Elimination of starting difficulties in SCR inverters is accomplished by the addition of two taps of the output winding of the inverter. On starting or under transient loads, the two additional taps deliver power through diodes without requiring quenching of SCR currents in excess of normal starting load

Moore, E. T.

Wilson, T. G.

English

NASA Technical Reports Server

June 1964
NASA TECH BRIEF
Brief 63-10600 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Circuit Controls Transients in SCR Inverters 
The problem: To eliminate starting difficulties en-	 can be started, when the voltage across the filter 
countered in d-c to d-c converters that employ an 	 capacitor C 1 is initially zero, with the first triggering 
SCR (silicon controlled rectifier) d-c to a-c inversion	 pulse directed to the gate of SCR 1 . When this SCR 
stage with large output-filter capacitances.	 turns on, a large current will be initiated in the circuit 
The solution: A modified parallel inverter provid- 	 consisting of the winding N 1 , diode D 2, and filter 
ing a full-wave rectified output that is applied to 	 capacitor C 1 . This capacitor will be quickly charged 
an L-C (inductive-capacitive) filter. 	 through D 2 to a lower voltage than that appearing 
How it's done: In addition to a center tap, the out-	 across the combined windings N 1 and N 2. Because of 
put winding of the inverter has two other taps. On
	 the low transient impedance of this "quick-charge" 
starting, or under transient loads the two additional
	 circuit, it is possible to complete the charging of C1 
taps deliver power through diodes D 1 and D 2 without	 so that the current through SCR, at the moment of 
requiring quenching of SCR currents appreciably in
	 quenching will nearly equal normal load current. As 
excess of normal starting load current. The converter 	 the current in the inductor L increases, the voltage 
(continued overleal) 
This document was prepared under the sponsorship of the National 	 this document, or that the use of any information, apparatus, method. 
Aeronautics and S pace Administration. Neither the United States Govern-	 or process disclosed in this document may not infringe privately-owned 
ment, nor NASA. nor any person acting on behalf of NASA: A. Makes 	 rights: or B. Assumes any liabilities with respect to the use of, or for 
any warranty or representation, express or implied, with respect to the 	 damages resulting from the use of, any information, apparatus, method, 
accuracy, completeness, or usefulness of the information contained in 	 or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000122 2020-03-11T16:48:10+00:00Z
across C 1 ultimately rises to its steady-state value 
and consequently renders D 1 and D 2 nonconductive. 
Excessive starting current transients through the	 2. 
SCR's are prevented by appropriately positioning the 
two off-center taps on the inverter, or by inserting 
small resistors. 
Notes: 
1. Although the primary purpose of this circuit is to 
eliminate starting difficulties in SCR inverters, it 
also eliminates the effects of large transient dips 
in the load voltage. In this instance, D 1 and D2 
become conductive as the output voltage drops, 
the reverse voltage across these diodes disappears,
and the quick-charge capacitor C,tends to offset 
transients. 
For further information about this innovation 
inquiries may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B63-10600 
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: Duke University under contract to 
Goddard Space Flight Center (GSFC-120) 
Brief 63-10600


Circuit controls transients in SCR inverters

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