# Hirofumi Akagi's research while affiliated with Tokyo Institute of Technology and other places

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## Publications (463)

This paper, based on modeling and scaling as well as simulation and experiment, provides a comprehensive discussion on a real-time real-power emulator for a medium-voltage, high-power, high-speed motor drive. A three-phase modular multilevel double-star chopper-cell (DSCC) inverter under test is connected in front-to-front (FTF) with the emulator....

This paper presents the performance of a three-phase bidirectional isolated DC-DC converter (3P-BIDC) in wye-wye (Yy), wye-delta (Yd), delta-wye (Dy), and delta-delta (Dd) transformer configurations, using enhanced switching strategy that combines phase-shift modulation and burst-mode switching. A simulation verification using PSCAD is carried out...

This paper provides an experimental discussion on a real-time real-power emulator that plays an important role in achieving a total test of medium-voltage, high-power, high-speed induction motor drives. The use of the emulator brings cost and time savings to the test. The test bench including the emulator is characterized by connecting two modular...

This paper presents the system design, operation and enhanced switching strategy of a three-phase bidirectional isolated dc-dc converter (3P-BIDC). The paper discusses the operating modes of the 3P-BIDC using phase-shift modulation (PSM), with analysis on its soft-switching characteristics. The phase-shift modulation is the simplest modulation tech...

This paper presents theoretical and experimental discussions on low-voltage-ride-through (LVRT) operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive...

This paper starts with a historical review of the family of modular multilevel cascade converters, and the topology and terminology of the family. Then, it answers the following question: ‘What motivated the author to apply phase‐shifted‐carrier pulse‐width modulation (PSC PWM) to the family?’ The success in academic research on this application ow...

This paper provides an analytical and experimental discussion on a power hardware-in-the-loop (P-HIL) test bench for a medium-voltage, high-power, high-speed synchronous motor drives. This test bench consists of two modular multilevel double-star chopper-cell (DSCC) converters connected in front-to-front (FTF) without transformer. An experimental d...

This paper presents a high-voltage hybrid dc circuit breaker that produces no conducting power loss during normal operating conditions and that has the capability to interrupt a large amount of short-circuit current within several milliseconds. It consists of a current-limiting inductor, a current-control inductor, the following two mechanical swit...

This paper presents an improved compact model for a discrete silicon-carbide MOSFET. This compact model based on the previous model features a new behavioral model of output characteristics and new non-linear models of internal capacitors. Simulation with the improved compact model is in better agreement with measurement than that with the previous...

This paper describes a compact model for an SiC- MOSFET, which features both characterization and modeling of a new drain-gate capacitor. In addition, the internal gate resistance and the internal stray inductances of the discrete package are experimentally evaluated and modeled by a newly-proposed method. The gate drive circuit is also modeled and...

This paper discusses the experimental verification of a virtual synchronous-motor drive test system. This test system consists of two identical modular multilevel double-star chopper-cell (DSCC) converters characterized by a front-tofront (FTF) connection. One converter acts as an inverter under test, while the other acts as a part of the virtual m...

This paper provides an experimental and theoretical discussions on dynamic braking for a medium-voltage induction motor driven by a modular multilevel double-star chopper-cell (DSCC) inverter. It is intended to apply the motor drive to large-capacity fans and compressors with a large moment of inertia. Each chopper cell consists of a bidirectional...

This paper presents a new hybrid dc circuit breaker producing no conducting power loss under normal operating conditions and having the capability to interrupt a large amount of short-circuiting current within several milliseconds. It consists of two reactors for current limiting and current control, two mechanical contactors, and a multilevel conv...

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 fluc...

This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system that combines two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with DC power cables. Hereinafter, a single MMCC-DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simpli...

This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cell (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, "inter-zigzag" inductors for th...

This paper discusses and compares phase-shifted pulsewidth modulation (PS-PWM) and level-shifted PWM (LSPWM) in a modular multilevel single-delta bridge-cells (SDBC) inverter for utility-scale grid-tied photovoltaic (PV) applications. This three-phase SDBC inverter provides the capability of operating even under power-distribution imbalances not on...

This paper provides a theoretical and experimental discussion on a modular multilevel triple-star bridge-cell (TSBC) converter with focus on mitigating the capacitor-voltage fluctuation contained in each bridge cell. A new control method proposed in this paper is characterized by properly superimposing both common-mode voltage and circulating curre...

This paper provides an experiment-based discussion on a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed high-torque motor drive. The TSBC is a direct ac-to-ac power converter capable of achieving bidirectional power flow as well as drawing and feeding three-phase sinusoidal input (supply-side) and...

This paper provides an experimental discussion on an adjustable-speed electrical drive fed by a modular multilevel triple-star bridge-cell (TSBC) converter, shortly called as a TSBC converter. The TSBC converter is suitable for medium-voltage, high-power motor drives with regenerative braking. However, it suffers from capacitor-voltage fluctuation...

This chapter presents some combined series/shunt active power conditioners, based on voltage-source converters (VSCs). An important issue related to VSCs is the switching technique of the converter. The hysteresis-band control with minor current feedback loop is a pulse-width modulation (PWM) technique that forces the converter to act as a controll...

This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book deals with the theory in a complete form for the first time, including comparisons with other sets of instantaneous power definitions. It considers the term 'power conditioning' which has much broader meaning than the term 'harmonic fi...

The series active filter acts like a dual device for the shunt active filter. The shunt active filter has a voltage source at the source side and a current source at the load side, where the current source includes harmonic currents that have to be compensated by the shunt active filter. In some cases, the combination of a voltage source and its im...

The prelims comprise: Half Title Title Copyright Dedication Contents Preface

This chapter covers in detail shunt active filters, including applications to three phase, four-wire systems. Additionally, an interesting solution has been proposed for allowing the use of (n-1)-leg PWM converter in n-wire systems. This was enabled by the use of the "split-capacitor" converter topology. The principle of shunt current compensation...

This chapter covers several important definitions of power, emphasizes their use in the control of active power-line conditioners. The theories that deal with instantaneous power can be mainly classified into the following two groups. The first one is developed based on the transformation from the abc phases to three-orthogonal axes, and the other...

This chapter presents an overview of some power theories, starting from the classical references dating from the 1920s. It starts with the power definitions under sinusoidal conditions that are quite common situations and well known to electrical engineers, they are necessary to create a solid base for the rest of the theory. The chapter summarizes...

This paper provides an experimental discussion on dynamic braking for an induction motor driven by a modular multilevel double-star chopper-cell (DSCC) inverter, intended for applications to large-capacity fans and compressors. Each chopper cell consists of a bidirectional chopper and a braking chopper connecting a single small-rated braking resist...

This paper provides a theoretical and experimental discussion on a modular multilevel triple-star bridge-cell (TSBC) converter with focus on mitigating the capacitor-voltage fluctuation contained in each bridge cell. This paper assumes that the TSBC converter drives an interior permanent magnet synchronous motor rated at 75 Hz loaded at the rated t...

This paper provides an intensive discussion on a modular multilevel cascade conversion system based on double-star bridge cells (DSBCs), which is referred to simply as a DSBC conversion system. This conversion system is defined as a power conversion system consisting of multiple DSBC converters and medium-frequency isolation transformers. A voltage...

This paper presents an intensive discussion on a high-voltage direct-current (HVDC) long-distance transmission system combining two modular multilevel double-star choppercells (DSCC) converters with dc power cables. Hereinafter, each converter is referred to simply as a DSCC converter, or just as a DSCC for more simplicity. Such an HVDC transmissio...

This paper presents an experimental discussion on modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). Hereinafter, a single MMCC-DSCC is referred to simply as a “DSCC”. A couple of DSCCs are used to form a front-to-front (FTF) system capable of dc voltage matching and galvanic isolation between two dc grids. The FT...

This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system that combines two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with dc power cables. Hereinafter, a single MMCC-DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simpli...

This paper describes a novel compact model for a SiC-MOSFET. The model is useful to achieve accurate simulation of output characteristics from a linear region to a saturation region, selecting both gate-source voltage and temperature as parameters. In order to construct the model systematically, attention is paid to a physics-based modeling procedu...

This paper provides a theoretical and experimental discussion on a modular multilevel triple-star bridge-cell (TSBC) converters. This paper also proposes a new control method for mitigating ac voltage fluctuation of the dc capacitor of each bridge cell. The proposed method is characterized by properly injecting both common-mode voltage and circulat...

This paper provides a theoretical discussion on a new phase-shifted rotating-carrier (PSRC) pulsewidth modulation (PWM) method for a modular multilevel double-star chopper-cell (DSCC) converter. The new method enables the DSCC converter to operate at a low switching frequency in a range of 50 to 100 Hz where the ac grid or line frequency is 50 Hz....

This paper presents a new hybrid dc circuit breaker producing no conducting power loss under normal operating conditions and having the capability to interrupt a large amount of short-circuiting current within several milliseconds. It consists of two reactors for current limiting and current control, two mechanical contactors, and a multilevel conv...

This paper describes a 750-Vdc, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using SiC-MOSFET modules without free-wheeling diodes, focusing on the output voltage ripple and power conversion efficiency. Intermittent operation brings higher conversion efficiencies in a low-power range to the dc-dc converter than doe...

This paper makes an intensive comparison in operating performance between a modular multilevel double-star chopper-cells (DSCC) inverter and a modular multilevel triple star bridge-cells (TSBC) converter. Both inverter and converter are intended to drive medium-voltage motors in industrial applications. Firstly, it makes numerical comparisons, thus...

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 fluc...

This paper provides a comprehensive discussion on voltage balancing of all the floating capacitors in a modular multilevel cascade inverter based on double-star chopper cells (DSCC) or a modular multilevel DSCC inverter. It intends to use the inverter for driving a medium-voltage synchronous motor. Theoretical and numerical design considerations on...

This paper provides a theoretical and experimental discussion on ac inductors used in a modular multilevel cascade converter (MMCC) based on triple-star bridge cells (TSBC) for motor drives. The TSBC converter is one of the most promising candidates suitable for low-speed, high-torque motor drives. It requires ac inductors for the cluster current c...

This paper provides a multiple motor drive using modular multilevel cascade converters (MMCCs) with galvanic isolation achieved by medium-frequency transformers. The motor drive is suitable for large-capacity pump and conveyor applications where multiple motors are required. A mitigating control method designed for the motor drive can reduce inhere...

This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system combining two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with dc power cables. Hereinafter, a single MMCC-DSCC is referred to simply as a DSCC converter. HVDC transmission systems are requir...

This paper provides experimental verification of a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed, high-torque motor drive. The TSBC is one of direct ac-to-ac power converters capable of achieving bidirectional power flow and drawing/feeding three-phase sinusoidal input (supply-side) and output (m...

This paper provides an experimental discussion on adjustable-speed electrical drives using a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) when the motor frequency is passing through, or equal to, the supply frequency. The TSBC converter is one of the most suitable candidates for medium-voltage, high-power motor...

The modular multilevel cascade converter (MMCC) family has been attracting attention from power electronics and power system engineers because it has been showing considerable promise as one of the next-generation high-power high-voltage/medium-voltage power converters. This paper provides an intensive discussion on power-flow analysis of three MMC...

This paper provides theoretical, numerical, and experimental comparisons in electrical-drive performance between a double-star chopper-cells (DSCC) inverter and a triple-star bridge-cells (TSBC) converter. The inverter and converter are two of the most promising members of the modular multilevel cascade converter (MMCC) family. Two sets of downscal...

Model Predictive control (MPC) is a powerful and emerging control algorithm in the field of power converters and energy conversion systems. This paper proposes a model predictive algorithm to control the power flow between the high voltage and low voltage DC buses of a bidirectional isolated full-bridge DC-DC converter. The predictive control algor...

This paper presents an intensive discussion on a transformerless back-to-back (BTB) system using modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). It is expected to be applied to a power distribution system with many distributed power generators. This paper designs, constructs, and tests a three-phase 200-V, 10-k...

This paper investigates an improved active-front-end (AFE) rectifier using model predictive control. The model predictive control (MPC) algorithm utilizes the discrete behavior of the power converter to determine the appropriate switching states by defining a cost function. The performance of the AFE rectifier has been verified with 3.0 kW experime...

This paper provides an experiment-based discussion on a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed high-torque motor drive. The TSBC is a direct ac-to-ac power converter capable of achieving bidirectional power flow as well as drawing and feeding three-phase sinusoidal input (supply-side) and...

This paper investigates the stability and performance of model predictive controlled active-front-end (AFE) rectifiers for energy storage systems, which has been increasingly applied in power distribution sectors and in renewable energy sources to ensure an uninterruptable power supply. The model predictive control (MPC) algorithm utilizes the disc...

This paper provides an experimental discussion on zero-voltage-ride-through (ZVRT) capability of a phase-shifted pulsewidth-modulation distribution static synchronous compensator (D-STATCOM) using the modular multilevel cascade converter based on single-star bridge cells (SSBC). The cluster-balancing control producing a significant effect on the ZV...

This paper focuses on the zero-voltage ride-through (ZVRT) capability of a transformerless back-to-back (BTB) system intended for installation on a power distribution system with many distributed power generators. The BTB system consists of two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) and their ac sides a...

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic (PV) systems. Both...

This paper provides a theoretical and experimental discussion about the performance, availability, and flexibility of a battery energy storage system (BESS) using a modular multilevel cascaded converter based on single-star bridge cells (MMCCSSBC). The SSBC-based BESS produces three-phase multilevel voltage waveforms, and eliminates both harmonic f...

Energy storage system has been widely applied in power distribution sectors as well as in renewable energy sources to ensure uninterruptible power supply. This paper presents a model predictive algorithm to control a bidirectional AC-DC converter, which is used in an energy storage system for power transferring between the three-phase AC voltage su...

This paper describes a high-speed protection circuit against a hard-switching fault (HSF) and a fault under load (FUL). The demand for high-speed protection circuits for insulated-gate bipolar transistors (IGBTs) subjected to an HSF increases with increasing power density of power semiconductor devices. The reverse transfer capacitance of an IGBT d...

The generator voltage of a cutting-edge wind turbine generation system (WTGS) is expected to increase from the conventional low-voltage level of 690 V to a medium-voltage level of 6.6 kV with a power level up to 10 MW without the application of a parallel connection of multiple power units. On the other hand, it is difficult to use a conventional t...

This paper provides theoretical and experimental discussions on an optimal carrier frequency for a phase-shifted pulsewidth modulation modular multilevel cascade converter for grid connections. The theoretical discussion concludes that a ratio of the optimal carrier frequency with respect to the supply (ac) frequency is 5/2. A three-phase downscale...

This paper describes an adjustable-speed motor with a quadratic-torque load such as fans, blowers, pumps, and compressors. The motor is characterized by being driven by the modular multilevel cascaded inverter based on doublestar chopper cells (MMCI-DSCC) A design for both mean dc-capacitor voltage and ac-voltage fluctuation in each dc capacitor us...

This paper presents a protection circuit for a fault under load (FUL). The protection circuit is characterized by the reverse transfer capacitance characteristic of IGBTs. The reverse transfer capacitance depends on the collector-emitter voltage and has a significant influence on the switching behavior under short-circuit conditions and normal cond...

This paper presents a theoretical discussion on triangular-carrier frequencies of a modular multilevel cascade converter based on double-star chopper cells (MMCC-DSCC, hereafter referred to as the DSCC) with phase-shifted PWM. The DSCC consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Low voltage steps bring signific...

This paper presents a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC), devoting itself to control and experiment. The TSBC is one of the direct ac-to-ac power converters capable of bidirectional power flow with three-phase sinusoidal currents with any power factor at both supply (input) and motor (output) sides. T...

This paper provides an experimental discussion on the modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed high-torque motor drive. The TSBC is a direct ac-to-ac power converter capable of achieving bidirectional power flow as well as drawing and feeding three-phase sinusoidal input (supply-side) and ou...

This paper provides an intensive discussion on analysis, simulation, and experiment of a back-to-back (BTB) systemunifying two modular multilevel cascade converters based on double-star chopper cells (MMCCs-DSCCs). Each of the twoDSCCs connected back-to-back consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Lowvoltag...

This paper presents a model predictive control algorithm of three-phase bidirectional AC-DC converter that can be used for V2G and G2V applications. This algorithm utilizes the discrete behaviour of the converter to determine appropriate switching states that minimize the cost function. The proposed predictive control scheme allows bidirectional po...

This paper describes a 750-V, 100-kW, 20-kHz bidirectional isolated dc/dc converter with the "dual-active-bridge" configuration using four SiC-MOSFET/SBD two-in-one modules. It pays particular attention to conversion efficiency and power-loss breakdown. The overall maximum efficiency from the dc-input to the dc-output terminals is measured accurate...

This paper focuses on an application of the modular multilevel cascade converter based on triple-star bridge-cells (MMCC-TSBC) to adjustable-speed motor drives. The TSBC is a direct ac-to-ac power converter capable of bidirectional power flow with three-phase sinusoidal input and output currents. Therefore, it is suitable to medium-voltage high-pow...

This paper presents a modular push-pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium- or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms based on a cascade connection of multiple bidirectional PWM chopper cells with floating dc capa...

A modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) has been expected as one of the next-generation multilevel PWM inverters for medium-voltage high-power motor drives. This inverter consists of cascaded bidirectional chopper cells with dc capacitors. One of concerns for the motor drive is how to achieve stable oper...

This paper describes the design, construction and testing of a 750-V, 100-kW, 20-kHz bidirectional isolated dual-active-bridge dc-dc converter using four 1.2-kV 400-A SiCMOSFET/SBD dual modules. The maximum conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be as high as 98.7% at 42-kW operation. The overal...