JP5419389B2 - Three-phase motor control device - Google Patents

Description

  The present invention relates to a control device for driving, for example, a three-phase motor used for driving a cooling tower fan in which a reduction gear is incorporated.

  For example, in order to obtain a predetermined rotational speed, a cooling tower fan is widely operated by incorporating a speed reduction device such as a belt or a gear and operating with a general-purpose three-phase motor. In this case, when the capacity is 7.5 kW or less, the three-phase motor is often started by directly putting it into a commercial three-phase AC power source. This is a cause of problems such as shortening.

  Therefore, as a countermeasure against such a problem, for example, a commercially available device called a soft starter and an inverter device are used as a driving device for a three-phase motor having a soft start function for slowly starting.

  Various types of three-phase motor drive devices having such a soft start function have been proposed.

  For example, Patent Document 1 discloses that a triangular wave synchronized with the zero cross point of an AC power supply is provided with a switching element such as a thyristor or triac that can be phase controlled in all three-phase power supply circuits from a three-phase AC power supply to a three-phase motor. Triangular wave generating means for generating a signal, command signal generating means for generating a command signal that changes along a time series, and conduction control of the switching element by phase control based on a level comparison between the triangular wave signal and the command signal A soft start control device configured to perform is described.

  In Patent Document 2, a starter is configured by interposing a switching element in all three-phase power supply circuits from a three-phase AC power source to a three-phase motor, and a bypass circuit that bypasses the starter is configured. The three-phase motor is started and stopped with a three-phase AC power source that is phase-controlled by the starter, and the three-phase AC power source is supplied from a bypass circuit that bypasses the starter by closing the electromagnetic switch during rated rotation. A drive device for a three-phase motor is described in which the phase motor is driven so that the power supply to the three-phase motor is switched between start / stop and rated rotation.

  In Patent Document 3, switching elements are interposed in two phases of a three-phase power supply circuit from a three-phase AC power source to a three-phase motor, and soft start control is performed by phase controlling these two-phase switching elements. A control device of a three-phase two-wire phase control system is described.

In Patent Document 4, similarly to Patent Document 2, switching elements are provided in two phases of a three-phase power supply circuit from a three-phase AC power source to a three-phase motor, and these two-phase switching elements are phase-controlled. In a device that performs soft start control, the firing angle of the switching element interposed in the two-phase power supply circuit is shifted in order to suppress the generation of unbalanced current between the phases and to enable stable start-up. A three-phase two-wire phase control system is provided that includes arithmetic means for controlling the gate trigger signal in accordance with a preset control pattern so as to gently start the three-phase motor while reducing the unbalanced amount of the line voltage. A control device is described.
Japanese Patent No. 3279173 JP 2000-201490 A JP 2003-47289 A Japanese Patent No. 3998395

  As described in Patent Document 1 and Patent Document 2, all of the three-phase power supply circuits are provided with switching elements, and these three-phase switching elements are phase-controlled to perform soft start control. Therefore, downsizing is difficult and the cost is increased.

  On the other hand, as in Patent Document 3 and Patent Document 4, switching elements are interposed in two phases of a three-phase power feeding circuit, and these two-phase switching elements are phase-controlled to perform soft start control. Although it is advantageous in terms of downsizing and cost, an unbalance of the current flowing through each phase tends to occur, and a smooth soft start cannot be realized unless this unbalance is reduced.

  Therefore, in Patent Document 4, as described above, each firing angle is appropriately set by a gate trigger signal in accordance with a specific control pattern set in advance so that the firing angle of the switching element interposed in the two-phase power feeding circuit is shifted. However, when controlling the firing angle according to this specific control pattern, when changing the firing angle of one phase, the operation to change the firing angle of the other phase is stopped. Since an interval occurs, the optimum value is deviated in this interval.

  The first object of the present invention is to solve such drawbacks and further reduce the unbalance of the current flowing through each phase to realize a smooth soft start.

  On the other hand, in the cooling tower fan described above, an inverter power supply may be used to perform variable speed operation. If a control device having a soft start function is connected to the inverter power supply and used, the inverter power supply may be used. The start by the and the start by the soft start function interferes, and normal start cannot be performed.

  Therefore, a second object of the present invention is to provide a controller-integrated three-phase motor that can operate normally regardless of whether the connected power source is a commercial power source or an inverter power source.

  In order to solve the above-described problem, in the present invention, a phase-controllable switching element is interposed in two phases of a three-phase power feeding circuit from a connection portion with a three-phase AC power source to a three-phase motor, and the power feeding circuit The voltage zero cross detection circuit connected to the two phases, the phase control drive circuit of the switching element, the conduction time detection circuit of the switching element, and the phase so that the conduction time of each switching element detected by this conduction time detection circuit becomes equal A control device for a three-phase motor is proposed which comprises control means for controlling a control drive circuit and performing a soft start operation.

  According to the present invention, in the above configuration, a bypass circuit that bypasses the switching element, an operation / non-operation switching unit of the bypass circuit, and a feeding frequency detection unit that is connected to two phases of the feeding circuit are configured. A control device for a three-phase motor is proposed which is configured to switch between a soft start operation and an operation of a bypass circuit by operating at a power supply frequency detected by a power supply frequency detection means.

  The present invention also proposes that, in the above configuration, the switching element is a power semiconductor element such as a thyristor or a triac, and the switching means of the bypass circuit is a relay.

  Further, the present invention proposes that, in the above configuration, the three-phase motor is for driving a cooling tower fan in which a reduction gear is incorporated.

  The present invention also proposes that the three-phase motor is an induction motor in the above configuration.

  In the invention according to claim 1, in the soft start operation, the control means operates the phase control drive circuit so that the conduction time of each switching element detected by the conduction time detection circuit becomes equal. Compared with the case where control is performed according to a specific control pattern, the unbalance of the current flowing through each phase can be further reduced to realize a smooth soft start.

  In the invention according to claim 2, when the operation is started with the power turned on, the control means detects the power feeding frequency by the power feeding frequency detecting means, determines whether or not the frequency is the frequency of the commercial AC power source, and the commercial AC power source. In the case of this frequency, since the soft start operation similar to that of the invention according to claim 1 is selected and the bypass circuit is not operated, the soft start operation similar to that of the invention according to claim 1 is performed.

  When starting by the soft start operation and reaching the rated rotation, the control means operates the bypass circuit by the switching means, and thereafter, the feeding current flows only through the bypass circuit and does not flow to the switching element. Therefore, since the switching element only needs to be cooled at the time of starting, the switching element can be reduced in size, and it is easy to perform sufficient cooling even when mounted on a terminal box or the like.

  On the other hand, if it is determined at the start of operation that the power supply frequency detected by the power supply frequency detection means is not the frequency of the commercial AC power supply, the control means operates the bypass circuit operation / non-operation switching means to operate the bypass circuit. To work.

  In this case, the three-phase AC power source connected to the three-phase motor is an inverter power source, and the feeding current flows through the feeding circuit of the phase not provided with the bypass circuit and the switching element and does not flow to the switching element. The operation and the start operation by the soft start function do not interfere with each other, and normal operation by the inverter is performed.

  As described above, since the switching element by the power semiconductor element such as the thyristor or the triac is interposed only in the two phases of the three-phase feeding circuit from the connection portion with the three-phase AC power source to the three-phase motor, This is more advantageous in terms of size and cost than interposing all of the phases.

Next, an embodiment of a control device for a three-phase motor according to the present invention will be described with reference to the accompanying drawings.
First, FIG. 1 is a perspective view showing an appearance of a cooling tower as an example of an apparatus using a control device for a three-phase motor according to the present invention, and FIG. 2 is an enlarged partially cutaway perspective view of a main part.
Reference numeral 1 denotes a cooling tower. In this case, a plurality of cooling towers 1 are arranged in a row, and control with increasing or decreasing the number of operating units is possible. A fan cylinder 3 that rotatably supports a fan 2 is provided in the upper part of the cooling tower 1. A belt speed reducer 4 that rotates the rotating shaft of the fan 2 on the fan cylinder 3 and a three-phase electric motor 5 for rotational driving. In this case, a three-phase motor is installed.

  The cooling tower 1 is a device that dissipates heat generated in air conditioning equipment and industrial equipment to the atmosphere. The heat is carried by the cooling water and is brought into contact with a large amount of air obtained by the fan 2 in the cooling tower 1. Heat is dissipated and the cooled cooling water is recycled.

  The cooling capacity of the cooling tower 1 is in contact with the atmosphere to dissipate its heat, so the summer is the most severe in the summer when the temperature of the atmosphere is the highest. When the temperature is lowered or when the heat load is lowered, the cooling water temperature is lowered more than necessary, resulting in overcooling. Therefore, there is a method of reducing the number of operating units as a method of lowering the cooling performance of the cooling tower 1 and raising the cooling water temperature. . When the cooling water temperature increases due to a decrease in the number of operating units, the number of operating units increases, and when the cooling water temperature decreases too much, an ON-OFF operation is performed in which the operating unit number is decreased.

  3 is a perspective view showing a three-phase motor 5 controlled by the control device according to the present invention, FIG. 4 is a front view, and FIG. 5 is a cross-sectional view taken along line AA of FIG. A terminal box 6 is provided on the side of the terminal box 6, and the terminal box 6 includes a lid 7.

  In this embodiment, the control device for the three-phase motor 5 according to the present invention is installed in the terminal box 7, but can be installed separately from the terminal box 7.

FIG. 6 is a system diagram showing an embodiment of the control device according to the present invention.
Reference numeral 8 is a connection terminal which is a connection portion 8 to the three-phase AC power supply as described above, and two phases of the three-phase power supply circuits 9r, 9s, and 9t extending from the connection portion 8 to the three-phase motor 5, in this case , R-phase and T-phase power supply circuits 9r and 9t, phase-controllable switching elements 10r and 10t, and in this embodiment, thyristors are interposed, and these switching elements 10r and 10t are respectively connected in parallel. The bypass circuits 12r and 12t provided with the bypass relay 11 including the contact portions 11r and 11t are connected. The phase interposing the switching elements 10r and 10t is not limited to the R phase and the T phase, and may be an appropriate two phase.

  Reference numeral 13 denotes a switching element driving circuit corresponding to the above-described phase control driving circuit, in this case, a thyristor driving circuit. The switching elements 10r and 10t are phase-controlled by receiving a gate trigger signal from the thyristor driving circuit 13. Each switching element 10r, 10t is connected to a thyristor conduction time detection circuit 14 for detecting a voltage at both ends and detecting a conduction time, and the R-phase and S-phase power supply circuits 9r, 9s are connected to each switching element 10r, 10t. The voltage zero-cross detection circuit 15 of these interphase voltages and the frequency detection circuit 16 are connected, and these thyristor drive circuit 13, voltage zero-cross detection circuit 15 and frequency detection circuit 16 are connected to a microcomputer as the control means 17. It is connected. Reference numeral 18 denotes a bypass relay switching circuit that operates the bypass relay 11 to open and close the contact portions 11r and 11t, and reference numeral 20 denotes a current detection circuit that detects the current of the S-phase power feeding circuit 9s by the current detection unit 19. The bypass relay switching circuit 18 and the current detection circuit 20 are also connected to the microcomputer as the control means 17.

  In this embodiment, each circuit and each means described above are installed in the terminal box 6, and elements and circuits constituting them are configured as a circuit board 21. As shown in FIG. 5, a radiation fin 22 is provided on a part of the wall of the terminal box 6, in this case, the side wall in the same direction as the axial direction of the three-phase motor 5. Elements 10r and 10t, for example, thyristor modules are fixed.

  In this embodiment, the three-phase motor 5 is fixed to a predetermined position of the belt speed reducer 4 of the fan cylinder 3 of the cooling tower 1, for example, and then the three-phase AC power supply line is connected to the connection terminal 8 in the terminal box 6. It is only necessary to connect to the cable, and installation is very easy. Reference numeral 24 denotes a support cylinder for drawing the power supply line into the terminal box 6.

  In the above configuration, when the power is turned on and the operation of the three-phase motor 5 is started, the control means 17 detects the power supply frequency by the power supply frequency detection circuit 16, determines whether the frequency is the frequency of the commercial AC power supply, When the frequency of the commercial AC power source is 50 Hz or 60 Hz, the soft start start operation is selected and the bypass circuit is not operated. That is, the control means 17 is configured so that the bypass relay switching circuit 18 maintains the contact portions 11r and 11t of the bypass relay 11 in the open state, and from the voltage zero cross detection circuit 15, the thyristor conduction time detection circuit 14, and the switching element drive circuit 13. The three-phase motor 5 is started by a soft start operation by controlling the phases of the two-phase switching elements 10r and 10t by the soft start means 25.

  As described above, the control device of the present invention derives an optimal control pattern from the integrated value of the line voltage in order to reduce the voltage imbalance in the method as described in Patent Document 3, that is, the soft start operation. However, the thyristor conduction time detection circuit 14 detects the conduction times of the switching elements 10r and 10t in each phase, instead of applying a method of performing a soft start operation by shifting the firing angles of the two phases according to this control pattern. Thus, by controlling the conduction times to be equal for each control period, voltage imbalance is reduced without requiring a specific control pattern.

Therefore, the soft start operation according to the embodiment of the present invention will be described with reference to the control pattern in the method of Patent Document 3.
First, FIG. 7 shows a specific control pattern set in advance in the method of Patent Document 3, and the black circles in the figure show the firing angles of the switching elements of each phase per unit time. A soft start is performed by shifting from the firing angle of 180 ° to the firing angle of 0 ° along the black circle firing angle.
8 to 12 show current waveforms of the switching elements 10r and 10t of the respective phases, R phase and T phase under the conditions of the firing angles of points A, B, C, D and E in FIG. The solid line represents the R-phase current, and the broken line represents the T-phase current.

  Referring to FIG. 8 showing a state in which the firing angle of the R phase and the T phase is 120 ° (point A), in the section where the firing angle of the R phase and the T phase is 180 ° to 120 °, both firings are performed. It can be seen that even if the corners are the same, the respective conduction times are equal.

  However, referring to FIG. 9 showing a state where the firing angles of the R phase and the T phase are 90 ° (point B), in the section where the firing angles of the R phase and the T phase shift from 120 ° to 90 °, both When the firing angles are the same, a difference in conduction time begins to occur, and at point B, a difference of 30 ° in conduction time occurs.

  On the other hand, referring to FIG. 10 where the R-phase and T-phase firing angles are 90 ° and 60 ° (point C), respectively, the R-phase firing angle is maintained at 90 ° and the T-phase firing angle is maintained. It can be seen that in the section where the angle shifts from 90 ° to 60 °, the difference in conduction time gradually decreases, and at point C, each conduction time becomes equal.

  Furthermore, referring to FIG. 11 showing the states of the R-phase and T-phase firing angles of 60 ° and 30 ° (point D), respectively, the R-phase firing angle is 90 ° to 60 °, and the T-phase firing angle. It can be seen that in the section where the angle shifts from 60 ° to 30 °, a difference starts to occur in the conduction time, and at point D, a difference of 30 ° occurs in the conduction time.

  On the other hand, referring to FIG. 12, which shows the R-phase and T-phase firing angles of 60 ° and 0 ° (point E), respectively, the R-phase firing angle is maintained at 60 ° and the T-phase firing angle is maintained. In the section where the angle shifts from 30 ° to 0 °, the difference in conduction time gradually decreases. At point E, each conduction time becomes equal, and thereafter the firing angles of the R phase and the T phase are both It can be seen that the respective conduction times are equal until 0 ° is reached.

  Therefore, in the control device according to the present invention, when the firing angle is gradually reduced in the soft start operation, the conduction time of the switching elements 10r and 10t of each phase is detected by the thyristor conduction time detection circuit 14, and the conduction time thereof is detected. Is controlled to be equal at every control cycle, and therefore, when the firing angles of the R phase and the T phase are both 180 ° from the point A to the point A along the solid line in the figure, the point A is shown in the figure. After reaching the point C through the broken line trajectory and then reaching the point E through the broken line trajectory in the figure, both the R-phase and T-phase firing angles reach the point at 0 ° along the solid line. The transition from point A to point E will be explained. First, from point A to point C, the manipulated value of the T-phase firing angle is twice as large as the manipulated value of the R-phase firing angle. Next, when transitioning from point C to point E, if the firing angle of the T phase is smaller than 60 °, the conduction time of the R phase is instantaneously increased by 30 °. The operation amount of the firing angle changes greatly.

  As shown in the above-mentioned Patent Document 3, if the ignition angle is controlled by a specific control pattern, the change operation of the ignition angle on one phase side is stopped at a certain ignition angle, and the operation on the other phase side is stopped. A section that operates only the firing angle occurs, and when the firing angle on the other phase side is manipulated while the operation on the firing angle on the other phase side is stopped, it deviates from the optimum value. End up.

  However, in the control device according to the present invention, the operation of the firing angle of each phase is controlled so that the conduction time becomes equal for each control cycle, so that the operation on one phase side does not stop and is always ineffective. A very smooth soft-start operation is achieved because the movement reduces the balance.

  Next, when it is determined that the power supply frequency detected by the frequency detection circuit 16 is not the frequency of the commercial AC power supply at the start of the operation described above, the control means 17 uses the bypass relay switching circuit 18 to each of the bypass relays 11. The bypass circuits 12r and 12t are operated by closing the contact portions 11r and 11t.

  In this case, the three-phase AC power source connected to the connection portion 8 of the three-phase motor 5 is an inverter power source, but the feeding current from the three-phase AC power source is provided with bypass circuits 12r and 12t and switching elements 10r and 10t. Since the current does not flow to the switching elements 10r and 10t through the non-feeding power supply circuit 9s, the start operation by the inverter and the start operation by the soft start function do not interfere, and normal operation by the inverter, that is, soft start A series of operations from operation to normal operation is performed.

  The control device for a three-phase motor according to the present invention is optimal for driving a cooling tower fan in which a speed reducer is incorporated, but is highly applicable to other appropriate applications.

It is a perspective view which shows the external appearance of a cooling tower as an example of the apparatus using the control apparatus of the three-phase motor which concerns on this invention. It is an expansion partially notched perspective view of the principal part. It is a perspective view which shows the three-phase motor using the control apparatus which concerns on this invention. It is a front view which shows the three-phase motor using the control apparatus which concerns on this invention. It is the sectional view on the AA line of FIG. It is a systematic diagram showing an embodiment of a control device for a three-phase motor according to the present invention. It is explanatory drawing which shows the soft start operation | movement in the control apparatus of this invention compared with the operation | movement by a control pattern. It is explanatory drawing which shows the current waveform of each phase in A point of FIG. It is explanatory drawing which shows the current waveform of each phase in B point of FIG. It is explanatory drawing which shows the current waveform of each phase in C point of FIG. It is explanatory drawing which shows the current waveform of each phase in D point of FIG. It is explanatory drawing which shows the current waveform of each phase in E point of FIG.

Explanation of symbols

1 Cooling tower 2 Fan 3 Fan cylinder 4 Belt reducer 5 Three-phase motor (three-phase induction motor)
6 Terminal box 7 Lid 8 Connection (connection terminal)
9r, 9s, 9t Feed circuit 10r, 10t Switching element 11r, 11t Contact part 11 Bypass relay 12r, 12t Bypass circuit 13 Switching element drive circuit (thyristor drive circuit)
14 Thyristor conduction time detection circuit 15 Voltage zero cross detection circuit 16 Frequency detection circuit (means)
17 Control means (microcomputer)
18 Bypass relay switching circuit 19 Current detection unit 20 Current detection circuit 21 Circuit board 22 Radiation fin 23 External heat dissipation unit 24 Support cylinder 25 Soft start means

Claims (5)

A voltage zero-crossing detection circuit connected to the two phases of the power supply circuit by interposing a phase-controllable switching element in the two phases of the three-phase power supply circuit from the connection with the three-phase AC power source to the three-phase motor, and switching Element phase control drive circuit, switching element conduction time detection circuit, and control for performing a soft start operation by controlling the phase control drive circuit so that the conduction time of each switching element detected by this conduction time detection circuit is equal. And a control device for a three-phase motor. A bypass circuit that bypasses the switching element, an operation / non-operation switching unit of the bypass circuit, and a feeding frequency detection unit that is connected to two phases of the feeding circuit are configured, and the control unit detects the feeding by the feeding frequency detection unit 2. The control device for a three-phase motor according to claim 1, wherein the control device switches between a soft start operation and an operation of a bypass circuit by operating according to a frequency. The control device for a three-phase motor according to claim 2, wherein the switching element is a thyristor or a triac , and the switching means of the bypass circuit is a relay.


The three-phase motor control device according to any one of claims 1 to 3, wherein the three-phase motor is for driving a cooling tower fan in which a reduction gear is incorporated. The three-phase motor control device according to any one of claims 1 to 4, wherein the three-phase motor is an induction motor.

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