Total harmonic distortion (THD) is one of the key technical indexes of inverter output voltage. Optimization o f switching points and filter parameters could ensure the switching-point-preset sinusoidal pulse width mo...Total harmonic distortion (THD) is one of the key technical indexes of inverter output voltage. Optimization o f switching points and filter parameters could ensure the switching-point-preset sinusoidal pulse width modulation (SPWM) inverters with low harmonyic content in theory.The THD value would be increased by switching time delay of power devices and control circuit. A new control coecuit with delay time compensation is presented in this paper. With this control scheme, the output of the inverter could be basically identified with the theory given.Test results of experimental circuit verify that the control circuit presented in this paper is feasible. The THD of the inverter output voltage could be reduced to a certain extent by this method.展开更多
We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low...We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low frequency shortage of environmental oscillators＇ spectral density, the coordinate and momentum correlation functions decay as T^-4 arid T^-6 respectively at zero temperature, where T is the correlation time. The low-temperature behavior of the mean energy does not violate the third law of thermodynamics, but differs largely from the Ohmic spectrum case.展开更多
The harmonic metric for Schwarzschild black hole with a uniform velocity is presented. In the limit of weak field and low velocity, this metric reduces to the post-Newtonian approximation for one moving point mass. As...The harmonic metric for Schwarzschild black hole with a uniform velocity is presented. In the limit of weak field and low velocity, this metric reduces to the post-Newtonian approximation for one moving point mass. As an application, we derive the dynamics of particle and photon in the weak-field limit for the moving Schwarzschild black hole with an arbitrary velocity. It is found that the relativistic motion of gravitational source can induce an additional centripetal force on the test particle, which may be comparable to or even larger than the conventional Newtonian gravitational force.展开更多
文摘Total harmonic distortion (THD) is one of the key technical indexes of inverter output voltage. Optimization o f switching points and filter parameters could ensure the switching-point-preset sinusoidal pulse width modulation (SPWM) inverters with low harmonyic content in theory.The THD value would be increased by switching time delay of power devices and control circuit. A new control coecuit with delay time compensation is presented in this paper. With this control scheme, the output of the inverter could be basically identified with the theory given.Test results of experimental circuit verify that the control circuit presented in this paper is feasible. The THD of the inverter output voltage could be reduced to a certain extent by this method.
文摘We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low frequency shortage of environmental oscillators＇ spectral density, the coordinate and momentum correlation functions decay as T^-4 arid T^-6 respectively at zero temperature, where T is the correlation time. The low-temperature behavior of the mean energy does not violate the third law of thermodynamics, but differs largely from the Ohmic spectrum case.
基金Supported by the Program for New Century Excellent Talents in University under Grant No.NCET-10-0702the National Basic Research Program of China(973 Program)under Grant No.2013CB328904the Ph.D.Programs Foundation of Ministry of Education of China under Grant No.20110184110016
文摘The harmonic metric for Schwarzschild black hole with a uniform velocity is presented. In the limit of weak field and low velocity, this metric reduces to the post-Newtonian approximation for one moving point mass. As an application, we derive the dynamics of particle and photon in the weak-field limit for the moving Schwarzschild black hole with an arbitrary velocity. It is found that the relativistic motion of gravitational source can induce an additional centripetal force on the test particle, which may be comparable to or even larger than the conventional Newtonian gravitational force.
