Robust control strategies of an extruder temperature control system are considered for a multi loop control. For an extrusion process, if production issues such as system changes, set-point changes and the input limits of the band-heater and fan are considered, the quality of product depends much on the dynamics of the plant within the operating range. The system must also satisfy the mechanical conditions. A computer simulation and experiment have shown that multivariable dynamics consideration can be successfully applied to the extruder despite uncertainty in the time delays, time constant, and gains under the extrusion issue.

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Sudden three-phase short circuit current of a turbine generator was calculated by a three-dimensional magnetic field analysis. That analysis takes into account the rotation, magnetic saturation, and eddy current at a rotor part.
To compare test results and calculated results, we proposed a method for short-circuit phase estimation at sudden three-phase short-circuit test by line voltage waveform of the test results. The calculated results of short-circuit current waveform are good agreement with the test results.

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This paper presents the newly-proposed hybrid resonant commutation bridge leg link (HRCB) snubber circuit which can achieve zero voltage and zero current soft-switching commutation for single-phase and three-phase voltage source-type inverter, along with its unique features and operation principle. The circuit parameter design approach for the HRCB snubber circuit and the determination estimating scheme of the gate pulse timing processing which is more suitable and acceptable for single-phase and space voltage vector modulated three-phase voltage source inverter using the HRCB snubber circuit are described in this paper. In particular the three-phase voltage source soft-switching inverter associated with the proposed HRCB circuits are evaluated and discussed from simulation and experimental viewpoint. The practical effectiveness of the HRCB snubber-assisted three-phase voltage source soft-switching inverter using IGBT power modules which is based on the instantaneous space voltage vector modulation is clarified on the output voltage waveform, actual efficiency and electromagnetic noises in comparison with three-phase voltage source-type conventional hard-switching inverter.

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This paper proposes a new dynamic mathematical model and new block diagrams for a newly emerging class of salient-pole hybrid-field synchronous motors (HFSM) that have rotor field by both permanent magnet and winding. The proposed new mathematical model has the following completeness and generality. 1) It consists of three consistent basic equations such as circuit, torque and energy-transmission equations. 2) It deals with pole saliency and contains non-saliency as a special case. 3) It is a dynamic model and contains static one as a special case. 4) It is established in the general reference frame including stator and rotor reference frames as special cases. The proposed new block diagrams using vector signals for salient-pole HFSM is established based on the new model. It has the following attractive features. 1) It succeeds in realizing clear configurations with physically meaningful vector signals, which are helpful for understanding motor electromagnetic mechanism and useful for designing controllers for the salient-pole HFSM. 2) Vector signals utilized as transfer signals between blocks are defined in the general reference frame. Consequently, the vector-signal block diagrams in the frame can be directly and easily reduced to the ones in such a specific frame as stator and rotor frames. 3) It is compact. Two typical and compact but sufficiently general vector-signal block diagrams are newly presented.

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The mutual leakage reactance between d-axis damper and field windings is ignored in conventional d-axis equivalent circuits. It has been pointed out, however, that the calculated value of the field current differs considerably from the measured value if this reactance is not taken into account. This is due to the difficulty of determining the physically-correct damper winding impedance value. A method to determine the equivalent circuit constants using the mutual leakage reactance has been reported previously, where the d-axis damper winding time constant is measured from the upper and lower envelopes of field current at sudden three-phase short-circuit. Yet there are machines for which the upper and lower envelopes of field current are not readily established, in which case this method is unsatisfactory. The authors describe a method to accurately identify the equivalent circuit constants taking into account the mutual leakage reactance, using a standstill test with a small-capacity DC power supply (DC decay testing method). The field current at sudden short-circuit can be simulated accurately using these equivalent circuit constants. The validity of the proposed method is demonstrated by implementation results on two salient-pole synchronous machines with the same specifications (one with damper winding, the other without). Furthermore, the dependent relation between the armature leakage reactance and mutual leakage reactance, as well as its influence on the calculation of field transient currents, are made clear.

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This paper proposes a novel fractional order PID^k controller for torsional system’s backlash vibration suppression control, in which the order k of D controller can not only be integer but also be any real number. Various methods have been proposed for two-inertia system’s speed control, but the control systems designed by these methods may not be able to suppress the vibration caused by gear backlash. In order to improve control system’s robustness against the backlash, several methods have been proposed. However their design processes are very complicated. Clear and straightforward design concept is required in practical applications. As a novel approach, in this paper the D controller’s order is expanded to include any real number. Robust PID^k controller against backlash is designed by adjusting the order k directly. An approximation method based on Short Memory Principle is also introduced to realize the discrete D^k controller. Design process and experimental results demonstrate straightforward robust control design through the novel FOC approach, the PID^k control system’s better robustness against backlash non-linearity and good approximation of the realization method.

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Aged people and disabled people who have difficulty in walking are increasing. As one of mobility support, significance of power assisted wheelchair which assists driving force using electric motors and spreads their living areas has been enhanced. However, the increased driving force often causes a dangerous overturn of wheelchair. In this paper, control method to prevent power assisted wheelchair from overturning is proposed.
It is found the front wheels rising is caused by magnitude and rapid increase of assisted torque. Therefore, feedforward control method to limit the assisted torque by tuning its magnitude or time constant is proposed. In order to emphasize safety and feeling of security, these methods make the front wheels no rise. The effectiveness of the proposed method is verified by the practical experiments and field test based performance evaluation using many trial subjects.

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The reason why this paper deals with GTO behavior mainly is that the reverse bias safety operating area (SOA) of GTO is narrower than the ones of GCT and IEGT. On the development of large-capacity GTO converter, it is important to evaluate the performance of snubber circuit. This paper is concerned with the spike voltage V_DSP during turning-off a GTO, and deals with the design and evaluation of stray inductance for snubber circuit, and shows investigation for transient forward voltage of snubber diode. Especially, the method is described that estimates stray inductance from aspect of snubber circuit structure by electromagnetic field analysis before making prototype. The experimental results of spike voltage V_DSP are in approximate agreement with the estimated results. Therefore, investigations on this paper are proper and applicable. The same manner of evaluation is also appropriate to IEGT application, and the development of IEGT converter is easier than in GTO converter because of the gate resistor adjustment for di/dt of main current and a wider SOA.

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By taking account the iron loss, we have proposed a vector control method to improve the torque accuracy and to realize the efficiency maximizing control. In this paper, the proposed control method is demonstrated by the experimental results compared with the theoretical results.

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The cage rotor of an induction motor can be diagnosed by the spectra of the stator current, the air-gap flux, and the leakage flux. However, it is not clear how the connection of stator winding, that is, series or parallel, affects on these spectra. In this letter, we discuss the measured results on spectra of stator current and leakage flux in the both case of parallel and series stator winding.

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