Multi-Port Converter And Its Control Technology Integrating Renewable Energy And Energy Storage

The energy crisis and environmental pollution due to the large-scale exploitation and utilization of fossil energy have greatly contributed to the development of renewable energy.The output characteristics of renewable energy are fluctuant and intermittent depending on climate and other environmental conditions,which may cause instability of the system and make it difficult to meet the demand of load.Therefore,renewable energy sources are generally combined with energy storage systems to provide reliable power to the loads,microgrids,or grid-connected inverters.The traditional renewable energy system,including renewable energy sources,energy storage systems and loads,generally uses multiple power electronic converters to achieve power conversion,which causes many disadvantages such as large system volume and high cost.The integration of renewable energy,energy storage and load with multi-port converter can effectively solve the above problems,and is the development trend of power conversion of renewable energy and energy storage system in the future.Therefore,it is of great significance to study the multi-port power converter and its control technology that integrates renewable energy source and energy storage.In view of the application requirements,this dissertation carries out the research on the multi-port converter integrating renewable energy source and energy storage system and its control technology.The main content includes two parts: In the first part,the topology derivation method and control technology of three-port converter which can integrate renewable energy source,energy storage system and unipolar load are studied.Then,a family of three-port converter topology with high performance is derived aiming at the application of unipolar dc bus.In the second part,the topology and control technology of four-port converters which can integrate renewable energy,energy storage system and bipolar load are studied.The non-isolated and isolated four-port converters which can realize symmetric bipolar output are proposed respectively.Part 1: Three-port converter integrating renewable energy source,energy storage system and unipolar dc bus and its control technologyBased on the power flow characteristics of three-port converter,this dissertation proposes a topology derivation method based on bidirectional power flow port embedding.Moreover,a family of non-isolated and isolated three-port converter topologies with low cost,compact structure,loose port voltage constraints and loop decoupling design are derived by using the basic quasi-H-bridge bidirectional power flow port.Further,the proposed topology derivation method is extended to derive the multi-port converter with multiple bidirectional power flow port,which can be used in hybrid energy storage systems.Taking non-isolated three-port SPEIC converter and isolated three-port forward converters as examples,the performance of the proposed converters is analyzed in detail in terms of operating principle,port voltage and power characteristics,parameter design considerations,control methods,and small signal modeling.and the proposed converter and theoretical analysis are verified by experiments.The results show that the proposed bi-directional power flow port embedding method based on quasi-H-bridge can be combined with various traditional twoport converters to derive the corresponding three-port converters,and only two semiconductor components need to be added.The proposed three-port converter can change the charge and discharge current of the storage energy port by regulating the duty cycle,so as to regulate the power balance of three ports.Compared with the existing topology,the proposed converter has the advantages of low-cost,high-power density and flexible port voltage relationship.In order to achieve the integration of renewable energy source and energy storage system with high-voltage dc bus,this thesis proposes and studies a soft-switching high-gain three-port converter based on coupled inductors.According to the power characteristics of the port,the operating principle and performance characteristics of the proposed converter under various operating modes,voltage gain characteristics,and the influence of the leakage inductor on the voltage gain are analyzed in detail.The parameter design guidance of magnetic element,semiconductor element,and capacitance in the converter is given.The soft switching range of semiconductor devices and the influence of parameters on soft switching conditions is analyzed in detail.The loss model of the system is established and the loss breakdown are analyzed.A reasonable energy management and control method is designed to enable the system to smoothly switch between different operating modes.Finally,the proposed converter and theoretical analysis are verified by experiments.The research results show that the proposed converter can boost the low voltage of renewable energy source and energy storage system to the high voltage required by the high-voltage dc bus and inverter within a limited duty cycle range,and can realize zero voltage switching of all switches and zero current switching of all diodes in all operating modes.Part 2: Four-port converter integrating renewable energy source,energy storage system and bipolar dc bus and its control technologyIn order to realize the integration of renewable energy source and energy storage system and bipolar dc bus,the thesis further proposed and studied a symmetrical bipolar output nonisolated four-port converter that combines a three-port Cuk converter and a three-port SEPIC converter.According to the port power relationship,the converter can operate in different modes,and the operating principle and steady-state characteristics of the converter under different modes are analyzed in detail.The influence of parasitic parameters on the symmetry of bipolar voltage is given,and the design criteria of inductors,capacitances and semiconductor components are given to guide parameter design.The research results show that the proposed four-port converter can achieve a strictly symmetrical bipolar output voltage,which is less affected by parasitic parameters.By the reasonable energy management and control method,the system can achieve smooth switching among different operating modes.The proposed converter and the theoretical analysis are verified by experiments.To realize the galvanic isolation and power conversion between sources and the bipolar bus,this thesis proposes and studies a symmetrical bipolar output isolated four-port converter based on the center-tapped winding.By combining the traditional single winding full wave rectifier and the center tapped winding full wave rectifier,a family of center tapped winding rectifier with symmetrical bipolar output characteristics is proposed.Then,the semi-active rectifier with bipolar output and the active clamping rectifier with bipolar output are further proposed.Therefore,the above rectifier can be combined with other primary side circuits to deduce a symmetrical bipolar output four-port converter.A four-port converter with interleaved bidirectional Buck/Boost on primary side,and semi-active rectifier on the secondary side is selected for detailed analysis,including its operating principle,steady-state characteristics,soft switching performance,current ripple and control method.The results show that the primary side switches of the proposed converter have a wide soft switching range,and the secondary side switches has inherent soft switching performance.The input current ripple is small because of interleaved driving of primary side switches,and the bipolar output voltage is strictly symmetrical regardless of load conditions.The correctness of the theoretical analysis is verified through experimental results.In order to realize the integration of conventional isolated three-port converter and voltage balancer,a symmetrical bipolar output full-bridge four-port converter based on phase-shifting modulation Buck-Boost voltage balancer is proposed.The interleaved bidirectional Buck/Boost converter is used in the primary side of the converter,and the proposed phase-shifting modulation Buck-Boost voltage balancer is used in the secondary.The operating principle,steady-state characteristics,soft switching characteristics,loss distribution and efficiency characteristics,parameter design and parasitic parameter influence of the proposed converter are analyzed in detail.The results show that the proposed converter has a small number of components,low cost,and simple design.The parasitic parameters have little effect on the symmetry of the bipolar output voltage.Meanwhile,the proposed converter can realize the soft switching operation of the primary and secondary side semiconductor devices.The power flow management and smooth mode switching are realized by pulse width modulation on the primary side and phase shift modulation on the secondary side.Finally,the proposed converter and theoretical analysis are verified by experiments.