GB1581049A - Alternating current power supplies - Google Patents

Description

(54) IMPROVEMENTS RELATING TO ALTERNATING CURRENT POWER SUPPLIES (71) We, STEWART CHARLES HINE, of 44 Waverley Rd., Middx., British, and ROBERT ALEXANDER SYMES-SCHUTZMANN, of Green Dene Cottage, Honeysuckle Bottom, East Horsley, Surrey, British, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: Domestic and industrial electric power is commonly supplied in the form of alternating current at 50 or 60 cycles per second In mobile equipment or in country districts such power is commonly generated by a petrol-or diesel-engine prime mover driving an alternator.Such apparatus, while efficient at full load, is wasteful of fuel at low loadings due to the mechanical power loss in the prime mover being more or less constant. In the invention to be described such a generating set is used in conjunction with a storage battery and an inverter capable of also acting as a charger for the battery, the arrangement being such that the alternator is automatically brought into operation when the power demand of the load exceeds the maximum power output of the inverter and alternatively when the battery is nearing full discharge.

The invention will now be described with reference to the drawing, in which a prime mover 1 is mechanically coupled to an alternating-current generator 2 which feeds a load 3 via a current sensor 4 and a voltage sensor 5. An inverter 6 is also connected to the load -and is arranged to recharge the secondary battery 7 when alternating current is produced by the alternator. The battery 7 is also furnished with current and voltage sensors 8, 9. The outputs of sensors 4 and 5 control a logic unit 10 which produces a control signal 11 to switch the inverter into the inverting or charging mode as required. The outputs of sensors 8 and 9 control a logic unit 12 which produces a signal 13 to start or stop the prime mover.

In the 'no load' condition the generator is stopped and power is provided by the inverter. It is a feature of such devices that the current drawn from the battery is almost exactly proportional to the alternat -ing current output. When the load current is increased so. that the battery current reaches a value corresponding to the maxi mum output of which the inverter is is capable logic unit 12 produces the signal to start the prime mover. This signal is also given when voltage sensor 9 indi cates that the battery is fully discharged.

When the prime mover has reached full speed voltage sensor 5 recognises full volt age and causes logic unit 10 to switch the inverter into the charging mode. Part of the current sensor 4b now recognizses the presence of load current and mantains the prime mover in motion; this sensor may be combined with sensor 4 or form part of the generator installation.

When the battery is fully charged volt age sensor 9 puroduces a further signal 14 which causes the inverter circuit to reduce charging current to a 'trickle' or maintain ing charge value. Such current may con veniently be taken from a point in the circuit such that it is not taken into account by current sensor 4 and therefore does not require the generator to run in the absence of other loads.

If the load is now reduced to a value less than the maximum output of which the inverter is capable, current sensor 4 causes the logic unit 10 to revert to the inverting mode. Sensor 4b now detects the absence of load current and the 'run' signal is withdrawn from the prime mover, which stops. Voltage sensor 5 is enable only after a delay of a few seconds, in order that voltage output from the alternator shall not be detected and so switch the inverter back to the charging mode before the alternator has had time to stop.

Where some of the units forming the load require a greater amount of power than the inverter can supply, their connection to the inverter will cause it to stop operating due to the action of its internal overload protection circuits. An output 15 from such circuits causes logic unit 12 to generate the starting signal 13 and so start the generator, but power supply will be interrupted for such time as the generator requires to run up to full speed. Such heavy loads: may be wired to a separate circuit 3a via a part of current sensor 4a so that they do not receive a 'no break' supply as above, but start the prime mover directly when connected by the action of sensor 4b. The supply 3 to lighter loads is then switched only when full output voltage is recognised by sensor 5. By this means the supply to loads 3 is uninterrupted.

The battery charging current is included in the total power demand in order to maintain operation of the prime mover only until the battery is fully charged.

WHAT WE CLAIM IS: - 1. Apparatus for supplying electrical power: a load, comprising a prime mover, an alternator, a storage battery and an inverter capable of operating also as a charger for the battery, arranged so that the alternator is automatically brought into operation when the power demand of the load exceeds the maximum power output of the inverter, and alternativly when the battery is nearing full discharge.

2. Apparatus as in Claim 1 arranged so that the prime mover is stopped automatically when the power demand of the load is reduced to a level within the maximum power of the inverter.

3. Apparatus as in Claims 1 and 2 arranged so that the battery charging current is included in the total power demand as seen by the sensors in order to maintain operation of the prime mover only until the battery is fully charged.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. back to the charging mode before the alternator has had time to stop. Where some of the units forming the load require a greater amount of power than the inverter can supply, their connection to the inverter will cause it to stop operating due to the action of its internal overload protection circuits. An output 15 from such circuits causes logic unit 12 to generate the starting signal 13 and so start the generator, but power supply will be interrupted for such time as the generator requires to run up to full speed. Such heavy loads: may be wired to a separate circuit 3a via a part of current sensor 4a so that they do not receive a 'no break' supply as above, but start the prime mover directly when connected by the action of sensor 4b. The supply 3 to lighter loads is then switched only when full output voltage is recognised by sensor 5. By this means the supply to loads 3 is uninterrupted. The battery charging current is included in the total power demand in order to maintain operation of the prime mover only until the battery is fully charged. WHAT WE CLAIM IS: -

1. Apparatus for supplying electrical power: a load, comprising a prime mover, an alternator, a storage battery and an inverter capable of operating also as a charger for the battery, arranged so that the alternator is automatically brought into operation when the power demand of the load exceeds the maximum power output of the inverter, and alternativly when the battery is nearing full discharge.

2. Apparatus as in Claim 1 arranged so that the prime mover is stopped automatically when the power demand of the load is reduced to a level within the maximum power of the inverter.

3. Apparatus as in Claims 1 and 2 arranged so that the battery charging current is included in the total power demand as seen by the sensors in order to maintain operation of the prime mover only until the battery is fully charged.