Microprocessor control of dc machines

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This project is concerned with the application of a microprocessor control system to a DC motor capable of fourquadrant operation utilising two anti-parallel three phase bridge rectifiers. The objective of the project was to develop a fast response current controller capable of changing the armature current of the motor from one steady state to another in two 3.33ms steps. For continuous current a novel control algorithm was derived which, by calculating the intermediate thyristor firing angle, enables feedforward control to be used and thereby avoids the inherent settling time of feedback control. This algorithm controlled the current waveform cusp current and used the thyristor firing instants as the sampling times. iscontinuous current control was based on a new approach using a simple look-up table for the appropriate firing angles. The system built around the Intel was 8086 based microprocessor development system running at 8 MHz and equipped with 8087 math-coprocessor together an with appropriate interfacing. The thesis presents the results of various current step response tests in alI four quadrants performed on a 3.5KW DC motor and frequency response tests for the current control which, for frequencies up to at least 70Hz, behaves as a fini te time delay of 5.2ms. A computer simulation was also developed to check the correctness of the measured values and to investigate thoroughly the system behaviour under many conditions.