Analysis and mitigation of dead time harmonics in the single-phase full-bridge PWM converters with repetitive controllers

In order to prevent the power switching devices (e.g., the Insulated-Gate-Bipolar-Transistor, IGBT) from shoot through in voltage source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in Pulse-Width Modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as "dead time harmonics" hereafter) have to be compensated in order to achieve a satisfactory current quality as required by standards. In this paper, the emission mechanism of dead time harmonics in single-phase PWM inverters is thus presented considering the modulation schemes in details. More importantly, a repetitive controller has been adopted to eliminate the dead time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional resonant-based fundamental current controller so as to mitigate the dead time harmonics and also maintain the control of the fundamental frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead time harmonics and other low-order distortions, and also it is a simple method without hardware modifications

A theory of dark energy that matches dark matter

In this paper, a theory of dark energy is proposed that matches dark matter. The relativistic quantum mechanics equations reveal that free particles can have negative energies. We think that the negative energy is the dark energy which behaviors as dark photons with negative energies. In this work, the photon number states are extended to the cases where the photon number can be negative integers, called negative integer photon states, the physical meaning of which are that the photons in such a state are of negative energy, i.e., dark photons. The dark photons constitute dark radiation, also called negative radiation. The formulism of the statistical mechanics and thermodynamics of the dark radiation is presented. This version of dark energy is of negative temperature and negative pressure, the latter regarded as responsible for the accelerate expansion of the universe. It is believed that there is a symmetry of energy-dark energy in the universe. In our previous work, the theory of the motion of the matters with negative kinetic energy was presented. In our opinion, the negative kinetic energy matter is dark matter. In the present work, we demonstrate that the dark substances absorb and release dark energy. In this view, the dark matter and dark energy match. Therefore, there is a symmetry of matter-energy match and dark matter-dark energy match in the universe. We present the reasons why the negative kinetic energy systems and negative radiation are dark to us

Structure-Soil-Structure Interaction between Underground Structure and Surface Structure

A numerical study is made on the dynamic through-soil interaction between underground station and nearby pile supported surface structure on viscous-elastic soil layer, under vertically incident S wave. This paper focuses on the dynamic interaction and the interactive influence on seismic response of adjacent surface structure and underground structure. To this end, ANSYS has been further developed for calculation in frequency domain, in which hysteretic damping can be considered, so that structure-soil-structure interaction (SSSI) can be investigated via direct methodology. Discussion is made on the influence of arrangement of structures, distances between structures, shaking direction of seismic wave, shear wave velocity and damping of soil, scale and burial depth of underground structure, storey number, stiffness, style and pile length of surface structure on SSSI, in terms of horizontal acceleration of surface structure and horizontal relative displacement of underground structure. Maximum acceleration and displacement is also presented for 12 seismic inputs. Arrangement and shaking direction are two of the most important factors. The response can be either amplified or attenuated according to the distance, related to dynamic properties of the overall system. The underground structure, surrounded by building with the fundamental frequency approximate to that of free field, is heavily affected