This paper intensively discusses control of the transformer-less hexagonal modular multilevel converter (HMMC). The HMMC is applied as a loop power controller (LPC) for a three-phase power system in which the ends of two power feeders are connected to form a power loop. The LPC is an attractive power system that enables changing the power flow balance between two feeders to avoid exceeding the current capacity. HMMC is a modular multi-level converter (MMC) topology, and has extensive ability for multilevel output voltage. MMC represents an emerging topology for three-phase BTB applications such as wind turbine generation systems, STATCOM, etc. The transformer-less configuration of MMC facilitates weight and size reduction of the converter, but the capacitor voltages in cell modules need to be regulated properly. This paper proposes a control scheme based on the current control of HMMC for LPC applications, which includes active and reactive power control, capacitor voltage control, and some related controls. This article describes the current flow control between two feeders; the three-phase load on each feeder is connected to HMMC. Especially, in order to maintain constant capacitor voltages, a combined circulating current control strategy including independent circulating current control for the primary and secondary sides and an internal circulating current control is proposed. This method is effective for operation under different phases between two feeders or three-phase unbalanced load for LPC applications. Further, simulations and experiments in typical cases verify the feasibility and effectiveness of the proposed control strategies.

This study introduces an optimal system combining a circuit configuration and control algorithm for wireless power transmitter with coils arranged in a square pattern. The system uses a four-leg half-bridge inverter to simultaneously feed power to four coils through a switch set. Inductances, including the mutual inductances between the transmitter coils, are eliminated using the reactance devices on the return path in the proposed circuit configuration. The proposed control algorithm enables uniform power transfer at maximum efficiency, independent of the receiver position. The experimental results obtained using a prototype of the transmitter confirm that the system can transfer 500W with a slight variation of 5.56% and efficiencies more than 80.6%.

This study presents a feedforward control method that reduces the seek time of hard disk drives (HDDs) using a sampled-data polynomial based on a causal first-order hold (CFOH). The method improves the seek time of the magnetic-head positioning control system of the HDDs, primarily because the CFOH responds faster than the conventional zero-order hold (ZOH). The sampled-data polynomial enables easy and real-time calculation of the feedforward control input using polynomials, eliminating the need for memory-consuming lookup tables. The sampled-data polynomial for CFOH meets the boundary conditions, including the CFOH characteristics. Moreover, it effectively corrects the discretization error caused by the CFOH without complex calculations. Replacing the ZOH with the CFOH in the feedforward control system of the HDDs improves the performance significantly. Simulation results of the track seeking control of the HDDs confirm that the proposed method successfully reduces the seek time compared to a conventional method.

This paper presents a new prototype of a single-phase class-E direct ac-ac converter for induction heating applications. In contrast to the multi-stage and traditional single-stage power conversion systems, the proposed direct ac-ac converter not only simplifies the topology of power conversion, but also enhances the efficiency, soft-switching, and EMI performance, optimizing the overall system performance. This converter features a power control methodology utilizing the reverse conducting and reverse blocking modes of a bidirectional switch based on pulse density modulation, which is suitable for a wide range of soft switching and fixed frequency operations. The performance of the direct ac-ac converter is investigated by experiments using a 1.2kW/56kHz prototype, where the high-frequency load power regulation and power conversion efficiency are revealed as well as soft switching were verified. The practical effectiveness of the power converter and power control scheme are evaluated.

Wireless power transfer (WPT) system for electric vehicles is expected for different manufacturers to construct the transmitting and receiving sides. This paper proposes a reference impedance plane method for interoperability by independently calculating the transmitting and receiving sides and comparing the regions where power transfer is possible. The proposed method also accommodates various constraints and self-inductance variations of the misalignment. A 6.6-kW rated WPT system was designed and constructed to demonstrate the effectiveness of the proposed method and confirm the power transferability and adherence to the constraint conditions.

This paper presents a practical and high-performance auto-tuning method for feedback controllers in industrial servo systems aimed at achieving fast and precise positioning. Conventional auto-tuning approaches generally limit control performance by avoiding an aggressive parameter search for fear of instability of the feedback control system during auto-tuning. To overcome this issue, the proposed method employs a stable parameter search space that ensures specified stability margins and searches for optimal parameters within this space. The proposed method is established by combining it with a genetic algorithm-based parameter search as an example global optimization-based auto-tuning method, and is adopted for fast and precise positioning control of a galvano scanner. The results of auto-tuning experiments demonstrate the effectiveness of the proposed method compared to a conventional auto-tuning method that does not consider a stable parameter space.

Cascade H-bridge (CHB) converters show promising potential across various applications, such as power electronic transformers and static synchronous compensator, because of their advantages such as modularity and the ability to generate multilevel output voltage. However, the DC-link voltage of each CHB module needs to be controlled individually. Imbalanced voltage is, therefore, a serious problem for the stable operation of CHB. In this study, we developed a hybrid modulation strategy for a single-phase CHB rectifier (CHBR) in a power electronic transformer used in the traction industry. In the proposed average voltage selected (AVS) method, the average DC-link voltage value is calculated. All modules whose DC-link voltage is lower than the average are charged, and all modules whose voltage is higher than average are discharged. Furthermore, a duty ratio saturation compensation is used. Compared with previous hybrid modulation strategy with a wide stable operation region, the AVS method can decrease the input current total harmonic distortion (THD) and DC-link voltage THD without sacrificing the stable operation region and switching loss. The effectiveness of the AVS method was verified by simulation and experiments.

In this paper, a control method to realize zero-voltage turn on in the discharging circuit is proposed of a single-phase converter based on a dual-active-bridge (DAB) dc-dc converter with an active energy buffer. The discharging circuit is composed of a buffer capacitor connected in series with a MOSFET switch. The main source of losses in the discharging switch is revealed theoretically through an analysis on the threshold level of the gate signal voltages and their switching timing. A modified gate signal with delay time for the discharging switch is proposed to prevent the parasitic output capacitor from short circuit of MOSFET and flowing inrush current to the DAB converter. Experimental results under 5.4kW power condition verifies the theoretical assumptions in terms of power losses on each switching devices. As a results, power conversion efficiency with the proposed control method has been improved to 93.5% from the results without the proposed one of 92.9%.

With electric motor emulators (EMEs) becoming a crucial testing apparatus for motor drives, enhancing the performance of the controller in an EME is important. Recent research has introduced feedforward terms based on the motor model to improve the control of EMEs. Therefore, this paper summarizes the derivation of the model-based feedforward voltage terms. Additionally, the mathematical models of the EME using the PI controller with and without feedforward terms are derived. Subsequently, the theoretical effectiveness of the feedforward terms is demonstrated by comparing the step responses and frequency characteristics of the EME to the motor model. Finally, the results are verified through computer simulations.

Stepping motors experience oscillation when positioning. A proposed sensorless tuning method for back-phasing damping can determine the appropriate excitation times to suppress the oscillation numerically according to added inertial load conditions after the motor model is estimated from the winding voltage. The driving experiments demonstrate suppression using the excitation times tuned for added loads.

The primary loop of the SCMaglev's DWPT system has several distinctive features compared to other DWPT systems. These include its length, order of several kilometers, its installation position close to the concrete roadbed and its working frequency near 10kHz. These were almost no findings and experiences regarding electric constants required for designing the electric resonance, theoretical considerations have been conducted to determine the constants, inductance and stray capacitance. The value obtained can be calculated using simplified methods and are close to the results obtained from the field test.

This paper presents a control method for the failure of one of the two units of a double three-phase-wound permanent magnet synchronous machine drive system without contact between these two units by estimating the state of the other unit based on magnetic coupling of a dual resolver. This paper proposes an another unit state estimation algorithm, in which the second unit extracts coupling signals from the output windings of the dual resolver. If the level of the extracted signals is smaller than threshold value, the first unit is determined to have failed. Experiments were conducted and the results showed the effectiveness of the proposed method.

This study presents a design method for high-torque-density air-core distributed windings with round wires applied to slotless permanent magnet synchronous motors (SL-PMSMs). The authors extend the conventional method to the case of applying round wires and Halbach-array magnets and clarify the optimization method considering interference with adjacent coils. As a result of the calculation, the objective function, which is the torque constant per square root of the copper loss, is limited to 0.86 times or less relative to the optimal solution. The actual test of a prototype SL-PMSM was conducted to validate the optimization method, and the experimental resistance of one coil is 6% larger than that of calculation, and the objective function measured from the current-torque characteristic at 60kr/min decreased by 30% to that of the calculation.