Electric power conversion systems – Frequency conversion without intermediate conversion to d.c.
Reexamination Certificate
2001-03-02
2002-05-07
Han, Jessica (Department: 2838)
Electric power conversion systems
Frequency conversion without intermediate conversion to d.c.
C439S001000, C439S620040, C439S076100
Reexamination Certificate
active
06385069
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a frequency converter.
BACKGROUND OF THE INVENTION
A frequency converter is a device for steplessly adjusting the rotation speed of an alternating-current motor, such as a short circuit motor. The rotation speed is adjusted in the frequency converter mainly by converting the voltage supplied to the motor and the frequency of the voltage. The frequency converter can be used for adjusting the acceleration and deceleration as well as braking and reversing of the motor. When the frequency converter is used for controlling the motor, the motor can be controlled and adjusted from a control unit by a computer.
In view of the characteristics mentioned above, frequency converters have become increasingly popular particularly in industrial uses associated with different processes. An alternating-current motor controlled and adjusted by a frequency converter currently often replaces a direct-current motor in industrial processes. The frequency converter is typically used for controlling electric motors for pumps, blowers, elevators, hoists, conveyors etc. Frequency converters are also increasingly being used in smaller applications, such as household appliances.
Frequency converters can be widely applied since electric motors are used in devices of many different types. Such a typical device to employ a steplessly controlled electric motor is an elevator for conveying persons or goods. The electric motor moving the elevator has thus to be operationally flexible in order to move the elevator between loading and unloading planes, accelerate and brake smoothly as well as position accurately between the loading and unloading planes. Elevators come in various sizes according to use. Elevators are also used in different environments, which means that humidity and temperature conditions vary greatly. Frequency converters of different capacity and type can then preferably be used for controlling the motors for elevators of varying sizes.
A problem with the current frequency converters is that a frequency converter suitable for controlling a motor of a particular capacity, such as a 0.75 kW motor, is a compact device wherein all structural components of the frequency converter are arranged in one and the same casing. The frequency converter mainly comprises a power part comprising means for converting alternating current into direct current and again into alternating current having an adjustable frequency, and a control and adjustment part comprising means for controlling and adjusting the operation of the power part and thus the operation of the electric motor. Additionally, according to the prior art, the control and adjustment part comprises a mother card and IO-cards (Input/Output), the IO-cards being arranged in parallel with the mother board, i.e. horizontally and on top of each other.
Such a compact frequency converter is problematic since different applications, such as different elevators, require a great number of different frequency converters designed for different uses. This results in a large range of frequency converters which is difficult to manage and uneconomic to maintain. On the other hand, as frequency converters are increasingly being used in different applications, more and more adaptable frequency converters are needed constantly.
A major problem with the prior art solutions is thus that the frequency converters are complex and hence uneconomic to arrange in different applications and environments. The problem is mainly caused by the structure of the prior art frequency converters wherein all structural components of the device are arranged in the same casing and the IO-cards of the control and adjustment part are arranged in parallel with the mother card, i.e. horizontally, and on top of each other.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is to alleviate drawbacks of the prior art and to provide an improved frequency converter whose structure enables the frequency converter to be more flexibly and more advantageously arranged in different applications of varying requirements.
This is achieved by a frequency converter of the invention characterized by what is disclosed in the claims. To be more precise, the frequency converter of the invention is mainly characterized by what is disclosed in the characterizing part of claim
1
.
Preferred embodiments of the invention are disclosed in the dependent claims.
The idea underlying the invention is that the power part and the control and adjustment part of the frequency converter are separated from each other, and the control and adjustment part is arranged as a separate control and adjustment unit of its own which is independent of the power part and which is preferably arranged in a separate casing or module. This solution provides several important advantages.
Since the structural components of the frequency converter are not arranged in the same casing but they are divided into two separate units, the important advantage achieved is that the features of a frequency converter using a power part of a particular capacity can be varied according to different applications by changing the control and adjustment part. The features of the control and adjustment part are arranged according to the different applications by varying the software and the mother card and IO-cards (Input/Output) of the control and adjustment part. The software in the control and adjustment part controls the operation of the power electronics in the power part of the frequency converter by means of measurement and adjustment messages received and transmitted through the IO-cards. Considerable advantages in terms of product differentiation of the frequency converter are thus achieved as regards enhancing the product range and cost-efficiency. A control and adjustment part having certain features can then be used with a power part of several power capacities; similarly, several different control and adjustment parts can be used with a power part having a certain capacity.
Dividing the power part and the control and adjustment part into two separate units substantially improves the possibilities of enhancing interference protection in the power part as well as in the control and adjustment part. The power part can then be encapsulated efficiently in order to improve the electromagnetic EMC protection. The power part of the frequency converter typically emits a large amount of electromagnetic interference radiation (EMC) into the environment, which impedes the operation of electronic devices. Secondly, arranging the control and adjustment part in a separate unit enables the electronics in the control and adjustment part to be advantageously protected, by encapsulation, against the electromagnetic interference radiation coming from outside.
Furthermore, dividing the power part and the control and adjustment part into two separate units substantially improves the possibilities to protect, by encapsulation, the power part as well as the control and adjustment part against damp, dust and gases in the environment as well as stress caused by other environmental factors. In addition, dividing the power part and the control and adjustment part into two separate units improves work safety during installation since the high voltage structural components of the frequency converter can be efficiently shielded from contact by encapsulating the power part as well as the control and adjustment part.
As an advantage associated with the manufacture and testing, dividing the power part and the control and adjustment part into two separate units enables the power part to be manufactured and tested independently of the control and adjustment part and, similarly, the control and adjustment part to be manufactured and tested independently of the power part. The parts can then preferably be manufactured and tested separately and in different places. A further advantage is that the final assembly of the frequency converter, i.e. interconnecting the power part and the control and adjustment part, does not have
Jaskari Jukka
Miettinen Osmo
Han Jessica
Oliff & Berridg,e PLC
Vacon Oyj
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