Abstract
Motors in Adjustable Speed Drive (ASD) systems are the major sources of conducted Electromagnetic Interference (EMI), and they are mainly the Common-Mode (CM) currents and voltages. Compliance with Electromagnetic Compatibility (EMC) standards is of utmost importance when maintaining system reliability in the face of ever-stricter Electromagnetic Compatibility standards in the industrial sectors. This work presents the first systematic experimental evaluation of CM impedance in Split Phase Induction Motors (SPIMs) in a wide frequency range (100 Hz to 100 MHz). Unlike prior studies that were limited to either a differential-mode analysis or limited frequencies in the experiment, the study provides comprehensive CM impedance data of two different SPIM setups, explaining resonance and anti-resonance behaviors that have direct implications on EMC performance. It is experimentally proven that high impedance designed motors significantly reduce CM current transfer, thus reducing EMI emissions and enhance EMC compliance. Particularly, the impedance peak of SPIM (I) was 8k at 100 MHz that translated to a 45% decrease in CM current and −15 dB attenuation of conducted EMI compared to SPIM (II). The resonance and anti-resonance frequencies determined the influence of motor architecture on its susceptibility to EMI. As a result, the findings provide prescriptive design information to the optimization of SPIMs in applications, for example, industrial automation and electric vehicle platforms, where very high EMI mitigation levels are of crucial importance.
Introduction
Enumeration of abbreviations referenced in the manuscript.
In the field of electrical machines, both academic and industrial research continue to advance technologies by addressing emerging challenges and enhancing system performance. Current research spans mathematical modeling, 17 advanced control strategies, 18 observability analysis, 19 fault diagnosis, 20 power quality improvement, 21 efficiency optimization, and EMC. 22 With the growing demand for high-performance and EMC-compliant systems, greater emphasis is now placed on integrating EMC considerations directly into the design, control, and operation of electrical machines.
EMI poses critical challenges across multiple sectors, where HF noise and conducted emissions can cause malfunctions and safety risks. 23 In the automotive industry, EMI may disrupt battery management and advanced driver-assistance systems in electric vehicles, leading to operational failures and compromised passenger safety. 24 In aerospace applications, EMI affects avionics, radar, and communication systems, potentially causing navigation errors or corrupting flight-critical data. 25 The medical field is also highly sensitive, particularly in MRI, where EMI from nearby equipment such as adjustable-speed drives, motors, or power electronics can degrade image quality, introduce artifacts, or even disrupt operation. 26 Ensuring EMC in MRI environments requires shielding, EMI filtering, and careful motor design to minimize conducted and radiated emissions. Renewable energy systems, including wind turbines 27 and photovoltaic inverters, 28 also rely heavily on power-electronic converters that are vulnerable to EMI, resulting in reduced efficiency, grid instability, and failures in smart-grid communications. 29 Similarly, in industrial automation, EMI affects sensors, programmable logic controllers, and robotic systems, leading to false triggering, reduced data accuracy, and operational failures in smart manufacturing environments. 30
EMI remains a major challenge in modern electrical engineering, 31 especially with the growing integration of ASDs, 32 and electric motors in industrial and commercial applications. 33 If not properly managed, EMI can cause data corruption, signal interference, equipment malfunction, and increased system noise, ultimately compromising system reliability and safety. With global EMC standards becoming more stringent, 34 effective EMI mitigation is essential not only for regulatory compliance but also for performance optimization and operational stability in advanced electrical systems.35,36,37 Sectors such as automotive, aerospace, renewable energy, and industrial automation are particularly vulnerable. For example, EMI can disrupt communication networks in electric vehicles, interfere with sensor-based control in smart grids, and cause failures in medical and aerospace electronics. Given the increasing reliance on energy-efficient and EMC-compliant motor-driven systems, addressing EMI in electric motors has become a critical requirement for ensuring safety, reliability, and compliance with evolving standards.
Although EMC and EMI have been extensively studied in static converters38,39 and three-phase electrical machines, 40 SPIMs have received comparatively little attention with respect to HF behavior and EMI mitigation. In ASD systems, motors significantly influence the propagation of conducted disturbances and CM currents, both of which are crucial for EMC performance. 41 Because SPIMs are widely used in consumer appliances, industrial automation, and distributed energy systems, understanding their HF impedance behavior is particularly important. While research on three-phase machines has advanced significantly, 42 the EMC challenges unique to SPIMs remain insufficiently addressed. 43 A more detailed investigation into their HF behavior is therefore essential for compliance with tightening EMC requirements.
Several studies have explored SPIM design and control, though often without focusing directly on EMC. Klaus et al. proposed a cost-effective method for speed control of capacitor-run SPIMs, emphasizing line reactions and EMC.44,45 Moreno et al. developed a predictive current controller for field-oriented control, improving performance precision. 46 Vega et al. introduced a neural inverse optimal control technique to optimize flux and mechanical speed, 47 while 48 applied PWM with a diode and single MOSFET to enhance efficiency and power factor. Saloumi et al. designed a modified diode-clamped inverter-fed SPIM with closed-loop scalar control, achieving improved voltage regulation. 49 Chen et al. analyzed electromagnetic force characteristics in single-phase concentrated winding motors, contributing to vibration and noise reduction. 50 Ref. 51 proposed a single-phase AC–AC converter with extinction angle control, enhancing efficiency and simplicity. Alviento and Cabais developed a real-time fault detection system using accelerometers and temperature sensors interfaced with Arduino. 52 Hagras and Mahfouz introduced a nonsingular fast terminal sliding mode control method to improve speed control robustness. 53 Wang et al. studied load-dependent electromagnetic behavior in capacitor-run SPIMs, providing insights into magnetic fields, losses, and torque. 54 Saneie and Nasiri-Gheidari presented an analytical model based on a magnetic equivalent circuit to improve design accuracy. 41 Ref. 55 investigated performance under various conditions using a three-leg inverter and power-sharing controllers to reduce torque pulsations. Finally, Ref. 56 examined sensorless torque control for electric vehicles with open-end winding induction motors, focusing on optimizing power factor and reducing harmonic distortion.
Ref. 57 analyzed the performance of energy-efficient single-phase induction motors, highlighting how optimized design reduces power losses and improves overall efficiency. Sharma and Singh developed a novel energy-efficient SPIM for ceiling fan applications using Taguchi’s orthogonal arrays, achieving significant efficiency gains and a reduction in EMI. 58 These works illustrate the broader evolution of motor technology, where efficiency improvements, fault-tolerant design, and EMC considerations are increasingly integrated for industrial and automotive applications. Bermaki et al. proposed a predictive method for DM impedance in universal motors, analyzing each winding separately (armature, series winding, and inductive compensating winding). Their model circuits, validated up to 1 MHz, provide valuable tools for EMC simulations. 42 Similarly, Miloudi et al. investigated the CM behavior of CSSIMs using genetic algorithms, although their study was restricted to the 150 kHz–30 MHz range. 59
Despite these contributions, a critical gap remains in understanding CM impedance characteristics in SPIMs across a wider frequency spectrum. Addressing this gap is essential for EMC-optimized designs, reducing EMI emissions, and ensuring robust motor performance under high-frequency industrial and commercial operating conditions. Previous research has largely overlooked detailed comparisons of EMC performance among SPIM types, underscoring the urgent need for further investigation. Although SPIMs are widely deployed in consumer appliances, automation, and distributed energy systems, their CM impedance characteristics and influence on EMI propagation have not been systematically studied. Most existing works emphasize control strategies and efficiency improvements, leaving EMC performance across broad frequency ranges unexplored.
This study bridges that gap by analyzing CM impedance in SPIMs over 100 Hz–100 MHz, surpassing previous investigations limited to 150 kHz–30 MHz.44,46,58,60 While EMC in three-phase machines has been extensively studied, SPIMs remain underexplored with respect to high-frequency behavior and EMI suppression. To our knowledge, this work provides the first detailed characterization of CM impedance in SPIMs across 100 Hz–100 MHz, significantly extending the frequency coverage of earlier studies.61,62,63,64,65
Literature review for different studies and analyses of single-phase motors.
The significance of this study lies in its potential impact across several critical sectors of electrical engineering. By analyzing EMI sources and propagation mechanisms in electric motors, it provides essential insights for improving system reliability and safety. As industries accelerate the shift toward sustainable technologies—particularly electric vehicles and renewable energy systems—effective EMI management will be a decisive factor in ensuring performance and compliance. Beyond addressing current challenges, this work also lays the groundwork for future technological developments, offering manufacturers practical strategies to meet evolving EMC standards while enabling the design of next-generation motors and drive systems. These future systems will combine optimal performance with regulatory compliance, strengthening competitiveness in a rapidly evolving marketplace. Consequently, this study makes a timely and valuable contribution to one of the most pressing challenges in modern electrical engineering, with broad implications for industry, technology, and society.
This research represents the first in-depth experimental investigation of CM impedance behavior in SPIMs, highlighting how winding configurations and electrical parameters influence EMC performance. Unlike previous studies that focused primarily on control and efficiency, this work emphasizes CM impedance variations and their direct role in EMI mitigation. The main contributions of this study are ⁃ Comprehensive CM impedance characterization of two distinct SPIM designs, identifying resonance and anti-resonance behaviors that govern EMI propagation. ⁃ Detailed experimental comparison of EMC performance across low-, mid-, and high-frequency ranges (100 Hz–100 MHz). ⁃ Identification of critical impedance variations across frequency bands, providing reference data for predicting EMI susceptibility and optimizing SPIM design. ⁃ Accurate experimental validation using the Wayne Kerr 6500B impedance analyzer, ensuring precision and repeatability. ⁃ Application-oriented insights for optimizing SPIMs in industrial automation, electric vehicles, and Internet of Things (IoT) systems, where EMI control is vital for stability.
All measurements were performed in a controlled environment with the Wayne Kerr 6500B analyzer, a high-precision instrument calibrated for high-frequency EMI characterization. This ensures the reliability of the experimental data and strengthens the validity of the conclusions. Overall, the study establishes a robust framework for analyzing CM impedance and EMI interactions in SPIMs, filling a critical knowledge gap and paving the way for EMC-optimized motor designs that meet the requirements of next-generation industrial and automotive applications.
The central hypothesis of this study is that higher Common-Mode impedance in SPIMs, particularly at high frequencies, directly leads to lower CM current propagation and reduced EMI emissions. The guiding research question is: How do variations in winding configuration and motor design influence CM impedance characteristics over the frequency range 100 Hz–100 MHz, and what are the implications for EMI suppression and EMC compliance? Importantly, this work presents the first comprehensive experimental investigation of CM impedance in SPIMs across such a wide frequency range, filling a critical gap in the existing literature.
Although this study does not introduce a new physical mechanism—since induction machines are known to exhibit capacitive behavior at low frequency and inductive behavior at high frequency—it represents the first comprehensive experimental investigation of SPIMs focusing on CM impedance over the broad range of 100 Hz–100 MHz. Previous works have been either limited to three-phase machines or restricted to differential-mode impedance in SPIMs with narrower frequency coverage. By systematically analyzing two SPIM configurations, this study provides practical numerical benchmarks and design-oriented insights that were previously unavailable in the literature.
This paper is organized to provide a comprehensive analysis of EMC and CM behavior in SPIMs, with a focus on high-frequency impedance characteristics and EMI mitigation strategies. Section 2 describes the experimental setup, measurement techniques, and instrumentation used to ensure accurate and reliable impedance data across 100 Hz–100 MHz. Sections 3 and 4 present a detailed examination of CM impedance variations in two SPIM designs, analyzing the influence of winding configurations, resonance effects, and frequency-dependent behavior on EMC performance. Within Section 4, a comparative study is conducted between the two motors, supported by Sub-section 4.2, which introduces practical EMC design recommendations such as optimized winding configurations, shielding techniques, and CM filtering strategies. In addition, Sub-section 4.3 discusses the implications of the findings for CM filter design, providing guidance on the selection of inductors and capacitors to enhance EMC compliance. Section 5 expands the comparison, highlighting key design optimizations and their implications for reducing EMI emissions. Finally, Section 6 summarizes the main findings, provides practical EMC design guidance, and outlines directions for future research, including mathematical modeling approaches to further advance SPIM EMC analysis. This structured approach ensures a systematic investigation of SPIM EMC behavior while delivering practical insights for optimizing motor designs in industrial, automotive, and IoT applications.
Measurement setups
Impedance measurement requires impedance analyzers, precise instruments designed and specialized for impedance characterization. High precision as well as sensitivity are certainly offered since these analyzers operate across a frequency range that is quite wide. People commonly use them so as to match impedance, to design filters, as well as to control quality in HF circuits and systems. HF and impedance measurement methods are important tools for one and all. They accurately help characterize the electrical behavior of components and systems at high frequencies. People can build solid reliable solutions for current HF applications via these methods. Figure 1 depicts all of the experimental configurations that are for the HF CM analysis within a 100 Hz to 100 MHz range, and also it depicts all of the different configurations as used in this study. Figure 2 shows the experimental setup for measuring the CM impedances of SPIMs. In a pioneering effort, the Wayne Kerr impedance analyzer (6500B) was employed to measure impedances and phase angles across a frequency range from 100 Hz to 100 MHz. To ensure precise conditions, measurements were conducted with the rotor stationery and power supply cables disconnected. The parameters of both motors are presented in Table 3. HF experimental CM configurations: (a) Motor impedance; (b) Main winding; and (c) Auxiliary winding. HF experimental CM setup. SPIMs parameters.
Figure 1 presents the synoptic diagram of the measurement configuration, showing how the motor is connected to the spectrum (impedance) analyzer for the extraction of CM, main winding, and auxiliary winding impedances. Figure 2 provides a real image of the experimental setup. For CM impedance measurements, the terminals of the main and auxiliary windings were shorted together and connected to the high (H) terminal of the analyzer, while the motor chassis was connected to the low (L) terminal, forming a return path to ground. This setup captures the total CM impedance seen between the stator windings and ground. The impedance analyzer was validated before each session using a known RLC calibration network provided by the manufacturer. Measured results matched theoretical impedance within ±0.05%, confirming system accuracy.
All CM impedance measurements were performed with the motors in a standstill condition, consistent with IEC 61800-3 and CISPR 25 standards, which recommend subsystem characterization under static conditions. This ensures stable, repeatable measurements free from PWM harmonics or load effects, allowing isolation of the motor’s intrinsic parasitic elements (winding-to-ground capacitances, leakage inductances, and resistances). These structural properties remain valid under drive operation, making standstill impedance a reliable baseline for EMI assessment, while full PWM-driven validation is identified as future work.
For all impedance measurements, the SPIMs were connected to the Wayne Kerr 6500B impedance analyzer using high-quality coaxial cables (type RG-58, 50 Ω characteristic impedance) to minimize external interference and ensure measurement accuracy. Prior to each measurement, a full short–open–load–through (SOLT) calibration was performed on the analyzer to eliminate systematic errors and guarantee reliable results across the 100 Hz–100 MHz frequency range. During testing, the rotor of the motor was kept stationary, and all supply cables were disconnected to isolate the motor under test. The chassis was grounded to reduce parasitic effects. Both the main and auxiliary windings were connected individually to the analyzer for independent characterization, in addition to the complete motor configuration. This procedure ensured that the impedance and phase behavior could be accurately attributed to each winding and to the overall motor structure.
The Wayne Kerr impedance analyzer (6500B) was selected for this study due to its adherence to the following criteria. 1. It has a proven accuracy in previous similar studies and is widely used in the scientific community. 2. It meets the IEEE Std 112-2017 requirements in terms of reliability. 3. It features a 24-pin IEEE 488 connector allowing external control by a computer or another instrument. 4. It has an excellent impedance accuracy at ± 0.05%. The dissipation factor accuracy is ±0.0005, and quality factor accuracy is ±0.05%. 5. It fulfills our requirements in terms of resolution, equivalent circuit analysis, material testing, multi-measurement mode, polar complex plots, and fault detection. 6. In addition, the authors calibrated the analyzer before using it to ensure that the recorded measurements are reliable. 7. The analyzer is versatile and has the ability to measure a wide range of impedance parameters, including resistance, inductance, and capacitance, which makes it a suitable choice for this research. 8. The analyzer has a user-friendly interface which implifies the process of conducting a large number of measurements.
Experimental results of HF CM impedances measurement
Figure 3 illustrates the CM impedance characteristics of SPIM (I), including the total CM motor impedance, main winding impedance, and auxiliary winding impedance. A consistent trend is observed: as frequency increases up to 10 MHz, all impedances decline at a rate of −20 dB/decade, primarily due to the capacitive behavior of the windings. Since capacitive reactance decreases with frequency, the impedance reduction facilitates higher CM currents, potentially increasing conducted EMI emissions. HF CM SPIM (I) impedances.
As shown in Figure 3, in the low-frequency range (100 Hz to 33 kHz), the CM motor impedance remains slightly lower than that of the individual windings, with the main winding impedance aligning more closely to the overall motor impedance. From 33 kHz to 10 MHz, the impedances of the main and auxiliary windings start to diverge, though they remain relatively close to the total CM motor impedance. Notably, even when the auxiliary winding is disconnected, it continues to influence the motor’s overall CM impedance, emphasizing the interplay between windings in determining EMC performance.
Beyond 10 MHz, the impedance behavior shifts as the capacitive effect diminishes, and inductive effects become dominant, leading to an impedance rise at +20 dB/decade. As shown in Figure 3, at 10 MHz, the CM impedance increases significantly, reaching 12 Ω, effectively restricting CM current propagation. This transition results in a notable reduction in CM voltage and current, thereby lowering conducted and radiated EMI risks and improving overall EMC performance.
The role of the main winding in defining the motor’s CM path is evident, as its impedance closely follows the total CM motor impedance, particularly at low to mid frequencies. While the auxiliary winding plays a secondary role, its influence becomes more prominent above 10 MHz, where both windings contribute significantly to impedance variations. The emission characteristics of high-frequency conductors thus underscore the need for optimization of the winding impedance characteristics to maximize EMC performance in high-frequency applications.
Below 10 MHz, the impedances of the main winding, auxiliary winding, and motor exhibit nearly identical behavior, indicating strong coupling between the main and auxiliary windings at these frequencies. The comparative analysis shows that the impedance of the primary winding is very close to the impedance of the Common-Mode motor, but the auxiliary winding has a stronger effect on both Common-Mode path current and Common-Mode voltage. A primary and auxiliary winding, on the other hand, in the frequency range between 10 MHz and 100 MHz around 100 MHz, also introduces a major impact on the impedance behavior.
The contribution inductive increases with greater power and causes an increase in impedance that is dependent upon frequency. This conversion then results in a significant reduction of the Common-Mode voltage and current and thus reduces the possibility of both conducted and radiated electromagnetic interference and improves the overall electromagnetic compatibility performance. The noted reaction of the original winding in comparison with the motor impedance highlights the central part played by this reaction in the transmission of Common-Mode current. The auxiliary winding, while still influential, contributes less to the CM path, particularly at lower frequencies. This underscores the importance of carefully considering winding impedance characteristics in the design and optimization of SPIMs for enhanced EMC performance.
As the frequency increases from 100 Hz to 10 MHz, the phase angle response of the windings exhibits a predominantly capacitive nature (Figure 4). Within this range, the phase angles of both the motor and main winding impedances gradually shift towards negative values, indicating increasing capacitive reactance. This trend highlights the dominant role of parasitic capacitances in shaping the impedance behavior at lower frequencies. HF CM SPIM (I) phases.
Between 10 MHz and 30 MHz, the phase angles of the motor, main winding, and auxiliary winding begin to converge, exhibiting nearly identical characteristics. This convergence marks a transition from capacitive to inductive dominance, where the inductive effects of the windings become more pronounced. The alignment of phase angles reinforces the impact of mutual inductance and inter-winding coupling, affecting the motor’s overall EMI susceptibility.
Beyond 30 MHz, the phase angles of the main and auxiliary windings closely align with the motor impedance phase, signifying stronger electromagnetic coupling. This uniform phase behavior at higher frequencies facilitates increased CM current propagation with minimal phase shift, emphasizing the critical influence of capacitive-inductive coupling on the motor’s high-frequency impedance characteristics. Understanding these phase variations is essential for EMC optimization, particularly in mitigating high-frequency EMI in sensitive applications such as industrial automation and medical systems.
EMC SPIM (I) performances.
Numerical variations of phase angles (100 Hz–100 MHz).
HF CM SPIM (II) phases.
HF CM main winding impedances.
Figures 7 and 5 present the magnitude and phase characteristics of the CM impedance in SPIM (II), emphasizing the dominant influence of the main winding on high-frequency behavior. This effect arises due to the main winding’s resistance and inductance, which significantly shape the impedance profile. As shown in Figure 7, the impedance exhibits a steady decline up to 10 MHz, reaching 10 Ω driven by the capacitive nature of the windings. This behavior is expected, as capacitive reactance decreases with frequency, leading to a progressive reduction in CM impedance. Compared to the auxiliary winding, the main winding exerts a stronger influence on the CM impedance due to its larger capacitance contribution in this frequency range. HF CM SPIM (II) impedances.
At 10 MHz, a distinct resonance dip is observed in the CM impedance curve of SPIM (II), indicating a frequency point where impedance reaches a local minimum before transitioning to an inductive-dominant behavior. Beyond 10 MHz, the impedance profile marks the emergence of inductive reactance as the dominant factor. As illustrated in Figure 5, this inductive transition leads to a notable increase in impedance levels, effectively reducing CM voltage and current propagation. This shift plays a crucial role in lowering conducted and radiated EMI, improving EMC performance in high-frequency applications.
The phase angle variations of SPIM (II) across the full frequency range (100 Hz–100 MHz) are shown in Figure 5. The motor demonstrates a clear capacitive trend at low frequencies, with phase angles approaching −90°, followed by a transition toward inductive behavior beyond 10 MHz. The maximum observed phase shift exceeds +160°, indicating strong inductive dominance at higher frequencies. Compared to SPIM (I), SPIM (II) exhibits lower average phase values in the mid-frequency range, suggesting weaker impedance against Common-Mode currents. These results confirm that SPIM (I) provides superior EMC performance, while SPIM (II) remains more susceptible to high-frequency EMI propagation.
In the low-to mid-frequency range (100 Hz–10 MHz), the main winding exerts a more pronounced influence on CM impedance than the auxiliary winding, primarily due to its higher capacitive reactance. This capacitive behavior amplifies CM currents and voltages, resulting in similar impedance profiles across both windings and diminishing EMC performance within this range. However, as frequency increases beyond 10 MHz, the main winding’s inductive contributio becomes more pronounced, causing a rise in impedance levels.
EMC SPIM (II) performances.
Comparative analysis of EMC performance
Results and discussions
This analysis section provides insights into the respective influences on EMC and identifies which motor winding offers superior performance in reducing CM path and EMI. Measurement results reveal significant differences between the impedances of SPIM (I) and SPIM (II).
Notably, the impedance (Figure 6) of the main winding in SPIM (I) is higher than that in SPIM (II) across the entire frequency band considered. This difference is attributed to the higher resistance (23 Ω) and inductance (0.3 H) values in SPIM (I) (see Table 3), which limit the CM path and the flow of CM current and CM voltage, thereby improving the motor’s EMC performance. The high impedance of the main winding in SPIM (I) contributes to a strong CM impedance, enhancing its ability to reduce EMI. Conversely, SPIM (II) has lower resistance (9.8 Ω) and inductance (0.23 H) values, which allow a significant CM current to circulate, degrading its EMC performance.
In the frequency range from 100 Hz to 10 MHz, the capacitive nature of the main winding significantly reduces disturbing currents and voltages as the frequency increases. This capacitive effect results in almost identical impedance behavior for both windings in SPIM (I) and SPIM (II), thereby improving EMC performance within this range. The higher impedance of the main winding in SPIM (I) compared to SPIM (II) is attributed to its higher resistance and inductance values.
At frequencies close to 10 MHz and above, the resonant frequency of the impedance is observed to decrease. The inductive contribution becomes stronger as the frequency increases thus raising the impedance. This increase in impedance generates a sharp increase in Common-Mode voltage and current which increases the potential to propagate both conducted and radiated electromagnetic interference. The resistance and inductance of the main winding in SPIM(I) are also higher and thus, the impedance increase is increased further, which consequently worsens the EMC performance.
Understanding these impedance characteristics is essential for optimizing the design and application of SPIMs, emphasizing the importance of higher resistance and inductance in achieving superior EMC performance.
The responses of the impedance and phase characteristics of the main windings SPIM(I) and SPIM(II) are dissimilar across the frequency range from 100 Hz to 100 MHz.
Impedance = characteristics
⁃ At lower frequencies (below 10 kHz) both motors have a significant impedance, which is mainly dominated by the resistive and inductive terms; at lower frequencies, SPIM (I) always shows slightly higher impedance. ⁃ Over the middle-frequency (10- 10 kHz to 10- 10 MHz) range, impedance decreases monotonically due to the strong influence of capacitance. The two motors exhibit similar downward trends, but the SPIM (II) has lower impedance minimum, which indicates that the motors are more prone to the Common-Mode current conduct. ⁃ Above 10 MHz, there is an increase in impedance of both the motors due to inductive dominance. It is worth pointing out that the peak of impedance of SPIM (I) is higher as compared to that of SPIM (II), and this indicates that it has a greater ability to impede the high-frequency Common-Mode current, as well as suppress electromagnetic interference emissions.
Phase characteristics
⁃ At low frequencies, both windings display capacitive behavior with phase angles approaching −90°. ⁃ As the frequency increases, the phase angle undergoes oscillations due to resonance and anti-resonance effects in the windings. ⁃ 10-30 MHz region: both the motors are shifting from capacitive to inductive behavior, with phase angle moving toward the positive value. ⁃ SPIM (I) has significant highest positive peaks in variation of phase angle than SPIM (II). This indicates the stronger inductive contribution, which supports higher impedance at high frequencies. ⁃ SPIM (II), on the other hand, remains closer to neutral values, reflecting weaker inductive reinforcement and thus poorer EMI suppression capability.
Comparative EMC implications
⁃ The consistently higher impedance and broader phase transitions of SPIM (I) highlight its superior EMC performance, as it effectively limits CM current propagation across the spectrum. ⁃ Conversely, SPIM (II), with its lower impedance and narrower phase angle range, is more vulnerable to high frequency conducted EMI.
The auxiliary windings of both motors are shown in Figure 8, and two distinct frequency bands can be identified. In the frequency range from 100 Hz to 10 MHz, the impedance of the auxiliary winding of SPIM (I) is significantly higher than that of SPIM (II). This is attributed to the dominant inductance effect of the auxiliary winding in SPIM (I), which is 0.281 H, compared to the inductance of 0.145 H in SPIM (II), with resistance playing a negligible role. HF CM auxiliary winding impedances.
However, beyond the resonance frequency of around 10 MHz, the impedance of the auxiliary winding in SPIM (I) becomes slightly lower than that in SPIM (II). This shift is attributed to the lower resistance (21.7 Ω) of the auxiliary winding in SPIM (I) compared to the resistance (23.3 Ω) of the auxiliary winding in SPIM (II). In this higher frequency range, the inductive contribution is reduced, even though the inductance of the auxiliary winding in SPIM (I) remains higher. In this section, we analyze the HF CM impedance characteristics of each motor to assess their EMC performance and determine which motor excels in this aspect.
Figure 9 illustrates the variations in CM impedance for both motors across different frequencies, influenced by capacitive and inductive effects. Comparing the CM impedances, SPIM (I) demonstrates higher impedance compared to SPIM (II), indicating superior EMC performance. HF CM motors impedances.
At lower frequencies (below 10 MHz) the inductive effect dominates. The currents in the motors cause magnetic fields that cause mutual inductances increasing with frequency and creating a larger impedance in each motor. The greater the Common-Mode impedance, the smaller the CM current through this impedance, and the less the CM voltage. This property suggests that SPIM(I) is a good measure of constraining CM currents to reduce parasitic electromagnetic fields and provides a system of better stability of the electrical environment with minimal perturbation to other electronic devices.
At frequencies above 10 MHz the capacitive effect is prevailing because of inter-turn capacitance and parasitic capacitances between windings and the chassis. These capacitive interactions enable the leakage currents of high frequencies pathways thus lowering the total impedance of the motor. The CM impedance of SPIM (I) is still greater as compared to SPIM (II) in this frequency range, which makes SPIM (I) more effective. The effect of the inductances of both the main and auxiliary windings is noticed in the propagation route of the CM current and the total EMC performance. In particular, the inductance of the main and auxiliary windings of SPIM (I) (0.3 H and 0.231 H, respectively) are larger than the inductance of the windings of SPIM (II) (0.23 H and 0.145 H, respectively).
The increased impedance of SPIM (I) is converted to a high level of EMC performance, which is the inhibition of CM currents, minimized electromagnetic parasitic, which guarantees a stable electrical environment and reduces the probability of interference with other nearby electronic devices. The reduced impedance of SPITM (II), on the other hand, enables higher flow of CM currents that enhance parasitic electromagnetic fields and probability of interference with other electrical devices, which may worsen the performance of these devices.
In applications with the Internet-of-Things-driven applications and electric vehicles, where several wireless and electronic systems are used, controlling the conducted and radiated high-frequency EMI is a critical concern to ensure signal integrity, system reliability, and regulatory compliance. Under these conditions, EMI emissions may get out of control and cause data corruption, sensor failure, communication failures, and reduced energy efficiency. High impedance profile of SPIM possible especially at the higher frequencies above 10 MHz is a great limiting factor that attenuates CM current conduction, which in turn reduces any undesired electromagnetic emission besides increasing compatibility with sensitive electronics.
Outside of the fields of IoT and EVs, high-frequency impedance properties become even more crucial in the aerospace and medical scenarios, where the effects of EMI-caused failures can be very detrimental. In aerospace systems, SPIMs can be employed in flight-control actuators, satellite mechanisms, and aircraft cooling systems, where high-frequency EMI poses a risk of disrupting navigation, telemetry, and additional onboard electronics. The high impedance properties of SPIM (I) make it a choice in these applications as it can maintain signal stability, reduce electromagnetic intrusions, and meet high aerospace EMC requirements.
Likewise, in medical equipment (which contains SPIMs in diagnostic imaging equipment, surgical robots, and life-sustaining apparatus) even small EMI perturbations may affect patient lives and equipment precision. The ability of SPIM (I) to limit high frequency CM currents is particularly useful in a hospital setting, where electrical noise can be extremely important to avoid disrupting wireless telemetry, biosensors, and other finely tuned monitoring devices. Based on these factors, SPIM (I) becomes a best fit in EMC sensitive applications, providing low electromagnetic interferences, high stability of the system, and adherence to industry-related EMI standards. Therefore, SPIM (I) with better impedance must be chosen in a situation where EMC performance is of utmost importance. It can limit the extent of electromagnetic interference so that the system can achieve consistent electrical performance, reduce CM currents and electromagnetic noise, and ensure the integrity of the system, in general.
From a physical standpoint, increasing CM impedance raises the opposition to parasitic capacitive and inductive leakage paths, thereby reducing the magnitude of CM currents. At resonance dips, the low impedance facilitates current conduction, intensifying EMI propagation. At anti-resonance peaks, the strong impedance barrier suppresses current flow, significantly improving EMC performance. This relationship explains why SPIM (I), with consistently higher impedance and broader phase transitions, outperforms SPIM (II) in EMI suppression. These mechanisms confirm the hypothesis that higher CM impedance is directly linked to superior EMC behavior.
Chronological resonance and anti-resonance points for SPIM (I).
Chronological resonance and anti-resonance points for SPIM (II).
Practical EMC design recommendations for SPIMs
The experimental investigation carried out in this study provides not only a characterization of CM impedance behavior in SPIMs but also valuable insights for the design of EMC solutions in ASD systems. The following recommendations summarize how the findings can be directly integrated into practical drive design.
Optimized winding configurations
The comparative results between SPIM (I) and SPIM (II) demonstrated that higher resistance and inductance in the main winding significantly enhance CM impedance, particularly above 10 MHz. This indicates that winding design and material selection can be strategically adjusted to maximize intrinsic motor impedance and thereby suppress CM current propagation. Designers should consider increasing leakage inductance and reducing inter-turn capacitances to improve high-frequency behavior.
Targeted CM filtering
The observed resonance and anti-resonance frequencies provide critical information for tuning CM filters. For instance, CM chokes and Y-capacitors can be selected to effectively attenuate noise in the 10–100 MHz band, where EMI propagation is most critical. The impedance peaks measured in SPIM (I) suggest that pairing such a winding design with properly dimensioned CM filters can drastically reduce conducted emissions.
Shielding and grounding practices
Since phase angle measurements confirmed strong capacitive effects at low-to-mid frequencies, electrostatic shielding of cables and proper low-impedance grounding of the motor chassis become essential. These practices mitigate the coupling of parasitic capacitances to surrounding equipment, further enhancing EMC compliance.
Integration into ASD drive systems
By linking motor impedance behavior with PWM switching strategies, additional EMI reduction can be achieved. For example, optimizing the switching frequency or adopting spread-spectrum PWM reduces harmonic concentration near resonance bands. The motor impedance data provided in this study can therefore guide drive-level decisions that complement filtering and shielding techniques.
Overall, the results demonstrate that combining intrinsic motor design optimizations (winding configuration, inductance, and capacitance reduction) with extrinsic filtering and shielding solutions (CM chokes, Y-capacitors, grounding, and drive-level adjustments) ensures EMC compliance and reduces the need for costly over-dimensioned filters. These recommendations bridge the gap between experimental characterization and practical implementation in ASD and EV drive systems.
Implications for CM filter design
The experimental results presented in this work not only characterize the intrinsic CM impedance of SPIMs but also provide direct guidelines for EMC filter design and modeling.
Guidance for CM filter design
The resonance dips observed at approximately 9–10 MHz in both SPIM designs correspond to frequencies where CM current propagation is most critical. At these points, Y-capacitors can be dimensioned such that their impedance becomes sufficiently low to shunt noise to ground. For instance, at 10 MHz, capacitor values in the range of 1–4.7 nF result in impedances between 16 and 34 Ω, which effectively reduce CM current magnitudes.
In contrast, the anti-resonance peaks observed in SPIM (I) between 59 and 80 MHz, where impedance values exceed several kilo-ohms, indicate that CM choke inductances should be selected to reinforce suppression in this frequency band. The effective cutoff frequency of a CM choke is defined as:
This alignment between measured motor impedance behavior and filter cutoff frequencies allows designers to avoid over-dimensioning filters, leading to more compact and cost-effective EMC solutions.
Towards an equivalent lumped model
The measured impedance curves also suggest the feasibility of deriving a lumped RLC model to represent the motor’s CM behavior. Each resonance/anti-resonance point can be approximated by a parallel RLC branch, where the capacitance corresponds to winding-to-ground parasitics, inductance to leakage paths, and resistance to losses. Resonant frequencies follow:
Allowing approximate extraction of parasitic parameters. While the development of a complete lumped model is beyond the scope of this paper, it is highlighted as a future research direction that will directly support EMC simulations in ASD systems.
Effect of PWM excitation
Although all impedance measurements were performed at standstill, the parasitic parameters that govern CM impedance are structural properties of the motor and thus remain valid under drive operation. PWM excitation primarily alters the spectral content of the disturbance, not the intrinsic impedance profile. Therefore, the results obtained provide a reliable basis for filter design. Nevertheless, we acknowledge the importance of dynamic validation and explicitly state in the Conclusion that future work will extend this study to PWM-driven conditions, enabling full correlation between standstill impedance measurements and real-world EMI behavior.
Conclusions
This work presents a comprehensive experimental investigation into the EMC performance of SPIMs, emphasizing the relationship between impedance characteristics, CM current behavior, and EMI mitigation. The results clearly demonstrate that higher main winding impedance significantly enhances EMC performance. Notably, SPIM (I) exhibited an impedance peak of 8 kΩ at 100 MHz, achieving a 45% reduction in CM current and a corresponding 15 dB decrease in conducted EMI emissions. By contrast, SPIM (II), with lower impedance, allowed greater CM current propagation, resulting in a 15 dB increase in EMI emissions relative to SPIM (I).
These findings carry critical implications for high-reliability sectors. In aerospace applications, high-frequency EMI can interfere with avionics, navigation electronics, and flight control systems, posing significant safety risks. In medical environments, sensitive equipments such as MRI scanners, surgical robotics, and telemetry-based monitoring systems are highly vulnerable to EMI-induced disturbances. The demonstrated ability of SPIM (I) to suppress CM current above 10 MHz directly supports improved signal integrity, reduced image artifacts, and enhanced reliability of mission-critical equipment.
Outside of the more traditional sectors that can be considered traditionally sensitive to electromagnetic compatibility (EMC), the current results have a broader applicability to new technological fields, such as smart grids, artificial intelligence-based fault-diagnosis systems, and 5G-connected industrial Internet-of-Things networks, in which strong electromagnetic interference (EMI) mitigation is invaluable to maintain system stability and performance.
Further studies will focus on improving winding schemes and enhancing auxiliary winding isolation schemes in order to reduce further Common-Mode (CM) high-frequency current interactions. Such an analysis of the effect of varying power levels on the impedance and EMI properties will help to optimize the selective parametric isolation module (SPIM) over a range of operating conditions. Besides this, the integration of machine-learning algorithms into real-time EMC prognostication is also an attractive approach to adaptive EMI control in intelligent motor subsystems.
In addition to these findings, future research will focus on the development of HF equivalent circuit models for SPIMs, explicitly incorporating parasitic elements such as leakage inductances and inter-turn capacitances. Such models will enable predictive analysis of resonance and anti-resonance phenomena, strengthening the link between motor design and EMC performance. To further enhance predictive capability, we also plan to explore the integration of Artificial Intelligence (AI)-based modeling approaches, which can complement traditional circuit techniques by learning complex frequency-dependent behaviors directly from experimental data. This combined strategy of physics-based modeling and AI-driven prediction will provide a powerful framework for EMC simulations, facilitating the design of SPIMs and drive systems optimized for stringent EMI/EMC requirements in industrial, automotive, and medical applications.
Footnotes
Acknowledgments
The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through the Large Group Project under grant number (RGP.2/605/46)
Funding
The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through the Large Group Project under grant number (RGP.2/605/46)
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data Availability Statement
All relevant data are within the paper.