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PREDICTING OVER LOADING CAPACITY OF A FREQUENCY CONVERTER

IP.com Disclosure Number: IPCOM000249828D
Publication Date: 2017-Apr-12
Document File: 4 page(s) / 95K

Publishing Venue

The IP.com Prior Art Database

Related People

Salmia Teemu: AUTHOR [+3]

Abstract

A novel solution is proposed in which a counter is created for giving a notification how long an output current, which exceeds the permitted continuous thermal current, can be used, before the current integral protection reaches the limit at which the output current is dropped from the permitted momentary maximum current to the permitted continuous thermal current.

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© Copyright [2017] ABB. All rights reserved.

PREDICTING OVER LOADING CAPACITY OF A FREQUENCY CONVERTER

Abstract

A novel solution is proposed in which a counter is created for giving a notification how long an

output current, which exceeds the permitted continuous thermal current, can be used, before the

current integral protection reaches the limit at which the output current is dropped from the

permitted momentary maximum current to the permitted continuous thermal current.

Background

A frequency converter is typically used cyclically, whereby the output current of the frequency

converter may momentarily exceed the output current that is permitted during a continuous

thermal loading of the frequency converter. The output current will on the other hand sometimes

remain under the limit for continuous thermal loading. Cyclic drives needing overloading capacity

momentarily are e.g. moving working machines, elevators and cranes.

A frequency converter comprises components with very different heat time constants. The time

constants of chips in IGBT-modules are in the order of 100 milliseconds, the time constants of the

bottom plate are in the order of 5 to 100 seconds (depending on the cooling method) whereas a

time constant for a big DC-capacitor may be in the order of hours. The greater the heat time

constant of the component is, the longer it takes for the component to heat up, and an overloading

of the component is possible for a short time, said short time being defined in relation to the heat

time constant of the component. For a frequency converter, the highest permitted momentary

maximum current (imax) and the highest permitted continuous thermal current (icont), are typically

determined by calculations and/or by testing. In a cyclic drive, the current may not exceed the

permitted momentary maximum current imax and the effective value of the current over a long

period may not exceed the permitted continuous thermal current icont.

A prior art solution to allow overloading is based on a current integration calculation (ifilt), in which

the output current of the apparatus raised to the power of two (iout^2) is compared to the permitted

momentary maximum current raised to the power of two (imax^2) as well as to the permitted

continuous thermal current raised to the power of two (icont^2). Additionally a time constant (tau)

is needed in order to determine how fast the current ifilt^2 increases or decreases. The decrease

speed and the increase speed may also be different. The magnitude of the time constant is

determined by calculations or by tests. The current limits imax ja icont may be constant or they

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© Copyright [2017] ABB. All rights reserved.

may depend on the operating point of the apparatus (e.g. the temperature of the semiconductor,

the temperature of the cooling liquid, the magnitude of the DC voltage, etc.). This protection may

be used for the output current and for the DC...