Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Patent
1992-05-07
1994-01-11
Sterrett, J. L.
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
363 56, 363 98, 363132, 361 87, H02M 5458
Patent
active
052787478
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention refers to a power supply and, more specifically, a power supply which generates a mainly sinusoidal voltage to be used in supplying apparatuses that are normally operated from the main power.
In caravans and motor caravans electric apparatuses and other equipment are found which are operated by low voltage DC current from, for example, a car battery or the like. In addition, there is often other equipment which is operated from the main power and which can be used only when the caravan is connected to the main power, for example at a caravan site.
Now, it is desired to provide a power supply by which it will be possible to use main power operated equipment even when the caravan is not situated at a caravan site, or the like, and, accordingly, cannot be connected to the main power. Such a power supply could be comprised by a unit generating a DC voltage and being associated with a DC/AC converter which, by means of switching technique known in the art, converts the DC voltage to a mainly sinusoidal AC voltage of the desired magnitude, for example 110 volts or 220 volts. Suitably, the DC voltage generating unit could be a three-phase AC generator of the kind to be found in cars for their electric supply. A generator of the kind referred to comprises a rectifying device providing a DC voltage output from the generator. Such a generator together with a DC/AC converter constructed by known techniques can be provided in the engine compartment of a car or motor caravan and be terminated with an AC outlet. Then, by a suitable line, the passenger compartment of the motor caravan or a caravan connected to the car can be supplied.
A power supply of the kind referred to has to be protected against excess current and to this end protecting arrangements are provided which disconnect the power supply when the load current exceeds a predetermined value. The art offers a solution in case of a disconnection reconnection is allowed after the lapse a time period corresponding to one or two periods of the AC voltage. If inductive loads, such as an induction motor of a refrigerator or an air conditioner, are to be supplied, the delayed reconnection is a disadvantage as sufficient energy will not be supplied to the motor to have it rotate before disconnection takes place due to overcurrent. Hence, under certain conditions it may happen that the compressor motor in the refrigerator or in the air conditioner, respectively, cannot be started.
SUMMARY OF THE INVENTION
The object of the invention is to remedy the drawback in the prior art and to provide a power supply of the kind referred to above at which reconnection takes place after a time period which is considerably smaller as compared to half the period of the AC voltage. This means that reconnection takes place almost immediately after a disconnection has occurred so that there will be no substantial drop of current below the predetermined current limit. Hence, the current is upheld and sufficient energy supplied for bringing the motor to start.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described more with reference to the enclosed drawings in which:
FIG. 1 is a block diagram for a power supply according to the invention, and
FIG. 2 is a practical circuit diagram for a preferred embodiment in non-essential parts have been omitted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 there is shown a block diagram for a power supply according to the invention in which an AC generator 10 is provided which, via a rectifier device 11, generates a DC voltage U across a positive terminal 12 and a negative terminal 13. A conductor 14 is connected to the positive terminal 12 while a conductor 15 is connected to the negative terminal 13. The generator 10 has a field winding 16 and the voltage U is controlled by a control device 17 which, upon need, increases or decreases the voltage to the field winding 16.
The circuit of FIG. 1 further comprises an DC/AC converter 18 in which are included four semicon
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Falt Johan A. M.
Karlsson Mats R.
Aktiebolaget Electrolux
Sterrett J. L.
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