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This paper proposes a high power density inverter utilizing SiC metal-oxidesemiconductor field-effect transistor (MOSFET) modules and an interstitial via hole (IVH) printed circuit board (PCB) for a motor drive system. The inverter also includes a power circuit, heatsink, cooling fan, gate drive circuit, and DC capacitors. The output power density of the proposed inverter is 81 kW/L. The inverter outputs 37 kW formotor drive applications. To achieve this superior output power density, this paper explains a prototype SiC MOSFETmodule without an antiparallel schottky barrier diode, and a unique multilayer laminate IVH PCB to connect the modules and DC capacitors. This paper describes the experimental results to verify the motor drive performance and the increase in temperature under the rated load operation. [ABSTRACT FROM AUTHOR]

This paper proposes a filter design for improving the control performance of the current control system of permanent magnet synchronous motors (PMSMs) using the overmodulation region of an inverter. The control performance of a vector control system for PMSMs using the overmodulation region of an inverter can be improved by suppressing harmonic components that are generated in this region. This paper utilizes band elimination filter (BEF) to eliminate harmonic components; however, unsuitable BEF setting leads to generation of large current oscillation at the resonant frequency of current feedback loop with BEF. In order to deal with these problems, the proposed filter design focuses on gain setting at the cutoff frequency of BEF. The proposed filter design can prevent the generation of current oscillation at the resonant frequency of the system, and can improve current control performance without complex adjustments. Simulations and experiments are carried out to show the effectiveness of the proposed BEF setting. [ABSTRACT FROM AUTHOR]

Abstract: A novel circuit topology for a single‐phase inverter with a power decoupling capability operated in discontinuous current mode (DCM) is proposed in this paper. An inverter connected to a single‐phase grid requires a power decoupling capability to compensate for a power ripple with twice the grid frequency. Bulky capacitors are used as DC‐link capacitors in conventional systems. In contrast, the proposed circuit topology can use ceramic capacitors instead of electrolytic capacitors by reducing the required capacitance based on the active buffer concept. Moreover, this active buffer requires no additional inductor because it uses DCM for the power decoupling capability. In this paper, a control method for the active buffer circuit operated in DCM is introduced. An experimental verification of a 1‐kW prototype shows that the proposed circuit reduces the input current ripple at twice the grid frequency by 96.8%, with a maximum efficiency of 95.2%. In addition, the Pareto optimization of power density and efficiency is used to clarify the maximum power density points. It is found that the maximum power density of the proposed circuit is 1.6 times higher than that of a conventional boost‐type active buffer. [ABSTRACT FROM AUTHOR]

The developments of SiC power devices has been proceeded remarkably since 1990. SiC power devices have been payed attentions as one of the candidate power devices for next HVDC transmissions and its R&Ds have been started in the KANSAI electric power company since 1995. In this paper, a series of R&Ds for the SiC devices and SiC inverters performed in the company are presented from the historical viewpoints. [ABSTRACT FROM AUTHOR]

SUMMARY This paper proposes a new high-efficiency photovoltaic (PV) converter for grid connection through a high-leg delta transformer, which is composed of a symmetrically connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. This circuit configuration enables to reduce the power losses in both boost converter and inverter. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in switching power loss. Experimental results show that the proposed circuit improves its European efficiency from 91.6% to 94.5%. [ABSTRACT FROM AUTHOR]

SUMMARY This paper proposes a configuration of a single-phase voltage source inverter that features power decoupling capability. Generally, the converter connected to a single-phase grid employs bulky dc link capacitors such as electrolytic capacitors in order to decouple the power ripple with twice the frequency of the power supply. The power ripple in the proposed circuit is compensated by an active buffer with small capacitors. In this paper, the fundamental operations of the proposed converter are confirmed by experimental results. From the experimental results, the output current total harmonic distortion (THD) is 3.51%, the ratio of the input current is 14.3%, and the output power factor is over 99%. In addition, the volume of the proposed circuit is reduced by 61% when the carrier frequency is 64 kHz compared to that with a carrier frequency of 16 kHz. Finally, from an evaluation of the power density using Pareto front curves, the proposed circuit achieves high power density in comparison with the conventional circuit. [ABSTRACT FROM AUTHOR]

Instabilities due to mutual interactions between inverters and grid impedance are observed sometimes. This paper proposes a new stabilization method, which improves the output frequency impedance characteristics, satisfying the Nyquist stability criterion. The principle is that the output impedance is designed to be passive with the feedfoward loop characteristics and the system is stable even for an unknown grid system impedance. The design principle for the proposed stabilization method is described and investigated and validated on the basis of simulation and experimental results. [ABSTRACT FROM AUTHOR]

Transient analysis is an indispensable tool for analyzing the voltage fluctuation of distribution systems according to the penetration of distributed generations with grid‐connected inverters. Electromagnetic transient (EMT) analysis is suitable for the purpose because it enables detailed modeling of the inverters and accurate simulation of their dynamic behavior. However, the EMT analysis requires a smaller calculation time step by a factor of 500 if the simulated power system includes the inverters. Simulation of the inverters is a bottleneck in speeding up the EMT analysis. This paper proposes a novel average‐value modeling method for the grid‐connected inverters. The proposed inverter model operates in a larger calculation time step, and speeds up the EMT analysis of distribution systems containing the inverters. The maximum error in the output power was 8% compared to the result by the conventional model. Dynamic voltage simulations are demonstrated with a test case, which includes tap changing transformers with a voltage controller and a photovoltaic generation facility. The proposed model reduces the required calculation time by a factor of 754 compared to the conventional model whereas there is no significant difference in the simulated result. [ABSTRACT FROM AUTHOR]

This paper proposes a wireless power transfer system using a series compensator GCSC (gate‐controlled series capacitor) as a primary side capacitor. The GCSC is a circuit module that functions as a series variable capacitor by controlling semiconductor switches. The advantage of applying the GCSC to the primary side capacitor is that it provides controllability of the output power factor for a high‐frequency inverter. Therefore, optimum operation of the high‐frequency inverter can be achieved irrespective of the coil parameters by controlling the output power factor. Experimental results with a 1 kW laboratory prototype confirmed that the proposed system can achieve optimum operation and high efficiencies of the high‐frequency inverter. [ABSTRACT FROM AUTHOR]

Abstract: A Z‐source inverter (ZSI) can work as an inverter with boost capability in one stage by using its impedance source and the short‐through mode as the switching mode. This paper discusses the circuit losses that depend on the boost ratio between the quasi ZSI, which is one of the ZSI topologies, using Superjunction‐MOSFETs and the conventional inverter with a boost chopper using IGBTs. Two‐kilowatt class three‐phase inverter systems for an AC output of 200 V were fabricated using the proposed method and the conventional method, and the losses for each component were analyzed experimentally. Experimental results confirmed that the proposed method can reduce the total loss in low boost ratio operations, in comparison with the conventional method, due to its reduced inverter conduction loss. [ABSTRACT FROM AUTHOR]

SUMMARY The capacity of distributed generators (DGs) connected to a grid by inverters is growing. The inverters are generally controlled by a phase locked loop (PLL) in order to achieve synchronization with the power system frequency. They cannot have synchronous power. Power systems become unstable if the capacity of the inverter-type DGs is increased. The concept of controlling inverters to behave like a synchronous generator is studied in this paper. The result is referred to as a 'virtual synchronous generator' (VSG). The VSG has synchronous power. Power systems become stable as a result of using the VSG. The VSG is useful in the parallel operation of DGs. The VSG can synchronize with other VSGs, synchronous generators, or the grid. In this paper, a method for the synchronous operation of a VSG is studied, and experimental results on a VSG running in parallel with a synchronous generator and other VSGs are presented. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, a technique is proposed to reduce the carrier noise of pulse width modulation (PWM) inverters for a permanent magnet motor drive. The carrier noise is generated by the motor and the reactor driven by the inverter and affected by the switching frequency. When a motor rotates and drives a machine, the carrier noise is hidden by the machine noise. However, when the motor speed is approximately zero, the carrier noise becomes dominant and raucous. The typical method to reduce the noise employs a switching frequency higher than the audible frequency of human hearing. However, the increase in switching frequency results in the inverter suffering a higher switching loss and lower efficiency. In particular, when the permanent magnet motor operates at approximately zero-speed and full-load, for example, in the hill-start conditions of electric vehicles and the start and stop conditions of elevators, the current flows in specific power devices and the switching loss further increases. The proposed technique uses a zero-sequence voltage, which is generated randomly with the M-sequence signal, and diffuses the frequency components of the ripple contained in the current. The technique is able to reduce the noise without increasing the switching frequency of the inverter when the motor speed is almost zero. Simulation and experimental results show that the proposed technique can diffuse the carrier noise and the cycle of the M-sequence signal changes the diffusion effect of the carrier noise. [ABSTRACT FROM AUTHOR]

This paper aims at minimizing capacitor-voltage fluctuations inherent in a modular multilevel cascade inverter based on double-star chopper cell (DSCC) or a modular multilevel DSCC inverter. The inverter can drive an induction motor loaded with a quadratic-torque load. Both theoretical analysis and numerical calculation reveal that the voltage fluctuations can be minimized when the ratio of a magnetizing-current component with respect to a torque-current component in the motor current is set to unity, regardless of the motor mechanical speed. A three-phase DSCC inverter is designed and constructed to drive a 380-V, 15-kW, 50-Hz, four-pole, induction motor loaded with a quadratic torque that is proportional to a square of the motor mechanical speed. Experimental results confirm the validity of the theoretical and numerical calculations. [ABSTRACT FROM AUTHOR]

SUMMARY A grid-connected inverter is indispensable for photovoltaic power generation and smart grid systems, and it must be designed for stable operation. The impedance method based on the Nyquist criterion is often utilized to analyze the stability of grid-connected inverter systems. The impedance method is based on the eigenvalues of the product of the inverter output admittance and the line impedance matrices in the frequency domain. However, the frequency characteristics have so far been derived only for inverters with analog control systems. A new frequency analysis method for inverters with digital control systems is proposed in this paper. First, a stability analysis example for a three-phase LCL-type inverter controlled digitally is shown and the results are compared and validated with those by simulation using a Saber simulator. Finally, they are also compared and validated with experimental results digitally controlled by a DSP-based system. [ABSTRACT FROM AUTHOR]

SUMMARY The present paper introduces a single-phase utility interactive inverter with a power decoupling function. In a conventional single-phase inverter, power pulsation at twice the grid frequency appears in the input power. Hence, electrolytic capacitors having large capacitances have been connected to the DC input terminal to stabilize the input DC-bus voltage. Because the lifetime of the electrolytic capacitor is relatively shorter than that of another component, the lifetime of the inverter is affected by the capacitor. In order to prevent such a problem, a novel single-phase inverter circuit with an active power decoupling function is introduced. The pulsating power on the input DC-bus line and the pulsated energy on the input DC capacitor is transferred to the energy in a small film capacitor. Hence, the extension of the inverter lifetime can be expected by substituting a small film capacitor for the large electrolytic capacitors. In addition, the loss in the power decoupling circuit is very small; hence, the reduction in the overall conversion efficiency of the inverter can be minimized. The effectiveness of the proposed method is verified using a 300 W experimental setup. [ABSTRACT FROM AUTHOR]

This paper presents a new air flow controller for a thermal power plant. When an inverter power source is used for a forced draft fan (FDF) in order to save power, the conventional countermeasures do not cover all abnormal states. The proposed controller is evaluated by performing a simulation. The power source is shown to change from the inverter to a commercial power source within 0.5 second in the abnormal state. The changing time is determined to be 0.55 second based on the mechanical tolerance of the design. Testing was performed in an actual plant using the proposed control method, and the transient response was compared with the simulated and measured data. The errors were less than 3.4%. The FDF changed over smoothly and the plant conditions remained the same as the normal state in the actual plant testing. This paper deals with the safe operation of a thermal power plant that employs the proposed air flow controller. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(4): 47-56, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21202 [ABSTRACT FROM AUTHOR]

This paper describes a direct-power-controlled CVCF inverter and presents its experimentally examined operation characteristics. The most important feature of this strategy is the direct selection of the switching states of the CVCF inverter to restrict errors between the feedback and command values of active and reactive power. In addition, this paper presents a theoretical analysis of the relationship between the instantaneous power and the switching state, which is essential for deriving a switching-state table for the controller. The feasibility of the proposed method was verified through several computer simulations and experimental tests using a 2.0-kVA prototype setup. The output voltages were confirmed to be stable sinusoidal waveforms with a total harmonic distortion of 1.13% under nonlinear load conditions. Excellent voltage balance was achieved by the proposed strategy even under unbalanced load conditions. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 62-69, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21023 [ABSTRACT FROM AUTHOR]

This paper proposes a new induction heating technology capable of controlling a precise exothermic distribution, which is termed zone-control induction heating (ZCIH). The ZCIH system consists of two or more sets of a high-frequency inverter unit and a work coil. The inverter units control the phase angle of the coil current to be in phase with each other. The ZCIH has the capability of operation with the mutual inductance, and enables locating the coils as close as possible. As a result, the ZCIH technology makes it possible to achieve rapid heating performance with extremely precise exothermic distribution. This paper presents experimental results of a 150-kW six-zone ZCIH system for semiconductor heat processing. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(1): 37–45, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20908 [ABSTRACT FROM AUTHOR]

This paper presents the STATCOM using the new concept of an inverter system which consists of three inverter units connected in series, and each inverter unit generates a different input voltage such as VC, 2VC, 4VC. This inverter system can output a high-quality voltage by a low-frequency switching operation. Thus, it can combine low loss and high quality. In this paper, we show the technique to apply STATCOM which uses the inverter system, and examination results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(4): 58–65, 2009; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/eej.20823 [ABSTRACT FROM AUTHOR]

This paper proposes a novel current-source multilevel inverter, which is based on a current-source half-bridge topology. Multilevel inverters are effective for reducing harmonic distortion in the output voltage and the output current. However, the multilevel inverters require many gate drive power supplies to drive switching devices. The gate drive circuits using a bootstrap circuit and a pulse transformer can reduce the number of the gate drive power supplies, but the pulse width of the output PWM waveform is limited. Furthermore, high-speed power switching devices are indispensable to create a high-frequency power converter, but various problems, such as high-frequency noise, arise due to the high dv/dt rate, especially in high-side switching devices. The proposed current-source multilevel inverter is composed of a common emitter topology for all switching devices. Therefore, it is possible to operate it with a single power supply for the gate drive circuit, which allows stabilizing the potential level of all the drive circuits. In this paper, the effectiveness of the proposed circuit is verified through experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 88–95, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20475 [ABSTRACT FROM AUTHOR]

This paper presents a characteristics comparison of a high-frequency multilevel inverter connected with small- capacity filter inverters. In general, PWM inverters require a low-pass filter in order to reduce switching harmonics. However, in the high-frequency systems such as class D power amplifiers, the cutoff frequency of the low-pass filter must be set at high frequency. Thus, harmonic distortion of the output voltage is enlarged to a harmful level. Increasing the number of output voltage levels is effective in reducing the harmonic distortion of the output voltage and the low-pass filter size. The proposed systems consist of a five-level inverter and several cascade-connected low-voltage full bridge inverters without any external DC power sources for filtering the output voltage. The five-level inverter generates a stepwise waveform with five-level voltage, and the low-voltage filter inverter superimposes harmonic components to compensate for the voltage waveform distortion. Therefore, the proposed system can reduce its total switching loss and can increase the number of the output voltage levels. In this paper, the effectiveness of the proposed systems is verified through several experiments. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 58–65, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20373 [ABSTRACT FROM AUTHOR]

This paper presents the newly proposed hybrid resonant commutation bridge-leg link (HRCB) snubber circuit which can achieve zero voltage and zero current soft-switching commutation for single-phase and three-phase voltage source-type inverter, along with its unique features and operation principle. The circuit parameter design approach for the HRCB snubber circuit and the determination estimating scheme of the gate pulse timing processing which is more suitable and acceptable for single-phase and space voltage vector modulated three-phase voltage source inverter using the HRCB snubber circuit are described in this paper. In particular, the three-phase voltage source soft-switching inverter associated with the proposed HRCB circuits are evaluated and discussed from simulation and experimental viewpoints. The practical effectiveness of the HRCB snubber-assisted three-phase voltage source soft-switching inverter using IGBT power modules which is based on the instantaneous space voltage vector modulation is clarified on the output voltage waveform, actual efficiency of electromagnetic noise in comparison with three-phase voltage source-type conventional hard-switching inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a new circuit topology of the three-phase soft-switching PWM inverter and PFC converter using IGBT power modules, which has the improved active auxiliary switch and edge resonant bridge leg-commutation-link soft-switching snubber circuit with pulse current regenerative feedback loop as compared with the typical auxiliary resonant pole snubber discussed previously. This three-phase soft-switching PWM double converter is more suitable and acceptable for a large-capacity uninterruptible power supply, PFC converter, utility-interactive bidirectional converter, and so forth. In this paper, the soft-switching operation and optimum circuit design of the novel type active auxiliary edge resonant bridge leg commutation link snubber treated here are described for high-power applications. Both the main active power switches and the auxiliary active power switches achieve soft switching under the principles of ZVS or ZCS in this three-phase inverter switching. This three-phase soft-switching commutation scheme can effectively minimize the switching surge-related electromagnetic noise and the switching power losses of the power semiconductor devices; IGBTs and modules used here. This three-phase inverter and rectifier coupled double converter system does not need any sensing circuit and its peripheral logic control circuits to detect the voltage or the current and does not require any unwanted chemical electrolytic capacitor to make the neutral point of the DC power supply voltage source. The performances of this power conditioner are proved on the basis of the experimental and simulation results. Because the power semiconductor switches (IGBT module packages) have a trade-off relation in the switching fall time and tail current interval characteristics as well as the conductive saturation voltage characteristics, this three-phase soft-switching PWM double converter can improve actual efficiency in the output power ranges with a trench gate controlled MOS power semiconductor device which is much improved regarding low saturation voltage. The effectiveness of this is verified from a practical point of view. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 64–76, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20207 [ABSTRACT FROM AUTHOR]

Control schemes for auxiliary switches of PWM controlled three-phase resonant snubber inverters (RSIs) are proposed. The control schemes proposed in this paper are based on a conventional PWM technique. To avoid zero voltage switching lost conditions, the conventional PWM technique is modified in the proposed schemes. The proposed control schemes are so simple that they are suitable for digital control. In this paper, a CPLD (Complex Programmable Logic Device)-based control IC, which realizes the proposed control schemes, for three-phase auxiliary RSIs is also proposed and implemented. The IC generates gate signals for the main and auxiliary devices of the three-phase RSI based on the proposed control schemes. The effectiveness of the proposed control schemes was verified through experiments. As a result, ZVS (Zero Voltage Switching) turn-on at the main devices was achieved and a smooth sinusoidal output current was obtained by use of the control IC. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(4): 57–67, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20125 [ABSTRACT FROM AUTHOR]

This paper proposes a novel inverter drive system to improve the input power factor of single-phase diode rectifier. Conventional rectifiers need a high-frequency switching device and a reactor to improve the input power factor. However, the proposed power converter does not need the switching device, electrolytic capacitor, or reactor. By making many ripples across the DC-bus voltage, the input power factor can be improved. The proposed system consists of only a single-phase diode rectifier, small film capacitor, three-phase inverter, and motor. The proposed system adopts an interior permanent magnet (IPM) synchronous motor. The IPM motor is well known as a high-efficiency motor and can realize field weakening. The basic ideas of the inverter control method are based on the following operations: the inverter's controlled synchronous with the DC-bus ripple voltage by field-weakening method, and direct active power feeding from the source side to the motor without smoothing the DC-bus voltage. This paper describes that the proposed method can obtain an input power factor of 97.3% by experimental tests, and realizes the goals of small size and long life of the system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 66–73, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20047 [ABSTRACT FROM AUTHOR]

The purpose of this paper is to improve power conversion efficiency of a three-phase voltage source type soft-switching inverter with a single auxiliary resonant DC link (ARDCL) snubber. First, the operating principle of an ARDCL snubber discussed here is described. Second, this paper proposes an effective pulse pattern generation method of the zero voltage space vector of the three-phase soft-switching inverter using IGBTs or power modules that can reduce power losses in the ARDCL snubber treated here. In particular, a zero voltage holding interval in the DC rail busline of this three-phase soft-switching inverter is to be regulated according to the generation method of the zero voltage space vector. Third, the maximum modulation depth Mmax under the condition of correction of the instantaneous voltage space vector can be improved by using a new zero voltage space vector generation method. Finally, the feasible experimental results of this inverter are obtained confirming the operating characteristics such as power conversion actual efficiency, as well as conventional efficiency THD and RMS value of the balanced three-phase output voltage for an experimentally built three-phase voltage source type soft-switching pulse modulated inverter using the latest IGBT modules and evaluated from the standpoint of practical applications in industry UPS and new energy systems. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 89–99, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10234 [ABSTRACT FROM AUTHOR]

This paper proposes a new speed servo system for a PM motor without a current sensor, which is constructed by the current simulator of a PM motor. The proposed speed servo system is simple and economical. The sensor of the proposed system is only a position sensor used as an encoder. Hence, the proposed speed servo system has little influence on the switching noise of a PWM inverter. Moreover, the resolution of the proposed current simulator can be higher than that of the conventional actual feedback system. In this paper, the experimental results point out that the proposed current sensorless speed servo system has the desired current and speed response. The current waveform of the proposed system is smooth and clean. Moreover, this paper proposes a new identification algorithm for motor resistance Ra and main flux Φfa by using only a position sensor. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 64–73, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10084 [ABSTRACT FROM AUTHOR]

This paper presents a new concept for back-to-back (BTB) dc systems. The main feature of the proposed BTB is referred to as “massively parallel.” This massively parallel BTB system consists of a number of small or mediumcapacity inverter units that are connected in parallel. The concept of transmission power control using the massively parallel BTB is investigated using MATLAB for a case where a fault occurs. In addition, a method for modeling the proposed BTB in EMTP is investigated. The work presented in this paper shows that the proposed BTB system is very promising for large power system applications because the losses of the system are very small compared to conventional BTB using VSC (voltage source converter). The massively parallel BTB can keep operating even if an inverter unit fails, thus improving overall power transmission capability. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 34–42, 2002 [ABSTRACT FROM AUTHOR]

This paper presents a zero-current-switched voltage-fed inverter equipped with resonant circuits on the ac side. The current flowing through a switching device, that is, IGBT, is the sum of the load current and the resonant current. When the amplitude of the resonant current is larger than that of the load current, the current in the switching device becomes zero at an instant in each resonant cycle. This allows the switching device to be turned on or off at the zero current. The zero-current switching makes a significant contribution to reduction of switching losses and electromagnetic noises. In this paper, the principle of zero-current-switching operation, along with a novel control scheme, is described from a theoretical and practical point of view. Experimental results obtained from a laboratory system of 5 kVA verify the practicability. Moreover, the switching and conduction losses of the proposed soft-switched inverter are compared with those of a conventional hard-switched inverter. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 85–95, 2000 [ABSTRACT FROM AUTHOR]

This paper describes the performance of the superconducting linear synchronous motor control system used for a transportation vehicle by using an exact dq0-axis mathematical model. The paper first shows the detailed block diagram of the speed control system, which includes the blocks of propulsion force and speed emf computations. A detailed discussion is devoted to the design of the control system. A cascade control system with PI controllers is designed as a numerical demonstration. It is also pointed out that the cascade control structure is a natural form for the power feeding method with three inverters. Performance simulations are shown for severe track conditions such as tunnel and track gradients as well as in a normal case. It is demonstrated that integrator windup of the speed controller can occur in the case of a severe condition in which one of the inverters is disabled. We present a design with more robustly stable performance by designing an antiwindup controller. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 45–52, 1999 [ABSTRACT FROM AUTHOR]

In a utility-interactive photovoltaic (PV)-generating system, a PWM inverter is used for the connection between the PV arrays and the utility. The inverter is controlled to keep the output power at the maximum point for the PV. Although the PV power can be easily found by using the measured PV voltage and PV current, the installation of two detectors in the system is indispensable to obtain the exact PV power. In system operation with the maximum power that is fed into the utility, the PV does not always operate at the maximum point of PV output power because of power losses in the system. It has been reported that the use of the measured ac voltage or ac current on the inverter output side can exclude system losses from consideration and achieve system operation with maximum utility power. In this manner, however, since the ac output waveforms of the PWM inverter consist of many pulse trains, a filter circuit may be necessary for the detector to obtain the exact values of the ac output. This paper proposes a method of calculation of the utility power in the PV-generating system by using a PWM-current source inverter. In this system, only the PV current is measured, and it is employed for power calculations in combination with the control parameter of the PWM inverter. Since the proposed approach monitors the utility power instead of the PV power, control that does not need to take system losses into consideration can be achieved. This paper presents a method of calculation of the power for a single-phase–inverter PV system and gives basic experimental characteristics. An application of the proposed method to a three-phase PWM inverter–PV system is also described, and experimental results are given. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 55–64, 1998 [ABSTRACT FROM AUTHOR]

This paper presents a new PWM scheme for NPC inverters that is suitable for large capacity GTO inverters. In conventional NPC inverters, a pulse of narrow width is needed to synthesize a low-voltage wave. A pulsewidth limitation due to the use of GTOs causes differences between output phase voltages and reference voltages. This paper proposes a scheme in which square waves are added to all three-phase voltage references to enable a low-voltage to be synthesized with no narrow pulses and significant reduction in harmonic components of output voltage results. Also, a new neutral point voltage control is proposed. Finally, a theoretical analysis and experimental results for the proposed scheme are presented. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 93–105, 1997 [ABSTRACT FROM AUTHOR]

This paper deals with an advanced static Var compensator (ASVC) using quad-series voltage-source PAM inverters. The ASVC consists of four three-phase voltage-source inverters with a common dc capacitor and four three-phase transformers, each primary winding of which is connected in series with each other. Each inverter outputs a square-wave voltage, while the synthesized output voltage of the ASCVC has 24-step wave shape. This results not only in a great reduction of harmonic currents and dc voltage ripples but also in fewer switching and snubbing losses. In this paper, transient analysis is performed with the focus on the response pf reactive power and the resonance between the dc capacitor and ac reactors. Experimental results obtained from a small-rated laboratory model of 10 kVA are also shown to verify analytical results help in the design of system parameters such as the capacity of the dc capacitor and feedback gains. [ABSTRACT FROM AUTHOR]

This paper describes a vector control system of an induction machine using a neutral-point-clamped voltage-source inverter (NPC-VSI) that is one of the double series-connected inverters. The NPC-VSI is able to output five-level step-shaped line-to-line voltage without output transformers or reactors, and it may reduce harmonic currents corresponding to torque ripples. However, the NPC-VSI has a problem in the excessive high voltage is applied to switching devices when a neutral point of two dc capacitors of the NPC-VSI varies from the center of the dc link voltage, because the neutral point is floating. This paper proposes also a current controller to which the space vector theory is applied. This can reduce harmonic currents to one-fourth those of a conventional voltage-source inverter using six switching devices, and regulate and neutral point potential within a preset range. To simplify the current controller, information about voltage space vectors is given from the vector controller to the current controller. The validity of the current controller is confirmed by a prototype using an induction machine of 2.2 kW. [ABSTRACT FROM AUTHOR]

This paper deals with static var compensators using self-commutated inverters (which is so-called SVG) compared with conventional SVC and Rotary Condenser. Improvement of power system stability is explained by using simple system model and checked by dynamic digital simulation. In the latter part of this paper, system outline, basic specifications and control diagram of the SVG rated 154 kV, ±80 MVA, which has been installed at INUYAMA Switching Station, are briefly presented. Field tests at INUYAMA verify that power swing is effectively damped and transmission capacity is increased. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to propose a low-cost voltage-source-type inverter capable to power regeneration as well as a new PWM control scheme suited for the proposed converter. Another objective of this paper is to propose a switching function suited for the analysis of the proposed PWM control scheme. In implementing PAM (pulse amplitude modulation) control, a thyristor bridge is already installed and therefore the power can be regenerated only by installing additional elements. For this reason, the proposed scheme is economically very advantageous. [ABSTRACT FROM AUTHOR]

This paper considers the problem of current distortion accompanying the dispersed power system added to the utility network, and the problem of disconnecting the dispersed power system in the event of an accident on the utility network. Among the components composed of the dispersed power system, the semiconductor power converter is mostly related primarily to the forementioned problems. For home use, the capacity of the dispersed power system is about 2 kVA, which is the main topic in this paper. For this purpose, voltage-fed inverters have been used being capable of self-sustaining operation, but the demerit of requiring large space and the generation of current distortion. We studied the effectiveness of using an instantaneous current controlled inverter, which has recently been used in active filters. [ABSTRACT FROM AUTHOR]

SUMMARY We were able to reduce heating irregularities in equipment for heating beverage cans by using the high-frequency induction heating method and determining the resulting improvement in the heating efficiency. The heating irregularity between the top and bottom of the can was reduced to less than 3°C by improving the arrangement of the heating coils for the beverage can by thinning the winding and changing the circuit configuration. The efficiency of power conversion was improved from 93.0% to 97.4%. In this paper, the configuration of the equipment and the experimental results are reported. [ABSTRACT FROM AUTHOR]

Multilevel inverters have very attractive features, such as lower harmonics in the output, lower EMI, and reduction of the required voltage rating of power semiconductor devices. Among them, lower harmonics in the output can reduce the volume of the output harmonic filter and additional losses caused by the harmonics. Therefore, multilevel inverters are expected to realize higher power density and higher efficiency. In this paper, as a basis of the quantitative investigation of these features, the harmonics in the PWM output voltage of multilevel inverters are analyzed theoretically. As an application of the theoretical results, the usefulness of the theoretical results is verified by the prediction of the harmonic contents of the load current. [ABSTRACT FROM AUTHOR]

SUMMARY This paper proposes a new current control method for an interior permanent magnet synchronous motor (IPMSM). In the case of ac motor control, two-axis current feedback control is performed to control the voltage amplitude and phase. When the inverter voltage is saturated, current control is achieved by controlling the voltage phase. Conventional techniques require switching the mode of the control system from variable voltage mode to voltage saturation mode. However, in the conventional techniques, transient voltage saturation occurs due to switching the control system. The proposed method achieves current control in the variable voltage mode and voltage saturation mode without switching the control system. Moreover, the current response is not affected by the rotor speed. Numerical simulation results and experimental results confirm the effectiveness of the proposed current control method. [ABSTRACT FROM AUTHOR]

SUMMARY Recently, photovoltaic (PV) power systems have attracted considerable attention in attempts to mitigate global warming. In a PV power system, it is necessary to synchronize the grid voltage when a PV inverter is interconnected with a grid. This paper proposes a high-speed and high-precision phase-locked loop (PLL) using complex-coefficient filters for a single-phase grid-connected inverter. The proposed PLL can detect the phase of grid voltage that has superimposed harmonic components for grid fault. Moreover, numerical results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

SUMMARY The capacity of distributed generators (DGs) connected to the grid by inverters is growing year after year. The inverters are generally controlled by a phase locked loop (PLL) in order to achieve synchronization with the power system frequency. Power systems may become unstable as the capacity of the inverter-type DGs continues to increase, because the inverter frequency is controlled just to follow the frequency determined by other synchronous generators. It has been suggested that inverters be controlled to behave like a synchronous generator. This concept is referred to as the virtual synchronous generator (VSG). In this paper, a control scheme for a VSG is presented, and the design method for the required energy storage and the capacity for grid stabilization control by a VSG is investigated by computer simulations. [ABSTRACT FROM AUTHOR]

This paper presents experimental results on a grid-connected inverter. The control of the inverter is based on a virtual synchronous generator model of algebraic type. When using the virtual synchronous generator model of algebraic type, there is no evidence for satisfactory opera-tion with unbalanced load and nonlinear load, because the generator models are constructed under the assumption that the load is linear and balanced. By choosing the feedback control loop gain appropriately, satisfactory operation is achieved even if an unbalanced and nonlinear load is con-nected. Experimental results show that the power controls, active and reactive, are achieved preferably in grid-connect-ing mode. Smooth transitions are also achieved from the connected mode to the island mode. The inverter can oper-ate satisfactorily when the unbalanced load is connected. Harmonic analysis is performed with a three-phase full-wave rectifier connected as a nonlinear load. The harmonic current is supplied by the inverter and its output LC filter. It is shown that the harmonic current is supplied mainly by the inverter and that the voltage waveform is acceptable for practical use. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-efficiency grid-connection inverter suitable for the interface with thin-film solar cells, which is composed of two bidirectional buck converters and an H-bridge PWM converter connected in series. The switching frequencies of the first bidirectional buck converters are equal to the grid frequency, while the second is operated at twice the grid frequency. The combination of these two converters synthesizes an AC rectangular voltage pulse train from the DC input power. The H-bridge PWM converter is operated at 20 kHz with a low DC capacitor voltage to compensate for the harmonic voltage included in the rectangular voltage pulse train. As a result, the proposed grid-connection inverter makes it possible to reduce both switching loss and common mode voltage. Experimental results obtained by a 1-kW single-phase inverter demonstrate a high efficiency of 98% without any common mode voltage. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 51-60, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22379 [ABSTRACT FROM AUTHOR]

We propose a novel inverter that can be operated either as a current source inverter (CSI) or as a voltage source inverter (VSI) by changing only the control signals. It is proper to use it for interconnecting systems with renewable energy, such as photovoltaic cells or wind generation systems, to a grid. This inverter is usually operated as a CSI connected to the grid. Even if the energy source has a lower voltage than the grid, energy can be supplied to the grid through the proposed inverter. The power factor can be briefly maintained close to unity. When power supply from the grid is interrupted, the proposed circuit should be operated as a VSI in the stand-alone operation mode. In this way, the circuit can maintain a constant output voltage to the loads. In this paper, the proposed circuit configuration and the control schemes for both the CSI and the VSI are described. The circuit characteristics for both are also discussed experimentally. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 45-53, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22349 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

A voltage source inverter with an LCL filter is often used for a utility interface to control its output current to a grid side because of its harmonic reduction advantages. The integral compensator is often used to reduce the steady-state errors. However, there is always a control delay due to sinusoidal variations. This paper proposes a digital sinusoidal compensator which is based on the internal model principle to realize a fast sinusoidal response with no delay. It is based on the internal model principle to realize a response with no deviation for a periodic sinusoidal reference input. It has a simple numerator and a denominator z2 − 2 z cos ωT + 1 of a transfer function which is equal to the z function of a sinusoidal waveform of the angular frequency ω and the sample time T. Compensator and feedback gains of the inverter are determined by the deadbeat or the optimal control principle. The proposed method is investigated for performances and it is validated through simulation and experimental results by a DSP control system. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 22-28, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22339 [ABSTRACT FROM AUTHOR]

This paper proposes a new topology for a current balancer with half-bridge inverters in single-phase three-wire distribution systems. Two half-bridge inverters are connected to the sources. The midpoint of the two capacitors on the DC-side is connected to a neutral line. The two half-bridge inverters function as a current balancer for single-phase three-wire distribution systems by exchanging the active and reactive power on each feeder through the two DC capacitors. The third leg functions as a DC-capacitor-voltage balancer for two DC capacitors connected to the half-bridge inverters. Thus, balanced source voltages and currents are obtained on the secondary side on the pole- mounted distribution transformer with balanced DC-capacitor voltages. The basic principle of the proposed current balancer is discussed in detail, and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results show that balanced source voltages and currents are obtained on the secondary side on the pole-mounted distribution transformer with balanced DC-capacitor voltages. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(4): 38-46, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.22277 [ABSTRACT FROM AUTHOR]

This paper considers the effectiveness of the service business approach for reducing CO2 emissions. 'HDRIVE' is a service business using inverters to reduce the energy consumption of motor drive. The business model of this service is changed to find new opportunities of CO2 emission reduction by combining various factors such as financial services or long-term service contracts. Risk analysis of this business model is very important for providing stable services to users over the long term. The HDRIVE business model is found to be suitable for this objective. This service can be applied effectively to industries such as chemicals or steel, where CO2 emissions are very large, and has the possibility of creating new business considering CDM or trading CO2 emission rights. The effectiveness of this approach is demonstrated through several examples in real business. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 40-48, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21242 [ABSTRACT FROM AUTHOR]

This paper presents a simple voltage control system for AC machines using a PWM voltage source inverter with output LC filters. By assuming a motor as a current source, the voltage is controlled by a simple proportional differential (PD) control. The vector control and PD control can be separately controlled in this system. A method for disturbance rejection is also described. The effectiveness of the proposed method is verified by simulations and experiments. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(4): 45-51, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21125 [ABSTRACT FROM AUTHOR]