JPH0793837B2 - Grounding accident protection device in variable speed operation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a grounding accident protection device in a variable speed operation system.

B. Summary of the Invention The present invention provides a grounding accident protection device in a system in which a plurality of motors are operated at a variable speed by one inverter device. One grounding detector is used to ensure system protection reliability by detecting with a detector and opening the high-speed switch when a grounding accident occurs and continuing the open circuit only for the switch where the grounding detector did not operate. Since only the arithmetic processing section is provided, the circuit configuration can be simplified and it is economically advantageous.

C. Prior art FIG. 4 is a circuit configuration diagram showing a system for operating a plurality of units M ₁ , M ₂ ... Mn at a variable speed with _one inverter device INV.
The system shown in the figure is usually called a multi-drive system. In this kind of multi-drive system, if an accident occurs in _one motor M ₁ of the plurality of motors M ₁ , M _2, ... Mn, an overcurrent flows into the inverter INV. Then, the overcurrent detector in the inverter device INV operates to take measures to protect the system from overcurrent.

Although the protection of the system can be achieved by such a protection operation, the operation of the sound motors M ₂ , M _3, ... Mn is also stopped. If such a protection operation is applied to a process for producing spinning cones in parallel, such as in the textile industry, the operation of the previous system will be stopped, resulting in a great loss. Therefore, it is necessary to avoid the above protection operation.

D. Problems to be Solved by the Invention As described above, it is not preferable to provide an overcurrent detector in the inverter device in order to protect the system from overcurrent. Therefore, if the accident motor can be disconnected from the inverter device before the overcurrent is reached, the protection will be ensured.
Therefore, by analyzing the contents of motor accidents leading up to overcurrent, it has been found by experiments that a grounding accident at the lead-out portion of the motor occurs first, and then an overcurrent occurs due to a phase-to-phase short circuit. From this, it is required to detect a grounding accident and prevent an overcurrent from occurring.

E. Means for Solving Problems The present invention relates to a system in which a single inverter device controls the operation of a plurality of motors, and a plurality of diodes having AC input terminals connected between the electric paths of the inverter device and the respective motors. A high-speed semiconductor switch consisting of a bridge circuit, a power transistor having a collector / emitter connected between the DC output terminals of these diode bridge circuits and opening / closing in an extremely short time, and a ground provided on the input side or the output side of the inverter device. When the detector and the grounding detector operate, the operation signal is input and arithmetically operated, and the arithmetic output is sequentially given to each of the high-speed semiconductor switches to sequentially open the high-speed semiconductor switches for a short time to detect the grounding. It detects the high-speed semiconductor switch that makes the device inoperative, and outputs an output that connects the open circuit only to the detected switch. It is obtained by an arithmetic unit for output.

F. Operation A switch that opens and closes in an extremely short time (hereinafter referred to as a high-speed switch) is opened by the open signal that is sequentially output from the calculation unit when the ground detector operates. If the operation of the ground detector is stopped when the high speed switch is opened, it means that the motor connected to the high speed switch has a ground accident. Therefore, if the high-speed switch is left open, it is possible to prevent an overcurrent due to a grounding accident.

G. Embodiment An embodiment of the present invention will be described below with reference to the drawings, in which the same parts as those in FIG. 4 are denoted by the same reference numerals. In FIG. 1, CT is a current transformer that detects the zero-phase current of the output of the inverter INV, and the secondary side of this current transformer CT is the comparator CP.
Entered in. The grounding detector GD is composed of the cooperator CP and the current transformer CT. The comparator CP determines that a ground fault has occurred when the zero-phase current exceeds a preset set value. The output of the comparator CP is input to the arithmetic unit PC which is a sequencer. When the ground fault signal is input from the comparator CP, this computing unit PC receives the inverter device.
Is intended to deliver the (semiconductor switch to be described later) SW _1, SW ₂ ... sequential signal to open the SWn fast switch interposed path between INV and the motor M _1, M ₂ ... Mn. High speed switch SW ₁ ,
SW ₂ ... SWn are opened and closed time to use a very short time and 20～50Myuesu.

In the embodiment configured as above, the comparator
When the output that the CP judges as a ground accident is input to the computing unit PC,
The computing unit PC computes the input signal, sequentially supplies the circuit signal from the high speed switch SW _1, and opens the switches SW ₁ , SW ₂ , SW ₃ ... SWn. Even if the switch is circuited, if the grounding detector GD continues to output the judgment that there is a grounding accident, the motors M ₁ and M ₂ connected to the switches SW ₁ and SW ₂ are judged to be normal, and SW ₁ and SW ₂ are closed again. Since the judgment time during this period is executed within 1 ms, both the mechanical time constant and the electric time constant of the motor are 100 ms or more, so the operation can be continued without the rush current flowing during reclosing due to phase shift.

However, it is assumed that the ground detector GD stops operating (does not operate) when the high-speed switch SW ₃ is opened by the output of the arithmetic unit PC. This operation stop determines that a grounding accident has occurred in the motor M ₃ , and the high speed switch SW ₃ is kept open thereafter. By this operation, the defective motor can be removed from the system, so that it is possible to prevent the system from going down because the overcurrent is not caused by the spread of the grounding accident.
Even when the ground detector GD is still outputting due to the subsequent open circuit signal, the output of the computing unit PC continues to give the open circuit signal to the high-speed switches SW ₄ , SW ₅ ... SWn and perform the same operation as above. .

FIG. 2 is a semiconductor switch circuit diagram showing an example of the high-speed switch SW ₁ . In FIG. 2, a smoothing capacitor C ₁ and an inverter INV are connected in parallel between the DC buses P and N. A bridge circuit in which diodes D _1U , D _2U , D _3U , and D _4U are bridge-connected as shown in the figure is inserted in the electric path connecting the U-phase output side of the inverter INV and the motor M ₁ . Common connection point 1 _U connecting the cathodes of diodes D _1U and D _3U and common connection point 2 _U connecting the anodes of diodes D _2U and D _4U
A semiconductor switch element, for example, a power transistor TR ₁ is connected between and in such a manner as shown by the polarity. Wherein the common connection point 1 path connecting the _U and the positive DC bus P wheeling diode DP _U illustrated polarity are inserted. Common connection point 2 _U
A freewheeling diode D _NU having the illustrated polarity is inserted in the electric path connecting the negative side DC bus N to the negative side direct current bus N. Diodes D _1V , D _2V , D _3V , D are provided in the electric path connecting the V-phase output side of the inverter INV and the motor M _1.
A bridge circuit in which _4V is bridge-connected as shown in the figure is inserted. Between the common connection point 1 _V that connects the cathodes of the diodes D _1V , D _3V and the common connection point 2 _V that connects the anodes of the diodes D _2V , D _4V, a semiconductor switch element,
For example, the power transistor TR ₂ is connected as shown by the polarity. A freewheeling diode D _PV of the illustrated polarity is inserted in the electric path connecting the common connection point 1 _V and the positive side DC bus P. Wherein the common connection point connecting the 2 _V and the negative DC bus N path freewheeling diode D _NV illustrated polarity are inserted. A bridge circuit in which diodes D _1W , D _2W , D _3W , and D _4W are bridge-connected as shown in the figure is inserted in an electric path connecting the W-phase output side of the inverter INV and the motor M ₁ . Diode D _1W ,
D _{3 W} common connection point connecting cathodes 1 _W and diode D
_A semiconductor switch element, for example, a power transistor TR ₃ is connected between the common connection point 2 _W that connects the anodes of _{2 W} and D _{4 W} with the polarity shown in the figure. In the electric path connecting the common connection point 1 _W and the positive side DC bus P, a freewheeling diode D _PW having the illustrated polarity is inserted. In the electric path connecting the common connection point 2 _W and the negative DC bus N, a freewheeling diode D _NW having the illustrated polarity is inserted.

Next, the operation of the circuit configured as described above will be described. If path connecting the inverter INV and the motor M ₁ is closed (i.e. the power transistor TR _1, TR _2, TR ₃ are in an on state), for example, a current flowing between the U-V-phase positive-side DC bus P → inverter INV → diode D _1U → power transistor TR ₁ → diode D _4U → motor M ₁ → diode D _3V →
Power transistor TR ₂ → diode D _2V → inverter IN
V → Negative-side DC bus N flows in the path, and in the case of reverse mode, positive-side DC bus P → inverter INV → diode D _1V
→ power transistor T _R2 → diode D _4V → motor M ₁ →
Diode D _3U → Power transistor TR ₁ → Diode D
_2U → Inverter INV → Negative side DC Bus N Between the U and W phases of the electric circuit that connects the inverter INV and the motor M ₁ ,
The current flowing between the V and W phases also flows in the same manner as described above.
Motor M ₁ when power transistor TR ₁ (TR ₂ , TR ₃ ) is off
Surge energy for by connexion applied to the accumulated energy and line inductance, the circulating diode D _PU (D
_PV , D _PW ) → Smoothing capacitor C ₁ → Recirculation diode D
_NU (D _NV , D _NW ) flows through the smoothing capacitor C
Absorbed by ₁ . Therefore, the power transistor TR ₁ (TR ₂ ,
The voltage applied to the transistor TR ₁ (TR ₂ , TR ₃ ) when TR ₃ ) is off can be clamped to the DC voltage of the inverter INV.

According to the semiconductor switch circuit as described above, the overcurrent that utilizes the fact that the V _BE voltage of the power transistor shown in FIG. 3 changes according to the collector current I _C is detected, and the bidirectional current flowing in each phase is detected. It is possible to cut off at a high speed by using one power transistor, and a surge voltage absorption circuit dedicated to the power transistor is not required, which makes it possible to miniaturize the circuit.

H. Effects of the Invention As described above, according to the present invention, the grounding detector does not operate when the switch is opened by sequentially opening and closing the high-speed switch before detecting the grounding accident of the motor and not causing overcurrent. At that time, only the switch is opened so that the accident motor is disconnected from the inverter device at the ground accident stage, so that the reliability of the system can be dramatically improved. Further, since only one grounding detector is provided on either the input side or the output side of the inverter device, the device can be simplified and it is economically advantageous.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a concrete structure of a semiconductor switch circuit applied to the present invention, and FIG. 3 is a V _BE -I of a power transistor.
_C characteristic diagram, FIG. 4 is a block diagram showing a conventional apparatus. INV ... inverter, GD ...... ground detector, PC ...... calculation _{unit, SW 1, SW 2 ... SWn} ...... fast _{switch, M 1, M 2 ... Mn} ...... motor.

Claims (1)

[Claims] 1. A system in which a single inverter device controls the operation of a plurality of motors, and a plurality of diode bridge circuits each having an AC input terminal connected between the electric paths of the inverter device and each motor, and the diode bridge circuits. , A high-speed semiconductor switch consisting of a power transistor having a collector / emitter connected between the DC output terminals thereof and opening and closing in an extremely short time, a ground detector provided on the input side or the output side of the inverter device, and this ground detector When the operation is performed, the operation signal is input to perform an operation, and the operation output is sequentially applied to each of the high-speed semiconductor switches to sequentially open the high-speed semiconductor switches for a short time, and the ground detector becomes inoperative. An operation unit that detects a semiconductor switch and sends an output that keeps the circuit open only to the detected switch. Ground fault protection device of variable speed drive system according to claim.