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Constant Open Loop Gain Phase Control Using Fixed Reference for Ramp Generation

IP.com Disclosure Number: IPCOM000085514D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Johari, GC: AUTHOR

Abstract

Power supplies operating from an AC source frequently use phase-controlled rectifiers to gate the AC input variably in response to a feedback signal. Conventional methods using a linear ramp do not provide a constant " open-loop gain", which introduces stability problems in a phase control or limits the range of operation.

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Constant Open Loop Gain Phase Control Using Fixed Reference for Ramp Generation

Power supplies operating from an AC source frequently use phase- controlled rectifiers to gate the AC input variably in response to a feedback signal. Conventional methods using a linear ramp do not provide a constant " open-loop gain", which introduces stability problems in a phase control or limits the range of operation.

In the illustrated control, a parabola shaped ramp is used to vary the firing angles Phi F with varying output voltages, in order to produce a constant open- loop gain over a wide range of operation. The parabola shaped ramp is generated by cascading two integrators 10, 12 and supplying the first integrator 10 with a constant reference L14. A reset pulse resets both integrators at the end of each firing cycle.

For error generation two operational amplifiers 16, 18 having an overall gain G are used to generate a noninverting error signal to be used in conjunction with the ramp.

The general rule for the open-loop gain function in a Phi control is: Open- Loop Gain - V(DC) tan Phi F/2 over d V(in) over d Phi F.

Utilizing this function, it can be shown that in the illustrated circuit, the resulting gain is as follows:

(Image Omitted)

A plot of the open-loop gain function is given in Fig. 2.

It should be noted that the value of the open-loop gain at zero firing angles is K/2 (a finite number), whereas most conventional methods of control yield open- loop gain equal to ze...