AU735775B2

AU735775B2 - Load shedding means

Info

Publication number: AU735775B2
Application number: AU94067/98A
Authority: AU
Inventors: Graham MCDONALD
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-11-20
Filing date: 1998-11-20
Publication date: 2001-07-12
Anticipated expiration: 2018-11-20
Also published as: AU9406798A

Description

P/00/01i1 Regulation 3.2

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ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "LOAD SHEDDING MEANS" The following statement is a full description of this invention, including the best method of performing it known to me: "LOAD SHEDDING MEANS" FIELD OF THE INVENTION This invention is related to the management of distribution of electrical power. In particular, it relates to means for controlled shedding of load to improve the efficiency of power generation.

00 00 0000 0000 oo 0 0. oo0 0000 gO gig 00oo 0 0 0 0000 oooo oooo ooo 0 oooo 0 go•• 0 BACKGROUND TO THE INVENTION Modern systems provide electrical power to domestic, commercial and industrial users from a state-wide or national power 10 distribution grid. Power is supplied to the grid from multiple power generation sites which may use a variety of power generation schemes. Power generation may be hydroelectric, gas powered, coal burning, nuclear, wind power etc. Each form of power generation has an optimum operating condition or conditions. Unfortunately, the demand for electric power is not uniform and is therefore not matched to the optimum generation condition.

Because the pattern of power demand does not match the optimum generation condition, the efficiency of generation is reduced. The difference between the peak demand and the average demand can be large.

A peak to average demand ratio of 10:1 or even 20:1 is common for domestic users. The ratio of peak to minimum demand can be 100:1 or even larger for commercial users that have virtually zero demand overnight. This means that power generating authorities must build a substantial overcapacity into power generation facilities and the power distribution grid.

A number of schemes have attempted to address the problem.

In Australia, the State generating authorities are working towards a national power distribution grid. The benefit of a national grid is that the grid will span a number of time zones and thus the peak loads will occur at different times.

This allows fdr slightly more efficient utilisation of power generation resources. Although this approach has benefits they are minimal and do not address the essential problem of shedding load at peak times.

One prior art approach that does shed load is described in Australian Patent Application number 31727/95 in the name of Boundary 10 Technologies Pty Ltd. The specification of this patent application describes a system whereby a power utility can manage the load on its electricity supply system by remotely deactivating specific loads connected to the system. This is accomplished by locating a power control module at a see 0: particular premises. In the preferred embodiment a paging network is utilised 15 to signal the power control module to disconnect a predetermined load.

It is also known to use ripple control to switch equipment such as hot water systems. Ripple control refers to a signal that is initiated by the power generation authority and carried by the supply cables. A receiver at the load receives the signal to disconnect the load. At a later time the receiver receives a further signal to reconnect the load. This scheme is widely used for storage hot water systems which are disconnected during peak load periods and reconnected to heat water during low load times.

The problem with all known load shedding schemes is that they result in inconvenience to the user if additional power is required during the load shedding period. Thus hot water metres using the above scheme also have a boost button to override the load shedding. Furthermore, only a limited range of loads can be shed. There will always be a majority of loads that are considered essential, such as lighting, cooking appliances, cooling appliances, television, etc.

What is required is a means that allows the power generation supply authority to supply power at an average level and to command users to draw alternative power during high load periods, thereby eliminating the need for a substantial overcapacity.

OBJECT OF THE INVENTION It is an object of the present invention to provide a means for controlled shedding of load.

It is a further object of the invention to provide a method of shedding load that allows a power supply authority to supply power at a substantially uniform average level.

Further objects will be evident from the following description.

DISCLOSURE OF THE INVENTION In one form, although it need not be the only or indeed the 0 so S"broadest form, the invention resides in a load shedding means for shedding load from a power distribution gird, said load shedding means comprising: a direct current power source; local storage means for storing direct current power from the direct current power source; inverter means for converting direct current power drawn from the storage means to alternating current power; and switch means response to a remote control signal provided so as to switch between a first condition and a second condition; wherein when the switch means is in said first condition, the switch means provides electrical connection between a load and a remote alternating current power source, and when the switch means is in said second condition, the switch provides electrical connection between the load and the inverter.

In preference, the direct current power source is a solar panel.

Alternatively, the direct current power source may be a wind turbine or a generator running on fossil fuel. In a further alternative, the direct current power source may be converted from an alternating power source such as iii mains supply.

The storage means is suitably a rechargeable battery although any rechargeable direct current storage means will suffice providing it can 6ogo supply adequate storage capacity for the particular insulation in which it is employed. The storage means may suitably provide storage at 24 volts or 12 volts or any other nominated DC voltage.

Most suitably the inverter converts the direct current voltage available from the storage means to an alternating current voltage. The inverter may convert the DC voltage output of the storage means to a z suitable AC voltage.

Preferably, the alternating current power source is supplied by a power supply authority.

The switch means is suitably a solid state, electronic means response to a ripple signal received from the power supply authority via the power distribution grid. The switch means may incorporate a unique address so that each switch means is individually addressable by the power supply authority. Alternatively, all switch means in a given region may be switched in response to the same signal.

BRIEF DETAILS OF THE DRAWINGS To assist in understanding the invention preferred embodiments will now be described with reference to the following figures in o which: FIG 1 is a schematic block diagram showing one embodiment o o o o s o• o.

7 DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals refer to like parts.

Referring to FIG 1, there is shown a load shedding device 1 connected to a power supply grid 2. The power supply grid 2 supplies AC power generated at a site remote from the load shedding device 1. The power supply grid 2 may include high tension power lines and step down •transformers but the supplied power is 240 volts at the load shedding device 1.

@000 @oo .The load shedding device 1 comprises a switch 3 that switches 00ig 10 a load 4 between the power supply grid 2 and an inverter 5. The inverter provides AC power converted from the DC output of a DC storage means 6, 0 which in the preferred embodiment is a 24 volt wet cell battery, but which can be any nominated voltage or could be a series of low voltage cells. The *e0battery is charged by a DC power source 7, such as a solar panel or wind ooe o turbine. It is preferable that the DC power source 7 be an external source that can minimise power costs for the user. However, the battery 6 could be recharged by power drawn from the power distribution grid during low load periods, possibly at a reduced tariff.

A control signal 8 activates the switch 3 to determine which power source supplies the load 4. In low load periods the load 4 will be connected directly to the power supply grid 2. As a peak load period approaches the power supply authority issues a signal over the power distribution grid for the switch 3 to connect the load 4 to the inverter 5 and 8 disconnect the load 4 from the power supply grid 2. The switch 3 reconnects the load 4 to the power supply grid 2 and disconnects the inverter 5 after a fixed time or when signalled to do so by another control signal 8. Since the switch 3 is always connected to the power supply grid 2 the power supply authority can issue any control signal at any time. It will be appreciated that, providing the DC storage 6 is adequately charged, there will be minimal inconvenience to the user. This overcomes the greatest drawback in known prior art systems which simply shut down part of a users load.

OSOS

It will also be appreciated that the load shedding means allows °0 10 the power supply authority to more effectively manage power distribution by r controlling the total load on the power generation system at any time without causing inconvenience to their customer. There are also a number of

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o *consequent advantages including the use of solar energy is encouraged; •consumers will have power available during black out or brown out of the 1 5 mains power supplier; the need for new fossil fuel power stations is reduced; •eb* "consumers may have reduced power bills; and other advantages.

0* Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features.

Claims

1. A load shedding means for shedding load from a power distribution grid, said load shedding means comprising: a direct current power source; local storage means for storing direct current power from the direct current power source; inverter means for converting direct current power drawn from the storage means to alternating current power; and switch means responsive to a remote control signal provided so as to switch between a first condition and a second condition; wherein when the switch means is in said first condition, the switch means provides electrical connection between a load and a remote alternating current power source, and when the switch means is in said second condition, the switch means provides electrical connection between S"the load and the inverter.

2. A load shedding means as claimed in Claim 1 wherein the direct current power source is one or more of a solar panel, a wind turbine or a generator powered by fossil fuel.

3. A load shedding means as claimed in Claim 1 wherein the alternating current power source supplies alternating current power that is rectified to provide the direct current power source.

4. A load shedding means as claimed in Claim 3 wherein the alternating current power source is mains supply current.

A load shedding means as claimed in any one of the preceding -claims wherein the storage means is a rechargeable direct current storage means.

6. A load shedding means as claimed in Claim 5 wherein the rechargeable direct current storage means is a rechargeable battery.

7. A load shedding means as claimed in anyone of the preceding claims wherein the inverter converts direct current voltage available from the storage means to an alternating current voltage.

8. A load shedding means as claimed in anyone of the preceding claims wherein the alternating current power source is supplied by a power supply authority.

9. A load shedding means as claimed in Claim 8 wherein the switch means is a solid state, electronic means responsive to a ripple signal received from the power supply authority via the power distribution grid.

A load shedding means as claimed in Claim 9 wherein the switch means may be switched in response to the same signal as at least one other installed switch means.

11. A load shedding means as claimed in Claim 9 wherein the switch means incorporates a unique address so that the power supply Sa-. authority may individually activate said switch means. a A load shedding means substantially as described herein with a. S"reference to the drawing. DATED this Seventeenth day of May 2001. GRAHAM McDONALD By his Patent Attorneys FISHER ADAMS KELLY