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UBC Theses and Dissertations

Digital control loop for power converter systems Duan, Yingran

Abstract

With the advance of microprocessors/DSP, digital control is increasingly used in various applications of switchmode power converter systems because of its advantages over analog control. The disadvantages, however, include limited signal resolution due to finite word length of processor and A/D converter; sampling time delay and limited computation power and control loop bandwidth. Adequate performance is difficult to realize by the current digital controllers with cost consideration. In order to achieve a good system performance, digital controller design becomes an important issue. Many digital design methods are available right now, and using different design methods results in different digital control performance. Choosing a better digital control design approach or method to improve the performance of the digital controlled power converter system is currently under consideration in this thesis. Digital controllers with different design methods are designed for a power inverter. A thorough and systematic evaluation on these methods is provided by comparing the performance of the digital controlled system. The performance of each approach is compared in terms of both the bandwidth and the phase margin of the control loop as well as the performance at nonlinear load condition. Furthermore, the difference of these design approaches under different sampling rates is studied. The best digital design approach for power converter system applications is identified based on the comparison results. Such a result is useful since, the control sampling rate can be several times lower than the converter switching frequency due to the limited computation power of low-cost processors. A modified direct digital design method is proposed for practicing engineers who are mostly familiar with the continuous domain design approach. Some other issues related to digital control design for switchmode power converter system, including digital controller implementation and delay modelling are discussed as well.

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