This paper proposes a space vector pulse width modulation (SVPWM) that reduces current harmonics flowing through DC-link capacitors of a three-level voltage source inverter in a three-phase motor drive system. The inverter input current harmonics are minimized by optimizing the applied voltage space vectors to reduce the fluctuation of the inverter input current around its average value. Furthermore, the proposed strategy can be used for a wide range of load power factors by changing the combination of voltage space vectors according to output phase current conditions. It is experimentally shown that the proposed SVPWM reduces the inverter input current harmonics by 27.4% at most, compared with that of the conventional SVPWM. Moreover, the analytical and experimental results clarify that the proposed SVPWM reduces the inverter input current harmonics at any load power factor.

Modular multilevel converter (MMC) has been widely used in medium/high-voltage direct current transmission, motor drive, and renewable energy power generation. The reliability requirements of the MMC system, which is composed of numerous sub-modules (SMs) as building blocks, are getting crucial. However, the testing for reliability of SMs in a full MMC system is time-consuming and costly. In this paper, a mission profile emulator for SMs in the MMC system is therefore focused; by using this mission profile emulator, the SMs can be tested individually without building a full MMC system. Simulation results have shown that arm current and capacitor voltage of the SM under test agree well with the SM in a complete MMC system. A scaled-down experimental platform is built and experimental results have proved the validity of this emulator.

This paper proposes a normalization design for series inductances in a triple active bridge (TAB) converter. The voltage variations and inductances are normalized based on percentage, and the complicated relationships between the elements of the TAB converter are clarified. The limitation of inductances corresponding to the different voltage variations is specified. The inductances are designed by considering the operation range of the phase shift angles. Based on this, the proposed method allows the inductances in TAB converter to be designed for various applications. A prototype converter rated at 200V and 500W is implemented to verify the proposed method. The experimental results show that the converter can operate under the rated power, indicating that the proposed method can be applied for designing of a TAB converter.

This paper proposes a multiple harmonics reduction method for the integrated on-board battery charging system of hybrid electric vehicles (HEVs). The proposed system allows the starter generator and its drive inverter to operate as a battery charging system. The reconfiguration of the system results in the elimination of the conventional on-board charger (OBC), thereby reducing the system volume, weight, and manufacturing cost of HEVs. In addition to the control method of the battery charging system, a harmonics compensation method is presented to improve the performance of the charging system. Different harmonics can be expressed as a unity variable in the synchronous reference frame by utilizing the phase sequence of the harmonics. The unified variable reduces the harmonic controller and simplifies the gain value selection. Simulation and experimental results verify the effectiveness of the integrated on-board battery charging system and its control method.

An LLC series resonant converter presents a viable opportunity for the realization of a DC solid-state transformer. As the DC-based power system increasingly garners the attention of academia and industry, the need for reliable, economical and efficient voltage transformation with galvanic isolation has emerged. The integrated gate-commutated thyristor (IGCT) is an attractive switch for such implementation because of its advantages over the insulated gate bipolar transistor, namely the lowest conduction losses in the class. This work shows that the IGCT can be easily implemented as a switching element in a resonant converter without the need for the protective clamping circuit. Resonant switching operation is demonstrated and supported by experimental data, and high efficiency is confirmed at high switching frequencies.

The transformer and output filter of the micro-inverter usually have a considerable footprint in the total system. In order to improve the power density of a micro-inverter, an integrated structure of passive components including transformer and output filter is proposed with flexible multilayer foils (FMLF). The topology of the micro-inverter is modified, which enables the integration of these passive components. In this paper, the design of the integrated structure is detailed. The distributed components model of the structure is established to verify the performance of the flexible foils. Finally, a prototype of the proposed structure is built and used in the micro-inverter. Experimental results are included to verify the integration design.

The back-EMF based sensorless drive of permanent magnet synchronous machines (PMSMs) is attractive for many industrial applications due to its simplicity and good reliability. For applications such as pumps and fans, in which there is no demand for high dynamic performance in the low-speed range, the I-f method for startup is considered as a much simpler solution than many high-frequency signal injection methods. This paper proposes an I-f startup method that enhances the performance by adopting a frequency compensation loop to improve the system stability and a current vector magnitude compensation loop to obtain a smooth transition to back-EMF based sensorless field-oriented-control (FOC). The experimental results verify the effectiveness of the proposed method and its superior performance compared with the existing I-f starting method.

A three-level buck converter in the discontinuous conduction mode (DCM), where the output power is typically less than 1W and the output current is less than several hundreds of mA, is a key circuit for integrated voltage regulators to achieve high efficiency at a light load in the standby mode operation of microprocessors. In this study, the fundamental circuit characteristics including the conversion ratio and transfer function are analytically derived for the first time. The derived transfer function is verified via time-domain small-signal-injection simulation as well as experimental measurements using a prototype of the three-level buck converter in the DCM with off-the-shelf ICs. Similar to conventional two-level buck converters in the DCM, three-level buck converters have a first-order lag transfer function, while those in the continuous conduction mode (CCM) have a second-order lag transfer function. A compensator design for the three-level buck converters in DCM and CCM in low-power application is discussed.

Power electronic converters comprise of solid-state switching devices and energy storage elements. With technological advancements in device technology, the power density of converters has significantly reduced since the 1970s. This paper discusses the principles of smart-switching pulse width modulation (PWM) approaches that can significantly reduce the energy storage requirements for high-density power conversion (0.1-10 µF vs. 100-1000 µF). Smart switching approaches feature an intelligent switching sequence, accurate duty ratio calculation, and robust fast bandwidth controls. Along with a discussion on the main features of smart-switching, several applications of smart-switching PWM approaches are presented with simulation and experimental results.

This paper considers the application of series-connected press-pack Injection Enhanced Gate Transistors (IEGTs) as semiconductor breakers for hybrid DC circuit breakers (DCCBs) in multi-terminal HVDC transmission systems. In order to interrupt a large current equivalent to a fault current without parallel connection of a press-pack IEGT, a snubber circuit was applied. With the snubber circuit, surge voltages and switching losses can be reduced. In order to balance the voltages across each series-connected IEGT, their characteristics and circuit conditions should be similar, and the operation timings should be adjusted. The performance a prototype hybrid DCCB was evaluated. The semiconductor breaker of the hybrid DCCB prototype was composed of four series-connected IEGTs (4.5kV, 2.1kA) with the snubber circuit. The experimental results show that it successfully interrupted a current of 9.5kA. The peak voltage across the semiconductor breaker was 14.3kV. The variation in the voltage across each IEGT was less than 5%. This means that the peak voltage of each IEGT was suppressed to less than the withstand voltage of the IEGT.

A new multiple dc-inputs direct electric-power converter (D-EPC) with legs reduction topology and its control has been developed. D-EPC is a multiple-dc-input inverter and can control power distribution for power sources. The original D-EPC has two positive terminals and a negative terminal in common, and each phase has the same circuit topology with upper arms between the positive terminal and the ac output using bi-directional switches. To reduce the number of bi-directional switch, this paper proposes D-EPC using multiple input leg reduction topology and discusses its control.

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.

External position sensors such as linear scales are frequently used in motion control systems of industrial machines, and they form a full-closed position feedback loop for accurate positioning. When the velocity signal calculated with the position signal from the motor encoder is used for the velocity control loop, resonance is less likely to occur than when using the velocity signal calculated with the position signal from the external encoder. If the position loop gain is increased, vibration is generated at the anti-resonant frequency, even if the velocity loop is stably controlled with respect to the resonance frequency. Since there is no control method for suppressing the vibration, such as the vibration control method in semi-closed control, the proportional gain of the position feedback loop cannot be made sufficiently high. In this paper, we propose a full-closed control method that suppresses the vibration at anti-resonance frequency and confirm its effectiveness through simulation and experiment.