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The design optimization procedure for a new active resonant snubber topology, specifically suited for high power insulated gate bipolar transistor (IGBT) converters, is introduced. After the basic operation principles and certain implementation consideration are discussed, the optimization strategy, based on an analytical loss evaluation, is described. Experimental results obtained on an IGBT phase-arm fitted with an optimally designed snubber are presented. Index Terms--Active resonant snubber topology, insulated gate bipolar transistor (IGBT).

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 drive. This test bench consists of two modular multilevel double-star chopper-cell (DSCC) converters connected front-to-front without a transformer. An experimental downscaled P-HIL test bench is designed, constructed, and tested to confirm its operating performance. The three-phase 400-Vdc 10-kW DSCC inverter with eight chopper cells per arm is used as a “real” inverter under test. The other DSCC rectifier is used as a set of a “virtual” three-phase 200-V 10-kW 300-Hz four-pole 9000-r/min synchronous motor and a “virtual” high-speed centrifugal compressor with a quadratic torque-to-speed load characteristic. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through 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 current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [ABSTRACT FROM AUTHOR]

This paper provides a chronological overview of the topology for multilevel converters, and discusses their different terminology usages and characteristics. The multilevel converters include three-level neutral-point-clamped (NPC) and neutral-point-piloted (NPP) inverters, three-level and four-level flying-capacitor (FLC) inverters, and a family of modular multilevel cascade converters. Some have already been put into commercial use, some have been on a research and development stage, and others have been on an academic research stage. This paper pays much attention to six family members of the modular multilevel cascade converters, intended for grid-tied applications and medium-voltage high-power motor drives. [ABSTRACT FROM PUBLISHER]

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. The phase shift of each carrier signal is rotated to enable capacitor–voltage balancing in such a low-carrier-frequency range while maintaining the same voltage in each arm as that of the original phase-shifted-carrier PWM. Theoretical analysis of harmonic-voltage spectrum at the arm side of a chopper cell is conducted on the basis of double-variable Fourier series. Then, the analytical results are compared to numerical ones. A three-phase grid-connected DSCC converter rated at 66 kV, 50 Hz, and 100 MW with 64 chopper cells per leg is used in circuit simulation to confirm the validity of the proposed PSRC-PWM method. The simulation results show that the PSRC-PWM can maintain stable operation of the DSCC converter even if the carrier frequency goes lower than 100 Hz. Several performance criteria conclude that the optimal carrier frequency is 75 Hz. [ABSTRACT FROM AUTHOR]

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 (motor-side) currents with any power factor at both sides. This paper designs, constructs, and tests a downscaled drive system combining a 400-V, 15-kW, phase-shifted-carrier PWM TSBC equipped with four bridge cells per cluster and a 320-V, 38-Hz, 6-pole, 15-kW induction motor loaded at the rated torque. Experimental waveforms obtained from the downscaled drive system verify stable operation across a broad range from a standstill to the rated speed, showing satisfactory start-up performance. [ABSTRACT FROM PUBLISHER]

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. Lowvoltage steps bring significant reductions in harmonic voltage and current to the BTB system. Neither dc-link capacitornor voltage sensor is required for regulating the dc-link voltage and controlling the dc-link current. A three-phase200-V, 10-kW, 50-Hz downscaled BTB system with phase-shifted PWM is designed, constructed, and tested to verify itsoperating principles and performance. Analytical, simulated, and experimental results agree well with each other insteady and transient states. Experimental waveforms confirm the effectiveness of a self-starting/restartingprocedure. [ABSTRACT FROM AUTHOR]

This paper presents the application of a modular multilevel cascade converter based on single-delta bridge-cells (MMCC-SDBC) to a STATic synchronous COMpensator (STATCOM), particularly for negative-sequence reactive-power control. The SDBC is characterized by cascade connection of multiple single-phase H-bridge (or full-bridge) converter cells per leg, which facilitates flexible circuit design, low voltage steps, and low electromagnetic interference (EMI) emissions. However, there is no published report on such a STATCOM with experimental verification or a control strategy. This paper designs, constructs, and tests a 100-V 5-kVA PWM STATCOM based on the SDBC with focus on the operating principle and performance. Experimental results confirm that this converter can control not only the positive-sequence reactive power but also the negative-sequence reactive power and low-frequency active power intended for the flicker compensation of arc furnaces. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 33-44, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22365 [ABSTRACT FROM AUTHOR]

This paper deals with a 50-MW self-commutated back-to-back (BTB) system intended for power-flow control between two ac transmission networks. It focuses on the dynamic behavior of the BTB system during single-line-to-ground and double-line-to-ground faults. Attention is particularly paid to the dc magnetic flux deviation in the grid and converter transformers, and the circulating current inside the grid transformers, which would produce undesirable effects on the system. Theoretical equations related to the amount of circulating current and the dc magnetic flux deviation are derived. The theoretical results developed in this paper are confirmed by computer simulation. [ABSTRACT FROM AUTHOR]

This paper deals with a 6.6-kV transformerless STATCOM cascading multiple single-phase H-bridge PWM converters in each phase. The AC voltage of the STATCOM is almost sinusoidal, so that it requires no harmonic filter. Each converter is equipped with a capacitor and a voltage sensor on the DC side, which are electrically isolated from each other. The STATCOM has the capability of self-starting and voltage-balancing without any external power supply or equipment. Experiments using a three-phase 200-V, 10-kVA laboratory system, along with computer simulations, are carried out to confirm the viability and effectiveness of the STATCOM. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 55–64, 2010; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/eej.20822 [ABSTRACT FROM AUTHOR]

This paper describes a transformerless energy storage system based on a cascade multilevel pulsewidth modulation converter with star configuration. The system is intended for power leveling of renewable energy sources, as well as for improving power quality and reliability of a power distribution system. This paper pays attention to active-power control and voltage- balancing control that are indispensable for proper operation of the energy storage system. A 200-V 10-kW 8.8-k.J downscaled laboratory system is designed, constructed, and tested, replacing electric double-layer capacitors with large-capacity electrolytic capacitors. Experimental results obtained from the laboratory system verify the viability and effectiveness of the 6.6-kV energy storage system. [ABSTRACT FROM AUTHOR]

This paper discusses the potential of a transformer-less STATic synchronous COMpensator (STATCOM) intended for installation on the 6.6-kV industrial and utility distribution systems. The STATCOM consists of a five-level diode-clamped pulsewidth-modulation converter rated at 1 MVA and a voltage-balancing circuit rated at 6 kVA. Moreover, this paper designs, constructs, and tests a 200-V 10-kVA STATCOM based on a five-level converter with a carrier frequency of 3 kHz and a voltage-balancing circuit with a switching frequency of 3 kHs. The STATCOM and its experimental waveforms verify the viability and effectiveness of the 6.6-kV transformerless STATCOM. [ABSTRACT FROM AUTHOR]

This paper addresses a bidirectional dc-dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to a dc side of the dc-dc converter without any chopper circuit. Nevertheless, the dc-dc con- verter can continue operating when the voltage across the energy storage device drops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc-dc converter. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit. [ABSTRACT FROM AUTHOR]

A 21-level (line-to-line) self-commutated BTB (Back-To-Back) system based on series connection of 16 converter cells has attractive features as follows: (i) Both active and reactive powers can be controlled independently even in transient states. (ii) The BTB system produces almost sinusoidal voltage at the AC side without performing PWM (Pulse-Width-Modulation) control, so that no harmonic filter is required. (iii) The BTB system provides an active power reason as high as 3 ms. This paper presents experimental verifications of the self-commutated BTB system intended for achieving power flow control in transmission systems. Experimental results obtained by a 200-V, 20-kW laboratory prototype confirm effectiveness and validity of both the system configuration and the developed control strategy. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 61– 70, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20324 [ABSTRACT FROM AUTHOR]

The so-called three-level inverters have been widely used for industry applications because of high-voltage output ability and low harmonic contents. These applications are mainly suitable for AC motor drives. Recent attention has been paid to larger-capacity inverters applicable to power system control. This paper describes their applications to power systems. First, harmonic analysis of a three-level inverter is achieved under the condition that its two DC capacitor voltage are unbalanced. Second, a control method for balancing the two DC capacitor voltages is described. Finally, applications of single-phase three-level inverters to STATCOM and BTB are introduced. Their control performance is confirmed by computer simulation. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 54–62, 2006; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20306 [ABSTRACT FROM AUTHOR]

This paper deals with an inverter system integrating a small-rated passive EMI filter with a three-phase voltage-source PWM inverter. The purpose of the EMI filter is to eliminate both common-mode and normal-mode voltages from the output voltage of the inverter. The motivation of this research is based on the well-known fact that the higher the carrier or switching frequency, the smaller and the more effective the EMI filter. An experimental system consisting of a 5-kVA inverter, a 3.7-kW induction motor, and a specially designed passive EMI filter was constructed to verify the viability and effectiveness of the EMI filter. As a result, it is shown experimentally that both three-phase line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter system were an ideal variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in complete solution of serious issues related to common-mode and normal-mode voltages produced by the inverter. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 88–96, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10206 [ABSTRACT FROM AUTHOR]

This paper deals with a self-commutated BTB (Back-To-Back) system for the purpose of power flow control and/or frequency change in transmission systems. Each BTB unit consists of two sets of 16 three-phase voltage-source converters, and their AC terminals are connected in series to each other via 16 three-phase transformers. Hence, the BTB unit uses totally 192 switching devices capable of achieving gate commutation. This results in a great reduction of voltage and current harmonics without performing PWM control. Simulation results verify the validity of the proposed system configuration and control scheme not only under a normal operating condition but also under a single line-to-ground fault condition. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(3): 68–78, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10124 [ABSTRACT FROM AUTHOR]

Discusses a study that dealt with a harmonic current-free ac/dc power conversion system. Materials that consist the harmonic-free ac/dc power conversion system; Stability analysis and characteristic comparison; Effect on system stability.

Harmonic interference problems generated by bulk semiconductor power converters become more serious in power systems with their wide use in industrial applications. Shunt passive filters consisting of LC tune filters or shunt active filters using PWM inverters have been used to suppress harmonic currents in distribution systems. To install the passive or active filters, it is necessary to find exactly a dominant harmonic source in distribution feeders. A harmonic power on each phase and order at a receiving terminal has been investigated by using a digital power meter including an FFT analyzer. However, the conventional detection method has a problem in that it is difficult to discuss exactly harmonic power flow because the detected harmonic power is much smaller compared with a fundamental active power at the receiving terminal. In this paper, the harmonic power in three phases, which can be detected on real time, is defined by applying the pq theory. Next, it is verified by a digital simulation that the proposed method can discuss harmonic flows more easily than the conventional method. As a result, it is more simple and precise to find the harmonic source. Moreover, measurement errors of the harmonic power are revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation. [ABSTRACT FROM AUTHOR]

In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage source inverters. This type of rectifiers, however, causes many problems such as poor power factor and harmonics. Recently, voltage source PWM rectifier-inverters have been studied to provide the following advantages; (1) harmonic-free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. It is however, difficult for a conventional one to regulate the capacitor voltage on transient states because of having only a voltage feed-back loop. This paper describes a voltage source PWM rectifier-inverter with feed-forward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feed-forward control of instantaneous power makes a great contribution to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed and some interesting experimental results of a laboratory model are shown. [ABSTRACT FROM AUTHOR]