High Frequency Common Mode Currents Research Articles

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Novel Stator Slot Opening to Reduce Electrical Machine Bearing Currents

Ball bearings are largely used in electrical machines, where the high frequency common mode currents affect their lifetime. This document presents a novel Zig-Zag stator slot opening geometry to reduce the winding-to-rotor capacitance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> with the consequent reduction of Bearing Voltage Ratio and electrical discharge machining bearing currents. An improved analytical model to permit the calculation of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> for unusual slot opening geometries is implemented. Electrostatic and electromagnetic Finite Element Analysis comparisons between the Zig-Zag, oblique and original (classical slot opening configuration) machines are performed. These comparisons suggest that the Zig-Zag model presents the best performance in terms of Bearing Voltage Ratio reduction, while keeping torque performance close to the original machine. An additional comparison between the novel Zig-Zag model and the classical one with reduced slot opening to have the same <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> values is proposed, showing an higher degradation in terms of torque performance for the latter. The study shows that the Zig-Zag model could be a good candidate to reduce effectively electrical machine bearing currents. A validation test is proposed on two motorette prototypes having classical and Zig-Zag slot opening configurations, respectively. Moreover, the improved analytical method can be helpful for engineers and researchers to calculate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C_wr</i> with a good accuracy for unusual slot opening geometries.

EMI Reduction in DC-Fed Electric Drives by Active Common-Mode Compensator

A novel common-mode (CM) EMI active filter for dc-fed motor drives is proposed. The active filter performs both the compensation of the CM voltage at the motor input and the mitigation of the leakage high-frequency CM currents, thus increasing the drive reliability and the vehicle electromagnetic compatibility (EMC). The filter scheme is based on a voltage feedback action and also includes a feed-forward action by exploiting a suitably estimated CM current. An optimized design of the CM voltage detection/injection systems is implemented. Moreover, the active filter is supplied by a smaller voltage than the dc link value; this permits a more performing amplifier to be used. The active filter behavior is analyzed theoretically and its performance is assessed by experiments. The realized prototype shows a good efficiency and compactness.

Internal Common-Mode Current Flow Path of Induction Motor

When induction motor is directly driven by PWM power converter, high-frequency common-mode current will be generated inside the motor due to the high-frequency common-mode voltage load. So in this paper, on the basis of the analysis of the coupling effect of the parasitic elements on high-frequency current which include elements between induction motor windings, between the winding and the stator and between the winding and the rotor, According to the structural characteristics of the motor, it is obtained that the parasitic element between the first turns of the stator winding coil and ground can provide low impedance flow path for high frequency common mode current, most of the high-frequency common mode current drain into ground through this path, and the motor stator winding has the uniform transmission line characteristics. The correctness of the conclusions is verified by the experimental results of two different induction motor.

An Optimized Feedback Common Mode Active Filter for Vehicular Induction Motor Drives

This paper proposes a common mode (CM) electromagnetic interference active filter devised for application in automotive induction motor drives. The active filter is based on a feedback scheme and it is realized using linear amplifiers. It performs the compensation of the CM voltage at the motor input, allowing an increase of the drive reliability and a reduction of the harmonic content of leakage high-frequency CM currents that affect the vehicle electromagnetic compatibility. A size-optimized layout is proposed and the influence of the power linear amplifier performance on the CM voltage compensation is discussed. General guidelines for the active filter design are given and its experimental implementation is presented. Finally, the filter performance is assessed by simulations and experimental tests.

Scaling Issues for Common-Mode Chokes to Mitigate Ground Currents in Inverter-Based Drive Systems

The additional high-frequency (HF) common-mode (CM) current of inverter-based drive systems can cause parasitic effects such as HF bearing currents. This HF CM current can be significantly reduced by purpose-designed CM chokes that are inserted in the drive at the inverter output. This paper discusses scaling issues related to the design of such CM chokes, of both wound and feed-through toroidal types. The requirements for the design of chokes for these applications can differ from those for CM chokes designed for use in the inverter input, such as those used for the purpose of electromagnetic interference filtering. This difference is notably due to the comparatively large magnitude of the currents involved. The developed correlations allow taking full advantage of the possibilities offered by such chokes to reduce the HF CM current and mitigate the resultant parasitic effects. The discussed relationships are derived analytically, and the results are supported by measurements.

Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverter

The recent increase in the use of speed control of ac induction motor for variable speed drive using pulse width modulation (PWM) inverter is due to the advent of modern power electronic devices and introduction of microprocessors. There are many advantages of using ac induction motor for speed control applications in process and aerospace industries, but due to fast switching of the modern power electronic devices, the parasitic coupling produces undesirable effects. The undesirable effects include radiated and conducted electromagnetic interference (EMI) which adversely affect nearby computers, electronic/electrical instruments and give rise to the flow of bearing current in the induction motor. Due to the flow of bearing current in the induction motor, electrical discharge machining takes place in the inner race of the bearing which reduces the life of the bearing. In high power converters and inverters, the conducted and radiated emissions become a major concern. In this paper, identification of bearing current due to conducted emission, the measurement of bearing current in a modified induction motor and to minimize the bearing current are discussed. The standard current probe, the standard line impedance stabilization network (LISN)), the electronics interface circuits are used to measure high frequency common mode current, bearing current and to minimize the conducted noise from the system. The LISN will prevent the EMI noise entering the system from the supply source by conductive methods, at the same time prevents the EMI generated if any due to PWM, fast switching in the system, will not be allowed to enter the supply line. For comparing the results with Federal Communications Commission (FCC) and Special Committee on Radio Interference (CISPR) standards, the graphs are plotted with frequency Vs, line voltage in dBµ V, common mode voltage in dBµ V and the bearing current in dBµ A with out and with minimizing circuits.

Reduction of Conducted Electromagnetic Emissions in Multi-Inverter Drive Systems

Conducted emissions are caused by circulation of high frequency common mode currents generated by steep variations of the common mode voltage. In this paper, an inexpensive technique is presented that allows to noticeably reduce conducted electromagnetic emissions of multi-inverter drive systems by compensating common mode voltage variations.