Reconsideration Of Loop Gain Measurement Of DC-DC Converters And Design Of Compensators

The control parameters can be optimized according to the loop gain of DC-DC converters, and thus satisfactory stability and dynamic performance can be achieved. The loop gain of DC-DC converters can be obtained directly through the measurement by using network analyzer. There are two loop gain measurement methods, namely, the modulating signal perturbation method and the pulse-width perturbation method. However, the measured loop gains by the two measure methods are different. This thesis investigates the differences of these two methods, and which method is accurate is analyzed. In addition, the design method of compensators is proposed.In Chapter II, the principles of modulation signal perturbation method and pulse perturbation method are introduced. Then, based on the analysis of sideband frequency components and the aliasing effects of the pulse-width modulation(PWM) modulator, theoretical loop gains of the aforementioned two methods are derived, and the causes of the differences of these two methods are revealed. Two measurement methods that are equivalent to the pulse perturbation method, namely the PWM modulation method and the sample-and-hold method with simpler circuits are proposed. Finally, experiments on three basic types of DC-DC converters have been conducted and the measurement results verify the validity of the analysis above and the measurement methods proposed.In Chapter III, the stability, and dynamic performance of DC-DC converters based on the loop gains measured by two measurement methods are analyzed and compared. The analysis indicates that both the loop gains are effective, and the loop gain measured by pulse perturbation method is easier to analyze the stability while the loop gain measured by modulating signal perturbation method is more direct to analyze the dynamic performance. The theoretical calculation methods of loop gain are given. By means of the theoretical loop gain calculating values, the experiments verify the validity of the analysis above finally.In Chapter IV, based on the three basic types of DC-DC converters, i.e., buck, boost, and buck-boost, with leading-edge modulation and trailing-edge modulation, the influence of sideband frequency components on the two types of loop gains has been analyzed. It indicates that both types of loop gains are affected by sideband frequency components and the loop gain measured by pulse perturbation method is a preferred loop gain for designing the compensator. By means of the theoretical loop gain of pulse perturbation method, the design method of the compensator is proposed. Finally, the experiments of the design examples verify the validity of the design method.