Effect of Transformer's Parameters on Harmonic Generation

The separation of differential mode and common mode noise in EMI analysis is a well known procedure which is useful especially for the analysis and the understanding of interference phenomena of power converters. However, separating both components is rarely done during measurements. Therefore, two different approaches are developed and evaluated in this paper to realize separated common mode and differential mode measurements.

This paper deals with Electro Magnetic Interference in switching power supplies. The EMI consists of mainly common mode and differential mode noises. Due to interference, the efficiency of the equipment reduces and some times the equipment may be damaged. A procedure to design a novel topology of EMI Filter to suppress these two noises is presented in this paper.

The effects of the transformer leakage inductance in a LLC converter that exploits the integrated magnetic concept are investigated. The vast literature on this subject always models the transformer considering its magnetizing inductance, together with a lumped leakage inductance located at the primary side. However, when the transformer windings are arranged so as to increase the leakage magnetic flux with the aim of achieving the desired value, two leakage inductances are indeed created, one associated to each winding. Using the Fundamental Harmonic Approximation (FHA), the converter behavior at steady-state is revised so as to highlight the effects of a split leakage inductance, while the dynamic behavior is investigated using the Generalized Averaging Method. A suitable design procedure is proposed that accounts for the more complex transformer model. Measurements taken on a 100 W rated LLC converter prototype confirm the theoretical forecasts.

This paper describes the investigation of Common Mode (CM) noise and Differential Mode (DM) noises in Dual Active Bridge (DAB) converter applied in Electric Vehicle (EV) in order to reduce the Electromagnetic Interference (EMI) that occurs in EVs. The DAB converter is designed and simulated using a spice simulator and the CM and DM noises from the converter circuit were measured as per the CISPR 25 EMI Standard. Based on the simulated results, the attenuation level of noise was calculated and used to design the components of the EMI filter. The design was validated using the simulation findings after the converter are created, tested and the experimental results compared. Based on the results and discussion, recommendations are made in this paper to reduce EMI in converters used in EV. Especially, suggestions to reduce the common mode and differential mode noises produced by Dual Active Bridge converters employed in EV were given as per the CISPR 25 standard.

In order to improve the stability and reliability of switch mode power supply, the mathematical model of high frequency transformer is established with considering the effects of the leakage inductance of the high frequency transformer on the working state of DC-DC full bridge converter circuit. A finite element analysis method for two dimensional transient field circuit directly coupled of transformer in the case of full bridge inverter is proposed. Transformer inductance parameters are calculated using the method of field energy, which may provides the basis for the design of switching mode power supply transformer.

Common mode electronic noise in differential circuits

EMI measurements and the design of proper filter to mitigate the EMI noise is very important, since the EU Directive 336/89 has been published. For conduction emission noise, the separation of the common and the differential mode noise is important for determining whether the differential or common mode component is dominant. Therefore, it will be possible determine whether an anticipated change in a value of an element in the power supply filter will be effective on the considered component. Two devices for the separation of the conducted EMI noise into the common and the differential mode components have been realized and tested. In this paper the authors show the design considerations that have to be taken into account for the realization of the two devices.

The concept of Frequency Response Analysis (FRA) has been widely accepted as a reliable diagnostic tool to detect winding and core deformations within power transformers. While the measurement of transformer FRA signatures has been standardized since the development of advanced frequency response analyzers, interpretation of the FRA signature which is provided as a graphical plot is still challenging. At this stage there is no interpretation code for FRA signatures published and widely accepted yet. To develop such codes, impact of various mechanical deformations on the FRA signature must be well investigated and fully understood through simulation analysis and practical measurements. For simulation analysis, a reliable high frequency transformer model is essential. This paper presents a state space representation for a high frequency transformer model in which the physical meaning of the model parameters facilitates the identification of the problem within the transformer. Various mechanical faults are simulated into the model to investigate their impacts on the FRA signature.

As a result of the advantages such as high efficiency, continuous current and high stability margin, push-pull converter with continuous current (PPCWCC) is competitive for battery discharge regulator (BDR) which plays an important role in power conditioning unit (PCU). Leakage inductance yields current spike in low-ripple current of PPCWCCs. The operating modes are added due to leakage inductance. Therefore the steady state performance is affected, which is embodied in the spike of low-ripple current. PPCWCCs which are suitable for BDR can be separated into three types by current spike characteristics. Three representative topologies IIs1, IIcb2 and Is3 are analyzed in order to investigate the factors on the magnitude and duration of spike. Equivalent current sampling method (ECSM) which eliminates the sampling time delay and achieves excellent dynamic performance is adopted to prevent the spike disturbance on current sampling. However, ECSM reduces the sampling accuracy and telemetry accuracy due to neglecting the spike. In this paper, ECSM used in PPCWCCs is summarized. The current sampling error is analyzed in quality and quantity, which provides the foundation for offsetting and enhancing the telemetry accuracy. Finally, current sampling error rate of three topologies is compared by experiment results, which verify the theoretical analysis.

A new test method is described which separates common (asymmetrical) and differential (symmetrical) mode noise and yields quantitative data about each mode from 100 kHz to 20 MHz. The essential feature of this method is a modified r-f current probe combined with a high pass filter. The purpose of the high pass filter is to enhance the rejection of the power frequency current in the output of the current transformer.

This E-Book focuses on conducted and radiated emission noise generated by different power converters such as Switch Mode power Supplies and DC-AC Inverters. EMI filter design and different approaches to predict common mode and differential mode noise are illustrated in detail. Common mode and surge voltage issues in AC machines have also been addressed and discussed in this E-book. The E-book is intended for helping engineers and students to analyze EMI problems in electrical and electronic systems.

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.

Increasing the switching frequency of the converter can reduce the size of the transformer. However, as the switching frequency increases, the losses and temperature of transformer also increase, especially the core loss. Improving the calculation accuracy of core loss models is important for the design and research of high frequency transformers. Nanocrystalline materials have a unique nanoscale grain size and a special microstructure that gives them a high saturation magnetic induction strength and permeability, resulting in smaller size and weight at high frequencies, and have gained widespread popularity in recent years. However, compared to other soft magnetic materials, nanocrystalline strips have high permeability and leakage inductance causes increased eddy current losses on the thin walls on both sides, resulting in high localized temperatures. The finite element model of nanocrystalline high frequency transformer is established by the Ansys/Maxwell software in this paper and the effect of temperature is considered on the core with the leakage magnetic, using Icepak to perform a bidirectional coupling calculation of electromagnetic and temperature. With two different primary and secondary winding arrangements, this model calculated the core losses and temperature distribution. It verified that as the leakage inductance increases, the core loss grows and the temperature rise accelerates.

High frequency common mode noise or a differential signal flowing on nontransmission lines, most often, does not reach the load and is lost as radiation and reflection within a fraction of a wavelength. The gradual reduction of common mode noise current or radiation along the cable can be determined using current and near field probes. Therefore radiated emissions from cables can be minimized by partially shielding a fraction of the cable length toward the source end where common mode noise or radiation is predominant. This paper describes partial cable shielding theory and practical considerations. The author has implemented partial shielding on several product lines. Radiated emission data on a product with unshielded cables and with partial shielding are presented and results discussed.

This paper proposes a computational high-frequency transformer model. The model parameters are obtained by using coupled-circuit-finite-element (FE) nonlinear analysis. The frequency response of the transformer was obtained by coupling the transformer FE model and external electric circuits. This technique would allow the physical representation of the nonlinear magnetization behavior of the transformer as well as the strong frequency dependence of the transformer parameters. The self capacitance of each conductor and the mutual capacitances between the turns were calculated by an electrostatic FE analysis. The capacitance order was then reduced to a lower order by shifting the capacitances connected to internal nodes (windings) to the external ones (coil nodes). The resulting reduced capacitances, along with the inductances and resistances, were then used in the circuit domain of the coupled circuit-FE analysis. The transformer frequency response was then obtained from FE analysis. This response was then fitted with rational function approximation. This rational function approximation is then used to construct a frequency-dependent branch (FDB) which is connected in parallel with the nominal frequency transformer model. The FDB branch represents the transformer high-frequency behavior over a wide frequency range. The implementation is performed on a 125-kVA transformer. The developed model terminal behavior was tested under different operating conditions. This includes different switching frequencies and connecting cable length.