This article proposes a new architecture for the hybrid distribution transformer (HDT) with a partially rated power converter connected in series with the existing distribution transformer. The proposed single-phase system is constructed by adding a three-legged power converter in series to the existing transformer's primary side. Here, the way the converter is connected to the transformer's two taps provides the following advantages: 1) It is possible to reduce the power converter's power rating, and 2) An additional current loop, which gives a degree of freedom, is added. For better power quality, the proposed system synthesizes a voltage vector to compensate for the voltage sags/swells and the grid voltage harmonics. Furthermore, it improves the grid's power factor to increase the power transmission efficiency. The proposed system meets the needs of smart grids in terms of resilience. The configuration, control strategies, analysis, and activation/deactivation sequence of the proposed system are discussed in this article. Real-scale simulations and lab-scale experiments were performed to validate the proposed system, and the system's effectiveness was verified through the obtained results.

The propulsion system of the electric-powered vertical take-off and landing aircraft requires a high level of performances, including power density, efficiency, noise vibration and harshness, and fault tolerance. Among many types of conventional electric motor, the outer rotor surface-mounted permanent magnet synchronous motor (SPMSM) is widely used for its high power density and low torque pulsation. However, these advantages are degraded when the multiphase winding is applied to secure the fault-tolerance characteristics. To overcome the limit of conventional motor topology, the dual stator permanent magnet synchronous motor with separately controlled dual three-phase winding is proposed. The advantages of the proposed topology are resulted from the feature of mechanical, electrical, and magnetic isolation. To maximize the distinctive feature, a design process considering separated current vector control (SCVC) method is established. A design example is presented to demonstrate the impacts of the proposed design process considering SCVC on the power density maximization, torque harmonic reduction, and efficiency improvement. Finally, the experimental verification is presented to validate the proposed design and control techniques.

This article proposes a magnetic flux saturation model that well represents the cross saturation of synchronous reluctance machines (SynRMs) and a parameter estimation method of the proposed saturation model. Existing magnetic flux models do not satisfy the reciprocity condition or express cross saturation well. The proposed flux saturation model consists of terms for self-saturation and cross saturation, and it expresses well the nonlinear relationship between current and flux of SynRMs, as well as satisfies the reciprocity condition. The data of flux saturation are obtained at standstill using the hysteresis voltage injection method. Using the flux saturation data, the parameters of the flux saturation model are estimated. Because the proposed magnetic flux saturation model includes an arctangent function, it is not possible to estimate parameters directly using the linear least-squares method (LSM). However, the proposed parameter estimation method integrates the self-saturation model and transforms it into a polynomial to which linear LSM can be applied. In addition, parameters related to cross saturation are also estimated using linear LSM. Therefore, the proposed parameter estimation method is easy to implement and can be applied to general-purposed inverter products. The effectiveness of the proposed model and its identification method are experimentally evaluated with a 1.5-kW SynRM. Additionally, the identified model is verified with the accuracy of the maximum torque per ampere table and the performance of sensorless control of the tested motor.

This article proposes an offline compensation method for current scaling gains in the AC motor drive systems with three-phase current sensors. Many articles have been presented about the current scaling gain compensations of inverters. Most of them can be adopted during rotations. Those were studied for two-phase current sensing. Applications, such as elevators and hoist cranes, generally measure three-phase currents directly using three current sensors in preparation for a fault in any one of them. In this article, we present a compensation method for a three-phase current sensing system. This article analyzes the effect of current scaling gain errors on the neutral current that is calculated with measured stator currents. Based on the analysis, a compensation strategy for the current scaling gains is presented. The proposed method is applicable only at a standstill. It can be used for initial commissioning since it works at a standstill regardless of whether the rotor is locked or not. The experiments that demonstrate the validity of the proposed method were carried out in an elevator system as well as a laboratory. The proposed method is simple to be implemented and it requires no additional hardware.

This paper proposes a new estimation process of the actual maximum junction temperature in multi-chip SiC MOSFET power modules. Temperature-sensitive electrical parameters (TSEPs) are common methods to estimate the junction temperature of power devices, but they have limitations in specifying the actual maximum junction temperature in multi-chip power modules with anti-parallel diodes. Common TSEPs includes body-diode forward voltage or on-resistance of MOSFETs, but it is difficult to distinguish the impact of the anti-parallel diodes and the on-resistance-based method has low sensitivity under low-current calibration. Especially, the TSEPs has difficulty to calibrate the actual maximum junction temperature of a power module, which should solely detect the hottest device in the module. Therefore, a new dynamic calibration method is proposed using fiber optics while simultaneously monitoring factors related to the maximum junction temperature. Four critical parameters were measured from two different combinations: 4-paralleled and 10-paralleled SiC MOSFET power modules with anti-parallel diodes. Because of the abundant amount of the measured data, data-driven modeling was conducted with a deep neural network (DNN). The trained models were evaluated, demonstrating distinctly better accuracy in the actual maximum temperature estimation, for both 4-paralleled (MAE of 0.61 °C) and 10-paralleled (MAE of 0.72 °C) MOSFET modules.

This article proposes an improved neutral-point voltage balancing control (NPVBC) with time delay compensation and an antiwindup loop based on a dynamic change limit for a three-level neutral-point clamped (NPC) voltage-source inverter. NPVBC is essential for a three-level NPC inverter since it has a separate dc link. In an NPVBC based on the carrier-based pulsewidth modulation (CBPWM), the neutral-point (NP) voltage is regulated by synthesizing the NP current. The conventional NP voltage balancing controller is designed as a proportional-integral controller; however, time delays due to the digital control and pulsewidth modulation, and antiwindup loop were not considered despite the fact that digital control delay disturbs the accurate synthesis of NP current and the windup phenomenon may appear on the regulator since synthesizable NP current range can be limited by operating condition. To solve these problems, this article proposes improvement methods for NPVBC with digital delay compensation and an antiwindup loop based on CBPWM. Analysis on the effect of digital delay is described, and the time delays compensation method is proposed. Furthermore, an NP voltage balancing controller with an antiwindup loop is proposed along with an analysis of the synthesizable NP current range. With the proposed method, NP voltage ripples can be reduced, and control stability of the NPVBC can be greatly improved by preventing the windup phenomenon that may occur when the inverter output is insufficient. To verify the proposed methods, simulations and experiments, including elevator tower test, were conducted, and the results verify the effectiveness of the proposed methods.