717 publications from this institution
This paper makes discussions on a battery energy storage system based on a multilevel cascade pulsewidth-modulated (PWM) converter for its practical use. Briefly discussed are several considerations including state-of-charge (SOC) balancing of multiple battery units, and fault tolerance of the system. An active-power control of individual converter cells is presented to make the multiple battery units charged or discharged at different power levels, producing a three-phase balanced line-to-line voltage. Experimental results obtained from a 200-V, 10-kW, 3.6-kWh battery energy storage system verify its effectiveness.
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 one of direct ac-to-ac power converters capable of bidirectional power flow with three-phase sinusoidal input and output currents. Therefore, it is suitable to medium-voltage high-power motor drives requiring regenerative braking. This paper designs, constructs, and tests a three-phase 400-V, 15-kW, downscaled model with four bridge-cells per cluster, adopting the so-called "phase-shifted PWM" to produce multilevel waveforms at both sides. Good operating performance is verified by some experimental results obtained from the downscaled model. On the other hand, the TSBC suffers from such a serious problem that capacitor-voltage fluctuation becomes larger as the motor (output) frequency is closer to the supply (input) frequency. This paper also has an intensive discussion on how to control the TSBC intended for achieving a broad range of frequency control. Theoretical analysis and computer simulation confirm the effectiveness and viability of the proposed control method.
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 ASVC has a 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 of 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 based on the p‐q transformation. The analytical results help in the design of system parameters such as the capacity of the dc capacitor and feedback gains.
SUMMARY 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 output (motor‐side) currents with any power factor at both sides. This paper discusses active dc‐capacitor‐voltage control applied to the low‐speed, high‐torque motor drive. A specially designed downscaled system combining a 320‐V, 38‐Hz, 6‐pole, 15‐kW induction motor with a 400‐V, 15‐kW TSBC is constructed and tested to confirm the validity of the motor drive. Experimental waveforms obtained from the downscaled system confirm stable operation with the rated load torque across a range from a standstill to the rated speed, including satisfactory start‐up performance.
No abstract is provided for this article.
This paper develops a systematic and mathematically formal study of the balancing theory of series-stacked multilevel converters. It is shown that the DC bus voltages of these converters balance naturally, provided that the switching frequency is chosen high enough. Two balancing mechanisms, one associated with losses and the other with the load impedance, are identified. A single phase of a 2 MVA series-stacked power quality device was constructed and the theoretical results were verified experimentally.
This paper presents the modular multilevel cascade converter (MMCC) family based on cascade connection of multiple reversible-chopper cells or multiple single-phase full-bridge cells. This converter family are classified from circuit configuration as follows; single-star bridge-cells (SSBC), singledelta bridge-cells (SDBC), double-star chopper-cells (DSCC), and double-star bridge-cells (DSBC). The term MMCC corresponds to a family name in a person while, for example, the term SSBC corresponds to a given name. Therefore, the term “MMCC-SSBC” can identify the circuit configuration without any confusion. Among the four circuit configurations, SSBC and DSCC are the most practical than the others in terms of cost and performance, although a distinct difference exists in application between SSBC and DSCC. This paper describes applications of SSBC and DSCC to a battery energy storage system and a motor drive, respectively.
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.
No abstract is provided for this article.
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 two-level or three-level converter in a WTGS with a dc-link voltage of 10-13 kV owing to the limitations on the voltage ratings of power devices. This paper presents a 10-MW WTGS consisting of a three-phase open-winding synchronous generator equipped with six lead terminals and a modular multilevel cascade converter (MMCC) formed by three identical subconverters. The MMCC carries out direct ac/ac power conversion from three single-phase voltages with a time-varying frequency (from the generator) to a three-phase voltage with a line frequency of 50 Hz. This paper discusses the operating principles and control methods for the WTGS, followed by simulations using the software package PSCAD/EMTDC. The experimental result obtained from a 200 V 6-kW downscaled system confirms the reliability of simulation results of the complete three-phase system.
This review examines a book that deals with the instantaneous active and reactive power theory in a complete for, for the first time. As it presents such an in-depth look at the subject, the book may be destined to be a classic.
The instantaneous active and reactive power theory or the p-q Theory is widely used to design controllers for active filters. This paper deals with some problems due to the misinterpretations of this theory. A historical background of the theory is presented and the problem caused by distorted voltages at the point of common connection (PCC) is analyzed. In addition, the appearance of source current harmonic component not present in the load current (hidden current) caused by different filtering characteristics for the calculation of the oscillating real and imaginary power components is discussed. The problem caused by the voltage distortion can be solved using a phase locked loop (PLL) circuit. For the hidden current, filters with similar characteristics can avoid them. These analysis and solutions are presented to clarify some aspects of the p-q Theory not clear in the original approach of the theory.
This paper proposes a new circuit configuration for a position-sensorless drive system using an interior permanent magnet synchronous motor (IPM motor) rated at 3.7kW. The configuration can decrease the number of the sample and hold circuits to four, though fourteen sample and hold circuits are required for the conventional system. In addition, the configuration makes it efficient to detect current variations. It is shown experimentally that the drive system has good position estimation characteristics with absolute and relative errors within ±2 deg and ±0.5 deg in electrical angle, respectively. Moreover, the position control response is improved by adding current control loops to the position-sensorless drive system.
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. Nowadays, 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 voltages 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.
This paper deals with a 50-MW self-commutated BTB (Back-To-Back) system intended for power-flow control between transmission networks. It focuses on the dynamic behavior of the BTB system during single-line-to-ground (SLG) faults. During an SLG fault, a dc magnetic deviation appears in the converter-transformers used for the BTB system just after the occurrence and restoration of the fault. It is indispensable to understand an amount of deviation because it may bring magnetic saturation as well as a large amount of magnetizing current to the transformers. This paper derives theoretical equations related to the deviation during the SLG fault. The theoretical analysis developed in this paper would make significant contributions to designing the transformers.
