Investigation Of Mulit-Frequency Control Technique For Switching Converter

With the rapid development of power electronics, switching power supply becomes in-creasingly used because of its light weight, high efficiency and small volume. More and more electronic equipments’power supplies are needed to meet the requirements of stability, regulation accuracy and higher transient response speed. The traditional pulse width modula-tion (PWM) technique, which represented by voltage-mode control and current-mode control, is mature and widely used, but it also has some disadvantages, such as low efficiency at light load, slow transient response speed and so on. For improving the performance of switching power supply, the multi-frequency (MF) control technique for switching converters is pro-posed and studied in this dissertation.MF control technique for switching converters can regulate output voltage by assem-bling control pulses with different frequencies, which is a novel control technique. It has faster transient response speed and greater robustness compared with PWM control tech-nique. It also has wider range of load, lower ripple of output voltage and higher efficiency at light load compared with bi-frequency (BF) control technique because it sets more pulses. MF control technique is based on BF control technique and different from PWM control technique.The basic principles and characteristics of BF control technique are studied firstly. Based on the combination of control pulses, output voltage ripple, transient characteristics and frequency characteristics, this dissertation points out that BF control technique can not make a compromise between output power range and output voltage ripple, and it is unsuit-able for light load and no-load operation in discontinuous conduction mode (DCM). BF con-trol technique has slow transient response speed and low-frequency fluctuation of output voltage in continuous conduction mode (CCM). The MF control technique studied in this dissertation not only retains the merits of BF control technique, but also resolves those prob-lems during in its application.The principle of MF control technique is analyzed. The voltage-mode control and cur-rent-mode control of MF control technique in DCM are studied. Meanwhile the stability, fluctuation quantities of voltage, combination of control pulses and the ripple of output volt-age are discussed. The loci of output capacitor voltage are studied by iterative solution of energy balance equation. The differences of performance and relationship between these two control techniques are compared. In this dissertation, MF control technique is extended to CCM converter. Based on the analysis of control principles and characteristics, the generate mechanism about low-frequency fluctuation of output voltage is studied by iterative solution of energy balance equation. Quantitative studies are made between the equivalent series re-sistance (ESR) of the output filter capacitor and low-frequency fluctuation. The principles and characteristics of MF control technique in pseudo continuous conduction mode (PCCM) and in CCM with the peak current constant off-time (PCCFT) are studied aiming at resolving the problems of low-frequency fluctuation in CCM. The study results indicate that the two methods can effectively inhibit the low-frequency fluctuation phenomenon.The one-dimensional dynamic model and the characteristic equation are constructed, which are about the voltage-mode control of BF control technique, the current-mode control of BF control technique, the voltage-mode control of MF control technique and the cur-rent-mode control of MF control technique in DCM converter. Through bifurcation diagrams, Lyapunov exponent, time domain, phase portraits and spectrum, the non-linear dynamic characteristics of MF and BF control technique in DCM converter are studied. The results indicate that border-collision bifurcations and multi-period behaviors exist in the volt-age-mode control buck converter of BF control technique. The period-3 behavior does not mean that the chaotic behaviors will inevitably occur. Compared with the voltage-mode con-trol of BF control technique, the current-mode control of BF control technique has similar bifurcation route and dynamic characteristic when the load is changed. The current-mode control of BF control technique holds quite different dynamic characteristic when the input voltage is changed. Compared with the voltage-mode control of BF control technique, the voltage-mode control and current-mode control of MF control technique show self-similarity and chaos phenomenon varies with margin of error voltage. In addition, the dynamic model of MF control technique in CCM converter is also constructed in this dissertation. The cor-responding dynamic characteristics are analyzed and the low-frequency fluctuation of MF control technique in CCM is revealed. CCM converter with the PCCFT MF control has strong multi-period behaviors, but no phenomenon of low frequency fluctuation.All the researches on various control techniques are based on buck converter and real-ized by the digital control strategy based on FPGA. The theoretical analyses in this disserta-tion are verified by simulations and experiments finally.