JPH0746916B2 - Overload detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overload detection device for monitoring a load amount for load protection.

[Conventional technology]

FIG. 7 is a circuit diagram of a conventional overload detection device disclosed in, for example, Japanese Patent Application No. 59-229581.
1 is a DC motor as a DC load, 2 is a thyristor converter for rectification, 3 is a current transformer placed on the AC side, 4 is a current detector of the main circuit current I connected to the current transformer 3, and 5 is a main circuit An analog-to-digital converter (hereinafter referred to as an A / D converter) for converting a current into a digital signal, 6 is an averaging processor provided in an arithmetic unit, which samples a digitized current signal at regular intervals and Obtain the average value I _A of the sampled current signals.

8 is the average current I _A that has been averaged and the instantaneous overcurrent determination reference value
Instantaneous overcurrent detection comparator to compare with I ₀ , 9 is averaged current
I _A square value I _A ² a seek operation units, 10 square value I by multiplying the load resistor R _A ² and the load power consumption (Joule heat) I _A ² calculator for obtaining the R, 11 is calculated value I _A first-order delay calculator that calculates the temperature rise Θ of the load from _A ² R, 12 is a temperature comparator for detecting time delay overload that compares the temperature rise Θ, 13 is a mixer, 14 is each comparator 8,
12 is an output circuit, and 15 is an overload relay whose operation is controlled by the outputs of the comparators 8 and 12.

Next, the operation will be described, but first, the relationship between the temperature increase of the load used for the timed load detection and the size of the load will be described.

As is well known, the general formula for increasing the temperature is as follows.

Q _dt = C _d Θ + Θ · A _dt (10) Where, Q: heat quantity generated in an object per unit time (W) C: heat capacity (J / K) A: heat quantity transferred per unit time per 1K (W / K) Θ: Temperature Deformation of equation (10) gives the following equation.

When the Laplace transform is performed with the initial value 0, the following equation is obtained.

On the other hand, considering that the calorific value is due to Joule heat, it is expressed by the following equation.

Q (t) = I ² (t) R (13) I (t): Current value (A) R: Circuit resistance (Ω) This shows that I ² R is related to heat generation temperature and density. Therefore, the time delay overload detection temperature can be calculated by the first-order delay calculator 11.

Next, the operation of the above circuit will be described. The current value I detected by the current detector 4 is converted into a digital signal by the A / D converter 5, and the averaging processor 6 samples M digital signals at regular time intervals. This sampling process is shown in the flow chart of FIG.

In FIG. 4, first start and then step ST1
The counter memory M is incremented by, and step ST2
The A / D converted value of the current is sampled by and stored in the memory.

In this way, the sampled M data are added and divided by the added value to obtain the average current I _A. Then, the calculation of overload detection is started. This averaging process is shown in the flow chart of FIG.

In FIG. 5, M pieces of data sampled in step ST11 are added, and the data added in step ST12 is divided by M to obtain an average value.

The load detection calculation is executed by the following method based on the average current I _A thus obtained.

To protect the DC motor 1 from overload, two points are monitored: instantaneous overcurrent detection that regulates the rectifying capability of the commutator and timed overload detection that regulates the temperature rise.

First, the instantaneous overcurrent detection will be described with reference to the flowchart of FIG. The determination reference value I _O of the instantaneous overcurrent is stored in advance in the memory of the arithmetic unit 7, and the instantaneous overcurrent detection comparator 8 compares the average current I _A with the determination reference value I _O read from the memory. , I _A > I _O (Step ST
21) shows that the overload relay 15
Is operated (step ST22).

When it is determined in step ST21 that I _A <I _O , the process of timed overload detection is automatically started, and the square value I _A ² of the average current I _A is calculated in the calculator 9 (step ST23). .
Furthermore, in the arithmetic unit 10, the load resistance (armature circuit resistance)
By multiplying the I _A ² to R seek I _A ² R (step ST24).

In addition, the rising temperature Θ corresponding to I _A ² R is calculated by the first-order delay calculator 11
Is calculated (step ST25).

Next, the rising temperature Θ thus obtained is compared with the time limit load determination reference temperature Θ _O defined as a rated item in the comparator 12 (step ST26), and when it is determined that Θ> Θ _O , operating the overload relay 15 detects an overload condition, if it is determined that Shitashita _O maintains the overload relay 15 off state, determines that the normal operating condition (step ST27).

As described above, when the overload relay 15 operates in step ST22, it is determined that the overload relay 15 is in the overload state, and control of power supply to the load and other load protection measures can be taken.

[Problems to be Solved by the Invention]

Since the conventional overload detection device is configured as described above, the increase in resistance value due to temperature rise is not considered, and the time constant of the first-order delay calculator 11 can be set to only one point, so that setting On the contrary, there is a problem that the operation area is limited depending on the point.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an overload detection device capable of monitoring the load amount in a wide time range.

[Means for Solving the Problems]

The overload detection device according to the present invention performs the averaging process for the preset effective value calculation cycle of the square value of the average current obtained by the averaging processing by the averaging processor to perform the averaging process calculation. A second averaging processor for calculating the average of the squared values of the effective values of the currents, and the average of the squared values and the preset square value of the reference effective value and the comparator for detecting the effective value overload. It is provided.

[Work]

The second averaging processor according to the present invention performs the averaging process for the preset effective value calculation cycle of the square value of the average current obtained by the averaging processor to obtain the average value for the effective value calculation cycle. Calculate the average squared value of the RMS current, compare the squared average value with the squared average current with the RMS overload detection comparator, and use this comparison result for overload relay control. , Detect overload.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, 1 to 15 are the same as those in FIG. 7, and 16 is the square value I _A ² of the average current obtained by the averaging processor 9, and is input to the preset effective value calculation period T _S. Is a second averaging processor that performs the averaging process of 1 and calculates the average _A ² of the square values of the current effective value during the effective value calculating period T _S.

That is, the second averaging processor 16 is the averaging processor 6
The squared value I _A ² of the average current I _A obtained in step S ² is sampled for each calculation, and N is calculated during the preset effective value calculation period T _S.
The number of squares is added, and this is divided by N to obtain the average value of the squares.

Reference numeral 17 is a comparator for detecting an effective value overload, which compares the average value of the squares with a square value A ² of a preset reference effective value to determine an overload and outputs it to the mixer 13. Other configurations are the same as in FIG. 7.

Next, the operation will be described. The square value I _A ² of the average current calculated by the calculator 9 is set to the second averaging processor 1 at regular time intervals.
Sampling at 6 and storing the latest data and the oldest data in N data tables TBL during the effective value calculation cycle T _S while storing them in time series, further averaging, and determining the effective value overload Is performed by the process shown in the flowchart of FIG.

First, as shown in FIG. 3, the table TBL stores N data in order to store N pieces of data in the effective value calculation cycle T _S.
The counter C expresses the position where the latest data is stored by offsetting it from the beginning of the data table TBL. This counter is incremented by 1 and the oldest data and the latest data are updated. Then, the same process is repeated for each sampling.

Incidentally, in FIG. 3, the counter C indicates t when
Indicates the position of the update data pointed to at.

Next, the process of FIG. 2 will be described. First, step ST
A counter C indicating the position of the latest sampling data at 31
Is incremented by 1 to find the position of the oldest sampling data.

Next, it is checked whether the value of the counter C exceeds the table length (step ST32). If it is over (CN), set counter C to data table TB
Set it again at the beginning of L (step ST33).

The oldest sampling data is input from the data table TBL and stored in the temporary memory Old (step ST34). After that, the latest sampling data I _A ² is stored in the position of the oldest sampling data table and prepared for the next time (step ST35).

Next, the oldest sampling data is subtracted from the added value _S during the effective value calculation cycle T _S (step ST36), and then the latest sampling data is added to obtain the effective value calculation cycle T _S.
The addition value S between is calculated (step ST37), this addition value S is divided by N, and the effective value calculation cycle by this sampling
The average value _A ² between T _S (step ST38).

Next, the average value _A ² between the effective value calculation periods T _S thus obtained is compared with a preset square value _A ² of the reference effective value in the effective value overload detection comparator 17 (step ST
39), if it is determined that _A ² > A ² , the overload relay 15
Is operated to detect the overload state, and when it is determined that _A ² <A ² , the overload relay 15 is maintained in the off state and it is determined that the operating state is normal (step ST40). The above process is performed every sampling period.

As described above, when the overload relay 15 operates in step ST41, it is determined that the overload relay 15 is in the overload state, and control of power supply to the load and other load protection measures can be taken.

In the above embodiment, as the effective value calculation cycle T _S increases, the data table also increases, so the averaging process of the effective value calculation cycle T _S is performed in multiple stages (T _S = T _S1 × T _S2 × …
...) can be disassembled, and by doing so, even a large effective value calculation cycle T _S can be averaged with a small data table.

Further, in the above-mentioned embodiment, the processor or the like dedicated to the digital signal processing is provided in the arithmetic unit 7, but it is also possible to use the processor or the like of another control arithmetic unit.

〔The invention's effect〕

As described above, according to the present invention, the averaging process for the effective value calculation cycle in which the square value of the average current is preset is performed by the second averaging processor, and the current for the effective value calculation cycle is calculated. Calculates the average of the squared values of the RMS values and compares the average with a preset square value of the standard RMS value to detect the overload due to the increase in the resistance value due to the temperature rise and the comparator for detecting the RMS value overload. The output of the comparator for detecting instantaneous current and the temperature comparator for detecting time-delayed overload is also added to the mixer, so that instantaneous overcurrent detection and time-delayed overload detection can be performed in three ways, effective value overload detection. It is possible to detect an overload due to an increase in resistance value due to temperature rise, and it is possible to accurately detect an overload with respect to a load amount in a wide time range.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an overload detection device according to an embodiment of the present invention, FIG. 2 is a flow chart of a processing process of effective value overload detection according to the embodiment, and FIG. FIG. 4 is a flow chart for explaining a sampling process of a conventional overload detection device, and FIG. 5 is a diagram for explaining an averaging process of the conventional overload detection device. 6 is a flowchart of the overload detection process, and FIG. 7 is a circuit diagram of a conventional overload detection device. 1 is a DC motor, 3 is a current transformer, 4 is a current detector, 5 is A /
D converter, 6 is an averaging processor, 8 is a comparator for instantaneous overcurrent detection, 9 and 10 are calculators, 11 is a first-order delay calculator, 12 is a temperature comparator for detecting timed overload, and 13 is a mixer. , 15 is an overload relay,
Reference numeral 16 is a second averaging processor, and 17 is a comparator for detecting an effective value overload. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A current transformer for detecting a main circuit current I of a DC load, and the detected main circuit current is converted into a digital quantity.
An A / D converter, an averaging processor that samples the main circuit current of this digital amount at regular intervals and averages it, an average current I _A obtained by this averaging, and an instantaneous overcurrent judgment reference. The instantaneous overcurrent detection comparator for comparing the value I _O and the average current I _A obtained by the averaging process are squared, and the calculated value I _A ² is multiplied by the DC load resistance R of the main circuit. Calculated value I ² R
Which calculates the temperature rise, the first-order delay calculator which calculates the temperature rise θ from the calculated value I _A ² R, and the temperature comparison for time-delay overload detection which compares the temperature rise θ with a preset reference temperature rise θ _O And the square value I _A ² of the average current is averaged during the preset effective value calculation cycle T _S , and the squared value of the effective value of the current during this effective value calculation cycle T _{S A} ^second averaging processor that calculates the average A ² and compares the average _A ² with a preset square value A ² of the reference effective value in order to detect an overload due to an increase in resistance value due to temperature rise. The RMS overload detection comparator, the RMS overload detection comparator output and the instantaneous overcurrent detection comparator output and the time limit overload detection temperature comparator output are combined to create the above overload relay. And a mixer for controlling the overload detection device.