Study On The Reconfigurable Structure Constant Power Source With Wide-Range Continuously Adjustable Output Voltage

One special application of switching power supply is wide output range continuously adjustable constant power source, whose output voltage can be adjusted continuously in a wide range and it can be working in constant output power mode in the working area. Due to the above features, the designed power level, the stresses and utilization of devices are compromised, leading to high cost, large volume, low efficiency, and low reliability. In order to resolve the above issues, a new reconfigurable structure (RS) converter is proposed, the general structure, mathematic model, stability and dynamic performance, global stability of cascaded system and control methods of the wide output range constant power source are studied in this dissertation, and several novel ideas and analytical approaches are presented.Firstly, the basic concept of reconfigurable structure converter is proposed. The reconfigurable structure DC-DC converters are an extension of the traditional isolated DC-DC converter by adding auxiliary active switches and diodes. Theoretical analysis indicates that the proposed RS converter is able to smoothly reconfigure the output channels in parallel or series to realize wide output voltage range. With this approach, the output voltage is shared equally in series mode and so is the output current in parallel mode. Therefore, the power rating of devices and the cost of system are significantly reduced and the efficiency is high in the whole output voltage range. Based on the concept of RS converter, the general topology of nested multistage reconfigurable structure converter is proposed. The mathematical model and optimized operating states are illustrated, which provide the foundation for the application of multistage reconfigurable structure converter.In order to ensure the same stability and dynamic performance in the whole output voltage range due to the variation of the structure and the quiescent operating point, the stability and load dynamic characteristics of RS converter are analyzed in detail with different control methods. Theoretical results show that the variation of the structure will effect on the load dynamic with voltage control, the variation of the quiescent operating point will effect on the load dynamic with voltage-input current control and there is no influence with voltage-inductor current control. Therefore, the adaptive sampling factor method for voltage control and the voltage reference feedforward method for voltage-input current control are proposed to ensure the same performance. The nonlinear duty ratio trip method, which can be easily performed based on digital control, is presented to ensure the smooth transition of the RS converter. Based on the features and relationship of the RS converter structures, the duty ratio is rapidly step to a scale of last value at the moment of the mode changing. With this smooth transition control method, it seems like the output voltage is regulated in the same structure, not related to the changing of operating mode. Therefore, the spike of the inductor current is limited and a much smoother transition is achieved.According to the time delay issue in digital control wide range test power supply, the delay forms in practical applications are summarized in detail and the corresponding small signal discrete-time models with time delay are established. Based on the models, the quantization effects of time delay with different time delay values are analyzed. To compensate the time delay and improve the performance of digital control, the duty ratio predictive control scheme based on linear extrapolation is proposed. The theoretical analysis and experimental results show that the proposed method is simple, independent on the system model and unnecessary to redesign the controller. Basing on these above, the duty ratio predictive control scheme is used for controlling the wide range RS converter, the results are accord with what we expect.In order to ensure the global stability of the cascaded system, based on the structure of the wide output range test power supply, the relationships of the input and output impedance of RS converter with the parameters of system and controllers are analyzed in detail and the stability of system is presented using the Middlebrook Criterion. The simulation results show that the stability is affected by the output power, the output filter capacitor and the phase margin of source converter. The optimization design of these sensitive parameters is obtained in the thesis.A prototype of a 40V-600V wide output range test power supply with digital control is built successfully, which meet the most requirements in the design index. The test results have shown that the prototype has good stability and dynamic performance, realizes the function of constant output power, has good line and load regulation and the ripple factor of output voltage is small too. Moreover, the relatively high efficiency in the whole output range is achieved. These experimental results further verify the correctness and effectiveness of the aforementioned analysis.