DE3437242A1 - Electronic power controller, especially for controlling the outlet temperature of electrical continuous-flow heaters - Google Patents

Abstract

An electrical power controller contains a rectifier bridge (10) which is supplied with mains AC voltage, and a downstream-connected Schmitt trigger (16). The pulses which are received at double the mains frequency are connected to a frequency divider (20) which consists of two J-K flipflops having two outputs (30) and (34). The signal at the output (30) is in each case set by one edge of each third pulse and is reset by the corresponding edge of the subsequent pulse. The signal at the output (34) is set by one edge of each third pulse and is reset by the corresponding edge of the respectively next-but-one pulse. A semiconductor relay (22) is optionally controlled by the signals at the output (30) or by the signals at the output (34), via a selector switch (40) or a logic circuit. In consequence, the semiconductor relay is switched on for one, two or three of three half cycles. <IMAGE>

Description

Electronic power controller, especially for

Regulation of the outlet temperature for electric instantaneous water heaters The invention relates to an electronic power controller, in particular for regulation the outlet temperature in electric water heaters containing (a) one of AC voltage applied to the mains frequency rectifier bridge, which has a of twice the mains frequency supplies pulsating DC voltage, (b) a Schmitt trigger, to which the pulsating DC voltage is applied to generate a square-wave pulse train with twice the mains frequency, (c) a frequency divider on which the square pulse train is switched on, (d) a semiconductor relay connected to the mains AC voltage with zero voltage switch behavior, through which the power can be switched and (e) Means for controlling the semiconductor relay in dependence on output signals of the Frequency divider.

The regulation of the outlet temperature for electric water heaters offers particular difficulties. Electric water heaters have a very high installed heating capacity of, for example, 22 kilowatts. The outlet temperature must be adhered to very precisely and may only be slightly adjusted to the desired temperature vary. It is difficult to regulate the heating power accordingly sensitively.

The electrical heating power can be controlled by a phase control regulate continuously. A phase control of the high power here however, is because of the harmonics generated and the resulting harmonic waves Interferences not allowed. It is only permissible to switch the alternating current fully on or off, whereby a zero voltage switch ensures that the switch-on and the switch-off takes place at times when the AC voltage goes through zero anyway, so that there is no phase control.

A regulation of the heating power by switching on and off requires but a relatively high switching frequency if the requirement is to be met, that a desired outlet temperature is maintained with high accuracy. if the heating power would be switched on and off with a low switching frequency, then a water heater would alternately run out of cold or too hot water, even if the average heating power is the desired Temperature corresponds. A high switching frequency of the switching on and off leads to a high heating output but again to other difficulties: The network impedance affects the high heating output of the electric water heater the mains voltage. A high Switching frequency would therefore cause an uncomfortable flicker of electric light bulbs bring yourself. The switched heating power approved by the utility company is therefore the smaller, the higher the switching frequency. These demands stand against the effort to reduce the outlet temperature of a high-performance instantaneous water heater to regulate with high accuracy.

For this reason, it is known for an electric water heater to divide the installed heating capacity into at least two levels.

A controller with a temperature sensor located in the outlet switches only one of the stages for temperature control (DE-OS 28 37 934).

From DE-OS 28 37 934 it is also known that for switching of the stages of the heating power a heating coil arrangement common to several stages is provided. A rectifier and switching stage are acted upon by the mains voltage generates a square-wave voltage that is synchronous with the line frequency and has twice the line frequency. The output signal of the controller from a temperature sensor located in the outlet is applied, is applied to comparators with graduated reference signals. the Output signals of the comparators and the outputs of the binary counter are on one Logic circuit switched on, through whose output signal the electronic Scarf termi ttel can be controlled so that when an increasing number respond of comparators periodically an increasing number of half-waves of the mains alternating voltage is switched through. In the known arrangement, the heating power is switched on in two stages by two comparators a binary counter with a single counting stage intended. The logic circuit has an AND element, at the inputs of which the Counting stage and the output of the comparator with the lower reference signal is present, and an OR element, at whose inputs the output of the AND element and the output of the comparator with the higher reference signal are present, the output of the OR gate forms the output of the logic circuit.

It is also known from DE-OS 28 37 934, part of the heating power to be controlled continuously by means of a pulse width module at a fixed clock frequency, wherein the pulse width modulator can be controlled by the output signal of the controller. Of the Pulse width modulator contains a comparator to which the output signal of the controller and a triangular signal with a fixed clock frequency is applied as a reference signal, so that the comparator provides an output signal during the intervals during which the output signal of the controller is greater than the reference signal. On when a level of heating power is switched on via a comparator at the output the signal appearing in this comparator is an additional signal superimposed on the reference signal switched to the comparator of the Pulsbreitmodual author, so that the Pulse width module ator controlled heating output by the heating output of the switched on Level is decreased.

The invention is based on the object of an electronic power controller of the type mentioned above, in particular for regulating the outlet temperature electrical water heaters to train so that on the one hand generates signals through which one or two of three half-waves of the AC mains voltage are controllable, and on the other hand by switching means independent of these signals one of the signals for control can be switched to the semiconductor relay is.

The mean value of the direct current is to be used by the consumer flowing current be zero.

According to the invention, this object is achieved in that (f) the frequency divider has a first output at which an output signal is passed through each third impulse is set and which resets the next impulse, (g) the frequency divider has a second output at which an output signal each set by an edge of every third pulse and by the corresponding one Edge of the next but one pulse is reset, (h) the semiconductor relay can be switched through for a half period each time if at a control input for At the time of the zero crossing of the mains voltage, a signal is present and (i) by said means for controlling the solid state relay in dependence on one further switching status of the first or the second output of the frequency divider the control input can be applied.

The Schmitt trigger delivers square-wave pulses in the range of the maxima or minima of the mains alternating voltage, the edges of which are sufficiently spaced apart from have the zero crossings of the mains AC voltage.

Such a zero crossing lies between two adjacent ones Pulses of the Schmitt trigger.

If at the first output of the frequency divider by such a pulse an output signal is set and this output signal is set by the next one Pulse is reset, then the output signal is available during the intervening Zero crossing of the alternating voltage. As a result, the solid state relay is used for the half-period following the zero crossing is switched through.

Since only every third pulse of the pulse train has such an output signal sets, the semiconductor relay is only activated for every third half-wave of the AC mains voltage switched through. This has the consequence that successive, through-connected half-waves have opposite polarity so that the DC mean value of the flowing Current becomes zero.

At the second output of the frequency divider, a signal is generated by a Edge of a pulse set and by the corresponding edge of the next but one Reset. As a result, appears at the second output of the frequency divider a signal that occurs during two consecutive zero corridors the AC mains voltage is present. When the solid state relay from the signal on the second Output of the frequency divider is controlled, then a full wave of the AC line voltage from the solid state relay switched through while connected to it subsequent half-wave is not switched through. Even with this mode of operation successive, through-connected waves of the mains alternating voltage are out of phase, so that the mean DC value of the current flowing through the consumer is zero will.

Lay the signals made available in this way at the frequency divider the respective mode of operation of the solid-state relay is already clearly established. You can can be connected to the semiconductor relay in various ways. In the simplest Trap are said means for controlling the solid-state relay from a selector switch formed, the position of which represents the said "further switching state". The invention but there is also the possibility of the output signals of the frequency divider via a suitable logic circuit depending on a controller output signal so on semiconductor relays to switch in three phases of a three-phase current that the total power in relatively small Steps can be switched.

Refinements of the invention are the subject of the subclaims.

Two embodiments of the invention are referred to below explained in more detail on the accompanying drawings: Fig. 1 shows schematically a first embodiment of an electronic power controller.

Fig. 2 shows the occurring in the power controller according to Fig.l. Waveforms.

Fig. 3 shows the three possibilities of the power controller current conducted by the consumer.

Fig. 4 shows another embodiment of an electronic power controller for three-phase current, which is used in particular to regulate the outlet temperature for electrical Water heaters is suitable.

The power controller according to FIG. 1 contains a rectifier bridge 10, which via a transformer 12 of line frequency, in-phase with the line frequency AC voltage is applied.

The rectifier bridge 10 supplies at an output 14 one with the double the mains frequency pulsating direct voltage. This pulsating DC voltage is connected to a Schmitt trigger 16. The Schmitt trigger 16 generates a Square pulse train, which is shown in the second line of Fig.2. The Schmitt trigger switches as long as the applied signal exceeds a specified threshold value. This means that the square-wave pulses 18 are essentially symmetrical to the maxima and minima of the AC mains voltage and at a distance from the zero crossings 20 of AC line voltage are present. The square pulse train is on a frequency divider 20 activated. At 22 is a Solid state relays with zero voltage switch behavior. The semiconductor relay 22 includes a triac 24, which is applied in series with a consumer 26 to the AC mains voltage. There are Means 28 for controlling the semiconductor relay 22 as a function of output signals of the frequency divider 20 is provided. In the arrangement described there is the frequency divider 20 from two J-K flip flops. Of the four outputs of the J-K flip flops only two outputs used. An output signal appears at a first output 30 32 (Fig.2) which each by a flank, here the front flank, every third Pulse 18 of the square pulse train set and by the corresponding edge of the next following pulse 18 is reset. The output signal at output 30 is thus a pulse train as shown in the third line of Fig.2. An output signal appears at a second output 34 of the frequency divider 20 36, which in each case by an edge of every third pulse 18 of the square-wave pulse train set and reset by the corresponding edge of the next but one pulse will. The output signal 36 provides a pulse train as shown in the fourth line of Fig.2 is shown. The semiconductor relay 22 is for one semiconductor period at a time can be switched through if at a control input 38 at the time of the zero crossing a signal is present at the mains voltage.

Such semiconductor relays are known per se and are commercially available. The structure of the semiconductor relay 22 is therefore only indicated schematically.

As can be seen from FIG. 2, there is a zero crossing 20 in each case the AC mains voltage between two adjacent pulses 18 the square pulse train. One pulse occurs in each pulse of the output signal 32 Zero crossing. Between successive pulses of the output signal 32 lie two zero crossings of the mains alternating voltage at which there is no output signal 32 is at output 30. Each pulse of the output signal 36 at the output 34 of the frequency divider 20 extends over two successive zero crossings 20 of the AC mains voltage. There is a zero crossing between successive pulses of the output signal 36 the AC mains voltage at which there is no signal at output 34. If that Semiconductor relay 22 is controlled by the first output signal 32, then the Semiconductor relay conducting for one half cycle of the AC mains voltage, which are then followed by two half-periods during which the solid-state relay 22 does not let any current through. When the semiconductor relay 22 from the second output signal 36 is controlled at output 34, then it will be consecutive during two Half-periods conducting, followed by a half-period during which the Solid state relay 22 is not conductive.

The current through the consumer 26 then has that in the penultimate Line of Fig.2 shown shape.

The means 28 for controlling the semiconductor relay are in the embodiment According to Fig.l formed by a selector switch, the switch arm 40 optionally to ground (Signal "L"), to the first output 30, to the second output 34 of the frequency divider 20 or to a permanent signal "H" can be applied. The switch arm 40 is across a resistor 42 connected to input 38.

With such an arrangement, different currents can flow through the consumer 26 are generated, as shown in Figure 3. When the switch arm 40 is constantly on the signal "L", then the triac 24 is constantly blocked. It flows no electricity. If the switch arm 40 is at the output 30 of the frequency divider 20, then is, as shown in the first line of Fig.3, every third half-wave of AC line voltage to consumer 26 let through. Is the switch arm 40 with connected to the third output 34 of the frequency divider 20, then the result is, as already has been explained in connection with Figure 2, a current curve in the consumer 26 accordingly of the second line of If 3 If the switch arm 40 is applied to the continuous signal H " is, then the triac 24 remains continuously conductive. The full AC mains voltage is used passed to the consumer 26. Accordingly, the consumer 26 is dependent on Position of the switch arm 40 either switched off, with 1/3 of the power, with 2/3 the performance or charged with the full performance. As can be seen from Fig.3 is, in any case, is the mean DC value of that flowing through consumer 26 Current zero.

In the exemplary embodiment according to FIG. 4, the "contain means for controlling of the semiconductor relay "for a semiconductor relay 44 a first AND gate 46, whose an input 48 is applied to the first output 30 of the frequency divider and a second AND gate 50, one input 52 of which at the second output 34 of the frequency divider 20 is applied and an OR gate 53 with three inputs 54, 56 and 58.

A comparator 60 is also provided, which is shown in FIG Addiction of an input signal at an input 62 when stepped threshold values are exceeded Output signals at a first, a second and a third output 64 and 66 or 68 delivers.

The first output 64 of the comparator 60 is with the other input 70 of the first AND gate 46 connected. The second output 66 of the comparator 60 is connected to the other input 72 of the second AND element 50. The exits AND gates 46 and 50 are connected to the first input 54 and the second input, respectively 56 of the OR gate 53 connected. At the third input 58 of the OR gate 53 is the third output 68 of the comparator 60. The output 74 of the OR gate 53 controls the semiconductor relay 44.

When the input signal 26 rises, a signal H "appears one after the other at the outputs 64,66 and 68. Correspondingly for a relatively small input signal for example a relatively small system deviation, an output signal appears at the first output 64 of the comparator 60. The AND gate 46 is therefore the Signal 32 (FIG. 2) from the output 30 of the frequency divider 20 to the input 54 of the OR gate 53 effective, while at the inputs 56 and 58 of the OR gate 53 no signal is present. The signal 32 thus appearing at the output 74 of the OR gate 53 controls the semiconductor relay 44 during every third half-wave, so that a current through the consumer accordingly the first line of Fig.3 flows. With a further increase in the signal at the input 62 a signal H ″ also appears at the output 66 of the comparator 60.

Via the AND gate 50, the signal 36 from the output 32 of the Frequency divider 20 at the input 56 of the OR gate 53 and thus also effective at the output 74 of the OR gate 53. The semiconductor relay 44 is each during two out of three half-periods of the alternating voltage turned on, so that by the consumer a current flows according to the second line of Fig.3. In the end If the signal at input 32 rises further, a signal H "will also be on the third output 68 of the comparator 60 effective, which is directly connected to the third Input 58 of the OR gate 53 is connected. At the output 74 of the OR gate 53 therefore a continuous signal "H" appears. The semiconductor relay 44 is constantly turned on, so that the full AC mains voltage is effective at the consumer.

In the preferred embodiment shown in FIG. 4, there are three semiconductor relays 76, 78 and 44 each provided for one phase of a three-phase current. The comparator 60 has three groups of outputs 80,82,84 as well as 86,88,90 and 64,66,68. Any of these Groups of outputs are each on a logic circuit 92,94,96 of two AND gates 98,100 as well as 102,104 and 46,50 and an OR gate 106,108,53 connected in in the manner described in connection with Group 96 and also by the outputs 30,34 of the frequency divider 20 is applied. Through the logic circuits 92, 94 and 96, one of the three semiconductor relays can each be controlled.

In the arrangement described, the signal H "appears at a Rise in the signal at the input 62 successively at the outputs 80,82,84,86,88,64,66 and 68. The semiconductor relay 76 is therefore first activated via the logic circuit 92 in the described benen way controlled in three stages until at Occurrence of a signal at the output 84 controlled by the semiconductor relay 76 Phase of the three-phase current is fully switched through. If the input signal continues to rise 62, the second phase of the three-phase current in the described is via the semiconductor relay 78 Way controlled in three stages, while the first phase continues to be fully controlled remain.

Finally, the third phase of the Three-phase current controlled by means of the semiconductor relay 44. The installed power can thus be switched in a total of nine stages.

In the embodiment shown, the three phases of the three-phase current gradually switched on one after the other. It is also possible to do this one after the other instead to switch on each of the three phases with a third of the power, then one after the other each of the phases with two thirds of the power and finally each one in turn of the three phases at full power.

Another option (when using a comparator with three Outputs) consists in controlling all three semiconductor relays 76, 78 and 44 at the same time and to switch in three stages.

The former variant is obtained by connecting the AND gates with the outputs 82 and 86, with the outputs 84 and 64 and with the Outputs 90 and 66 swapped. This variant has the advantage of being more even Load on the three-phase network.

In the embodiment shown, the input signal is at the input 62 of the comparator 60 from a continuously variable control voltage at an input 110 and a triangular voltage superimposed on the control voltage in a summing point 112 formed by a triangle generator 114. Such an arrangement causes a pulse width modulation, where the power is between the two highest controlled power levels is switched back and forth. For example, a signal H "appears at the output 90 as a continuous signal, while at the output 64 a signal with a pulse width occurs, which changes continuously with the signal at input 110. It can be based on this Way the supplied power can be constantly changed. The pulsed power corresponds to where the difference in performance between two successive levels. The frequency The triangular generator 114 specifies with which the power is pulsed.

With an arrangement of the type described, temperature control can be achieved for an electric water heater, with the requirements of DIN EN 50006 / VDE 0838 are met.

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Claims (6)

Claims El Electronic power controller, in particular for regulating the outlet temperature in electric water heaters, containing (a) a rectifier bridge (10) to which AC voltage is applied, which supplies a direct voltage pulsating with twice the mains frequency, (b) a Schmitt trigger (16) to which the pulsating DC voltage is applied is to generate a square-wave pulse train with twice the network frequency, (c) a Frequency divider (20) to which the square pulse train is switched, (d) on The semiconductor relay (22) connected to the AC mains voltage with zero voltage switch behavior, through which the power can be switched and (e) means (28) for controlling the semiconductor relay as a function of the output signals of the frequency divider, characterized in that that (f) the frequency divider (20) has a first output (30), at which an output signal (32) in each case by an edge of every third pulse (18) is set and reset by the corresponding edge of the next following pulse is, (g) the frequency divider (20) has a second output (34) at which an output signal (36) is set and passed through every third pulse (18) the next but one pulse is reset, (h) the semiconductor relay (22) can be switched through for a half cycle each time, if at a control input (38) a signal is present at the time of the zero crossing (20) of the mains voltage and (i) by said means (28) for controlling the solid state relay (22) in dependence from a further switching state the first or the second output (30 or 34) of the frequency divider (20) can be applied to the control input (38). 2. Electronic power controller according to claim 1, characterized in that that said means (28) for controlling the solid state relay from a selector switch are formed, the position of which represents said further switching state. 3. Electronic power controller according to claim 2, characterized in that optionally no signal continues via the selector switch or a permanent signal can be applied to the control input (38) of the semiconductor relay (22). 4. Electronic power controller according to claim 1, characterized in that that said means for controlling the solid state relay (44) (a) is a first AND gate (46) included, one (48) input at the first output (30) of the frequency divider (20) is applied, and (b) a second AND element (50), one of which is input (52) the second output (34) of the frequency divider (20) is present, (c) an OR gate (53) with three inputs (54,56,58), at the first input (54) the output of the first AND element (46) and at its second input (56) the output of the second AND element (50) is applied, and (d) comparator means (60), (d 1 which depends on a Input signal when stepped threshold values are exceeded Output signals at one supply first, a second and a third output (64,66,68) and (d 2) their first output (64) with the other input (70) of the first AND element (46), the second output (66) of which with the other input (72) of the second AND element (50) and its third output (68) with the third input (58) of the OR gate (53) is connected. 5. Electronic power controller according to claim 4, characterized in that that (a) three semiconductor relays (76,78,44) are provided for each phase of a three-phase current (b) the comparator means (60) are three groups of three outputs (80, 82, 84; 86.88.90; 64,66,68) and (c) each of these groups of outputs on each a logic circuit (92,94,96) of two AND gates (98,100; 102,104; 46,50) and an OR gate (106,108,59) is connected, which is also connected to the outputs (30,34) of the frequency divider (20) is applied, and (d) by the logic circuits (92,94,96) one of the three semiconductor relays (76,78,44) can be controlled. 6. Electronic power controller according to claim 1, characterized in that that the input signal of the comparator (60) from a continuously variable control voltage and a triangular voltage superimposed on the control voltage is formed.