Dc to ac inverter provides optimum frequency and voltage to ac induction motor, in response to different motor-load and speed requirements. Inverter varies slip frequency of motor in proportion to required torque. Inverter protects motor from high current surges, controls negative slip to apply braking, and returns energy stored in momentum of load to dc power source

Nola, F. J.

English

NASA Technical Reports Server

Variable-Frequency Inverter
April 1974	 1	 B73-10525 
•	
NASA. TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Variable-Frequency Inverter Controls Torque, Speed, and 
Braking in AC Induction Motors 
S
A new variable-frequency dc to ac inverter provides 
optimum frequency and voltage to an ac induction 
motor, in response to different motor-load and speed 
requirements. The inverter varies the slip frequency of 
the motor in proportion to the required torque. In 
addition, the inverter protects the motor from high 
current surges, controls the negative slip to apply 
braking, and returns the energy stored in the momentum 
of the load to the dc power source. 
As shown in the inverter block diagram, speed is set 
by a speed input command (dc) voltage level. Feedback 
voltage, generated by the frequency-to-linear dc con-
verter, is combined with the command voltage in the 
summing amplifier and is applied to the voltage-
controlled oscillator. A magnetic pickoff is used as a fre-
quency sensor in the speed feedback loop. The oscillator 
output is multiplied by the control voltage to produce a 
sinusoid with an amplitude proportional to the control
voltage. The sinusoid is converted to a pulse train, with 
variable pulse width, to feed the motor winding drivers. 
The four drive transistors, Q 1 through Q4, operate. 
in pairs to alternate current flow through the motor 
winding. Q1 and Q4 are one pair, and Q2 and Q3 are the 
other. Diodes D 1 through D4 allow charge current flow 
back into the battery during braking. In this mode, the 
peak winding voltage (ac) exceeds the battery voltage, 
allowing the diodes to act as a bridge rectifier and 
conduct in pairs. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10525 
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000525 2020-03-17T07:17:40+00:00Z
Patent status: 
This invention is owned by NASA, and a patent 
application has been flied. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: F. J. Nola

Marshall Space Flight Center

(MFS-22088)
S 
S 
B73-10525	 Category 02
	 0


Variable-frequency inverter controls torque, speed, and braking in ac induction motors

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server