JPH05328739A - Power conversion equipment and detection ground fault method thereof - Google Patents

Abstract

PURPOSE:To detect a ground fault without connecting a current detector to all the phases of output-terminals for detecting the ground fault, to reduce the cost of a device and to miniaturize the device. CONSTITUTION:A base drive circuit 7 is operated by the signal (b) of a drive control circuit 8 at the time of normal operation. A signal (a) is generated in response to the requirement of ground fault inspection at the time of a shutdown, a DC/AC conversion circuit 3 brings only the Z-phase of a switching element constituted in a bridge to a conductive state, and ground fault currents IG at the time of the occurrence of a ground fault is detected by a current detector 5. An output from the current detector 5 is compared with a reference value by a ground fault detector 9, thus detecting the ground. When the ground fault is detected, the operation of the base drive circuit 7 which is the DC/AC conversion circuit 3 is stopped and protected while an alarm signal (g) is output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting and protecting a ground fault in an output side circuit of a power conversion device having a switching element in a rotary electric machine drive device.

[0002]

2. Description of the Related Art A ground fault detection method for an output terminal circuit in a forward conversion device or an inverse conversion device used for driving a conventional AC rotary machine or DC rotary machine is a commercially available zero-phase current detection method. This is done by using a detector or by providing a current detector for all phases of the output terminal. For example, in the case of an inverter device, as shown in FIG. 6, the current detectors 5 are provided on all phases of the output terminal, and the fact that the sum of the currents of the respective phases is normally zero is used to detect the unbalanced current at the time of ground fault , The ground fault was detected.

A conventional example of FIG. 6 will be briefly described below. The AC power supply 1 is a grounded power supply, and is connected to the rectifier 2 via a breaker 15. The AC power is once converted into DC power by the rectifier 2 and then converted into variable frequency AC by the inverter 3. The electric motor 4 connected to the output of this inverter is driven at a variable speed based on a speed command (not shown). The current detector 5 is inserted in all phases between the inverter and the electric motor, and its output is input to the ground fault detection circuit 25. In the ground fault detection circuit 25, the sum of all phases of the input electric motor current is calculated and it is determined whether or not this value exceeds the reference value vs1. Since there is a leakage current due to the harmonics of the inverter, it will not be completely zero, so a reference value for judging a ground fault is set in advance. When a ground fault occurs, the sum of all phases of the motor current exceeds the reference value vs1. Therefore, the ground fault detection circuit 25 outputs a ground fault detection signal. The operation of the base drive circuit 7 is stopped by this ground fault detection signal, and thus the operation of the inverter 3 is stopped. This protects the inverter device from a ground fault. Further, a DC current detector 23 is provided separately from the current detector 5 in this inverter device, an overcurrent is detected by an overcurrent detection circuit 26, and the operation of the base drive circuit 7 is stopped by this output. ing.

The above is the conventional technique of the inverter for AC conversion. However, in the case of a DC machine driving device for converting a DC of a variable voltage to drive a DC machine, the current detector 5 is not attached to all phases of the output terminal. The equilibrium current is detected and the ground fault is similarly detected.

[0005]

In the above-mentioned prior art, it is necessary to attach a commercially available zero-phase current detector, or to attach a current detector to all phases of the output end, and to downsize the device,
It was disadvantageous in lowering the price.

According to the present invention, it is possible to detect a ground fault without installing a commercially available zero-phase current detector or inserting a current detector in all phases of the output terminal as in the prior art shown in FIG.
An object of the present invention is to provide a drive device for a rotary electric machine that realizes a simplified circuit configuration, a reduced cost, and a downsized device.

[0007]

In order to achieve the above object, according to the present invention, when a specific switching element is made conductive, a power supply short circuit or a normal load current circuit is not formed and a load and a power supply are connected to each other. In a power converter capable of electrically connecting the above-mentioned specific switching element in response to a ground detection request signal when the power converter is not operating. Ground fault detection base driving means, current detection means for detecting the current of the switching element brought into the conducting state when the specific switching element is brought into the conducting state by the ground fault detecting base driving means, and this current A ground fault detecting means for outputting a signal based on the magnitude of the output of the detecting means is provided.

[0008]

When the specific switch element is turned on by the ground fault detecting base driving means, and if a ground fault occurs on the output side, the specific state is made conductive by the ground fault detecting base driving means. A ground fault current flows through the switching element. This ground fault current is detected by the current detection means, and the ground fault detection means detects the ground fault based on the magnitude of the output of the current detection means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 is a grounded AC power supply, 2 is an AC / DC conversion circuit (rectifier circuit), which is composed of a diode bridge and a smoothing capacitor CB. Reference numeral 3 denotes a DC / AC conversion circuit, which forms a bridge circuit with transistors and diodes in each arm of U, V, W, X, Y, and Z phases. The DC / AC conversion circuit 3 outputs a three-phase AC having an output frequency and an output voltage corresponding to the command according to the frequency command. The induction motor 4 is connected to the output of the DC / AC conversion circuit 3 and is driven at a variable speed. This induction motor 4
The Z-phase load current is detected by the current detector 5, and its output becomes a signal i proportional to the current. This signal i is constantly compared by the overcurrent detection circuit 6, and when an overcurrent is generated, the operation of the DC / AC conversion circuit 3 is stopped to perform overcurrent protection. Further, this signal i is input to the comparator 11 of the ground fault detection circuit 9. The comparator 11 compares the signal i with the reference value vs2, and outputs when the reference value vs2 is exceeded. "
1 "signal c is output. The drive control circuit 8 outputs a signal b for turning on / off the transistors of the U-, V-, W-, X-, Y-, and Z-phase arms during normal driving operation to the base drive circuit 7.
Output to. When the drive control circuit 8 does not output the signal b, the drive control circuit 8 may inspect the ground fault condition if necessary.
The ground fault detection command signal a is output. When the signal a is input to the ground fault detection base drive circuit 10, the ground fault detection base drive circuit 10 outputs a drive signal to the Z-phase transistor for a certain period. At this time, if there is a ground fault in the output, the Z-phase transistor will have a ground fault current IG as shown in FIG.
Flows. At this time, the current detector 5 naturally causes the Z-phase current IG
Is generated and a signal i is generated. This signal i and the reference value vs
2 is compared, and when the reference value vs2 is exceeded, a signal c of output "1" is output. The signal a is input to one input terminal of the AND circuit 13, and the signal c is input from the comparator 11 to the other terminal of the AND circuit 13. When both the signal a and the signal c are "1", the AND circuit 13 outputs the signal d of the output "1". The output of the AND circuit 13 is input to and latched by the latch circuit 14. The output signal g of the latch circuit 14 inhibits the operation of the base drive circuit 7, and is further output to the display 12 to display and warn the occurrence of a ground fault. Further, it is output to the outside as a ground fault detection signal.

The output timing of the ground fault detection command signal a is synchronized with the base drive circuit signal OFF signal when (1) the initialization processing is performed when the power is turned on, and (2) the inverter output is cut off when the electric motor is stopped. To run,
(3) A method such as execution in response to an external ground fault diagnosis request signal (a signal from a higher-level device, a manual switch signal, or the like) is conceivable, and any method may be used.

The ground fault detection command signal a is output by a soft timer or a hard timer for a certain period. This period is set to a time sufficient to detect the ground fault current.

In the circuit in which the rotating machine is connected to the output terminal, if no ground fault occurs, current does not flow due to conduction of only the Z-phase transistor (the same applies to all other phases). Therefore, the signal c is "0".

Next, the operation when a certain phase at the output end is grounded by the ground resistance 15 (ground resistance value RΩ) will be described with reference to FIG. In this case, a circuit is formed which passes through the earth grounded from the AC power supply 1, the ground resistance 15, the rotary machine circuit 4, the primary circuit of the current detector 5, the Z-phase transistor, and the negative side diode of the AC / DC conversion circuit. Then, the ground fault current IG flows there. The ground fault current IG is detected by the current detector 5 and output as the signal i. This signal i is input to the ground fault detection circuit shown in FIG. The signal i is the comparator 11
Of the reference voltage vs. At this time, when the magnitude of the signal i exceeds the reference voltage vs, the output signal c of the comparator 11 becomes "1", and the ground fault / ground fault is detected.

FIG. 3 shows an embodiment in which the current detector (current detector 23) is on the DC side. Reference numerals in FIG. 3 that are the same in FIGS. 1 and 2 indicate the same elements. Reference numeral 26 is an overcurrent detection circuit. Also in this case, the ground fault can be detected by the same operation as in FIGS. In this case, not only the Z-phase transistor but also any of the X-, Y-, and Z-phase transistors may be turned on, or the X-, Y-, and Z-phase transistors may be connected.
Current detector 2 with one or more transistors conducting
3 can be detected. Current detector 23 to rectifier 2
The same can be done by inserting it on the positive side of. In this case, one of the U, V, and W phase transistors is made conductive.

FIG. 4 shows another embodiment of the present invention. The operation of FIG. 4 will be described. The output of the ground fault detection command signal a is set to "1" for a predetermined period in response to the request of the ground fault inspection. On the other hand, when the breaker 15 is turned on and the DC output voltage of the rectifier 2 rises, the output of the control power supply circuit 17 connected to this DC section also rises. This control voltage is the comparator 1
At 8, the value is compared with the reference value vs3, and when it becomes equal to or larger than the reference value vs3, the output of the comparator 18 becomes "1". The output of the comparator 18 is input to the timer 19, which causes the timer 19 to output the signal j having the same width as the signal a. These signals a and j
Is input to the OR circuit 20 and outputs a signal a'when either the signal a or the signal j becomes "1". Therefore, according to this embodiment, the ground fault inspection is always executed by the signal j when the power is turned on, and the signal a is generated from the drive control circuit in response to the request.

In the above embodiments, the device having a DC / three-phase AC converter as 3 has been described, but the same applies to a DC / DC converter having a bridge connection of two phases or four phases or more. Even when the DC converter is driven by a forward converter having a switching element having a bridge structure, the switching element of only one of the upper arm and the lower arm can be made conductive to perform the same operation. In this case as well, it can be applied to a forward converter in which two or more phases are bridge-connected. It can also be applied to a cycloconverter with a bridge connection or a Glets connection. Thus, the form of the power conversion device to which the present invention can be applied is that when a specific switching element is turned on, the load and the power supply are electrically connected without forming a power supply short circuit or a normal load current circuit. What is necessary is just to be able to form a ground fault current loop.

As can be seen from the above description, it can be detected by conducting two or more phases of either the upper arm or the lower arm, but it is preferable in terms of circuit simplification, downsizing and cost reduction. It is better to detect in one phase.

In the above embodiments, the ground fault detection base drive circuit 10 and the normal base drive circuit 7 are separated from each other. However, it can be said that the same phase amplification circuit portion can be implemented in common. There is no end.

According to the present embodiment, the current detector for overcurrent detection and the current detector for control which have been conventionally installed are provided without providing a zero-phase current detector and current detectors for all phases of the output terminals. By using it, it becomes possible to detect a ground fault, which is effective for downsizing and cost reduction of the device.

The above ground fault detection circuit can be implemented in the same manner even if it is processed by software according to the flowchart of FIG. The processing routine of FIG. 5 includes (1) a ground fault detection request signal generated at the time of initialization processing at power-on,
(2) A signal synchronized with the base drive circuit signal OFF signal when the inverter output is cut off when the motor is stopped, (3) A ground fault diagnosis request signal from the outside (a signal from the host device, or a manual switch signal), etc. Is started according to. The following is a description of FIG.

First, referring to the signal b, it is judged whether or not the transistor drive signal is being cut off (step S).
1).

If it is in the cutoff state, the signal a for driving only the Z-phase transistor is output (step S2).

Next, the output signal i of the current detector 5 is fetched as data (S3).

After outputting the driving signal a which is predetermined enough to detect the ground fault current, the signal a is cut off (step S4).

The magnitude of the signal i is compared with a predetermined reference value for ground fault detection, and it is determined whether or not it exceeds the reference value (step S5).

If the ground fault detection reference value is exceeded, a ground fault protection process is executed to inhibit the operation of the base drive circuit (step S6).

Then, a signal is output to the ground fault occurrence display and a ground fault warning signal is output to the outside (step S7).

If the ground fault detection reference value is not exceeded in step S5, the ground fault warning signal is cleared (step S8).

When the output of the signal b is determined in step S1, the signal a is not generated and the process is terminated.

According to the embodiment shown in FIG. 5, it is not necessary to provide a special hardware circuit as the ground fault detection circuit, and the circuit configuration can be simplified.

[0031]

According to the present invention, a ground fault can be detected without adding a current detector for detecting a ground fault, which is effective in downsizing the device, reducing the cost, and reducing the number of parts.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment according to the present invention.

FIG. 2 is an operation explanatory diagram in the case of a ground fault of the embodiment according to the present invention in FIG.

FIG. 3 is another embodiment of the present invention and an operation explanatory diagram thereof in the case of a ground fault.

FIG. 4 is a diagram showing still another embodiment according to the present invention.

FIG. 5 is an embodiment of a ground fault detection flowchart according to the present invention.

FIG. 6 is a diagram showing an example including a conventional ground fault detection circuit.

[Explanation of symbols]

1 ... AC power supply, 2 ... AC / DC conversion circuit, 3 ... DC / AC conversion circuit, 4 ... Electric motor, 5 ... Current detector,
6 ... Overcurrent detection circuit, 7 ... Base drive circuit, 8 ... Drive control circuit, 9 ... Ground fault detection circuit, 10 ... Ground fault detection base drive circuit, 11 ... Comparator, 12 ... Indicator, 13 ...
AND circuit, 14 ... Latch circuit, 15 ... Circuit breaker, 1
6 ... Ground resistance, 17 ... Control power supply circuit, 18 ... Comparator, 19 ... Timer circuit, 20 ... OR circuit, 22 ...
Ground fault detection circuit, 23 ... Current detector, 24 ... Drive control circuit, 25 ... Ground fault detection circuit, 26 ... Overcurrent detection circuit.

Claims (8)

[Claims] 1. A bridge-connected switching element, a plurality of input terminals that are power input sections of the bridge connection, and a plurality of output terminals that are power output sections of the bridge connection and to which a load is connected. In the power conversion device, when there is no other output of a signal for conducting the switching element, only the switching element connected to one specific input terminal among the plurality of input terminals according to the ground drop detection request signal is output. A ground fault detection base drive means for conducting, a current detection means for detecting a current of the switching element which is brought into a conduction state when the switching element is brought into a conduction state by the ground fault detection base drive means, and A signal based on the magnitude of the output of the current detecting means when the switching element is made conductive by the ground-fault detecting base driving means. An electric power converter comprising: a ground fault detection unit that outputs 2. The power conversion device according to claim 1, wherein all the switching elements of the power conversion device are made non-conductive according to the signal output of the ground fault detection means. 3. The current detecting means includes a connection point to which one terminal of the switch element is connected,
It is provided between the load and the load.
The power converter described. 4. The power conversion device according to claim 1, wherein the current detection means is provided between the common connection point of the other terminal of the switch element and the power supply. 5. The electric power converter according to claim 1, wherein the rotary machine driving device further includes ground fault display means, and operates the ground fault display means in response to a signal output from the ground fault detection means. apparatus. 6. A power converter in which terminals of a load are respectively connected to a power source via a switching element, wherein the load is electrically and temporally connected to only one power source terminal by conduction. And a ground fault detection base driving means for conducting the switching element, and when the switching element is brought into a conducting state by the ground fault detecting base driving means, a current of the switching element brought into the conducting state is detected. And a ground fault detecting unit that outputs a signal based on the magnitude of the output of the current detecting unit when the switching element is brought into a conducting state by the ground fault detecting base driving unit. A characteristic power conversion device. 7. One of a plurality of switching elements, one terminal of which is connected to an output terminal and the other terminal of which is commonly connected.
Power conversion including one or a plurality of switching element groups and one or a plurality of switching element groups in which the other terminals of the other plurality of switching elements are respectively connected to the output terminal and one terminal is commonly connected In the device, when there is no other output of a signal for turning on the switching element, at least one of the switching elements belonging to a specific one of the switching element groups is turned on in response to the ground detection request signal. Ground fault detection base driving means, current detection means for detecting a current of the switching element brought into a conducting state when the switching element is brought into a conducting state by the ground fault detecting base driving means, and the ground fault A large output of the current detecting means when the switching element is made conductive by the detecting base driving means. Power conversion apparatus characterized by comprising a ground fault detection means for outputting a signal based at the. 8. A bridge-connected switching element, a plurality of input terminals that are power input sections of the bridge connection, and a plurality of output terminals that are power output sections of the bridge connection and to which a load is connected. In the power converter, the first step of determining that the drive signal of the switch element is being cut off, and the switch element belonging to the specific switch element group when the determination of the cutoff is made in the first step A second step of conducting one of them for a predetermined period of time, a third step of detecting a current of the switch element conducted in the second step, and a current detected in the third step and a predetermined reference A fourth step of comparing the values to determine the magnitude of the detected current with respect to the reference value, and, when a large determination is made in the fourth step, the power converter is held in the inoperative state, Judgment of And a fifth step of outputting a signal corresponding to the ground fault detection method.