This paper provides an experimental discussion on a real-time real-power emulator for a medium-voltage, high-power, high-speed motor drive. This emulator is characterized by integrating mechanical dynamics of both motor and load into it. The power-electronic circuit of the emulator consists of a three-phase modular multilevel double-star chopper-cell (DSCC) rectifier, three inductors, and a single two-winding common-mode inductor. This paper designs, builds, and tests a 400-Vdc 10-kW downscaled test bench in which a three-phase DSCC inverter under test is connected in front-to-front (FTF) with the emulator. The DSCC inverter is the same in circuit configuration as the DSCC rectifier. Experimental waveforms obtained from the downscaled test bench lead to the following conclusion: The emulator can reproduce both electrical and mechanical dynamics of a three-phase 200-V, 10-kW, four-pole, 9 000-r/min induction motor coupled with a centrifugal compressor.
This paper presents a dynamic voltage restorer (DVR) that is characterized by the use of a high-frequency unidirectional isolated dc-dc converter. A traditional DVR has a large and bulky series transformer even for low-voltage (200 or 400 V) applications because the transformer operates at the line frequency (50 or 60 Hz). The emergence of the state-of-the-art semiconductor devices and magnetic cores has driven power electronics engineers to develop compact high-frequency isolated dc-dc converters. This paper discusses control and performance of a DVR including a high-frequency isolated dc-dc converter intended for 200 or 400-V applications. The high-frequency (20 kHz) transformer in the dc-dc converter is much smaller, say one-hundredth, in volume than the line-frequency transformer. Moreover, connecting the shunt converter to the load side brings a significant reduction in energy-storage capacity to the DVR. Experimental results obtained from a 200-V 5-kW laboratory system confirm the viability and effectiveness of the system configuration.
We describe a boy with a deletion of the short arm of chromosome 3; (46, XY, del (3) (p25-pter) who presented several minor craniofacial anomalies at birth. Only 34 cases of small distal 3p deletion have been described in the literature, seven of them showed hearing loss and four of the 34 cases had brain anomalies. But in none of the 34 cases the middle and internal ear were radiographically examined. Despite the severe hearing loss detected by auditory brainstem evoked responses (ABR), computerized tomographic scanning (CT-scan) of the ear showed a normal anatomy in this patient. The head CT-scan and magnetic resonance imaging (MRI) disclosed a hypoplastic corpus callosum and an enlargement of the lateral ventricles.
This paper deals with DC-flux deviations occurring in a doubly-fed flywheel generator with stator-current feedback control. An AC output voltage of the PWM inverter connected to the rotor produces the DC-flux deviations in the stator. It is difficult to detect the DC flux from the stator current and/or voltage, because the DC flux induces no electromotive force on the stator windings. This paper proposes a new control method for suppressing the DC flux deviations based on calculating the magnetizing current from the stator and rotor currents. Experimental results verify the viability of the proposed control method.
This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm proposed in this paper determines the inductance matrix including rotor position information from current harmonics produced by switching operations of an inverter driving the IPM motor, and then estimates the rotor position every period of pulse-width modulation (PWM). Position estimation without any special signal injection is achieved with a satisfactory response and accuracy even at a standstill and at low speed. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 68–79, 2000
This paper deals with a leakage current flowing out of the heat sink of a voltage-source PWM inverter. The heat-sink leakage current is caused by a steep change in the common-mode voltage produced by the inverter. It flows through parasitic capacitors between the heat sink and power semiconductor devices when no EMI filter is connected. Experimental results reveal that the heat-sink leakage current flows not into the supply side, but into the motor side. These understandings succeed in describing an equivalent common-mode circuit taking the parasitic capacitors into account. The authors have proposed a passive EMI filter that is unique in access to the ungrounded motor neutral line. It is discussed from this equivalent circuit that the passive EMI filter is effective in preventing the leakage current from flowing. Moreover, installation of another small-sized common-mode inductor at the ac side of the diode rectifier prevents the leakage current from flowing into the supply side. Experimental results obtained from a 200-V, 3.7-kW laboratory system confirm the effectiveness and viability of the EMI filter.
This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in the 400-V, 15-kW induction motor driven by a voltage-source pulsewidth modulation (PWM) inverter. A shaft-to-frame voltage can be observed at either shaft end with respect to the grounded motor frame. A shaft end-to-end voltage can be observed as a voltage difference between the shaft-to-frame voltage at the drive end (DE) and that at the nondrive end (NDE). Experimental waveforms lead to the following interesting observations: motor internal coupling and parasitic capacitance, along with the high-frequency common-mode voltage generated by the PWM inverter, cause a shaft-to-frame voltage with a peak of 8 V at both DE and NDE. When the shaft-to-frame voltage at either DE or NDE exceeds a dielectric breakdown voltage of thin bearing lubricating grease films, a shaft end-to-end voltage with a peak of 2 V and a width of 30 ns occurs along the motor shaft. This paper makes experimental discussions on the shaft end-to-end voltage generation. Installing a differential-mode filter and/or a common-mode filter on the motor drive system gives a hint on the mechanisms of the occurrence of the shaft end-to-end voltage.
This paper presents theoretical and experimental relationships in between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source PWM inverter. A method of reducing both the currents is proposed, based on an equivalent model taking parasitic stray capacitors inside an induction motor into account. Electromagnetic interference (EMI) radiated by a 3.7 kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3m]. Experimental results verify that the combination of the already proposed common-mode transformer and the normal-mode filters being proposed in this paper is a practically viable and effective way to reduce the EMI resulting from both the common-mode and normal-mode currents.
No abstract is provided for this article.
No abstract is provided for this article.
A combined system of shunt passive and small rated series active filters, as well as its operating principle and steady compensation characteristics, was previously presented by the authors (1988). The combined system can greatly reduce problems of using only the shunt passive or shunt active filters and is suitable for harmonic compensation for large VA-rated loads in power systems. Transient compensation characteristics and the stability of the system are discussed and analyzed theoretically and experimentally in detail. A control method enables the combined system to be applied to cycloconverter compensation. Some results obtained with the experimental model are presented to demonstrate and confirm the method's validity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An active power filter using quad-series voltage-source PWM converters is used to suppress ac harmonics by injecting PWM modulated currents to the ac side. In this paper, the calculation circuits for the harmonic currents to be injected, the compensation characteristics, and the capacity of the dc capacitor are discussed. A new control circuit for the dc capacitor voltage is proposed. These discussions focus on transient states and are on the basis of the instantaneous reactive power theory. Finally, a passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the ac side. Some experiments to illustrate the details of the study are shown.
A voltage-source PWM inverter produces common-mode and normal-mode currents flowing through stray capacitors inside an ac motor every switching. Therefore, the currents may cause radiational EMI to electronic equipment, e.g., AM radio receivers, because its oscillation frequency ranges from 100kHz to several MHz. However, few technical papers related to the radiational EMI have been reported although attention has paid to the EMI.This paper discusses relationships between radiational electromagnetic noises and the commom-mode and normal-mode currents. Reduction methods of both the commom-mode and normal-mode currents are also discussed on the basis of a motor model including the stray capacitors. It is shown theoretically and experimentally that both the currents can be damped by the combination of the common-mode transformer which has already been proposed by the authors and normal-mode filters proposed in this paper. Radiational EMI of a vector-controlled induction motor drive system of 3.7kW is measured according to the VDE 0877. Experimental results show not only that the radiational EMI results from the high-frequency oscillatory currents, i.e., the common-mode and normal-mode currents, but also that the combination of the common-mode transformer and the normal-mode filters is an effective, practical way of reducing the EMI.
This paper presents a battery energy storage system with a modular push-pull PWM converter (MPC), which is intended for grid connection to medium-voltage or high-voltage power systems. The converter is equipped with a center-tapped transformer and two arms consisting of a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, to achieve voltage balancing of all the floating capacitors. Moreover, a comparison is made between the MPC and a modular multilevel converter (MMC) as the battery energy storage system. The validity of the concept and control method developed in this paper is confirmed by computer simulations using the “PSCAD/EMTDC” software package.
This paper describes the control and operating performance of a modular multilevel PWM inverter for a transformerless medium-voltage motor drive. The inverter is prominent in the modular arm structure consisting of a cascaded stack of multiple bidirectional chopper-cells. The dominant ac-voltage fluctuation with the same frequency as the motor (inverter) frequency occurs across the dc capacitor of each chopper-cell. The magnitude of the voltage fluctuation is inversely proportional to the motor frequency. This paper achieves theoretical analysis on the voltage fluctuation, leading to system design. A downscaled model rated at 400 V and 15 kW is designed and built up to confirm the validity and effectiveness of the nine-level (17-level in line-to-line) PWM inverter for a medium-voltage motor drive.
This paper presents the modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC), which is intended for installation on the 6.6-kV Japanese industrial and utility distribution systems without using line-frequency transformers. The converter is characterized by an arm structure based on the module consisting of cascade connection of multiple bidirectional PWM chopper-cells and floating dc capacitors per arm. This arm structure requires voltage-balancing control for all the chopper-cells. However, the voltage control combining averaging- with individual-balancing controls imposes certain limitations on operating conditions. This paper proposes an arm-balancing control to achieve voltage balancing in all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is confirmed by computer simulation.
No abstract is provided for this article.
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 with 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.
