Tsuneo Kume

A novel neutral point potential stabilization technique using the information of output current polarities and voltage vector

This paper proposes a new neutral point potential control technique for the three-level neutral-point-clamped PWM inverter. Utilizing the phase current polarity information, this technique distributes the redundant voltage vectors in a manner to obtain stable neutral point voltage under all operating conditions including the zero power factor condition. Detailed analysis and computer simulations show the superiority of the proposed method. The feasibility of the proposed method has been proven via laboratory experiments.

Common mode current attenuation techniques for use with PWM drives

The most common modulation strategy adopted for motor control in adjustable speed drives (ASDs) is pulse width modulation (PWM). In general, the output is modulated at a carrier frequency ranging from 1.0 kHz to 20.0 kHz. Experiences with PWM drives have shown that there exist two important concerns: (1) common mode current; and (2) over-voltage at the motor when the distance between motor and the inverter is larger than the critical distance. The high carrier frequency along with fast rise and fall time of the insulated gate bipolar transistors (IGBTs) employed results in nontrivial common-mode or ground currents. The high dv/dt causes shaft voltage, which leads to bearing currents. This phenomenon has been identified as one of the reasons for premature bearing failure in PWM driven motors. A new scheme to attenuate the common mode noise and hence reduce shaft voltage is proposed. Experimental results showing the effectiveness of the proposed solution is also presented.

The matrix converter drive performance under abnormal input voltage conditions

The matrix converter (MC) is a direct frequency conversion device with high input power quality and regeneration capability. As a device without energy storage elements, it has higher power density than pulse-width modulation (PWM) inverter drives. However, for the same reason, the AC line side disturbances can degrade its performance and reliability. In this paper, the behavior of the MC drive under abnormal input line voltage conditions has been investigated. A technique to eliminate the input current distortion due to the input voltage unbalance has been developed and its feasibility proven via computer simulations and laboratory experiments. The power line failure behavior has also been investigated and the rapid restarting capability of the MC drive has been demonstrated via laboratory experiments.

A wide constant power range vector controlled AC motor drive using winding changeover technique

A high-performance vector-controlled induction-motor drive with a very wide constant power range of 1:10 to 1:30 has been developed for use in spindle drives of machine tools. The motor has two combinations of winding connections, and one of them is selected in accordance with the operating conditions. Using this technique, the gear box in the spindle drives is eliminated. Theoretical analysis and test results are presented.<<ETX>>

Neutral-point clamped three-level general purpose inverter - features, benefits and applications

This paper introduces a neutral-point clamped three-level PWM inverter for general industry applications in the 400-480 volt range. Since the voltage stress applied to the power devices of three-level configuration is half that of the two-level version, this topology was traditionally used for medium voltage drives both in industrial and traction areas. Basic behavior of the NPC topology brings significant advantages to the low voltage applications as well. Especially, the lower voltage steps associated with the switching help in the mitigation of problems related to surge voltages at the motor terminals, leakage current, shaft voltage and bearing current, and so on. The three-level NPC inverter newly introduced for general-purpose application combines sophisticated PWM technique and modern control laws to yield high performance drive. The features and benefits of this product are presented along with measured waveforms.

High-Performance Vector-Controlled AC Motor Drives: Applications and New Technologies

A high-performance ac motor control has been developed by employing the vector control concept. Its versatility has been proven through the six years of experience in applications to pinch roll drives of continuous casting plants, machine tool spindle drives, and other drive systems in industry. Equivalent torque characteristics are achieved with ac motors compared to dc motors without direct detection of the magnetic flux. The effect of rotor temperature on the torque characteristics has been compensated to a satisfactory level in actual industrial use by various means. Servo drives, both synchronous motor and induction motor types, have been introduced. The test results show that the performance of ac servo drives is equivalent or superior to that of the PWM-controlled dc servo drives. Furthermore, an example of the direct-drive servo is described, where an ultra-low speed high-torque motor and an ultra-high resolution position sensor play key roles. In addition, the possibility of a more sophisticated servo drive exploiting modern control theory is suggested.

A novel high-torque reluctance motor with rare-earth magnet

An entirely new concept of an electromagnetic structure which exploits the excellent characteristics of a rare-earth magnet is proposed. Thin rare-earth metal magnet pieces are mounted on the surface of the stator teeth which face the airgap. The rotor has a variable reluctance structure type. This type of motor is suitable for low-speed high-torque applications by the action of tooth and slot structure. The relationship between the performance and electromagnetic geometry is investigated through the finite element method (FEM) analysis and experiments. The principle of torque generation and the associated characteristics is also introduced. >

Common-mode voltage characteristics of matrix converter-driven AC machines

This paper investigates the common-mode voltage characteristics induced by PWM switching of the Matrix Converter (M/spl times/C). Since the three-phase matrix converter has 27 output voltage vectors available, different common-mode voltage patterns exist even with the same line-to-line output voltages. High common-mode dv/dt contributes high leakage currents to the ground through the parasitic capacitances. Since output voltage vectors can be grouped according to the magnitude of common-mode voltage, PWM patterns should be designed to select the low common-mode voltage vector groups satisfying the requirement of output voltages and input currents. In this paper, practical PWM patterns of M/spl times/C are illustrated and their common-mode voltage characteristics are presented. A new PWM method is proposed and discussed considering both low common-mode voltage and low dv/dt in the PWM pattern. The results are also compared with the data obtained by the Voltage Source Inverter (VSI).

Output voltage distortion in matrix converter by commutation of bi-directional switches

The matrix converter is an AC-to-AC conversion device without intermediate DC link and the associated large capacitive filter. Three-phase matrix converter consists of nine bi-directional switches, which allows PWM control of input and output currents. Commutation from one switch to another is important for reliable operation. During commutation sequence, unwanted output voltage distortion occurs because actual commutation is dependent on magnitude of input voltage and direction of output current. In this paper, output voltage distortion during current commutation between bi-directional switches is analyzed and effective compensation method is proposed. The feasibility of the analysis results is proved by experimental results.

An Efficient Resonant Gate-Drive Scheme for High-Frequency Applications

Gallium Nitride (GaN) and Silicon Carbide (SiC) devices have been found to withstand high voltages without showing degradation [1] and can be switched at high frequencies making them attractive for high power drives. Though GaN/SiC devices can be operated at high temperature and high frequencies, it is important to develop gate drive circuits to turn ON and OFF these devices efficiently at high speeds. This paper proposes a resonant gate drive circuit that aims at reducing the power loss associated with high frequency switching of power IGBT/MOSFETs. The proposed circuit is compared with traditional gate drive circuits from power consumption and switching speed points of view. Experimental results are given to illustrate the concept.