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It is important to acquire the impedance of switched-mode power supply (SMPS) under its operating condition for designing electromagnetic interference (EMI) filter. The online impedance extraction technique has become a research hot topic. However, the result of current online measurement technique is inaccurate due to ignorance of the different impedance of two power lines to ground of SMPS. To cope with this, an online impedance extraction technique is proposed in this paper. Considering the practical characteristics of impedance of two power lines to ground, the extraction principle and method is developed based on the established measurement models. Finally, the measurement platform with SMPS and measurement device under operating condition is built. Experimental results validate that the proposed technique can extract the differential mode (DM) and the impedance of two power lines to ground.

Smaller size and lower loss are always the target of EMI filter which suppresses EMI emitted by power electronics converter. Digital EMI filter (DEF) is the best solution to suppress the conducted EMI in size and loss, especially for high-power converters. However, for current DEF model, it is not enough to describe the filtering ability. The model which can describe DEF stability is absent. To cope with these, this paper proposes a modeling technique about filter and stable behavior of DEF system. In proposed technique, the insertion gain model can accurately describe the filtering behavior, and the loop gain model can predict the stability of DEF system. Experimental testbed based on a Boost converter as EMI interference is built. Experimental results validate that the proposed model can successfully predict the stability and performance of DEF system.

Arc welding inverter supply with switch and digital control is widely used, due to the advantages of high controllability, small size, and high efficiency. With the constant increasing of switching frequency and decreasing of arc welding machine size, the conducted electromagnetic interference (EMI) becomes serious, especially for common mode (CM)-conducted EMI. Meanwhile, as the development of digital processing technique, digital active EMI filter (DAEF) technology, which uses digital control and embedded mode, has become a hot research topic. However, the conventional DAEF fails to consider time delay effect. Its model cannot accurately describe DAEF filtering behavior. Moreover, decoupling circuit lacks scientific design method. To cope with these, this paper proposes a precise DAEF model which considers both the time delay of digital processing portion and the parasitic parameters of passive components. Moreover, based on impedance matching principle, a detailed and scientific design method of decoupling circuit is put forward. Meanwhile, the arc welding inverter system with embedded DAEF is designed, modeled, and compensated. Finally, experiment results show that the proposed precise model can predict the system filtering performance accurately. And the proposed design method of decoupling circuit is very effective to suppress the CM-conducted EMI. The embedded DAEF can improve system stability and dynamic performance.

The high frequency high voltage (HFHV) transformer is one of the biggest contributors for conducted electromagnetic interference (EMI) emission of switching power supply. The transformer technologies for reducing conducted EMI emission focus on the shielding and changing the winding structures. However, for suppressing conducted EMI, the suppression capability of shielding is limited; current methods of changing the winding structures don't fully reduce all the distributed capacitance, especially in the HFHV switching power supply. This paper proposes a novel winding method to suppress the conducted EMI. The proposed method not only considers the distributed capacitance between the primary winding and secondary winding, the interlayer distributed capacitance of the primary or secondary winding, but also considers the interturn distributed capacitance of the winding. Experimental testbed based on 1kV DC switching power supply is built. Simulation and experimental results show the proposed winding method is very effective in reducing conducted EMI emission.

For suppressing of the conducted electromagnetic interference (EMI), passive EMI filter (PEF) is the most widely applied technique at present. The near-field coupling due to PEF passive components layout has great influence on filtering performance. Currently, the layout of PEF components completely dependents on the experience of EMC engineer. However, there is a lack in systematic design method and scientific design basis. For this reason, in this paper, an optimization design method of PEF layout is presented. The method is based on distribution rule and mechanism of near-field coupling of PEF components, which can decrease volume and improve the filtering performance of PEF. Finally, theoretical analysis and experimental results show that the presented method of PEF layout can effectively improves the filtering performance of PEF.

As the switching frequency of switching power supply increases, its size become smaller and smaller. This phenomenon results in serious electromagnetic interference (EMI) problem. General passive EMI filter cannot meet the demand of size, weight, power losses and filter performance at the same time. Digital Active EMI Filters (DAEF) is a good choice, for it implement EMI suppression using digital and active. However, the cost-effectiveness of current DAEF is low. This paper proposes a novel switching period control method for the DAEF to reduce the cost and increase the efficiency of the whole EMI filtering system, which, in turn, improves the filtering efficiency of the DAEF. This paper gives detailed design procedure and parameter calculation of DAEF. Experimental testbed based on boost DC/DC converter is built. Simulation and experimental results of DAEF show the proposed switching period control is very effective in reducing cost and improving filtering performance of the DAEF system.

Digital high-frequency arc welding inverter is widely used in welding areas because of its many advantages such as high efficiency, small size, easy to control etc. However, with the development of high frequency of the switching, the conducted EMI generated by arc welding inverter becomes increasingly serious, especially common mode conducted EMI. Based on Digital Active EMI Filter (DAEF) controller, this paper proposes a new method which can reduce common mode conduction EMI for arc welding inverter. It is a closed EMI control loop by sensing EMI signal, sampling, digital compensation control, DAC output and injection. The EMI control can be embedded in original controller of arc welding inverter to reduce costs. Moreover, since there is no component in series connect with the power circuit, DAEF solves the problem of traditional EMI filter in filter size and power consumption fundamentally. In this paper, the arc welding inverter system with DAEF is designed, molded and compensated. Meanwhile, by simulation and analyses, the advantages of arc welding inverter with DAEF in system stability and dynamic performance are showed. Finally, experiment results showed that the proposed method has advantages in reducing conducted EMI emission and improving dynamic performance of arc welding inverter.

Digital Active EMI Filtering (DAEF) technique is a new direction of conductive EMI suppression technologies for switched-mode power converters. However, the conventional DAEF topology only suppresses EMI to ground on the AC (or DC) ports. It doesn't definitely aim to Common Mode (CM) or Differential Mode (DM) EMI. In this paper, a novel DAEF topology is proposed. It can flexibly suppress CM and DM EMI, and also effectively adjust EMI suppression ability as well as prevent interconversion between CM and DM EMI. On the other hand, because of the parasitic parameters of circuit and the time delay of controlling system, the traditional model of DAEF cannot describe the system behavior accurately. This paper proposes a precise model of DAEF system. The model not only considers the passive device parasitic parameters of sense circuit, injection circuit and decoupling circuit, but also considers the time delay of the digital control system. This model can accurately describe filter performance of DAEF. Finally, simulation and experimental results show that the proposed DAEF effectively suppress CM EMI. Moreover, the precise model can predict the system filter performance accurately.

Passive Power Filter (PPF) is widely used in power system because of its advantages in performance-price ratio. For PPF, there are several topologies, each of which has different frequency characteristic. In power system, in order to achieve the certain filtering effect, it is necessary to combine different filter topologies. Currently, the selection of PPF topologies is based on the engineering practical experience of PPF designer. However, there is a lack in systematic design method and scientific design basis. For this reason, this paper, taking the filtering effect and filters cost as the design indices, deeply investigates the selection problem of PPF topologies, and proposes a selection method of PPF topologies. The research results show that the most reasonable combination of different filter topologies can be obtained by this method for different situation needed to mitigate harmonic and compensate reactive power.

Switching power supply of low voltage and high current based on power electronic technology is widely applied in some industry fields, especially in electroplating, welding and heating. Harmonics in high-power switching supply pollute power system heavily, which must be suppressed effectively. On basis of analyzing harmonic current of switching supply that the output technical specification is 60V/500A, this paper designs active power filter for switching power supply with high power and frequency, which adopts ip-iq current detecting method and hysteresis current control method. Based on simulation platform of Matlab/Simulink, the filtering effect is simulated and analyzed. Simulation results demonstrate the active power filter has expected performance, which can not inhibit harmonic current instantaneously, but also compensate reactive power. The designed active power filter can effectively improve the power quality. Keywords-low voltage and high current; switching power supply; active power filter; harmonic current; hysteresis current control.

In order to meet the requirements of the magnetron sputtering, an asymmetric bipolar pulsed power supply based on DSP is presented in this paper. It can freely adjust the pulse parameters including pulse amplitude, frequency, duty cycle, and even the number and transition time of the positive and negative pulse according to the sputtering demands. Finally, a 5kW/ 100kHz prototype is designed. It adopts two isolated DC/DC converters as the current source, and an asymmetric pulses generator. The digital signal processor (DSP) fulfills the digital closed loop control of current sources. Meanwhile, it achieves the adjustment of pulse segment. The experimental results verify the designed.