Towards construction of ghost-free higher derivative gravity from bigravity

In this paper, the ghost-freeness of the higher derivative theory proposed by Hassan et al. in [Universe 1 (2015) 2, 92] is investigated. Hassan et al. believed the ghost-freeness of the higher derivative theory based on the analysis in the linear approximation. However, in order to obtain the complete correspondence, we have to analyze the model without any approximations. In this paper, we analyze two scalar model proposed in [Universe 1 (2015) 2, 92] with arbitrary nonderivative interaction terms. In any order with respect to perturbative parameter, we prove that we can eliminate the ghost for the model with any nonderivative interaction terms.Comment: Published in Phys. Rev.

Suppression of common-mode voltage in a PWM rectifier/inverter system

This paper proposes a PWM rectifier/inverter system capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). An active common-noise canceler (ACC) developed for this system is characterized by sophisticated connection of a common-mode transformer which can compensate for common-mode voltages produced by both PWM rectifier and inverter. As a result, the size of the common-mode transformer can be reduced to 1/3, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI</p

Rotor position estimation based on magnetic saliency of an IPM motor-realization of a wide-speed range from zero to the rated speed

This paper describes position estimation based on magnetic saliency of an interior permanent magnet synchronous motor (IPM motor) for the purpose of achieving a wide-speed range. The position estimation, which has been proposed by the authors, is characterized by the real-time algorithm estimating the rotor position at every PWM period. Selection of PWM patterns proposed in this paper expands the speed range capable of estimating the rotor position to a higher-speed range. The PWM patterns are switched over, depending on an amplitude and phase of the average output voltage vector. Experimental results obtained from an IPM motor drive system of 100 W demonstrate that the selection of the PWM patterns makes it possible to estimate the rotor position in a wide-speed range from zero to the rated speed</p

Analysis and reduction of EMI conducted by a PWM inverter-fed AC motor drive system having long power cables

This paper analyzes conducted EMI generated by a PWM inverter-fed induction motor drive system. It is shown experimentally and analytically that resonant phenomena in a high-frequency range beyond a dominant resonant frequency are originated from the behavior of power cables as a distributed-constant circuit. Spectra of common-mode and differential-mode currents are simulated by means of introducing a distributed-constant model of the power cables, which consists of a 20-step ladder circuit. As a result, it is also shown that these resonances can be damped out by a single common-mode transformer (CMT) and three differential-mode filters (DMFs), both of which have been proposed by the authors</p

An approach to real-time position estimation at zero and low speed for a PM motor based on saliency

This paper presents a magnetic saliency based position estimation approach for a PM motor fed by a voltage-source PWM inverter. The proposed real-time estimation algorithm detects the motor current harmonics and calculates the inductance matrix including the rotor position information. The position estimation can be performed every period of pulse-width-modulation or carrier cycle. An experimental system using an interior permanent magnet (IPM) synchronous motor has been constructed. Experimental results verify that the position estimation within 10 degrees in electrical angle is obtained at standstill and such an extremely low-speed as 1 r/min by the proposed approach</p

Modeling and damping of high-frequency leakage currents in PWM inverter-fed AC motor drive systems

This paper presents an equivalent circuit for high-frequency leakage currents in pulsewidth modulation (PWM) inverter-fed AC motors, which forms a series resonant circuit. The analysis based on the equivalent circuit leads to such a conclusion that the connection of a conventional common-mode choke or reactor in series between the AC terminals of a PWM inverter and those of an AC motor is not effective to reduce the rms and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transformer which is different in damping principle from the conventional common-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the rms value of the leakage current to 25%, where the core used in the common-mode transformer is smaller than that of the conventional common-mode choke</p