CA1311797C - Power source using high frequency phase control - Google Patents

Abstract

POWER SOURCE USING HIGH-FREQUENGY PHASE CONTROL
ABSTRACT OF THE DISCLOSURE
A power source using high-frequency phase control possessing an ability to cause the transfer of electric power between a power source side and a load side to be made through a high-frequency transformer and to effect control of the output voltage by subjecting the power source side and the load side circuits to on-off control with a certain phase difference. This power source can be used as an uninteruptible power source, a device for controlled drive of a motor, a DC constant-voltage power source, or a constant-current device, for example.

Description

-13~7 ~7 POWER SOURCE USING HIGH-FREQUENCY PHASE CONTROL

BACKGROUND OF THE INVENTIOM
1) Field of the Invention:
This invention relates to a power source for deriving from a DC power source desired DC output, sine-wave AC
output, etc. having voltages.different from the voltage of the DC power source, and more particularly to a power source of -the type using a high-frequency phase difference control and possessing an ability to cause the transfer of electric power between the power source side and the load side to be made through a high-frequency transf~rmer and to effect control of the output voltage by subjecting the power source side (input side) and the load side circuits to ON-OFF control with a certain phase difference, where the power source side and the load side are required to be insulated from aach other in terms of D5.
This device can be advantageously used as an uninter-ruptible power source, a device for controlled drive of a motor, a DC constant-voltage power source, or a constant-current device, for example.2) Description ot the Prior Art:
Most, lf not all, recent data processing devices never tolerate an interruption of power supply even momentarily.
In the Gircumstances, uninterruptible AC power sources which are provided with an inverter and enabled to derive~a sine-wave AC output from a DC power source by switching the DC

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power source have been finding growing utility in actual applications. In this case, more often than not there arises a need for keeping the sine-wave AC output insulated from the DC power source in terms of DC.
With respect to the prior art power source using high-frequency phase control, as will be described below, there are such problems that a transformer becomes so bulky as to occupy a large space and weigh heavy, a surge voltage is easily generated when a load is not a pure resistance because the flow of electric power is restricted to only one direction and the reactive power is not regenerated in the power source, and/or a configuration of the circuit is rather complicated.
BRIEF SUMMARY OF THE I NVENTION
This inven-tion has been initiated for the purpose of eliminating the disadvantages suffered by the conventional power sources as described above. It aims to provide a power source of the type using a high-frequency phase control which permits efficient regeneration of the 20 reactive power without either entailing complication of the configuration of circuit or necessltating:an increase of the dimensions, volume, or weight of the transformer.
To be more specific, an object of this invention is to provide a power source of the type using a high-frequency phase difference control which enables a DC output, a sine wave AC output, and other outputs of desired wavefor~ or voltage to be derived frorn a DC power source through the medium of an ", ~ 3 ~ ~3~9~
ON-OFF control switching element and a high-frequency transformer, permits simpl:ification of the configuration of circuit and reduction of the volume, weight, and dimensions of the entire device, produces a highly reliable operation, and realizes high economy of the device.
According to the above object of the present invention, from a broad aspect, there is provided a power source of the type using a high-frequency phase control and wherein the power source comprises a high-frequency transformer having a primary winding and a secondary winding. First and second switch means are each connected at terminal thereof to the opposite terminals of the primary lS winding of the high frequency transformer and each connected at the other terminal thereof to the other, with the common point of connection of the first and second switching means being adapted for connection to a constant polarity source of voltage. A center tap in the primary winding of the high-frequency transformer adapted for connection to a reference source of voltage.
Third and fourth switch means each connected at one terminal thereo to the opposite terminals of the secondary winding of the high-frequency transformer and each connected at the other terminal thereof to the other. A reactor is connected between the common point of connection of the third and fourth switch means and one of a pair of output terminals. A center tap of the secondary winding of the high-frequency transformer is connected to the other of the pair of output terminals. A controlling device fox B
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-3a - ~ 3~7 97 effecting ON-OFF switching control alternately of the first and second switch means and, at the same time, effecting ON-OFF switching control alternately of the third and fourth switch means with a selected phase difference with reference to the switching of the first and second switch means. The control device comprises an error amplifier for generating a deviation signal representing any deviation from a reference signal of any output voltage appear:ing between the pair of output terminals. A flipflop is provided for generating a first rectangular wave controlling signal possessing an amply high frequency as compared with a frequency of the reference signal and exhibiting a duty ration of 1/2, and a second rectangular wave controlling signal of a reverse phase relative to the phase of the first rectangular wave controlling signal. Means is provided for generating a triangular wave signal 2~ which is synchronized to the first and second rectangular wave controlling signals. A
comparator is provided for comparing the triangular wave and the deviation signal to generate a prelimlnary rectangular wave signal in response to the difference in their amplitude with a duty ratio depending on the amount of this difference. A logic circuit is supplied with the preliminary rectangular wave signal and one of the first and second rectangular wave controlling signals to provide third and fourth rectangular wave controlling signals of opposite phase, and with a phase differing from that of the first and second rectangular wave controlling signal . ~ . . .
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~31~7~7 - 3b -depending on the duty ratio of the preliminary rectangular signal. Means is also provided Eor effecting ON-OFF control of the first through fourth switch means in accordance with the first through fourth rectangular wave controlling signals.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1, Fig. 2 and Fig. 3 are block diagrams illustrating outlined configurations of conventional AC power sources of the type deriving a sine-wave AC output from a DC power source.
Fig. 4 is a circuit diagram typically illustrating the operating principle o~ the present invention.
Fig. 5 is a waveform diagram for aiding in the description of the operation of the embodiment of Fig. 4-Fig. 6 is a graph showing the relation between the output voltage Eo and the phase difference 0.
Fig. 7 is a block diagram illustrating another embodiment of the present invention.
Fig. 8 is a block diagram illustrating yet another embodiment of the present invention.
Fig. 9 is a block diagram illustrating a typical con-trol circuit used in the embodimehts of Fig. 7 and Fig. 8.
Fig. 10 is a time chart depicting the operation of the control circuit of Fig. 9.

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~3~797 DETAILED DESCRIPTION 0~ THE PREFERRED EM~ODIMENTS
Fig. 1, Fig. 2, and Fig. 3 are block diagrams illus-trating outlined configurations of conventional AC power sources of the type deriving a sine-wave AC outpu-t by the ON-OFF control of a DC power source. In these diagrams, like symbols denote identical or similar parts.
In the power source of Fig. 1, the electric power from a DC power source 1 is converted in-to an AC of the frequency:
of commercial power supply by a switching device 2 which is adapted to derive a sine-wave AC output by the On-OFF control of a switching element incorporated therein, and the AC power thus produced is supplied via a transformer 3 to a load 4 ("Principles of Inverter Circuits," pp 310 to 318, written by B. n . Bedford et al. and published by John ~iley & Sons, Inc.).
This power source has a disadvantage that since the AC
power of a low frequency (50 or 60 Hz) is transmitted via the transformer 3 to the load ~, the transformer 3 inevitably becomes so bulky as to occupy a large space and weigh heavy.
In the power source of Fig. 2, the electric power from the DC power source l is converted into an AC of high frequency by a DC-AC converter 5 and then supplied via a high-frequency tr~nsformer 3H to a rectifier 6. The DC fod .

.,-5 ~ 797 out of the rec-tifier 6 is conver-ted into a sine-wave AC of the frequency of commercial power supply by the same switching device as used in the power source of Fig. l and the produced AC is supplied to the load 4.
In the power source of Fig. 2, since the electric power is transmitted in the form of a hi~h-frequency AC via the transformer 3H, the hi~h-frequency transformer 3H is prevented from becoming so bulky as mentioned above. On the other hand, however, this power source has a disadvantage that since the rectifier 6 is unidirectional element - restricting the Elow of electric power to only one direction and the reactive power is not regenerated in the power source and tends to give rise to a surge voltage where the load is other than a pure resistance, the power source requires a measure for preventing the adverse effect of the reactive power and inevitably suffers from heavy complication of the configuration of circuit.
In the power source of Fig. 3, the electric power from the DC power source l~is converted by a switching device 2P

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into a high-frequency AC which is pulse-width~modulated in the form of a full-wave rectified sine wave and supplied to the high-frequency transformer 3~-i. The high-frequency AC
secondary output of the transfor~er 3H is rectified by the rectifier 6 to be converted into a full~wave rectified sine-wave AC and then is converted f`urther by an unfolding circuit 7 such as a bridge circuit into a sine-wave AC with the commercial frequency (an article written by Alan Cocconi et al. ~nder the title of "High Frequency Isolated 4KW Photovoltaic Inverter For Utility Interface" at pages 325 through 345 in "ADVANCES IN SWITCHED_ MODE POWER CONVERSION," Vol. III, published by TESLA Co.).
The power source of Fig. 3, similarly to that of Fig. 2, enjoys freedom from undue increase in volume and weight of the transformer 3. Similarly to the power source of Fig. 2, however, it has a disadvantage that it requires a measure for preventing the otherwise inevitable occurrence of a surge voltage due to the reactive power and suffers from complication of the configuration of circuit.

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_ 7 ~ ~3~797 Fig. 4 depicts a principal embodiment of the power source of the type using a high-frequency phase control by this invention. Fig. 5 is a time chart drawn to aid in the description of the operation of the device of Fig. 4.
In E~ig. ~1, the opposite tertninals of a primary winding of a high-frequency transformer 3~1 are interconnected through the medium of a switch 21 and a switch 22 respectively and are connected to one terminal (positive terminal) of a DC
power source 1. A center tap of the primary winding is connected to the other terminal (negative terminal) of the DC power source 1. The opposite terminals of the secondary winding of the high-frequency transformer 3H are intercon-nected through the medium of a switch 23 and a switch 24 and are further connected to one end of a load 4 through the medium of a reactor 8. ~ center tap of the secondary winding is connected to the other end of the load 4.
Further, to the load 4 is parallelly connected a capacitor 10. The small blaclc dot indicated at one end of each of the windings represents the polarity of the winding and Nl andN2 denote the nu~bers of the first and second windings of the transformer 3 In the wave~forms (a) and (b) illustrated in Fig. 5, 51, S2, S3, and S4 denote the ON periods of switches 21, 22, 23, and 24 respectively. As clearly noted from the diagram, the periods Sl through S4 have equal durations for retaining the ON state and ~he periods Sl and 52 and the periods S3 and S4 ' - 8 - ~3~797 are alternately subjected to ON-OE'F control at fixed equal intervals.
Where a phase difference of ~ exists as illustrated in Fig. 5 between the ON periods, S3 and S4, of the switches 23 and 24 on one hand and the ON periods, Sl and S2, of the switches 21 and 22, a modulatecl rectangular voltage waveform illustrated in Fig. 5 (c~ is issued at the point A of Fig. 4.
To be more specific, the combinations of ON~OFF states of the individual switches are divided into the four kinds as shown in Table 1 below.

Table 1 State A C D

Switch 21 ON ON OFF OFF
15~ Switch 22 OFF OFF ON ON
Switch 23 ON OFF OFF ON
Switch 24 OFF ON ON OFF
Voltage at Point A _ ~ ~ -In the state A, since electric currents flow through the primary and secondary windings of the high-frequency transformer 3H as indlcated by arrows of solid line in Fig. 4/ a voltage of positive polarity is generated at the point A of Fig. 4. In the state C, the same relation exists. In contrast/ it will be readily inferred that in the states B and C~ voltages of negative polarity are generated at ~he point A mention-d above. The potential ~t :
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: ' ~3~7~7 the point A, therefore, changes in a rectangular waveform like the waveform (c) in accordance with the time-course change of the combinations of the ON OFF states of the individual switches 21 through 24 illustrated in Fig. 5 ~a) and (b).
A mean value (DC) voltage Eo illustrated in Fig. 5 (c) is obtained when the modulated rectangular waveform generated at the point A is deprived of the AC component by the use of a filter composed of a reactor 8 and a capacitor 10 as illustrated in Fig. 4 and is then averaged.
Let Ei stand for the input voltage, then the relation between the DC output voltage Eo and the phase difference will be represented by the following formula (l).
Eo (1 - 2~/~)Ei~N2/N1 15Fig. 6 shows the relation between the output voltage Eo and the phase difference ~ in accordance with the formula (l) given above. It is noted from the graph that the output voItage ; Eo is a first-order function of the phase difference ~ and is linearly varied throughout the entire range from the positive voltage to the negative voltage.
By the embodiment of Fig. 4, a power source which is enabled to derive from a DC power source of a certain voltage a DC outputj a sine-wave AC output, and other similar outputs of desired voltages different from the v~ltage f the DC source y suitably adjusting the phase ~ 3 ~ 7 difference ~ can be easily constructed.
Fig. 7 is a block diagram illustrating a specific embodiment oE the present lnvention. In the diagram, the same symbols as used in Fig. 4 denote identical parts~
Between the power source 1 and the primary winding of the high-frequency transformer 3H, the switch 21 and -the switch 22 are connected similarly to those in Fig. 4. The switch 23 and the switch 2~ are connected, similarly to those of Fig. 4, to the secondary winding of the transformer 3H and the reactor 8 is connected between the load 4 and the switch 23 and the switch 24. The switches 21, 22, 23, and 24 are driven by a control device 9 on the same timing as described above with reference to Fig. 4 and Fig. 5.
The control device 9, as described more fully later on, controls the output voltage and current by comparing the output voltage or current signal with the sine-wave, DC, or other reference signal issued from a reference signal ; generating device 91 and accordingly regulating the phase difference between the switch signal to be given to the switches 21 and 22 and the switch signal to be given to the switches 23 and~24.
Fig. 9 illustrates a specific configuration of :
the control circuit 9 and the reference signal generator ; 91 to be used when the power source of Fig. 7 is adopted as a commercial AC power source.
The sine-wave reference~signal generator 91 comprises a ~` ' .

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PLL (phase locked loop) 13, a counter 14, a ROM (read only memory) 15, and a DC-AC converter 16. The PLL 13 receives a commercial AC of 60 Hz and, in response thereto, generates a high~frequency signal raised to 1,024 (= 21) times of th~
original frequency, for example. The counter 14 makes count of this signal on the binary basis and designates an address of the ROM 15 with the output of each of the digits (10 bits in the present case). In the addresses of the ROM 15, the values of amplitude in 1,024 phase points into which one cycle of sine wave is divided are stored.in advance.
These values of amplitude are sequentially read out and supplied to the DC-AC converter 16. The DC-AC converter 16, therefore, is enabled to issue a sine-wave reference signal Vref. Of course, the sine-wave reference signal generator need not be .restricted to the construction described above may be in some other suitable construction.
To a noninverting input terminal of an error amplif~.er 42, the sine-wave reference signal Vre:f is supplied. To an : inverting input terminal of the error amplifier 42 is fed in the output voltage (or current) applied to the load 4 illustrated in Fig. 7. The error output from the error .~
amplifier 42 is fed to an inverting input terminal of a comparator 43. ~
An oscillator 44 generates a signal of amply high frequency (suah as, for example, 200 KHz) as compared with the fre:uency o~ the refe_ence singal Vref and, based on this .
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~ 12 - ~3~7~7 signal, a triangular wave generator 45 and a trigger signal generator 46 generate a triangular signal (Fig. 10 b) and a trigger signal (Fig. 10 a) which are in a mutually synchronized relation.
The triangular wave is supplied to the noninverting input terminal of the comparator 43. The comparator 43 compares the triangular wave and the error output and, only duri.ng the period in which the triangular wave is larger than the error output, feeds out a rectangular waveform (Fig. 10 c) rising to a high level. Evidently, the rising time of the rectangular wave c is delayed and the duration of the rectangular waves is shortened, in proportion as the output voltage applied to the load 4 is decreas~d.
A FF (flipflop) 47 is triggered by the trigger signal and generates at the Q output terminal thereof a rectangular waveform having the duty thereof halved as illustrated in the waveform (d) of Fig. 10. This Q output serves as a signal Sl for effecting the ON-OFF control of the switch 21 of Fig. 7. The Q output of a reverse phase relative to the Q output serves as a signal S2 for controlling the switch 22.
The Q output and the output c of the comparator 43 are supplied to an XOR (exclusive OR circu1t) 48 and converted therein into an ON-OFF control signal S3 for the switch 23 as illustrated in the waveform (e) of Fig. 10. The control signal S- is ~n.erted by an inver-er 49 into an ON-OFF

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,: , - 13 - 'L31~7~7 control signal S4 for the switch 2~.
When the switches 21-24 of Fig. 7 are subjected to ON-OFF control using the switch control signals Sl through S4 obtained as described above, the output voltage is always made to equal the reference signal Vref because the phase difference 0 is increased and the output voltage is decreased in proportion as the output voltage applied to the load 4 is increased. When the reference signal Vref is in the form of a sine wave, so is the output voltage. And the same relation holds true when the reference signal is in the form of DC.
Fig. 8 is a bloc~ diagram illustrating another embodi-ment of this invention using bipolar (npn) transistors 21-24 as switching elements. Diodes 60-69 serve the purpose of enabling the transistors 21-24 to function as bidirectional switching elements.
In Fig. 8, while the secondary circuit of the high-frequency transformer 3H is identical with that of Fig. 7, the primary circuit thereof is different from that of Fig. 7 in respect that it uses switches 21 and 22 disposed in a half-bridge connection~
Capacitors 51 and 52 are serially connected to the DC
power source 1 and are severally charged to one half of the voltage of the DC power source to function as operating power sources respectively for the switches 21 and 22.
To the transistors 21 and 22 connected to the primary .

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- 14 - ~31~7~7 winding of the high frequency transformer 3H and to the transistors 23 and 24 connected to the secondary winding of the same transformer 3H, drive signals of such rectangular waveforms as illustrated in Sl and S3 of Fig. 10 are respectively supplied by the control circuit 9 via controlling transformers 31 and 32. As the result, a forward bias voltage is generated be-tween the base and the emitter of one of the transistors 21 and 22 so that, for example, the one transistor 21 will assume an ON state and the other transistor 22 an OFF state. To the primary winding of the high-frequency transformer 3H, therefore, the electric current of forward direction is supplied from the capacitor 51 via the transistor 21. When the driving signal is inverted, the transistor 22 assumes an ON state and the transistor 21 an OFF state conversely relative to the former case, with the result that the electric curr~nt of the primary winding of the high-frequency transformer 3H will be supplied in the reverse direction from the other capacitor 52 via the transistor 22.
In this case, since the two secondary windings of the controlling transformer 31, i.e. the base windings of the two transistors 21 and 22 are tightly coupled, if one transistor is turned on, a reverse bias voltaee is generated between the base and the emitter of the other transistor through the co~pl-ing of the secondary windings. Thus, the transistors 21 and 22 are never allowed to assume the state of electric conduction at . ' ' ` ~ ~

1311 ~7~7 the same time. This condition similarly applies to the transistors 23 and 24. Since the transistors serving as paired switching elements, therefore, are not required to provide any special dead time for preventing simultaneous occurrence of electric conduction therein, their switching frequency can be allowed highly increased. ~hile Fig. 8 depicts an embodiment using bipolar transistors as switching elements, FETs (field effect transistors) and other similar switching elements may be adopted instead without any difficulty.
In the embodiments of Figs. 4, 7 and 8, the capacitor 10 may be omitted when the harshness of the demand for the voltage waveform applied to the load is low or when the load is capacitive.
As clearly noted from the description given above, adoption of the power source of the type using a high frequency p~ase difference control as illustrated in Figs.
~, 7, or 8 permits the transformer serving for mutual insulation of the DC power source side and the load side to be rated for an higher frequency and to be constructed in decreased si~e and weight and enables the switching opsration heretofore effected with a complicate device to be carried out efficiently with a simple device, realizing an economic power source. Further, since the power source of the configuration of Fig. ~, Fig. 7, or Fig. 8 incorporates therein no unidirectlonal ci cuit element ,uch a: a diode or ;....................... : .

1 3 ~ 7 a rectifier, it enables the electric power to be transmitted in either direction and prevents the reactive power from glving rise to a surge voltage. When this power source is adopted as an uninterruptible power source, it of'fers an advantage that while the commercial power source is normally operating, it permits -the DC power source to be charged from the commercial power source.

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Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A power source of the type using a high-frequency phase control, which comprises:
a high-frequency transformer having a primary winding and a secondary winding, first and second switch means each connected at one terminal thereof to the opposite terminals of the primary winding of said high-frequency transformer and each connected at the other terminal thereof to the other, with the common point of connection of said first and second switching means being adpated for connection to a constant polarity source of voltage, and with there being a center tap in said primary winding of said high-frequency transformer adapted for connection to a reference source of voltage, third and fourth switch means each connected at one terminal thereof to the opposite terminals of the secondary winding of said high-frequency transformer and each connected at the other terminal thereof to the other, a reactor connected between the common point of connection of said third and fourth switch means and one of a pair of output terminals, a center tap of said secondary winding of saidh high-frequency transformer connected to the other of the pair of output terminals, a controlling device for effecting ON-OFF
switching control alternately of said first and second switch means and, at the same time, effecting ON-OFF switching control alternately of said third and fourth switch means with a selected phase difference with reference to the switching of said first and second switch means, said controlling device comprising:
an error amplifier for generating a deviation signal representing any deviation from a reference signal of any output voltage appearing between said pair of output terminals, a flipflop for generating a first rectangular wave controlling signal possessing an amply high-frequency as compared with the frequency of said reference signal and exhibiting a duty ratio of 1/2 and second rectangular wave controlling signal of a reverse phase relative to the phase of said first rectangular wave controlling signal, means for generating a triangular wave signal which is synchronized to the first and second rectangular wave controlling signals, a comparator for comparing the triangular wave and the deviation signal to generate a preliminary rectangular wave signal in response to the difference in their amplitude with a duty ratio depending on the amount of this difference, a logic circuit being supplied with the preliminary rectangular wave signal and one of the first and second rectangular wave controlling signals to provide third and fourth rectangular wave controlling signals of opposite phase and with a phase differing from that of the first and second rectangular wave controlling signal depending on the duty ratio of the preliminary rectangular signal, and means for effecting ON-OFF
control of said first through fourth switch means in accordance with said first through fourth rect-angular wave controlling signals.

2. A power source using high-frequency phase control according to claim 1, wherein a capacitor is connected between the pair of output terminals.

3. A power source using high-frequency phase control according to claim 1, wherein said logic circuit performs an EXCLUSIVE OR logic function.

4. A power source of the type using a high-frequency phase control, which comprises:
a high-frequency transformer having a primary winding and a secondary winding, first and second switch means each connected at one terminal thereof to the other to be in series, the other terminal of the first switch means being adapted for connection to a first constant polarity source of voltage, and the other terminal of the second switch means being adapted for connection to a second constant polarity source of voltage with the primary winding of said high-frequency transformer having a first terminal connected between the common points of connection of the first and second switch means and a second terminal adapted for connection to a reference voltage, third and fourth switch means each connected at one terminal thereof to the opposite terminals of the secondary winding of said high-frequency transformer and each connected at the other terminal thereof to the other, a reactor connected between the common point of connection of said third and fourth switch means and one of a pair of output terminals, a center tap of the second winding of said high-frequency transformer being connected to the other of the pair of output terminals, a controlling device for effecting ON-OFF
switching control alternately of said first and second switch means and at the same time effecting ON-OFF switching control alternately of said third and fourth switch means with a selected phase difference with reference to the switching of said first and second switch means, said controlling device comprising:
an error amplifier for generating a deviation signal representing any deviation from a reference signal of any output voltage appearing between said pair of output terminals, a flipflop for generating a first rectangular wave controlling signal possessing an amply high-frequency as compared with the frequency of said reference signal and exhibiting a duty ratio of 1/2 and a second rectangular wave controlling signal of a reverse phase relative to the phase of said first rectangular wave controlling signal, means for generating a triangular wave signal which is synchronized to the first and second rectangular wave controlling signals, a comparator for comparing the triangular wave and the deviation signal to generate a preliminary rectangular wave signal in response to the difference in their amplitude with a duty ratio depending on the amount of this difference, a logic circuit being supplied with the preliminary rectangular wave signal and one of the first and second rectangular wave controlling signals to provide third and fourth rectangular wave controlling the signals of opposite phase and with a phase differing from that of the first and second rectangular wave controlling signal depending on the duty ratio of the preliminary rectangular signal, and means for effecting ON-OFF
control of said first through fourth switch means in accordance with said first through fourth rectangular wave controlling signals.

5. A power source using high-frequency phase control according to claim 4, wherein a capacitor is connected between the pair of output terminals.

6. A power source using high-frequency phase control according to claim 4, wherein said logic circuit performs an EXCLUSIVE OR logic function.