UA129728U - METHOD OF CURRENT PROTECTION OF ELECTRIC MOTOR WITH POWER FROM A SEMICONDUCTOR CONVERTER - Google Patents

Abstract

Method for current protection of a semiconductor-powered electric motor for measuring currents, determining their squares, forming a time series of partial sums of squares of currents by removing content from the last element of this series and moving one step ahead of the content of all its elements upon arrival operating current, setting it in the first place and summing it to the components of the remaining elements of the time series of partial sums of squares of operating currents. DC or AC motor is connected to the output of the corresponding semiconductor converter, measure the values of the currents at its input, determine the squares of the currents and divide them by the square of the rated current of the motor, obtained a one-dimensional number of multiplicities of the acting currents in two dimensions time of averaging of equivalent currents, for which form a number of partial sums of the multiplicity of squares of currents, partial sums are divided by the corresponding number the number of additions of partial sums in the elements of this series, the axis of the currents of the graph of the time curve of the overload of the electric motor is divided into uniform segments, from the ends of which are drawn parallel to the axis of time lines to the intersection with this curve, obtained by the projection of points of intersection by the axis of time, divide the values of time at the time of sampling the signals of the current sensor and receive the number of partial sum supplements for the elements of the series to be controlled, if the allowable level is exceeded in any controlled element of the number of particles Closed amounts generates a signal to turn off the electric power source.

Description

The useful model belongs to electrical engineering and can be used for current protection with predetermined accuracy of operation of a direct current or alternating current electric motor when powered by a semiconductor converter.

There is a known method of protecting an electric motor, which includes measuring currents, generating a signal proportional to the square of the electric motor current, averaging the specified signal over time, disconnecting the electric motor from the power supply when the permissible duration of current overload is exceeded.

Pre-specified accuracy of protection activation in this method is not possible due to the fact that the calculation of the equivalent load current is carried out on a specific averaging time interval, which cannot be the same for short-term and long-term overloads |11.

The closest to the claimed device is a method of protecting an electric motor from overloads, which includes measuring operating currents, determining their squares, forming a time series of partial sums of squares of operating currents with the removal of the content from the last element of this series and shifting the content of all its elements one step forward upon arrival of the next square of the active current, setting it to the first place and summing up the partial sums of the squares of the active currents to the components of the remaining elements of the time series.

Pre-specified accuracy of the protection operation in this method is not possible because the discreteness of the time series and the size of the information points of the time series are chosen arbitrarily |21.

The basis of the useful model is the task of ensuring pre-specified accuracy of activation of the current protection of a direct or alternating current electric motor when powered by a semiconductor converter by dividing the coordinate axis of the current of the curve of the squared multiplicity of current overload into uniform segments, the number of which ensures the pre-selected accuracy of protection activation.

The solution to the problem is achieved by the fact that the method of current protection of an electric motor with power from a semiconductor converter, which includes measuring the active currents, determining their squares, forming a time series of the partial sums of the squares of the active currents with the removal of the content from the last element of this series and shifting the content of all its elements upon arrival of the next square of active current, by setting

From it to the first place and summation to the components of the remaining elements of the time series of the partial sums of the squares of the active currents, differs in that a direct or alternating current electric motor is connected to the output of the corresponding semiconductor converter, the values of the active currents at its input are measured, the squares of the active currents are determined and they are divided per square of the nominal current of the electric motor, the obtained one-dimensional series of the multiplicity of the operating currents is built into a two-dimensional space by combining the time axis with the time axis of the averaging of the equivalent currents, for which a series of partial sums of the multiplicities of the squares of the operating currents is formed, the partial sums are divided by the corresponding number of terms of the partial sums in the elements of this series, the current axis of the graph of the time-current overload curve of the electric motor is divided into uniform segments, from the ends of which lines parallel to the time axis are drawn to the intersection with this curve, obtained, with the help of projections of the intersection points on the time axis, the value of the time part t at the time of discretization of the current sensor signals and obtain the number of terms of partial sums for elements of the series to be controlled, if the permissible level is exceeded in any controlled element of the series of partial sums, they form a signal to disconnect the electric motor from the power source.

The method is carried out as follows. The values of the squares of the operating currents at the input of the semiconductor converter - electric motor system are measured, for example, a controlled rectifier - a direct current motor, a soft start device - an asynchronous or synchronous motor, a frequency converter - an alternating current motor, a valve motor of direct current or alternating current, and so on. Determine the squares of the operating currents and divide them by the square of the rated current of the electric motor. A one-dimensional series of the multiplicity of the squares of the active currents as a function of time is obtained. This series is embedded in two-dimensional space by combining the time axis with the time axis of averaging the equivalent currents. For this, a series of partial sums of the multiplicity of the squares of the active currents is formed. Partial sums are divided by the corresponding number of terms of partial sums. A two-dimensional series is obtained, in which the time axis coincides with the time axis of the averaging of the squares of the equivalent currents and has the form

IJ om NIV) 2 nom NIV NIV) Zinome R. (KIV OA) d.

When the next, again determined value of the square of the active current is received, the contents of all the memory elements of the time series of the partial sums of the multiplicity of the squares of the active currents are shifted one step forward. The newly determined value is placed first and summed up to 60 terms of the remaining elements of the time series. The last value of the time series is deleted. In this way, a series of multiples of the squares of the currents depending on the time of averaging of the equivalent currents will be obtained.

The averaging time of the equivalent currents of the electric motor cannot be the same to detect with predetermined accuracy large short-term and small long-term overloads. So, if the time of averaging the equivalent currents is tens of minutes, it is impossible to detect significant short-term overloads in tens of seconds in time. The averaging time of the equivalent currents in each of the controlled elements of the time series is different and is equal to the number of the element of the time series (or the number of terms in this element) multiplied by the sampling time of the active current sensor. This solution allows simultaneous monitoring of equivalent currents with all possible averaging times. In practice, it is sufficient to monitor the equivalent currents with the averaging time from the sampling time of the current sensor to 3...5 constant heating times of the electric motor.

The dependence of the permissible operating time of the electric motor on the frequency of its current overload is calculated or obtained from the electric motor manufacturer. For example, the frequency and and and IA AK -1) the room characteristic is calculated in accordance with the expression - With the help of this dependence, a curve of the permissible operating time of the electric motor is drawn from the multiplicity of kt overloads by the squares of the operating currents. The axis of the multiplicity of the squares of the active currents is divided into uniform segments, from the ends of which lines parallel to the time axis are drawn to the intersection with the time-current curve. Using the projections of intersection points on the time axis, time is found, divided by the sampling time of the active current sensor, and the numbers of the elements of the time series of the partial sums of the multiplicity of the squares of the active currents to be monitored are obtained.

The numbers of the elements in the series are equal to the number of terms of the partial sums in the elements of the series.

If a predetermined accuracy of 1 95 is required, then the axis of multiples of the squares of the active currents is divided into 100 uniform segments. This means that only 100 elements of the time series of the partial sums of the multiplicity of the squares of the active currents are subject to control. If an accuracy of 5 95 is required, then the axis of the multiplicity of the squares of the active currents is divided into 20 equal segments and only 20 elements of the time series are subject to control.

If the permissible level is exceeded in any controlled element, a number of partial sums form a signal to disconnect the electric motor from the power source.

З Permissible values are obtained at the ends of uniform segments of the axis of multiples of the squares of the operating currents.

Sources of information: 1. Author's certificate of the USSR. 510) Mo. 1365226 A, "Method of thermal protection of the electric motor of tracking systems". IPC НО2Н 55/04, 7/08. Aistov V.V., Levashov B.I.,

Medyakov I.N. Publ. 07.01.1988. 2. Patent of Ukraine for utility model SHA 101343, "Method of protecting an electric motor from current overloads". IPC НО2Н 7/08. Lebedev L.M., Dubovik V.G., Kovalchuk A.O.,

Lipsky M.V. Publ. 10.09.2015.

Claims (1)

USEFUL MODEL FORMULA The method of current protection of an electric motor with power from a semiconductor converter, in which the measurement of active currents, determination of their squares, formation of a time series of partial sums of squares of active currents with the removal of the content from the last element of this series and the displacement of the content of all its elements by one step forward the arrival of the next square of the active current, setting it to the first place and summing up to the components of the remaining elements of the time series of the partial sums of the squares of the active currents, which differs in that the direct or alternating current electric motor is connected to the output of the corresponding semiconductor converter, the values of the active currents at its input are measured, determine the squares of the operating currents and divide them by the square of the nominal current of the electric motor, the obtained one-dimensional series of the multiplicity of the operating currents is built into a two-dimensional space by combining the time axis with the time axis of averaging the equivalent currents, for which is formed by a series of partial sums of multiples of the squares of the active currents, the partial sums are divided by the corresponding number of terms of the partial sums in the elements of this series, the current axis of the graph of the time-current overload curve of the electric motor is divided into uniform segments, from the ends of which lines parallel to the time axis are drawn to the intersection with this curve , obtained with the help of projections of intersection points on the time axis, the time values are divided by the sampling time of the current sensor signals and the number of terms of partial sums for the elements of the series to be controlled is obtained, if the permissible level is exceeded in any controlled element of the series of partial sums, a signal is formed to disconnect the electric motor from the power source.