This paper presents a detailed analysis and improved control strategy for modular multilevel converters (MMC) under asymmetric arm inductance conditions. Unlike symmetric conditions, the fundamental ...ac current is not split equally between the upper and lower arms under asymmetric conditions and the dc and double-frequency components in the common-mode current also flow into the ac side. To solve these issues, a theoretical analysis of the effect of asymmetric conditions on MMC operation is carried out using equivalent circuits at different frequencies. Three control targets are then presented to enhance the operational performance. A control strategy providing the control of differential-mode current, common-mode current and power balance is designed. The feasibility and validity of the proposed analysis and control strategy are demonstrated by simulation results from a three-phase MMC system and simulation and experimental results from a single-phase MMC system.
The issue of electromagnetic interference (EMI) holds significant importance in the design of variable speed drives (VSDs). Even if the VSD is the source of radiated EMI due to the high-speed ...switching devices, the power cables are the main emission parts for the radiated EMI as antennas. The common-mode (CM) current of an output power cable of the VSD has been investigated as a radiation part. However, considering the radiation EMI, it is crucial to examine the CM current not only in the output power cable but also in the input power cable. This paper investigates the differential-mode (DM) and CM currents of input and output power cables of a three-phase AC/DC/AC VSD system using simultaneous time domain measurements to estimate the radiated EMI. The result demonstrated that the input and output power cables act as antennas, and the radiated EMI can be evaluated by considering the integrated CM currents of the input and output power cables, especially the comprised of the 3-phase wire and earth wires' CM current.
In three-phase voltage source converters (VSCs), the high-frequency leakage current can be easily suppressed by the common-mode choke, while low-frequency component would be an unfavorable factor to ...the inductor design. Thus, as the excitation source, the low-frequency common-mode voltage (CMV) should be properly managed. This article analyzes the low-frequency CMV impulse by constructing a 3-D voltage vector space, and a novel modulation method is proposed to eliminate the low-frequency CMV. Meanwhile, a comparative study is conducted between the proposed method and the other four typical space vector pulsewidth modulation (PWM) (SVPWM) method from the view of CMV and differential-mode current (DMC). In the analysis, a double-current-ripple-envelopes method is proposed to describe the current ripples. Besides, the influence of modulation indexes and power factors on DMC are considered and evaluated. And a guiding rule for choosing the appropriate modulation method for three-phase VSCs is provided. Finally, the theoretical analysis and proposed method are experimentally validated under a 5-kW three-phase PWM converter.
A dual-port pulsed differential-mode current injection (DPDCI) method is proposed for high-level wide-band electromagnetic pulse (EMP) radiated susceptibility testing of interconnected systems. By ...employing the designed wide-band differential-mode (DM) coupling device, the susceptibility of the equipment under test (EUT) at both ends can be assessed at the same time. In order to enforce the equivalence between EMP radiation and DPDCI, the methods to obtain the waveforms of the two equivalent injection sources and their time delay difference are proposed. By using the linear extrapolation method, the results for high-level EMP radiation can be reproduced by DPDCI even if the responses of the two EUTs are non-linear. To confirm the effectiveness of the proposed method, the conversion of common-mode interference into DM disturbance on the cable inside the EUT is assessed by experiment and the impact of connecting the injection devices into the system is discussed. By using a typical interconnected system composed of a coaxial cable and typical non-linear equipment at both ends, the feasibility of the proposed method is verified.
Development of an EMC demonstration unit Degraeve, Andy; Claeys, Tim; Vanhee, Filip ...
2016 International Symposium on Electromagnetic Compatibility - EMC EUROPE,
2016-Sept.
Conference Proceeding
When teaching electromagnetics and electromagnetic compatibility (EMC) to engineering students and graduated engineers, it is important to bridge the gap between theory and practice. To reduce the ...need for a broad range of expensive and voluminous demonstration setups, a new EMC demonstration unit has been developed which allows to demonstrate present day conducted and radiated phenomena.
Using a signal generator and an oscilloscope, measurements were made of the differential-mode current and the common-mode current in a twin-conductor cable installed on a test rig, over a range of ...frequencies which included half-wave resonances. Test data was used to assign component values to a Triple-T circuit model of the assembly. This model was then transformed into a transient coupling model. The signal generator was reset to generate square waves, and photographs were taken of the waveforms of the input voltage and the common-mode current. A close correlation was achieved between these waveforms and those of the transient coupling model. This demonstrates that the technique of circuit modelling and bench testing is reliable and accurate, in both the frequency domain and the time domain. The technique allows potential hazards due to transient interference to be analysed, tested, and quantified during the design process. Electromagnetic interference can be analysed without recourse to the mathematics of full-field modelling. It is also shown that, from the point of view of Electromagnetic Compatibility, the concepts of the single-point ground and the equipotential ground are both misleading and counter-productive.
Three-phase motor drive systems are the foundation of modern industrial and commercial applications, providing an efficient and dependable way to operate electric motors. In order to meet ...electromagnetic compatibility requirements within the frequency range of 0 to 2 kHz, magnetic chokes are frequently utilized, being connected to either the DC or AC sections of drive systems. Recently, worldwide standard committees adopted new emission limitations for the 2-9 kHz frequency range to minimise power quality problems caused by the increased penetration of power electronics equipment. The influence of choke location on differential-mode supra-harmonics in the 0-9kHz frequency range is investigated in this work. Mathematical calculations are employed to conduct a comparative analysis in choosing between two DC-link inductors or three AC line inductors for mitigating differential-mode noise at the grid. To that end, single-phase equivalent circuits are used to calculate differential-mode noise components. Following that, supra-harmonic contents of currents are estimated based on the commutation of the front-end rectifier. In consequence, through the derived mathematical equations, conducted noise emissions entering to the grid are analytically modeled. The findings of laboratory tests are utilised to verify the theoretical concepts.
This paper describes a high-density motor drive system in which the power transmission lines are formed by a multi-layer printed board, making it possible to reduce inductance of lines. The structure ...of the power transmission lines between the converter and the inverter is determined, based on calculations of the magnetic field distribution generated by the differential (normal) mode current, which leads to an increase in radiated emissions due to the common mode current. The printed power circuit is experimentally verified as an effective way to reduce the electric field intensity from the radiation.
The relation among the common-mode current generated by PLC system, the longitudinal conversion loss (LCL) and the common-mode impedance (Zcm) of the T-ISN and the electrical unbalance that exists in ...the PLC device is investigated in order to realize a low emission PLC device. It is necessary to decrease the common-mode current to reduce the radiated emission generated from PLC system. In this case, the LCL and the common-mode impedance of the outlet are examined. For this examination, the formula of the common-mode current, the LCL, and the common-mode impedance is obtained. First of all, the relation among the common-mode current, the LCL and the common-mode impedance is shown. Next, the influence of the electrical balancing of the PLC device on the common-mode current reduction is shown. The effectiveness of the improvement of balancing by means of the components layout and the wirings of the PLC device is shown.
The common-mode current on AC cable is one of radiated disturbance source below 300 MHz. The method of using common-mode absorbing device (CMAD) is discussed to improve reproducibility of test result ...by stabilizing the termination impedance of AC cable. However, CMAD can't stabilize the differential-mode impedance because this acts as a kind of common-mode choke coil. In this paper, the influence of the differential-mode termination impedance was studied. The measurement results of disturbance current on AC cable showed that the differential-mode level between AC power line and ground line is larger than the common-mode level. The study using a simple circuit model suggested that the differential-mode current could be converted to the common-mode current by changing the termination impedance between AC power line and ground line. The experiment was carried out by using the artificial AC network which has a function to change both common-mode and differential-mode termination impedance. The results showed that a common-mode level fluctuated by changing the termination impedance. The results also showed that the influence to the common-mode current and the radiated electric field strength in the case of the comb generator was smaller than that in the case of the PC.
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