CH623687A5 - Device for regulating an electrical current flow by phase load-shedding - Google Patents

Description

The subject of the invention is a device for regulating an electrical current flow by phase shedding for an AC power source with at least one phase, the flow of which must be limited to a maximum.

It will relate, for example, to a device capable of relieving the main current of each phase of a residence with integrated electric heating with single-phase or multi-phase supply by reducing the average heating current for the benefit of the other uses of the installation considered to be priority.

It is known that, in a conventional electrical heating installation, the current is normally made to depend on a regulator of the type with proportional action by energy duration modulation, the temperature measurement bridge of which is essentially a Wheatstone bridge comprising, in addition to three calibrated resistors, a resistor with a negative temperature coefficient known as CTN with an adjustable resistance or potentiometer, the assembly, known as room sensor, being intended to influence the cyclic modulation modulation ratio of the regulator.

According to the conventional assembly, the four resistive elements of the measurement bridge are arranged two by two in two branches mounted under the same continuous voltage drop and each of them has a reference point, located between its elements, whose potential is advantageously the same when the bridge is in equilibrium; in the latter case, it will be said that the error voltage E of the bridge is zero.

By manually adjusting the potentiometer, the desired temperature, called the set temperature, is displayed; if the temperature of the room to be heated falls below the set temperature, the bridge error voltage takes on a meaning and a value such that the heating power automatically increases. On the other hand, if the temperature of the room and, therefore, of the room sensor, rises above the set temperature, the bridge error voltage takes on a meaning and a value such as the heating power automatically decreases.

In the case of an installation with integrated electric heating, it is known to place a room sensor in each room to adjust the temperature according to the destination of the room, by influencing the cyclic modulation ratio of the average heating current. . However, the other electrical installations of the residence, for example the various household appliances, some of which have high electrical powers, have an unmodulated current consumption which is added to the modulated heating powers.

This clear separation between heating consumption and other consumption presents a drawback from the point of view of the power subscribed to the network. Indeed, the independent operation of the two parts of the installation results in either frequent overruns of the subscribed power resulting in tariff charges, if not untimely decommissioning by tripping of circuit breakers, or the need to provide a higher subscribed power incurring additional costs.

The object of the invention is to eliminate this drawback.

According to the invention, the device is characterized in that it comprises, for each phase, means providing an alternating voltage proportional to the alternating current in the phase of the means for rectifying this voltage and generating a direct voltage whose amplitude is proportional to the current in the phase, a comparator circuit provided with a comparator receiving said DC voltage and a reference DC voltage representing said maximum current and a voltage divider formed by a diode and a resistor connected in series in the output of the comparator, which is arranged to produce an output voltage which changes polarity, thereby changing the conduction state of the diode when said direct voltage exceeds said reference voltage so that the voltage divider emits an output signal, and an output circuit connecting the junction point between the diode and the resistance of the voltage divider to means which respond to the signal l output of the voltage divider by decreasing the current flow in the phase.

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It can thus be seen that the use of a load shedding device per phase makes it possible to protect each phase separately and simultaneously against possible overloads.

The drawing shows, by way of example, an embodiment of the device which is the subject of the invention, the same elements being designated by the same reference indices in the different figures.

Fig. 1 shows the block diagram of an individual phase shedding device for heating installation of a residence with integrated electric heating;

fig. 2 is a block diagram of the installation of FIG. 1,

and fig. 3 is the block diagram of a proportional regulation module on which load shedding information can be superimposed.

The residence includes, for example, 9 rooms to be heated by means of electrical appliances H1 to H9 (fig. 2) each supplied by a strong alternating current drawn between the neutral Mp and one of the phases of a supply three-phase A with neutral;

thus, the Hl, H4, H7 devices are powered by the R phase, the H2, H5, H8 devices by the S phase and the H3, H6, H9 devices by the T phase.

The starting and stopping of each device is ensured by means of a known device called a triac, designated by TRI at TR9, included in a proportional regulation module Ml to M9, the operation of which depends on a room sensor. SAI to SA9 mounted on a Wheatstone bridge in a known manner (fig. 3) and, for each phase, of a zero determination device DZR, DZS or DZT (fig. 2).

Of course, the load shedding device (fig. 1, 2, 3) is supplied with low current by means of a DC auxiliary auxiliary supply (fig. 2) coming from a current of one of the phases, for example R.

The electrical installation panel can include a device B (fig. 1) for the possible connection of a meter of the electrical energy absorbed by the heating alone.

We interpose in each general start of phase R, S, T, before the branches for household electrical use ED, shunts SH or all other devices for measuring the intensity whose terminals carry respectively the references SR1-SR2, SS1- SS2, ST1-ST2.

As the drawing shows, the voltages across the. shunts, which are alternating voltages proportional to the phase currents, are applied respectively to three peak detector amplifiers AR, AS, AT which rectify the incoming alternating voltage into a direct voltage proportional to the peak values, applied to a photodiode of PCR, PCS or PCT photocoupler which ensures the transfer of current while achieving the essential galvanic isolation between the part of the high current device and its part with low current.

The DC voltages V (VR, VS, VT) appearing on the collector of the photocoupler transistors are proportional to the luminescence of the photodiodes and, consequently, to the voltages at the terminals of the shunts or, in other words, proportional to the phase currents. .

Each of said voltages is therefore applied to one of the two inputs of comparator C (CR, CS, CT) which plays the role of differentiator. A direct reference voltage U (UR, US, UT) is applied to the other input of comparator C, the output of which is constituted by a voltage divider DT comprising in series a resistor RC and a diode D4 whose anode is put to ground. The junction point F of RC and D4 is the point of diversion to the various proportional regulation modules.

Said reference voltage U is taken from the cursor of a potentiometer RD forming part of a voltage divider connected to the terminals of the auxiliary DC power supply. This reference voltage U, adjustable using the potentiometer RD, is chosen so as to represent the admissible main phase current Imax as a function of the power subscribed to the network.

Comparator C is arranged so that its output voltage is negative as long as the reference voltage U is greater than the input voltage V of the comparator. Under these conditions, the voltage on the branch line L to the proportional control modules is equal to the ground potential thanks to the presence of the diode D4 (D4R, D4S, D4T) and this voltage therefore has no influence on the modules which operate in a conventional manner, only taking into account the signal from the room sensors.

If, on the contrary, the comparator input voltage V becomes greater than the reference voltage U, which means that the current of a phase exceeds the current Imax corresponding to the subscribed power, the comparator output voltage becomes positive and a positive voltage W (WR, WS, WT) appears on the branch line to the modules.

Thus the branch line LR, for example, possibly containing the offset voltage WR, will be connected to the points 19 of the modules Ml, M4 and M7 (fig. 2) and in a similar manner for the lines LS and LT.

In each module, this correction voltage, called the offset voltage, causes the operating point of the latter to slide in the direction of an increase in the out of service period of the heating cycle.

This happens as follows:

As is known, a proportional regulation module (fig. 2, 3) includes a Wheatstone bridge 11-12-13-14 intended to supply an error voltage E, a zero detector DZ serving as clock to mark precisely the moments of zero crossing of the alternating current of the network, zero crossings which are used as a basis for the formation of trigger pulses G for a triac TR described below, and an operational amplifier AO playing the role of modulator influenced by the error voltage E. The modulator output is applied to an AND circuit, the other input of which receives the zero-crossing pulses from the zero detector DZ. These pulses have a frequency equal to twice the frequency of the network (frequency of zero crossings of the network current). The regulation module comprises an aforementioned triac intended for the passage and non-passage of the modulated heating current. The periods of passage and non-passage of the heating current determine the amount of electrical energy consumed by the heating installation and are therefore controlled by the output of the AND circuit which, during the period of passage, delivers pulses applied to the trigger G of the triac which is passing at this time, the output of the AND circuit being zero during the non-passage period, the triac then being blocked.

According to the known technique, the error voltage E constituting the output of the Wheatstone bridge is only influenced by the comparison between the set temperature and the actual temperature of a room to be heated considered.

For this purpose, the measurement bridge 11-12-13-14 comprises four arms mounted in bypass in the manner of conventional thermostats under a direct voltage Ucc between two terminals 11 and 12, where 11 is at the positive voltage of the power supply DC direct current auxiliary (fig. 2) and 12 is at the negative voltage of said auxiliary power supply. The arm 13-12 contains a variable resistor P2, used to determine the chosen heating temperature, and a resistor with a negative temperature coefficient CTN, measuring the real temperature of the room to be heated, these two elements constituting a room sensor SA; arm 11-13 contains a variable PI calibration resistor, and arms 11-14 and 14-12 respectively contain fixed resistors RI and R2.

The error voltage E or output voltage of the measuring bridge appears between point 14 (foot of the fixed resistor RI) and point 13 (foot of the variable resistor PI).

When the bridge is in equilibrium, E = 0.

If the room temperature decreases, the value of CTN increases, the bridge is no longer in equilibrium and the output voltage E takes

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a direction and a value such that the duration of the passage or heating period is increased relative to the duration of non-passage or non-heating.

The opposite occurs if the temperature of the room increases.

On the other hand, a photocoupler 16 (fig. 3) is grafted onto the measurement bridge so that its phototransistor PT is bypassed on the fixed resistor RI, while its photodiode PD is inserted in a circuit 19-20 which can contain an offset voltage W (WR, WS, WT).

As long as the main phase current does not exceed the maximum tolerated, the offset voltage, represented overall by W, is absent, that is to say that W = 0. Under these conditions, the phototransistor PT is not influenced by PD, the resistance of PT is infinite and, consequently, the leakage current of said transistor is zero. If the value of the resistance RI is the same by construction as that of the resistance R2, the potential of point 14 effectively represents half of the direct voltage Ucc, i.e. the so-called positive information voltage Uin + of the measurement bridge where the symbol Uin indicates a tension of information.

The adjustable resistors (or potentiometers) PI, P2 of the other branch of the bridge are advantageously adjusted so that the potential of point 13 is the same as that of point 14 when the bridge is in equilibrium, the adjustable resistance P2 being used to the display of the set temperature of the room to be heated. The potential of point 13 is the so-called negative information voltage Ui - of the bridge and we denote by the symbol E, said error voltage of the bridge, the potential difference between points 13 and 14, ie Uin + - Uin - = E, with E = 0 when the point is in equilibrium; it will be conventionally said that the bridge error voltage is positive or negative respectively depending on whether the ambient temperature of the room to be heated is higher or lower than the set temperature.

Thus, to request the heating to be switched on from the equilibrium position, the bridge must be unbalanced (E <0), i.e. move the thermostat cursor so that the set temperature is higher at room temperature, which consists in increasing the resistance of P2. As the room temperature rises, the resistance of the CTN element gradually decreases until the decrease in the CTN exactly compensates for the increase in P2, and the bridge is again in equilibrium.

Conversely, if one wants to reduce the heating, it suffices to display a temperature below the ambient temperature in the thermostat, which amounts to reducing the resistance of P2. The error voltage will remain positive or zero (E> 0), i.e. there is no heating as long as the resistance of the CTN element increases as a function of the cooling of the part will not have exceeded the lowering of the resistance of P2.

It goes without saying that the triggering of the heating is determined by the polarity of the error voltage E of the measuring bridge, voltage perceived by an operational amplifier AO. As shown schematically in the drawing, the amplifier supplied by line 17 and equipped with resistors R3, R4, R5 and a capacitor CD grounded to the electrical ground ME of the device, necessary for its operation, can deliver at its output 18 pulses capable of modifying the duration of conduction of the triac and, consequently, the heating state.

These concepts mentioned remain valid for load shedding devices; the offset voltage, applied to the overloaded phases of the regulators, acts on the modules as if the resistance of P2 had been lowered.

When the main phase current exceeds the maximum tolerated, the offset voltage W (fig. 3) is present and can give rise to an offset current Iw which crosses the photodiode PD from 19 to 20. The photodiode transfers energy luminous to the phototransistor PT and makes it conductive: a current It, proportional to the offset current Iw, can therefore cross PT from 11 to 14.

It can easily be demonstrated that if all the other conditions remain unchanged, the error voltage E becomes more positive by the value R2 x lt. The offset voltage therefore exerts an effect similar to that of P2 actuated in the sense of reducing the modulation ratio of the regulator; everything happens as if the set temperature, displayed on the regulator, had been lowered and, consequently, the triac release time, compared to the non-heating period, is reduced. The particular advantage of the assembly is the fact that the modules can be completely separated since they are galvanically isolated from the offset voltage, and introduce into the measurement bridges a common offset voltage on equipment the electronic masses of which are carried potential of different phases; the control modules therefore have no common ground or common point.

These principles are most successfully applied in the construction of homes with integrated heating. Photocoupling made it possible to use strictly identical control modules, which not only facilitates connection, but also mass production; moreover, they do not necessarily have to be connected to a common electronic ground since they are galvanically isolated.

It appears from the preceding description that, thanks to the load shedding device of the present invention, it is possible to automatically limit and at all times the power consumed to the above-mentioned power, which makes it possible to reduce the subscribed power to the minimum compatible with comfort. heating required.

The invention is also applicable to a single-phase electrical installation.

The load shedding device can also be used for other applications than the electric heating of a residence, for example in all cases where it is desired to limit the power drawn from the network to the power subscribed with or without use. proportional control modules. It then suffices to use the output voltage of the comparator to actuate any regulation means, for example by lowering the supply voltage.

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Claims (5)

623,687 1. Device for regulating an electrical current flow by phase shedding for an AC power source with at least one phase, the flow of which must be limited to a maximum (Imax), characterized in that it comprises , for each phase, means (SH) supplying an alternating voltage proportional to the alternating current in the phase, means (AR-PCR; AS-PCS; AT-PCT) for rectifying this voltage and generating a direct voltage (VR; VS ; VT) whose amplitude is proportional to the current (I) in the phase, a comparator circuit provided with a comparator (CR; CS; CT) receiving said direct voltage (VR; VS; VT) and a reference direct voltage (UR; US; UT) representing said maximum current (I „, ax) and a voltage divider formed by a diode (D4R; D4S; D4T) and a resistor (RCR; RCS; RCT) connected in series in the output of the comparator, which is arranged to produce an output voltage (WR; WS; WT) which changes polarity by changing so i the conduction state of the diode when said continuous voltage (VR; VS; VT) exceeds said reference voltage (UR; US; UT) so that the voltage divider outputs an output signal (WR; WS; WT), and an output circuit (LR; LS; LT) connecting the point of junction (FR) between the diode (D4R; D4S; D4T) and the resistance (RCR; RCS; RCT) of the voltage divider to means (Ml, M4, M7; M2, M5, M8; M3, M6, M9) which respond to the output signal of the voltage divider by decreasing the current flow in the phase (R; S; T). 2. Device according to claim 1, for a power source supplying electrical power to heating equipment (H) and to other equipment (ED) of a building, said means (Ml, M4 ...) responding to the output signal of the voltage divider comprising a temperature control device controlling heating equipment (H) as a function of the ambient temperature, this control device itself comprising a measurement bridge (PI, P2, CTN, RI, R2) producing an error signal (E) to modulate the current supply of the heating equipment in response to the ambient temperature, characterized in that said output circuit (LR; LS; LT) connects said junction point (FR) between diode and resistance to the measuring bridge of the temperature-sensitive control device, so that an output signal in the output circuit modifies the balance of the bridge in a direction increasing the duration of the periods of non-functioning of the heating equipment ffage as long as said determined maximum current (Imax) of the phase is exceeded. 2 3. Device according to claim 2, characterized in that said means for rectifying the alternating voltage and generating a direct voltage proportional to the current in the phase comprise a peak detector amplifier (AR, AS, AT) for rectifying the alternating voltage and producing a DC voltage proportional to its peak value, and a photocoupler (PCR; PCS; PCT) in the output of the amplifier to connect its output to the comparator circuit (CR; CS; CT). 4. Device according to claim 2, characterized in that said output circuit connecting the voltage divider to the measurement bridge comprises a photocoupling device (16) connected in parallel to one of the arms (RI) of the measurement bridge. 5. Device according to claim 4, characterized in that a branch (PI, CTN, P2) of the bridge contains a resistance with negative temperature coefficient (CTN) and in that the photocoupling device (16) is connected in parallel to an arm (RI) of the other branch (RI, R2) of the bridge.