This paper presents a zero-voltage (PWM) inverter with active voltage clamping technique using only a single auxiliary switch. The structure is particularly simple and robust. It is very attractive for single-phase high power applications. Conduction and switching losses are reduced due to implementation of the simple active snubber circuit, that provides ZVS conditions for all switches, including the auxiliary one. Its main features are: Simple control strategy, robustness, lower weight and volume, lower harmonic distortion of the output current, and high efficiency. The principle of operation for steady-state conditions, mathematical analysis and experimental results from a laboratory prototype are presented.
We constructed open MRI superconducting magnets with an iron yoke that generates a 0.7T highly uniform magnetic field. A program that compensates for the error field of those magnets was developed that uses linear programming to achieve an optimal arrangement of a large number of small iron shims. Since additional homogeneity compensation near the target value becomes difficult, we also used nonlinear programming. We must evaluate all shim magnetizations precisely by making a 3D finite element shim model. Since, it is impossible to make such shims in a large magnet model, we describe a fast calculation method of shim magnetizations without that model. Homogeneity of 0.35ppm (Vrms) at 35cm Diameter Spherical Volume (DSV), which is the top value of an open MRI magnet, is obtained by applying these methods. The number of correction times were reduced by half of initial manufactured magnets.
Recently bicycles are widely used as a convenient transportation tool. A mechanical design of bicycle has improved well and it has an ability to self-stabilize, but it is essentially unstable and a driving skill of bicycle users is required for a realization of its stable motion. From a view point of wide use for the future aging society, the assist control of the bicycle that makes a bicycle motion more stable independently of the environment condition is expected. As well known, the power assistance of a bicycle has been used, but a practical assistance of bicycle motion, in particular, the stable control of bicycle configuration has not been developed. In this paper, the two handle control algorithms for autonomous stable running are proposed with the aim of developing a stable human assistance bicycle. The proposed algorithms are verified by numerical and experimental results.
A 3-D boundary integral equation is applied to a model of a short primary linear reluctance motor. The model is a double-sided construction where the primary member is surrounded by a set of secondary iron plates on both sides. Six kinds of different secondary geometries are calculated and their characteristics are discussed. For the confirmation of calculation results, a test machine is manufactured. Test results are compared with calculated ones. Furthermore, the static thrusts of a single-sided machine and a coreless PMLSM are measured and compared with that of the double-sided machine
Two frequencies are often used in induction heating, that is, a lower frequency fL for preheating and a higher frequency fH for main heating in order to decrease thermal stress. In this case, each of fL and fH is generated by the different inverter, and fH approximately equals several times to ten times of fL. Then we propose a new quasi-resonant inverter that two-way short-circuit switches across the resonant capacitor. The proposed inverter has features that its operating frequency is adjustable and the frequency range is so wide that the higher frequency can be ten times as much as the lower frequency. It is considered that the output current has only a fundamental wave by properly manipulating the shorting time of the resonant capacitor even though the output current is not a sinusoidal wave. More over the output power of the inverter can be controlled, which is obtained by subtracting the loss power from the input DC power.
In traditional coordinated traffic signal control on an urban road network, the following two problems have been known. First, the conventional method involves a time lag between traffic measurement and signal control. Second, an abrupt switching of control parameters throws the traffic flow into disorder. This paper proposes a new approach to avoid these problems. We increase the frequency of switching. The control parameters are switched as frequent as every two cycles. At the time of switching, minor variations of the on-going plan are generated. For each variation of plan, traffic delay at each intersection is predicted based on measured traffic data at up-stream detectors. Then the plan minimizing the delay is chosen to be the control parameters in the next cycle. In order to evaluate the validity of this approach, experiments were carried out using a traffic simulator. The experiments indicate that the proposed method reduces the queue length significantly, compared with the conventional method.
Damage due to fire can be minimized by discovering fires early. Fires produce smoke as well as flames, so detecting smoke from data like surveillance camera images data can make it easier to discover fires early. However, in attempting to discover fires at locations which are hard to see with the human eye, as in cases like forest fires, we are faced with a problem in that smoke does not have a determinate form in camera images. It has a pattern similar to features like clouds, sky and forests, and thus is difficult to detect with processing approaches like simple background subtraction or pattern matching. So this paper proposes a technique for extracting smoke regions from an image using fractal encoding concepts. We were led to this idea by noticing that smoke shapes have the property of self-similarity, and here we attempt to extract smoke regions by discovering the distinguishing features of smoke regions in the code produced by fractal encoding of an image.
In this paper, the modified optimal design method is suggested, in which the simple dynamic analysis method is coupled with Genetic Algorithm (GA). The motion analysis of the Linear Oscillatory Actuator (LOA) is coupled with the magnetic field analysis using the finite element method (FEM). This method is applied to the unique LOA with the active vibration absorber to obtain the maximum amplitude and the least vibration. The computed results are compared with the results of both usual analysis method and the measurement. The usefulness of this method is confirmed in analysis accuracy.
Transformers are used in power converter systems in order to isolate input circuit and output circuit of the system and to obtain a suitable output voltage to loads. Ideal AC power sources do not include DC component, however some time output voltage of the power converters include DC component in its output voltage because of difference of switching behaviour of power devices which are used in the power converters. Also offset error of voltage transducers, current transducers, analog circuits and A/D converters produce the DC component in the output voltage. The component leads the magnetic field saturation of the transformers, which causes loss and acoustic noise from them. Then it is required to prevent the DC component. However, it is difficult to achieve to select switching devices, which have some switching behaviour. It is achievable to prevent the DC component if the component can be measured and compensate it. However it is difficult to measure the DC component because it is very small compare to the output voltage and offset of the measuring system cannot be ignored. In this paper, a novel magnetic field saturation of the transformers detecting method, which is based on a correlation function to exciting current of it is proposed and effectiveness of the DC component compensation in accordance with the value measured by the novel method is shown.
A power factor correction scheme using a cycle-control is proposed without switching devices, where output voltage can be much reduced. A certain application requires such control like significantly lowering the output voltage. In the proposed method, the output capacitor is divided into two parts, in which the input current waveform becomes balanced one. Hence, the harmonic characteristics can be much improved, where the lower order harmonics, such as the fifth and seventh orders are sufficiently reduced. The results are confirmed by the theoretical and experimental implementations.
This paper proposes a new sensorless vector control method for permanent-magnet synchronous motors (PMSM), which uses a new full-order (4th order) state-observer in stationary reference frame combined with the “integral-feedback type speed estimation method". The proposed method can be applied to both of salient and nonsalient PMSM.