Common-mode Filter Design Research Articles

An optimal zero‐sequence voltage injection‐based common‐mode voltage reduction pulse‐width modulation for the reduction of common‐mode voltages in both amplitude and third‐order component

An optimal zero-sequence voltage injection-based common-mode voltage reduction pulse-width modulation (CMVRPWM) for the reduction of common-mode voltages (CMVs) in both amplitude and third-order component is proposed in this paper. On the basis of general symmetrical switching patterns of CMVRPWM, a constrained mathematical programming model is established with the objective of optimizing the volt-second value of CMV in each switching period. By solving the mathematical model, the limitation of the CMV amplitude and the reduction of third-order harmonic in CMV can be achieved simultaneously, contributing to better CMV suppression and common-mode filter design in the applications of two-level voltage source inverters (2L-VSIs). The optimal zero-sequence voltage under the given target is obtained, and the calculation method of the switching pattern and modulation wave is studied. Simulation and experimental results show that the proposed method can restrict the CMV amplitude within one-sixth of the DC bus voltage, and the third-order component in CMV is effectively reduced compared with the conventional methods.

Analysis and Mitigation of the Common-Mode Noise in a Three-Phase SiC-Based Brushless DC Motor Drive With 120° Conduction Mode

The generation and propagation of the common-mode (CM) noise depends on the pulsewidth modulation (PWM) technique, parasitic capacitances, and rate of change of voltages imposed on the motor. In the literature, the CM noise analysis of the brushless dc (BLdc) drive operated with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$120^\circ$</tex-math></inline-formula> conduction mode is reported neglecting the impact of the floating phase, and the analysis is restricted to low-voltage silicon-based drives. In this article, an in-depth theoretical analysis of the CM noise in the BLdc drive is presented considering two commonly used schemes in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$120^\circ$</tex-math></inline-formula> conduction mode: six-step commutation and bipolar PWM. It is proven through experiments that the impact of the floating phase cannot be neglected especially with the high-voltage slew rate imposed by silicon carbide (SiC)-based inverters on the drives. By considering the impact of the floating phase, the CM noise in the BLdc drive is modeled through mathematical equations, and suitable equivalent circuits are presented. Finally, a step-by-step design procedure of the CM filter for the BLdc drive is presented. Experimental results on a three-phase star-connected SiC-based BLdc drive are provided to substantiate the analysis and CM filter design.

An alternating high‐low impedance common‐mode filter for differential striplines

The conventional quarter/half-wavelength common-mode filter (CMF) cannot work well for a differential stripline when there is no ground via. A new and effective via-free CMF design for the differential striplines is proposed in this study. An alternating high-low impedance structure is developed to increase the coupling between the stripline and the CMF, thus achieving a good filtering effect. A cascaded CMF design is further studied to enhance the stopband without deterioration of the differential signals. Both simulation and measurement results demonstrate the effectiveness of the proposed high-low impedance CMF. The significant advantage of the proposed CMF is its compactness and simplicity, which has almost no impact on the original layout of differential striplines.

PWM Strategy to Alleviate Common-Mode Voltage with Minimized Output Harmonic Distortion for Five-Level Cascaded H-Bridge Converters

High-frequency components of common-mode voltage (CMV) induce the shaft voltage and bearing current, which lead to premature failures in motors. In addition, due to non-zero average CMV, the low-frequency components of CMV, particularly the third-order harmonic component, have been reported to cause difficulties in common-mode filter design. Furthermore, the utilization of distant voltage vectors in the pulse-width modulation (PWM) with reduced CMV magnitudes gives rise to high output harmonic distortion compared to PWM ones without CMV reduction. In an attempt to solve the aforementioned issues, this article presents a PWM strategy that features reduced CMV magnitudes, zero average CMV, and improved output harmonic distortion for a five-level cascaded H-bridge (CHB) converter. In addition, the carrier rotation technique based on the phase-leg redundancy of the CHB topology is also combined with the proposed scheme to achieve equal power loss distribution among power switching devices. Both simulation and experimental results confirm that the proposed strategy produces better output harmonic distortion than that of POD-SPWM and APOD-SPWM under the condition of reduced CMV magnitudes, zero average CMV, and equal power loss distribution.

A Novel Ultrawideband Absorptive Common-Mode Filter Design Using a Miniaturized and Resistive Defected Ground Structure

An ultrawideband absorptive common-mode filter (A-CMF) with a newly developed defected ground structure (DGS) is proposed in this article. The DGS miniaturized to a subwavelength size is able to totally suppress the common-mode noise while maintaining the signal integrity of the differential mode. In addition, the reflection and radiation of the common-mode noise are negligible in the stopband. For quick design, a simplified equivalent circuit model is also proposed. This model can be employed to estimate the resistances of the lumped resistors embedded in the DGS to obtain a very wide absorption band. In the demonstrated example, the fractional bandwidth determined by a 90% absorption efficiency can achieve as large as 104% around 3.55 GHz for an A-CMF realized on a simple two-layer printed circuit board. Such a widely absorptive bandwidth is never achieved before to our knowledge. The design methodology is validated by full-wave simulation. Finally, real measurement of the design is also carried out to confirm the design and analysis.

EBG Common-Mode Filter Design Using Uncoupled Coplanar Waveguide to Microstrip Transitions

This letter investigates the effects of an Electromagnetic Bandgap (EBG) common-mode filter design using coplanar waveguide (CPW) to microstrip transitions on differential signals. Specifically, the improvements in the frequency and time domains are studied by s-parameters and eye diagrams. EBG structures are based on a periodic alteration of even-mode impedances to create stop bands in the common-mode, while not affecting the differential mode as much as possible. The proposed common-mode filter is unique in the way that a broad bandwidth is achieved by choosing one of the even-mode characteristic impedances as small as possible. This EBG structure is implemented on a printed circuit board (PCB) and characterized using a 4-port vector network analyzer (VNA).

Quad-Mode LTCC Surface Mounted Packaging Common-Mode Filter Based on the Asymmetric Short-Stub Loaded Resonator

A novel quad-mode common-mode filter (CMF) with ultra-wideband and high common-mode (CM) rejection-level is proposed based on the asymmetric short-stub loaded resonator (ASSLR). By utilizing the ASSLR, four resonant modes can be introduced for the initial CMF design under the even-mode operation, and correspondingly generate four CM transmission zeros. However, the initial CMF design achieves a weak CM noise suppression performance. Then, the CMF using the modified ASSLR is proposed for CM stopband enhancement. Finally, a surface mounted packaging CMF prototype is fabricated with the physical size of 6mm×4.5mm×0.6mm by using low-temperature co-fired ceramic (LTCC) technology. The measured results agree well with the simulated ones. The proposed quad-mode CMF exhibits excellent performances including high differential-mode cutoff frequency (10GHz), and an ultra-wide -15dB CM stopband with a fractional bandwidth of 104.5%.

Systematic Common-Mode Filter Design for Inverter-Driven Motor System Based on In-Circuit Impedance Extraction

Inverter-driven induction machines often suffer from premature bearing failure due to high-frequency common-mode (CM) voltage and induced CM current. One effective remedy is adding a CM filter to suppress the CM current. Optimal CM filter design requires prior knowledge of both noise source and termination impedances. With an improved in-circuit impedance measurement setup, the CM noise source impedance of a high-power inverter-driven motor system with strong background noise can be extracted. The setup also protects the measurement instruments from surges and transients from the harsh operating environment. The extracted noise source impedance allows a CM filter to be designed systematically without overdesigning. In the evaluation of the first-order single-inductor and second-order LC filters, it is found that the second-order CM filter is prone to differential-mode to common-mode (DM-to-CM) conversion, especially at the resonant frequency caused by the leakage inductance of the CM choke and the equivalent DM capacitance of the line-to-ground capacitors. Therefore, an additional DM inductor is necessary to curb the mode conversion, which may not necessarily result in final size reduction as compared to that of first-order single-inductor filter.

Grounding Concept and Common-Mode Filter Design Methodology for Transformerless MV Drives to Prevent Bearing Current Issues

Recently, the transformerless design of medium-voltage drives is an emerging design concept of variable-speed drives (VSD). Here, no dedicated feed transformer is used. The VSD is directly connected to the on-site facility transformer, where multiple other loads are connected as well. The benefits of such a transformerless VSD are reduced total volume, weight, losses, and system costs. However, without a dedicated feed transformer, the converter-generated common-mode (CM) voltage may generate harmful bearing currents that could yield serious bearing failures within a short time. For this reason, the suppression of bearing currents is a fundamental design aspect of VSD systems. In this publication, a comprehensive bearing current study highlights the two dominating bearing current mechanisms in transformerless VSDs. Both mechanisms are caused by the converter-generated CM voltage applied to the machine terminals. Their physical understanding is used to define thresholds that ensure a sufficient mitigation of bearing currents. The newly introduced CM voltage limits allow the development of a generalized CM filter design for transformerless VSDs. Accordingly, a suitable filter grounding concept including a CM filter design methodology for transformerless high-power medium-voltage converters is presented for the first time. Here, both the CM voltage injection to the grid and the CM voltage applied to the machine terminals is considered. At the machine-side, the novel design reference to prevent bearing currents is applied. By this, the reliable transformerless operation of general purpose drives and retrofit applications is feasible.

A Virtual Space Vector Modulation Technique for the Reduction of Common-Mode Voltages in Both Magnitude and Third-Order Component

A virtual space vector modulation technique reducing both magnitude and third-order harmonic component of the common-mode voltage (CMV) in a two-level voltage-source inverter (VSI) is proposed in this paper. The presented method employs a set of virtual space vectors constructed from original stationary space vectors to conduct modulation. Since the created virtual vectors have the lowest instantaneous and zero average CMVs, both the magnitude and third-order harmonic component of the generated CMV are reduced, contributing to better overall CMV performance and common-mode filter design in VSI applications. Three variants of the proposed modulation method using different virtual space vector combinations are presented. The concept of the virtual space vector modulation technique demonstrated with two-level inverter in this paper can also be extended to multilevel inverters. Simulation and experimental results, as well as comparisons with existing methods are provided to verify the proposed technique.

Common-Mode Suppression in Microstrip Differential Lines by Means of Complementary Split Ring Resonators: Theory and Applications

This paper is focused on the application of complementary split-ring resonators (CSRRs) to the suppression of the common (even) mode in microstrip differential transmission lines. By periodically and symmetrically etching CSRRs in the ground plane of microstrip differential lines, the common mode can be efficiently suppressed over a wide band whereas the differential signals are not affected. Throughout the paper, we present and discuss the principle for the selective common-mode suppression, the circuit model of the structure (including the models under even- and odd-mode excitation), the strategies for bandwidth enhancement of the rejected common mode, and a methodology for common-mode filter design. On the basis of the dispersion relation for the common mode, it is shown that the maximum achievable rejection bandwidth can be estimated. Finally, theory is validated by designing and measuring a differential line and a balanced bandpass filter with common-mode suppression, where double-slit CSRRs (DS-CSRRs) are used in order to enhance the common-mode rejection bandwidth. Due to the presence of DS-CSRRs, the balanced filter exhibits more than 40 dB of common-mode rejection within a 34% bandwidth around the filter pass band.

Compact Configuration for Common Mode Filter Design based on Planar Electromagnetic Bandgap Structures

A planar electromagnetic bandgap configuration of a compact common mode filter that is laid out on printed circuit board is studied. This filter is used to mitigate the common mode noise traveling on high-speed differential signal traces. These differential signal lines may be connected to I/O connectors and cables and small amounts of common mode noise can result in significant electromagnetic emissions. The filter is obtained by a very simple planar geometry based on the electromagnetic bandgap structures. A cavity made by a rectangular/square patch (together with a solid plane underneath) has a well known and predictable resonant behavior; the coupling between the differential pair routed on top of the patterned plane and the patch cavity, occurring when the traces cross the gap between adjacent patches, is used to reduce the energy associated with the propagation of the common mode noise. The properties of this filter are studied taking into account the layout of a real differential microstrip and the number of gap crossings. A compact configuration is proposed. Time domain simulations validate the suggested layout approach.

Common mode modelling and filter design for a three-phase buck-type pulse width modulated rectifier system

The EMC input filter design for a three-phase pulse width modulated (PWM) rectifier is usually separated into the design of the differential mode (DM) and common mode (CM) stages. While for the DM filter design rules and procedures are well known and easier to predict, the CM filter design is often based on trial-and-error methods and/or on the experience of the designer. In the present study, a comprehensive design procedure for a CM EMC input filter is performed for a three-phase three-switch buck-type PWM rectifier. A model of the CM noise propagation is developed and the relevant parasitic impedances are identified. A capacitive connection from the star-point of the DM input filter to the capacitive centre point of the rectifier output voltage is proposed and the effect of this measure-concerning CM is verified. Finally, a two-stage CM filter is designed and compliance to the conducted emission (CE) requirements of CISPR 22 Class B is verified through measurements on a 5 kW prototype.