensions, and airgap. Depending on the transformer design, the magnetizing inductance may vary over a wide range, adding to the complexity of the converter design. In this paper, the impact of the magnetizing inductance on the converter real and reactive powers, transformer primary and secondary side currents, arm current, differential-mode current, capacitor voltage ripple, and soft-switching operation is investigated. The presented analysis is validated by time-domain simulation in the Matlab/Simulink software environment and experiments on a scaled-down prototype.

Crosstalk analysis of twisted bundle of twisted wire pairs (TBTWPs) and star‐quad cables under the effect of inner and outer excitations

AbstractIn this article, deep neural network (DNN) and chain parameter methods are used to analyze the crosstalk coupling of a star‐quad and a twisted bundle of twisted wire pairs (TBTWP) cables for different excitations, respectively. A DNN is used to extract the per‐unit‐length (p.u.l) resistance, inductance, capacitance, and conductance (RLCG) parameters at any position for the star‐quad and TBTWP cables. The induced common mode (CM) and differential mode (DM) currents due to crosstalk are calculated by combining the obtained RLCG parameters with the chain parameter method. The obtained results show good agreement with that of FEKO software. Moreover, it is found that the star‐quad cable can reduce the external coupling more effectively than that of the TBTWP cable. Finally, measurements are performed to further validate the accuracy of our proposed algorithm.

A Novel Current Self-Balancing Method for High-Gain and High-Frequency Converter

Matrix transformer is deemed the most widely used structure for large current application due to its natural current sharing. However, multiple transformers suffer from large core volume and core loss, especially with high frequency operation. In this paper, a novel current self-balancing method for high-gain and high-frequency converter is proposed. Only one magnetic core is employed and all secondary windings for large current are wrapped parallelly around the core. The H-bridges with two filtering inductors on the DC positive and negative bus are cascaded by these secondary windings to form a proposed cascaded H-bridge structure. Due to the large impedance in filter inductor loop in high frequency, the differential-mode current between different windings is largely suppressed and the current sharing of secondary windings and SR MOSFETs is achieved naturally. The filtering inductor can be easily implemented by using PCB-routed inductance without iron core, which means that the power density and efficiency will not be impaired. A 750V/48V-2kW unregulated LLC converter prototype is built and achieves the power density of 7 kW/L with maximum efficiency of 96.5%. With the proposed cascaded H-bridge structure, current self-balancing is achieved perfectly and the efficiency improvement reaches to 0.8% at full loading condition.

Common Mode Current Measurements in Traction Systems for Electric Vehicles

The market for partly or fully electrified vehicles is expanding fast. The number of sources and loads that are connected to the vehicles traction voltage systems (TVS) increase and thus also the ElectroMagnetic Compatibility (EMC) requirements on these sources and loads. These requirements should make sure that neither function nor lifetime of any source or load is severely affected by another. The EMC requirements include both Common Mode (CM) and Differential Mode (DM) voltages and currents created by the modulation of the various power electronic converters involved as well as intentional and parasitic impedances of the TVS and reach up to at least 10 MHz for CM and 100 kHz for DM. This article presents a theory for the dimensioning of CM-capacitances in an Electric Machine Drive (EMD) that is confirmed by measurements on a commercial electrical Volvo truck. The conclusions point out a recommendation for selection of the CM-capacitances of the EMD vs. the CM capacitance of the Electrical traction Machine (EM). As a rule of thumb the recommendation is that the CM-capacitance of the EMD is around 50 times the CM-capacitance of the EM and mounted inside the EMD to avoid big loops of CM currents in the vehicle.

Passive Paralleling of Multi-Phase Diode Rectifier for Wireless Power Transfer Systems

To improve the power level of a diode rectifier, a multi-phase diode rectifier can be employed to increase the current rating. This brief proposes a passive current balancing method for a multi-phase diode rectifier in a series-series compensated wireless power transfer system. For an N-phase diode rectifier, the receiver-side compensating capacitance is split into N branches, forming a parallel resonant network with the newly added parallel resonant inductors. The circulating currents can be greatly suppressed by the parallel resonant network. The resonant inductors only withstand differential-mode currents, which are small. Thus, these inductors are small and low-cost. Experimental results reveal that the proposed method can well balance the phase currents of the three-phase diode rectifier.

Protection scheme against turn-to-turn fault for novel magnetic valve controllable reactor

This paper focuses on the inter-turn protection scheme of a new type of reactive power compensation device-magnetic valve reactor. Aiming at the problem that the existing inter-turn protection scheme has insufficient sensitivity and causes the protection to refuse to act, this paper first introduces the topology of the new type of magnetic valve reactor in detail and analyzes the working state of the positive half cycle of its power supply and establishes mathematical model and physical model of valve reactor. Based on this model, the excitation winding of the magnetic valve reactor is analyzed, and the differential mode current component of the excitation winding is introduced to characterize the fault characteristics. According to the change of electric quantity before and after the fault, a new inter-turn protection scheme of magnetic valve reactor based on the fundamental frequency component of the differential mode current of the excitation winding group is constructed. After a large number of simulation experiments, the feasibility and effectiveness of the scheme are verified.

A high-frequency modeling of AC motor in a frequency range from 40 Hz to 110 MHz

Introduction. Most electromagnetic compatibility models developed for the study of three-phase induction machines are generally valid for low and medium frequencies (<< 1 MHz). This frequency limit seems to be too restrictive for the overall study of conducted electromagnetic interference. In this paper, the model is using the proposed model and compared with experimental results in low and medium frequency. And then, the high-frequency modeling of induction motor is presented new method based on transfer function model. The proposed methodology is verified on an experimental and simulation, it’s suitable for prediction of the terminal overvoltage analysis and electromagnetic interference problems and common-mode and differential-mode currents. The novelty of the work consists to develop an improved high-frequency motor model based on transfer function to represent the motor high-frequency behavior for frequency-domain analyses in the frequency range from 40 Hz up to 110 MHz .The purpose of this work is to study the common-mode impedance and the differential-mode impedance of AC motor. The determination of these impedances is done for firstly both common and differential modes at low and medium frequency, and then common-mode and differential-mode characteristics at high frequency. Methods. For the study of the path of common-mode and differential-mode currents in typical AC motor (0.25 kW, 50 Hz) an identification method in high frequency for induction motor has been proposed based on the transfer function in differential-mode and common-mode configuration. The low and medium frequency model were presented in the first time based on equivalent circuit of electrical motor. Then, the common-mode and differential-mode impedances were defined in high frequency using asymptotic approach. This motor was studied by MATLAB Software for simulation and also experimental measurements. Results. All the simulations were performed using the mathematical model and the results obtained are validated by experimental measurements performed in the University of the Federal Armed Forces Hamburg in Germany. The obtained results of common-mode and differential-mode at low frequency, medium and high frequency are compared between simulation and experiment.

Transmission Line Modeling and Crosstalk Analysis of Multibraided Shielded TWP/Twinax Cables

In this article, the transmission line model of multibraided shielded cables is improved by including the proximity effect in the shield model. This is performed by deriving the analytical expressions of the transfer impedance and admittance of a shielded structure with nonuniform current distribution around the shield surfaces. After that, the formulations are generalized to be applicable for shielded twisted-wire pair (TWP) and twinax cables with line apertures and braided structure with nonuniform shield current. It is found that the nonuniform distribution of the currents in the outer and inner shield surfaces have high effects on the inner induced common-mode and differential-mode currents of braided shielded cables. In addition, the crosstalk between multishielded TWP and twinax cables is investigated in detail, indicating that the proximity effects between the shields have a critical impact on generating the crosstalk between the shielded cables. The proposed model is validated with the commercial software FEKO and excellent agreements are achieved.

PWM Inverter with 4-Phase Carrier for Grid Connection Via Combined LCL Filter

A PWM power conversion system connected to a grid through parallel-combined LCL filter is proposed in this paper. The system has four inverters paralleled and operates with PWM using 4-phase carrier for powering up and performance improvement. Four LCL filters have four separate filter inductors connected to individual inverters and one common LC filter which is composed of a filter capacitor and a grid inductor. The differential mode current circulates only through four inverters and four filter inductors. The differential mode current is completely eliminated from the filter capacitor and the connected power grid. Accordingly, performance improvement can be achieved since the current in the filter capacitor is reduced and the harmonic current into a grid is reduced. An 1.3kW single phase prototype system has been constructed and tested, and the proposed system has been verified.

A Novel Zero-Sequence-Voltage-Balanced SVPWM With the Analyses of Common-Mode Voltage and Differential-Mode Current

In three-phase voltage source converters (VSCs), the high-frequency leakage current can be easily suppressed by the common-mode choke, while low-frequency component would be an unfavorable factor to the inductor design. Thus, as the excitation source, the low-frequency common-mode voltage (CMV) should be properly managed. This article analyzes the low-frequency CMV impulse by constructing a 3-D voltage vector space, and a novel modulation method is proposed to eliminate the low-frequency CMV. Meanwhile, a comparative study is conducted between the proposed method and the other four typical space vector pulsewidth modulation (PWM) (SVPWM) method from the view of CMV and differential-mode current (DMC). In the analysis, a double-current-ripple-envelopes method is proposed to describe the current ripples. Besides, the influence of modulation indexes and power factors on DMC are considered and evaluated. And a guiding rule for choosing the appropriate modulation method for three-phase VSCs is provided. Finally, the theoretical analysis and proposed method are experimentally validated under a 5-kW three-phase PWM converter.

Transmission Line Model for a Shielded TWP With Apertures and Generalization to Braided–Shielded TWP Cables

An efficient multiconductor transmission line (MTL) model of a shielded twisted wire pair (TWP) with apertures on its sheath is developed for predicting common mode (CM) and differential mode (DM) currents induced in the shielded TWP cable. Its transfer impedance and admittance with one-line apertures on its sheath are derived in a closed form. Therefore, the MTL equations are formulated and solved to obtain the CM and DM currents induced in the shielded TWP. Moreover, the proposed MTL model is generalized to be applicable for the braided–shielded TWP, in which the transfer impedance and admittance are formulated analytically. Results showed that the induced DM current inside the braided–shielded TWP is suppressed dramatically due to the uniform structure of the cable. The models are validated by comparing their results with those obtained by the commercial software FEKO; good agreements are obtained.

Inclusion of frequency dependences into prediction model of conducted electromagnetic emissions for a VFD motor system

This paper presents a quantitative prediction model of conducted electromagnetic emissions (EME) for a variable frequency drive (VFD) motor system based on the macro-modeling approach. This model relies on the effective representations of the frequency dependent characteristics of the parasitic behaviors between converter arms and heatsink, of shielded power cable, and of motor windings. The frequency dependent performances between converter arms and heatsink, and of the motor windings are obtained by processing measurement data. Then the vector fitting method (VFM) with passivity enforcement and circuit synthesis method are adopted to obtain the corresponding equivalent circuits. The equivalent circuit implementation of shielded power cable is achieved by applying a node-to-node admittance functions (NAFs) model, which considers the propagation phenomenon and frequency dependent losses accurately. The conducted EME model is compatible with commonly used transient circuit solvers since it only includes constant circuit elements. The conducted emissions of the VFD system are then evaluated by analyzing the common mode (CM) and differential mode (DM) voltages and currents.

Mixed-Mode Effect on Motor Common Mode Current

This paper presents the mixed-mode effect on motor common mode current (CMC) in an adjustable speed drive (ASD). It is expected that the motor CMC is lower than inverter output CMC. However, the measurement result of the ASD shows that the AC motor input CMC is higher than the inverter output CMC in a frequency range. By using a mixed-mode (MM) 6-port networks, it is proven that the AC motor input CMC is higher due to an MM CMC which is generated from differential mode current.

DC Grid Protection Method Based on Phase Planes of Single-End Common-and Differential-Mode Components

This study develops a high-speed protection method for a modular multilevel converter (MMC)-based DC grids. The method utilizes the single-end derivative of common-mode (CM) and differential-mode (DM) currents to construct a protection phase-plane that divides different DC fault types into different regions. When the protection starts, the first sampling point that enters the fault regions of the protection phase-plane has the largest value. When five sampled data satisfy the corresponding fault conditions, the protection signal will be sent. This scheme ensures the rapidity of protection. CM and DM circuits of MMC, DC transmission line, and fault transition resistance under different fault types are derived following the principle of modulus decomposition. Finally, the synthesized equivalent circuits are obtained. On this basis, the expressions of CM and DM currents are derived to analyze the characteristics of fault currents on the protection phase-plane and provide the rules for distinguishing different fault types. A four-terminal MMC-based DC grid simulation model is established in PSCAD/EMTDC. The rapidness and reliability of the proposed protection method are then verified using different simulation cases. The proposed method is also validated on a scaled-down hardware setup in the laboratory.

Stochastic Analysis of Multitwisted Cables With Random Parameters Excited by Random Plane-Wave Fields

A generalized multiconductor transmission line (MTL) model is integrated with the polynomial chaos stochastic Galerkin method (PC-SGM) in order to predict the stochastic response of a nonuniform multitwisted bundle of twisted-wire pairs (MTB-TWP) with random parameters, which is excited by random plane waves. The twist pitches of such nonuniform MTB-TWP are considered to be spatial stochastic functions, where its parametric equations are derived in their general form. Moreover, by taking the geometry deformation of the MTB-TWP cable into account, some of its parameters are represented by random variables, and the incident plane-wave fields can also be changed in some random ways. After that, the PC-SGM is applied to the stochastic telegrapher's equations in order to obtain deterministic ones that can be solved by using the MTL model. Therefore, the effects of the uncertainties of the parameters on the common mode and the differential mode currents are investigated in details, where, in each case, the probability density function is given. The results are validated in comparison with Monte Carlo (MC) method, where a very good agreement is obtained. It is shown that the PC-SGM simulation time is much smaller than that of the MC method as the number of random variables is relatively small.

Characterization of Electromagnetic Wave Coupling With a Twisted Bundle of Twisted Wire Pairs (TBTWPs) Above a Ground Plane

A multiconductor transmission line model is developed to characterize electromagnetic wave coupling with a twisted bundle of twisted wire pairs (TBTWPs) running above a ground plane. A set of parametric equations of each wire in each bundle is derived at first, together with its unit tangent vector defined analytically. Furthermore, its averaged per-unit-length parameters are determined according to the derived analytical equations, and the equivalent voltages for describing field–wire coupling are presented. The proposed model is employed for predicting both common mode and differential mode currents induced at different terminal loads of the TBTWP, where fire-side, end-fire, broad-side, and arbitrary electromagnetic wave incidences are investigated. The numerical results of our model are validated in comparison with that of the commercial software FEKO, with good agreement achieved between them. Furthermore, such TBTWP model can be extended for studying electromagnetic wave coupling with multiple TBTWPs employed in many cable systems.

Circulating current reduction of a grid-connected parallel interleaved converter using energy shaping control

This paper proposes a method to control low frequency circulating currents generated in parallel interleaved converters. In this configuration, inverters are parallelized using magnetically linked inductors. Generally, to improve the harmonic content of the output voltage, carrier interleaving is used. This results in a higher circulating current (differential mode current) to flow through the two Voltage Source Converters (VSCs). High frequency components of circulating currents are efficiently reduced by the mutual inductance of the Coupled Inductors (CI). However, CI cannot efficiently filter the low frequency components. When the uncontrolled circulating currents become too high; they lead to CI saturation, higher switching losses, and degrade the overall performances of the converter. Therefore, this paper presents a global control strategy for a grid-connected parallel interleaved converter based on the concept of Port Controlled Hamiltonian (PCH). With this controller, active and reactive powers delivered to the grid are efficiently controlled. In addition, the controller considerably reduces the value of the low frequency circulating current. Converter performances are evaluated by simulation and compared with the classical PI control and the Linear Quadratic (LQ) control. An experimental setup was developed to verify the feasibility of the proposed system. Results obtained from experiments show a good agreement with the simulation, confirming the performances of the proposed method.

A Universal High-Frequency Three-Phase Electric-Motor Model Suitable for the Delta- and Star-Winding Connections

A universal high-frequency three-phase electric-motor model to be used in the design process of the electric-motor drive systems is proposed. The model can be combined with the models of the filter, cable, and inverter to form a complete drive system. It allows for a common and differential-mode high-frequency analysis in studying the bearing currents, electromagnetic interference, and overvoltages in the motor windings caused by the high-frequency reflections. The model phase is symmetrical meaning that the beginning and end of each phase are equal and the central part is inserted between them. This enables modeling of both the delta and star-winding connections of the three phases. The equations used to calculate the model parameters are presented. They are based on the common and differential-mode impedance measurements. The model can be simplified when considering only electric-discharge machining bearing currents, as they are affected only by the common-mode states. A simplified model to be used in the delta-winding connection is also presented. The model-calculated common and differential-mode impedances are compared with the impedances measured on a 6.5-kW outer-rotor brushless direct-current motor. This paper ends by providing the obtained simulation and measurement results for the common and differential-mode currents and bearing voltages of the studied three-phase delta-winding-connected electric motor.