Study of Voice Communication System Based on FreeSWITCH

With the rapid development of communication technology, modern communication technology has been widely penetrated into modern national defense, science and technology, people's life and other fields, and has become a means to provide high-quality and seamless information communication between people and machines. With the rapid development of computer technology and the Internet, the traditional program-controlled switching technology has come to an end, and the soft-switch network based on IP technology and packet switching has gradually replaced the program-controlled switching network based on circuit switching and become the mainstream of today's communication network world. The rapid development of VOIP telephony reduces the cost of domestic and international long-distance telephony, benefiting consumers. Digital mobile communication expands channel capacity, improves service quality and promotes the rapid development of this industry. Based on the secondary development of the open source FreeSWITCH software, this paper develops a VOIP voice system based on IP technology to meet different user needs intelligently [1].

The research of configuration for stability control device in smart substation

A unified specification to design and operate the stability control device in smart substation has not been formed yet, which has greatly affected the promotion and application of stability control device in smart substation. Thus, referring to the technical specifications of protection device and combining to the specificity of stability control device, a full and detailed configuration scheme is proposed to meet the requirement, including the device configuration principle, the access configuration of SV and GOOSE for variable primary connection types, the virtual terminal and soft switch. This solution is beneficial to standardize the R&D of stability control device in smart substation, and to facilitate on-site debugging, operation and maintenance.

Automatic Current Balance for Multi-Phase Switching Converters with Ripple Control or Soft Switch

This paper proposes a new multi-phase switching converter with atuotomatic current barance technique. It is well-known that the multi-phase switching converter is suitable to handle large output current with small output voltage ripple for the buck converters which use the clock pulse. This paper investigates a multi-phase controlled method for the ripple-controlled converters and the soft switching converters, that use no clock pulse; for this reason, these converters are difficult to realize multi-phase converter configurations. There are some multi-phase hysteretic controlled converters; they utilize a main clock generator or an external sub-clock pulse, which has the master-slave synchronization method. But it is difficult to respond to a frequency change of the master converter. These multi-phase converters have not considered the imbalance among phase currents caused by variations of inductors and semiconductor switches in the power stage. For the commercialized multi-phase Voltage Regulating Modules (VRMs), the inductors and the semiconductor switches are selected to adjust the balance among the phase currents. However, there is no multi-phase soft switching converter.Then we have developed the multi-phase ripple-controlled converter and the multi-phase soft switching converter with the technique of detecting 180-degree from the variable operating frequency of the main converter. Moreover, in these converters, there appears the current imbalance because of the element variations among inductors and capacitors, if some cares are not taken there. Then we have developed the automatic correction for the current imbalance by modifying the width of the Constant On Time (COT) pulse or modifying the slope of the saw-tooth signal.

A DC-DC Center-Tapped Resonant Dual-Active Bridge with Two Modulation Techniques

Power converters with higher efficiency in a wide load range are important for reducing the overall energy consumption of renewable energy generation systems. A center-tapped LC series resonant dual-active bridge (LC-DAB) converter for DC-DC conversion is proposed in this paper. The proposed converter utilizes a center-tapped bridge to block reverse current and eliminate back flow power to reduce conduction losses. Two modulation methods for the proposed topology (i.e., fixed frequency modulation (FFM), and variable frequency modulation (VFM)) are proposed and analyzed. Both modulation methods can realize soft switch over the entire load range to reduce switching losses. In addition, the proposed modulation techniques guarantee soft switching for all devices and synchronous rectifier is realized by the center-tapped bridge to further reduce the conduction losses. Furthermore, a comprehensive comparison in terms of conduction losses and switching losses has been carried out to highlight the superiority of the proposed converter over the existing LC resonant converters. Finally, simulated and experimental results for a 1.5 kW prototype are presented to validate the theoretical analysis and performance of the proposed converter.

A Converter with Automatic Stage Transition Control for Inductive Power Transfer

An automatic stage transition converter for an inductive power transfer system is presented in this paper. An effective control strategy with two working stages of independent energy injection stage and free resonance stage is employed in the proposed converter. With the automatic stage transition strategy, when the frequency of the resonance network changes, the ending time of the free resonance stage is automatically determined. At the same time, the phase angle of the free resonance stage is automatically set as half a resonant cycle. As the stage transition is not triggered by the switches, the switch motion can be executed in advance of the transition moments. Time margins are offered for every switch in the converter, which make the switching moments of the switches flexible and the control simple. Another feature of this converter is that during the energy injection stage, the energy is injected into the inductor independently. Therefore, the input power can be easily regulated by adjusting the energy injection time. A prototype for the converter and the inductive power transfer system was implemented experimentally. From the experimental results, the automatic stage transition and power regulation capability of the proposed converter are verified. The switches all operated at the soft switch condition. When the energy injection time was adjusted from 10 μs to 25 μs, the output power changed from 143 W to 740 W.

Soft-Switching Technology of Three-Phase Six-Switch PFC Rectifier

An active clamp, three-phase, six-switch power factor correction rectifier with a one-cycle controller is proposed, which can effectively suppress the reverse recovery of the reverse parallel diode of the bridge arm switch and reduce the reverse recovery loss. The main switches and auxiliary switch are both zero-voltage switches. It works in a fixed switching frequency and low power stress during the switching period. The specific working process and control circuit are analyzed in detail, and the model simulation is carried out. The experimental platform of a 2.5 KW prototype, with a complete test and verification of the soft switch technology proposed in this paper, was set up in the laboratory.