JPH0750995B2 - Predictive stall prevention device for motor drive inverter - Google Patents

Description

The present invention relates to a predictive stall prevention device for a motor drive inverter,
In particular, the present invention relates to an improvement of a predictive stall prevention device capable of preventing the inverter from being cut off controlled when the load current suddenly increases.

[Prior Art] FIG. 2 shows an example of a conventional motor drive inverter system. The motor drive inverter (1) uses a three-phase AC power supplied from an AC power supply (2) for motor drive. Is converted into three-phase AC power, and the drive control of the induction motor (3) is performed. In the figure, for simplification of description, only one phase is extracted from the three-phase AC power and a circuit diagram is shown.

Usually, such a motor drive inverter system is provided with a stall prevention device in order to prevent the inverter (1) from failing due to overcurrent and to prevent the inverter system from going down.

The conventional stall prevention device detects the output power I of the inverter (1) using an ammeter (4) as shown in FIG.

Then, as shown in FIG. 3, the detected current I is the rated current.
At the same time as exceeding the stall prevention level I1 set to about 150% of In, a constant speed control command or deceleration control command is output from the first comparator (5) to the acceleration / deceleration control circuit (7),
The output current I of the inverter (1) is controlled so that the motor (3) is decelerated or decelerated.

By doing so, for example, even when the motor (3) is suddenly accelerated or the motor load is suddenly increased and an overcurrent flows through the inverter (1), the inverter (1) is affected by this overcurrent. It is possible to prevent the destruction of the entire system due to its destruction.

In particular, by preventing such a current, it is possible to prevent the transistor, thyristor, etc. provided on the output side of the inverter from being damaged, so that the inverter system for driving the motor should be operated stably. Is possible.

However, when the motor (3) is accelerated extremely rapidly or when the motor load increases extremely rapidly, the load current I rises steeply, and the detected current I becomes the rated load. When the stall prevention level I1 set to about 150% is reached, even if the inverter 1 is slowed down or decelerated, the load current I is all slow and the stall prevention level is low.
Even if I1 is exceeded temporarily, the inverter (1) will be destroyed due to overcurrent.

In order to prevent such a situation, the conventional stall prevention device sets the cutoff level I2 to a value of about 200% of the rated current In as shown in FIG. At the same time when the level I2 is exceeded, a cutoff command is output from the second comparator (6) to the inverter (1).

In this way, the inverter (1) is forcibly controlled to stop, so that the inverter (1) is prevented from being destroyed by an overcurrent having a rapid rise.

[Problems to be Solved by the Invention] By the way, depending on the use of the motor (3), there are many cases where the system down is extremely disliked. For example, the three-phase motor (3) is used as a power source for the cable car operation. In some cases, stable operation of the cable car is required.

However, the load current I1 supplied from the inverter (1) is interrupted by the overload that is applied at the start of the cable car or the overload that occurs due to the fluctuation that occurs when the cable car is running at a constant speed. Even if it exceeds I2 momentarily, the inverter (1) will be forcibly stopped and the cable car itself will stop.

In addition to the above, the same problem occurs when the motor (3) is used as the power source of the overhead crane.

Further, in a device in which the motor (3) is connected to some load by using a clutch, a similar problem occurs because a sudden load is applied when the clutch is connected.

As described above, in the conventional device shown in FIG. 2, the inverter (1) is forcibly stopped in any of the cases described above, and the entire system goes down. Therefore, stable operation of the motor (3) is performed. However, effective measures have been demanded.

The present invention has been made in view of such a conventional problem, and detects a sudden increase in load current quickly, and controls the inverter to perform constant-speed control or deceleration control to suppress an increase in load current. It is an object of the present invention to provide a predictive stall prevention device for a motor drive inverter, which is capable of preventing the system down of the drive inverter.

[Means for Solving Problems] A predictive stall prevention device for a motor drive inverter according to the present invention includes a differentiator that differentiates a load current of the inverter to detect a current increase rate, a detected current increase rate, and a predetermined value. And a deceleration command circuit that outputs a constant speed or deceleration command of the motor when a significant increase tendency of the load current is detected by comparing the reference increase rates of the above.

[Operation] Therefore, when the motor is extremely accelerated, or when the motor load is suddenly increased, this is detected as the increase rate of the load current immediately to control the motor at a constant speed or deceleration. The load current hardly increases to the cutoff level I2, and it becomes possible to effectively prevent the system down of the motor drive inverter.

[Embodiment] Next, a preferred embodiment of the present invention will be described with reference to the drawings.
The members corresponding to those in the apparatus shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 shows a preferred embodiment of the predictive stall prevention device according to the present invention. The characteristic feature of the present invention is that a differentiator (8) that differentiates the load current I and detects the current increase rate. )When,
And a third comparator (9) that outputs a constant speed or deceleration command when the current increase rate exceeds a predetermined reference increase rate S.

In this embodiment, the output of the third comparator (9) and the output of the first comparator (5) are input to the acceleration / deceleration control circuit 7 via the OR gate (10).

Therefore, according to the present invention, even if the load current I suddenly increases due to the rapid acceleration of the motor (3) or the sudden increase of the load connected to the motor (3), the load current I can be quickly increased by the current increase rate. Since it is detected as an increase and the motor (3) is controlled at a constant speed or deceleration, the load current I does not increase rapidly in a short time, and the load current I does not rise to the cutoff level I2.

Therefore, according to the present invention, even when the load is used as a power source of a system in which the load is suddenly increased or momentarily increased, such as a motor (3) cable car or an overhead crane, or a clutch is used. Even when the load is used as a power source for rotationally driving the load, the load current I is prevented from rising to the cutoff level I2, and the system down of the motor drive inverter is effectively prevented. It becomes possible.

Further, according to this embodiment, in addition to the third comparator (9), the first comparator (5) and the second comparator (6) are used in the same manner as in the conventional device, It is possible to more effectively prevent damage to the inverter (1) due to an increase in load current.

As described above, the present invention differentiates the load current, detects the current increase rate, and outputs a constant speed or deceleration command of the motor when the current increase rate exceeds a predetermined reference increase rate. Therefore, even when the load current I increases due to the sudden acceleration of the motor or the sudden increase of the load,
It is possible to detect this promptly, suppress an increase in load current, and prevent the system down of the inverter system.

In particular, according to the present invention, it becomes effective when a motor is used as a power source of a system that is extremely reluctant to down the system, and the device of the present invention is used as a power source of, for example, a cable car or an overhead crane. If the motor is used in such a way that the motor is connected to the load via the clutch, it effectively prevents the load current from rising to the cutoff level even temporarily, thus ensuring stable operation without system down. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a block diagram showing a preferred example of a predictive stall prevention device for a motor drive inverter according to the present invention, FIG. 2 is a block diagram of a conventional stall prevention device, and FIG. 3 is the above-mentioned FIG. 1 and FIG. It is operation | movement explanatory drawing of the 1st and 2nd comparator shown in a figure. In the figure, (1) is a motor drive inverter, (2) is an AC power supply, (3) is a motor, (4) is an ammeter, and (5) is a first
Comparator, (6) is a second comparator, (7) is an acceleration / deceleration control circuit, (8) is a differentiator, (9) is a third comparator, and (10).
Is an OR gate. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A load current of an inverter for driving a motor is detected, and when the load current exceeds a stall prevention level, the inverter is controlled so as to decelerate or decelerate the motor, and when the load current exceeds a cutoff level. In a stall prevention device for a motor drive inverter that forcibly stops the inverter, by comparing the detected current increase rate with a predetermined reference increase rate with a differentiator that differentiates the load current and detects the current increase rate. Includes a deceleration command circuit that detects a noticeable increase in load current and outputs a constant speed or deceleration command for the motor if an increase is detected. A predictive stall prevention device for a motor drive inverter, which prevents the vehicle from reaching a cutoff level.