Dc grids are recognized as a promising solution for next-generation power distribution systems due to their high efficiency and reduced energy conversion stages. Since modern electronic sources and loads operate with dc power, dc-dc converters serve as key components. In particular, nonisolated dc-dc converters are gaining attention due to their high efficiency and power density. However, the removal of galvanic isolation significantly lowers common-mode (CM) impedance, leading to increased leakage current and electric shock to users. To address these issues, a nonisolated three-switch converter topology is employed, which uses fewer switches while effectively suppressing CM currents. A low-frequency (LF) leakage current controller with a feedforward for enhanced transient response is developed, based on the CM equivalent circuit analysis. The operable range of the converter is analytically derived with consideration of the voltage fluctuations in both bipolar and unipolar dc grids. In addition, a hybrid pulsewidth modulation scheme is introduced to suppress high-frequency (HF) CM currents, along with the dc CMV injection method to enhance the suppression performance. Experimental results in the bipolar and unipolar grids confirm that the proposed methods effectively suppress both LF and HF CM currents, ensuring the user safety. The 11 kW hardware prototype achieves a peak efficiency of 99.38% and reduces the rms leakage current by over 91.35% compared to the conventional designs.

This paper proposes an interoperable control method of three-phase and single-phase wireless power transfer systems for electric vehicles. In-phase excitation currents are applied to the three-phase pad to generate an equivalent single-phase magnetic field, enabling stable coupling and efficient energy transfer. Then, a single-phase equivalent circuit model is established by analytically deriving the equivalent mutual inductance and coupling coefficient between the three-phase and single-phase pads. In addition, a transmitter inverter structure is proposed that realizes the proposed in-phase excitation without additional inverter legs. Based on the analytical model, the pad and resonant parameters are designed, and the control degree of freedom is utilized to achieve the target power transfer. The proposed structure and control are validated experimentally. Experimental results at 11 kW demonstrate a DC/DC efficiency of approximately 96%, confirming interoperable operation between the three-phase transmitter pad and the single-phase receiver pad.

Transformerless power converters are increasingly getting attention in the ac-dc power conversion due to their advantages in improving the efficiency and the power density. However, the removal of the isolation barrier with high common-mode (CM) impedance generates a leakage current issue due to the common-mode voltage (CMV), posing a human safety risk. This article comprehensively analyzes the influence of the CMV sources on the leakage currents, dividing into the low- and high-frequency (HF) components. To this end, a CM equivalent circuit is developed, considering the filter and grounding system. In order to mitigate the low-frequency (LF) leakage currents, a CMV control method is proposed, which generates the LF CMV through the pulsewidth modulation (PWM) converters. The leakage current flowing into the ground wire is directly measured and utilized as a feedback for the controller. Subsequently, a high-dimensional space vector PWM (HDSVPWM) is introduced to synthesize both differential mode voltage and CMV references for the single-/three-phase PWM converter. The proposed HDSVPWM minimizes the HF CMV ripple, reducing the HF leakage currents. The effectiveness of the proposed control and modulation methods is verified with an experimental setup of grid-connected transformerless PWM converter, ensuring a compliance with the safety regulations.

This paper proposes pulse-width modulation (PWM) strategy for synthesizing both common-mode voltage (CMV) and differential-mode voltage (DMV) in three-phase transformerless grid-connected converter. Unlike conventional space vector PWM (SVPWM), which does not explicitly consider the CMV, the proposed method introduces an additional axis in the extended vector space to represent CMV, enabling a unified representation of CMV and DMV as a single vector. Then, the voltage synthesis is achieved through the four voltage vectors, forming a tetrahedral space vector region. To minimize leakage current, the tetrahedron with the shortest distance along the CMV axis is selected for the voltage synthesis. With the selected space vector region, the duration of each voltage vector is calculated through a transfer matrix approach. The proposed method is further extended to multi-level PWM converters. In addition, a simple carrier-based implementation is presented for digital control system. The proposed modulation strategy is experimentally validated by the three-phase two- and three-level PWM converters, effectively suppressing the leakage current across wide operating conditions and converter topologies.

As interest in climate issues grows, research on electric vehicles (EVs) and their charging technologies is advancing. Non-isolated topologies have been proposed to improve EV charger efficiency and power density. However, removing the galvanic isolation stage increases leakage currents, potentially causing electric shocks to users. These currents, generated by low-frequency (LF) common-mode voltage (CMV), are difficult to attenuate with EMI filters. Injecting LF CMV into the power converter can reduce leakage currents but requires higher DC-link voltage, increasing losses and reducing efficiency. This paper proposes a two-stage non-isolated EV charger with an AC/DC power factor correction (PFC) converter and a DC/DC three-level regulator. The PFC and regulator synergistically share the CMV to lower the DC-link voltage while maintaining leakage current reduction. The proposed method enables operation at lower DC-link voltage and higher modulation index (MI) regions. Experimental validation using a prototype confirms its effectiveness.

Recently, electric vehicle (EV) charging technology has been evolved to address the environmental challenges, with a particular attention to the non-isolated EV chargers for their potential to improve efficiency and reduce both size and cost. However, the absence of an isolation barrier in the system raises the challenge of human safety and electromagnetic compatibility. This paper conducts a detailed analysis of common mode voltage (CMV), identifying the impact of various CMV sources on leakage current. To mitigate the leakage current, a direct leakage current control method is proposed, which employs low frequency CMV injection by a power converter. The leakage current flowing into the ground wire is directly measured and utilized as a feedback of the controller. Then, the CMV reference of the power converter is synthesized by a proposed two-dimensional space vector pulse-width modulation (2DSVPWM). The high frequency CMV ripple is minimized by utilizing only two voltage levels. The effectiveness of the proposed methods is validated through experiments with a single-phase two/three-level AC-DC converter, demonstrating the attenuation of both high and low frequency leakage current.

Recently, electric vehicle (EV) and its charging technology have been studied with the aim of improving environmental issues. Among them, a non-isolated charger is getting attention for its potential to enhance efficiency while reducing size and cost. However, the absence of an isolation barrier in the charging system raises the challenge of leakage current. Through a comprehensive analysis of common mode voltage (CMV), this paper identifies that a low-frequency CMV generates a leakage current and poses a touch current hazard, which is difficult to attenuate by passive filters. To overcome this issue, a novel direct leakage current control method is proposed which synthesizes low-frequency CMV using a power converter. The leakage current flowing into the ground wire is directly measured and employed as a feedback of the controller. Utilizing a plant model from the common mode equivalent circuit, the controller is designed in a form of band-pass filter. The proposed control method is verified through experiments using a single-phase AC-DC converter, attenuating touch current to satisfy IEC 61851-23 standard.

This paper presents an approach for diagnosing faults in reciprocating compressors used in commercial refrigerators. With the increasing importance of fault detection in electrical drives, machine learning techniques, particularly unsupervised learning, have gained popularity due to the difficulty in obtaining faulty data. This study employs an auto-encoder (AE) based anomaly detection model trained exclusively on normal data. The AE compresses the input data into a latent space and reconstructs it, enabling the detection of anomalies when the reconstruction error exceeds a certain threshold. Key input features are selected and extracted without the need for additional sensors, utilizing harmonic information of the compressor’s torque derived through a heterodyning method. The effectiveness of the proposed model is verified on a compressor system using an STM32G431RBT6 digital signal processor (DSP). Experimental results demonstrate 100% accuracy in identifying various mechanical faults, including demagnetized compressors and those operating without oil or refrigerant.

In order to enhance the saliency-based position sensorless drives with a single current sensor (SD-SCS), this paper proposes a current derivative-based sensorless control using a tri-active vector pulse width modulation (TAVPWM). In the SD-SCS, the performance of the position estimation is deteriorated due to the injected voltage at the current reconstruction dead zone (CRDZ) and the unaligned sampling with a single current sensor. To improve the performance of the SD-SCS, the TAVPWM scheme is adopted to eliminate the CRDZ in the low-modulation region. Furthermore, the phase current derivatives, which are accurately reconstructed at each active vector of the TAVPWM, are utilized to minimize the position estimation error resulting from the unaligned current sampling. Owing to the proposed method, the switching frequency has been increased up to 16 kHz, which eliminates the audible noise virtually in the SD-SCS. Lastly, the enhanced dynamic performance of the SD-SCS is verified by various experiments.

Load torque identification is one of the most important factors in making a high-performance motor drive system. The paper proposes an enhanced sliding mode observer for the load torque estimation. To suppress the chattering, which is a significant issue in the sliding mode observer, this paper utilizes a feedforward compensation of the state variable. The error of the rotor position and the rotor speed is utilized in DCCSMO and SCCSMO respectively to make the feedforward compensation. With the modified structure of the sliding mode observer, the ripple of the estimation is effectively suppressed without any phase delay. The proposed method only requires the position sensor, and the implementation is easy. Also, the method does not require high computational cost. The improved performance of the proposed method is verified by various experimental results. The results show that the proposed method reduces the chattering up to 85% and achieves strong antidisturbance ability in comparison with the conventional method.

This paper proposes a position sensorless control method of permanent magnet synchronous motor (PMSM) using the current derivative measurement with the hybrid pulse width modulation (PWM). Ensuring a sufficient duration of the voltage vector for the current derivative measurement is a main issue in fundamental PWM excitation-based (FPE) sensorless control method. The proposed method overcomes this issue by extracting the position error from the phase voltage and current in only one voltage vector. Then, the hybrid PWM method is introduced to enhance the accuracy of the position estimation regardless of the modulation index (MI). In addition, the current derivative is accurately measured using the multi-point current sampling (MPCS) and the least square curve fitting (LSCF). To improve the performance of the sensorless control, the time delay compensation and average current calculation methods are presented. As a result, the proposed method enables a full-region sensorless control of PMSM without any voltage injection or phase shifting, which deteriorates the field-oriented control (FOC). The effectiveness of the proposed method is verified by a 1kW PMSM drive system in various driving conditions.

This article proposes pulse width modulation (PWM) methods for low inductance brushless dc (BLDC) motor drives that minimize the commutation torque ripples. An uneven current of noncommutation phase generates the commutation torque ripples. In the low inductance BLDC motor drives, two types of time delays in PWM also induce critical torque ripples. In this article, the analyses of the time delays in PWM and their effects are introduced. Then, two PWM methods are proposed to eliminate the time delays in the commutation region and the conduction region, respectively. The commutation period is controlled to be synchronized to the switching period. In addition, the proposed methods synchronize the switching period to the commutation interrupt. As a result, the proposed methods effectively maintain the minimum commutation period as well as minimize the commutation torque ripples in the low inductance BLDC motor drives. The validity of the proposed methods is demonstrated by the simulation and experimental results in various driving conditions. The results show that the commutation period is remarkably shortened and the commutation torque ripples are reduced by 27.6% in comparison to the conventional method.

This paper proposes analytical modeling and design of a 27.12 MHz single-switch dc-dc converter with galvanic isolation using a PCB transformer. The ODE-based analytical approach provides a more accurate circuit design by considering the high-order harmonics and non-ideal components such as the diode capacitances. The proposed dimensionless mathematical model simplifies the design of the desired circuit model and requires less tuning procedure. In addition, the effective analytical model offers the design curves to obtain the optimized circuit parameters at any duty ratio. Meanwhile, the multilayer planar PCB transformer is designed to achieve the isolation and high power density for the high-frequency dc-dc converter. Based on Neumann’s formula, the analytical model of the PCB transformer is proposed to calculate the inductances for the spiral structure accurately in the high-frequency conditions. As a result, the computational burden for calculating the coil inductances is alleviated using the proposed method. The simulation and experimental results using a 3W converter prototype verify the effectiveness and feasibility of the analytical modeling and design of the proposed converter.

In a coreless stator brushless DC motor, ripple-less torque control is a challenging issue. Especially, due to its low inductance, conventional commutation methods that exclude the effects of the stator resistance and the digital sampling are less effective and even detrimental to minimizing the torque ripple. To overcome the limitations, this paper proposes a new commutation method for low inductance brushless DC motor. The proposed method synchronizes the period of the commutation region with one digital sampling period and it also considers the effect of stator resistance. Three cases of the proposed method, depending on the relation between the sampling period and the motor electric constant, are introduced. In addition, the back electromotive force is measured offline and the time delay due to the full-digital system is also compensated for the accurate duty ratio calculation. The validation of the proposed method is demonstrated by the experiment and the results show that the torque ripple is reduced by 18% compared to the conventional method.