GB2181576A - Interruption-free power supply arrangement - Google Patents

Abstract

A load 12 is normally connected to an A.C. supply 13, 14 via a switch 11 which then also connects the primary winding 4 of a transformer 1 to the supply for charging of a battery 6 via a secondary winding 3 and a rectifier 5. The charging voltage is controlled by means of a comparator 27 which compares the battery voltage with a reference to thereby supply pulse width modulated signals to a control winding 2 which controls the coupling between windings 4 and 3. The rectifier 5 comprises a diode bridge with each diode shunted by a respective transistor 18 to 21, the transistor being turned on at the peak of the A.C. supply. If the mains supply fails, the rectifier 5 acts as an inverter to supply A.C. to the load 12 and the load voltage is controlled by the control winding 2 which is energised in dependence on a comparison by comparator 27 of the load voltage with the reference voltage. <IMAGE>

Description

SPECIFICATION Interruption-free power supply arrangement The invention concerns an interruption-free power supply arrangement comprising a transformer which has a primary winding and a secondary wind ing,wherein connected to the secondarywinding is a rectifier circuit which feeds a battery,wherein an a.c.

voltage source which supplies a load can be applied bywayofaswitchtotheprimarywinding andthe load and wherein, in the event offailure ofthe a.c.

voltage source, the load can be supplied from the batter by way ofthe transformer, the a.c. voltage source being separted from the primary winding and the load by the switch and a control means in that situation controlling the powerflowing from the bat terytothe load.

lnterruption4ree power supply arrangements of thatkind are known. For example, German published specification (DE-AS) No 1803221 discloses an arrangement for interruption4ree power supply, in which a battery supplies a direct current in the event of mains failure. The direct current is converted by way of an inverter circuit into an alternating current which is applied to the load by way of a transformer.

Normally, the battery is charged by the power transmitted from the mains byway ofthetrans- former, by way of the inverter, in the other direction.

The arrangement includes a switch which then applies the a.c. voltage to the load. As soon as the a.c.

voltagefalls below a predetermined threshold value, the switch interrupts the connection between the mains and the load.

Asimilar interruption-free powersupply arrange- ment is disclosed in 'elektrotechnik', edition 22 of 23rd November 1984, in which, in the event of a mains fail u re, an a.c. voltage is generated from the d.c. voltage ofthe battery by way of a four-quadrant rectifier. In that arrangement, the rectifier comprises a diode bridge in which a transistor is connected in parallel with each diode, wherein the transistors are actuated in a pulse width-modulated mannerforthe purposes of generating an a.c. voltage by a control circuit with a high clock frequency.

The problem of the present invention is that of providing a practicableviable interruption-free power supply arrangement in which, in the event offailure ofthe a.c. voltage orthe mains, the arrangement switches over automatically and as rapidly as pos sible, thereby to provide that the a.c. voltage is disconnected from the load and the load is supplied by the battery with the same phase angle. The invention further seeks to provide that the power supply arrangement requires a lower level of expenditure in regard to the electronics and can thus be produced more economically and also requires a small amount of space.

That problem is solved by an interruption-free power supply arrangement in which the transformer has a control winding to which can be applied a control signal for controlling the coupling between the primarywinding and the secondary winding ofthe transformer, and the control means generates the control signal in dependence on a comparison between a referencevalueand an actual value which represents the voltage ofthe battery or the a.c. voltage applied to the load.

A major advantage of the present invention is that the interruption-free power supply arrangement which in the normal situation operates in such a way thatthe load is supplied directlyfrom the mainsand the battery is charged by way ofthe transformer in the rectifier mode, permits immediate disconnection ofthe mains in the event offailure thereof, and provides for immediate and automaticsupplytotheload from the battery in the inverter mode by way ofthe transformer. Immediate disconnection ofthe mains is advantageous because the failed mains can give rise to a short-circuit. Advantageously, the present interruption-free power supply arrangement can be constructed at low cost, by virtue of the simplicity of its construction.In particular, the control means which is used in the power supply arrangement according to the invention is of an extremely simple design.

Advantageously, the inverter and rectifier losses are significantly reduced in the normal mode of operation. For that reason, the problems and costs involved in removing the heat due to losses are only slight, in comparison with conventional arrangements.

In a preferred embodiment ofthe arrangement according to the invention for interruption-free power supply, a bridge rectifier with diodes, or a full-wave rectifier, is used as the rectifier circuit.

Because each diode ofthe rectifier circuit has connected in parallel therewith an electronic switch which is preferably a transistor, wherein the elec tronicswitchesarecontrolled by the control circuit by clock signals generated by a clock generatorsyn chronously with respect to the frequency of the a.c.

voltage, in such a waythatthe respective electronic switches connected in parallel to the diodes which are then in a conducting condition, conduct during the corresponding alternations, and the switches connected in parallel with the diodes which are not conducting are in a non-conducting condition, that arrangement advantageously provides that, in the event of a mains failure, energy flows from the battery to the secondary winding of the transformer automatically and immediately by way of the elec tronic switches. A particularly low level of alternating current loading on the battery can be achieved by the corresponding electronic switches being switched into a conducting condition in the charging operation only in the region ofthe peakvalue ofthe a.c. voltage.

A particularly simple and advantageous develop ment of the present invention is one in which the control circuit comprises a comparator, wherein a voltage corresponding to the reference value is applied to one input ofthe comparator and a voltage corresponding to the actual value is applied to the other input. Inthatcase,asignal which is pulsewidthmodulated bythe ripple component of the actual value then appears as the control signal at the output ofthe comparator. When a pulse of that control signal is present, in a development of the invention, the current of an auxiliary voltage source is sent through the control winding of the transformer, by way of a transistor circuit.Preferably, that arrangement has free-wheel diodes which demagnetisethe inductance ofthe control winding by way of the auxiliaryvoltage ofthe auxiliary voltage source when the control signal is zero in value. That can ensure symmetrical characteristics in regard to the rise and fall of current in the control winding.

The clock signalsfor actuation ofthe electronic switches which are connected in parallel with the diodes of the rectifier circuit are preferably generated by a clock generator which is synchronised with the a.c. voltage and which includes a counter which is started by the respective passages th rough zero of the a.c. voltage and which generates the clock signals atthe even intheeventofmainsfailurein proper time relationship at predetermined counterconditions. That ensures that, in the event of mains failure, the electronic switches continue to be clockcontrolled in the appropriate manner.

In orderto detect the failure ofthe a.c. voltage, it is particularly advantageous for the control means to comprise a retriggerable monoflop which istrigge- red by the passages through zero ofthe a.c. voltage.

The monoflop has a hold time which is greaterthan the time corresponding to an alternation of the a.c.

voltage.

The invention is described in greaterdetail hereinafterwith reference to Figures 1 to 3 in which: Figure Ishowsthecircuitdiagram of an interruption-free power supply arrangement according to the invention, Figures 2A to 2Care diagrams clearly showing the generation ofthe control signal, Figure3shows a possible embodiment of a load or mains disconnection switch, and Figure4shows a detail of the interruption-free power supply arrangement.

The present interruption-free power supply arrangement essentially comprises a transformer 1 which has a control winding 2, a secondary winding 3 and a primary winding 4, a rectifier circuit 5 which is connected between the secondary winding 3 and a battery 6, a switch 11 which normally connects an a.c.

voltage source orthe mains 13, 14to the load 12 and the primarywinding4, and a control circuit 15which hasa logic control means 16which generatesthe control signal forthe control winding 2 and clock signals for operation of the rectifier circuit.

In the normal situation,the load 12 its supplied dir ectlyfromthe mains 13,14, forexample with an a.c.

voltage of 220 V, by way ofthe switch 11. At the same time, the a.c. voltage of 220 V is applied by way of the switch 11 to to the totheprimarywinding4ofthetransformer 1 and is transmitted by waythereofto the secondary winding 3, underthe control ofthe control signal applied to the control winding 2. In that case, in perse known fashion, the coupling factor ofthetransformer 1 is varied between 0 and 1 in dependence on the magnitude ofthe control signal applied to the control winding 2, the generation of which control signal will be described in greater detail hereinafter.

To put that more precisely, the coupling between the primarywinding 4 and the secondarywinding 3 is varied by partial saturation oftheflux-carrying circuits in dependence ofthe magnitude of the control current at the control winding 2. Desirably, the coupling factor increases as the control signal becomes smaller.

The alternating current which flows through the secondary winding 3 is rectified by the rectifier circuit 5 which is preferably a bridge rectifier consisting of the diodes 7 to 10, and passed to the battery 6. The battery is in that way always charged up to its maximum value in the normal condition. In that case for example a current flows by way ofthe diodes 8 and 9 to the battery 6 during the one half-wave of thealternating current flowing by way of the secondary wind- ing 3. The diodes 7 and 10 are in a non-conducting condition during that alternation. The direction of flow of the current is indicated by the arrows 22.During the other alternation, during which the diodes 9 and 8 are in a non-conducting condition, the current flows as indicated by the arrows 23 to the battery 6 by wayofthediodes7and 10.

An electronic switch, preferably a transistor 1 to 21, is connected in parallel with each of the diodes 7 to 10, in the manner shown in the drawing. Thetransistors 18 to 21 which are desirably bipolartransistors are controlled in accordance with the flows ofcurrent 22 and 23 by clock signals which are generated bya clock generator35 in the logic control means 16, which is synchronised by the a.c. voltage. Accordingly, while the current flows in the direction 22, the transistors 19 and 20 are switched into a conducting condition so that they by-pass the diodes 8 and 9.At the same time the transistors 18 and 21 which are connected in parallel with the diodes 7 and 1 Owhich are then non-conducting are put into anon- conducting condition. While the currentflows in the direction 23,thetransistors 18 and 21 are conducting andthetransistors 19 and 20 are in a non-conducting condition. The clock signals of the clock generator 35 are generated synchronouslywith the a.c. voltage of the mains 13 and 14 and continue to be generated continuouslyafter mainsfailure. The a.c. voltage is applied to the logic control means 16 byway ofthe terminals 13' and 14'.The clock generator35 prefer- ably comprises in perseknown manner a counter which is started up by the respective passages through zero of the a.c. voltage, the clock signalsfor the transistors 18,19,20,21 being generated in the proper time relationship at predetermined counter conditions. The passages through zero of the a.c. vol- tage are preferably detected by monoflops generating suitabletriggersignals.

For actuation purposes, the control electrodes 18' to 21 ' of the transistors 18to 21 are connected to the outputs 18" to 21" ofthe clock generator 35 ofthe logic control means 16.

In the event a mains failure, the direction of energyflow is automatically and immediately reversed by a currentflowing from the battery 6 to the secondary winding 3 by way of the transistors 18to21 which are actuated in the above-described manner.

To put that more precisely, a current flows from the battery 6 to the secondary winding 3 by way for ex ample of the transistors 19and 20 during one half phase. During the other half-phase, a currentthen flows to the secondary winding 3 byway ofthetrans- istors 18 and 21. The rectangularwavewhich istrans mitted in that way in the event of mains failure from the battery6 bywayofthetransistors 19 and 20 or 18 and 21 respectively to the secondary winding 3 and from there to the primarywinding 4 precisely corresponds in respect of its phase position to the corresponding alternation ofthefailed alternating current.

Although the associated effective value of the rectangularwave is clearly lowerthan the nominal value of the mains voltage (220 V effective), the peak value ofthe rectangular wave is however sufficiently accurately coincident with the mains voltage so that the period at which the mains failure occurs appears to be entirely normal, in regard to the load 12 which is connected to the primary winding 4. Inthesubse- quent periods, the control circuit 15 switches over to the a.c. voltage effective value (220 V effective) by virtue ofthe actuation ofthe control winding 2. For that purpose, to alter the coupling of the transformer 1,the control winding 2 is operated in such a way that an effectivevalue of 220V is always supplied tothe load 12 by way of the primary winding 4.

Before describing the electronic control system 15, itwill be further pointed out that the switch 11 is switched oversimultaneouslywith the failure ofthe mains sothatthe mains 13 and 14 isdisconnected from the load 12 and the primary winding 4, whereby the load 12 isconnected solelytothe primarywind- ing 4. That is necessary as the failed mains 13 and 14 could give rise to a short-circuit. The disconnection switch 11 is actuated by the logic control means 16, byway of the line 24. For that purpose, the logic control means 16 preferably includes a retriggerable monoflop 37 with a hold time of for example 11 ms.

When that monflop 37 is no longer triggered by the sig nals at the passage th rough zero of the a.c. vol- tage, the switch 11 is actuated.

The control circuit 15 operates in the following manner: the actual value corresponding to the voltage ofthe battery 6 is supplied to the logic control means 16 byway of the line 25 which is connected to the rectifier circuit 5. The actual value which corresponds to the a.c. voltage is applied to the logic control means 16 by way ofthe input terminals 12".

The logic control means 16 also receives a reference value in respect ofthe power to be produced bythe battery 6. A d.c. voltage signal corresponding to that reference value appears at the output 26 of the logic control means 16 or at the input of a comparator 27. A voltage signal which corresponds to the actual value appears at the other input of the comparator 27 or at the output 28 of the logic control means 16. Depending on the direction in which the present arrangement is operating, that actual value is generated from the actual value ofthe battery voltage atthe line25or the actual value ofthe load a.c. voltage attheter minals 12".That means that, when charging the bat- tery 6, the coupling factor of the transformer 1 is determined in dependence on the actual value which is representative of the battery voltage and in the event of mains failure it is determined in dependence on the actual value which is representative of the load a.c. voltage. The actual value attheterminal 28 has a ripple component of about 1% or less, both when it is supplied from the battery side and also when it is supplied from the load side. That ripple component provides for pulse width modulation with the con stant reference value which occurs at the output 26.

That will be described in greater detail hereinafter with reference to Figures 2A to 2C.

In Figure 2A, the half-waves at the bridge rectifier are identified at 40, forthe battery charging operation. The voltage which occurs on the line 25 and which is applied as the actual value to the input 28 of the comparator 27 and which is determined by the charge condition ofthe battery 6 and the peaks ofthe half-waves at the bridge rectifier is in the configuration ofthe continuous line 41. It includes a ripple componentof about 1%, in dependence on the battey charge condition.

Figure 2B showsthe referencevalue 42 and the curve 41.

In Figure 2C, rectangular pulses whose width is re spectively determined by the duration for which the peaks of the curve 41 project beyond the reference value 42 in Figure 2B occur atthe output 29 ofthe comparator 27. Itwill be appa rent that the greaterthe amplitudes ofthe peakvalues ofthecurve 41 (ripple component), the greater is the pulse width.

The variable-pulse width rectangular signal which occurs at the output 29 of the comparator 27 is applied as a control signal to the control winding 2 of the transformer 1. Preferably, that variable pulse-width control signal is applied byway of the transistors 30 and 31 to the control electrodes ofthe transistors 32 and 33. When the transistors 32 and 33 are switched on by the control signal, a currentflows by way of those transistors 32 and 33 from the potential source U by way ofthe control winding 2 to earth. When a zero voltage occurs at the output 29 of the comparator 27, the transistors 30 to 33 are switched into a non-conducting condition.The inductance ofthe control winding 2 is then demagnetised against the force of the auxiliary voltage U by way of the perse known free-wheel diodes 34. That mode of operation ensures symmetrical characteristics in respect of current rise and currentfall as the same driving elec tromagnetic force occurs for both modes of operation. The mean value which occurs in the control winding 2 is predetermined in accordance with the requirements of the working point of the control circuit by way of the mean value of the rectangularvoitage. The coupling factor of the transformer 1 is reduced in the range between 0 and 1 in the event of an increase in the pulse width ofthe rectangular pulses (Figure 2C), that is to say therefore when there is an increase in the battery charge, and vice-versa.

When the load 12 is supplied by the battery, the processes shown in Figures 2Ato 2C occur atthe comparator, but the curve 41 corresponds to the ripple component of a voltage which is generated from the a.c. voltage occurring at the load 12, for det- ecting the effective value, by rectification and smoothing.

The load disconnection switch 11 is for example in the form ofthe electronic switch shown in Figure3.A diode bridge 45 is connected in front of the mains terminal 13. When the cross tra nsisto r 44 is in a closed condition, the current flows either in the direction indicated by the arrow 46 or in the direction indi cated by the arrow 47, in dependence on the alternation ofthe alternating current. As soon as thetransis tor 44 is switched off in the event of mains failure, current can no longer flow by way of the diode bridge 45 and the mains system is separated from the primarywinding 4andthe load 12. The control electrode ofthe transistor 44 is actuated for example by way ofthe retriggerable monoflop which has already been referred to hereinbefore.

Preferably, the transistors 18 to 21 are actuated during the charging operation only in the vicinity of the peak value of the sinusoidal a.c. voltage. That provides for a lower level of alternating current loading at the battery 6. Instead of the bridge rectifiercir cuit 5, it is also possible to use other rectifier circuits, for example a full-wave rectifier.

Figure 4 shows a preferred embodiment of a circuit fora logic control arrangement as shown in Figure 1.

The circuitsuppliesthe actuating signals 1 18to 121 for a power semiconductor in the inverter bridge (transistors 18 to 21 in Figure 1), provides for mains failure detection and switches over the controller feedbackfrom the direct current circuit to the a.c. circuit. Synchronised reconnection is effected in the event of mains restoration.

A clock generator 135 generates a clock frequency with a multipleof50 Hz. That signal is supplied asa clock signal to a ring counter 122whose maximum counter condition corresponds to that multiple. A group of higher-significance bits ofthe counter output signal is fed to a corresponding number of inputs of an AND-gate l23whichthusformsawindow discriminator and which transmits a signal fed to its further input only in a given phase region ofthe counting cycle. Inthatelectrical phase region of 330 to 360 degrees, synchronisation is effected with the mainsfrequencybytheoutputsignal ofanAND-gate 124 which will be described hereinafter. That circuit is an arrangement of the PLL-type.In the event of failure ofthe synchronisation signals, control ofthe invertertransistors is continued in accordance with the phase position ofthe last-detected passage through zero ofthe mains voltage at 50 Hz.

The power output stages of a driver unit 125 dir ectly actuate the transistor switching modules and are activated by the output signal of the counter 122 byway of an AND-gate 126.

A rectangularvoltage is generated from the mains signal 13', by 14', by means ofafull-wave rectifier 128 which is connected on the output side of a transformer 127, and a threshold value discriminator 129.

The rectangularvoltage produces the synchronisation signal for the counter 122, in the positive pas sages through zero ofthe mains sinusoidal curve. In that case, the positive slope in the passage through zero is detected by means of a differentiator 130 which in that case outputs an output signal to the AND-gate 124 which, with that signal, is in a transmitting condition forthe output pulses of the discriminator 129, which occur during the passages through zero.

The output signal of the rectifier 128 passes to a change-over switch 131 which, in the position of 'fixed pulse width', feeds that signal byway of a further change-over switch 132 which in the event of mains failure goes into the corresponding position to the inverting input of the operational amplifier or comparator 27 (as shown in Figure 1) so that it is compared to a fixed signal level Uref at the noninverting input of the comparator 27 and when the level of the existing mains voltage is exceeded the battery 6 is charged during the peakvalues. The transistor switching modules are thus switched on in the charging operation only in the vicinity ofthe peak value ofthe sinusoidal voltage. That thus provides fora lower level of alternating current loading atthe buffer battery.Controlled charging ofthe battery occurs in the other position of the switch 131 in which the battery voltage '+' is fed to the operational amplifier 27 and compared to Uref so that the abovedescribed control action by means of the 'ripple component'takes place.

A retriggerable monoflop 133 with a hold time of 11 msservesasthe discriminatorformainsfailure. If it is no longer triggered by the passage-through-zero signals from the output ofthe circuit 129, the con trollerfeedbackfrom the direct current side to the alternating current side is switched over and a full 180 degrees phase region is freed for the inverter in each alternation, for operation of the transistor switching bridge. That change-over switching action is effected by the switch 132 which in that case feeds the inverting input ofthe operational amplifier27 with the load voltage Lwhich is only moderately smoothed by a filter member 134.

Atransformer construction as set forth in German laid-open application (DE-OS) No 3423 160 is particularly advantageously suitable for the interruptionfree power supply arrangement according to the invention.

Claims (11)

1. An interruption-free power supply arrangement comprising a transformer which has a primary winding and a secondary winding, wherein connected to the secondary winding is a rectifier circuit which feeds a battery, wherein an a.c. voltage source which supplies a load can be applied by way of a switch to the primarywinding and the load and wherein, in the event of failure of the a.c. voltage source, the load can be supplied from the battery by way ofthe transformer, the a.c. voltage source being separated from the primary winding and the load by the switch and a control means in that situation controlling the power flowing from the battery to the load, characterised in that the transformer has a control winding to which can be applied a control signal for controlling the coupling between the primary winding and the secondary winding ofthetrans- former, andthatthe control means generates the control signal in dependence on a comparison between a reference value and an actual value which representsthevoltageofthe batteryorthea.c.vol- tage applied to the load.

2. An arrangementaccording to claim 1 characterised in that the rectifier circuit is a bridge rectifier having diodes.

3. An arrangement according to claim 2 characterised in that an electronic switch is connected in parallel with each diode and that the electronic switches are controlled by the control circuit by means of clock signals generates by a clock generator synchronously with respect to the frequency of the a.c. voltage, in such a way that the electronic switches connected in parallel with the diodes which are respectivelythen conducting conductduringthe corresponding alternation and the switches which are connected in parallel with the diodes which are not conducting are in a non-conducting condition.

4. An arrangement according to claim 3 characterised in that transistors are provided as the electronic switches.

5. An arrangementaccording to claim 3 orclaim 4 characterised in that the corresponding electronic switches are switched into a conducting condition in the charging operaiton only in the region of the peak value of the a.c. voltage.

6. An arrangement according to one of claims 1 to 5 characterised in that the control circuit comprises a comparator wherein a voltage corresponding to the reference value can be applied to one input ofthecomparatorandavoltagecorrespondingtothe actual value can be applied to the other input ofthe comparator, and a signal which is pulse widthmodulated by the ripple component ofthe actual value occu rs at the output of the com parator as the control signal.

7. An arrangement according to one of claims 1 to 6 characterised in that the current of an auxiliary voltage source is sent through the control winding, when there is a pulse of the control signal, by way of a transistor circuit.

8. An arrangement according to claim 7 char- acterised in that there are provided free-wheeling diodes which demagnetisethe inductance ofthe con trolwinding by way of the auxiliary voltage of the auxiliary voltage source when the control signal is of a value zero.

9. An arrangement according to one of claims 3 to 8 characterised in that the control circuit comprises a clock generator for generating the clock signals, which is synchronised with the a.c. voltage and which includes a counter which is started by the respective passages through zero of the a.c. voltage and which generates the clock signals even in the event of mains failure in propertime relationship at predetermined counter conditions.

10. An arrangementaccording to one of claims 1 to 9 characterised in that the control means (detecting mainsfailure) has a retriggerable monoflop which is tripped by the passages through zero ofthe a.c. voltage and which has a hold time which is greaterthan the half period of the a.c. voltage.

11. An interruption-free power supply arrange ment substantially as described with reference to the drawings.