Masaaki Sakui

A maximum power control of wind generator system using a permanent magnet synchronous generator and a boost chopper circuit

The wind generator system using a boost chopper for generation control of permanent magnet synchronous generator is proposed. And, the theoretical analysis of characteristics of power generation is discussed. By replacing the main circuit composition of generator and boost chopper with the equivalent circuit, characteristics for generating power and DC output voltage were expressed by the function of duty ratio of the boost chopper and generator rotational frequency. Electric power supplied from the generator is characterized by the condition of the load with the peak point. Therefore, the optimum duty ratio for obtaining the maximum power was theoretically determined by differentiating the characteristic equation of generating power with respect to duty ratio of the boost chopper. It was verified experimentally by the construction of the simulator of the wind generator system, and the validity of derivation technique for the maximum power point was confirmed.

A new configuration of single-phase symmetrical PWM AC chopper voltage controller

With the increased availability of power MOSFETs and insulated gate bipolar transistors, a new generation of simple choppers for AC inductive loads is foreseen. These new power semiconductors ease the use of forced commutations of thyristor switches to improve the supply power factor, even with highly inductive loads. The AC controllers with thyristor technology can be replaced by pulsewidth modulation (PWM) AC chopper controllers which have important advantages. In this paper, a symmetrical PWM AC chopper designed to operate with single-phase inductive loads with a reduced number of controlled switches is described. The operation as a variable voltage source of this converter is evaluated. This includes the conversion characteristics, harmonic generation, harmonic distortion factor, and input power factor. By digital simulation, these characteristics are investigated theoretically, and to correlate the measurements with theory, an experimental setup is presented to confirm the analytical analysis.

An analytical method for calculating harmonic currents of a three-phase diode-bridge rectifier with DC filter

Commonly, three-phase diode bridge rectifiers with an LC filter at the DC side are often used to convert AC input into a DC voltage. It is well known that they generate large amounts of harmonic currents. This paper proposes an analytical method for calculating the harmonic currents for both the continuous and discontinuous current conductions. The equations for the harmonic currents are derived, taking into account the effects of the DC and AC side impedances. All the calculations are conducted only by algebraic calculation with high accuracy. The validity of the proposed method is demonstrated by comparison to the results of time simulation. >

A method for calculating harmonic currents of a three-phase bridge uncontrolled rectifier with DC filter

A practical method is proposed for calculating the harmonic currents of a three-phase bridge uncontrolled rectifier with a DC filter, taking into account the AC source reactance. The method is based on the frequency-domain method and the rectifier switching functions. Analytical equations for the harmonic currents on both the DC and AC sides are derived. The validity of the method is demonstrated by comparison with the results of time simulation. The approach can be extended to the harmonic analysis of a thyristor rectifier as well as a rectifier with unbalanced line conditions. >

AC chopper voltage controller-fed single-phase induction motor employing symmetrical PWM control technique

Abstract Due to the growing demand in improving the performance of motor drives, there is an increasing need to improve the quality and reliability of the drive circuit. AC-to-AC converter schemes using pulse width modulation (PWM) are proved to achieve substantial advantages over conventional line-commutated AC controllers. With the increasing availability and power capability of MOSFETs and IGBTs switches, PWM converters can efficiently and economically be used in low and medium power applications. However, such controllers have been applied only to control the voltage of passive R-L loads. In this paper, the performance characteristics of a symmetrical PWM AC chopper controller-fed single-phase induction motor drive are evaluated. The developed analysis is experimentally verified by an experimental verified mathematical model is used for this purpose.

Structure of One-Axis Controlled Repulsive Type Magnetic Bearing System With Surface Permanent Magnets Installed and Its Levitation and Rotation Tests

This paper deals with a new bearing structure of one-axis controlled repulsive type magnetic bearing system that has a motor function of a surface permanent magnet (SPM). We evaluated the magnetic bearing structures by using the 4-pole 4-segment type and 4-pole Halbach array, which were placed around cylindrical permanent magnet sets as field magnets. The comparison of magnetic flux density in the radial direction measured by finite-element analysis indicated that the Halbach array has advantages over the 4-segment type in terms of the total harmonic distortion and internal magnetic influence. Additionally, levitation and rotation tests were performed by implementing each bearing configuration in a newly developed equipment. In both bearing configurations, stable levitation at zero-power position was established and high-speed rotation up to around 16 000 rpm was achieved. As a result, the Halbach array slightly saved electric power. Its total input power to the motor was approximately 1.2 W.

Conveyance test by oscillation and rotation to a permanent magnet repulsive-type conveyor

Various applications of a single-axis controlled repulsive-type magnetic bearing have been proposed earlier. However, most conventional systems are equipped with a set of passive magnetic bearings and an active magnetic bearing. In this paper a new repulsive-type conveyor system with many passive magnetic bearing pairs is proposed. This system enables an easy rotation with negligible friction and soft conveyance by radial stiffness between the rotor and the stator permanent magnets. This paper also reports a conveyance test using ellipse motion of each shaft.

Improved circuit of AC choppers for single-phase systems

In this paper, an improved circuit of AC choppers for single-phase systems are proposed and investigated. This new circuit employs a DC chopper modulated switch with a diode bridge rectifier and two switches to provide a freewheeling path for the load current when the modulated switch is off. The attractive feature of this improved circuit is that it uses only a single modulated switch. The improved circuit has many advantages compared with the conventional AC choppers such as simple design requirements, easy implementation, higher power capacity, fast dynamic response, high reliability, high power factor, low cost, low switching loss and consequently high efficiency. By digital simulation several characteristics are investigated.

Three-Dimensional Motion of a Small Object by Using a New Magnetic Levitation System Having Four I-Shaped Electromagnets

In common active magnetic levitation systems, a floating object is controlled stably by an electromagnet with a narrow air-gap, which reduces the leakage flux. However, in order to move a floating object dynamically, it is necessary to arrange electromagnets for horizontal motion and to make the air-gap wide for vertical motion at the expense of leakage flux. In this paper, we propose a novel magnetic levitation system having a compact electromagnet composed of four I-shaped electromagnets. We report constructional features, control techniques, and three-dimensional motion of the floating object.

Characteristics of high efficiency and low distortion single phase 7 level inverter without using LC filter

Recently, the problem of global warming and environmental deterioration, depletion of fossil fuel are remarkable, and the method of power generation and energy conversion with efficient using the natural energy is proposed. This technology will be quickly commercialized in future and the popularization is widely expected for the reduction of CO2. In this paper, new single phase inverter circuit which efficiently converts DC voltage generated from natural energy into AC voltage is proposed. The voltage output from conventional bridge type inverter circuit was generally controlled by the PWM control. The sum of loss in the switching and loss by the LC filter for the removal of high frequency component occupied the most part of the loss, and there was a limit for the efficiency improvement. Then, by generating the quasi-sine wave without using PWM control, the frequency of the switching was reduced. The improvement on the efficiency was attempted by reduction of the switching loss and LC filter loss. And, the optimization of the switching was attempted on the generation method of quasi-sine wave by the coexistence of stability and low distortion of the voltage. Here, circuit configuration, operation principle, and the optimization of switching phase of proposing circuit is described.