High-order linearizing pulsewidth modulator for three-phase power converters

The feasibility of using an analog pulsewidth modulator (PWM) to linearize balanced three-phase converters is investigated in this dissertation. Prototype circuits, models, and analysis techniques are developed.;Most balanced three-phase PWM converters that are controlled by the conventional analog PWMs have nonlinear relationships between the control and output voltages/currents. This study shows that these nonlinear relationships can be linearized by an analog high-order linearizing pulsewidth modulator (LPWM) that makes the output voltage track the control voltage linearly. Instead of multipliers/dividers, the high-order LPWM uses only integrators with the reset, and sample/hold to compute the switching instants for the switches in the converter. The inputs to the integrators are just linear functions of the control and state variables, but nonlinear functions when other analog PWMs, such as feed-forward PWMs and one-cycle controllers, are used.;The analog high-order LPWM is synthesized from switching-function averaging (SFA) equations of the three-phase PWM converter. Thanks to the SFA model of the PWM switch, the derivation of SFA state-space equations of the converter is simply done by inspection and application of definition of circuit elements, Kirchhoff's law, and other electrical principles without probing into topological details of the converter. The set of SFA equations can be transformed into an equivalent circuit in the abc coordinates to make simulation more efficient.;In order to analyze three-phase converters that are controlled by the LPWM or other pulsewidth modulation techniques, all three-phase component models in the ofb coordinates, including PWM switches, sources, and passive components, are developed. After three-phase components are replaced by their ofb models, the time-variant three-phase circuit is transformed into a time-invariant equivalent circuit that makes analysis and design much easier. The model of the high-order PWM is also developed. It is useful to analyze the LPWM-controlled converter and evaluate time delay caused by sampling effects.;The synthesis and analysis theories of the high-order LPWM are verified by a 1 KW prototype of a three-phase boost inverter. Both simulation and experimental results agree with the analysis. It is shown that the control circuit is simple, and the output voltages of the inverter can track the control voltages linearly, and they have good sinusoidal waveforms.;In summary, the synthesis and analysis techniques are developed for linearization of a three-phase boost inverter in the dissertation, but as general methods, they can be applied to other three-phase topologies, multi-phase or multi-level converters.