A Study On Step-down Active Capacitor Converter

With the development of social economy, the energy issues have become increasingly serious. The solutions mainly contain two aspects, the one is to enlarge the source, another one is to reduce expenditure. To enlarge the source mainly refers to the development of new energy power generation technology in wind power and photovoltaic power generation. However, to reduce expenditure mainly refers to develop the technology of electric vehicle and LED lighting as the representative of the Energy utilization technology. In the system mentioned above, power electronic converter is the key equipment, such as a rectifier, inverter and so on. Due to the input and output instantaneous power of the rectifier or the inverter are not equal to each other, large electrolytic capacitors are always be used to achieve power balance. However, the electrolytic capacitor has a short service life and its high failure rate is the inherent bottleneck, which are the obstacles to improve reliability of the whole device and to prolong the actual service life. Therefore, this paper mainly studies the Step-down active capacitor converter(ACC) to replace the electrolytic capacitor and to keep the instantaneous power balance of the input and output, so as to improve the reliability of power electronic device and to prolong the service life, which has much important theoretical and practical value. And the contents and achievements of this researches are as follows:First, the significance and necessity of non-electrolytic capacitor solutions used in the existing PV inverter, electric vehicle charger, LED drive power and other power electronic devices was discussed. And then, the main ideas, circuits and control strategies employed by the researches on non-electrolytic capacitor solutions were summarized.Secondly, the concept of ACC was proposed in this paper. The topology based on bi-directional DC/DC converter is improved and a new double-loop control strategy is proposed, including an outer voltage loop to keep the output voltage stability and an inner current loop, which is used to control the input current of ACC to meet the differential relationship with the bus voltage. The reference of inner current loop is consisted of the voltage loop output and the current of non-electrolytic capacitor located in the input side, so as to realize the active capacitor with fixed capacitance.Thirdly, the operating principle of ACC is analyzed in detail. Based on this, the quantitative design of parameters for the power circuit and control circuit was completed. The parameters design of power circuit includes the quantitative analysis of ACC internal capacitor, inductor, the voltage and current stress of switches. About the control circuit parameter design, firstly, the small signal model of ACC was established, including switch-cycle small signal model and semi-power-cycle small signal model. And then, inner current and outer voltage compensator design was completed based on the switch-cycle small signal model and semi-power-cycle small signal model.Finally, regarding electric vehicle on-board charger as an object, the compensator was built and parameter design was completed according method proposed by this paper. Then, simulation model was built to complete the relevant simulation analysis using Matlab-simulink. On the basis of the simulation analysis, the experiment design and experimental verification were completed. The simulation and experimental results verified the feasibility of solution and the correctness of the design method.