Common-mode Inductor Research Articles

Suppression of Initial Charging Torque for Electric Drive-Reconfigured On-Board Charger

This paper presents a new electric drive-reconfigured on-board charger and initial electromagnetic torque suppression method. This proposed reconfigured on-board charger does not need many components added to the original electric drive system: only a connector is needed, which is easy to add. Specifically, the inverter for propulsion is reconfigured as a buck chopper and a conduction path to match the reconfigured windings. Two of the machine phase windings serve as inductors, while the third phase winding is reutilized as a common-mode inductor. In addition, the initial charging torque is generated at the outset of the charging process, which may cause an instant shock or even rotational movement. In order to prevent vehicle movement, the reason for the charging torque and suppression method were analyzed. Further, predictive control of the model based on mutual inductance analysis was adopted, where the charging torque was directly used as a control object in the cost function. Finally, experimental performances were applied to verify the proposed reconfigured on-board charger under constant current and constant voltage charging.

Leakage Current Analysis of Non-Isolated Photovoltaic Grid-Connected System

Amidst mounting concerns over energy scarcity and the environmental repercussions of fossil fuels, renewable sources, spearheaded by solar energy, have garnered substantial societal attention, thereby propelling advancements in photovoltaics (PVs). In the realm of grid-connected (GC) PV systems, a pressing issue is the leakage current suppression in non-isolated GC PV inverters. As a ubiquitous architecture in PV systems, the non-isolated GC configuration is of paramount importance in practical applications. Yet, intrinsic attributes of PV systems have amplified the leakage current challenge within this setup. This paper endeavors to dissect the leakage currents in non-isolated PV GC systems, delving into the salient factors influencing them. It embarks on an exploration of the origins of leakage currents, subsequently analyzing the repercussions of LC filter parameters—spanning filter capacitance, Y capacitance, and common-mode inductance—on these currents. Drawing insights from extant scholarly discourse on leakage current mitigation, this study offers a synthesized perspective accentuated with augmented strategies, elucidating a comprehensive path forward for leakage current suppression.

Experimental Study of Radiated Emission Due to Secondary Common-Mode Current in Buck Converters

High switching frequency and fast switching speed of wide bandgap power semiconductor device-based power converters may increase radiated emissions more than conventional silicon-power device-based power converters. Based on the background, this article experimentally investigates radiated emission sources in buck converters. The experimental system constructed in this article has two common-mode noise paths, the primary common-mode and the secondary common-mode. First, this article outlines that a secondary common-mode voltage source is caused by a primary common-mode current and an imbalance of power supply side impedances, and the secondary common-mode current path acts as a monopole antenna. The common-mode currents and the radiated emissions are measured in an anechoic chamber when the common-mode inductor for each mode is connected. The measurement results show that the primary common-mode current generates the secondary common-mode noise, and the secondary common-mode noise is the dominant source of radiated emission in the experimental system.

Predicting Common-Mode Inductor Current Using a Time-Domain Hysteresis Model

Common-mode inductors are generally designed so that their operation is in the magnetically linear region of the core material. Very few works consider magnetic hysteresis in the core in terms of the common-mode current waveform. This work validates one such magnetic model and enhances it by including the common-mode current due to the inductor's parasitic capacitance. This work establishes the considerable impact of hysteresis and parasitic capacitance on the ability of a common-mode inductor to reduce common-mode current.

Improving differential mode inductance in toroidal common mode inductors

Improving differential mode inductance in toroidal common mode inductors

Enhanced Three-Phase AC Common-Mode Filter With Optimized Damping Network for VFDs

This paper presents a highly integrated three-phase AC common-mode (CM) filter with optimized damping network for low voltage, high current motor drive applications. Simplified reduced order models and design guidelines for tuning of RLC parameters are proposed. A single turn AC-CM inductor can be realized using the proposed circuit and design technique, due to lower magnetizing inductance requirement. The RC network is found to provide 50% higher attenuation to peak CM currents compared to a conventional AC inductor alone. At the same time, the peak-volt-second across the CM inductor can be reduced, which is critical for weight sensitive applications. A trade-off between AC-CM inductance and damping resistor losses is evaluated to extract the desired optimal RLC parameters of the AC filter. The proposed circuit is designed and verified with high power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SiC</i> -based Three Level T-type inverter.

A Novel SiC Device Model With Power Stage and Gate Driver Uncoupled

Silicon Carbide (SiC) power transistors have fast switching speed but are more inclined to be affected by parasitics. Miller capacitor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_gd</i> ) and common source inductor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L_s_com</i> ) are two major cross coupled parameters across gate driver loop and power loop, which cause overshoots, crosstalk and decreased switching speed. To ensure a reliable and efficient switching, the impacts of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_gd</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L_s_com</i> need to be identified and fully compensated in the gate driver. However, state-of-arts failed to provide a straightforward compensation approach with the coupling effects extracted and un-coupled model accurately represented. In this paper, a novel SiC device model with decoupled equivalent miller capacitance and common-mode inductance extracted for both gate driver loop and power loop is presented following the Miller theorem in micro-electronics. The decoupled equivalent circuit is verified to have decent accuracy in predicting the actual SiC switching transients. Furthermore, this paper proposed an improved resonant gate driver (RGD) design using the proposed decoupling model under the effects of common-mode inductance. The pre-charging current and driving pulse width are adjusted to ensure a full resonance driving transient with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L_scom</i> . The experimental results show that impact of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L_scom</i> is fully compensated, where SiC's <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di_ds/dt</i> is improved from 1.88A/ns to 2.102A/ns, which is close to the results without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L_scom</i> .

Full Electromagnetic Integration of Impedance-Balanced EMI Filters for Single-Phase Power Converters

Utilizing passive electromagnetic interference (EMI) filters is the most widely used approach to restrain the conducted emissions from power converters. However, the introduction of these filters will significantly raise the weight and size of the systems. Using the emerging flexible multi-layer foil (FMLF) technique, this paper investigates a complete electromagnetically integrated design concept of single-phase EMI filters based on EE-type cores, which can be applicable to engineering application scenarios with different EMI noise attenuation requirements. Two types of integrated structures are constructed with different well-designed FMLF-windings and terminal configurations. One is a common-mode (CM) choke with controllable leakage inductances, which is able to realize the integration design of CM inductor, CM capacitors and differential-mode (DM) inductors. The other is an EMI choke with integrating the CM and DM inductances & capacitances, which achieves electromagnetic integration of all the CM and DM filtering components. Compared to the existing UU-type core based integration methods, the proposed methods can ameliorate the noise suppression performance while reducing filter's weight and volume. Theoretical analyses for modeling and design of the EMI chokes is presented. Then prototypes of different FMLFs based EMI filters have been built for a 500W 100kHz SiC-MOSFET inverter, experiments demonstrate the feasibility and validity of the proposed structures.

Integrated CM Inductor for Both DC and AC Noise Attenuation in DC-Fed Motor Drive Systems

Using passive electromagnetic interference (EMI) filter to suppress the common mode (CM) noises on the dc and ac side of motor drive systems is a common filtering method. Shrinking the volume of CM inductors is the key to the miniaturization of EMI filters. In order to reduce the volume, this article proposes a new method to integrate the dc and ac CM inductors by magnetic coupling. The principle of the filter and the design constraints of coupled CM inductors are analyzed. The filter volume reduction advantage gained by using the proposed method is illustrated. A model is built to describe the relationship between the coupling coefficient and filtering performance. Finally, the procedures for design of coupled inductors are addressed and the results are verified by experiments. In the comparative case study, the volume of coupled inductor is 90% of that of discrete inductor.

Estimation of Number of Cores for Preventing Common-Mode Inductor Saturation in Railway Traction Inverters

In the traction system of rolling stock, the common-mode (CM) voltage is over 500 V, so the inductors that suppress the CM current are prone to saturation. To prevent saturation, the traction inverter needs many numbers of cores inside CM inductors, but the required number of cores has been determined empirically. This paper proposes a method calculate the approximate number of nanocrystalline cores to avoid saturation of CM inductors in railway traction inverters without circuit simulation. Using the only the CM capacitance of traction motor and the core characteristics on the datasheet, the maximum flux density of the inductor is calculated. Comparing calculated results of the maximum flux density with the results measured with a 1500 V DC inverter indicates that the proposed method can better identify the occurrence of saturation than the methods based on CM current presented in the literature. Furthermore, for the entire CM voltage range from 500 V to 3000 V, the minimum number of cores which saturation is prevented by the proposed calculation method is shown to be in reasonable agreement with the simulation results.

A Common-Mode Shorting Network to Reduce Common-Mode Excitation of Three-Phase Two-Level Electric Drives

Common-mode voltage and current in an electric machine are undesirable. Although the strategic placement of a common-mode inductor and dc input side capacitors may reduce the common-mode current produced by an electric drive system, the effectiveness of this mitigation is a function of machine parasitic capacitance. This engenders the need to insert another electrical component into the system to effectively mitigate the common-mode current. With this purpose, a common-mode shorting network for an inverter-based drive system is proposed in this work. This network, in conjunction with a common-mode inductor and dc input side capacitors, reduces the machine common-mode voltage and current. The proposed approach is experimentally demonstrated.

Decoupled Magnetic Integration of Symmetrical LCL Filter With a Common-Mode Inductor for Single-Phase Grid-Connected Converters

High-frequency power electronic devices in grid-connected converters excited vast switching harmonics and electromagnetic interference (EMI) noises. Conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type harmonic filters can well attenuate switching harmonics, but have a poor EMI suppression capability, especially for common-mode (CM) noise. Symmetrical filter structure and an additional EMI filter are generally needed to effectively suppress EMI in power converters, but this will inevitably increase the size and cost of the output filter. In order to tackle this issue without sacrificing the filter performance, this article proposes a decoupled magnetic integration of symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filters with a CM inductor for single-phase grid-connected converters. The harmonic inductors of a symmetrical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter and a CM inductor are integrated on the side-limbs and middle-limb of an EE-type magnetic core, respectively. Due to the decoupled magnetic structure and the reasonable assignment of the windings, the magnetic coupling between converter-side inductors and grid-side inductors can be greatly canceled to improve the performance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filters on the basis of the integration of CM inductor to suppress CM EMI. The detailed design guidance of the proposed integration method is presented. A single-phase decoupled magnetic integration filter is fabricated and tested, and the experimental results verify the effectiveness and feasibility of the proposed method.

Research and Modeling on the Characteristic Changes of EMI Filter Passive Components under the Influence of Aging

At present, the power density of power electronic devices in data centers and electric vehicles is constantly increasing, and numerous electronic components are concentrated in a tight, high-temperature environment, which aggravates the performance degradation of electronic components. Consequently, X and Y capacitors, common-mode inductors, and differential-mode inductors used for electromagnetic interference (EMI) suppression suffer from aging effects, and their performance continues to decline. However, the electromagnetic compatibility test is often conducted immediately after the power electronic equipment leaves the factory. The electromagnetic compatibility of power electronic equipment is affected by aging, which is not assessed in current industrial testing. This study conducts aging experiments on passive electronic components in EMI filters and measures the impedance in the frequency range from 150 kHz to 30 MHz. Subsequently, a multi-element aging model based on electromagnetic field analysis is established. The proposed model is suitable for electromagnetic compatibility analysis considering aging. Finally, the aging performance of a commercial two-stage EMI filter is predicted to verify the model proposed in the study. The proposed model explains the degeneration of the EMI filter with aging in the frequency range of 150 kHz to 1 MHz, with a maximum amplitude error of 0.58 dB and phase error of 1.0°.

Design of a Modified Single-Stage and Multistage EMI Filter to Attenuate Common-Mode and Differential-Mode Noises in SiC Inverter

The SiC inverter switching at high frequencies introduces increased common-mode (CM) and differential-mode (DM) electromagnetic interference (EMI) issues, such as shaft voltage, bearing currents, insulation degradation, and poor current quality in the motor. These EMI issues are commonly addressed with EMI filters employing CM and DM inductors. The increased volume and poor performance of a CM inductor designed for SiC inverter switching at high frequency require a modified EMI filter design procedure for enhanced performance and volume minimization. In this work, three EMI filters are presented with modified design procedures. A single-stage EMI filter is designed by incorporating a DM filter offering an equal attenuation to DM and CM noise at switching frequency. Here, the additional CM attenuation demand is fulfilled by a marginal value of the CM inductor, while, in multistage EMI filters, the required CM attenuation is split between the two stages. The multistage EMI filter 1 is designed using an additional CM inductor and existing load capacitance as the second stage, whereas the multistage EMI filter 2 is designed with a lesser value of CM inductance to provide CM attenuation over the entire conducted EMI frequency range. The modified EMI filters are tested on an SiC inverter operating at 200 kHz.

Design method of wide‐band high‐current air‐core inductor EMI filter for high voltage DC power of motor inverter of electric vehicle

Passive filters are often used for electromagnetic interference (EMI) suppression of high voltage (HV) DC power supplies of electric vehicle (EV) motor controllers. The high current of the DC bus saturates the differential mode (DM) magnetic ring, while the leakage inductance of common mode (CM) inductor used as the DM inductance is usually very small, resulting in almost no suppression of DM EMI. A design method of broadband high-current air-core inductor passive filter is proposed. By using the air-core inductor as DM inductor, the problem of easy saturation of the DM inductor core and the small leakage inductance of the CM inductor is solved, and improves the low frequency DM EMI suppression. Through the calculation and selection of the turning frequency point of the multi-stage filter circuit, the effective frequency band can be improved. By analysing the influence of parasitic parameters, the problem of insufficient insertion loss of the filter at high frequency is solved. The experimental verification shows that the proposed air-core inductor filter achieves 50 dB of CM and DM insertion loss in frequency range of 150 kHz–108 MHz, and meets the requirements of system conducted disturbance voltage specified in CISPR25-2016Rd level 3.

High-Attenuation Wideband Active Common-Mode EMI Filter Section

A high-attenuation wideband active common-mode filter (ACF) section is presented. Each section is composed of an active capacitor and a small common-mode (CM) inductor. The active capacitor is realized by using several coupling capacitors and a class-A bipolar-junction-transistor based amplifier for its low-cost, fast response, and good immunity to high voltage transients. The structure of the amplifier consists of a common-collector amplifier and a high-gain common-emitter amplifier with an active load. The working bandwidth of the ACF ranges from 150 kHz to 30 MHz. By cascading several ACF sections, a multistage structure that exhibits high filtering attenuation can be designed. The number of cascaded sections is optimized by considering the required filtering attenuation. The performance of single-stage and multistage ACFs is evaluated on two commercial power supplies with rated power of 90 and 1000 W, respectively. The CM noise of the power supplies with the proposed ACF and with the original passive filters is compared. The results show that the physical volume of the ACF is significantly smaller than that of the passive filter, and the power dissipation of the ACF is similar to that of the passive filter.

Bidirectional Nonisolated Fast Charger Integrated in the Electric Vehicle Traction Drivetrain

Integrated chargers, where the traction inverter is used as the primary charging interface, have emerged as a solution for reducing the cost and footprint of electric vehicle (EV) charging. This article proposes a bidirectional nonisolated integrated charger topology that also provides benefits to motor lifetime and reliability through a reduction in bearing currents and voltages. This is achieved by adding to an EV drive: an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter per phase with a common-mode (CM) voltage control; a CM inductor for additional leakage current filtering; contactors to switch between traction and charging modes; and a residual current device to satisfy standards for transformerless charging. To obtain high efficiency and make the filter small for traction applications, variable frequency critical soft switching is leveraged. Traction mode experimental validation demonstrates torque and speed steps with no degradation compared to a standard drive, a decrease in leakage currents and shaft voltages of more than 90%, and an increase in motor drive efficiency of 0.6% at 5-kW output power. Charging mode validation shows active and reactive power steps and peak efficiency of 99.4% and 98.4% at a rated power of 11 kW. Charging mode leakage current is measured to be 22 mA, which satisfies standards permitting the transformerless operation.

A Compact EMI Filter Design by Reducing the Common-Mode Inductance With Chaotic PWM Technique

Passive electromagnetic interference filters (PEFs) are the most common way to solve electromagnetic interference (EMI) problems in power converters. However, PEFs bring additional volume, weight, and cost for power converters, especially common-mode (CM) inductors in PEFs, and it is a tricky issue for the high-power-density converters that must meet the electromagnetic compatibility specification. In order to design compact PEFs for power converters with pulsewidth modulation (PWM), a volume reduction method of CM inductors with chaotic PWM (CPWM) is proposed in this article. First, the mechanism that CPWM reduces the CM inductance by increasing the corner frequency is analyzed. Second, the relationship between the reduction of EMI spectrum magnitude by CPWM and the decrease of the CM inductance is quantitatively calculated. Third, utilization rate of the magnetic core <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> is defined to reasonably compare the size of the different inductors under traditional PWM and CPWM. Finally, the proposed design method of CM EMI filters is applied into a dc–dc converter and a dc–ac inverter, respectively, to verify its effectiveness and feasibility. In a dc–dc converter with the switching frequency 100 kHz, 275 W, the volume of the CM inductor and the volume of CM EMI filters are reduced by 63.5% and 48.3%, respectively, by using the proposed compact EMI filter.

Experimental Investigation of the Dimensional Effect on Small-Signal Characteristics of Common-Mode Inductors

Due to their high permeability and high effective permittivity, manganese zinc (MnZn) ferrites exhibit magnetic resonance depending on the core dimension. Once magnetic resonance occurs, the relative permeability of MnZn ferrites decreases drastically in the high-frequency (HF) range. The decrease in the relative permeability can influence the HF noise reduction performance of common-mode inductors (CMIs). Based on the above, this study experimentally investigates the impact of the dimensional effect of MnZn ferrites on the small-signal characteristics of CMIs. First, the CM small-signal characteristics of CMIs with different core dimensions indicated that the dimensional effect of MnZn ferrites decreases the CM impedances of the CMIs in the HF range. Two types of core division (air gap insertion and core lamination) were applied to the core to mitigate the dimensional effect on the CM impedances of the CMIs. The influence of the core divisions on the complex permeabilities and the small-signal characteristics of the CMIs were evaluated based on the experimental results. The measurement results clarified that core lamination might be the appropriate option in EMI filtering applications because it can mitigate the dimensional effect and increase the CM impedance of CMIs in the HF range without increasing the number of turns.

Effect of Semiconductor Parasitic Capacitances on Ground Leakage Current in Three-Phase Current Source Inverters

This paper investigates the influence of power semiconductor parasitic components on the ground leakage current in the three-phase Current Source Inverter topology, in the literature called H7 or CSI7. This topology allows reducing converter conduction losses with respect to the classic CSI, but at the same time makes the topology more susceptible to the parasitic capacitances of the semiconductors devices. In the present work, a grid-connected converter for photovoltaic power systems is considered as a case study, to investigate the equivalent circuit for ground leakage current. The same analysis can be extended to applications regarding electric drives, since the HF model of electric machines is characterized by stray capacitance between windings and the stator slots/motor frame. Simulation results proved the correctness of the proposed simplified common-mode circuit and highlighted the need of an additional common-mode inductor filter in case of resonance frequencies of the common-mode circuit close to harmonics of the power converter switching frequency. Experimental results are in agreement with the theoretical analysis.