Apparatus for Regulating the Charging of a Storage Battery

1. Field of the Invention

The present invention relates to apparatus and a method for regulating the charging of a storage battery from an aleatory source of energy such as a battery of photocells. In such apparatus the battery of photocells supplies energy whenever it receives light, regardless of whether or not the storage battery is charged.

2. Description of the Prior Art

The charging of a storage battery is generally regulated by a regulator connected in parallel, the regulator serving to reduce or interrupt the current supplied to the storage battery whenever the battery reaches a desired level of charge. The regulator usually further includes means for dissipating the excess energy once the battery has been completely charged.

The excess energy is thus wasted. It is advantageous to conserve it either in the form of potential energy by pumping water or in the form of heat energy by heating material of large thermal capacity or else in the form of electricity injected into a mains grid.

Conventional regulation connected in parallel with the storage battery is no the best way of solving this problem. An object of the present invention is to provide apparatus for regulating charging of the storage battery in such a manner that the excess energy can be conserved.

The present invention provides apparatus for regulating the charging of a storage battery from an aleatory source of energy, said battery feeding a load, the apparatus being arranged so that whenever the battery has been charged to a given level of charge, and the energy being supplied by the source is in excess of that drawn by the load, the excess energy from the source is diverted in the form of an electric current to conserving means other than the storage battery, the allocation of available electric current to the storage battery and to the other conserving means being controlled by a parameter representative of the state of charge of the battery.

In the preferred embodiment the regulation parameter is the battery voltage. A second parameter can also be used, namely the quantity of energy stored in the battery as measured by an ampere-hour meter.

In one particular embodiment which uses a mains grid as the conserving means other than the storage battery, the regulation parameter is the voltage across the terminals of the storage battery, which is applied to the speed regulator of a DC motor fed from the said storage battery and driving an asynchronous machine for feeding power into the said grid.

The present invention also provides a method of husbanding electrical energy from an aleatory source, and of feeding said energy to a load, the method comprising:

providing a storage battery;

feeding the load with energy derived from the aleatory source;

making up any shortfall in energy from the aleatory source by drawing stored energy from the battery;

monitoring the state of charge of the battery; and

whenever the aleatory source is supplying energy in excess of that being drawn by the load, using said excess energy: firstly to charge the battery until the charge in the battery reaches a predetermined threshold level; and secondly, when the battery is charged to at least the threshold level, diverting excess energy in the form of electric current to conserving means other than the storage battery, the allocation of available energy to the storage battery and to the said other storage means being controlled as a function of a parameter representative of the state of charge of the battery.

An embodiment of the invention is described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of apparatus for regulating the charging of the storage battery in accordance with the invention; and

FIGS. 2A and 2B constitute a circuit diagram of a particular embodiment of the apparatus outlined in the block diagram of FIG. 1.

In FIG. 1 an aleatory source of energy 1, e.g., a battery of photocells receiving light from the sun, is used to charge a storage battery 3 via a diode 2. A portion of the energy supplied by the aleatory source is consumed in a load 5 (lighting, heating, etc.) for which the system is provided. Excess energy which is neither consumed by the load 5 nor storable in the battery 3 once fully charged, is delivered to another conserving means 6. The delivery of energy to the other conserving means 6 is regulated by a regulator 7 which receives information directly related to the state of charge of the battery, e.g., the voltage across the battery terminals.

The energy supplied from the aleatory source 1 may be further regulated by means of an ampere-hour meter 8 connected across a current-sensing resistor 4, itself connected in series with the storage battery. An output from the meter 8 is used to modify the reference voltage used by the regulator when the storage battery is fully charged, and to disconnect the load circuit by means of a switch 9 when the usable capacity of the storage battery has been depleted.

A particular embodiment of the invention is described below with reference to apparatus for regulating the charging of a storage battery from photocells. The normal use of energy supplied by the storage battery is the domestic electricity supply for a group of houses; whenever necessary this supply of energy to the houses is augmented by electricity from a main supply grid. Any energy supplied by the photocells in excess of the requirements for charging the storage battery and supplying the load is conserved by transforming this energy into alternating current at the frequency and voltage of the main supply grid, and by feeding this AC into the grid.

FIGS. 2A and 2B together form a simplified circuit diagram of the preferred apparatus used to implement the invention in the application outlined above. They should be placed side by side so that the letters S, U, V, X, Y, and Z on the two diagrams coincide.

In these figures, block 1 designates a battery of photocells feeding power to a storage battery 3 via a diode 2. The normal load for battery 3 is a group of houses 5a, 5b, 5c, and so on. Peaks in demand are supplied from the main electricity supply grid, symbolized by block 10. Two- and three-conductor connections are symbolised in this drawing respectively by two or three slashes (e.g.//) through a single line. Thus, for example, the grid 10 is shown having a three phase connection to the apparatus.

For use in the houses, the energy supplied by the photocells and/or storage battery is converted into AC by means of a generator set comprising a DC motor 11 having a parallel excitation winding 12 and an asynchronous machine having a stator 21, and a rotor 22 on the same shaft as the motor.

When the battery 3 is charged above a threshold value, the asynchronous machine operates nonsynchronously as a generator, supplying power to the houses. If the photocells are supplying energy, any excess is fed into the main grid, and any deficit is made up by the battery.

For the asynchronous machine to operate as a generator, it is necessary for the rotor slip rings 22a to 22c to be short circuited. This is performed by actuating from the main supply grid a normal-relief relay having a winding 30 and contacts 30a to 30d. The closing of contact 30d operates a relay 32, whose contacts 32a to 32c then close.

At night during off-peak hours, and if the battery has discharged a large proportion of its capacity, e.g., following a sunless day, the battery is recharged from the grid via a charger 34. Charging from the grid is limited to off-peak periods by a clock 35, which closes a contact 35a during off-peak hours. The state of the battery is detected by an ampere-hour meter 80 having contacts 80a and 80b. When the battery is discharged to below a given threshold, following a sunless day, for example, the contact 80a closes; then at the beginning of the low rate off-peak period, the clock closes its contact 35a. A relay 36 is then excited and closes its contacts 36a and 36b, thereby connecting the main grid 10 to the charger 34. The ampere-hour meter 80, is preferably an up/down counter, advantageously of the type described in the commonly assigned French published patent application No. 2,361,754, corresponding to U.S. Ser. No. 823,659, now U.S. Pat. No. 4,194,146, incorporated herein by reference.

The generator set, and consequently the charging of the storage battery, is regulated as follows:

information U.sub.B concerning the voltage across the terminals of the battery is obtained at the output of an operational amplifier 41, having one input connected to a reference voltage U.sub.REF and its other input connected to the positive pole of the battery via a potentiometer 42. The reference potential U.sub.REF is representative of full charge, but its exact value is modifiable by the meter 80;

information I.sub.D concerning the difference between the total energy being supplied by the generator set and the energy being supplied to the load 5 is available at the output of an operational amplifier 51 having one of its inputs connected by a rectifier 52 to the secondary winding of a current transformer 53 whose primary winding is looped around the output cable of the stator 21, and another of its inputs connected via a rectifier 54 to the secondary winding of a current transformer 55 whose primary is looped around the cable feeding the load.

The operational amplifiers 41 and 51 have diode-protected outputs which are simply commoned together so that it is the greater of their two output voltages which appears at their common output. The polarities are so arranged that so long as the battery voltage is below U.sub.REF, the information I.sub.D is effective at their common output, and once the battery voltage exceeds U.sub.REF, it is the information U.sub.B which is effective at their common output.

When the battery is sufficiently charged (e.g. to 50% capacity) to start up the generator set by means of a relay 39 with contacts 39a to 39c, as will be explained below, it is the information I.sub.D which is available at the commoned output of the amplifiers 41 and 51. This information is used to modify the speed reference for the generator set as given by a tachometer dynamo 61 associated with the shaft of the generator set. This modified speed reference is applied to an operational amplifier 60.

The information at the output of the amplifier 60 is supplied to a conventional thyristor control circuit 62 for controlling the firing of thyristors in a mixed bridge 63 which feeds a supplementary subtractive winding 12a in the field winding of the motor 11. The speed of the motor is thus regulated to equalize the current supplied by the generator to the current drawn by the load, up to the limit current of the motor.

This limit is monitored by information representative of current flowing through the motor armature as supplied by an operational amplifier 64 with its inputs connected across a shunt 65.

The outputs of the operational amplifiers 60 and 64 are also diode-protected and simply commoned together. Their common output is applied to a control input of the thyristor control circuit 62 to determine the phase instants at which the thyristors are fired. The control circuit 62 also has a phase reference input connected to the primary winding of the transformer from which the bridge 63 draws its current. In the absence of a control voltage, the control circuit 62 is arranged to fire the thyristors as soon as possible in each half cycle of the reference phase, and the effect of increasing voltage being applied to its input is to increasingly retard the firing instants. Thus in normal operation the current sensing amplifier 64 supplies a smaller output voltage than the tachometer sensing amplifier 60, thereby leaving control to the amplifier 60. However, as the armature current increases, so does the output voltage of the current-sensing amplifier 64, and at excessive armature current the thyristors are thus automatically transferred to the control of the current-sensing amplifier 64.

When the battery voltage exceeds a predetermined value representing full charge, it is information U.sub.B which appears at the common output of the amplifiers 41 and 51 to correct the order signal from the tachometer generator. The corrected order signal speeds up the generator set, and the current which the generator supplies in excess of that needed by the load is applied to the main grid, while the battery voltage is maintained at a constant value.

If there is a power outage, a relay 30 in the main line is deenergized, thereby opening its contact 30d, which releases the relay 32, thus opening its contacts 32a and 32c and removing the short circuit across the slip rings of the rotor 22 of the asynchronous machine. At the same time, the winding of a relay 31 is deenergized by opening of contact 30b, and the mains power supply contact 31a is opened. A relay 70 is energized by the closing of contact 30c, thereby closing its contacts 70a and 70b to excite the rotor 22 of the asynchronous machine via an excitation generator 71 after a delay (e.g., 5 seconds) produced by a delay contact 30c. The asynchronous machine then operates synchronously as an alternator, with its alternating voltage regulated by regulating the current in inductor 72 of the generator 71 by means of an operational amplifier 73 which has one input connected to a reference voltage U.sub.REF and its other input proportional to the stator voltage via a three-phase rectifier 74 and a resistive voltage divider 75, thereby biasing the base of a transistor 76 connected in series with the inductor 72.

After the main power is restored, the normal-relief relay 30, reoperates, the contact 30c opens, and the relay 70 is released, breaking the connection between the excitation and the rotor of the asynchronous machine (70a, 70b) and opening the contact 70c. After a delay (the contact unit 30d being delayed to ensure that the generator 71 is no longer excited), relay 32 is reenergized, again short circuiting the rotor slip rings.

The ampere-hour meter 80 receives information representative of the current passed through the battery by means of a current sensing resistor 81 connected in series with the battery. This makes it possible:

to automatically recharge the battery when its charge drops below a given threshold (e.g., 30% of its nominal charge) as explained above; and

to stop the battery discharging once its discharge has reached a given level (e.g., when the battery is down to 20% of its nominal capacity) by the contact 80b releasing the relay 39 and thereby shutting down the generator set. The load is then supplied entirely from the main grid.

Once the battery has been recharged to a sufficient proportion of its total capacity (e.g., 50%) the meter's contact 80b closes, restarting the generator set via the relay 39, with a resistance 95 inserted in series in the armature circuit. A delay contact 39b short circuits this resistance by means of a contact 90a of a relay 90 once the generator set has reached sufficient speed. The delay contact 39b also causes a relay 94 to close its contact 94a thereby connecting the asynchronous machine to the load.

The generator set may be stopped and started manually by means of a contact 91.

The use of an asynchronous machine has numerous advantages, among them being that (a) there is no problem in coupling it to the grid, and (b) there is no risk of supplying power to a grid which has been deliberately disconnected (e.g., while work is being carried out thereon).

The energy supplied by the grid to the load is measured by a two-tariff meter 85, the tariffs for full-rate and off-peak rate being controlled by the clock 35. The energy supplied to the grid by the generator set is measured by a meter 86. The total energy supplied by the generator set is measured by the meter 87 and this information is used for monitoring and statistical purposes.

If too high a current is fed to the motor, a relay 92 opens a contact 92a; if the asynchronous machine is overloaded, a relay 93 opens a contact 93a.

The invention is in no way limited to the embodiments described. In particular the generator set could be replaced by an inverter having the same operating safety precautions.

It is also possible to have a plurality of generator sets receiving power from the same battery or from a plurality of batteries. If there is a power cut, one of the generator sets operates synchronously and the others are locked onto it.

Further, the details of the manner in which the energy flows are controlled can naturally be modified to suit specific requirements such as may be imposed by the Authority controlling any particular electricity grid. For example, it would be possible to use the battery to continue supplying energy to the grid for at least a short period after the sun has gone in, thereby smoothing fluctuations in total electricity supplied to the grid.