Electric power conversion systems – Current conversion – Having plural converters for single conversion
Patent
1991-09-18
1993-03-02
Voeltz, Emanuel T.
Electric power conversion systems
Current conversion
Having plural converters for single conversion
307 35, 307 38, 307 40, H02J 1300
Patent
active
051915200
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a power supply system for use in conjunction with one or more electrical loads, and has particular but not exclusive application in the control of lift machines.
DESCRIPTION OF THE PRIOR ART
A discussion of the prior art and the description of preferred embodiments will be made with reference to the application of lifts. It should be understood that the invention is equally applicable to other applications having electrical loads.
In modern lift installations, it is common to use DC machines as the prime-mover for lift cars and their associated counterweights; these machines being connected to the ropes suspending the lift cars and counterweights via a gearbox, or alternatively through direct connection to the sheave wheel. Since lift cars must travel in both the upward and downward directions, DC machines are required to be controllable direction-wise and have precise speed control.
Pulse width modulated (PWM) converters are often used in conjunction with DC machines to provide either two or four quadrant control over the machine. A four quadrant control allows for the regeneration of power into the supply network during deceleration of the lift car. PWM (converters) usually operate from a multi-phase AC supply, which supply is then rectified and controlled to give the appropriate output voltage and polarity to achieve the desired speed and direction of rotation of the DC machine.
It is also known to utilize slow speed AC machines in lift applications, which must again be speed controllable. For this purpose, AC-AC converters are most often used whereby the multi-phase supply is rectified to a DC bus, then inverted to provide the required output frequency in voltage, in turn to cause the AC machine to operate the desired speed with the requisite torque. Optionally, cycloconverters can provide direct frequency conversion synthesizing lower frequency outputs from the mains supply.
It is particularly desirable that lift drives be of low cost, have low radiated acoustic noise and radio frequency interference, and can provide at least partial service under all supply conditions. The discussed known systems have the drawback of being particularly costly and complex.
Further, in the case of a DC machine, when a fault occurs on the machine itself there may be arcing between the rotor brushes. These arcs are inherently difficult to extinguish, given that there are no zero crossings in voltage to allow natural commutation as is the case for AC machines.
Circuit breakers are not cost effective in protecting DC drives from localised faults such as output short circuits, and can often cause significant damage to both the motor and the converter.
Whilst DC machines have the problems discussed, they have often been preferred over AC machines, given that they have superior speed regulation and torque characteristics.
As for AC machines, constant field (synchronous) machines offer advantages over the cheaper induction (non-synchronous) motors. They can provide inherent braking capability on power loss where a stator load is provided and especially if permanent magnetic fields are used, the air gap is large enough to allow reasonably lightweight design providing for deflection as a result of lateral rotor loads, and afford greater efficiency at low speed or stall conditions.
The present invention has an object the provision of a power supply system which will overcome the problems referred to above.
SUMMARY OF THE INVENTION
Therefore the invention in one aspect, provides a power supply system comprising:
a controllable converter suitable for connection to an input supply and being adapted to generate an output supply;
a plurality of loads each making a demand for power from the converter;
a plurality of load controllers each interposed between the and a load; and
a supply controller which can communicate with all of said load controllers and control the generation of the output supply, said supply controller receiving requests from each controller in response to a dem
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Boral Johns Perry Industries Pty. Ltd.
Voeltz Emanuel T.
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