JP2005039890A - Ac motor driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC motor driving device which can continuously operate a motor even if the cooling fan of an inverter for driving the motor is faulted. <P>SOLUTION: The AC motor driving device includes the inverter 2 inputting an AC power 1 and driving the AC motor 3 having a square torque load at a variable speed, an inverter control means 4 for controlling an output voltage/frequency of the inverter 2, cooling fans 51, 52 disposed commonly with an air duct on a board upper part which contains the inverter 2, and a fan control means 9 for controlling the cooling fans 51, 52. The fan control means 9 selectively operates one of the cooling fans 51, 52 normally, and switches an operation from the faulted cooling fan to another sound cooling fan and imparts a command for lowering the speed reference of the AC motor 3 in the inverter 2 to a predetermined value or less to the inverter control means 4 when the fault of this one cooling fan is detected during the inverter operating. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive device for an AC motor, and more particularly to an AC motor drive device that can continue to operate the motor even if a cooling fan of an inverter that drives the motor fails.
[0002]
[Prior art]
In an inverter that drives an AC motor, a cooling fan is usually provided in the inverter housing panel in order to cool the converter main circuit of the inverter. If the cooling fan fails during inverter operation, the cooling fan failure is usually detected to prevent power devices (eg, IGBT, IEGT, etc.) constituting the converter main circuit from being damaged by heat. Treated as a serious failure signal, inverter operation is stopped.
[0003]
However, depending on the equipment to be applied, even if a cooling fan or the like breaks down, there is a demand to continue operation without stopping the inverter as a system. For example, a blower for a boiler used in a petrochemical plant corresponds to this.
[0004]
When there is such a request, the cooling fan is doubled, and when the cooling fan for continuous operation breaks down, the system reliability is improved by switching to the standby cooling fan and operating ( For example, see Patent Document 1.)
[0005]
[Patent Document 1]
Japanese Patent Publication No. 5-72119 (page 2-3, Fig. 2)
[0006]
[Problems to be solved by the invention]
In an inverter for driving a hydrodynamic machine (hereinafter referred to as a square torque load) that is used in a chemical plant or the like and whose load torque is proportional to the square of the speed, two cooling fans are provided above the inverter housing panel. If the cooling fan breaks down during the inverter operation, the inverter operation is performed by operating one of the two cooling fans, as described in Patent Document 1 above. In addition, by detecting a failure of the cooling fan, the operation is switched to the standby cooling fan so that the inverter can be continuously operated. The reason why the two cooling fans are provided at the top and bottom is to improve the space factor.
[0007]
By the way, the failure of the normal cooling fan is often caused by the failure of the bearing which is a worn part of the cooling fan, and therefore, it is assumed that the cooling fan is locked. Considering operating the other cooling fan while one cooling fan is locked, one of the upper and lower cooling fans is locked. There was a problem that the fan lost the cooling air and could not secure the ability to cool the inverter that continued to operate. This can be solved by increasing the capacities of the two cooling fans. However, increasing the capacities increases the size of the cooling fan and the inverter storage board, which is not preferable for the AC motor driving device.
[0008]
The present invention has been made in view of the above problems. Even if the cooling fan breaks down without increasing the size of the cooling fan and the inverter storage panel, the remaining cooling fans are automatically set to the standby state. It is an object of the present invention to provide an AC motor drive device that can be switched to continuously operate an inverter.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an AC motor drive apparatus according to the present invention includes an inverter that receives an AC power supply and variable-speed drives an AC motor having a square torque load, and an inverter that controls the output voltage / frequency of the inverter. A control unit, and a plurality of cooling fans arranged on the upper part of the panel accommodating the inverter with a common air path, and a fan control unit for controlling the cooling fan. When one of the plurality of cooling fans is selectively operated and a failure of the cooling fan is detected during the inverter operation, the operation is switched from the one failed cooling fan to the healthy cooling fan. And giving a command to the inverter control means to lower the speed reference of the AC motor in the inverter to a predetermined value or less. And it features.
[0010]
According to the present invention, since the speed reference of the inverter is lowered during the switching operation of the cooling fan, it is possible to provide an AC motor drive device that can continuously operate the inverter.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment of an AC motor driving device according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of an AC motor driving device according to the present invention.
[0012]
The electric power supplied from the three-phase AC power source 1 is converted in voltage and frequency by the inverter 2 and drives the AC motor 3. The inverter 2 is usually composed of a converter that converts alternating current into direct current and an inverter that converts the obtained direct current into alternating current again. Here, the inverter 2 includes a converter function. did. The inverter 2 may be a cycloconverter or a matrix converter that directly converts alternating current into alternating current.
[0013]
The inverter 2 houses an input voltage detector 22, an output voltage detector 23, an output current detector 24, and the like in addition to a power conversion main circuit 21 that performs power conversion using a plurality of power devices. . As will be described later, the inverter 2 may include a heat generating component such as a transformer or a reactor if necessary.
[0014]
The inverter control unit 4 is for controlling the inverter 2. The inverter control unit 4 receives a speed command from the outside and a speed reduction command from a fan control circuit 9 which will be described in detail later, receives a speed reference circuit 41 that outputs a speed reference, and receives the speed reference. A voltage detector 22, an output voltage detector 23, and an inverter control circuit 42 that performs input / output control of the inverter 2 in cooperation with the feedback output from the output current detector 24.
[0015]
In order to suppress the temperature rise due to heat generation of the power device used in the power conversion main circuit 21 of the inverter 2, two inverter main circuit cooling fans 51 and 52 are provided in the upper part of the storage board of the inverter 2. Arranged as common. The drive motors for these cooling fans 51 and 52 are supplied with electric power from a control power source through circuit breakers 61 and 62, overload relays 71 and 72, and contactors 81 and 82, respectively.
[0016]
The fan control circuit 9 controls the operation of the cooling fans 51 and 52. The overload signal detected by the above-described overload relays 71 and 72 is input to the failure detection circuit 91. The failure detection circuit 91 issues a signal indicating which cooling fan has failed and which cooling fan is healthy to the fan sequence circuit 92. Upon receiving this signal, the fan sequence circuit 92 fails via the fan switching circuit 93. The cooling fan is automatically switched to a standby healthy fan, an alarm signal is output to the outside, and a speed reduction command is output to the speed reference circuit 41 of the inverter control unit 4.
[0017]
Hereinafter, the operation of the AC motor driving device according to the present invention will be described with reference to FIG. FIG. 2 is an explanatory diagram of the cooling characteristics of the AC motor driving device of the present invention.
[0018]
FIG. 2A shows a characteristic curve of the cooling fan and a pressure loss curve of the power conversion main circuit cooling system when the horizontal axis represents the air volume and the vertical axis represents the discharge pressure. The characteristic curve of the cooling fan has a downward-sloping characteristic in which the discharge pressure gradually decreases as the air volume increases. The pressure loss of the power conversion main circuit cooling system has a curve that increases in proportion to the square of the air flow as the air volume increases.
[0019]
The pressure loss curve shown by the solid line is a steady state pressure loss curve when two cooling fans are normal and one of them is operated. On the other hand, a one-dot chain line indicates a pressure loss curve when one cooling fan has a lock failure. Therefore, during normal operation, when the fan is operated at the intersection A between the characteristic curve of the cooling fan and the solid pressure loss curve, the fan breaks down and is locked, and when it is switched to another standby fan and reaches a steady state. The operation is performed at the intersection B between the characteristic curve of the cooling fan and the pressure loss curve of the one-dot chain line. That is, the air volume of the fan decreases from fa to fb.
[0020]
FIG. 2B shows a thermal resistance curve of the cooling fin with respect to the cooling air velocity by the fan. Note that the cooling fin is disposed in close contact with the power device of the power conversion main circuit, and discharges the generated loss of the power device to the outside through the cooling air.
[0021]
As described above, when one fan fails and the air volume decreases from fa to fb, the air speed of the cooling fin portion is proportional to this and decreases from Sa to Sb. When the wind speed (air volume) decreases, the thermal resistance of the cooling fin increases from ra to rb by Δr as shown in the figure, and the temperature of the power device increases by an amount corresponding to this Δr. For this reason, for example, when the inverter 2 is rated, it is necessary to stop the operation in order to protect the power device.
[0022]
However, even if the thermal resistance increases by Δr, if the loss of the power device is reduced by an amount corresponding to this, the operation can be continued without increasing the temperature of the power device. The temperature rise of the power device is proportional to the loss and the thermal resistance, and if the load of the AC motor 3 is a square torque load, the load current is proportional to the square of the speed. Assuming a state where the loss of the power device is almost proportional to the load current, for example, when the increase Δr of the thermal resistance is 20% of the initial thermal resistance ra, the upper limit of the operating speed is reduced by 10%, and the 90% speed You can drive at
[0023]
As can be seen from the above description, it is necessary to reduce the operating speed by the characteristics of the cooling fan used, the characteristics of the machine driven by the AC motor 3, the characteristics of the cooling fins of the power device, and the like. Can be determined uniquely. The upper limit value of this operation speed is defined as a limit speed fL.
[0024]
FIG. 3 is a time chart showing the transition of the operation speed when the cooling fan fails. FIG. 3A is a time chart when the vehicle is operated in a state where the speed command fR is larger than the limit speed fL. When a failure occurs at time T, the speed reference is maintained at the limit speed fL even if the speed command fR is greater than or equal to the limit speed fL by the speed reference decrease command as shown in the figure. On the other hand, as shown in FIG. 3B, when a failure occurs when the speed command fR is equal to or less than the limit speed fL, the speed reference is maintained at fR.
[0025]
In this way, the speed reduction command is output to the speed reference circuit 41. Based on this command, the speed reference circuit 41 lowers the speed reference to the limit speed fL when the speed command is larger than the limit speed fL. When the command is smaller than the limit speed fL, the speed reference outputs the same value as the speed command as it is. By controlling in this way, if the cooling fan fails in the locked state, switching to the standby cooling fan causes the locked cooling fan to lose the cooling air for the operating cooling fan, and the cooling capacity However, when the motor load is a square torque characteristic load, the speed reference is lowered and the operation is continued.
[0026]
Thus, since the inverter speed reference is lowered during the switching operation of the cooling fan, the inverter operation can be performed without increasing the capacity of the cooling fan and the inverter storage panel, and without overheating the inverter power device. Can be continued.
[0027]
Although the above description has been given for the case where there are two cooling fans, the number of cooling fans is not necessarily two. For example, two of the three cooling fans may be used for normal operation, and when one of the two fails, the operation may be switched to another standby unit.
[0028]
(Second Embodiment)
FIG. 4 is a block diagram of an AC motor drive device according to the second embodiment of the present invention. About each part of this 2nd Embodiment, the same part as each part of the alternating current motor drive device which concerns on 1st Embodiment of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. However, the second embodiment is different from the first embodiment in that the overload relays 71 and 72 in FIG. 1 are omitted and rotation detectors 51S and 52S for the cooling fans 51 and 52 are added, respectively. However, the signals of these rotation detectors 51S and 52S are input to the failure detection circuit 91.
[0029]
As described above, if the failure detection is performed using the signals of the rotation detectors 51S and 52S instead of the overload relays 71 and 72, the locked state of the cooling fan can be detected more accurately.
[0030]
In addition, you may detect a failure using both an overload relay and a rotation detector. If failure detection is performed using the logical product of both, more reliable cooling fan lock detection can be performed, and if failure detection is performed using a logical sum of both, quick failure detection is possible.
[0031]
The description so far has been made with respect to the cooling of the panel containing the power conversion main circuit of the inverter, but as mentioned in the description of the first embodiment, the input transformer necessary for configuring the inverter. Alternatively, when there are heat-generating parts such as a reactor, a standby configuration may be considered by arranging a plurality of cooling fans above and below these parts. Even in such a case, the remaining cooling fans of multiple installed cooling fans are automatically detected by detecting the failure of the cooling fan by the overload relay or rotation detector and the combination of the overload relay and rotation detector. In addition to switching, when the speed command is equal to or greater than a predetermined value, the operation of the inverter can be continued by lowering the speed reference to the predetermined value.
[0032]
【The invention's effect】
As described above, according to the AC motor driving device of the present invention, even if the cooling fan fails without increasing the size of the cooling fan and the inverter storage board, the remaining cooling fans It is possible to provide an AC motor drive device that can be automatically switched to continuously operate the inverter.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of an AC motor drive device of the present invention.
FIG. 2 is an explanatory diagram of cooling characteristics of the AC motor driving device of the present invention.
FIG. 3 is a time chart showing changes in operation speed when a cooling fan fails.
FIG. 4 is a block configuration diagram of an AC motor drive device according to a second embodiment of the present invention.
[Explanation of symbols]
1 Three-phase power supply 2 Inverter 21 Power conversion main circuit 22 Input voltage effector 23 Output voltage effector 24 Output current detector 3 AC motor 4 Inverter control unit 41 Speed reference circuit 42 Inverter control circuits 51 and 52 Cooling fans 51S and 52S Rotation Detector 61, 62 Circuit breaker 71, 72 Overload relay 81, 82 Contactor 9 Cooling fan control circuit 91 Failure detection circuit 92 Fan sequence circuit 93 Fan switching circuit

Claims (4)

An AC power source as an input and an inverter for variable speed driving an AC motor having a square torque load;
Inverter control means for controlling the output voltage / frequency of the inverter;
A plurality of cooling fans arranged with a common air passage on the top of the panel housing the inverter,
Fan control means for controlling the cooling fan,
The fan control means normally selects and operates one of the plurality of cooling fans, and detects a failure of the cooling fan during the inverter operation. The AC motor driving device is characterized in that the operation is switched to the cooling fan and an instruction to lower the speed reference of the AC motor in the inverter to a predetermined value or less is given to the inverter control means. 2. The AC motor drive device according to claim 1, wherein failure detection of the cooling fan is performed by detecting overload of the cooling fan drive motor. 2. The AC motor drive device according to claim 1, wherein the failure detection of the cooling fan is performed by detecting the number of rotations of the cooling fan. The predetermined value of the speed reference is obtained from the pressure-air volume characteristics of the plurality of cooling fans, the air volume-pressure loss characteristics of the cooling system, and the heat resistance-air volume characteristics of the cooling fins provided in the heat generating portion of the inverter. 2. The AC motor drive device according to claim 1, wherein the AC motor drive device has a value commensurate with an increase in thermal resistance.

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