This article presents a current controller design for an open-end winding permanent magnet synchronous motor (OEW-PMSM) supplied by a common DC source. Conventional control approaches for OEW-PMSMs have typically treated the zero-sequence (n-axis) component as an independent variable, ignoring its dynamic influence on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> components. In this work, a unified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dqn</i> motor model is first established by incorporating mutual inductances and rotor position-dependent spatial harmonics across all axes. Then, based on the proposed model, a multivariable controller is analytically derived to achieve fully decoupled current dynamics while ensuring stable operation under load variations. The proposed controller accounts for interaxis coupling in its structure, enabling active regulation of the zero-sequence current. This leads to improved steady-state and transient performance. Experimental validation is conducted on a motor developed for electric vehicle applications. The results confirm the effectiveness of the proposed method over conventional control, demonstrating improved steady-state waveform quality, and a reduction in total harmonic distortion (THD) of the current from 6.61% to 4.86%. In addition, the transient response is significantly enhanced. Even during abrupt torque changes, the zero-sequence current remains stable, unaffected by disturbances in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> currents.

Estimating contact force for a robot manipulator without an force/torque (F/T) sensor poses challenges due to uncertain torques, such as backlash and flexibility. To address this limitation, this article proposes a data-driven uncertain torque model and an overall gray-box structured approach. The contributions of this article are threefold. First, a joint domain unified neural networks (DUNNs)-based model is proposed to compensate for the uncertain torques. This model effectively captures uncertain torques beyond studies focusing solely on individual uncertainty. Second, the DUNNs model receives dynamic and joint domain information, enabling a single DUNNs model to estimate all joint uncertain torques through joint domain knowledge. This approach reduces the model size while maintaining performance. Third, the structure in which the DUNNs model works with conventional static friction models is introduced. This structure improves contact force estimation performance and enhances robustness against untrained data compared with the black-box model. Experimental results verify the method's effectiveness.

Position sensorless drive with single current sensor (SD-SCS) is widely utilized in cost-effective applications. The drive performance of saliency-based SD-SCS can be easily deteriorated due to several reasons: inaccurate phase current reconstruction (PCR) and the interference in injected voltages for the PCR and position estimation. Here, this article proposes an enhanced sensorless control strategy employing six-vertex voltage injection for PCR and position estimation. First, the parameter dependency in position estimation is eliminated by using the current derivative measurements at six active vectors. In addition, by modifying the sequence of voltage vectors, the proposed pulsewidth modulation scheme reduces the current ripple caused by the injected voltages. Experimental results verify that the proposed method shows high accuracy of position estimation and significantly reduces the total harmonic distortion of the phase current in SD-SCS, making it comparable to that of a position-sensored drive.

Voltage source inverters (VSIs) are widely used in electric vehicle due to their high control performance and efficiency in electric motor drive systems. However, the output voltage of the inverter during switching instances generates bearing currents, leading to bearing damage. This article analyzes the relationship between bearing currents and bearing damage, and proposes a new method for reducing bearing currents. First, a precise bearing current measurement system using a current transformer is introduced. This system verifies the phenomenon of bearing damage caused by bearing currents at low speeds. Fourier transform analysis of audio signals from bearings is employed to confirm this phenomenon. Subsequently, a two-phase pulse-width modulation (PWM) method that considers the saliency of interior permanent magnet synchronous machines (IPMSMs) and a capacitive filter topology is presented. The proposed method is validated through experimental results in a commercial electric vehicle drive system. As a result, the bearing current is reduced by 91% compared to that of space vector PWM (SVPWM) method.

In saliency-based sensorless control with switching frequency voltage injection, the accuracy of rotor position estimation is deteriorated by the injected voltage errors arising from pulsewidth modulation (PWM). To resolve this issue, current derivatives within an active voltage vector are employed for precise position estimation. Accurate measurement of current derivatives requires a sufficient active vector time, necessitating additional voltage injection in low-speed regions. Considering the increased losses from additional injection, this article proposes two types of voltage injection methods that ensure only the minimum active vector time without modifying the PWM scheme. In the proposed methods, the magnitude and direction of injected voltages are analytically determined by considering the angle between the injected and fundamental voltages. Consequently, the proposed injection methods reliably ensure the minimum active vector time regardless of the load conditions, thereby improving the position estimation accuracy. Experimental results under various operating conditions verify the effectiveness of the proposed methods.

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, non-isolated 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 non-isolated 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 pulse width modulation (PWM) 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.

GFM inverters have been widely recognized for their enhanced stability in weak grid conditions compared to GFL inverters. However, their power output capability (P–Q capability) may still be limited by both physical and stability-related constraints, particularly under low short-circuit ratio (SCR) conditions. While numerous studies have investigated P–Q capability in voltage control mode with constant voltage set points, a comprehensive characterization of P–Q capability in the widely adopted reactive power control mode, where significant voltage variations arise from elevated grid impedance, remains limited. This study provides a thorough evaluation of the P-Q capability in reactive power control mode, taking into account the combined constraints of inverter voltage limit, current limit, angle stability limit, and voltage stability limit. The explicit mathematical models of these capabilities are developed in a unified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P-Q</i> framework, incorporating the effects of the interface filter and virtual impedance. Our analysis demonstrates that the angle stability and voltage stability align along the same capability curve in reactive power control mode, suggesting that both challenges emerge concurrently. Leveraging these models, two adaptive reactive power control strategies are proposed to maximize the active power output while optimizing the reactive power and output current, respectively. The effectiveness of the proposed models and control strategies is substantiated through experimental results.

Switched capacitor converters require large capacitors due to the burden of high peak currents, which imposes a limitation on the minimum volume of passive components. This paper structurally proposes a new topology that reduces the DC voltage stress of capacitors, aiming to decrease stored energy and improve passive component volume. It is derived by modifying the connection state of the flying capacitors in the conventional Dickson converter. A consistent derivation method is applied to generalize it for a voltage conversion ratio of N:1. The improvement in passive component volume due to the reduction in DC voltage stress is confirmed through the output impedance analysis. Furthermore, the theoretical decrease of output impedance is derived through an equivalent circuit analysis based on the switch connection states. The proposed topology is experimentally verified with 48 V input to 8 V, 20 A output prototype. A full load efficiency of 96 %, which is 0.8% higher than that of the conventional Dickson converter, was achieved, with a 43.3 % reduction in passive component volume.

This article presents a current controller design for an open-end winding permanent magnet synchronous motor (OEW-PMSM) supplied by a common DC source. Conventional control approaches for OEW-PMSMs have typically treated the zero-sequence (n-axis) component as an independent variable, ignoring its dynamic influence on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> components. In this work, a unified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dqn</i> motor model is first established by incorporating mutual inductances and rotor position-dependent spatial harmonics across all axes. Then, based on the proposed model, a multivariable controller is analytically derived to achieve fully decoupled current dynamics while ensuring stable operation under load variations. The proposed controller accounts for interaxis coupling in its structure, enabling active regulation of the zero-sequence current. This leads to improved steady-state and transient performance. Experimental validation is conducted on a motor developed for electric vehicle applications. The results confirm the effectiveness of the proposed method over conventional control, demonstrating improved steady-state waveform quality, and a reduction in total harmonic distortion (THD) of the current from 6.61% to 4.86%. In addition, the transient response is significantly enhanced. Even during abrupt torque changes, the zero-sequence current remains stable, unaffected by disturbances in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> currents.

Estimating contact force for a robot manipulator without an force/torque (F/T) sensor poses challenges due to uncertain torques, such as backlash and flexibility. To address this limitation, this article proposes a data-driven uncertain torque model and an overall gray-box structured approach. The contributions of this article are threefold. First, a joint domain unified neural networks (DUNNs)-based model is proposed to compensate for the uncertain torques. This model effectively captures uncertain torques beyond studies focusing solely on individual uncertainty. Second, the DUNNs model receives dynamic and joint domain information, enabling a single DUNNs model to estimate all joint uncertain torques through joint domain knowledge. This approach reduces the model size while maintaining performance. Third, the structure in which the DUNNs model works with conventional static friction models is introduced. This structure improves contact force estimation performance and enhances robustness against untrained data compared with the black-box model. Experimental results verify the method's effectiveness.

Position sensorless drive with single current sensor (SD-SCS) is widely utilized in cost-effective applications. The drive performance of saliency-based SD-SCS can be easily deteriorated due to several reasons: inaccurate phase current reconstruction (PCR) and the interference in injected voltages for the PCR and position estimation. Here, this article proposes an enhanced sensorless control strategy employing six-vertex voltage injection for PCR and position estimation. First, the parameter dependency in position estimation is eliminated by using the current derivative measurements at six active vectors. In addition, by modifying the sequence of voltage vectors, the proposed pulsewidth modulation scheme reduces the current ripple caused by the injected voltages. Experimental results verify that the proposed method shows high accuracy of position estimation and significantly reduces the total harmonic distortion of the phase current in SD-SCS, making it comparable to that of a position-sensored drive.

Voltage source inverters (VSIs) are widely used in electric vehicle due to their high control performance and efficiency in electric motor drive systems. However, the output voltage of the inverter during switching instances generates bearing currents, leading to bearing damage. This article analyzes the relationship between bearing currents and bearing damage, and proposes a new method for reducing bearing currents. First, a precise bearing current measurement system using a current transformer is introduced. This system verifies the phenomenon of bearing damage caused by bearing currents at low speeds. Fourier transform analysis of audio signals from bearings is employed to confirm this phenomenon. Subsequently, a two-phase pulse-width modulation (PWM) method that considers the saliency of interior permanent magnet synchronous machines (IPMSMs) and a capacitive filter topology is presented. The proposed method is validated through experimental results in a commercial electric vehicle drive system. As a result, the bearing current is reduced by 91% compared to that of space vector PWM (SVPWM) method.