This paper presents different designs for the realization of a variable transmission magnetic gear (VTMG). The proposed designs utilize permanent magnets and copper coils. The basic concept is varying the gear ratio by pole changing. The FEM simulation results show that a VTMG can be realized and that the symmetry of the designs is vital for the correct operation of the VTMG. The VTMG is useful in variable speed/torque applications such as wind power generation, electric traction, power tools, and so on.
This paper analytically demonstrates the optimal layout of permanent magnets for generating a sinusoidal flux density distribution in the air gap of the interior permanent-magnet synchronous machines with multiple flux barriers. In addition, practical design methods for realizing the optimal layout are proposed, and the designs are verified by conducting finite element analysis.
This paper presents a new control strategy of variable speed permanent magnet wind generator for stability augmentation of wind farm including fixed speed wind turbine with Induction Generator (IG). A new control scheme is developed for two levels back-to-back converters of Permanent Magnet Synchronous Generator (PMSG), by which both active and reactive powers delivered to the grid can be controlled easily. To avoid the converter damage, the DC link protection controller is also proposed in order to protect the dc link circuit during fault condition. To evaluate the control capability of the proposed controllers, simulations are performed on two model systems composed of wind farms connected to an infinite bus. From transient and steady state analyses by using PSCAD/EMTDC, it is concluded that the proposed control scheme is very effective to improve the stability of wind farm for severe network disturbance and randomly fluctuating wind speed.
In this study, we investigate the loss reduction effect by stator-teeth slits in turbine generators on the basis of electromagnetic field analysis and basic experiments. First, the loss reduction effect in the generator is estimated by the 3-D finite element method and the theoretical solution of eddy current loss. Next, an experiment using a simple model that simulates the stator-core ends of the turbine generator is carried out. It is clarified that the loss reduction effect by the slits depends on the frequency, flux density, and permeability of the stator teeth because the loss reduction effect weakens with the skin effect.
The DC tests can predict the operational impedance of rotational machines by a simple standstill test. This paper presents a new DC test using a voltage-source PWM inverter, which does not require a specially assembled DC-power-source unit that is required to perform conventional DC tests. In this paper, three DC tests (DC decay, step response method, and pulse response methods) using the inverter as a power source are discussed. These tests are performed on an air-core reactor and 5.5kW semi-closed squirrel-cage induction machine to verify their validity. In addition, the authors propose an improved DC decay test that can consider the magnetic saturation of the main flux; this test is referred to as the two-step-voltage DC decay test. This test is also carried out on the tested induction machine. Using the test results, the authors demonstrate the calculation of not only no-load saturation performance by considering the magnetic saturation flux but also the starting performance. By comparing between these calculation results and actual measurement data, the authors validate the proposed two-step-voltage DC decay test.
A straightforward solution for minimizing the cost of major materials used in motors, such as permanent magnets and silicon steel sheets, is to reduce the motor size as far as possible. However, there is a trade-off between the motor size and temperature rise in the motor that should be taken into account while reducing the motor size. For achieving this, we have been developing an optimal design method based on a combination of a thermo-magnetic field coupling analysis and a direct search algorithm. This paper reports the details of this design method. An outer-rotor, multipole permanent-magnet synchronous motor is the test motor. The results of the torque-density-maximization problem involving constraints on the terminal voltage, coil-temperature rise, and demagnetization of the magnet are shown. The usefulness of our method is also demonstrated.
The high-flux permanent magnet and flux-barrier structure of permanent magnet synchronous machine (PMSM) has strong magnetic saturation and harmonics components. When control algorithms for such machines are examined by performing control simulation, the use of the conventional motor model based on the voltage equation can cause problems. To avoid these problems, we introduce the technique of coupled analysis of the magnetic-field-control/circuit simulation. Further, iron losses generated in PMSM can be estimated by the coupled analysis system. The iron losses at various driving conditions are calculated by the coupled analysis system and are compared with measured losses. The comparison results show that the coupled analysis system is suitable for accurately estimating the iron losses of PMSM.
The arrangement of permanent magnets in double-layer interior permanent-magnet motors is optimized for variable-speed applications. First, the arrangement of magnets is decided by automatic optimization. Next, the superiority of the optimized motor is discussed by the d- and q-axis equivalent circuits that consider the magnetic saturation of the rotor core. Finally, experimental verification is carried out by using a prototype motor. It is confirmed that the maximum torque of the optimized motor under both low speed and high speed conditions are higher than those of conventional motors because of relatively large q-axis inductance and small d-axis inductance.
We propose a novel inverter that can be operated either as a Current Source Inverter (CSI) or as a Voltage Source Inverter (VSI) by changing only the control signals. It is proper to apply it to the interconnecting system with renewal energy, such as photovoltaic cells or wind generation systems, to a grid. This inverter is usually operated as the CSI connected to the grid. Even if the energy source has a lower voltage than the grid, the energy can be supplied to the grid through the proposed inverter. The power factor can be briefly maintained at almost unity. When power supply from the grid is interrupted, the proposed circuit should be operated as the VSI in the stand-alone operation mode. In this way, the circuit can maintain a constant output voltage to the loads. In this paper, the proposed circuit configuration and the control schemes for both the CSI and the VSI are described. Further, the circuit characteristics for both are discussed experimentally.
This paper proposes a new output voltage control for an inverter system, which has time-delay and nonlinear load. In the next generation X-ray computed tomography of a medical device (X-ray CT) that uses the contactless power transfer method, the feedback signal often contains time-delay due to AD/DA conversion and error detection/correction time. When the PID controller of the inverter system is received the adverse effects of the time-delay, the controller often has an overshoot and a oscillated response. In order to overcome this problem, this paper proposes a compensation method based on the Smith predictor for an inverter system having a time-delay and the nonlinear loads which are the diode bridge rectifier and X-ray tube. The proposed compensation method consists of the hybrid Smith predictor system based on an equivalent analog circuit and DSP. The experimental results confirm the validity of the proposed system.
This paper describes a power-transfer principle and power-loss analysis of phase-shift-controlled switched-capacitor-based resonant converters (PSC-SCRC). Power loss in the PSC-SCRC is theoretically derived and compared with that in a conventional switched-capacitor converter (SCC) and a frequency-controlled SCRC (FC-SCRC). As a result, it is clarified that a PSC-SCRC has no theoretical power loss unlike an SCC and an FC-SCRC. The experimental results agree well with the theoretical ones.
In an AC motor, the quick detection of an initially small fault is important for preventing any consequent large fault. Various detection approaches have been proposed in previous papers, for example, by the Park vector (PV), AI techniques, wavelet analysis, and negative-sequence analysis. This paper proposes a method for diagnosing the stator-winding faults of an induction motor by the direct detection of its negative-sequence current. Before starting the diagnosis, the asymmetry admittances for the considered fault cases are obtained by analysis or simulation. The amplitude and phase of the positive-sequence voltage, Vp, and of the positive-sequence current, Ip, are extracted from the voltage PV and current PV, respectively. The amplitude and phase of the negative-sequence, In, are extracted from the residue. The asymmetry admittance, Ya, is calculated from In and Vp. When the positive-sequence admittance is known, Ya can also be calculated from Yp, Ip, and In. These steps are repeated for each sample time and the motor condition is diagnosed according to the variations in the Ya values. The simulation and experimental results are also shown and the proposed method is investigated and validated.
High-frequency voltage oscillation is occasionally observed in bipolar power semiconductors during a turn-OFF operation. The mechanism of generation of the turn-OFF oscillation is explained by the plasma extraction transit-time (PETT) oscillation theory. According to this theory, a packet of holes propagate through the drift region with constant velocity and induce current flow in the external circuit. The waveform of the corresponding current density is trapezoidal. Negative resistance is generated in the circuit by the current density and RF voltage applied to the semiconductors. The negative resistance is the origin of generation of the turn-OFF oscillation. The author investigates the generation of the IGBT turn-OFF oscillation by performing a 2D device simulation. The simulation results show generation of the negative resistance is different from that described in the PETT oscillation theory. The velocity of the packet of holes depends on the electric field in the drift region and is not constant. The simulated current density oscillates with an almost negative phase compared to the RF voltage oscillation. Further, on the basis of the simulation results, the author will propose the practical method to estimate the oscillation frequency in this paper.
This paper describes nongrounded common-mode equivalent circuit for a motor driven by a voltage-source PWM inverter. When the capacitance of the rotor was small, the phenomenon that polarity of the common mode voltage and shaft voltage reversed was observed. In order to model this phenomenon, the bridge type equivalent circuit is proposed. It is verified with the calculation and experiment that shaft voltage values and polarity are accurately calculated with the proposed equivalent circuit.
The optimal design problem for a stator and a mover of a surface motor, which is a multi-objective optimization problem, is transformed into a single objective constrained optimization problem in this letter. The optimal design problem is solved by the integrated optimization system consisting of Particle Swarm Optimization, Radial Basis Function Network, and Electromagnetic Field simulator. While the obtained shapes of a surface motor are evaluated, the advantage of the proposed approach is also verified.