A Study Of Component Modeling And WCA Technique In Power Supply Circuit

Worst case circuit analysis(WCA) is a technique to predict the performance of the circuit in the design limits. The reliability requirement of power supply system in aerospace application is so high that the WCA must be performed. However, no unified circuit analysis tool in domestic research institutions and the lack of special components’ testing parameters for aerospace application result in the seldom use of WCA. The few institutions that perform WCA have employed different tools and methods, leading to the difficulty of evaluating the WCA results. This thesis aims at researching in the WCA techniques of power supply systems. The methods of modeling electrical components in Saber tool, a widely used simulation tool within the industry, are presented. In addition, the flow and methodology of WCA based on Saber is proposed. The detailed contents are as follows.1. Study on the methodology of WCA techniques. The WCA related concepts are introduced, including tolerance analysis, sensitivity analysis, worst case circuit performance analysis, worst case stress analysis. The 3 ways to perform WCA are compared. A flow of circuit design and WCA is proposed. Establishing a complete aerospace dedicated device database and a perfect component model library is critical to circuit design and WCA, directly affecting the precision of simulation results.2. Study on component modeling with Saber tool. The common modeling methods in Saber tool are summarized. Besides, the modeling methods of common components, like diode, transistor, MOSFET, OPAMP, digital components, etc, are given with specific examples. And the models are verified with certain circuits. A compare on different modeling methods to the same type of component and their applicability are made.3. Study on the principle of switching power supply. Working theories and control ways of switching power supply are discussed. Then a Boost voltage converter, converting the 12 V input voltage to the 20 V output voltage, is designed with Saber. The simulation results show that the converter meets the performance specification.4. Study on the method of circuit design and WCA based on Saber tool. The usages and features of the integrated sensitivity analysis tool, Monte Carlo analysis tool, stress analysis tools, WCA tool are introduced. The Boost circuit designed is analyzed as an example, in different WCA ways. The analysis results show that the worst case performance of the circuit still meets the requirements. The analysis result of WCA tool which adopts the fast search algorithms to search for the extreme point is the worst. The analysis result of Monte Carlo analysis tool depends on the times of sampling and tolerance distribution. If the sampling times are fewer, the result may not be the worst case, but the distribution of performance parameters is presented. By sensitivity analysis and WCA, the deviation of output voltage in worst case is decreased. Through worst case stress analysis, the current sensing resistor and inductor are found to be overstressed, proving the importance of WCA. Although the circuit meets the performance requirement, the reliability problems still exist. WCA can help to distinguish the weak points of the circuits and give a reference to component selection and circuit reinforcement.