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This article proposes a novel continuous pulsewidth modulation (CPWM) method to reduce dc-link current harmonics in voltage source inverters over wide range of load power factor. This modulation method contributes to a current stress reduction of dc-link smoothing capacitor and a suppression of its temperature rise. Furthermore, high-cost digital hardware, such as a field-programmable gate array, is not necessary because this modulation is implemented with only one carrier. The dc-link current harmonics are reduced by shifting voltage references in every half control period to reduce a fluctuation of the dc-link current around its average value. Experimental results confirm that the application of the proposed CPWM reduces the dc-link current harmonics by 24.2% at most and lowers an equilibrium capacitor temperature by 6.0 °C compared to the conventional CPWM.

This paper proposes a novel space vector pulsewidth modulation (SVPWM) strategy to reduce the switching-frequency-order inverter input current harmonics for a two-level three-phase voltage-source inverter operating over a wide range of the load power factor. The fluctuation of the inverter input current around its average value is minimized by optimization of the utilized voltage space vectors to reduce the inverter input current harmonics, which extends the lifetime of the dc-link electrolytic capacitors. Furthermore, the proposed strategy can be adapted to a motor drive system, where a wide variation of the load power factor is desired, by changing the optimized combinations of the voltage space vectors according to the polarities of the output phase currents. Experiments with the application of the novel SVPWM confirm that the inverter input current harmonics is reduced by up to 29.5% compared to that with the conventional SVPWM strategy. Moreover, the analytical and experimental results confirm that the proposed SVPWM reduces the inverter input current harmonics in both driving mode and regenerative braking mode, as well as with any load power factor.

This paper proposes a comprehensive design strategy for an LCL filter and controller parameters of an active damped LCL filter which has low inverter-side inductance in a grid-tied inverter. Design methods of a current controller and an active damping gain become more challenging because grid impedance affects the stability when the inverter-side inductance is low. First, a maximum damping gain range is derived to achieve a virtual positive damping resistor with cutoff frequency of high-pass-filter (HPF) and the LCL resonance frequency. Next, the practical implementation solutions are discussed based on the proposed design procedure. The detailed design strategy is exhibited with the design procedure and the design example. The validity of the theoretical analysis is demonstrated by a 1-kW prototype with or without the designed active damping. The grid current THD below 1.2% is maintained over the grid impedance range from 0% to 10%.

Ultra-high-speed motors has frequently been considered for many applications because to increase rotational speed of motors is effective in improving output power density and reducing motor size. In this paper, a 4-pole ultra-high-speed motor with concentrated winding structure is discussed in order to achieve even higher output power density. However, applying 4-pole magnetization to conventional ultra-high-speed motors using Nd sintered permanent magnet (PM) and concentrated winding structure will extremely increase total loss, total loss density, and especially rotor loss density. Therefore, from the viewpoint of cooling and continuous operation, it is important to propose a 4-pole ultra-high-speed motor with concentrated winding structure that can achieve even higher power density without increasing the total loss density and the rotor loss density. This paper shows that there are four important key points in the motor design to realize the proposed motor. It is found that the proposed motor can accomplish 1.5 times higher output power density without increasing the total loss density and the rotor loss density than the conventional 2-pole ultra-high-speed motor with Nd sintered PM and concentrated winding structure.

This paper provides an experimental discussion on the 6.6-kV, 200-kVA transformerless static synchronous compensator (STATCOM) based on a modular multilevel single-delta bridge-cells (SDBC) converter that is also referred to as an "SDBC converter" shortly. This STATCOM has multi-functions to control both positive-sequence and negative-sequence reactive power for voltage-flicker mitigation, as well as to achieve power-factor correction of a load(s) in industrial power systems. This paper pays more attention to the latter, showing satisfactory performance under both steady-state and transient conditions. The combination of the SDBC converter with the latest 3.3-kV SiC-MOSFET modules allows both manufacture and customer to put the STATCOM into practical use because no line-frequency transformer is required for installing it on medium-voltage utility and industrial power systems.

This paper demonstrates the thermal stress reduction for the DC-link capacitors with multiple PWM strategies. An optimized positioning of the gate pulse reduces the DC-link capacitor current. The capacitor current reduction space vector PWM (SVPWM) strategies reduces the film capacitor core temperature by a maximum of 9.0°C compared to those obtained with the conventional strategies, whereas the maximum allowable temperature of the film capacitor is 105°C. The carrier-based PWM approaches also reduce the thermal stress; however, the reduction amount is not as large as the SVPWM approach. In addition to the trade-off between the implementation requirement and the reduction effect on the capacitor current, the analytical and experimental results confirm that there is a trade-off between the improved capacitor current harmonics and the worsened load current harmonics.

This paper describes a compact model of SiC MOSFETs along with structural parasitic in a 1200-V 320-A half-bridge power module, with intrinsic interdependence of variation of gate threshold voltage and on-state voltage incorporated through a TCAD-based response surface methodology. The model can reproduce experiment static characteristics with a relative error less than ±10% curve-wisely at nominal gate voltage in 25-175°C range with the presence of variations. Current imbalance ratio of paralleled 2-module is verified to be within ±2.5% error to experimental results. Incorporating gate bias dependence in terminal capacitances improves overall switching waveforms agreement with experimental results, with switching loss error less than ±10%. The model could be employed to derive switching loss and gate driving conditions for module parallel applications with tolerance requirement on modules’ characteristics variation.

This paper proposes a novel continuous PWM (CPWM) method to reduce DC-link current harmonics in voltage source inverters (VSIs) over wide range of load power factor. This modulation method contributes to a lifetime extension of smoothing capacitors in motor drive systems. Furthermore, a high cost digital hardware such as a field-programmable gate array (FPGA) is not necessary because this modulation is implemented with only one carrier. The DC-link current harmonics are reduced by shifting voltage references in every half control period to reduce a fluctuation of the DC-link current around its average value. Experimental results confirm that the application of the proposed CPWM reduces the DC-link current harmonics by 24.2 % at most.

This paper describes a transformerless STATCOM (static synchronous compensator) intended for 6.6-kV power distribution system in Japan. The STATCOM is characterized by the use of MMCC-SDBC (modular multilevel cascade converter – single-delta bridge-cells) topology and SiC MOSFETs. The paper discusses a control method developed for the 6.6-kV system for reactive-power and negative-sequence compensation with focus on dc-capacitor voltage control. The dc-capacitor voltage control is comprised of (a) inter-phase balancing control and (b) intra-phase balancing control. The latter uses a new technique that is based on the control of dead times of bride cells. A three-phase 200-V 6-kVA experimental system is designed, constructed and tested to verify the effectiveness of the control method.

This paper describes a transformerless STATCOM (Static synchronous compensator) based on the MMCC-SDBC (modular multilevel cascade converter — single-delta bridge-cells) for independent control of positive- and negative-sequence reactive powers. A three-phase 200-V 6-kVA experimental system is designed, constructed and tested to verify the effectiveness of the topology and the control method including dc voltage regulation.

This paper proposes a novel discontinuous PWM (DPWM) in order to reduce dc-link current harmonics of a voltage source inverter (VSI) over wide load-power-factor range. This modulation method, which requires only one carrier, contributes to a lifetime extension of smoothing capacitors in a motor drive system. Furthermore, by realizing this modulation method with only one carrier, a high cost hardware such as a field-programmable gate array (FPGA) is not necessary. By adding an offset to voltage references of conventional DPWM, and shifting two unclamped voltage references in every half control period, the dc-link current harmonics are reduced even when load power factor changes. It is clarified by experiments that the proposed DPWM reduces the dc-link current harmonics by 18.4% at most at modulation index of 0.705 and load power factor of 0.819.

The conducted EMI noise flowing from power converters to an AC utility line is regulated by international commissions such as the International Electrotechnical Commission (IEC). Adherence to the IEC regulations requires that EMI filters should be used in power electronics equipment. This paper proposes a method for analyzing conducted EMI noise in multiple power converters connected to the same power line. In this method, the phase difference between subharmonic modulated carrier signals at each power converter is taken into account. The phase difference among the power converters determines the EMI noise level in a multiple converter system, as is evident from the analysis of the waveform of the common mode current. In addition, EMI noise suppression using carrier phase control is proposed. In order to reduce the size of the EMI filter effectively, the phase difference θ should be set to 360/nN°, where n is a high-order harmonic component near 150 kHz and N is the number of power converters. Therefore, the conducted EMI noise can be reduced effectively with the help of the proposed phase control. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 56–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21305

This paper proposes space vector modulation (SVM) which reduces the current harmonics flowing through the DC-link capacitor of three-phase motor drive systems. In a conventional SVM, the selection of the space vectors results in the long zero vector period, which increases the inverter input current harmonics. On the other hand, in the proposed SVM, the space vectors are selected in order to actively shorten the zero vector period. Furthermore, by applying the proposed SVM only in the regions where the instantaneous value of the input current is positive, the input current harmonics are reduced even when the load power factor becomes low. Through the experiment applying the proposed SVM, it is confirmed that input current harmonics is reduced by up to 33.9% of that of the conventional method. Moreover, it is confirmed that the input current harmonics with the proposed SVM are reduced in all range of the load power factor compared to that of the conventional SVM.

The conducted EMI noise flowing from power converters to an AC utility line is regulated by international commissions such as the International Electrotechnical Commission (IEC). Adherence to the IEC regulations requires that EMI filters should be used in power electronics equipment. This paper proposes a method for analyzing conducted EMI noise in multiple power converters connected to the same power line. In this method, the phase difference between subharmonic modulated carrier signals at each power converter is taken into account. The phase difference among the power converters determines the EMI noise level in a multiple converter system, as is evident from the analysis of the waveform of the common mode current. In addition, EMI noise suppression using carrier phase control is proposed. In order to reduce the size of the EMI filter effectively, the phase difference θ should be set to 360/nN°, where n is a high-order harmonic component near 150 kHz and N is the number of power converters. Therefore, the conducted EMI noise can be reduced effectively with the help of the proposed phase control. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(3): 56–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21305

High-frequency leakage current that may cause serious conducted EMI problems flows through an inverter system. The paths of the leakage current are stray capacitances that are formed inside of motors, cables, and IGBT modules. This paper proposes a new IGBT module that realizes low conducted emission noise by flipping the IGBT chip of the lower-voltage side to decrease its stray capacitance. The leakage current flowing through the low-noise IGBT module becomes small, since the stray capacitance is a main path of the current. Through an experiment, it is clarified that the conducted emission level is reduced by 13 dB at a maximum when the low-noise IGBT module is applied to a resonant-type inverter. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(4): 45–52, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20971

This paper describes the characteristics of the cogging torque based on four factors through the coordination between analysis and experiment. Four factors are air-gap of fitting part of divided core, annealing, a shape of inside diameter of stator, and eccentricity. This paper clarifies the influence of each factor. It is noted that air-gap of fitting part of divided core, annealing, and eccentricity have an influence to the cogging torque based on the least common multiple of pole number and slot number in 8-pole 12-slot PM motor. On the other hand, the shape of inside diameter of stator has the influence to the cogging torque of pole number order. The adequacy of the analysis model is proved by experiments.

This paper proposes a method for quantitative estimation of conducted emission from an inverter system, which helps the optimal design of EMI filters. The basic concept of the proposed method is the usage of a circuit simulator with detailed modeling of the components of the inverter system, i.e. passive devices, switching devices, and measurement instruments. The proposed method provides the conducted emission of the inverter in the form prescribed in CISPR 22, that is, the simulation results can be compared to the experiments directly. It is revealed that the simulation result agrees very well with the experiment with the error of ±6dB ranging from 150kHz to 5MHz. A great benefit from the proposed method is that the mode separation, differential and common, of the conducted emission becomes possible. Discussions and analyses are set forth in this paper with making full use of this benefit, which greatly makes the design of the EMI filter efficient.

A unique generating system for Gas heat pump system (GHP) is presented. The GHP is an air-conditioning system, in which the compressors are driven by a gas engine. The proposed system is applied to the outside unit of GHP to feed the electrical equipments inside. The system utilizes a permanent magnet synchronous generator, which is connected to the gas engine, to realize high-efficiency and small-size. The generator is controlled by a converter with sensorless control technology to eliminate the position sensor. Another major topic is the “free-run startup" technique to start the converter when the generator is rotating. The system configuration and principles of the techniques are set forth, followed by experimental results which show that the system works properly and successfully.

This paper presents a novel lightweight linear actuator using permanent magnets and having its coils on the stator concentratedly. The rated force is 6 N, the stroke is 30 mm, and the weight is below 300 g owing to its unique structure. The machine is to be applied to, e.g., a pick-and-place actuator of tiny electronic parts, and the performance for the application is confirmed through experiments with a prototype. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 59–67, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20158

This paper presents a novel lightweight linear actuator using permanent magnets and having its coils on the stator concentratedly. The rated force is 6N, the stroke is 30mm, and the weight is below 300g owing to its unique structure. The machine is to be applied to e.g. a pick-and-place actuator of tiny electronic parts, and the performance for the application is confirmed through experiments with a prototype.

This paper presents a fast calculation method for major electrical characteristics of Surface Permanent Magnet Vernier Machine; SPMVM. This method enables a parametric calculation of the characteristics from a set of specifications and thus brings rough values of the maximum performance with given conditions in a few seconds. A calculation flow is presented, followed by detailed explanations for the equations comprising the proposed method. Validity of the proposed method is confirmed by comparing the calculation results with numerical analyses and experiments. Results of case studies are set forth, which include comparison of the characteristics of the SPMVM with conventional permanent magnet machines. The case studies show that the PMVM has higher torque and efficiency, but poorer power factor, than the conventional permanent magnet machines.

This paper reviews recent technical trends in variable flux motors. Permanent magnet motor is a major component to realize high torque density with keeping high efficiency. However, when high speed revolution is required for further miniaturization, as well as the large torque in the low speed region, the flux yielded by the permanent magnet encounters a serious trade-off, i.e. the former needs less flux and the latter requires much. The solution for this trade-off is varying the flux. In general, the flux of the permanent magnet is constant, and many efforts are under development to overcome this as to be shown in this paper.

This paper presents a new auxiliary resonant commutated pole inverter that has series-connected batteries as the DC source. This inverter has two main switches and two auxiliary switches, and of all these devices achieve soft switching. The resonant operations are employed only during the commutating intervals; therefore, pulsewidth modulation (PWM) can be applied to the circuit. This circuit has the feature of using two internal voltage points of the DC source. Consequently, the circuit has the advantages of stability, simplicity in control, and high efficiency. The principle of the circuit operation and the experimental results are described in this paper.

In order to improve the control performance and to make main circuit components small, high frequency switching strategy is applied to PWM inverters. On the other hand, switching loss on the switching devices tends to increase as the switching frequency goes high. To prevent the increase of switching loss, many kinds of resonant type inverter topologies have been proposed. It is called that an auxiliary resonant commutated pole (ARCP) inverter is one of the most suitable topology for PWM control and low switching loss operation. On the other hand, it is reported that efficiency of the ARCP inverter does not so high compared with that of the conventional so-called hard switching inverters on the practical applications. These discussion will be concluded if the theoretical loss estimation of the ARCP inverter is reported.In this paper, a theoretical loss calculation method and a optimum circuit parameter condition for the ARCP PWM inverter is proposed. It is clarified that the efficiency on the optimum circuit parameter condition will rather be increased but it is difficult to use the parameter in the practical application. Then, the modified parameter that is applicable to the practical circuit is obtained. Unfortunately, even on the modified condition, the resultant efficiency does not extremely high compared with that of the conventional hard switching inverter. These results are coincide well with the experimental results on the bread board set-up and the up to present efficiency which are reported on the practical application. By the way, ARCP inverters are going to recognized as the suitable strategies for reducing EMI noise. Then, the proposed loss estimation method and the practical parameter calculation method will be useful for designing the ARCP inverter with low EMI and high efficiency.

Development and qualification results are described for a three-dimensional, time-domain core dynamics analysis program for commercial boiling water reactors (BWRs). The program allows analysis of the reactor core with a detailed mesh division, which eliminates calculational ambiguity in the nuclear-thermal-hydraulic stability analysis caused by reactor core regional division. During development, emphasis was placed on high calculational speed and large memory size as attained by the latest supercomputer technology. The program consists of six major modules, namely a core neutronics module, a fuel heat conduction/transfer module, a fuel channel thermal-hydraulic module, an upper plenum/separator module, a feedwater/recirculation flow module, and a control system module. Its core neutronics module is based on the modified one-group neutron kinetics equation with the prompt jump approximation and with six delayed neutron precursor groups. The module is used to analyze one fuel bundle of the reactor core with one mesh (region). The fuel heat conduction/transfer module solves the one-dimensional heat conduction equation in the radial direction with ten nodes in the fuel pin. The fuel channel thermal-hydraulic module is based on separated three-equation, two-phase flow equations with the drift flux correlation, and it analyzes one fuel bundle of the reactor core with one channel to evaluate flow redistribution between channels precisely. Thermal margin is evaluated by using the GEXL correlation, for example, in the module. In the upper plenum/separator module, the upper plenum is modeled as a single volume in the thermal-equilibrium state and water spiraling in the separator is modeled by an effective length in the momentum equation. In the feedwater/recirculation flow module, the single-phase flow model is solved with the assumption of incompressive flow. Finally, the control system module includes the recirculation flow control minimodule, the pressure control minimodule, and the feedwater control minimodule, as well as the interlock functions, which work during a transient to allow analysis of general transient phenomena. The program was verified to provide satisfactory results within reasonable computational time based on application analysis of stability and scram phenomena in a BWR-5 type plant.

In the power conversion system of electric vehicles, the inverter is shut down when the system fails in the cause of a drastic load change or other protection reasons. However, in the case if the inverter is shut down in regeneration mode, the DC link capacitor voltage is increased dramatically, which will potentially break the switching devices. In this paper, the authors propose a halt method to overcome the over voltage and over current problems in the case of system failure during the regeneration. The proposed method consists of two phases, in the phase I, the DC link capacitor voltage is controlled by charge and discharge switching patterns based on space vector of the inverter. Then, the phase II performs the short circuit operation in order to avoid the regenerating current from the motor flows into the DC link capacitor. The experimental results demonstrate that the DC link capacitor voltage is 80% lesser comparing to the conventional method. Furthermore, the circulating current can be suppressed by 46% from the proposed method.

A method is proposed for the analysis of conducted electromagnetic interference (EMI) in multiple power converters connected to the same power line. This method is focused on the phase differences of the sub-harmonic modulation carrier signal for each power converter. It is confirmed that the phase difference among the power converters determines the EMI noise value in a multi-converter system by analyzing waveform of the common-mode current. In addition, EMI noise suppressions based on a novel phase-difference control technique are also proposed. In order to reduce volume of EMI filter effectively, phase difference θ should be set to 360/nN°, here n is high-order harmonic component near 150 kHz, and N is the number of power converters. On the other hand, in order to prevent radio disturbance, another phase-difference τ should be set to 180f c /f x ° not depending on the number of converters (N), here f C is carrier frequency of the converters, and f X is center frequency of frequency band of AM radio. Therefore, Conducted EMI noise can be reduced effectively based on the proposed phase-control for any purpose.

A method is proposed for analysis of the attenuation characteristics of electromagnetic interference (EMI) filters for multiple power converters connected to same power line. The analysis results indicate that increase of the conducted EMI noise may occur, because the cut-off frequencies of the EMI-filter are varied according to the number of power converters. A mathematical solution for the cut-off frequencies is derived by simplification of the circuit configuration based on Thevenin's theorem. Finally, an effective design method of EMI filters is proposed to avoid such problem of a multi-converter system.

High reliability generating apparatus with a PWM rectifier equipped with a DC reverse-blocking diode is proposed. The PWM rectifier adjusts the power from a permanent magnet synchronous generator by means of position sensorless control. Due to the DC diode, the PWM rectifier is shoot-through free, i.e. the switches in one arm are not broken with their simultaneous turning-on caused by electromagnetic interferences, etc. The apparatus is applied to the gas heat pump system (GHP), which is an efficient air-conditioning system powered by fueling gas, to satisfy its requirement of high reliability to the electrical equipment. There is a control issue in the proposed circuit, that is the DC bus capacitor is electrically separated from the switches when the DC diode is reverse-blocking, which results in the voltage fluctuation at the switches side. This is overcome by adding a stabilization control. The system is tested with a 1.5 kW-class experimental setup, which demonstrates desirable performances as expected, and it is confirmed that the rectifier is durable to the simultaneous turning-on of the switches in one arm