| Research and exploration on DC-DC converters with wide voltage range and modular DC power conversion system have been promoted due to the rapid development of space power system and renewable power generation system.The topology,control strategy and derivation method of isolated Buck-Boost(IBB)converter,which is suitable for wide voltage range operation,as well as the system configuration and control strategy of modular DC power conversion system based on IBB converters are studied in this thesis,in order to provide effective solutions to meet the increasing demands of high efficiency,high power density,high power capacity,high voltage and ultra-wide voltage range.A systematic method for developing the primary-side Buck-type IBB converters is proposed.By integrating the AC Buck cell,AC Boost cell,AC inductor and high frequency transformer,a family of primary-side Buck-type IBB converters are generated.Furthermore,a family of semi-active rectifiers(SARs)is proposed to serve as the AC Boost cell,and is derived by integrating active switch into passive rectifiers.The voltage-doubler type ones can be merged with the Boost switched-capacitor circuits to further generate voltage-multiplier type SARs,which is suitable for high voltage gain applications.The operational principles,control strategy and characterisitics of a full-bridge IBB converter are analyzed in detail as an example.Compared to the converters with passive rectifiers,the proposed IBB converters feature the better voltage regulation ability and soft-switching performance.Meanwhile,IBB conversion can be achived with reduced current stress and conduction loss,which makes the proposed IBB converters more suitable for the wide voltage range applications with high effciecy being required within full range.A systematic method for developing the primary-side Boost-type IBB converters is proposed.The isolated Boost circuits have the abilities of voltage step-up and transforming the DC voltage to high frequency AC voltage.By integrating the isolated Boost circuits,the SARs,AC inductor and high frequency transformer,a family of primary-side Boost-type IBB converters are generated.Detailed analysis about operational principles,control strategy and characterisitics of the proposed converter are presented.With PWM plus phase-shift control,duty cycle is adjusted to ensure the well match of mid-point voltages of primary-and secondary-side circuits to achieve optimal performance,and hence high efficiency can be ensured within wide voltage range.Thanks to the voltage step-up abilities of isolated Boost circuit and voltage-multiplier type SAR,voltage gain is greatly improved.Input current ripple is effectively reduced due to the interleaved operation of primary-side circuits.Furthermore,the primary-side Boost-type IBB converters can be upgraded as three-port converters(TPCs),since the primary-side capacitor-port is a bidirectional-port and can be connected to an input source,or an energy storage device or a DC bus.An ultra-wide output voltage range DC power conversion system based on modular IBB converters with a segmented regulation control strategy is proposed.With cascaded connection of multi-stages series-parallel flexible-structured power conversion units,an input-parallel and output series-parallel flexible-structured system with multiple DC-DC converters is generated.By controlling the auxiliary switches in multi-stages series-parallel flexible-structured power conversion units,the connections of all DC-DC converters' output-ports can be changed flexibly to achieve segmented regulation of output voltage.Then the system output voltage range can be greatly widened,and the voltage range of each DC-DC converter can be narrowed to simplify design.Operation principles and control requirements in all possible operating modes are analyzed in detail.With input current sharing control,stable operation and voltage/current sharing performance can be achieved.With the proposed system with its control strategy,ultra-wide voltage operation with constant peak output power and high efficiency can be achieved.A distruibuted DC grid-connected PV system based modular TPCs with a fully-autonomous control strategy is propsed.The input-port of each TPC is connected to an independent PV energy source,and all the output-ports are connected in series to achieve medium or high output voltage,while all the bidirectional-ports are in parallel to build a low-voltage(LV)DC bus,which is used to realize power balance control among all TPCs.Independent input control is ensured to achieve maximum power point tracking(MPPT)operation of all the PV energy sources.Meanwhile,by regulating the voltage of bidirectional-port in a linear relationship with output voltage,the stable bidirectional-port's voltage and autonomous output voltage sharing can be obtained.With the proposed control strategy,MPPT operation and voltage sharing control can be achieved simultaneously.Meanwhile,fully-autonomous control,high system modularity,stable operation,fault-tolerant and hot-swap capability are ensured.Prototypes are built with experimental and simulated results given in detail to verify the validity and feasibility of the researches mentioned above. |
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