Differential Mode Noise Research Articles

A Survey of Active EMI Filters for Conducted EMI Noise Reduction in Power Electronic Converters

Wide bandgap devices enable high power density power converters. Despite the advantages of increased switching frequency, the passive components are still a major bottleneck toward enabling high power density. Among the passive components in the converter, the passive electromagnetic interference (EMI) filters are unavoidable to ensure compliance with conducted EMI standards. Active EMI filters (AEFs) help reduce the volume of the passive components and have been around for three decades now. The design and implementation of the AEFs depend upon the type of noise (common-mode or differential-mode) and power converter (ac–dc, dc–dc or inverter). This article presents a comprehensive survey of different AEFs and their implementations for different power converters presented in the literature. A comprehensive survey of noise-sensing, noise-processing, and noise-cancellation circuits is presented. Also, a comparison of attenuation provided by the AEFs for common-mode and differential-mode noises for different converters is carried out. Furthermore, other facets of AEFs such as the auxiliary power supply, power loss, and protection methods for the AEF are also summarized. This article is intended to be a useful reference for power converter designers in both industry and academia.

Analysis and Reduction of the Near Magnetic Field Emission From Toroidal Inductors

The near magnetic field emitted from magnetic components may generate electromagnetic interference (EMI) and degrade EMI filter's performance. This article discussed the near magnetic field emission from toroidal inductors. The emission mechanisms are analyzed for different inductor winding structures with either common-mode (CM) or differential-mode (DM) excitation. The winding structures with low near magnetic field emission are identified. A CM inductor structure is proposed to improve inductor's high-frequency CM performance and greatly reduce its near magnetic field emission due to DM currents. The improvements are achieved with a small extra toroid. The proposed structure can also increase CM inductor's DM inductance for DM noise reduction at the expense of a reduced DM saturation current. To avoid saturation, a design procedure is developed for the proposed CM inductor to achieve desired CM inductance, minimized near magnetic field emission, high DM inductance, and optimal magnetic flux density. Three-dimensional (3-D) finite-element analysis models were developed and experiments were conducted to validate the developed theory and techniques. EMI measurement results show that the proposed CM inductor has a better performance for both DM and CM noise reduction than a conventional CM inductor.

Constant Switching Frequency Control for CRM Buck PFC Converter

Critical conduction mode (CRM) buck power factor correction (PFC) is widely used in low-power applications because of its several advantages. However, the switching frequency is dependent on the electrical angle of the input voltage, and the variation range of the switching frequency is large, especially at high input voltages. This makes the conducted electromagnetic interference (EMI) spectra appearing great differences and complicates the design of the EMI filter. For this issue, a novel constant frequency control scheme is proposed by varying the on-time of the switch. Compared with the original control, the proposed method realizes a constant switching frequency operation in a line cycle. Consequently, the design of the power devices especially the magnetic components can be simplified. Meanwhile, a higher efficiency and a lower output voltage ripple are achieved. The proposed strategy also yields a higher PF at low input voltages and a lower PF at high input voltages. A 120-W prototype with 90–264-VAC input and 90-V output is built in the lab. The experimental waveforms of input voltage, input current, inductor current, and output voltage ripple, the measured input current harmonic contents, the PF and efficiency curves regarding the input voltage, and the common-mode (CM) and differential-mode (DM) noises’ spectra of the converter are presented to show the validity of the proposed scheme.

Contactless direct torque measurement system for a single cylinder engine transient test cell

This paper describes the design and implementation of a low cost, contacless, reliable and sensitive direct torque measurement system applied to small single cylinder engine transient test cell. The experimental set-up consists of a three-phase induction machine, used as a transient a.c. dynamometer, and non-regenerative frequency inverter connected to an internal combustion engine. Coupling the engine to the dynamometer is by a low stiffness PA-6 nylon shaft with magnetic pickups at its ends. The sensors phase are zero when torque in PA-6 nylon shaft is null, adjusted in static conditions and engine/dynamometer turned off. Contactless torque measurement occurs by magnetic pickup phase difference during PA-6 nylon shaft torsion promoted by engine in operation. Engine speed is measurement by frequency of magnetic pickup signal. PA-6 nylon shaft torsion promotes a misalignment between sensors phase, proportional to torque application in both direction.The electronic capture unit using pulse train rising edge detection measures this phase change (time shift) in pulses. An embedded microcontroller development kit acquires the time-shifted pulses. This board has circuits for A/D signal conditioning, pulse width modulate channels, and a specific circuit for magnetic pickups signals conditioning, which can measure less then 0.09 Nm resolution, taking 96 time-shifts values. The design and implementation of all embedded electronics and data acquisition system follows electromagnetic compatibility premises, which have resulted in an adequate signal-to-noise ratio so that common and differential mode noises have not edges with amplitude approximately equal to the output magnetic sensors signals. The maximum measurement uncertainty associated with the contacless direct torque measurement system were calculated at ±0.54% to 99% confidence interval.The performance is presented under different load conditions, defined by engine throttle position and the results are compared with the engine datasheet performance curves.

Novel Measurement Procedure for Switched-Mode Power Supply Modal Impedances

The measurement of modal impedances of switching-mode power supplies (SMPSs) is of paramount importance in electromagnetic compatibility applications, especially when designing electromagnetic interference filters to suppress the conducted and radiated electromagnetic emissions is the target. A novel measurement technique that makes use of an impedance analyzer and a coupling transformer and allows extracting the complex value of common- and differential-mode noise source impedance of an SMPS is proposed. The measurement procedure is first studied from the theoretical point of view, then experimentally validated with passive components, and eventually implemented in a CISPR-25 conducted emission test setup to measure the magnitude and phase of modal impedances of an automotive SMPS under different operation conditions.

Smart Shielding Techniques for Common Mode Chokes in EMI Filters

This work analyzes the effect of conducting bands placed close to a common mode choke on the attenuation provided by an electromagnetic interference filter where the common mode choke is mounted. The main aim was to determine whether the response of the common mode choke can be modified and to clearly identify and quantify the physical mechanism responsible for the changes found in the attenuation of the common mode choke and the electromagnetic interference filter. The impact of grounded and ungrounded conducting surfaces was studied for the two more typical configurations of common mode chokes: vertically and horizontally mounted. This study has allowed us to devise an optimum shield for a common mode choke that can significantly improve the attenuation to both common mode and differential mode noise of an electromagnetic interference filter at high frequencies, where parasitic effects usually undermine the performance of the filter. Key features of the technique described here are that it can be applied easily and that it does not result in an increase of the weight, volume, or cost of the filter.

Modeling and Experimental Assessment of the EMI Characteristics of Switching Converters With Power Semiconductor Filters

An input filtering technology named “power semiconductor filter (PSF)” has been proposed recently. Its operating principle is based on using a series pass device (SPD) to profile the wave shape and magnitude of the input current of converters. The voltage across the SPD is regulated around the “knee point” of the current–voltage characteristic of the SPD to minimize the power dissipation of the SPD. This paper reports the conducted electromagnetic interference (EMI) performance of the converters with the PSF. To suppress differential-mode (DM) EMI, a fast current regulation circuit is proposed to tightly regulate the current through the SPD. To suppress common-mode (CM) EMI, a single CM noise bypass capacitor is proposed. Detailed mathematical models for describing the frequency response of the SPD and main components in the driving network are formulated. A set of selection guidelines for the components will be given. The derived models will be validated by comparing the theoretical prediction with the measurement results of a 100 W, 90–264 Vac LED driver using a buck–boost converter. Results reveal that the PSF reduces the DM noise level by 47.47 dBμV. The CM noise level is reduced by 21.4 dBμV with the bypass capacitor. An integrated circuit for the controller is illustrated to demonstrate the feasibility of reducing the form factor of the filtering section.

Time Domain Analysis of Transmission Failure on CAN System due to Differential-Mode Noise Emitted from a Buck Converter

Time Domain Analysis of Transmission Failure on CAN System due to Differential-Mode Noise Emitted from a Buck Converter

Extraction of Equivalent Noise Source Model From Photovoltaic Systems

Photovoltaic (PV) systems have become popular as one of the renewable energy sources in recent years. With increasing number of PV systems, potential electromagnetic interference (EMI) issues from the PV systems cannot be ignored. In order to evaluate the EMI potential of a PV system, an in-circuit measurement method to extract its equivalent common-mode and differential-mode noise source models is described and validated. These noise source models serve as black boxes for further EMI analyses.

Three-Phase EMI Filter Designs for Three-Phase Induction Motor Drives

In this paper, a three-phase EMI filter design procedure for a three-phase inductor motor drive system is proposed. With the proposed design procedure, an unnecessary differential-mode (DM) choke can be eliminated. In order to verify the effectiveness of the proposed approach, three-phase EMI filters have been designed using the proposed design procedure and other well-known procedures. The total noise, the common-mode (CM) noise and the DM noise have been measured and compared. From the experimental result, it can be concluded that with the proposed design procedure comparing with other approaches, an unnecessary DM choke can be eliminated, and the size of the used X-capacitor can be minimized. Thus, with the proposed method, fewer filter components and lower the cost of designed three-phase EMI filters are achieved.

Common mode electronic noise in differential circuits

Differential circuits are assumed to reject common-mode noise yet no parameter is available to describe that rejection as the Common Mode Rejection Ratio (CMRR) applies only to deterministic signals, not to random noise. We propose a model and a method to analyze the contribution of the input common-mode electronic noise to the output voltage noise of differential circuits. The analysis shows that the same parameter-matching conditions that improve the CMRR determine common-mode noise rejection but CMRR is more sensitive to mismatching. For example, a low-frequency CMRR as low as 8 dB implies that more than 82% of common-mode noise is rejected. Thus, often only differential-mode noise is relevant. However, if the equivalent input current noise sources predominate over equivalent input voltage noise sources, cross-correlation between them partially yields common-mode noise that will also be rejected. We also propose a simple test that yields an estimate of that correlation.

Differential Mode Active EMI Filter Design for a Boost Power Factor Correction AC/DC Converter

The objective of this paper is to introduce a methodology to design an active differential mode (DM) filter at the input side of ac/dc converters to cancel DM electromagnetic interference noise within concerned frequency range. The boost power factor correction ac/dc converter was taken as an example for DM active filter design. The active filter is analyzed based on the developed DM noise model. The design of DM active filter to achieve desired insertion gain and stability is addressed in detail. Both simulations and experiments were conducted to validate the proposed methodology. It is found that the proposed design methodology can meet the design objective and the stability challenge for the DM active filter of ac/dc converters.

EMI filter design of single-phase SiC MOSFET inverter with extracted noise source impedance

This paper presents an electromagnetic interference (EMI) filter design procedure for a single-phase SiC MOSFET inverter. To ensure the EMI filter performance is both accurate and effective, the equivalent noise source impedances of common mode (CM) and differential mode (DM) noise models are extracted. Then the CM and DM EMI filters can be designed based on the known CM and DM noise source impedances, respectively. The EMI filter design based on the proposed method is validated both through simulation and experiments. The simulation and experiment results have verified the effectiveness of the proposed method.

Reliability of Boost PFC Converters with Improved EMI Filters

The switching device in a power converter can produce very serious electromagnetic interference (EMI). In order to solve this problem and the associated reliability and stability issues, this article aimed to analyze and model the boost power factor correction (PFC) converter according to the EMI conduction path. The sources of common-mode (CM) and differential-mode (DM) noise of the boost PFC converter were analyzed, and the DM and CM equivalent circuits were deduced. Furthermore, high-frequency modeling of the common-mode inductor was developed using a precise model, and the EMI filter was designed. According to the Class B standard for EMI testing, it is better to restrain the EMI noise in the frequency range (150 kHz to 30 MHz) of the EMI conducted disturbance test. Using this method, a 2.4-kW PFC motor driving supply was designed, and the experimental results validate the analysis.

A 1–2-MHz 150–400-V GaN-Based Isolated DC–DC Bus Converter With Monolithic Slope-Sensing ZVS Detection

This paper presents a wide-range high-voltage (HV) isolated phase-shifted full-bridge dc–dc bus converter with eGaN power FETs driven by an integrated synchronous CMOS gate driver. The monolithic slope-sensing zero-voltage switching detector (SS-ZVSD) is developed to automatically provide adaptive deadtime control with near-constant short turn-on delay for enabling ZVS of synchronous power transistors during switching transitions under different input voltages and load currents. This not only minimizes the switching loss and the reverse conduction loss but also supports high-frequency operation, leading to high-frequency high-efficiency converters. A HV-level shifter with differential-mode noise blanking scheme is also proposed in the gate driver to enhance the converter reliability in high input voltages. To verify the performances of the isolated converter using 650-V eGaN power FETs, the gate drivers were implemented in a 1.45- $\mu \text{m}$ 700-V BCD process. The converter supports the input voltage from 150 to 400 V and delivers a maximum output power of 250 W. The proposed SS-ZVSD achieves adaptive deadtime with about 13-ns turn-on delay over wide ranges of the input voltage and load current, thereby enabling the converter running up to 2 MHz with 1.6-W power saving. The proposed converter operates 14 $\times $ faster than the prior art with comparable power efficiency.

Reduction of conducted electromagnetic interference by using filters

Electromagnetic interference (EMI) is described as the unwanted noise created by electromagnetic (EM) waves. EMI is divided into two forms, that is, conducted and radiated. There exists Common mode (CM) and differential mode (DM) noise in the conducted EMI. Hence, All the electronic wireless equipment must provide the EMI filters (EMIF) to filter the CM and DM noise components within the circuits. In this paper, an inductor filter, choke filter (IF and CF) and Pi-Filter (PF) are designed to eliminate conducted EMI. This system is named as EMIF-CM-DM (i.e., EMI filter for avoiding the common mode and differential mode noise). The IF and CF has low ripple factor at heavy load currents and very good load regulation, respectively. Pi-Filter also gives low ripple factor and high output voltage. This EMIF-CM-DM system improved the CM and DM noise voltages and insertion loss (IL).

Development of a Measurement Apparatus for Conducted Electromagnetic Emissions

Due to the intensive dissemination of high frequency electrical and electronic systems nowadays, several issues regarding electromagnetic interference (EMI) are more and more observed in our environment. This continuous growing of EMI everywhere, can leads to a malfunction of the more susceptible electrical products and systems. In order to face this problem, one has to take into account the various aspects of electromagnetic compatibility during the design phase of electrical and electronic systems. Among the tools that can be used for this purpose, there is the impedance stabilization network (LISN) and the noise separator device. With such tools, it is possible to carry out a series of EMI measurements in the prototype phase of the product, avoiding a fail in the final test of conducted electromagnetic emissions. This paper describes the development of a low-cost LISN with support for a noise separator device, which can provide valuable information regarding common-mode and differential-mode electromagnetic noise, allowing to solve more easily EMI issues on a product or system.

A new ellipse fitting method of the minimum differential-mode noise in the atom interference gravimeter**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFC0601602) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2017FZA3005 and 2018FZA3005).

Ellipse fitting is a useful tool to obtain the differential signal of two atom interference gravimeters. The quality standard of ellipse fitting should be the deviation between the true phase and the fitting phase of the interference fringe. In this paper, we present a new algorithm to fit the ellipse. The algorithm is to minimize the differential noise of two interference gravimeters and obtain a more accurate value of the gravity gradient. We have theoretically derived the expression of the differential-mode noise and implemented the ellipse fitting in the program. This new algorithm is also compared with the classical methods.

An Active EMI Choke for Both Common- and Differential-Mode Noise Suppression

In this paper, an active electromagnetic interference (EMI) choke for both common-mode (CM) and differential-mode (DM) noise suppression is proposed. Three isolated windings with a different number of turns are wound on the same magnetic core. One of the windings is served as the auxiliary winding connecting to an active circuit called the negative impedance circuit. The inductance of the EMI choke is substantially boosted up to effectively attenuate the low-frequency noise. This technique leads to a greater inductance but fewer turns and smaller size of the EMI choke. Different from the design of a conventional EMI filter, which uses separated CM and DM chokes, this proposal saves the cost and space of the EMI filter. The enhancement to the CM and DM impedance is individually analyzed and experimentally confirmed. Based on the classical CM and DM noise models, CM and DM noise insertion losses are predicted using computer simulation. The simulation results are validated by a network impedance analyzer. Finally, conducted EMI tests are carried out to verify the effectiveness of the proposed technique.

EMI Noise Separation Method for Three-Phase WBG Inverters With Low Sensitivity to Parasitic Parameters

Accurate measurement of common mode (CM) and differential mode (DM) noise is crucial for electromagnetic interference filter design. With the application of wide bandgap devices, the measurement results require higher accuracy at high frequency. This letter proposes a novel CM and DM noise separation method where a 20 dB attenuator is integrated to allow the measured results less sensitive to the parasitic parameters in the 150 kHz-30 MHz frequency range. The proposed method improves the flatness of the noise separator in the 150 kHz-30 MHz frequency range, which is 0.3 dB for common mode transmission ratio and 0.6 dB for differential mode transmission ratio. Simulation and experimental results are provided to validate the effectiveness of the proposed method.