Modular Multilevel Cascaded Converters (MMCCs) have advantages in the application of high or medium voltage without transformers. They can also generate high quality voltage with fewer harmonics. Their unique merits make them leading technology candidates for high/medium voltage applications. However, a concern still exists that the number of parts may be increased. In this study, an MMCC topology using high-voltage IGBT (HV-IGBT) with snubber capacitor connected in parallel as a cell module arm is proposed, by which the number of cells can be halved and conduction loss can be significantly reduced owing to the output current flowing through the HV-IGBT in 1/3 of the cycle. Meanwhile, the proposed control stratagem can control the cell capacitor voltage, suppress the HV-IGHT surge voltage, and avoid short-circuiting of the snubber capacitor by circulating current. This study reports the evaluation results of capacitors and the experimental results of bi-directional active power conversion operation.

A cooperative control scheme for a power conversion system having several energy sources and modular dc/dc converters is proposed in this paper. The proposed cooperative control approach has the advantage of realizing constant dynamic characteristics even when the different input voltages fluctuate or when the output power of each input voltage source is limited. The effectiveness of the proposed cooperative control method is verified via simulation and experiment.

This study proposes a reduction method for iron loss in stator core using the optimum pulse pattern for a high-speed interior-permanent-magnet-synchronous-motor (IPMSM). In this paper, a simple evaluation function for iron loss of stator core in a pulse-width-modulation (PWM) drive is introduced. In particular, the iron loss in stator core is approximately estimated from the flux level obtained from the integral of the line-to-line voltage of the PWM drive. In addition, the pulse pattern is optimized to reduce the iron loss in stator core based on the introduced evaluation function. To validate the evaluation function, the correlation coefficient between the evaluation value and the measured iron loss is calculated in 12 random pulse patterns applied to the inductor and IPMSM. As a result, the correlation coefficients are 0.991 and 0.982 in the inductor and IPMSM, respectively. In addition, the iron loss of the IPMSM with the optimum pulse pattern is reduced by 8.5% and 3.7% in comparison with a carry-asynchronous PWM and carry-synchronous PWM, respectively.

In power converter circuits, a gate drive circuit is connected to the power devices for the switching operation. The gate drive circuit transmits both signal and power to the power devices, simultaneously. At present, multi-level converter circuits using large numbers of devices have been proposed for power electronics circuits, but these are complicated to implement in a circuit. Hence, simplification of the signal and power transmissions of the gate drive circuit is required for circuit implementations. This paper proposes a gate drive circuit using SAW (Surface Acoustic Wave) devices that can transmit signal and power to the power devices, simultaneously. To use the several-hundreds MHz signal output from the SAW filter as the gate signal, this paper presents the design procedure for the internal parameters of the detection circuit that demodulates the signal into a several kHz signal. The usefulness of the proposed design is demonstrated by experimental evaluation of a half-bridge inverter and gate drive circuit with SAW filters.

A wireless power transfer (WPT) technology has recently garnered significant attention owing to its advantages of removing wire and mitigating charging concerns. In a conventional resonance-based compensation circuit design, the power transmission characteristics strongly depend on the coupling condition of the transmitter and receiver coils. Therefore, some non-resonance-based designs have been proposed. However, they are complicated and lack the resonance condition; therefore, circuit designers cannot comprehensively understand their power transmission characteristics. This study proposes a visualization method for the power transmission characteristics based on a divided analysis of WPT systems. The proposed visual map, which consists of simple circles and lines, can help in intuitively understanding the tendency of WPT and evaluate the transmission power of the compensation circuits, including the non-resonance condition. The tendency obtained from the visual map was validated via numerical simulations and experiments. The experimental results were significantly consistent with the intuitively estimated tendency and the evaluated power transmission.

Air conditioners with built-in active filters have excess distortion compensation capacity during off-season and light-load periods. It was assumed that the excess capacity during these periods could be used to improve the leading power factor. This study investigates the possibility of using the excess distortion compensation capacity in an automatic power factor regulator of an air conditioner with a built-in active filter to improve the leading power factor of the electric system during light-load periods, i.e., off-season.

Based on the analysis and evaluated results, the desired level of control was achieved for the improvement of the power factor.

This paper proposes a kernel principal component analysis (KPCA) based multivariate statistical process control (KPCA-MSPC) method for fault detection of refrigeration showcase systems using a feature selection method with maximal information coefficient (MIC). Refrigeration showcase system data include non-linear relationships among pairs of features, and only normal data can be available for training generally. KPCA-MSPC is suitable for the fault detection because it is an unsupervised method and can handle non-linear relationships. In showcase systems, a large number of measured data can be obtained and they can be utilized as features for fault detection. However, considering system costs, the number of sensors installed in the showcase systems and the amount of data stored in data centers are limited. Therefore, a feature selection method based on MIC and k-nearest neighbor algorithm (KNN) (MIC-KNN-FS) suitable for KPCA-MSPC is proposed. The effectiveness of the combination of KPCA-MSPC and the proposed MIC-KNN-FS for showcase systems is verified by comparison with the Laplacian Score feature selection method (LS-FS) and the KNN feature selection method (KNN-FS), which are typically utilized as feature selection methods, and cumulative autoencoders (CAE) and MSPC based on PCA (PCA-MSPC), which are unsupervised fault detection methods.

This paper reports a variable flux PM motor based on a new principle of self-excitation utilizing space harmonics that are inevitably generated in concentrated winding structures. In addition, it has a passive variable flux function. Its rotor is composed of consequent poles for each N- and S-pole pair and self-excited wound-field poles. The effects of the passive variable flux function on the driving performance and its efficiency map are demonstrated via the prototype.

Undesirable torque ripples in permanent magnet synchronous motors occur because of the spatial harmonics of the inductance and permanent magnet fluxes. Previous studies have proposed several methods for suppressing these torque ripples based on mathematical models. However, most of them do not consider the magnetic saturation. Hence, the torque ripple estimation accuracy may deteriorate, and the torque ripple suppression performance is reduced in the magnetic saturation range. Therefore, this paper proposes a torque ripple suppression method by considering the magnetic saturation based on the estimated harmonic component of the flux linkage and clarification of its effectiveness through simulations and experiments. From the experimental results, the proposed method is seen to suppress the 6th-order torque ripple by 69.1%, which is higher than that of the conventional method. Therefore, it is verified that the proposed method can suppress torque ripples, including those in the magnetic saturation range.