Novel techniques for switch-mode power supplies

In this thesis, a novel bi-directional DC-to-AC inverter is proposed to achieve dynamic robustness of the output voltage, i.e., the output voltage of the inverter remains dynamically unchanged when there are large disturbances of the supply voltage or the load current. The control technique is to simultaneously feedback the output voltage and feed-forward the supply voltage and inductor voltage and combine them in a non-linear construction so that the output voltage is independent of supply voltage and output current and has fast dynamic response. The bi-directional configuration makes the inverter suitable for both resistive and reactive loads. The principle of operation of the inverter is explained in detail. The computer simulation results and the experimental results demonstrate that excellent performance can be achieved by using this inverter.; Also in the thesis, a new current mode control technique is proposed for DC-to-DC converters. The inductor current and the diode current are sensed and fedback to program the inductor current in a special way. As a result, the inductor current is solely determined by the reference current. When the output of the voltage error amplifier is used as the reference current signal, the output voltage of the DC-to-DC converter can be regulated. The stability analysis for the current loop shows that the proposed current mode control is inherently stable. The design procedure for the voltage feedback loop is presented. Both computer simulation results and experimental results show that the average inductor current is insensitive to large supply voltage and load current disturbances, and follows a step change in reference current very fast. They also show that the closed loop output voltage has good line noise rejection. Compared to the presently used current mode control methods, the proposed technique has the advantages of inherent stability and ease of synthesis.; The current mode control technique proposed in this thesis for DC-to-DC converters is also applied to AC-to-DC converters to shape the input current waveform to achieve a close-to-unity power factor. In this approach, the reference current is derived from the fully rectified input voltage. The principle of operation is illustrated. Computer simulation and experimental tests are carried out to confirm the feasibility of the proposed circuit.; A novel power factor correction technique is proposed for AC-to-DC converters. Instead of sensing the inductor current or the active switch current, the diode current is sensed and utilized in the synthesis of a control scheme which makes the input current sinusoidal. and in phase with the input voltage. To improve the dynamic performance and minimize the harmonic distortions of the input current, a double-injection compensation method is presented for the voltage feedback loop. The circuit is studied by computer simulation and then verified by means of an experimental prototype. The experimental results agree well with those of simulation. Close-to-unity power factor is achieved at the input port of the AC-to-DC converter.