Apparatus for DC/AC power conversion by electromagnetic induction

Apparatus for direct current to alternating current power conversion by means of progressive variation of magnetic flux in associated magnetic paths. A direct current input is subdivided into power pulses in two permeance controlled transformers. The pulses are modified, stabilized and recombined in phase opposition to produce a single alternating current output.

RELATED PATENT 
This invention is closely related to my U.S. Pat. No. 4,020,440 issued Apr. 
26, 1977, which is incorporated by reference. 
FIELD OF THE INVENTION 
This invention relates to the field of control of electrical energy, and 
more specifically to direct current to alternating current power 
conversion by static magnetic means. 
SUMMARY 
Control of magnetic flux in a closed magnetic path is accomplished by the 
progressive control of permeance in an assigned section of the path. 
Several configurations for continuous permeance control by progressive 
saturation and/or domain rotation are described in my related U.S. Pat. 
No. 4,020,440. 
Utilizing this technology, I have developed a unique apparatus for DC/AC 
power conversion by purely static magnetic means. More specifically, in a 
direct to alternating current power converter two identical permeance 
controlled direct current power pulse transformers are alternately 
switched in a time sequence controlled by the zero crossover points of the 
input reference alternating current waveform. In this way the direct 
current power input is subdivided into consecutive power pulses that are 
modified within the direct current power pulse transformers, under control 
of the input alternating current reference signal and feedback system, 
into the desired waveform, typically sinewave. The addition of a closed 
loop feedback system stabilizes the output and enables control of 
amplitude through internal or external means. The combined outputs of the 
two transformers, connected in phase opposition, produce a continuous 
alternating current power waveform. 
It is, therefore, an object of this invention to provide electrical power 
control by controlled electromagnetic induction. 
Still another object of this invention is to provide a controlled 
electromagnetic induction means for direct to alternating current power 
conversion and control. 
Still another object of this invention is to generate, by static means, 
polyphase alternating current power from direct or alternating current 
power at any frequency. 
Another object of this invention is to reduce size and weight of electrical 
conversion and control structures by the generation, conversion and 
control of high frequency electrical power. 
A still further object of this invention is to provide an electric power 
control means responsive to a sensed physical state, such as: voltage, 
current, power, temperature, pressure, strain, humidity, acidity, or the 
like. 
An object of this invention is to convert constant current power sources to 
other forms of electrical energy. 
Another object of this invention is to provide control of electrical power 
by electronic control of magnetic means in static configurations. 
An object of this invention is to provide the means for the computer 
control of power subsystems in an electric power network. 
Still another object of this invention is to provide means for control of 
voltage, current, and phase of a power subsystem of an electrical power 
network.

DESCRIPTION OF A PREFERRED EMBODIMENT 
DIRECT TO ALTERNATING CURRENT POWER CONVERTER OF FIG. 1 
FIG. 1 shows the direct to alternating current power converter of this 
invention. Two identical three legged magnetic cores 221 and 221A are used 
to provide for the subdivision of direct current input power into a series 
of alternating current power pulses by means of alternated operation 
between the two identical magnetic structures. 
In this invention, direct current power is transformed into alternating 
current power of sine waveform by a controlled magnetic circuit 
configuration which, in addition, provides power control capabilities 
through an integrated feedback system to satisfy specific load 
characteristics. This is a unique combination and advances the state of 
the art beyond that currently practiced which entails, among other 
limiting elements, separate function elements as switching transistors, 
silicon controlled rectifiers, or plasma discharge devices, a voltage 
coupling transformer, and a low pass or resonant filter. 
Conversion and control is accomplished by subdividing the input direct 
current power into consecutive power pulses through the medium of the 
alternately activated permeance controlled power pulse transformers and 
then transforming such power pulses into consecutive positive and negative 
lobes of sine waveform which are then combined at the output circuit. In 
this way a low level sine waveform reference signal, injected into the 
feedback system, is amplified into alternating current power. This power 
control flexibility enables, in general, the transformation of direct 
current power to a range of predetermined alternating waveforms, and 
operation at a range of frequencies, limited only by the availability of 
permeable magnetic materials for the highest frequency structures. 
In the design of practical systems, the transformer-like construction of 
the magnetic elements permits scaling of power levels, voltage, and 
current to values limited only by the state of the art in power 
transformer technology. Additionally, polyphase interconnection, typically 
three phase, is simply made by the wye or delta connection of the outputs 
of three single phase converters with an alternating current sine waveform 
reference signal appropriately phased. 
The flux excursion in each transformer core structure is limited to 
approximately one half of the flux excursion within a conventional 
alternating current power transformer for the same power frequency. This 
inefficiency in core utilization must be assessed in terms of overall 
performance advantages in a system tradeoff consideration. 
A unique direct to alternating current conversion principle emerges from 
this invention that permits the generation of low frequency power, 
typically 60 Hertz, from a direct current power source, with much smaller 
magnetic components than would be previously dictated by the 60 Hertz 
requirement. By the arbitrary selection of small magnetic structures, size 
of such structures determines the power frequency that can be supported. 
Self generation of high frequency power is determined solely by structure 
size and magnetic properties. Power at this frequency is then modulated 
fully by a control signal frequency of the desired 60 Hertz through the 
feedback control system. The 60 Hertz power is derived from the modulated 
power envelope by alternately switched controlled rectifier pairs which 
extract the positive and negative lobes, respectively, of 60 Hertz power. 
An important contribution of this invention is that this system makes use 
of static magnetic devices to generate sine waveform power. 
The two identical three legged magnetic cores 221 and 221A are the same in 
structure and in operational capabilities. Referring to one of the cores, 
221, for purposes of explanation, the structure constitutes a pair of 
magnetic paths through which flux can be controllably routed for 
generating sine waveform pulses from timed pulses of direct current flux 
generating inputs. A center leg 222 has input winding 223 therearound. A 
closed bypass path includes the permeance control section 224, bypass leg 
225, connection arm 226 and center leg 222. A closed output path includes 
a second permeance control section 227, output leg 228 with output winding 
229 therearound, connecting arm 231, and center leg 222. 
Direct current is applied as an input to this device to terminals 232 
through input lead 233 to winding 223 and on through lead 233A to winding 
223A and through lead 233B back to terminals 232. The leads 233, 233A and 
233B connect windings 223 and 223A in series. Output windings 229 and 229A 
are also serially phase-opposing connected through leads 234, winding 229, 
lead 234A, winding 229A, and lead 234B. Output terminals 235 are cross 
lead 234 and 234B. To output load terminals 236 is connected load 237. 
Between the output terminals 235 and load terminals 236 are connected a 
voltage sensing transformer 238, with primary windings thereof connected 
across the output leads 234 and 234B, and a current sensing transformer 
239, with primary windings thereof connected in series with the grounded 
side of output 234 and the corresponding load terminal 236. The secondary 
winding of the voltage sensing transformer 238 is connected as an input to 
a full wave rectifier 241 which presents an input through connector 242 to 
a voltage comparator 243 wherein the voltage representation of the system 
output is compared with a voltage signal from an internal or external 
sinusoidal fullwave reference source 244. The secondary winding of current 
sensing transformer 239 is connected as an input to a second fullwave 
rectifier 245 which presents an input through connector 246 to a voltage 
comparator 247, wherein the current representation of the system output is 
compared with an internal or external sinusoidal fullwave reference source 
244. Internal or external control 248 in voltage comparator 243 is used to 
provide the set points for the comparator. This is in the form of an 
amplitude adjustment. Voltage comparator 243 produces an error signal 
indicative of the voltage variations in the output of the system and 
supplies such information through voltage error amplifier 250 as an input 
to a mode selector 249 through a connector 250A. Voltage comparator 247 
has an internal or external control 251 which is used to provide the set 
points for the comparator. The output of such voltage comparator 247 is an 
error signal indicative of the current variations in the output of the 
system and supplies such information when dictated by load conditions as a 
second input through current error amplifier 250B and a connector 250C to 
mode selector 249. Voltage or current control selected by the mode 
selector is determined by the respective set points in relation to load 
conditions. Lead 252 is connected to the output of the mode selector 249 
and extends to be one of the inputs to each of a pair of complementary 
drive, flux apportioning amplifiers 253 and 253A. 
A flux density sensor 254 is secured to center leg 222 of core 221 in such 
a manner as to be responsive to flux density changes within such leg 222. 
A pair of connector leads 255 connects the output of sensor 254 as a first 
input to a cycling control and override limit sensor 256. A second flux 
density sensor 254A is secured to center leg 222A of core 221A like sensor 
254 is connected to leg 222. A pair of connector leads 255A connects the 
output of sensor 254A as a second input to cycling control and override 
limit sensor 256. A connector 257 connects an output of the internal or 
external sinusoidal fullwave reference 244 as a third input to the cycling 
control and override limit sensor 256. An electronic switch 259 has two 
input connectors 258A and 258 which are also connected as outputs of the 
cycling control and override limit sensor 256 and two output leads 261 and 
261A. Output lead 261 is connected as a second input to amplifier 253 and 
output lead 261A is connected as a second input to amplifier 253A. 
Amplifier 253 has a first output lead 262 which is connected to one end of 
a coil 263 of permeance control section 224. The other end of coil 263 is 
connected to a lead 264. Amplifier 253 has a second output lead 265 which 
is connected to one end of a coil 266 of permeance control section 227. 
The other end of coil 266 is connected to a lead 267. Leads 264 and 267 
are joined at junction 268 to which also is connected a connector 269. 
Connector 269 is the return lead to amplifier 253. Amplifier 253A is 
connected to permeance control sections 224A and 227A in the same manner 
that amplifier 253 is connected to permeance control sections 224 and 227, 
with equivalent elements having the letter A added to identical numbers. 
A reverse transient suppressor 271 with its unidirectional current device 
272 is mounted around leg 226. A second reverse transient suppressor 271A 
with its unidirectional current device 272A is mounted around leg 231, 
both of said first two suppressors being mounted on core 221. A third 
reverse transient suppressor 271C with its unidirectional current device 
272B is mounted around leg 231A. The fourth suppressor and current device 
are mounted around leg 226A on core 221A. 
OPERATION OF THE DIRECT TO ALTERNATING CURRENT CONVERTER OF FIG. 1 
Direct current power applied to terminals 232 is distributed alternately 
between input windings 223 and 223A by a commutation process. With a 
structure 221 in the active state nearly all of the applied direct current 
input power is transmitted through its input winding 223. The input 
winding of structure 221A, in its inactive state, absorbs negligible power 
since its associated magnetic core permeance is at its minimum value. 
The time sequence chart in FIG. 2 illustrates the operation of the 
converter of FIG. 1. 
In the time sequence chart of FIG. 2, the topmost illustrated signal 
represents a typical external alternating current reference signal 244E 
which is applied to the reference 244. The half cycle shown in interval 
273 illustrates the positive half cycle of such external reference signal 
244E. Within the internal or external sinusoidal fullwave reference 244, 
the reference signal 244E is changed, as is any external or internal 
reference signal source passing therethrough, into a fullwave reference 
signal 244F. Signal 244F is applied as inputs to the comparators 243 and 
247 and to cycling control 256. Within cycling control 256, the fullwave 
244F are used to produce the commutation trigger signals 258C which are 
delivered through connectors 258 and 258A as controlling inputs to the 
electronic switch 259. 
Electronic switch 259 functions to activate, alternately, flux apportioning 
amplifier 253 and flux apportioning amplifier 253A. This results in the 
alternated operation of the two magnetic cores 221 and 221A. The magnetic 
flux .theta..sub.2 274 in leg 228 of core 221, for example, is illustrated 
by waveform 274 wherein the flux density increases sinusoidally to a 
maximum within the first interval 273 as shown in the time sequence chart 
of FIG. 2. It is to be noted that during this first interval, the magnetic 
flux .theta..sub.2 274A in leg 228A of core 221A is at a relatively zero 
level and effectively inactive. The flux density threshold limit 275 and 
275A is set into override limit sensor 256 whereby, when the flux level 
sensed by flux density sensors 254 and 254A reaches such limit, the 
override limit sensor 256 will assume control in the event of a failure of 
reference 244, to limit the operation of the system to a safe condition. 
During the second interval of the time sequence chart of FIG. 2, the 
magnetic flux in leg 228 is at relatively zero level while the flux in 
228A increases sinusoidally to a maximum. Also, in the first interval 273, 
the induced voltage in output winding 229 rises to form one half of the 
output sinewave while the induced voltage in output winding 229A is at 
relatively zero level. In the succeeding interval 276, the induced voltage 
in the reverse phased output winding 229A rises to form the negative half 
of the output sinewave while the induced voltage in output winding 229 is 
at relatively zero level. The interconnection of lead 234, winding 229, 
lead 234A, winding 229A and lead 234B combine these two half sinewaves to 
produce the full sinewave output available at output terminals 235. 
Stated another way, the onset of the high permeance state of structure 221 
causes a rise in magnetic flux from the magnetomotive force developed by 
input winding 223. The rise in flux is coupled to the output path 228 and 
bypass path in the proportion dictated, typically, by a sinewave form 
signal through the voltage comparator 243 or 247 and permeance control 
flux apportioning amplifier 253. The rising flux coupling the output 
winding 229 generates the output voltage which serves the load 
requirement. The sine waveform lobe induced in winding 229 is followed by 
a contiguous sinewave lobe of opposite polarity induced in reverse phased 
winding 229A during the following activation of magnetic structure 221A. 
The series apposed output windings 229 and 229A combine the alternate 
sinewave output power pulses into sinusoidal alternating current power. 
Voltage feedback and current feedback signals over leads 242 and 246, 
respectively, are processed by the fullwave rectifiers 241 and 245, 
respectively, to produce fullwave unidirectional sine waveforms for 
application to the respective voltage comparators 243 and 246, where the 
deviation of the sinewave form and the amplitude output from the sine 
waveform control signal 244 appears as an error signal at connections 243A 
and 247A for voltage and current, respectively. These error signals are 
amplified by their respective error amplifiers 250 and 250B, the outputs 
of which are combined in mode selector 249 which establishes either a 
voltage or current control operation mode as determined by the respective 
control setting at the voltage comparators 243 and 247 in combination with 
the demand of the load connected to output terminals 235. 
Sine waveform reference source 244 supplies fullwave unidirectional 
waveforms to each voltage comparator 243 and 247 and of opposite polarity 
to the feedback voltages. In addition, the fullwave unidirectional 
waveform is applied as an input to the cycling control 256. The cycling 
control 256 generates the commutating signal 258C for electronic switch 
259 from the zero crossover points of the fullwave reference signal from 
244. Signals from flux density sensors 254 and 254A are applied to the 
override limit sensing function of 256 and serve as a safety override in 
the event of reference signal failure. 
To minimize the response time feedback system to output variation and 
switching activations, the permeance control drive amplifier is designed 
with a constant current control characteristic. The inherent high dynamic 
resistance of this configuration greatly diminishes the reluctance over 
resistance time constant of the permeance control circuit. 
Although the previous description covers sine waveform generation, the 
invention is sufficiently versatile to enable the conversion from direct 
current to virtually any arbitrary alternating waveform, that is to say, 
squarewave, sawtooth waveform, triangular waveform, and the like. 
A simpler configuration of the invention is afforded for squarewave 
alternating current generation by eliminating the feedback circuitry and 
applying external commutating pulses to the commutating switch 259, 
through cycling control 256. These external commutating pulses must have a 
period less than the inherent rise time of flux in core 221 and 221A up to 
the point where the flux density sensor 254 or 254A signals the 
termination of the period. 
Magnetic energy stored throughout the activated period in a pulse 
transformer is normally dissipated as thermal energy in the reverse 
transient suppressors 271, 271A, 271B, and 271C. During the transitional 
period at the time of commutation between pulse transformers. In large 
power handling equipment, this stored energy may be economically recovered 
by charging a capacitor bank or secondary battery to provide a power 
source for accessory applications. 
The direct to alternating power converter as described herein is uniquely 
applicable as the terminal subsystem of the direct current power 
transmission system and for the conversion of electrical power derived 
from advanced primary energy converters, which are inherently direct 
current generators. These advanced sources are: magnetohydrodynamic 
generators, electrofluiddynamic generators, thermionic and thermoelectric 
generators, solar cells, and the projected controlled thermonuclear fusion 
direct conversion generators. 
As an electrical energy coupling means to supply the input of an electrical 
power transmission system or its terminal subsystem converter, permits the 
introduction of external control means to effect the management of network 
power distribution and control by computer or other automatic means. 
Alternating current power generated by conversion from a direct current 
power source is required to be of sine waveform for most applications and, 
furthermore, be stabilized and adjustable over a wide range of voltage and 
current. In this invention, these requirements are completely satisfied by 
commutated permeance controlled pulse transformers, which subdivide the 
direct current input power into consecutive power pulses. Controlled 
electric induction in each of the pulse transformers is accomplished 
through a feedback system including a stabilized reference waveform and a 
means for internal or external voltage or current adjustment. The combined 
output of the commutated pulse transformers forms the useful alternating 
current power source.