We have developed a low-loss method for suppressing the switching surge voltage, which is an issue in power electronics systems. Conventionally, resistance snubber circuits have been used to suppress the switching surge voltage, however, they increase the system loss because of the loss of switching surge energy due to the resistance thermal loss. We have developed an “Isolated regenerative snubber circuit” that suppresses the switching surge voltage by regenerating the surge energy to the system without consuming the surge energy. This paper describes the operation evaluation of the regenerative snubber circuit through prototype evaluation.

Large-capacity air conditioners are widely used in office buildings, schools, hospitals, and so forth. Downsized and energy-efficient large-capacity air conditioners are strongly required in such applications. This paper proposes a new low-loss boost-chopper circuit, which is applicable in large-capacity air conditioners. The basic principle of the proposed low-loss boost chopper is discussed in detail. Experimental results of the proposed boost chopper demonstrate that the conversion efficiency is improved, achieving a stable boost operation of dc-bus voltage. A new compressor motor is also proposed considering the stable boost operation of the dc-bus voltage. It is also demonstrated that the total conversion efficiency between an ac-side input terminal and an output terminal of an inverter including a diode rectifier and the proposed low-loss boost-chopper circuit with the newly proposed compressor motor is improved. This improved efficiency of inverter system contributes to reduce the installation area and weight of the newly developed model by 50% and 31%, respectively, as compared to those of the previous model.

This paper proposes a simple position sensorless speed control method for permanent magnet synchronous motors (PMSMs) using flux vector. The proposed method is simpler than direct torque control and does not require speed and torque controller. Speed control can be realized by applying a synchronous drive instead of a speed controller, which is not affected by speed estimation and torque estimation accuracy. In addition, stabilization control is realized by feeding back torque pulsation because only the synchronous drive becomes oscillatory. The stability of the proposed method is analyzed by root locus, and it is shown that the gain design is easy to obtain a desired response. Furthermore, maximum torque-per-ampere control, which is known as the high-efficiency drive method, is realized by applying armature flux reaction control, which is robust against parameter errors of PMSM and voltage errors due to an inverter. Finally, the effectiveness of the proposed method is confirmed by analysis and experiments.

Recently, the reverse power flow of photovoltaics during daytime and the concentration of electric vehicle charging at night have caused voltage violation in distribution lines. One of the methods to regulate the distribution line voltage and suppress voltage violation is to control the reactive power by using grid side equipment and distributed generators. However, the installation cost of grid side equipment and the possibility of output power reduction of distributed generators are obstacles with regard to controlling the reactive power. In this research, to reduce the additional installation cost of grid side equipment and to avoid reduction in distributed generator output power, reactive power control by using power factor correction (PFC) converters in consumer loads is introduced and its control ability is evaluated through experiments. Its effect on PFC converter output voltage ripple is also evaluated. From the experiments, the reactive power control ability with the use of PFC converters is verified, and it is found that the increase in output voltage ripple is not large. The proposed reactive power control method can achieve reactive power control by using consumer loads.

The grid connection inverter is built in the PCS (Power Conditioning Subsystem) for the distributed power supply, such as photo voltaic system. Recently, there has been considerable advances in the research on power flow using PCS. In order to adjust the power in the PCS, it is necessary that the grid connection inverter of the PCS predicts the load and output fluctuation in the customer side. Therefore, this paper investigates a load estimation in the grid connection inverter of the PCS. The proposed estimation method adds a superimposing pseudo-white signal to the inverter reference. The validity of the proposed estimation method is verified experimentally. In addition, the pseudo random binary sequence creates a pseudo-white signal for load estimation. As a result, it is experimentally clarified that the proposed method reduces the estimation time and improves the estimation accuracy.

This paper proposes an LED driver that consists of a ceramic-capacitor-input rectifier and a buck-boost converter. The LED driver has an advantage of long-life because it does not contain any electrolytic capacitors. However, the issue with electrolytic capacitor-less LED driver is that the ripple of the smoothed voltage becomes large due to insufficient capacitance of the smoothing capacitor. The proposed method, which uses the discontinuous current mode of a buck-boost converter, reduces the output current ripple under such conditions. Experimental results using a 5.7W LED driver prototype demonstrate that the proposed method reduces the output current ripple and that the percent flicker becomes 4.4%, which is smaller than the recommended upper limit of 8%.

This paper proposes a linear PFC regulator with a light flicker compensating circuit for LED lighting applications. The proposed circuit is small in size because it includes no reactors or electrolytic capacitors. The light flicker compensating circuit, which is connected in parallel to the LED string, consists of four ceramic capacitors and diodes. These capacitors are operated in series in the charge state and in parallel in the discharge state by using a diode network circuit. Therefore, an external controller and large capacitors are not required. The proposed circuit is experimentally validated using a 9W prototype. From the experimental results, it is found that the power fluctuation of the LED string is less than the JIS and JLMA limitations, and the power factor is 0.95. In addition, the power loss is analyzed at an efficiency of 89.4% for the prototype circuit. Also, by modulating the current regulator, sinusoidal input current can be achieved. The second proposed circuit is experimentally validated using a 7.5W prototype, and the power factor and input current distortion are found to be 0.999 and 2.1%, respectively.

Energy harvesting methods such as vibration generators have attracted considerable attention. For proper utilization of the generated power, its performance needs to be improved. This study investigates a current compensation method with a circulating current control circuit for improving the output characteristics. As a result, the output power increases compared to that of conventional circuit due to current compensation. The validity of the proposed circuit is experimentally verified in this report.

This paper presents signal conditions taking motor efficiency into account for position sensorless control of interior permanent magnet synchronous motors (IPMSMs). Signal injection is necessary for position estimation based on an extended electromotive force (EEMF) model at standstill and low speeds. We have proposed a maximum torque control reference frame and the EEMF model suitable for signal injection, and we executed sensorless control in the entire driving area. However, its effects on motor efficiency have not been evaluated in the previous study. Therefore, in this paper, we optimize the amplitude, phase, and frequency of signal current. Moreover, we applied a signal current amplitude adjusting method. This method makes the signal current amplitude minimum based on the EEMF. As a result, we can maintain constant efficiency including copper loss and other losses of the motor, regardless of the signal frequency. The signal frequency can be freely selected in terms of the motor efficiency, so that the proposed method can improve the flexibility to design the injection signals for the position sensorless control of the IPMSMs.