JPH01248929A - Inverter - Google Patents

Abstract

PURPOSE:To prevent an inverter from being damaged due to the overvoltage of a smoothing capacitor by inhibiting supply of the following current of a ground-fault current based on a remaining voltage generated in an induction motor to the capacitor, and supplying it to a discharge resistor and a discharge transistor. CONSTITUTION:A discharge resistor 11, and a discharge transistor 12 are connected in series with the smoothing capacitor 3 of an inverter 4. The base of the transistor 12 is connected to a base driver 7. When the driver 7 receives the ground-fault current detection signal of a ground-fault detector 5, the transistor 12 is turned ON. Thus, the ground-fault current based on the remaining voltage generated in an induction motor flows to the resistor 11 and the transistor 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device, and particularly to protection of the inverter device against a ground fault in the output of the inverter device.

[Prior art] FIG. 2 is a diagram showing a circuit of a conventional inverter device.

In the figure, (1) is commercial power supply, (2) is commercial power supply (1
) diode converter that converts alternating current to direct current, (3
) is a smoothing capacitor that converts the DC voltage converted by the diode converter (2), (4) is a transistor inverter that converts the DC smoothed by the smoothing capacitor (3) into AC, and (5) is the ground of the zero-phase reactor. circuit detector, (6) is an induction machine as a load, (7) is a base drive circuit that drives the base of transistor inverter (4), and (8) is an arbitrary voltage and frequency output from transistor inverter (4). The base drive circuit (7
), (9) is a contactor switch that is turned on and off by the base drive circuit (7), (10)
is an electromagnetic contactor that is connected to the contactor switch (9) and the commercial power supply (1), and is deenergized when the contactor switch (9) turns off; (10a) is a commercial type 1Fj (1)
The electromagnetic contactor (10a), which is a interrupting element inserted in series between the input side of the diode converter (2)
) is the normal oven contact point.

Next, the operation will be explained. FIG. 3 is a diagram showing a path of a ground fault current when a ground fault occurs in the output phase of the inverter device.

Since the ground fault current flows through the earth along the path indicated by the arrow in the diagram,
As shown in Figure 2, a ground fault detector (5) is attached to the output side of the transistor inverter (4), and the ground fault current detection signal of the ground fault detector (6) is sent to the base drive circuit (7). The base drive circuit (7) that receives the signal stops its operation and cuts off the output of the transistor inverter (4), thereby blocking the follow-up of the ground fault current and protecting the inverter device from damage due to overcurrent. Can be done.

The above-mentioned method is generally used to protect an inverter device against a ground fault.

However, even after the applied voltage is cut off, a residual voltage due to residual magnetism remains in the induction motor (6) for several seconds, so after the transistor inverter (4) is cut off, the arrow points to the ground as shown in Figure 4. Since a ground fault current flows due to a fault, it is necessary to consider the induction motor (6) as a power source.

In this way, in the case of the example shown in FIG. 4, the ground fault current continues to flow along the path shown in the figure even after the output of the transistor inverter (4) is cut off. Therefore, charging of the smoothing capacitor (3) may be interrupted, and the smoothing capacitor (3) may be charged to a voltage equal to the sum of the three power sources Vl, V2, and V3. Therefore, in this case, the voltage charged to the smoothing capacitor (3) will be higher than the voltage charged by the normal commercial power supply (1) depending on the phase, and the voltage charged to the smoothing capacitor (3) will be higher than the voltage charged by the normal commercial power supply (1).
Alternatively, the rated voltage of the transistor inverter (4) or the like may be exceeded, and the inverter device may be damaged due to the overvoltage.

Therefore, as shown in FIG. 2, the base drive circuit (7) that receives the ground fault current detection signal from the ground fault detector (5) stops its operation and cuts off the output of the transistor inverter (4). Turn off the contactor switch (9), de-energize the electromagnetic contactor (lO), and open the contact (10a).
) to shut off the power supply and connect the smoothing capacitor (3).
) to prevent overvoltage caused by connecting the charging current to the

[The problem that the invention tries to solve! ! 1] In the conventional inverter device as described above, in order to prevent damage to the inverter device due to a ground fault accident, a ground fault detector (5) is provided on the output side of the transistor inverter (4). The ground fault current detection signal stops the operation of the base drive circuit (7), cuts off the output of the transistor inverter (4), and connects the contact (10a) of the electromagnetic contactor (lO) to the input of the diode converter (2). A contact switch (9) is installed on the side to open and close the electromagnetic contactor (lO
) was turned off by the base drive circuit (7) that received the ground fault current detection signal from the ground fault detector (5) to cut off the follow-on path of the ground fault current. ), the configuration of the inverter device is complicated, and there are problems in that it becomes large and expensive.

In addition, since charging of the smoothing capacitor (3) due to the continuing ground fault current is completed within 30 to 100a+sec,
The problem was that the electromagnetic contactor had to have a quick response.

This invention was made to solve the above-mentioned problems, and uses a smoothing capacitor discharging circuit, which is generally built into an inverter device, to detect ground faults without using an electromagnetic contactor. The object of the present invention is to obtain an inverter device that can suppress the voltage of a smoothing capacitor in the event of an accident.

[Means for Solving the Problems] An inverter device according to the present invention connects a discharging resistor and a discharging transistor in series to a smoothing capacitor, connects the base of the discharging transistor to a base drive circuit, and connects the base drive circuit to the base drive circuit. The discharge transistor is turned on when receiving a ground fault current detection signal from a ground fault detector.

[Function] In this invention, a discharge resistor and a discharge transistor are connected in series to a smoothing capacitor of an inverter device, the base of the discharge transistor is connected to a base drive circuit, and the base drive circuit is connected to the ground of a ground fault detector. When receiving a fault current detection signal, the discharging transistor is turned on, so when a ground fault fault occurs and a ground fault current flows through the inverter, the ground fault detector detects the ground fault current. Detects and outputs a ground fault current detection signal. Upon receiving this signal, the base drive circuit stops its operation, cuts off the output of the transistor inverter, and turns on the discharge transistor. Therefore, the follow-on current of the ground fault current based on the residual voltage due to the residual magnetism generated in the induction motor after the output of the transistor inverter is cut off is not charged to the smoothing capacitor, but flows through the discharging resistor and the discharging transistor.
Overvoltage is no longer applied to the smoothing capacitor.

[Embodiment] FIG. 1 is a diagram showing a circuit according to an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 2 showing the conventional example indicate the same or corresponding parts, and the explanation of the structure will be omitted. (11) is a discharge resistor connected to the smoothing capacitor (3), (12) is a discharge transistor whose collector and emitter are connected in series to the discharge resistor (11) and the smoothing capacitor (3), and whose base is the base It is connected to the drive circuit (7). The discharge resistor (11) and the transistor for discharge 7u (12) are originally designed to cause the smoothing capacitor (3) to overflow due to the energy regenerated from the induction motor (6) when the driven induction motor (6) is in a regenerative state. This is standard equipment in general inverter devices for controlling the voltage of the smoothing capacitor (3) to prevent overvoltage from occurring due to charging. This embodiment utilizes such a discharge resistor (11) and a discharge transistor (12).

Next, the operation of the above embodiment will be explained.

When a ground fault current flows through the inverter device due to the occurrence of a ground fault accident, a ground fault detector (5) detects the ground fault current and outputs a ground fault current detection signal. When the base drive circuit (7) receives the ground fault detection signal from the ground fault detector (5), it stops its operation and cuts off the output of the transistor inverter (4). At the same time, the base drive circuit (7) turns on the discharge transistor (12). Then, after the output of the transistor inverter 4) is cut off, the induction motor (8)
) is not charged to the smoothing capacitor (3), but the discharge resistance (
11) and the discharge transistor (12), and no overvoltage is applied to the smoothing capacitor (3). Therefore, damage to the inverter device due to overvoltage of the smoothing capacitor (3) is prevented.

[Effects of the Invention] As explained above, in this invention, a discharge resistor and a discharge transistor are connected in series to a smoothing capacitor of an inverter device, the base of the discharge transistor is connected to a base drive circuit, and the base drive circuit is connected to a ground fault. By turning on the discharging transistor when receiving the ground fault current detection signal from the detector, the follow-on current of the ground fault current based on the residual voltage generated in the induction motor is not charged to the smoothing capacitor, and the discharging resistor and Since the current flows through the discharge transistor and prevents overvoltage from being applied to the smoothing capacitor, damage to the inverter device due to overvoltage of the smoothing capacitor is prevented. Moreover, the discharge resistor and discharge transistor are standard equipment in general inverter devices. Since it utilizes the same components, it has the advantage of being simple in structure, miniaturized, and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a circuit of an embodiment of the present invention, FIG. 2 is a diagram showing a circuit of a conventional inverter device, FIG. 3 is a diagram showing a path of ground fault current when a ground fault occurs, and FIG. FIG. 4 is a diagram showing the path of ground fault current when the residual voltage of the induction motor is considered. In the figure, (3) is a smoothing capacitor, (5) is a ground fault detector, (7) is a base drive circuit, (11) is a discharge resistor,
(12) is a discharge transistor. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] An AC power supply, a converter that converts the AC of the AC power supply into DC, a smoothing capacitor that smoothes the DC converted by the converter, an inverter that converts the DC smoothed by the smoothing capacitor into AC, and drives the base of the inverter. It is equipped with a base drive circuit, a control circuit that controls the base drive circuit so that an arbitrary voltage and frequency is output from the inverter, and a ground fault detector that is installed on the output side of the inverter and detects ground fault current. In an inverter device in which a base drive circuit receives a ground fault current detection signal from a fault detector and cuts off base current to the inverter,
A discharge resistor and a discharge transistor are connected in series to a smoothing capacitor, and the base of the discharge transistor is connected to a base drive circuit, and when the base drive circuit receives a ground fault current detection signal from a ground fault detector, the discharge transistor is connected in series. An inverter device characterized by turning on a transistor.