The direct ac/ac converters have been investigated in the last two decades because they had no dc-link component for large energy storage. In, Japan, 10kVA-40kVA matrix converters were developed in 2005. The direct ac/ac converters are classified into two main categories, namely, the matrix converters and the direct ac/ac converters with dc Link. And various control strategies for them have already been proposed. This paper discusses and summarizes main circuits, control strategies, overvoltage protection, and ride-through capability of the direct ac/ac converters.

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A single-phase PWM current source converter with three legs is proposed in this paper. The converter consists of main bridge circuit and ac chopper circuit, and a leg is commonly used for both circuits that are connected in parallel. The ac chopper with the PWM operation outputs the double-frequency ac voltage in the dc side, which cancels the dc pulsation of the main bridge. The pulsation-free dc voltage of the converter leads to the smooth dc current and the sinusoidal utility current. This allows the dc inductor to be greatly reduced. The experiments prove that the converter has good waveforms in small dc inductance. Moreover, the harmonic components of the currents are derived from the PWM switching pattern and are compared with measured ones. Theoretical results can be utilized for the determination of the circuit parameters in values.

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This paper describes a comparison of PWM patterns for matrix converter. There are two PWM patterns with keeping the command of the output voltage and input current. The output voltage sequence of the pattern A is maximum-minimum-medium-minimum-maximum of each input voltage, and the pattern B is maximum-medium-minimum-medium-maximum of each input voltage in one switching period. The switching loss and the harmonics of the output voltage are analyzed for every PWM patterns. The pattern B has advantages for the low harmonics of the output voltage and reducing switching loss.
Next, an improved method of the virtual AC/DC/AC method is described in this paper. The virtual AC/DC/AC method can generates only pattern A. Thus, the improved method changes the sequence of the output pulse in order to reduce switching loss and harmonics of the output voltage. Moreover, the proposed method is very simple because it does not require a special triangular waveform. The effects of the proposed PWM generation method are confirmed by the experimental results with 22kW induction motor. The converter loss decreases by 30% and the total harmonics distortion of the input and output current are improved by 1-2points to the conventional method.

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In this paper, a novel control method for a matrix converter is proposed. The proposed method is a PAM (Pulse Amplitude Modulation) control method based on a virtual AC/DC/AC conversion method. Output voltage amplitude is controlled by controlling a virtual DC link voltage with a virtual rectifier. Output frequency is controlled by a virtual inverter.
Firstly, the proposed method is explained. Next, the validity of the proposed method is confirmed thorough simulation and experiment using a 750W prototype matrix converter. Moreover, various characteristics of the proposed method and conventional virtual AC/DC/AC method are compared through experiment. As a result of experiment, it has been understood that total harmonic distortion of output current and common-mode voltage can be reduced compared with the case of using a conventional virtual AC/DC/AC conversion method.

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This paper presents a control scheme of matrix converters for reducing the output voltage harmonics. The feature of the proposed control scheme is the reduction of both the output voltage harmonics and the number of the commutations. The control ranges of the output voltage and input power factor are denoted. Using the input power-factor control, the authors propose the input power factor regulation scheme that compensates for the capacitive current through an input LC filter. The effectiveness of the proposed control algorithm of the matrix converters has been verified by experiments.

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A new type of a magnetic rotary encoder for servomotors is proposed. A salient feature of the proposed encoder is its small size, high resolution, and simple construction. An encoder based on the proposed method having a width of 10mm, a height of 10mm, and a depth of 3mm was developed and is reported here. In addition, the developed encoder has a high resolution of 4096ppr and is capable of detecting absolute angular position. The proposed encoder comprises of a disc magnet magnetized in one direction with all the magnetic domains in the material parallel to each other, a stationary body made up of a magnetically soft material, and four Hall effect devices. This paper describes the configuration of the encoder and the proposed detection process of the rotational position. The characteristics of the prototype encoder are also presented. The accuracy of the encoder depends on the distortion of a pseudo-sinusoidal output waveform, and therefore for achieving high accuracy the distortion of the output waveform should be minimal. The magnetic flux distribution and the output waveform of the encoder were simulated using finite element method (FEM). Based on FEM analysis, the optimal shape of the disc magnet and its housing, relative position of the Hall effect devices and the material of the disc magnet were determined to achieve high performance characteristics.

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This paper presents a system starting strategy for a multi channel temperature control system. Generally, each channel of MIMO temperature system is almost independent and the settling times and loci are different. In this case, energy loss, quality deterioration and product decrease are caused due to the different heat conduction of each channel. This paper developed a novel system starting method “FOLLOWER control", which can be automatic stating to solve the above product problems. Experiments showed that the proposed control system strategy could be successfully and also be easily applied in practice.

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Magnetic energy recovery switch (MERS) has a function of automatic power factor correction of series connected load. The MERS is applied for a single-phase induction motor to improve the power factor. Two control methods of the MERS for power factor correction are described in this paper. Experiments were carried out and confirmed that the input power factor of a single-phase induction motor is improved.

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This paper proposes two new “disturbance-observers in the D-module" for sensorless drive of synchronous motors including permanent-magnet synchronous motors and synchronous reluctance motors. The disturbance filter for the observers can estimate speed-varying rotor-phase (in other words, rotor-position) with zero phase-lag. It is constructed by means of “the filter in the D-module", which has the following desired characteristics for variable sensorless drive: 1) it makes distinction between positive and negative frequencies of two-phase signals; 2) it can allow to process the signals based on frequency polarities; 3) it can also change dynamically its center frequency of band-pass filtering according to rotor speed estimates; 4) its passband and transition can be designed independently; and 5) it can be easily realized. The new disturbance-observers also have a generality such that they contain the recently proposed disturbance-observer as a special case.

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This paper proposes a new friction free bilateral system based on twin drive control system considering it's resonant frequency. The twin drive system consists of two motors that are coupled by the differential gear. The output torque becomes a differential torque of both motors. The nonlinear friction torque of the twin drive system is easily compensated. However, this system has the resonant frequencies and the anti-resonant frequencies which are caused by the torsional vibration. This paper proposes a new three-inertial-model of twin drive system, and identifies the resonant frequencies and it's friction torque. The proposed controller can suppress the torsional vibration without high order control design. Therefore, the operationality of bilateral teleoperation is improved by the proposed system.

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This paper describes a dc micro-grid system interconnecting distributed power generators. The system consists of five generation and control units; a solar-cell generation unit, a wind-turbine generation unit, a battery energy-storage unit, a flywheel power-leveling unit, and an ac grid-interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the dc grid voltage. This method brings high reliability, high-flexibility and maintenance-free operation to the system. The method pays attention to dc output voltage performance of each unit. Each of the power control unit and the energy-storage unit is controlled to act as a voltage source with imaginery impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power-leveling unit is controlled to act as a current source having the function of frequency selectivity like a high-pass filter. A 10-kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the dc-grid system.

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Recently, many robots have been utilized in unknown environment, for example, slave robots of teleoperation systems, walking robots and so on. They are called environment-adaptive robots. It is very important for the environment-adaptive robots to contact stably and to recognize unknown environment. In this paper, a compliance controller of attitude of a planar end-effector is proposed to achieve stable contact with unknown environment. The robot utilized in this research has parallel mechanism as a whole, since the planar end-effector is supported by three arms. With the assumption that only face-to-point contact exists between the end-effector and unknown environment, an estimation method of the contact point without sensors is also proposed. Moreover, excessive stress is not exerted on the robots and the environment by means of the controller we propose, when the contact point is estimated. Our new approach of contact motion can be widely applied to the robots using parallel mechanism. The validity of the proposed method is shown by the numerical and experimental results.

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Eddy current flaw testing that uses changes in the impedance of the test coil as the electromagnetic field interacts with the test material is a non-destructive testing method. It can be used to inspect test material at high speed without bringing the test coil into contact with the test material. Therefore, it is widely used for product inspection. In the inspection of heat exchanger tubing in power plants and chemical plants, eddy current flaw testing is performed by using an inner probe, because of the structural restrictions of such plants. However, high levels of wobble noise and support plate noise occur in the conventional method using a rotating pancake coil. The authors therefore propose new minimal-noise eddy current inner probes. Two new types of probes have been developed: one for detecting axial flaws, and the other for detecting circumference flaws. These probes can detect flaws with a low level of noise. The phase of the flaw signal by the new probes changes according to the flaw depth. As a result, the signal phase by the new probes can be used for evaluating the depth of surface flaws.

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This paper describes a method to analyze higher harmonic currents resulting from higher space harmonics, depending on the winding pattern of a doubly-fed generator. A 1.5-MW generator was used for the analysis, and the results are compared using finite element magnetic field analysis and measurements.
The results revealed that the proposed analysis, which focuses on the winding pattern and takes into account higher space harmonics, allows us to calculate higher harmonic currents at high precision, understand the mechanism of changing higher harmonic currents due to the slip or the load of the generator and considerably reduce higher harmonic currents at the armature by restricting higher harmonic currents at the magnetic field. In addition, the sensitivity analysis of design parameters clarified the relationship between current distortion and basic characteristics on electric designs.

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Recently, the discontinuous armature PM-LSM is proposed as a driving source in the transportation systems. We have proposed and examined constant load angle control without position feedback, to decrease the velocity ripple which occurs at the re-accelerator with the aim of achieving smooth drive of the discontinuous armature PM-LSM. We continuously aimed at the improvement of the positioning accuracy, and examined the velocity ripple occurred at the deceleration. This paper presents the examination of constant load angle control without position feedback with the aim to suppress the velocity ripple, which occurs in the decelerator.

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This paper presents the performance analysis method for the DC-DC converter with the MHz band transformer. In this method 3D electromagnetic field analysis employing finite element method (FEM), in which the displacement current is taken into consideration, is coupled with the circuit analysis. The performances of the transformer, such as input/output power and efficiency, are computed, and the validity of this method is confirmed through comparison of the computed and measured results. Furthermore the performances of a DC-DC converter with the transformer are calculated using the equivalent circuit of the transformer obtained from the results of FEM analysis. As the results, it is found that the calculated and measured input/output performances are in good agreement.

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