Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1994-01-28
1997-06-24
Krishnan, Adtya
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
H02P 540
Patent
active
056422709
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to electric vehicles and, more particularly, to battery powered vehicles having power transfer systems, either integral or separate, capable of transferring power between utility supplies and the vehicles.
The present invention further relates to battery charging systems required for electric vehicles and so-called "electric-hybrid" vehicles of the type having a main electric drive and an auxiliary internal combustion engine (AICE) drive.
Environmental issues have heightened the interest in recent years in alternative means for providing personal and commercial transportation. Economic and regulatory issues have combined to promote the view that electric powered vehicles will, over the next ten years, appear in significant numbers. It is possible that the number of electric or electric-hybrid (EH) vehicles in key areas may be around 100,000 or more by the year 2000.
Aside from the known modest performance levels of electric and hybrid vehicles, a major issue is that of cost. Presently, EH vehicles with performance levels acceptable to personal users are expected to sell at considerably greater prices than functionally comparable conventional vehicles. Of particular importance here is the cost of the traction battery which is always much more expensive than a fuel tank. There are unlikely to be any compensating cost savings elsewhere within the vehicle, at least for the next few years. This means that a battery powered electric vehicle will always have a considerable purchase cost disadvantage in comparison with a conventional vehicle. The day to day running cost is dominated by the need to replace the battery every few years. Without this need, the running costs of an electric vehicle can be very low.
Electric vehicles of this type require charging of their batteries from time to time, most commonly overnight. The charging process can take from less than 1 hour to perhaps 10 hours or more depending on the initial state of charge and the charging rate possible. Electric utilities are keen to sponsor the use of large numbers of electric vehicles, primarily to increase their sales of electricity.
A major problem for utility electricity suppliers is the matching of supply to instantaneous demand. This involves a considerable amount of planning including estimates of TV audience patterns and weather forecasting. The load can also vary significantly due to unforeseen circumstances.
The utility companies attempt to ensure continuity of supply whilst minimising total cost of generation. Several means are used to do this. Firstly, a utility will prefer to keep its most economical generators running where possible, though these typically take longer to bring up to speed and are expensive to use at very low loads. In parallel with this it will keep some `spinning` reserve available. This reserve consists of generators running at no or part load but synchronised with the grid. These can generate additional electricity very rapidly. The cost of maintaining such reserve is significant however. In addition to this, utilities maintain a number of other generators in a state where they can be started and brought into use in perhaps 1 to 30 minutes. In general the smaller systems can be brought on-line faster but generate electricity less economically than larger systems.
Other systems are in use, or being considered, including pumped storage systems which use surplus, low-cost electricity to pump water from a one reservoir to a second reservoir located physically higher. This procedure can then be reversed when additional power is needed. Battery storage is also becoming more attractive, including the use of high temperature batteries, though this requires additional rectification and inverter equipment to interface to the grid. The capital and running costs of this reserve capacity are high. Such techniques as are described above are generally known as "load levelling" techniques. Recently there has been increased interest in providing means for carrying out this function by giving utilities
REFERENCES:
patent: 4484130 (1984-11-01), Lownes et al.
patent: 5099186 (1992-03-01), Rippel et al.
Green Ross Martin
Kellaway Michael John
Krishnan Adtya
Wavedriver Limited
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