| The goals of carbon peaking and carbon neutrality speed up the constructions of the modern energy system with the merits of low carbon,high safety and high efficiency,which provides the chances to the developments of distributed renewable energy generation.Thanks to the ability of managing the distributed eneriges autonomously,a microgrid is one of the main methods to consume the renewable energies.Since the control of DC microgrid does not need to consider the frequency,homonics and reactive power,the DC microgrid possesses high reliability.In addition,the DC microgrid is also a useful platform to link numerous DC distributed energy sources,energy storage devices and loads.Hence,the DC microgrid plays an important role in the power supply area.The energy storage system(ESS)is usually a key component in the DC mirogrid.It can be used to compensate the unbalance power between the distributed power supplies and the loads,which stabilize the DC bus voltage and ensure the stable operation of the microgrid system.Among the ESS,the hybrid energy storage system(HESS)wins wide attentions due to the ability of responding the power demands in multi-time scale.In this thesis,five research works are carried out based on the batterysupercapacitor(SC)HESS.All the works focus on the systematical solutions of the challengs,from the hardward topology to the cooperative control method,in the HESS.Noted that the researches provide solid theoretical supports which covers the hardware design,power allocation technique and practical applications.The contents of the main works are given as the follows:(1)To overcome the voltage levels dismatching issue between the HESS and the DC bus,a bidirectional non-isolated DC/DC converter,which adopting the structure of connecting the low voltage side(LVS)of two traditional buck/boost converter parallely and connecting the high voltage side(HVS)of those buck/boost covnerters in series,for the HESS is proposed,and its operating principles are also given.The proposed converter possesses both high voltage gain and wide voltage gain range In addition,to increase the converter efficiency,the synchronous rectification technique is used,which realizes the zero voltage swiching of the power swiches.To verify the correctness of the theoretical analysis and the feasibility of the proposed topology,an experimental prototype is bulit.(2)In order to improve the volume of magnetic elements,an active switching inductor(A-SL)based non-common ground bidirectional converter is proposed.Thanks to the current split feature of the LVS,the sizes of the inductors are effectively reduced.In addition to that the converter integrates with the advantages of high voltage gain,wide voltage gain range,the adoption of the zero current ripple circuit significantly suppresses the LVS current ripple,which effectively protects the battery and extends its service life.In addition,to eliminate the voltage resonance on the power switches which is the inherent drawback of the traditional A-SL converter,the active clamping structure is used.An experimental prototype is established to verify the advantages mentioned above.(3)To overcome the drawback of the floating-ground in the A-SL based noncommon ground bidirectional converters,I propose an active clamped common-ground A-SL converter with high voltage gain range and zero current ripple.Compared to the previous A-SL based converter,the proposed converter using the same numbers of the circuit components and enjoys the merits of the common-ground and the wider voltage gain range without any compromises.Also,an experimental prototype is established to verify the feasibility of the proposed converter.(4)To fully show the advantages of the HESS and improve the transient response performance of the microgrid,a decentralized improved Ⅰ-Ⅴ droop control strategy for the battery-SC based HESS,which overcomes the drawbacks of the traditional Ⅰ-Ⅴdroop control strategy,is proposed.Considering the limited current changing rate of the inductor and linear volt-ampere characteristic of the resistor,the virtual inductance and virtual resistance are introduced into the system throught feedbacking.As a result,the dynamic power sharing between battery and SC is realized.Sepcifically,the virtual inductance for the battery side converter and virtual resistance for the SC side converter.Besides,thanks to the inherent integration feature of the virtual inductance in the battery side converter,negligible DC bus voltage deviation can be achieved without extra voltage compensator.Moreover,a feed-forward state-of-charge(SoC)recovery compensator is also considered to extend the service life of the HESS.Both the controller design guidelines and system analysis are conducted comprehensively.The real-time simulations carried out using the hardware-in-the-loop(HIL)platform and experimental verification platform is also established to verify the effectiveness and feasibility of the proposed strategy.(5)To overcome the issue that the above proposed improved Ⅰ-Ⅴ droop control strategy cannot be adopted in microgrid system which contains multiple HESSs,a droop controller using the output voltage of the SC converter as the unified feedback voltage in each HESS is proposed.Thanks to using unified feedback voltage,the impacts of non-negligible line resistances on the performance of the power allocation performance and the bus voltage tracking are eliminated.In addition,to improve the stability and robustness of the HESSs against the CPLs which is widely connected to the DC bus of the microgrid,a distributed P-V2 droop-based control strategy is proposed.A related stabilization analysis is described comprehensively.Finally,the hardware-inthe-loop(HIL)imulations have been carried out for multiple HESSs to verify the effectiveness of the proposed power allocation strategy. |
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