Common-mode Inductor Research Articles

Integrated common‐mode inductor design for parallel interleaved converters

Paralleling power converters can increase the power rating and reliability of the overall system. Interleaving the carrier in parallel converters helps in reduction of output current distortion, and in reduction of electromagnetic interference noise. This study presents a common-mode inductor design for parallel interleaved converters, which integrates the inter-phase and boost inductors together in a novel structure. It is shown that the proposed magnetic structure accommodates a wider range of desirable electromagnetic parameters. Step-by-step design procedure of the proposed integrated common-mode inductor (ICMI) is presented. The proposed ICMI design results in fewer components, reduces the size and the cost of overall system. The proposed ICMI is compared with a design available in literature using an example. Existing design procedure imposes constraints on the core geometry that are not suitable for high-power designs. The proposed design makes use of standard C cores that improves manufacturability. Experimental results from a 7.5 kVA parallel single-phase power converter show the effectiveness of the proposed ICMI.

Common-Mode Filter Design for a Transformerless ZVS Full-Bridge Inverter

The zero voltage switching (ZVS) full-bridge inverter can achieve high efficiency using ZVS sinusoidal pulsewidth modulation (ZVS SPWM) and superjunction MOSFET. For further application in a photovoltaic (PV) system, the leakage current problem of a ZVS full-bridge inverter is investigated. First, the common-mode model of the ZVS full-bridge inverter is presented. The common-mode voltage with the ZVS SPWM is found changing with high frequency and leakage current with such frequency is generated. In order to suppress the leakage current below safety standards, the common-mode filter composed of common-mode inductor and bypass capacitor is applied. The impedance of the common-mode path is analyzed, and the parameters of a common-mode filter are designed based on the common-mode model. With a small common-mode inductor and bypass capacitors, the leakage current of the ZVS full-bridge inverter is remarkably reduced, and the method is verified by the experiment.

A State Machine Decoder for Phase Disposition Pulsewidth Modulation of Three-Phase Coupled-Inductor Semi-Bridge Converters

Coupled-inductor semi-bridge converters, assembled from magnetically linked pairs of complementary unidirectional phase legs, can achieve a substantially improved harmonic output voltage performance with the same number of silicon devices as traditional converters. However, they must be operated so as to ensure that a continuous common-mode current always flows through each coupled inductor, to ensure each phase leg can always produce the required switched output voltage. This is particularly challenging for a three-phase coupled-inductor bridge controlled by phase disposition (PD) modulation, since there is no direct correlation between the modulator output and the individual phase leg switching device commands. This paper presents a novel strategy to control each phase leg’s common-mode inductor current under PD modulation, by introducing a square wave offset signal into the modulator reference command, and feeding the modulator output through a postprocessing state machine to correctly switch each semi-bridge phase leg to maintain the required dc common-mode current. The strategy has been verified by detailed simulation studies and matching experimental results.

A Common Mode Inductor With External Magnetic Field Immunity, Low-Magnetic Field Emission, and High-Differential Mode Inductance

This paper proposes a stacked common-mode (CM) inductor for electromagnetic interference (EMI) attenuation. The proposed stacked CM inductor consists of two CM inductors with identical cores and the same number of winding turns but with opposite winding directions. The proposed stacked CM inductor has three advantages. First, it is much less susceptible to external magnetic field interference than conventional CM inductors. This suppresses the EMI due to the near-magnetic-field coupling to the CM inductor. Second, the proposed winding structure effectively increases the leakage inductance of the CM inductor, which enhances its ability to suppress differential-mode (DM) noise. Third, the magnetic field generated by the DM current in the stacked CM inductor is partially canceled outside of the inductor. As a result, the stacked CM inductor has lower magnetic field emission than that of a conventional CM inductor. Simulation and experimental results validate the advantages of the proposed CM inductor, which show the proposed technique greatly improves the performance of CM inductors.

New Optimal Pulsewidth Modulation for Single DC-Link Dual-Inverter Fed Open-End Stator Winding Induction Motor Drive

The multilevel topology with dual inverters feeding both ends of an open-end stator winding of an induction motor has been introduced around two decades ago. A common-mode inductor is usually required in series with motor windings to suppress zero-sequence or common-mode currents. In case of medium voltage high-power drives, low device switching frequency operation is preferred to improve the overall system efficiency. However, it increases the harmonic distortion of machine stator currents. Therefore, the goal of our study is to propose new optimal pulse width modulation to achieve: low device switching frequency, minimal harmonic distortion of machine stator currents, and elimination of zero-sequence currents. The main idea is to select the switching angles of two inverters such that zero-sequence components are eliminated and, then, perform optimization to determine switching angles that minimize the harmonic distortion of machine stator currents. The experimental results obtained from dual two-level and dual three-level inverter fed 1.5-kW open-end stator winding IM drive demonstrated the effectiveness of a proposed modulation technique.

A Magnetic Structure Integrating Differential-Mode and Common-Mode Inductors with Improved Tolerance to DC Saturation

A Magnetic Structure Integrating Differential-Mode and Common-Mode Inductors with Improved Tolerance to DC Saturation

Improving High-Frequency Performance of an Input Common Mode EMI Filter Using an Impedance-Mismatching Filter

This letter investigates into the impedance interaction between the electromagnetic interference (EMI) filter and the noise propagation path, and its influences on the filter design. It proves that the impedance resonance in the propagation path decreases the filter's high-frequency in-circuit attenuation. This letter proposes a method to improve the filter's high-frequency performance using an impedance-mismatching filter. The impedance-mismatching filter damps the resonance in the common mode (CM) noise propagation path and eliminates the high-frequency noise spike. By applying this method in the filter design, the CM inductor of the EMI filter can be significantly reduced since the EMI filter avoids the overdesign caused by its high-frequency performance degradation, and the filter can potentially achieve high power density. This letter also proposed a design procedure for this impedance-mismatching filter. An improved EMI filter design method considering this impedance mismatching is also proposed in this letter.

Techniques for Improving the High-Frequency Performance of the Planar CM EMI Filter

This paper has developed two techniques to reduce the parasitic parameters and improve the high-frequency performance of the planar integrated electromagnetic interference (EMI) filter. First, each developed technique has been analyzed, respectively, then the performance of an EMI filter with both the developed techniques has been researched. The research contents are as follows. 1) Analyzing the improvement of the equivalent parallel capacitance (EPC) for a common mode (CM) EMI filter by two CM windings overlapped and interleaved layout. The EPC of the integrated EMI filter is about 14% of the reference EMI filter. 2) Analyzing the improvement of the equivalent series inductance (ESL) in the parallel branch for a CM EMI filter by each CM winding coupled with two ground winding layers. The resonance frequency brought by ESL is shifted to a higher frequency. At 30 MHz, the insertion loss is increased by 45 dB compared with the reference. In the mean time, the structure is equivalent to a two-stage L-type low-pass filter, which can largely increase the high-frequency attenuation compared with the one-stage L-type low-pass filter for the reference one. (3) Researching the performance of an EMI filter with both the proposed techniques. The developed EMI filter can not only decrease the EPC, but also reduce the negative effect of ESL. The developed EMI filter improves the high-frequency performance dramatically compared with the EMI filter with only one of the developed techniques. In the mean time, the differential mode (DM) capacitor is formed by the two overlapped and interleaved windings, and does not need an extra lumped DM capacitor. Therefore, CM inductors, CM capacitors, and DM capacitors can be integrated in the overlapped and interleaved L-C winding structure, so miniaturized EMI filter can be realized. The experiment results indicate effectiveness of the developed integrated EMI filters, and the cost and complexity is the same as the reference EMI filter.

Modelling and control of a multi‐stage interleaved DC–DC converter with coupled inductors for super‐capacitor energy storage system

Interleaved converters with coupled inductors are widely used to share load current in high power applications. It offers high equivalent switching frequency and reduced output current ripples using small size magnetic components. Owing to smaller common-mode inductance, control system can be designed to achieve fast dynamic response. This study proposes eight-channel interleaved DC/DC converter for interfacing super-capacitor energy storage system to a 400 V DC voltage bus. Multi-stage interleaving magnetic circuit with two-phase coupling inductor as a building block is proposed. A methodology is developed to construct the model of the multi-stage magnetic circuit from the basic two-phase coupled inductor model. The derived model is successfully used to evaluate the system power losses and to design the magnetic circuit parameters and its current controller to fulfil the DC/DC converter steady state and dynamic performance specifications. A 20 kW/four stage/8-channel DC/DC converter laboratory prototype has been built to connect a super-capacitor stack to 400 V DC voltage bus. Experimental investigation validates the modelling, the system losses calculations and the design specifications of the system.

Far Field Extrapolation from Near Field Interactions and Shielding Influence Investigations Based on a FE-PEEC Coupling Method

Regarding standards, it is well established that common mode currents are the main source of far field emitted by variable frequency drive (VFD)-cable-motor associations. These currents are generated by the combination of floating potentials with stray capacitances between these floating potential tracks and the mechanical parts connected to the earth (the heatsink or cables are usual examples). Nowadays, due to frequency and power increases, the systematic compliance to EMC (ElectroMagnetic Compatibility) becomes increasingly difficult and costly for industrials. As a consequence, there is a well-identified need to investigate practical and low cost solutions to reduce the radiated fields of VFD-cable-motor associations. A well-adapted solution is the shielding of wound components well known as the major source of near magnetic field. However, this solution is not convenient, it is expensive and may not be efficient regarding far field reduction. Optimizing the components placement could be a better and cheaper solution. As a consequence, dedicated tools have to be developed to efficiently investigate not easy comprehendible phenomena and finally to control EMC disturbances using component placement, layout geometry, shielding design if needed. However, none of the modeling methods usually used in industry complies with large frequency range and far field models including magnetic materials, multilayer PCBs, and shielding. The contribution of this paper is to show that alternatives regarding modeling solutions exist and can be used to get in-deep analysis of such complex structures. It is shown in this paper that near field investigations can give information on far field behavior. It is illustrated by an investigation of near field interactions and shielding influence using a FE-PEEC hybrid method. The test case combining a common mode filter with the floating potentials tracks of an inverter is based on an industrial and commercialized VFD. The near field interactions between the common mode inductance and the tracks with floating potentials are revealed. Then, the influence of the common mode inductance shielding is analyzed.

Nanocrystalline Core Material for High-Performance Common Mode Inductors

Modern power electronic semiconductors are switching very fast to reduce heat dissipation. Due to parasitic capacitances in the system, for instance, in a motor driven by an adjustable speed electrical power drive system, common mode currents are developed creating electromagnetic interference. The high common-mode current can saturate the core of conventional common mode inductors. Nanocrystalline material shows excellent properties, with high saturation, and high permeability in a broad frequency range. This combination makes them more suitable for common mode inductors than laminated or powder iron, and ferrites. Nanocrystalline material properties are discussed and compared with conventional materials. Common mode inductors for power drives systems have been designed and electromagnetic interference tests have been carried out.

An Integrated AC Choke Design for Common-Mode Current Suppression in Neutral-Connected Power Converter Systems

This paper presents an integrated ac choke that incorporates the common-mode (CM) suppression function into a three-phase differential-mode (DM) inductor. The proposed choke, together with other filter components, provides a transformerless solution to issues caused by the switching CM voltage in neutral-connected power converter systems. The required high CM-to-DM inductance ratio is generated by different magnetic paths in the novel structure. An approach based on magnetic circuit calculation can be applied to the weight-minimized design in which a reasonably small core loss confirms the choke's heat dissipation capability. The existence and uniqueness of the optimization are proven by a design example and analysis. Comparison to separate DM and CM inductors demonstrates the benefits of integration: the iron and copper material savings, the volume and weight reduction, and overall system efficiency improvement. The finite element method is used to tune the design parameters with which a prototype is implemented. The simulation and experimental results of the prototype in a voltage source converter verify the feasibility and effectiveness of the integrated choke.

The Three-Phase Common-Mode Inductor: Modeling and Design Issues

This paper presents a comprehensive physical characterization and modeling of the three-phase common-mode (CM) inductors along with the equivalent circuits that are relevant for their design. Modeling issues that are treated sparsely in previous literature are explained in this paper, and novel insightful aspects are presented. The calculation of the leakage inductance is reviewed, along with the magnetic core saturation issues, and a new expression for the leakage flux path is derived. The influence of the core material characteristics on the performance of the component is discussed, and a new method for the selection of the material for the minimized volume CM inductors is proposed in order to simplify the design procedure. Experimental results which validate the model are presented.

A High-Performance PWM Algorithm for Common-Mode Voltage Reduction in Three-Phase Voltage Source Inverters

A high-performance pulsewidth modulation (PWM) algorithm with reduced common-mode voltage (CMV) and satisfactory overall performance is proposed for three-phase PWM inverter drives. The algorithm combines the near-state PWM (NSPWM) method that has superior overall performance characteristics at high modulation index, and MAZSPWM, a modified form of the active zero-state PWM method (AZSPWM1), which is suitable for low modulation index range of operation. Since AZSPWM1 has line-to-line voltage pulse reversals with small zero-voltage time intervals, in its naive form, it causes overvoltages, in particular in long-cable motor drive applications. Obtained by reorganizing the duty cycles of the utilized voltage vectors of AZSPWM1, MAZSPWM has sufficiently long zero-voltage time intervals between pulse reversals such that during pulse reversals, overvoltages are avoided. The combined algorithm performs satisfactorily throughout the inverter operating range and the transition from NSPWM to MAZSPWM and vice versa is seamless. The performance of the proposed algorithm is proven by theory, computer simulations, and detailed laboratory experiments. The paper also shows that the proposed reduced CMV PWM algorithm is effective in reducing the motor leakage current, and it is most beneficial when a small common-mode inductor is included in the drive.

A Novel Hybrid Common-Mode EMI Filter With Active Impedance Multiplication

This paper presents a novel hybrid common-mode (CM) electromagnetic interference filter for a military power supply. The proposed filter is composed of an active impedance multiplication circuit cascaded with a benchmark CM inductor. The active impedance multiplication circuit is very effective in boosting the impedances of both the benchmark CM inductor and the noise source. Thus, the total equivalent impedance of the filter is enlarged by the active booster to a great extent. An important advantage of the approach is that only a small-size CM choke is used as the passive filter instead of a traditional CLC filter. Furthermore, the noise source is turned to be an inevitable part of the hybrid filter by the impedance multiplication effect. Experimental results were carried out according to MIL-STD-461. It is shown that the proposed approach can acquire good noise attenuation performance within a wide frequency range.

一种脉冲高电压测量探头的地电位隔离方法

一种脉冲高电压测量探头的地电位隔离方法

Passive and Active Hybrid Integrated EMI Filters

Two new planar integrated electromagnetic interference (EMI) filter structures that reduce the filter volume and that are based on standard printed circuit board (PCB) process technology are presented in this paper. First, a passive integrated EMI filter is presented, which results in a volume reduction of 24% compared to the discrete solution. However, this filter requires a planar ferrite core for the common-mode inductor. In order to eliminate the ferrite core and reduce the filter volume further (-40% versus discrete filter), a passive integrated structure is combined with an active EMI filtering circuit. The transfer function, the volume, and the losses of the discrete and the two integrated filters, which are designed for a 600 W power-factor-corrected converter, are compared.

Design of Inductor Winding Capacitance Cancellation for EMI Suppression

In this paper, the parasitics in both differential-mode (DM) and common-mode (CM) inductors are first discussed. The methods for both DM and CM inductor winding capacitance cancellation are then proposed. Prototypes are designed and tested, using a network analyzer. Finally, the prototypes are applied to practical power converters and electromagnetic interference (EMI) is measured. Both small signal measurement and practical EMI measurement prove that the proposed methods can efficiently reduce the effects of winding capacitance and therefore improve the inductor's filtering performance

Reduction of Conducted EMI on Parallel Operation for AC Module Inverters

An AC photovoltaic module system is recognized as a novel photovoltaic power generating system. However, serious EMI troubles caused by the photovoltaic inverters are suspected, because many inverters operate simultaneously. This paper discusses common-mode conducted EMI and its a reduction method of parallel operation of grid connectable inverters. In the case of parallel operation of inverters, the characteristic impedance of the series resonant circuit in a common-mode equivalent circuit decreases and it increases a noise voltage on grid lines. When a common-mode inductor is connected in series to the total output line, the reduction effect of common-mode noise is larger compared to when individual inductors are connected to each inverter output.

An Approach to Eliminating High-Frequency Shaft Voltage and Ground Leakage Current From an Inverter-Driven Motor

This paper proposes a small-sized passive electromagnetic interference (EMI) filter for the purpose of eliminating high-frequency shaft voltage and ground leakage current from an ac motor driven by a voltage-source pulsewidth-modulation inverter. The filter requires access to the neutral point of the motor. A common-mode inductor is connected between the inverter and the motor. The neutral point of the motor is connected to the dc-bus midpoint via a resistor. The dc-bus midpoint is created by using two capacitors in series across the dc positive and negative buses. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. The validity and effectiveness of the EMI filter is verified by experimental results obtained from a 5-kVA laboratory system.