| Communication power provides power to communication equipments with security, reliability,high efficiency and stability which is an essential part of communication systems. At present, A hybridpower supply systems with AC UPS and-48VDC are employed currently in the communicationscenter. With the rapid development of communications industry, such issues as reliability, security andhigh energy consumption in the current power systems become increasingly serious. Consequently,reliable and efficient high voltage DC (HVDC) power supply system has become a new research anddevelopment trend.HVDC power supply system usually consists of AC power supply, high-frequency switchingmode rectifier, DC power distribution and monitoring unit. This thesis focuses on hardware topologyand control strategy of rectifier unit which is composed by two stage cascade converters. Thefront-end converter is a three-phase PFC with VIENNA topology which has the advantage of highpower factor, low input current THD, low switching stress, high reliability, etc. Improved ZVS controlstrategy is applied in the three-level half bridge DC/DC back-end converter. Firstly, the rectifier withVIENNA topology and related control strategies are analyzed including operation principle, smallsignal average model, digital phase locked loop (DPLL), decoupling current control and capacitormidpoint balance control. Secondly, based on the traditional three-level half bridge ZVS DC/DCconverter, an improved ZVS topology is proposed which effectively optimizes the ZVS effect of thelag switches in light load case. The small-signal model of back-end converter is analyzed and thecontrol strategies are depicted in detail, and an improved PWM control strategy is adopted to optimizethe control scheme in different operation modes and transfer smoothly between defferent modes.Finally, A5.8kW prototype of HVDC rectifier is designed and developed to evaluate the previoustheoretical analysis. |
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