Differential Mode Interference Research Articles

An EMI filter design method based on improved Foster network model for Boost PFC converter

In this paper, the problem of conducted electromagnetic interference in Boost PFC converters is studied, through the analysis of its common-mode and differential-mode interference conduction paths in Boost PFC converters with or without the balanced capacitor, the causes and suppression methods of mixed-mode conducted electromagnetic interference in Boost PFC converters are studied. The core material frequency parameter characteristics and winding parasitic capacitors are added to analysis to build more accurate models, the non-linear parameter characteristics of choke impedance and the disadvantage of traditional Foster network model are researched. Moreover, this paper proposed a series model based on improved Foster network, and design an EMI filter based on proposed improved Foster network with the optimized high-frequency characteristics. Experiments were carried out using a prototype of a built Boost PFC converter. The results show that after the EMI filter with proposed designed method was added to the circuit, the prototype under test can successfully pass the corresponding EMI test. It indicates the effectiveness of the proposed method.

Analysis Methodology for Differential Mode Interference in Energy Supply System of Hybrid DC Breaker

High di/dt during the close-open operation process of hybrid dc breaker will cause differential mode interference (DMI) in the energy supply system of the breaker's driver units due to their inductive coupling. The generated DMI may lead to false action of the breaker, which is an important issue that should be carefully considered in design stage. A method to analyze DMI based on time-domain wideband circuit simulations is proposed in this article. First, a time-domain waveform expression of DMI voltage source is derived, and then wideband equivalent circuit models of major components in the energy supply system are established. Furthermore, a standardized design methodology to reduce DMI is suggested. Applying the method to a high-frequency energy supply system of a ±200 kV hybrid dc breaker, simulation results show that the DMI level for two DMI mitigation measures is reduced by about 90% and 80% of the initial value, respectively.

A Fast and Precise Method for Modeling EMI Source in Two-Level Three-Phase Converter

Currently, frequency-domain electromagnetic interference (EMI) modeling has become the most commonly used method for EMI prediction and filter design. However, because of the unpredictability of the ringing effect in the present frequency-domain EMI modeling methods, the precision of the predicted EMI interference source is notably limited, which results in the inaccuracy of the system level EMI prediction. In order to achieve an accurate EMI prediction, this study presents a systematical study on the interference source of a 10 kVA three-phase bridge converter. The precise mathematical models of the common-mode and differential-mode interference source are constructed. Then, the characteristics of the multiple ringing effect, which is an important part of the interference source, are intensively analyzed. Based on the investigation of interference source, an improved interference source synthesis method is proposed. It can quickly and precisely predict the CM and DM interference source with multiple ringing effect, which can be used to achieve accurate frequency domain EMI prediction. Moreover, the multiple ringing effect is extended for IGBT parasitic parameter measuring. Instead of complicated device-level measurement, the grounding capacitance and junction capacitance can be effectively extracted through the ringing frequency measurement.

Electromagnetic interference filter for spacecraft power bus

The paper considers the protection of radio-electronic equipment against common and differential mode interference by means of a filter based on lumped elements. The authors have developed a schematic diagram of the filter to be used in power supply circuits of a spacecraft, and present and compare the results of circuit simulation and experiment. The results are useful for further development of noise protection devices for the spacecraft power bus.

Common-mode noise cancellation circuit for wearable ECG.

Wearable electrocardiogram (ECG) is attracting much attention for monitoring heart diseases in healthcare and medical applications. However, an imbalance usually exists between the contact resistances of sensing electrodes, so that a common mode noise caused by external electromagnetic field can be converted into the ECG detection circuit as a differential mode interference voltage. In this study, after explaining the mechanism of how the common mode noise is converted to a differential mode interference voltage, the authors propose a circuit with cadmium sulphide photo-resistors for cancelling the imbalance between the contact resistances and confirm its validity by simulation experiment. As a result, the authors found that the interference voltage generated at the wearable ECG can be effectively reduced to a sufficient small level.

Research on Differential-Mode Conducted EMI of Three-Phase PWM Rectifier AC Side

Taking three phase PWM rectifier as the research object, according to interference mechanism of the rectifier bridge, this paper describes the equivalent circuit of AC side differential mode interference and calculates the interference source voltage and differential mode interference voltage of the three phase PWM rectifier AC side in 150KHz-30MHz frequency band. Then we analyze the model of the equivalent circuit diagram using the Saber software and verify the validity of the model and the accuracy of the calculation through experiments.

A Modal Model of Common-Mode Chokes for Conducted Interference Prediction

In this paper, a new methodology to characterize common-mode chokes is presented. It is based on a model where common-mode and differential-mode interference is separated into different ports. This methodology is used to explain modal conversion inside common-mode chokes, predict the common-mode and differential-mode conducted emissions when common-mode chokes are connected to electric devices, and improve the filtering performance of common-mode chokes by finding the optimal common-mode choke parameters.

Modal Characterization of Power-Line Filter Capacitors

A typical power-line filter is composed, essentially, by common-mode chokes, X-class and Y-class capacitors. A good characterization of these components is needed to develop a technique to design the optimal power-line filter for an electric or electronic device by finding their best values. In this paper, a new methodology to characterize the behavior of power-line filter capacitors is presented. This methodology is based on a model where common-mode and differential-mode interference are separated into different ports in order to facilitate the study of the propagation phenomena. The methodology is used to explain modal conversion inside impedance networks with X-class and Y-class capacitors, to predict the common-mode and differential-mode emissions when these capacitors are connected to electric or electronic devices, and to improve the classical methodology of power-line filter implementation finding the optimal capacitances of the impedance networks. This new methodology has been successfully tested by using real measurements from capacitors and electric devices.

Direct Interference Canceling for Two-Electrode Biopotential Amplifier

A two-electrode biopotential amplifier, though simpler than a three-electrode amplifier, has problems rejecting 60 Hz power-line interference due to the imbalance of electrode-skin impedance. A direct interference canceling (DIC) scheme to reject 60 Hz interference for a two-electrode biopotential amplifier is proposed. The DIC scheme cancels differential-mode interference directly by adding to the interference to be canceled a feedback signal that has the same magnitude and frequency as the interference, but that has phase shifted 180 degrees. When the DIC is started by closing a switch, transient interference appears, which decreases within several seconds. In steady state, the DIC amplifier rejects a very narrow bandwidth (BW) centered at the interference frequency. The proposed circuit was implemented and the DIC operation yielded 54 dB interference canceling with 0.6 Hz rejection BW.