Fundamental Frequency Time Research Articles

Super-twisting sliding mode control for neutral point voltage of three-phase four-wire inverter based on SiC/Si hybrid switch

The three-phase four-wire voltage source inverter (3P4W VSI) is widely used in applications like uninterrupted power supply (UPS) and bidirectional onboard charger. The increasing power density demand requires higher switching frequency and lower switching loss. To fulfill the conflicting objectives, two-fold methodology is proposed in this paper: 1) SiC/Si hybrid switches (HyS) together with recently reported gate trigger are reported for the first time in the 3P4W VSI; 2) the natural point voltage is controlled to track a sinusoidal voltage with the frequency equal to 3 times of fundamental frequency in order to achieve higher DC-bus voltage utilization rate, and further reduce the switching loss. The traditional PI controller is very hard to achieve desired performance due to both the nonlinearity and the variant reference of the natural point voltage control system. Thereby, the super-twisting sliding mode control (ST-SMC) is proposed in this paper to achieve desired tracking performance and fast dynamic response. The effectiveness and superiority of the system are verified by both simulation and experiment comparison with the existing methods using a 5 kW prototype.

Nonlinear hunting stability of high-speed railway vehicle on a curved track under steady aerodynamic load

ABSTRACTThis paper investigates the nonlinear hunting stability of a high-speed vehicle on a curved track under steady aerodynamic load. We first established a nonlinear dynamic model of high-speed vehicle on a curved track while considering the effect of aerodynamic load. Then, we wrote a numerical simulation programme and verified the validity. The following two types of aerodynamic conditions were concerned in this study: considering only the aerodynamic lift and considering the crosswind loads. The influence of aerodynamic load on the creep force, the restoring force and moment generated by gravity, and the equilibrium position of the vehicle on the curved track can all change the hunting stability. We calculated bifurcation diagrams, limit cycle motions, nonlinear critical speeds, and frequency spectrum considering those two types of aerodynamic conditions, then compared with those without considering the aerodynamic effects. The results show that multiple frequencies including double frequency, triple frequency, quadruple frequency, and high frequencies will appear in addition to the fundamental frequency when hunting motion occurs. The higher frequencies which are even times of fundamental frequency are caused by the deviation of equilibrium position from track centre, while the deviation of equilibrium position is generated by curve track or crosswind load. Additionally, a positive aerodynamic lift and a crosswind load in the centrifugal direction will decrease the vehicle’s motion stability, while a negative aerodynamic lift and a crosswind load in the centripetal direction can improve the stability.

Identification of fin whale 20-Hz pulses and other vocalizations from passive monitoring with a coherent hydrophone array

A large variety of sound sources in the ocean, including biological, geophysical and man-made activities can be simultaneously monitored over instantaneous continental-shelf scale regions via the passive ocean acoustic waveguide remote sensing (POAWRS) technique by employing a large-aperture densely-sampled coherent hydrophone array. Millions of acoustic signals received on the POAWRS system per day can make it challenging to identify individual sound sources. An automated classification system is necessary to enable sound sources to be recognized. Here each detected acoustic signal is represented by an amplitude weighted pitch track which describes its fundamental frequency-time and amplitude variation. Multiple features are extracted from the pitch track including mean, minimum and maximum frequencies, bandwidth, signal duration, frequency-time slope and curvature, as well as several amplitude weighted features. A large training data set of fin whale 20-Hz pulses and other vocalizations are gathered after manual inspection and labeling. Next, multiple classifiers including logistic regression and decision tree are built and tested for identifying the fin whale 20-Hz pulses and other vocalizations from the enormous amounts of acoustic signals detected per day. The performance of the classifiers are evaluated and compared

The Design of Wide-Stopband HTS Bandpass Filter

This paper presents the design of a wide-stopband HTS bandpass filter (BPF). The 9-pole wide-stopband BPF has a center frequency 2.21GHz and bandwidth 100 MHz. Based on the step impedance resonator,this filter increase the harmonic frequency to more than 3 times of fundamental frequency. Optimization simulation results shows that insertion loss is less than 0.3 dB in the passband,and stopband suppression is greater than 80 dB within 0~f0-BW and greater than 60 db within the f0 + BW ~ 3 f0. Within the passband, dB (S (2, 1)) < -20. This design not only achieved a good wide stopband and solved the interference problem but also had a simple structure which is easy to implement.