This paper describes a PWM pulse pattern optimization method using the carrier frequency modulation (CFM) technique. This new technique is aiming at not only reducing the magnetic acoustic noises of the driven motors but also improving the performance of sinusoidal inverters. The PWM pulse patterns are basically controlled so that the time-integral function of voltage vectors in the space vector notation may draw a circular locus. In addition to this, the carrier frequency, practically the sampling frequency for inverter control, of PWM is also regulated so that a performance index (PI), which represents the degrees of achieving objectives, may be minimized. Here two PIs, one is for minimizing the distortion of output currents and the other is for minimizing the torque ripples of driven motors, are discussed respecively. Finally, CFM is implemented using a single-chip microprocessor, and the experimental results demonstrate the validity of the proposed mehtod.
High performance power conversion requires high switching frequency power converters. Resonant DC link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant oscillation and occurrence of high peaks in the resonant capacitor voltage are serious problems. In this paper, we investigate a control method for resonant DC link inverters which can overcome these problems. First of all, we summarize the basic control principle of an ideal resonant DC link inverter. Then we present an analyzing method for the practical resonant DC link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we propose an optimum control strategy which can sustain the oscillation and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described. Some experimental results are included to confirm the validity of the analytical results and the effectiveness of the proposed control method.
As to the vector control method, the inverter slip angular frequency ω2 of an induction motor is controlled for the purpose of the output torque being proportional to the torque current. However, the correct vector control requires the precise estimating parameters. If the parameters have a error, there are many problems, i.e., the system stability is reduced or magnetic saturation of iron core occurs. Especially in all of these parameters, the secondary resistance R2 varies extremely with the rotor temperature, and the variation of this parameter has a great influence upon the system characteristics. Some countermeasure has been proposed for estimating the parameter R2 in driving induction motor, but these have many problems, for example, the system construction is complicated, needs other parameters and more correct sensors of current and voltage. This paper proposes the auto-tuning circuit to adjust phase difference between γ-δ and d-q axis due to estimating error of R2 to zero. In the circuit, only a PI compensator is needed in the loop to decide ω1. This paper describes the characteristics of the vector controlled system with the estimating error of R2 by a simulation, and emphasize the requirement of compensation of secondary resistance. The simulation and experimental results of the tested machine show that this method can adjust this difference to zero by using simple compensating circuit. This method is also available for improving characteristics of system not only in the field constant range but also field weakening range.
Since a synchronous motor is held heavy nonlinearity, the transient stability analysis of it is generally laborious. Conventionally, this analysis has been used numerical solution or equal-area method, whereas this paper is proposed a new transient stability criterion by applying Lyapunov method which is powerful for nonlinear systems to estimate these stability. Lyapunov method is easy to evaluate the system stability without solving the nonlinear differential equations of the motor, and is possible to evaluate the system stability based on a physical concept by a generalized energy function. The disturbances considered in this paper are abrupt changing of load and dropping source voltage. The influence of machine parameters for the transient stability is studied by analyzing the stability boundaries and the stable limits subjected to these disturbances. The results are obtained that the influence of relative damping coefficient for the transient stability is effectively large and the authors evaluation method of stability using Lyapunov method is more better profitable for stability criterion than the equal-area method. Moreover, good stable limits at changing of load is obtained by this method in comparison with experiments, and validity of authors method results is verified.
The urban transit with single-sided linear induction motor (SLIM) propulsion and wheel on rail support and guidance has been developped in Canada and Japan. The maximum speed of the urban transit is about 70km/h and the trains repeat the powering, coasting and braking operation in the relatively short inter station distances. On the design of such SLIMs operated under condition that the load changes every moment, we must take into account the energy consumption as well as the motor weight, input KVA, the performance characteristics. In this paper, we investigate such SLIM design theoretically. The performance characteristics are estimated using space harmonic analysis. The energy consumption is reduced by decreasing the mechanical clearance. Then, the flux density should be low value from 0.5 T to 0.6 T. The motor length of from 2m to 2.5m and the pole pitch of about 300mm are advisable.
A method is given for determining equivalent circuit parameters of a squirrel-cage induction motor, by which calculated values of the current, input power and the slip agree with measured ones. Based on the method, equivalent circuit parameters are obtained on 6 test machines and compared with values determined from other methods. Effects of secondary frequency, shape of the rotor slot and the magnetic saturation on secondary parameters are discussed.
This paper deals with finite element calculation of electromagnetic force based on permeance concept. The value of permeance coefficient of actuaters and motors using permanent magnet is determined mainly by effective magnetic flux density and magnetomotive force. Electromagnetic force calculation is made based on permeance, a popular concept for magnetic circuit analysis. The paper includes: (1) The torque and the electromagnetic force is expressed in farms of the change of permeance. (2) Magnetic flux density distribution for determing the permeance and its coefficient is numerically calculated by finite element method. The value of the torque and the electromagnetic force thus conducted agree well with the measured values and the calculated based on other methods. (3) The permeance coefficient in the operating point, which represents a performance capability of actuaters, is estimated.
The fault diagnosis of an induction motor by analyzing the abnormal frequency components of the current or power waveform has been already proposed by the authors, and its characteristics with faulty cage rotor such as broken bars have been presented also. As the results, it becomes clear that the amplitude of abnormal component of the stator currents and so on, increases with the number of broken bars, while it decreases with the number of broken end-rings, in the case of consecutive fault positions within 90 degree in electrical angle. So, in this paper the more direct diagnosis methods by detecting the air-gap flux are investigated to avoid the above inconsistency. In this paper we discuss in detail the relation between the various fault conditions and the MMF distributions of a three-phase induction motor with faulty cage rotor such as broken bars and endrings, and analyze quantitatively the search coil output and its harmonic component to detect those faults adequately from the air-gap flux density. The measured results obtained by the artificially faulted machine demonstrate the availability of those analytical results and this diagnosis method.