JPH04372551A - Method for protecting motor driving element - Google Patents

Abstract

PURPOSE:To prevent a motor driving element from burning, by transferring a current signal through a primary filter, whose time constant is the same as the inner thermal time constant of the motor driving element, and by breaking a motor driving current when the output of the primary filter exceeds an allowable value corresponding to the allowable maximum temperature of the motor driving element. CONSTITUTION:A current sensor 1 is inserted in the driving line of a motor 2. The direction of the current sensed by the sensor 1 is determined by a direction discriminator 3. When the direction is plus, the output of the direction discriminator is inputted to a primary filter 4a, under the determination of the current flowing through a motor driving element Tr1. When the direction is minus, the output of the direction discriminator is inputted to a primary filter 4b, under the determination of the current flowing through a motor driving element Tr2. The outputs of the primary filters 4a, 4b are inputted to comparators 5a, 5b respectively. When the outputs exceed preset reference voltages E2a, E2b respectively, they act on a gate driving part 7 and make the gate of the motor driving element Tr1 or Tr2 off respectively. Thereby, the motor driving elements Tr1, Tr2 can be prevented respectively from burning due to overcurrents.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection system for a motor drive element, and more particularly to a protection system for a motor drive element that prevents the motor drive element from overheating due to excessive current.

0002

[Prior Art] Conventionally, in this type of motor drive element protection system, in order to prevent the motor drive element from burning out due to excessive current, a thermostat placed on a heat sink placed near the motor drive element is used to protect the motor drive element from burning out due to excessive current. The case temperature of the motor drive element was detected and the gate of the motor drive element was turned off to protect the motor drive element.

FIG. 3 is a block diagram showing the structure of a conventional protection system for motor drive elements.

In the case of FIG. 3, two motor drive elements T
r1 and Tr2 each receive the DC voltage E1 and output motor drive currents in opposite directions to drive the motor 2.

[0005] The motor drive elements Tr1 and Tr2 detect the case temperature of the motor drive elements Tr1 and Tr2 with a thermostat 9 disposed on the heat sink 8, and based on this detected temperature, the gate drive unit 7 controls the motor drive elements Tr1 and Tr2. Tr
1, Tr2 was controlled to be in an off state.

[0006]

[Problem to be Solved by the Invention] In the conventional motor drive element protection method described above, the temperature of the heat sink near the motor drive element is detected, so it is necessary to detect a time delay with respect to the temperature inside the motor drive element. As a result, the motor drive elements cannot be completely protected from overheating, and this is countered by setting the overheat detection temperature of the heat sink to a sufficiently low temperature. Therefore, in order to obtain a predetermined drive current, there is a drawback that the rank of the motor drive element must be increased by one rank or more.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, an object of the present invention is to provide a protection system for a motor drive element that can avoid burnout due to overheating without increasing the rank of the motor drive element.

[0008]

[Means for Solving the Problems] The method of the present invention is a motor drive element protection method for protecting a motor drive element connected to a DC power source and outputting a directional motor drive current from overheating. Direction determining means for determining the flow direction of the motor drive current and switching an output destination in accordance with the determined direction; and sending out an output corresponding to the internal temperature of the motor driving element through the current value switched by the direction determining means. a filtering means for filtering so as to reduce the temperature of the motor driving element; and comparing the output of the filtering means with a reference value corresponding to a maximum allowable temperature of the motor driving element, and turning off the operation of the motor driving element if the temperature exceeds the reference value. and gate driving means.

Further, the system of the present invention has a configuration in which the filtering means is a filter having a time constant equal to a thermal time constant inside the motor driving element.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The embodiment shown in FIG. 1 takes as an example the case where two motor drive elements are used, and the two motor drive elements Tr1 and Tr2, to which a current voltage E1 is applied and arranged on a heat sink 8, In addition to the motor 2, there are a current detector 1 and a direction discriminator 3 that constitute direction discriminator means directly related to the present invention, two primary filters 4a and 4b as filtering means, and two comparators that constitute gate drive means. 5a, 5b, reference voltages E2a, E2b, an OR gate 6, and a gate driver 7.

Next, the operation of this embodiment will be explained.

[0014] The DC voltage E1 is applied to the motor driving element Tr1.
and Tr2, and outputs a driving current for the motor 2. The motor 2 is driven by controlling the motor driving element Tr1 and the driving element Tr2 on and off.

The current direction of the detection output of the current detector 1 inserted into the drive line of the motor 2 is determined by the direction discriminator 3, and if it is in the + direction, it is determined that the current is flowing through the motor drive element Tr1. It is determined and input to the primary filter 4a. If the current is in the - direction, it is determined that the current is flowing through the motor drive element Tr2, and the current is input to the primary filter 4b.

The outputs of the primary filters 4a and 4b are inputted to comparators 5a and 5b, respectively, and when they exceed preset reference voltages E2a and E2b, they act on the gate drive section 7, causing the motor drive elements Tr1, Turn off the gate of Tr2.

Here, if the filter time constants of the primary filters 4a, 4b are set to be equal to the internal thermal time constants of the motor drive elements Tr1, Tr2, the outputs of the primary filters 4a, 4b can be used to drive the motor. elements Tr1, Tr2
It takes a value corresponding to the internal temperature of the comparators 5a and 5b.
The reference voltages E2a and E2b of the motor drive element Tr1,
If it is set to correspond to the maximum allowable temperature of Tr2, it becomes possible to protect the motor drive elements Tr1 and Tr2 even in the event of excessive current.

The protection of the motor driving element described above will be explained in more detail with reference to FIG. 2 as follows.

Now, the motor drive element conduction current flowing through the motor drive element is ITr, and as shown in FIG. 2, I1 is up to time t1, I2 is up to time t2, and time t2 and t3.
Let us consider a case where the control is performed so that the control becomes I4 during the time t3 and I3 after the time t3.

Comparing the temperature change in the heat sink temperature TC shown by the broken line and the temperature change in the motor drive element internal temperature Tj shown by the dashed line, it is clear that the motor drive element internal temperature Tj
The temperature change is more rapid. This is based on the fact that the thermal time constant tH of the heat sink and the internal thermal time constant tTr of the motor drive elements Tr1 and Tr2 generally have the relationship shown in the following equation (1). tTr<<tH…(
1) In Fig. 2, time t2, t of t3-t2=tTr
3, when an excessive current shown by I4 flows, the internal temperature Tj of the motor driving element exceeds the maximum allowable temperature T2 and burns out, even though the heat sink temperature TC does not exceed the set temperature T1.

Conventionally, in order to prevent the occurrence of such burnout, the overheat detection temperature of the heat sink 8 was set to be sufficiently low, and for this reason, in order to ensure a predetermined motor drive current, one rank higher in capacity was used. As mentioned above, the motor drive element was used.

On the other hand, in this embodiment, the filter time constants of the two primary filters 4a and 4b arranged in correspondence with the direction of flow of the motor drive current, and therefore the motor drive elements, are set to the motor drive elements Tr1 and Tr2. By setting the internal thermal time constant equal to the internal thermal time constant, the output can be set to a value corresponding to the internal temperature Tj of the motor driving element in FIG. , E2b are set to values corresponding to the maximum allowable temperature T2 that can avoid burnout of the motor drive elements Tr1 and Tr2, and the motor drive elements Tr1 and Tr2 are controlled, thereby making it possible to protect the motor drive elements Tr1 and Tr2 from burnout due to excessive current. .

[0023]

[Effects of the Invention] As explained above, the present invention determines the direction of the current flowing through the motor drive element, passes it through a primary filter having a time constant equal to the internal thermal time constant of the motor drive element, and outputs the By turning off the gate of the motor drive element when the current exceeds a preset allowable value, this has the effect of protecting the motor drive element from burning out due to excessive current.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

[Figure 2] Motor drive elements Tr1 and Tr2 in Figure 1
It is an explanatory view of prevention of burnout.

FIG. 3 is a block diagram of a conventional protection system for motor drive elements.

[Explanation of symbols]

1 Current detector 2 Motor 3 Direction discriminator 4a, 4b Primary filter 5a, 5b Comparator 6 OR gate 7 Gate drive section 8 Heat sink 10 Thermostat E1 DC voltage E2a, E2b Reference voltage

Claims (2)

[Claims] 1. A protection method for a motor drive element that protects a motor drive element that is connected to a DC power source and outputs a motor drive current having directionality from overheating, comprising: determining the flow direction of the motor drive current; a direction determining means for switching an output destination in accordance with the determined direction; a filtering means for filtering the current value switched by the direction determining means so as to output an output corresponding to the internal temperature of the motor driving element; Gate driving means for comparing the output of the filtering means with a reference value corresponding to the maximum allowable temperature of the motor driving element and turning off the operation of the motor driving element if the temperature exceeds the reference value. A protection method for motor drive elements characterized by the following. 2. A protection system for a motor drive element according to claim 1, wherein said filtering means is constituted by a filter having a time constant equal to a thermal time constant inside said motor drive element.