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For the practical design of a common-mode filter (CMF), the substrate uncertainty and process deviations always result in the stopband offset of the CMF at high frequencies. To compensate the stopband offset, in this paper, a general method for expanding the bandwidth of a CMF is proposed. A three-conductor model is used to analyze the coupling characteristic between the CMF and the differential lines, and then etching slot on the ground plane for stopband bandwidth expansion is developed. A wideband CMF with a central frequency around 25 GHz and an all-pass performance (from DC to 40 GHz) for differential signals is designed. Both the simulation and measurement results verify the effectiveness of the proposed improved CMF. The –10 dB stopband bandwidth of the coplanar CMF is increased by five times without SI problems. This greatly increases the robustness of the CMF against the substrate uncertainty and the printed circuit board process deviations.

It is important to identify the impulse performance of the grounding system for lightning protection. However, the performance is nonlinear and dynamic under impulse condition. The electrical parameters of the grounding system are not only frequency dependent, but are also time dependent. Moreover, the mutual couplings between the grounding conductors cannot be ignored. Based on the hybrid electromagnetic method and vector fitting, a time-domain approach for the transient performance of the grounding system is developed. All the aforementioned phenomena can be covered in this method. Meanwhile, the sudden change of the parameters resulting from the soil ionization is also successfully dealt with in this paper. Compared with previous study results and field tests, the method proves to be reliable and effective.

An analogue chaotic carrier is designed to be embedded in a chaotic pulse width modulation (PWM) boost converter, and to be used for reducing electromagnetic interference (EMI) in dc-dc converters. The analogue chaotic PWM has its advantages over the digital one in its low costs and easy-to-design, making it suitable for high-frequency operation and situations when design flexibility and low cost are required. Finally, simulations and experiments are conducted to illustrate the effectiveness of the proposed analogue chaotic PWM in reducing EMI.

In order to analyze the lightning transient of a thin-wire system, a time-domain method of reducing the thin-wire conductor system into an equivalent active multiport network based on the partial-element electric-circuit model is presented in this paper. A modified-mesh-current (MMC) approach is developed, uses node charge and mesh current as its variables, and takes into account both capacitive coupling and inductive coupling among conductors. Equations given by MMC are expressed in a state-space form. These equations are reduced to an active multiport network model using the trapezoidal scheme. The active multiport network is described by a constant-input-conductance matrix and a vector of currents that are updated using passed values. The multiport network can easily interface with linear and nonlinear components in an electromagnetic transient program. Since the proposed method requires only one-time calculation of the inverse of the system matrix, it is more efficient in comparison to the conventional full-wave method in the frequency domain. For a large system, well-established model-order-reduction techniques can be applied to the MMC formulation to reduce it to a small scale one. The proposed method is validated by comparing its results with NEC-calculated ones and published field measurements. Finally, the method is used to simulate two lightning-strike scenarios.

Wideband frequency electromagnetic (EM) noise generated during the turn-on and turn-off processes of thyristor valves in converter stations is conducted along the primary circuitry, and may interfere with secondary systems. The EM interference (EMI) problem in a plusmn800 kV ultra-HVDC converter station is an important issue that should be studied carefully in the design stage. A method to analyze the conducted EM disturbance (EMD) based on time-domain wideband circuit simulation is proposed here, which is verified through the field test results of a plusmn500 kV converter station. Models of major equipment are described. The EMD levels of a plusmn800 kV converter station, which is currently being planned and built in China, are calculated, and compared with those of a plusmn500 kV converter station.

In this paper, a simulation model is proposed to evaluate the electromagnetic transient surge current distribution in a lightning protection system (LPS) due to a direct lightning stroke. The model is based on the coupled transmission line network in the frequency domain combined with the Fourier transform technique. The conductor of the LPS is described using the coupled transmission line model, and can be reduced to an active two-port equivalent circuit. The unknown quantities are the node voltages of the LPS at the physical junction, which leads to a fast solver at each frequency. The validation of the proposed approach is performed by comparing the results with those in the technical literature. The numerical examples show the flexibility, efficiency, and accuracy of the model in the range of practical application of LPS.

The design of grounding system often relies on the performance simulations. The evaluation of the current distribution of grounding system for many frequencies by using the method of moments (MoM) may take a long time since the impedance matrix must be recomputed at each new frequency. A multiobject adaptive spatial sampling approach is presented to construct the fitted model of the electric field intensity generated by a horizontal electric dipole. The [Z] matrix spatial interpolation technology with MoM is described to reduce the computational time needed for the transient characteristics analysis of a horizontal grounding system. The accuracy and computational time of the [Z] matrix interpolation method are compared with those of the direct MoM. The numerical examples show that the [Z] matrix spatial interpolation method can reduce the computation requirement effectively