GB1604305A - Method for the control of the electric power supplied from an alternating-current main to a consumer and an apparatus for carrying out the method - Google Patents

Abstract

In regulating power by phase control, the deviations of the load current from the sinusoidal variation should be small and occur at a high frequency so that they can be suppressed by simple filters. For this purpose, the on time is controlled with high keying frequency over each half wave of the alternating mains voltage, in such a manner that the mean value of the switched current tracks a sinusoidal wave. A nominal sinusoidal voltage is generated by means of a first circuit arrangement (R5, R6, P2, R7, G2). An actual voltage is derived from a load current by means of a second circuit arrangement (R1, G3). A comparison circuit (V2) outputs an output signal when the actual voltage is greater than the nominal voltage. A pulse oscillator (10) outputs high-frequency square wave pulses to the set input of a flip flop (FF), the reset input of which is connected to the output of the comparison circuit. The output signal of the flip flop (FF) controls a semiconductor switch (T1) which is connected to one arm of a rectifier bridge (G1), the other arm of which is located in the load circuit. An output signal of the flip flop (FF), generated in the set state of the flip flop (FF), keeps the semi-conductor switch (T1) in its conducting state. <IMAGE>

Description

(54) METHOD FOR THE CONTROL OF THE ELECTRIC POWER SUPPLIED FROM AN ALTERNATING-CURRENT MAIN TO A CONSUMER AND AN APPARATUS FOR CARRYING OUT THE METHOD (71) I, PAUL HAHN EVERS, of Danish Nationality, of Castelletto di Pura, 6984 Pura, Switzerland, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method for the control of electric power supplied from an alternating current main to a consumer by the control of the relative duration of voltage application. The invention further relates to an apparatus for carrying out that method.

Known methods for achieving this result employ a control of the current flow angle according to a phase shifting method, where in each half cycle of the main voltage the current flow interval may stretch either from a certain time after the main voltage passes through zero to the subsequent pass through zero, or from passing through zero to a certain time before the subsequent zero pass. Such methods suffer from the disadvantage that the harmonic content of lower number is undesirably or unacceptably high. This characteristic necessitates extensive filtering in order to meet standards, for instance that of the European Standard EN 50 006.

It is an object of the present invention to produce a method of the kind described heretofore wherein the deviations of the consumer current from the sine curve are at most of such high frequency that their reduction for the suppression of main disturbances is possible by simple ffltering measures.

According to a first aspect of the invention there is provided a method for controlling the electric power provided from an alternatingvoltage main to a consumer by controlling the relative duration of voltage application by means of a power switching arrangement connected in the current path to the consumer, and comprising continuously measuring the current supplied to the consumer, deriving a voltage from the measured current, comparing the derived voltage with a variable reference voltage derived from the main alternating voltage, said reference voltage having the main frequency and being at least substantially of sine wave form, and switching off the power switching arrangement with a cycle frequency which is substantially higher than the mains frequency during each half-wave of the main alternating voltage when the voltage derived from the measured current has a higher magnitude than the reference voltage.

According to another aspect of the invention there is provided apparatus for controlling the electric power provided by an alternatingcurrent main to a consumer by means of a bridge rectifier,. whose one diagonal is connected in series to the consumer and to whose other diagonal a controlled semiconductor switch is connected and comprising a first circuit arrangement for producing a rated voltage having at least substantially half sine wave configuration; a second circuit arrangement for tapping an actual voltage from the consumer current; a comparison circuit, connected to both said circuit arrangements, which provides an output signal when the actual voltage is higher than the rated voltage; a pulse oscillator for the production of rectangular pulses whose frequency is substantially higher than the main frequency; and a storage device whose set input is connected to the output of the pulse oscillator, whose reset input is connected to the output of the comparison circuit and whose output is in connection with the semiconductor switch in such a way that an output signal from the storage device generated in the set state thereof maintains the semiconductor switch in its conducting state.

An embodiment of the invention will now be described by way of example with reference to and as illustrated in the accompanying drawings wherein: Figure la shows a diagram of the harmonics of the voltage of a disturbed alternatingcurrent main Figure lb a diagram of the harmonics of the current of fluorescent lamps which are connected as consumers to the alternating-current main of Figure 1 a, Figure 1 c is a diagram of the harmonics of the same current when the method in accordance with the invention is used, Figure 2 shows a circuit scheme of an arrangement for carrying out the method in accordance with the invention, Figure 3 a diagram of the voltage course in time in an assumed disturbed altematingcurrent main, Figure 3b is a diagram of the voltage course in time at the output of a first rectifier circuit of Figure 2 to discharge a rated value, Figure 3c a diagram of the voltage course in time at the output of a second rectifier circuit of Figure 2 to discharge an actual value, Figure 4a a diagram of the voltage course in time at the output of a pulse oscillator of Figure 2, Figure 4b a diagram of the voltage course in time at the output of a differential circuit of Figure 2, Figure 4c a diagram of the voltage course in time at the output of a bistable flip-flop circuit of Figure 2, Figure 4d shows a diagram of the voltage course in time on a measuring rheostat for the current of the alternatingcurrent main, Figure 4e a diagram of the voltage course in time on a measuring rheostat of Figure 2 for the collector current of a semiconductor power switch of Figure 2.

In Figure la the harmonics with order number n of the voltage E of an alternatingcurrent main are shown as they can be generally found. In view of this considerable harmonics content no sine-shaped current drain of a consumer connected to the main may be expected without special measures being employed. This is made clear by Figure ib which presents the actually measured harmonics of the current I of parallel-compensated fluorescent lamps which are connected to the main of Figure 1. The harmonics content is, when compared with Figure la, again noticeably higher.

In Figure ic the harmonics of the current I for the same main and the same consumer are shown, this time however with the application of the method in accordance with the present invention or with the interconnection of a power switch arrangement working in accordance with the method of the present invention and with the reduction of the consumption to 50% of the rated value. Here it is perhaps somewhat surprising to note that the content of harmonics of low order n is substantially reduced. There are harmonics of higher order, although of a relatively smaller amplitude.

These harmonics are particularly of the order around 100 and 200, which are conditioned in the embodiment to be described hereafter by control time constants and by a selected switch frequency of around 10 kHz. This disturbance may, however, be reduced to bearable values by using an input filter to be described hereafter.

The arrangement for carrying out the method in accordance with the present invention shown in Figure 2 includes a power switch arrangement by means of which a consumer may be connected to this alternatingeurrent main for a period which is variable by one halfwave of a supplying alternating-current main in such a way that a consumer current is obtained, which consumer current is at least approximately sine-shaped and has a minimum content of harmonics of the low order number in relation to the main frequency.

Terminals V, to which the consumer may be connected, are connected with main terminals N via one of the diagonals of a bridge-rectifier G1, which bridge-rectifier has in each branch one or more diodes. A main input filter, provided with a choke L1 and two capacitors C1, C2 as well as a current measuring rheostat, is connected to the circuit joining the consumer terminals V with the main terminal N. The main terminal N, which is assigned to the neutral conductor of the alternatingcurrent main, is connected with the earth of the arrangement via a reference line B1.

To the other diagonal of the bridge-rectifier G1 the collectoremitter path of a Darlingtontransistor T1 is joined via a choke L2 and a further current measuring rheostat R2. The base of the transistor Tl is connected with its emitter via a resistor R3. For the control of the transistor T1 its base is connected with the output of an integrated complementary driver T2 via a limiting resistance. The choke L2 limits the rate of the current rise at the control of the complementary driver T2 and the corresponding collector current course of the transistor T1. In order to avoid voltage peaks, a free-wheel diode D1 is switched in parallel to the choke L2.

The control of the driver T2 takes place separately from the voltage via a first optocoupler K1.

The voltage on the measuring rheostat R2 in relation to the emitter of the transistor T1, where the voltage is proportional to the collector current of the transistor Ti , is applied to one of the inputs of a differential circuit V1. On the other input of the differential circuit V1 a reference voltage is applied, which reference voltage is tapped from the negative feed current of the complementary driver T2 via a setting potentio-meter P1. The output signal of the differential circuit V1 is connected, via a second optocoupler K2, to a control logic to be described hereafter, thereby serving to limit to an adjustable maximum value the collector current of the transistor Tl.

The illustrated power switch arrangement operates in such a way that, during each halfwave of the alternating-current main when the transistor Tl is switched to the conducting state, the current of the alternating-current main always flows from one of the main terminals N via the choke L1 of the main input filter, a diode of the bridge-rectifier Go, the choke L2, the collector-emitter path of the transistor Tri, the measuring rheostat R2 and a second diode ofthe bridge-rectifier G1 to the customer, connected to the terminal V, and back via the measuring rheostat to the other main terminal N, or in the reverse direction respectively. If the transistor T1 is closed in all other intervals of each half-wave, then no current flows to the consumer.

In the arrangement illustrated in Figure 2 for the production of the desired load current of the consumer a reference input, which has at least an approximately sine-shape, is tapped off and compared with an actual load current value of corresponding size, the result of that comparison serving in one cycle, whose frequency is substantially higher than that of the main frequency, to control the transistor T1.

For tapping the said reference input between the phase conductor, joined via the main terminal N, and the neutral conductor of the feeding alternating-current main a frequency dependent voltage divider is switched which covers the series connection of the resistors R5, R6, R7 and potentiometer P2, where the resistor R5, which is joined to the phase conductor via a fuse S, is connected via a capacitor C3 with the neutral conductor. The voltage tapped off the potentiometer P2 is fed via a resistor R8 to the input of a rectifier circuit G2, which contains an operational amplifier O1 and, in its return lead, two diodes D2, D3 and a resistor R9. The output of the rectifier circuit G2 is connected with the input of a differential circuit V2.

For the tapping of the input, corresponding to the actual value of the load current, the voltage measured on the rheostat R1 in relation to the potential of the neutral conductor of the alternating-current main or the earth of the present arrangement respectively is fed via a filter section, including two resistors and a capacitor C4, to the input of a second rectifying circuit G3, which also includes an operational rectifier 02 and, in its return lead, two diodes D4, D5 and a resistor R12. The output of the rectifier circuit G3 is connected with the other input of the differential circuit V2.

When the output voltage of the rectifier circuit G3 (which is derived from the actual value of the load current) reaches, on the second said input of the differential circuit V2 at the first said input of the differential circuit G2, the output voltage of the rectifier circuit G2 which is derived from the main alternating voltage as a function of frequency, then at the output of the differential circuit V2 a corresponding pulse signal appears which is fed to a bistable switch FF, which in an especially preferred embodiment may be a flip-flop, as reset signal. The set input of the flip-flop switch FF is connected with the output of a pulse oscillator 10, which oscillator 10 includes, for instance, a comparator V3 in a way known in itself, one of the inputs of that comparator being joined to a voltage divider of a reference direct voltage, including the resistors Ri 3, R14, R15, and the other input of that comparator being joined to a discharge member which includes the series connection of a resistor R16 and a capacitor C5. The frequency of the rectangular pulses generated by the pulse oscillator IO is, for instance, 10 kHz and its keying ratio, for instance, 50 to 50. The output signal of the flip-flop switch, which has a keying ratio changed in accordance with the measure of the output signal of the comparators V2, is fed to the light emitting element of the opto-coupler K1 and controls accordingly the complementary driver T2 and with it the Darlington transistor T1. .

Furthermore the light receiving element of the opto-coupler K2 is joined to that input of the differential circuit V2 to which the signal derived from the actual value of the load current is fed. This signal, corresponding to the maximum collector current of the transistor Tl set on the potentiometer P2, resets the bistable flip-flop switch FF via the opto-coupler K2 prematurely when the collector current reaches the maximum value.

The feed and auxiliary voltages for the two described circuit parts of the present apparatus, which are separated galvanically by the optocouplers K1 and K2, are also produced separately by the rectifying and filtering circuit G4, which is connected to the alternating-current main via a fuse S. Here the auxiliary voltages +El and -El (e.g. +6V), provided for the described control logic, are referenced via the reference lead B1 to the potential of the neutral conductor of the alternatingcurrent main and the other auxiliary voltages +E2 and -E2 (e.g.

+6V), provided for the power control, are referenced via a reference lead B2 to the emitter of the transistor T1.

The mode of operation and the effect of the apparatus described with the aid of Figure 2 is explained hereafter with the aid of the diagrams of current and voltage courses as shown in Figures 3 and 4.

Figure 3a shows the voltage curve of a disturbed alternating- current main as it is often observed in practice. Here it is shown how, at the time tl of a half-wave of the main alternating voltage, a disturbance takes place.

Figure 3b shows the corresponding voltage curve at the output of the rectifier circuit G2 which provides the reference input (that is the rated vlaue) for the differential circuit V2. As a result of the filtering measures undertaken with the aid of the capacitor C3 before the "ideal" rectifying with the rectifier circuit G2, which circuit contains the operational amplifier 01, the deviation from the sineffhaped ideal curve is suppressed at time ti . This has the consequence that the power switch arrangement described heretofore also has a filtering effect against the harmonics of the main via the comparison of actual value with rated value and the corresponding connecting of the consumer to the main. By the described comparison in the differential circuit V2 the swftchingon duration of the transistor T1 is extended when surges are present in the main alternating voltage or shortened respectively, when an overswing occurs. This raises the question whether it is sensible to draw current propor tionally to the voltage by means of circuitry measures, such as the arrangement and sizing of capacitors C3, or whether a non-linear behaviour with positive and negative signs seems expedient. The course of the reference input illustrated in Figure 3b is based on the assumption that by means of the capacitor C3, arranged in the voltage divider R5, R6, P2, R7 of Figure 2, at least approximately the originally expected sine-shaped course of the current should be achieved.

Figure 3c shows the voltage curve at the output of the rectifier circuit G3, where the dotted sine curve indicates that the corres ponging current curve has, when the cycle frequency (frequency of the pulse oscillator IO) is kHz, wthin each half-wave of the main current harmonics in the region of the 100th and 200th harmonics, due to the cyclic switch ing on and off of the transistor T1. From .Figure lc the size of these harmonics may be seen, their effect is damped by the main input .filter C1, C2, L1 of Figure 2.

In Figures 4a to 4e the time curve of various signals of the arrangement of Figure 2 is shown in the region of time tl of Figure 3a, that is at a scale extended in time.

Figure 4a shows the curve of the output voltage of the pulse oscillator IO, which generates rectangular pulses with constant fre quency and a cycle ratio of 1. It is also possible to provide a changing or additionally controlled pulse frequency. Under the effect of the reference input derived from the main alter naming voltage this cycle ratio is shifting, as is illustrated hereafter.

Figure 4b shows the curve of the output signal of the differential circuit V2, that is the result of the comparison of the reference input (reference voltage) with the actual value derived from the measured current value. When the output signal of the rectifier circuit G1 exceeds that of the rectifier circuit G2, at the outlet of the differential circuit V2 the pulse-shaped signal shown in Figure 4b appears, which signal resets the bistable flip-flop switch FF.

Figure 4c shows the output signal of the bistable flip-flop switch FF which receives the output signal of the pulse oscillator IO as setting signal and the original signal of the differential circuit V2 as resetting signal. From this it can be seen that an effective output signal as fed to the opto coupler Kl is always present until a reset signal arrives from the differential circuit V2, subsequently to which the next effective output signal commences as soon as fed to the opto-coupler K1 is always present until a reset signal arrives from the differential circuit V2, subsequently to which the next effective output signal commences as soon as the next cycle pulse of the pulse oscillator IO arrives as setting signal. The output signal of the bistable flip-flop switch FF is fed via the optocoupler K1 to the control input of the complementary driver T2 which provides a corresponding controlling or clearing current respectively for the power transistor T1. Subsequently, the control current of the transistor Tri, which connects or separates respectively the consumer with the alternating-current main, follows up in pulse the main alternating voltage corrected by the capacitor C3 and adjusted by the potentiometer P2.

Figure 4d shows the course of voltage in time on the measuring rheostat of Figure 2, again in the region of time tl of Figures 3a to 3c. It can be seen that the current is wavy, caused by the irregular conducting intervals of the transistor, this waviness being flattened by the main input filter Cl, C2, L1. Furthermore, it may also be seen from the presentation extended in time that, according to Figure 3b, the current increases in the mean, that is in correspondence with the reference input.

Figure 4e shows the time curve of the voltage on the measuring rheostat R2 of Figure 2 shaded, this represents the course of the collector current of the transistor T1. The maximum values of the voltage and current pulses lie on a dotted curve, which is a function of voltage and/or load. From Figure 4e also the effect of the choke on the moderate rate of voltage or current increase respectively can be seen.

The present method and the present apparatus may be used advantageously for the control of any desired consumer provided from the main, particularly such with proportionally high capacitive character, such as consumers with compensated reactive load.

An important application of the method in accordance with the present invention is the control of the light volume of a lighting installation. The method may especially be used for the control of fluorescent lights at lighting installations without a substantial interface with the existing installation and for the optimum compensation of the reactive load at the same time. The control of the light volume of an electrical lighting installation is not only important from the point of view of maintaining the same optimum working place lighting at fluctuating day light, but also in view of the increasing importance of energy saving.

A further application of the method is the control of electric motors.

Claims (16)

WHAT I CLAIM IS:

1. A method for controlling the electric power provided from an alternating-voltage mains to a consumer by controlling the relative duration of voltage application by means of a power switching arrangement connected in the current path to the consumer, and comprising continuously measuring the current supplied to the consumer, deriving a voltage from the measured current, comparing the derived voltage with a variable reference voltage derived from the main alternating voltage, said reference voltage having the main frequency and being at least substantially of sine wave form, and switching-off the power switching arrangement with a cycle frequency which is substantially higher than the main frequency during each half-wave of the main alternating voltage when the voltage derived from the measured current has a higher magnitude than the reference voltage.

2. A method according to Claim 1, the variable reference voltage is derived by filtering the main alternating voltage.

3. A method according to Claim 1 or 2, wherein the power supplied to the consumer is controlled by adjusting the amplitudes of the variable reference voltage.

4. Apparatus for controlling the electric power provided by an altematingcurrent main to a consumer, by means of a bridge rectifier whose one diagonal is connected in series to the consumer and to whose other diagonal a controlled semiconductor switch is connected and comprising a first circuit arrangement for producing a rated voltage having at least substantially half sine waves configuration; a second circuit arrangement for tapping an actual voltage from the consumer current; a comparison circuit, connected to both said circuit arrangements, which provides an output signal when the actual voltage is higher than the rated voltage; a pulse oscillator from the production of rectangular pulses whose frequency is substantially higher than the main frequency; and a storagedevice whose set input is connected to the output of the pulse oscillator, whose reset input is connected to the output of the comparison circuit and whose output is in connection with the semiconductor switch in such a way that an output signal from the storage device generated in the set state thereof maintains the semiconductor switch in its conducting state.

5. Apparatus as claimed in Claim 4, wherein said first circuit arrangement includes an adjustable voltage divider connected between the leads carrying the main altemating-current and a first rectivying circuit connected to the tapping of the voltage divider, and wherein the second circuit arrangement includes a measuring resistor connected to one of the leads carrying the main altemating.current and a second rectifying circuit connected to the measuring resistor.

6. Apparatus as claimed in Claim 5, wherein the voltage divider of said first circuit arrangement includes at least one reactive circuit element.

7. Apparatus as claimed in Claim 6, wherein said at least one reactive circuit element is a capacitor.

8. Apparatus as claimed in any one of Claims 5 to 7, wherein the tapping of the voltage divider is a potentiometer for the adjustment of the power provided to the consumer.

9. Apparatus as claimed in any one of Claims 5 to 8, wherein each rectifying circuit includes an operational amplifier and a diode arrangement.

10. Apparatus as claimed in any one of Claims 4 to 9, wherein the storage device is a bistable switch.

11. Apparatus as claimed in Claim 10, wherein said bistable switch is a flip-flop.

12. Apparatus as claimed in any one of Claims 7 to 11, wherein the output of the storage device is connected to the semiconductor switch via an opto-coupler and a complementary driver.

13. Apparatus as claimed in Claim 12, wherein the semiconductor switch is a Darlington transistor whose base is connected to the output of the complementary driver via a limiting resistance and whose collector-emitter path is connected to the said diagonal of the bridge rectifier via a current rise limiting inductor.

14. Apparatus as claimed in Claim 13, wherein, for limiting the collector current of the semiconductor switch a measuring resistor is arranged in its collector current circuit and is connected to a first input of a further comparison circuit, a second input of which is supplied with an adjustable reference voltage, and wherein the output of the further comparison circuit is connected via an opto-coupler with that input of the first mentioned comparison circuit to which the actual voltage derived from the consumer current is supplied.

15. A method for controlling the electric power provided by an altemating-current main to a consumer, substantially as described herein and with reference to the accompanying drawings.

16. Apparatus for controlling the electric power provided by an aiternatingcurrent main to a consumer substantially as described herein and with reference to the accompanying drawings.