No abstract is provided for this article.
This paper discusses the potential of applying the soft-switching technique to a dc voltage-controlled static var compensator. The main circuit of the static var compensator (SVC) consists of quad-series voltage-source six-step inverters and four three-phase transformers. The SVC is characterized by a “commutation capacitor” connected in parallel with each switching device, without any additional active or passive element. The commutation capacitor plays an essential role in achieving soft-switching.Experimental results obtained from a small-rated laboratory model of 10kVA verify the operating principle and effectiveness of the soft-switched SVC proposed in this paper. The zero-voltage-switching enables to reduce dv/dt across each switching device, thus resulting in reduced EMI and switching losses.
This paper proposes a control method for eliminating dc magnetic flux from the series transformer of a DVR. The method is characterized by intentionally injecting no compensating voltage during a one-sixth line cycle (=3.3 ms at 50 Hz). The control sequence is independent of an initial phase angle of a voltage sag, thus requiring no flux detection. The period, during which no compensating voltage is injected, is one-third as short as that of an existing method. This paper verifies the effectiveness and viability of the proposed method, using a 200-V, 5-kW laboratory system. The proposed method brings no dc magnetic flux to the series transformer.
Renewable energy sources such as wind turbine generators and photovoltaics produce a fluctuating electric power. A battery energy storage system (BESS) should be installed in the vicinity of these sources. The fluctuating power is compensated by appropriately controlling an active power stored in the battery. This paper describes a feasible circuit configuration of a 6.6-kV transformerless battery energy storage system based on a multilevel cascade PWM (pulse-width-modulation) converter, with focus on a control method for active power and SOC (state-of- charge) balancing. A 200-V, 10-kW, 3.6-kWh (13-MJ) laboratory system combining a multilevel cascade PWM converter with nine NiMH (nickel metal hydride) battery units is designed, constructed, and tested to verify the viability and effectiveness of the 6.6-kV system.
A high performance ac servo system with permanent magnet synchronous motor, including a field-weakening control and a high-speed current response control of PWM inverter is proposed. For the field weakening, the d-axis armature current is adequately controlled through a microprocessor. The novel current control scheme of PWM inverter includes the motor neutral point potential stabilization and the switching carrier frequency equalization.
The modeling, analysis, and design of an active power filter using quad-series voltage source pulsewidth modulated (PWM) converters are presented. Some instantaneous space vectors of voltage and current are used for the analysis. A vector differential equation derived in this paper makes it easy to achieve the analysis and design of the active power filter. Experimental waveforms obtained from a prototype active power filter with a rating of 7 kVA, along with simulation waveforms, are included to verify the theory presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
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 switches; a low-voltage quasi circuit breaker (LV-qCB) and a high-speed disconnecting switch (HS-DS), and an advanced multilevel converter based on the cascade connection of multiple single-phase bridge cells. This hybrid dc circuit breaker is characterized by achieving current commutation from the LV-qCB to the multilevel converter capable of fast current control. This circuit configuration makes it possible to eliminate power switching devices from the main current path. This elimination leads to producing no conducting power loss during normal operating conditions. This paper provides a theoretical and experimental discussion on the operation, control, and performance of the hybrid dc circuit breaker. It includes verification through a downscaled experimental system rated at 300 Vdc and 150Adc, as well as confirmation through circuit simulation using the “PSCAD” software package.
A modular multilevel cascade converter based on double-star bridge-cells (MMCC-DSBC) is expected to be one of the next-generation medium-voltage PWM converters intended for grid connections. This converter is formed by six modular arms, each of which consists of a cascaded stack of multiple full-bridge converters. The DSBC is capable of single-phase to three-phase direct ac/ac conversion provided that the input and output frequencies are different. In this operation mode, the conversion efficiency can be improved compared to the ac/dc/ac indirect conversion. Hence, the DSBC is applicable to grid-connected high-power wind turbine generation systems using permanent-magnet synchronous generators. This paper presents experimental results obtained from a 200-V 6-kW downscaled system, which carries out single- to three-phase direct conversion, to verify the validity of the operating principles and control method developed in this paper.
An active power filter using quad-series voltage-source pulse-width-modulated (PWM) converters to suppress AC harmonics by injecting compensating currents into the AC system is described. The circuit used to calculate the compensating current references, the compensation characteristics, and the capability of the DC capacitor are discussed theoretically and experimentally. A control circuit for the DC capacitor voltage is proposed. The discussions focus on transient states, based on the instantaneous reactive power theory. A passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the AC side. Some experimental results that illustrate the details of the study are shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper proposes a new dc-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically-isolated windings. The dc magnetic fluxes in the magnetic core, which are generated by the two windings, cancel out each other. Therefore, the inductor does not generate any dc-magnetic flux in the magnetic core. This makes the inductor compact by a factor of six compared to previously used balancing circuits containing two non-coupled inductors. Experimental results obtained from a 200-V 5.5-kW downscaled model verify that the dc mean voltages of the four split dc capacitors are balanced well under all operating conditions.
This paper describes a five-level diode-clamped PWM inverter intended for a medium-voltage motor drive without regenerative braking. It is equipped with a specially-designed circuit that plays an important role in achieving voltage balancing of the four split dc capacitors connected in series at the dc input terminals of the inverter. The voltage-balancing circuit frees the inverter to concentrate on the motor control. Then, this paper has an intensive discussion on the modular multilevel cascade converter (MMCC) family that are characterized by the modular structure of either bridge cell or chopper cell. The four family members are compared from various points of view, along with applications of two promising members to a medium-voltage battery energy storage system and a medium-voltage motor drives for energy savings.
The authors have developed an electrical cart using two direct drive motors. It has two drive wheels and one caster wheel. A driver riding on the cart gives speed and steering commands through a joystick to operate the cart. Each motor is directly mounted into the drive wheel and is fixed on the body, frame. A speed difference between the two drive motors is controlled to turn the cart. Such a steering method which is called “differential-drive method” makes a great contribution to simplification of the mechanical structure.First, modeling of the cart is discussed in this paper, because few researches have been done in which dynamic equations are derived theoretically. The validity of this modeling is verified by comparing experimental results with reasonably calculated ones. Second, the authors propose a control system with fuzzy theory to get stable straight runnig performance, which can keep the caster wheel stragiht as long as a driver wants the cart to run straight. This fuzzy control system produces such a control signal that the cart automatically runs straight even if anything which may disturb the straight running occurs. It is verified experimentally that the proposed fuzzy control system helps a driver to keep the cart in a straight course.
No abstract is provided for this article.
This paper deals with a passive EMI filter designed for a 400-V, 15-kW induction motor driven by a three-level diode-clamped PWM inverter with a carrier frequency of 8 kHz. The EMI filter consists of a common-mode filter and a small-sized dv/dt reduction circuit. The common-mode filter is unique in terms of access to the motor neutral point. It can remove the common-mode voltage produced by the inverter from the motor terminals. This succeeds in eliminating both high-frequency motor shaft voltage and ground leakage current from the inverter-driven motor. The viability and effectiveness of the EMI filter is verified by experimental results even in the case that the motor is 100 m away from the inverter.
