Electromagnetic Interference Issues in Power Electronics and Power Systems

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The common mode inductors, or common mode chokes, are a key component of electromagnetic interference filters. Engineers usually face significant design challenges such as size, cost and weight while working with these components. To avoid the construction of several prototypes, often oversized, engineers need an analytical method to predict performances of the filter. The analysis of the common mode inductors starts with a presentation of the different ferromagnetic materials: their properties are the cornerstone of the design of the component. Based on this study, the impedances used to characterize the choke are related to the designable parameters. The derived model shows the role of the parasitic currents to ground and the common mode impedance in the overall common mode current attenuation. A certain attenuation of differential mode current is also to be expected due to the parasitic currents of the common mode choke itself: the turn to turn capacitance and the leakage inductance. This model is validated by measurements. Sensitivity studies provide an additional insight into the behavior of the choke by giving an understanding on how variations of parameters, influence the final performance. The deviation calculation and the influence of the designable parameters are addressed at the end of this chapter.

An accurate measurement method to extract common mode (CM) and differential mode (DM) noise source impedances of a switched-mode power supply (SMPS) under operating condition is presented in this chapter. With a proper pre-measurement calibration process, the proposed method allows extraction of both the CM and the DM noise source impedances with very good accuracy. These noise source impedances come in handy to systematically design an electromagnetic interference filter for a SMPS with minimum hassle.

In power electronic systems, large transient phenomena excites the conducting structures and induces parasitic currents via heatsink stray capacitance thus causing radiated emissions. The key demands made by PCB mounted power circuits are related to low conduction losses, improved thermal performance, and lower inductance board layouts. Thermal management of power devices involves the use of heatsinks which are seen as parasitic elements from an EMI point of view. In order to reduce radiation the heatsink can be grounded at the cost of increased common mode currents to the power supply, escalating conducted EMI. Increased parasitic capacitance between the power device and the heatsink reduces the common-mode current but may upset the cooling efficiency of the heatsink. Thus, the connection of a heatsink to a power device and the packaging technology is a design issue involving EMI and thermal performance. The parasitic coupling path of a nongrounded heatsink can be mainly considered capacitive within the EMI regulated frequency range of 2 GHz. The common-mode coupling models for various heatsink configurations such as open frame, folded frame or PCB mounted configuration can be easily implemented in numerical computations by considering proper boundary conditions and energy sources. The heatsink models for numerical computations depend on the design, power level, switching frequency and packaging technology of the power electronic system.

Investigation of conducted electromagnetic interference in AC motor drives fed by pulse width modulated voltage converters requires considering parasitic capacitances in converters, motor windings and feeding cables to be taken into account. Motor voltage transients and related conducted electromagnetic emission are significantly correlated with resonance effects occurring in load circuits. The levels of intensity of these phenomena depend mostly on frequency dependant impedance - frequency characteristics of motor windings with an accompanying feeding cable. An analysis of frequency converter load impedance characteristics allows for identification and determination of representative frequency ranges in which the foremost contributions to EMI noise generation have voltage ringing phenomena associated with the load parasitic capacitances. This chapter presents a method to model an AC motor with a feeding cable. AC motor windings have distributed parasitic capacitances and a particular focus on the influence of the feeding cable's parameters is modeled as a ladder circuit model. The proposed circuit model allows for an analysis of the influence of the cable parameters on conducted EMI emission generated by an AC motor drive system. The simulation results based on the proposed ladder circuit model are verified by the experimental tests which were carried out for an exemplary adjustable speed AC motor drive application with different lengths of feeding cables.

As wind power generation undergoes rapid growth, lightning damages involving wind power systems have come to be regarded as a serious problem. This chapter gives an introduction to lightning phenomena, lightning location systems and important parameters regarding lightning protection. The wind turbine is described and the main characteristics of its components, like the tower, the generator, the blades, and the electrical and electronic equipment, are highlighted. This chapter also introduces fundamentals of risk analysis method based on international standards, and describes how the rolling sphere method can be used to identify the vulnerable points on a structure. Computer tools and simulations using the LPS 2008 computer program are presented and discussed. Finally, wind turbine issues are discussed.

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