Common-mode Transformer Research Articles

A Common-Mode Voltage Reduction Method Using an Active Power Filter for a Three-Phase Three-Level NPC PWM Converter

This article proposes a common-mode (CM) voltage reduction method using an active power filter (APF) and common-mode transformer (CMT) for a grid-connected three-phase three-level neutral-point-clamped (NPC) AC-DC pulsewidth modulation (PWM) converter. The CM voltage can be caused by switching operations of converters and the CM voltage should be reduced because it is one of the main causes of electromagnetic interference (EMI) noises. In this article, the CM voltage of the three-phase converter with the proposed APF is analyzed to explain the CM voltage reduction using the proposed APF. Based on this analysis, the application of a specific PWM method to the three-phase converter for an optimal reduction of the CM voltage is described. Besides, the APF circuit design and its switching method are proposed considering practical problems such as the self-resonance of inductors and the effect of the dead-time on the CM voltage. To prove the effectiveness of the proposed APF on the CM voltage reduction, experimental results for the CM voltage and current are presented in this article. Furthermore, EMI noise measurement results are shown to verify the performance of the noise reduction capability of the proposed APF.

Premature Wear and Recurring Bearing Failures in an Inverter-Driven Induction Motor—Part II: The Proposed Solution

In a previous work, a real case of recurring bearing failures in an induction motor had been extensively studied. As a result, the cause of the problem was revealed to be the circulation of electric current through the bearings. In this way, the present paper deals with the high-frequency leakage currents in ac motors fed by pulsewidth-modulation inverters, contextualized in the analysis of an actual case. From the parameters of an equivalent circuit representing the connecting cable, motor, and inverter return path, a filter, characterized by a common-mode transformer, is designed to mitigate the common-mode quantities and the correlated problems. Both simulated and experimental results show that the proposed solution represents an advantageous alternative in comparison to the traditional $RC$ and $RLC$ filters, since, in addition to its effect on the common-mode quantities, it dissipates a negligible amount of power.

A Novel Inverter-Output Passive Filter for Reducing Both Differential- and Common-Mode $dv/dt$ at the Motor Terminals in PWM Drive Systems

A novel inverter-output filter, which cannot only filter the differential-mode voltage dv/dt but also suppress the common-mode voltage dv/dt and their rms values, is proposed in this paper. The filter is in combination with a conventional RLC filter and a common-mode transformer. The main advantage is that the functions of filtering a differential-mode voltage and suppressing a common-mode voltage can be integrated into a single system. Furthermore, the structure and design of the proposed filter are rather simple because only passive components are used. Simulations and experiments are conducted to validate the performance of the proposed filter. Both of their results indicate that about 80% of the rms value of the common-mode voltage are suppressed, while the demand of differential-mode voltage filtering is still met

A PWM rectifier/inverter system capable of suppressing both harmonics and EMI

AbstractThis paper proposes a new PWM rectifier/inverter system that is capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). The conversion system consists of a PWM rectifier and inverter, and an active common‐noise canceler (ACC) which has been proposed by the authors. The ACC developed for this system is characterized by the sophisticated connection of a common mode transformer which can compensate for common mode voltages produced by both the PWM rectifier and inverter. As a result, the size of the common mode transformer can be reduced to one‐third, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 59–68, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10062

Configurations and characteristics of active canceling and compensating circuits for reducing common‐mode voltage generated by voltage‐source PWM inverters

AbstractThis paper deals with active circuits for cancellation and compensation of common‐mode voltage caused by a PWM inverter. A nonnegligible amount of leakage or ground current flows through stray capacitors between stator windings and the motor frame due to a large step change in the common‐mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common‐noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge the applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors propose another type of ACC, the purpose of which is not to achieve complete cancellation but to restrain only a slope in a change of the common‐mode voltage applied to the motor. As a result, the core size of the common‐mode transformer used in the active compensating circuit becomes considerably smaller. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 57–65, 2001

Configurations and Characteristics of Active Canceling and Compensating Circuits for Reducing Common-Mode Voltage Generated by Voltage-Source PWM Inverters

This paper deals with active circuits for cancellation and compensation of common-mode voltage caused by a PWM inverter. A non-negligible amount of leakage or ground current would flow through stary capacitors between stator windings and a motor frame due to a large step change in the common-mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common-noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge an applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors proposes another type of ACC, the purpose of which is, not to achieve complete cancellation, but to restrain only a slope in a change of the common-mode voltage applied to the the motor. As a result, the core size of the common mode transformer used in the active compensating circuit becomes smaller considerably. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI.

Investigation of a Novel Series Connection type Common Mode Voltage Reduction Circuit

Recently, high frequency switching strategies are being increasingly used in many converter systems. However, high frequency EMI noise caused by high dv/dt or di/dt transition in the high frequency switching action adversely affects many electric systems. In response, many kinds of study for solving this EMI problem have been reported. In this paper, a novel noise reduction method combined with soft-switching topology and a series connected common mode transformer is proposed. By using the proposed noise reduction method, the numerical expression of the common mode current can be derived from a simple equivalent circuit, and thus the common mode current without an oscillatory component can be investigated easily. Furthermore, the operational region of reducing EMI noise is expected to expand to much higher frequency compared with that of the method which utilities some active components, such as transistors, because the proposed method uses only some passive components having excellent characteristics at high frequency region. Based on the root locus theory, the optimum circuit parameters are calculated to effectively reduce the EMI noise.

An active circuit for cancellation of common-mode voltage generated by a PWM inverter

This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage.

Active cancellation of the common-mode voltage produced by a voltage-source PWM inverter

This paper proposes an “active common-mode noise canceler” that is capable of eliminating the common-mode voltage produced by a voltage source PWM (pulsewidth modulated) inverter. It generates a compensating voltage which has the same amplitude as, but the opposite phase to, the common-mode voltage produced by the PWM inverter. The compensating voltage is superimposed on the inverter output by a common-mode transformer. As a result, the common-mode voltage applied to the load is canceled completely. The design method of the active common-mode noise canceler is also presented in detail. A prototype has been constructed and tested to verify the effectiveness for an induction motor drive system of 3.7 kW using an IGBT (insulated gate bipolar transistor) inverter. Some experimental results show that the proposed active common-mode noise canceler makes a significant contribution to eliminating the common-mode current or the ground current, and it prevents an electric shock from being received by anyone handling it. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 64–72, 1998

Active cancellation of the common-mode voltage produced by a voltage-source PWM inverter

This paper proposes an “active common-mode noise canceler” that is capable of eliminating the common-mode voltage produced by a voltage source PWM (pulsewidth modulated) inverter. It generates a compensating voltage which has the same amplitude as, but the opposite phase to, the common-mode voltage produced by the PWM inverter. The compensating voltage is superimposed on the inverter output by a common-mode transformer. As a result, the common-mode voltage applied to the load is canceled completely. The design method of the active common-mode noise canceler is also presented in detail. A prototype has been constructed and tested to verify the effectiveness for an induction motor drive system of 3.7 kW using an IGBT (insulated gate bipolar transistor) inverter. Some experimental results show that the proposed active common-mode noise canceler makes a significant contribution to eliminating the common-mode current or the ground current, and it prevents an electric shock from being received by anyone handling it. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 64–72, 1998

Active Cancellation of the Common-Mode Voltage Produced by a Voltage-Surce PWM Inverter.

This paper proposes an “active common-mode noise canceler” that is capable of eliminating the common-mode voltage produced by a voltage-source PWM inverter. It generates a compensating voltage which has the same amplitude as, but the opposite phase to, the common-mode voltage produced by the PWM inverter. The compensating voltage is superimposed on the inverter output by a common-mode transformer. As a result, the common-mode voltage applied to the load is canceled completely. The design method of the active common-mode noise canceler is also presented in detail.A prototype has been constructed and tested to verify the effectiveness for an induction motor drive system of 3.7 kW using an IGBT inverter. Some experimental results show that the proposed active common-mode noise canceler makes a significant contribution to eliminating the common-mode current or the ground current, and it prevents an electric shock from being received by anyone who is touching.

Measurement and reduction of EMI radiated by a PWM inverter-fed AC motor drive system

This paper presents theoretical and experimental relationships between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source pulsewidth modulation (PWM) inverter. A method of reducing both currents is proposed, based on an equivalent model, taking into account parasitic stray capacitors inside an induction motor. Electromagnetic interference (EMI) radiated by a 3.7-kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3 m]. Experimental results verify that the combination of the already proposed common-mode transformer (CMT) and the normal-mode filters (NMFs) being proposed in this paper is a practically viable and effective way to reduce EMI resulting from both common-mode and normal-mode currents.

Measurement and Reduction of EMI Radiated by a PWM Inverter-Fed AC Motor Drive System.

This paper presents theoretical and experimental relationships between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source pulsewidth modulation (PWM) inverter. A method of reducing both currents is proposed, based on an equivalent model, taking into account parasitic stray capacitors inside an induction motor. Electromagnetic interference (EMI) radiated by a 3.7-kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3 m]. Experimental results verify that the combination of the already proposed common-mode transformer (CMT) and the normal-mode filters (NMFs) being proposed in this paper is a practically viable and effective way to reduce EMI resulting from both common-mode and normal-mode currents.