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Abstract:
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This dissertation examines the effects of instantaneous constant -power loads (CPLs ) on power converters . These CPLs are prevalent in distributed power architectures and are also present in certain motor -drive applications . CPLs introduce a destabilizing nonlinear effect on power converters through an inverse voltage term that leads to significant oscillations in the main bus voltage or to its collapse .
Boundary control is studied in order to stabilize dc -dc converters with instantaneous CPLs . The three basic topologies are studied : buck , boost , and buck -boost . Converter dynamics are analyzed in both switching states and the various operating regions of switch interaction with a first -order switching surface are identified . The analysis reveals important characteristics of CPLs . For non -minimum phase converters , in order to avoid issues related with the fact that the closed -loop state -dependent switching function is undefined on the switching surface , reflective mode solutions to both converter systems are defined in the sense of Filippov . Sufficient conditions for large -signal stability of the closed loop converter operating points are established . It is shown that first -order switching surfaces with negative slopes achieve large -signal stability , while positive slopes lead to instability . In particular , for the boost converter it is illustrated via simulations and experiments that positive slopes may lead to another closed -loop limit cycle . It is also shown that instability as well as system -stalling , which is termed the invariant -set problem , may still occur in reflective mode . However , a hysteresis band that contains the designed boundary may be used to prevent system -stalling , and also allow for a practical implementation of the controller by avoiding chattering . Regulation is also achieved .
The dynamic behavior of single -phase full -wave uncontrolled rectifiers with instantaneous CPLs is also explored . Stable operation is shown to be dependent on initial condition and circuit parameters , which must fall within reasonable ranges that validate a CPL model . A necessary condition for stable operation of the rectifier system is thus derived . Furthermore , input and output characteristics of the rectifier with a CPL are investigated , and comparisons are made with the resistive case . A more complete model for the rectifier system that incorporates line -voltage distortion is also utilized to study the rectifier system . Simulations and experimental results are included for verification . |