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The power transfer characteristics of dual active bridge (DAB) converters are highly dependent on the resonant network, even under the same pulsewidth modulation (PWM) technique. This article mainly addresses the design and analysis of resonant networks for DAB converters. Unlike previous studies that typically focus on tuning predetermined resonant network structures, this study introduces a methodology for determining both the structure and specific parameters of resonant networks that fulfill the system’s input-output requirements. Through theoretical analysis using a general two-port passive network model, the design degrees of freedom and their impact on the properties of resonant networks are explored. Because there are numerous candidate resonant networks, it is crucial to compare the properties of DAB converters utilizing each network. To facilitate comparison, PWM solutions that achieve soft switching and minimize root-mean-square (rms) currents for each resonant network are derived. A detailed analysis is carried out on how these PWM solutions vary with the resonant network design and how they impact the DAB converter’s power transfer properties, including rms currents, reactive power, and control sensitivity. The proposed design methodology and analysis are experimentally validated with two distinct 3.5-kW DAB converters.

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.

The six-step operation is widely used with its advantages in voltage utilization increased by 10.27% without boost circuits. However, the six-step operation causes nonideal low-order harmonics in the currents due to the uneven ratio between the sampling frequency and the fundamental one. Moreover, transitioning between pulsewidth modulation and the six-step operation needs consideration of factors such as current shocks and parameter dependencies in voltage limit conditions. The proposed overmodulation method facilitates a seamless transition to the six-step operation while maintaining the closed-loop current regulator. Furthermore, the nonideal low-order current harmonics are eliminated through a variable time step control. The proposed method achieves a reduced number of switchings by utilizing edge voltage vectors. In addition, the current ripple is reduced by solving a minimization problem targeting the weighted total harmonic distortion of the phase voltage.

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.

In capacitive power transfer systems, coupling variation inevitably occurs due to air gap variation and coupler misalignment. This paper presents a single-sided compensation network design method for capacitive power transfer systems considering coupling variation. The proposed method adopts a single-sided compensation network to reduce the volume and weight of the receiver side circuit. The proposed compensation network, within a preselected narrow operational frequency range, effectively transforms the variable load impedance into a single resistive point, resulting in constant output power and zero-phase angle operation under coupling variation. The proposed method employs the impedance matching network design based on a two-port network analysis. The validity of the proposed design method is confirmed with a simulation and a 1.2 kW small air gap capacitive power transfer system prototype. The experimental prototype system achieved a maximum efficiency of 91.2% under no misalignment and a minimum efficiency of 89.9% under a maximum 40% area displacement in coupling conductor plates, with a near-constant output power and zero-phase angle operation.

This study proposes a model for detecting anomalies in induction motors using audio signals. Compared to existing anomaly detection methods based on deep generative models, the model is presented in two main aspects. First, the proposed model consists of two generative adversarial network (GAN) modules, each processing the two types of mel-spectrograms with distinct time and frequency resolutions. These modules are trained to reconstruct input data effectively, enabling each module to extract the high-resolution time and frequency domain features. Secondly, the ensemble approach is proposed for calculating the anomaly score and loss function. This approach ensembles all the reconstruction losses and Comprehensive Feature Distances (CFDs) obtained from the two GAN modules. The CFD is calculated as the Maximum Mean Discrepancy (MMD) between the outputs of the encoder and decoder layers of the generator. The effectiveness of the proposed scheme is validated through experiments conducted with 0.75 kW induction motors.

Electromagnetic navigation systems (eMNS) for medical applications, such as cardiovascular diseases, employ stationary coils and soft magnetic cores. Electrical currents in the coils synthesize magnetic fields to wirelessly control millimeter-sized microrobots, such as magnetic guidewires. Previous control methods of calculating the current references for the eMNS focus on either low conduction loss with pseudoinverse or wide magnetic-feasible workspace (MFW) with a linear combination of pseudoinverse and minimum infinity-norm. However, with the merits of both wide MFW and low conduction loss, this article proposes an iterative control method that modifies the initial pseudoinverse iteratively, while ensuring that the current limits of the coils are not exceeded. A detailed description of the control method, accompanied by a comprehensive analysis, is provided. The prototype of eMNS with eight coils is used for the experimental verification. It is shown that, in the current limits, MFW is increased by more than 45% compared with the pseudoinverse method, and the conduction loss is reduced by more than 2 kW compared with the linear combination method.

This article presents a single shunt current sensing drive method for ultralow inductance permanent magnet synchronous motors that can reliably reconstruct phase currents even at very low speeds. Single current shunt inverters using dc current measurement entail the problem of having dead zones where the phase currents cannot be reconstructed. Voltage injection at the switching frequency can be a solution to avoid this, but at the expense of the newly introduced current ripple. That current ripple is exacerbated in ultralow inductance motors and can cause drive failure, especially at low speeds. To rule out voltage injection, this article presents a drive scheme that combines sequential two-phase excitation with a dc current averaging method using an RC low-pass filter. This permits three-phase current reconstruction from the average of dc current measurements per half-switching period, regardless of the active vector duration. Experimental demonstrations in this article show that the proposed driving method allows reliable current reconstruction at both startup and low speed without a significant current ripple. The current reconstruction and dynamic control performance are demonstrated with both steady-state and transient experiments.

In vector-controlled drive systems, a position sensorless drive with a single current sensor (SD-SCS) is an attractive system due to the minimum number of sensors. However, when the saliency-based SD-SCS is applied, the position estimation accuracy is deteriorated due to the errors in the injected pulsewidth-modulated voltage and the reconstructed current. This article proposes a current-derivative-based sensorless control using a three active vector pulsewidth modulation (TAVPWM) to enhance the saliency-based SD-SCS. First, the TAVPWM scheme, which eliminates the current reconstruction dead zone in the low-modulation region, is adopted to improve the low-speed drive. Next, the derivatives of the phase currents are utilized and analyzed to minimize the position estimation error in the overall operating regions. Finally, the transition strategy with respect to the speed is proposed for the full-speed sensorless drive. Owing to the proposed method, the switching frequency increases up to 16 kHz and the audible noise is virtually eliminated in the saliency-based SD-SCS. Furthermore, the enhanced dynamic performance is verified by various experimental results.

This article presents a modulation method for the series-resonant dual-active half-bridge (SR-DAHB) converter. The proposed method employs four control degrees of freedom: primary- and secondary-side duty ratios, voltage phase shift angle, and switching frequency. The proposed modulation method minimizes the rms current of the resonant tank while achieving complete zero-voltage switching of all primary and secondary switches for all operational ranges. Time-domain analysis of the SR-DAHB converter, which takes into account every harmonic, has been performed to obtain control value sets. Accurate steady-state values, such as half-bridge inverter switching current/voltage, output current, and rms current of the resonant tank, are derived in closed-form expressions. The derived expressions are utilized in numerical optimization algorithms to calculate optimal control value sets. Since closed-form equations are used, the computational burden of the numerical solver is relieved. The effectiveness of the proposed modulation method is verified through simulations and experiments on a 9.0 kW, 600 V full-SiC converter prototype. Compared to existing modulation methods, it is advantageous when primary- and secondary-side dc-link voltages have a large voltage difference. Particularly, in 0.25 voltage conversion ratio operation, the proposed modulation method presents an efficiency boost of up to 2% compared to the existing modulation methods.

Wireless power transfer (WPT) technology has become increasingly popular due to its ability to transmit energy without mechanical contact, making it suitable for various industrial fields. This article deals with an inductive power transfer system, which is driven with a single-switch inverter such as Class E in several megahertz or higher frequencies. One of main issues with such systems is that the output and efficiency are significantly affected by the relative position of transmitter and receiver coils. Many existing solutions require additional tunable components and driving circuits, leading to increased cost and complexity. This article provides a systematic optimization procedure of two-port impedance matching networks for wireless power transfer systems to achieve constant output power characteristics even with misalignment or air-gap variation. Since the system itself has a characteristic that is robust against misalignment, the need for any control and tunable component can be significantly reduced. The effectiveness of the proposed method is verified through a prototype of 6.78 MHz/60 W and experimental results.

Low-voltage direct current (LVDC) distribution is an efficient way to accommodate high penetration of renewable energy sources, energy storage systems, and electronic loads in the distribution systems. This article presents an enhanced dual-active bridge (DAB) converter for bipolar LVDC distribution systems. By employing a dedicated winding connection in the ac-link transformer, the operation of two dc poles on the input side can be fully decoupled. Hence, the DAB can provide full bipolar operation capability on the input side without additional power-semiconductor devices or magnetic components. The positive- and negative-pole dc currents on the input side could be independently controlled by the dedicated differential- and common-mode current controllers. Hence, in case one pole of the bipolar LVDC distribution is failed due to, e.g., damage of cable, the dc-link input current of the faulty pole on the input side of the DAB converter can be transferred to the healthy pole immediately and sustain the power supply to the output side. The effectiveness of the topology and the current control scheme proposed in this work are verified through simulations and experiments on a fabricated 7.2 kW 600 V SiC converter prototype. In asymmetric operations, the proposed three-phase DAB (DAB3) converter presents efficiency boost up to 1.5% compared with the conventional system with a DAB3 converter and a voltage balancer attributed to the reduced stage of power conversion.

In the field-oriented control of an induction machine (IM), a full-order flux observer has been widely used to estimate the flux. It has several critical issues, such as discrete-time domain instability, dynamics deterioration, and another instability in a low-speed sensorless flux estimation. This article addresses and analyzes these three issues. And it proposes a feedback gain design method for the full-order flux observer to solve the problems. In additional, the parameter sensitivity in the flux estimation is analyzed with a frequency response function. The experiments were conducted with an EV-traction IM. The results show the performances of the proposed feedback gain design in the high-speed operation over the conventional discrete-time domain stability limit, the dynamics improvement in mid- and high-speed region, and the stable operation in the low-speed regeneration mode.

This article proposes a method to extend the operating area of the interior permanent magnet synchronous machines (IPMSMs). In general, the power factor (PF) of the voltage source inverter becomes lower to maintain the maximum torque per ampere (MTPA) current of the motor. Therefore, the voltage–ampere (VA) capacity of the inverter is not fully utilized. In order to maximize the VA capacity utilization of the inverter, the capacitor network is proposed, which is located between the motor and the inverter. The PF of the inverter increases, as the capacitive impedance of the network cancels the inductive motor impedance. In this way, the maximum speed of the constant torque region increases without changing the inverter and the motor. Due to the capacitor network, this method generates a higher power than the conventional drive method. The design method and analysis results of the capacitor network are presented. The current control method in the proposed system is also presented. At the end of this article, the effectiveness of the proposed system is verified through the experimental results.

It is difficult to use the conventional fixed sampling pulse-width modulation (PWM) method in a motor drive system due to the harmonics and beat phenomenon when the number of switchings is low. Synchronous PWM is a solution to overcome these problems. However, it is difficult to implement a closed-loop current controller, since synchronous PWM only has merits when the switching frequency is synchronized with the operation speed. This paper proposes a closed-loop current controller for synchronous permanent magnet machines which are driven by synchronous PWM. The proposed controller uses the concept of variable time step control. The control variables are the sampling time interval and the output voltage magnitude. The proposed controller dynamically controls the dq-currents, while the steady-state merits of the synchronous PWM are maintained. This paper presents the design procedures and a dynamic analysis of the proposed current controller. The effectiveness of the proposed method is verified by experimental results.

The recent emergence of the hydrogen (H2) fuelcell electric vehicle (FCEV) guarantees the benign nature of the transportation industry. Several companies, e.g., Toyota and Hyundai, have started to commercialize H2 FCEV with relatively comparable properties to meet the renewable energy-based future. For instance, the Hyundai Tucson can drive around 400 mi after 3 min of a simple H2 charge. Additionally, to keep abreast of supporting H2 FCEVs, Germany has decided to help construct the fueling stations by supporting funding and restricting oil-based vehicles production.