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Active Power and DC Voltage Coordinative Control for Cascaded DC–AC Converter With Bidirectional Power ApplicationTian, Yanjun; Chen, Zhe; Deng, Fujin; Sun, Xiaofeng; Hu, Yanting; University of Chester (IEEE, 2015-10-31)Two stage-cascaded converters are widely used in dc–ac hybrid systems to achieve the bidirectional power transmission. The topology of dual active bridge cascaded with inverter DABCI) is commonly used in this application. This paper proposes a coordinative control method for DABCI and it is able to reduce the dc-link voltage fluctuation between the DAB and inverter, then reduce the stress on the switching devices, as well as improve the system dynamic performance. In the proposed control method, the DAB and inverter are coordinated to control the dc-link voltage and the power, and this responsibility sharing control can effectively suppress the impact of the power variation on the dc-link voltage, without sacrificing stability. The proposed control method is also effective for DABCI in unidirectional power transmission. The effectiveness of the propose control has been validated by both simulations and experiments.
Impedance coordinative control for cascaded converter in bidirectional applicationTian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting; University of Chester (IEEE, 2015-06-30)Two stage cascaded converters are widely used in bidirectional applications, but the negative impedance may cause system instability. Actually the impedance interaction is much different between forward power flow and reversed power flow, which will introduce more uncertainty to the system stability. This paper proposes a control method for the constant power controlled converter in cascaded system, and consequently it can change the negative impedance of constant power converter into resistive impedance, which will improve the cascaded system stability, as well as merge the impedance difference between forward and reversed power flow. This paper addresses the analysis with the topology of cascaded dual-active-bridge converter (DAB) with inverter, and the proposed control method can also be implemented in unidirectional applications and other general cascaded converter system. The effectiveness has been validated by both simulation and experimental results.
Impedance interaction modeling and analysis for bidirectional cascaded convertersTian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting (2015-06-30)For the cascaded converter system, the output impedance of source converter interacts with the input impedance of load converter, and the interaction may cause the system instability. In bidirectional applications, when the power flow is reversed, the impedance interaction also varies, which brings more uncertainty to the system stability. An investigation is performed here for showing that the forward and reverse interactions are prominently different in terms of dynamics and stability even though the cascaded converter control remains unchanged. An important guideline has been drawn for the control of the cascaded converter. That is when voltage mode converter working as the load converter; the constant power mode converter as the source converter, the system is more stable. The concluded findings have been verified by simulation and experimental results.