Abstract
A feedback control scheme for PWM systems is considered, on the basis of a conventional triangular carrier wave scheme.
When disturbances such as power supply fluctuation or switching delay exist, the conventional PWM scheme produces output error because of its open loop structure. To cope with this, the present scheme adopts a feedback switching control structure that measures mean output error during each period of the triangular carrier wave and determines the subsequent switching timing to eliminate the error. The scheme is realized by adding a simple circuit to the conventional one. The resulting PWM system has an integral compensation property, thereby the mean output error should vanish in the steady-state. Moreover, when its input and disturbances are of step-type, the response settles down perfectly in 2 periods. Furthermore, a feed forward path can be easily implimented, which makes the input response similar to that of the conventional open loop scheme.
The authors have applied the scheme to a PWM controlled voltage source in a DC electric motor velocity control system. Results of experiments on the system verify the abovementioned merits of the present scheme.
