# US 4,395,751 A · Flux-balanced variable frequency inverter

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- Number: US 4,395,751 A
- Document ID: US4395751A
- Status: Granted
- Kind: A
- Application number: 06/303,780
- Filed: 1981-09-21
- Granted: 1983-07-26
- Earliest claimed: 1981-09-21
- Assignees: McDonnell Douglas Corporation
- Inventors: Lawrence G. Meares
- Web page: https://patentgrep.com/patent/US4395751A

## CPC

- H02M 7/5381: Parallel type
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)

## Abstract

Replacing the timing core of a conventional two-core inverter with a magnetic amplifier allows for control of frequency and for B-H loop symmetry. Switching of the magnetic amplifier results in inverter commutation rather than the familiar pulse width modulation.

## Claims

### Claim 1

In a two-core inverter comprising two transistor switches, a power core and a timing core, the improvement comprising a flux-balanced, variable frequency inverter wherein the timing core of the two-core inverter is replaced by a magnetic amplifier assembly comprising a control core assembly having two cores which are connected with a control winding; said inverter further comprising:
a control current feedback means connected between a frequency-proportional control current source and the control winding of the magnetic amplifier; and,
a flux excursion balancing means comprising two separate feedback magnetic amplifier windings about the control core assembly of the magnetic amplifier connected in opposing directions between an input DC voltage source and a center tap on the input side of an output transformer on the power core of the inverter.

### Claim 2 (depends on 1)

The inverter of claim 1 wherein the control current feedback means comprises a secondary winding on the power core of the inverter connected through a resistive element to one side of the control winding of the magnetic amplifier.

### Claim 3 (depends on 1)

The inverter of claim 1 wherein the flux excursion balancing means further comprises: the first feedback winding of the two feedback windings connected between the center tap of the input side of the output transformer of the inverter and a first node; the second feedback winding of the two feedback windings connected between a first side of an inductive element and the first node, the other side of the inductive element being connected to a first side of the input DC voltage source; the first node connected to a second node through a resistive element and a capacitive element; the end taps of the input side of the output transformer connected in parallel through the two transistor switches to the second node; and the second node connected to the other side of the DC voltage source.

### Claim 4

A flux balanced, variable frequency inverter comprising:
two transistor switches, a power core assembly which comprises a set of primary windings comprising a center tapped input winding and an output winding, and a magnetic amplifier assembly which comprises a core assembly having two cores having a common control winding and separate gate windings;
a control current feedback means connected between a frequency-proportional control current source and the control winding of the magnetic amplifier; and
a flux excursion balancing means comprising first and second separate feedback windings about the cores of the magnetic amplifier core assembly connected in opposing directions between an input DC voltage source and a center tap on the input winding of the power core assembly.

### Claim 5 (depends on 4)

The inverter of claim 4 wherein the control current feedback means comprises a center-tapped secondary winding on the power core of the inverter the end taps of which are connected through a resistive element to one side of the control winding of the magnetic amplifier and the center tap of which is connected to the center tap of the input winding of the power core.

### Claim 6 (depends on 4)

The inverter of claim 4 wherein the flux excursion balancing means further comprises the first feedback winding connected between a center tap on the input winding on the power core assembly and a first node; the second feedback winding connected between a first side of an inductive element and the first node, the other side of the inductive element being connected to a first side of the input DC voltage source; the first node connected to a second node through a resistive element and a capacitive element; the end taps of the input winding on the power core connected in parallel through the two transistor switches to the second node; and the second node connected to the other side of the DC voltage source.