JP2009171745A - Motor driving system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor driving system which can decelerate the driving of a load while consuming regenerative power with braking resistance, and in which there is no need to insulate the braking resistance at high voltage. <P>SOLUTION: The motor driving system is constituted of an inverter device 10 having an inverter decelerating means 9, an AC motor 5 driven by the inverter device 10, a breaking means 6 connected to an output side of the inverter device 10 and having a transformer 61 at an input part. The inverter decelerating means 9 reduces the output frequency of the inverter device 4 so that the AC motor 5 is excited and the regenerative power of the AC motor 5 is supplied to the braking means 6 when the AC motor 5 is decelerated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric motor drive system using an inverter device, and more particularly to an electric motor drive system using a high-voltage inverter device having no power regeneration function.

In an electric motor drive system that drives a load such as a pump or a blower having a relatively large moment of inertia (GD ² ) using an inverter device that does not have a power regeneration function, the motor must be decelerated by free run when decelerating / stopping. / Because it is stopped, deceleration time and stop time become very long. This is because the load torque (load loss) becomes extremely small in a low speed region in a so-called square load such as a pump or a blower.

If a power regeneration function that regenerates power to the power supply is added to the inverter device, it is possible to decelerate and stop in a short time. However, the device is not only large, but also becomes complicated and has a problem in terms of cost. . In particular, in a multiplex type high-voltage inverter device in which the single-phase outputs of a plurality of unit inverter devices are connected in series to form three phases, it is necessary to add a power regeneration function to each unit inverter device. Therefore, it becomes a complicated circuit configuration. For this reason, a proposal has been made to add a braking resistor to the direct current portion of the unit inverter device and consume the regenerative power at the time of deceleration with this braking resistor (see, for example, Patent Document 1).
JP 2001-238455 A (page 3-4, FIG. 1)

  According to the technique disclosed in Patent Document 1, it is possible to decelerate while consuming the regenerative power at the time of deceleration with the braking resistance. However, since the insulation level of the braking resistance becomes a high voltage, Not only does the apparatus become large, but it is also necessary to consider the influence of heat generated by the braking resistor on the unit inverter device, which further increases the size and cost of the apparatus.

The present invention has been made in view of the above, and an object of the present invention is to provide an electric motor drive system that can decelerate while consuming regenerative power with a braking resistor and that does not require high-voltage insulation of the braking resistor.

  In order to achieve the above object, an electric motor drive system according to the present invention includes an inverter device having an inverter reduction means, an AC motor driven by the inverter device, an output side of the inverter device, and a transformer at an input unit. The inverter speed reducing means excites the AC motor and degenerates the AC motor to supply the regenerative power of the AC motor to the braking means when the AC motor is decelerated. It is characterized in that the frequency is reduced.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the electric motor drive system which can decelerate, consuming regenerative electric power with braking resistance, and does not need to carry out high voltage insulation of braking resistance.

  Embodiments of the present invention will be described below with reference to the drawings.

  A motor drive system according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a system configuration diagram of an electric motor drive system according to the first embodiment. In FIG. 1, the AC voltage of the AC power source 1 is converted to DC by the rectifier 2, and the DC voltage is smoothed by the DC capacitor 3. The smoothed DC voltage is converted back to AC by the inverter 4 and the AC motor 5 is driven by this AC output. Here, the rectifier 2, the DC capacitor 3 and the inverter 4 constitute an inverter device 10.

  The output side of the inverter 4 is connected to a braking circuit 6 including a transformer 61 and a braking resistor 63 connected to the secondary side of the transformer 61 via a switch 62. A DC voltage detector 7 is provided at both ends of the DC capacitor 3, and an AC voltage detector 8 is provided at the output side of the inverter 4.

  The inverter 4 has a configuration in which switching elements such as a high voltage IGBT are bridge-connected, and these switching elements are controlled by an on / off signal supplied from the control circuit 9.

  Hereinafter, the internal configuration of the control circuit 9 will be described. Here, the description will focus on the internal configuration for performing deceleration control of the AC motor 5. The deceleration command is given to the deceleration rate circuit as a frequency command. The deceleration rate circuit 91 outputs a frequency reference whose deceleration rate is variable and supplies it to the V / F circuit 92. The V / F circuit 92 outputs an output voltage reference corresponding to the input frequency reference. The output voltage reference and the AC feedback voltage detected by the AC voltage detector 8 are compared by the comparison circuit 93 and the deviation is given to the voltage control circuit 94. The voltage control circuit 94 gives a three-phase voltage command to the PWM circuit 95 so that the deviation becomes small. The PWM circuit 95 performs on / off control of the switching element of the inverter 4 so that the inverter 4 outputs a voltage corresponding to the three-phase voltage command.

  The DC feedback voltage detected by the DC voltage detector 7 is compared with the set voltage by the comparator 96, and the difference is given to the DC voltage controller 97. Then, the DC voltage controller 97 adjusts the deceleration rate of the deceleration rate circuit 91 by outputting the deceleration rate reference so that the difference becomes smaller. The output of the deceleration rate circuit 91 is given to a free-run switching control circuit 98, and normally, free-run deceleration is performed until the frequency reference that is the output of the deceleration rate circuit 91 reaches a predetermined value.

  The operation of the present embodiment having the above-described configuration will be described below based on the deceleration operation explanatory diagram of FIG. This explanatory diagram of the deceleration operation shows the time transition of the rotational speed N of the AC motor 5 during the deceleration control.

  First, it is assumed that a deceleration command is given when driving at a rotational speed N0 at time t = T0. At this time, the free-run switching control circuit 98 detects that the command is a deceleration command at a predetermined rotational speed or higher, blocks the inverter 4 and performs a free-run operation. For example, at time t = T1 obtained from the load characteristics of the AC motor 5, the gate block is released to operate the inverter 4, and the switch 62 is turned on to start deceleration control by the braking circuit 6. When this deceleration control is started, the rotational speed N1 of the AC motor 5 during free-running is detected, and if necessary, the residual magnetic flux of the AC motor 5 is detected, and the operation is smoothly restored using these signals. However, the description thereof is omitted here. In addition, disturbances when the switch 62 is turned on may be a problem during the above-described operation return control. For this reason, it is conceivable that a high resistance is connected in parallel with the switch 62, and a small current is allowed to flow through the braking resistor 63 at all times.

  The control operation after time T1 is as follows. By operating the inverter 4, an excitation current is supplied to the AC motor 5. Therefore, when the output frequency of the inverter 4 is lowered, the AC motor 4 operates as a generator, and the regenerative power (generated power) is consumed by the braking resistor 63. If the deceleration rate for decreasing the frequency is within a predetermined range, the vehicle can be decelerated as it is. However, when the deceleration rate exceeds a predetermined value, the regenerative power due to the deceleration of the AC motor 5 can be absorbed by the braking resistor 63 alone. Disappear. For this reason, since excessive regenerative electric power is stored in the direct current capacitor 3, the direct current voltage of the direct current link portion rises.

  Here, since the deceleration rate is controlled by the operation of the DC voltage controller 97 so that the DC voltage becomes the set voltage, according to this embodiment, the maximum deceleration using the capacity of the braking resistor 63 fully. It becomes possible to decelerate at a rate. If the set voltage is set slightly higher than the normal operating voltage within a range where there is no problem in terms of loss, the deceleration rate can be further increased.

  Here, the rotational speed N1 at which the braking circuit 6 is operated is determined from the loss characteristic of the load. Depending on the loss characteristics of the load, it is possible to set the rotational speed N1 to the rated speed and not to provide a free-run deceleration period.

  As described above, in this embodiment, the control circuit 9 excites the AC motor 5 and controls the deceleration so as to reduce the output frequency of the inverter 4 so that the regenerative power of the AC motor 5 is supplied to the braking circuit 6. The point is to do.

  Hereinafter, an electric motor drive system according to a second embodiment of the present invention will be described with reference to FIGS. 3 and 4.

  FIG. 3 is a system configuration diagram of an electric motor drive system according to Embodiment 2 of the present invention. In the second embodiment, the same parts as those in the system configuration diagram of the motor drive system according to the first embodiment of the present invention shown in FIG. The second embodiment is different from the first embodiment in that the comparator 96 and the DC voltage controller 97 are omitted, and the output of the DC voltage detector 7 is provided to the free-run switching control circuit 98.

  The operation of the present embodiment in the above configuration will be described below based on the decelerating operation explanatory diagram of FIG. The operation from time t = T0 to time t = T1 is the same as the operation of the first embodiment shown in FIG. In the second embodiment, the deceleration operation starting from time T1 is performed at a constant deceleration rate set in advance by the deceleration rate circuit 91. In this way, the AC motor 5 decelerates at a constant deceleration rate as shown in FIG. When time t = T2 is reached, the regenerative power cannot be absorbed by the braking resistor 63, and the DC voltage rises. This DC voltage rise is detected by the DC voltage detector 7, and the gate block of the inverter 4 is performed by the free run switching control circuit 98.

  According to the second embodiment, it is necessary to supply extra power to the braking resistor 63 from the AC power source 1 side during the regenerative braking operation. However, deceleration control with a constant deceleration rate or regenerative power is applied to the braking resistor 63. Deceleration control within the absorbable range is possible.

  Hereinafter, an electric motor drive system according to Embodiment 3 of the present invention will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a system configuration diagram of an electric motor drive system according to Embodiment 3 of the present invention. In the third embodiment, the same parts as those in the system configuration diagram of the electric motor drive system according to the first embodiment of the present invention shown in FIG. The third embodiment is different from the first embodiment in that the braking circuit 6A uses a transformer 61A with a tap instead of the transformer 61, and a deceleration rate detection that detects the deceleration rate from the signal of the deceleration rate circuit 91. The circuit 99 is provided.

  The operation of the present embodiment in the above configuration will be described below based on the decelerating operation explanatory diagram of FIG. The operation from time t = T0 to time t = T1 and the operation from time t = T1 to time t = T3 are the same as the operation of the first embodiment shown in FIG. At time t = T3, the tap applied to the transformer 61A with tap is switched to step up the voltage applied to the braking resistor 63. In this way, since the electric power consumed by the braking resistor 63 is increased, the deceleration rate after time t = T3 can be increased.

  In this embodiment, the time t = T3 is detected when the deceleration rate becomes a predetermined value or less, but may be switched by a timer, and the rotational speed N3 corresponding to the time t = T3 is set to some value. Detection may be performed by a method. The deceleration rate detection circuit 99 can be replaced with a difference detection between the frequency reference that is the output of the deceleration rate circuit 91 and the actual operation frequency of the inverter 4.

  Further, although the present embodiment shows an example in which the taps are switched in two stages, switching in three or more stages may be performed instead of switching in two stages.

  Hereinafter, an electric motor drive system according to Embodiment 4 of the present invention will be described with reference to FIG.

  FIG. 7 is a system configuration diagram of an electric motor drive system according to Embodiment 4 of the present invention. In the fourth embodiment, the same parts as those in the system configuration diagram of the electric motor drive system according to the first embodiment of the present invention shown in FIG. The fourth embodiment differs from the first embodiment in that a variable braking resistor 63A is used in place of the braking resistor 63 in the braking circuit 6B, and a deceleration rate for detecting the deceleration rate from the signal of the deceleration rate circuit 91. The detection circuit 99 is provided. For example, a variable braking resistor 63A having a configuration in which two unit resistors connected in series are switched so as to be connected in parallel is used.

  The operation of the present embodiment in the above configuration is basically the same as the deceleration operation explanatory diagram of FIG. In FIG. 6, the tap is switched at time t = T3. However, in this embodiment, the tap may be switched so that the resistance value of the variable braking resistor becomes small at time t = T3.

  Hereinafter, an electric motor drive system according to Embodiment 5 of the present invention will be described with reference to FIG.

  FIG. 8 is a system configuration diagram of an electric motor drive system according to Embodiment 5 of the present invention. In the fifth embodiment, the same parts as those in the system configuration diagram of the motor drive system according to the first embodiment of the present invention shown in FIG. The fifth embodiment differs from the first embodiment in that a short-circuit switch 64 for short-circuiting the primary and secondary of the transformer 61 is provided in the braking circuit 6C.

  The operation of the present embodiment in the above configuration is basically the same as the deceleration operation explanatory diagram of FIG. In FIG. 6, the tap is switched at time t = T3, but in this embodiment, the short-circuit switch 64 may be closed at time t = T3. Since the rotational speed N3 at time t = T3 is sufficiently low, the driving voltage at that time is sufficiently low. Further, since the frequency is also low, when the transformer 61 is passed through, the low frequency characteristics of the transformer 61 may become a problem. Therefore, according to this embodiment, it is possible to ensure the braking force at the time of low speed.

  Hereinafter, an electric motor drive system according to Embodiment 6 of the present invention will be described with reference to FIG.

  FIG. 9 is a system configuration diagram of an electric motor drive system according to Embodiment 6 of the present invention. Regarding the respective parts of the sixth embodiment, the same parts as those of the system configuration diagram of the electric motor drive system according to the second embodiment of the present invention shown in FIG. The sixth embodiment is different from the second embodiment in that a semiconductor switch circuit 62A is provided in place of the switch 62, and the output of the DC voltage detector 7 is received to control the semiconductor switch circuit 62A. This is the point.

  As described in the second embodiment, when decelerating at a constant deceleration rate, wasted power is supplied from the AC power source 1 to the braking resistor 63. In this embodiment, the ON / OFF circuit 100 turns on the semiconductor switch circuit 62A when the DC voltage becomes equal to or higher than the first predetermined value, and the semiconductor switch circuit when the DC voltage becomes equal to or lower than the second predetermined value. 62A is turned off. By performing such control, it is possible to reduce a loss when the AC motor 5 is decelerated at a constant deceleration rate, and the braking resistor 63 can be reduced in size.

  Hereinafter, an electric motor drive system according to Embodiment 7 of the present invention will be described with reference to FIG.

  FIG. 10 is a circuit configuration diagram of an inverter device 10A of the motor drive system according to the seventh embodiment of the present invention. In FIG. 10, the AC power source 1 is connected to a primary winding of an input transformer 20 having a plurality of secondary windings. Outputs of the plurality of secondary windings are connected to unit inverter devices 21u1, 21u2, 21v1, 21v2, 21w1, and 21w2. Although these unit inverter apparatuses have the same configuration, the inside of the unit inverter apparatus 21u2 will be described as an example.

  The unit inverter device 21u2 is provided with a rectifier 2a at its input, and its DC output is supplied to an inverter 4a that outputs a single-phase AC through a DC capacitor 3a. The voltage of the DC capacitor 3a is detected by the DC voltage detector 7a as necessary.

  The outputs of the unit inverter devices 21u1 and 21u2, 21v1 and 21v2, and 21w1 and 21w2 are connected in series. One end of each series circuit is connected to each other as a neutral point, and the other end is connected to the output of the inverter device 10A. Become. In FIG. 10, the number of unit inverter units connected in series is 2, but any other natural number may be used.

  As described above, the electric motor drive system according to the first to sixth embodiments of the present invention can be realized even by using the multiple-configuration inverter device 10A shown in FIG. In this embodiment, the DC voltage detector 7 can be replaced with a representative one, for example, the DC voltage detector 7a of the unit inverter device 21u2.

  In the first to seventh embodiments of the present invention described above, the control of the inverter 4 or the inverter 4a has been described as open-loop V / F control, but current minor control or current limit control may be added, Alternatively, vector control or sensorless vector control may be performed in which control is performed separately for excitation and torque.

  In an application in which the power consumed by the braking resistor 63 is excessive, it is possible to regenerate all or part of the power on the secondary side of the transformer 61 to the power source.

1 is a system configuration diagram of an electric motor drive system according to Embodiment 1 of the present invention. Explanatory drawing of deceleration operation | movement of Example 1. FIG. The system block diagram of the electric motor drive system which concerns on Example 2 of this invention. Explanatory drawing of deceleration operation | movement of Example 2. FIG. The system block diagram of the electric motor drive system which concerns on Example 3 of this invention. Explanatory drawing of deceleration operation of Example 3. FIG. The system block diagram of the electric motor drive system which concerns on Example 4 of this invention. The system block diagram of the electric motor drive system which concerns on Example 5 of this invention. The system block diagram of the electric motor drive system which concerns on Example 6 of this invention. The circuit block diagram of the inverter apparatus part of the electric motor drive system which concerns on Example 7 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2, 2a Rectifier 3, 3a DC capacitor 4, 4a Inverter 5 AC motor 6, 6A, 6B, 6C, 6D Braking circuit 7, 7a DC voltage detector 8 AC voltage detector 9, 9A Control circuit 10, 10A Inverter device 20 Input transformer 21u1, 21u2, 21v1, 21v2, 21w1, 21w2 Unit inverter device 61 Transformer 61A Transformer with tap 62 Switch 62A Semiconductor switch 63 Braking resistor 63A Variable braking resistor 64 Short circuit switch 91 Deceleration rate Circuit 92 V / F circuit 93 Comparator 94 Voltage control circuit 95 PWM circuit 96 Comparator 97 DC voltage controller 98 Free-run control switching circuit 99 Deceleration rate detection circuit 100 ON / OFF control circuit

Claims (12)

An inverter device having an inverter deceleration means;
AC motor driven by the inverter device;
Connected to the output side of the inverter device, and composed of braking means having a transformer at the input part,
The inverter deceleration means is
When the AC motor is decelerated, the output frequency of the inverter device is reduced so that the AC motor is excited and the regenerative power of the AC motor is supplied to the braking means. . The inverter device has a DC capacitor in the DC link part,
The motor drive system according to claim 1, wherein the inverter speed reduction unit reduces the output frequency of the inverter device so that the voltage of the DC link portion does not exceed a predetermined value. The inverter device is a multiple inverter device in which the single-phase output of a plurality of unit inverters is connected in series to obtain the voltage of each phase,
The output frequency of the inverter device is reduced so that the voltage of the DC link portion of any one of the plurality of unit inverters does not exceed a predetermined value. Electric motor drive system. The inverter deceleration means is
4. The AC motor according to claim 1, wherein the AC motor is free-run decelerated when the AC motor has a predetermined rotational speed or more, or when the output frequency of the inverter device is a predetermined value or more. The electric motor drive system according to any one of claims. The inverter deceleration means is
4. The motor drive system according to claim 2, wherein when the voltage of the DC link section exceeds a predetermined value, the AC motor is subjected to free-run deceleration. The braking means includes
The motor drive system according to any one of claims 1 to 5, comprising a transformer and a braking resistor connected to a secondary side of the transformer via a switch.   The motor drive system according to claim 6, wherein a resistor is connected in parallel with the switch.   The transformer is a tapped transformer, and when the output frequency of the inverter device is reduced, the tap of the tapped transformer is switched so that a secondary voltage increases. The electric motor drive system according to claim 6 or 7.   The resistance value of the braking resistor can be changed by switching, and when the output frequency of the inverter device is reduced, the braking resistor is switched so that the resistance value of the braking resistor decreases. The motor drive system according to claim 6, wherein the motor drive system is configured as described above.   A short-circuit switch for short-circuiting the primary side and the secondary side of the transformer is provided, and the short-circuit switch is closed when the output frequency of the inverter device is reduced. The electric motor drive system according to claim 6.   11. The electric motor drive system according to claim 8, wherein the timing for performing the switching or closing is when the output frequency of the inverter or the reduction rate thereof becomes a predetermined value or less.   The switch is a semiconductor switch, and when the voltage of the DC link portion of the inverter device exceeds a first predetermined value, the semiconductor switch is turned on, and the voltage of the DC link portion of the inverter device is a second predetermined value. 7. The electric motor drive system according to claim 6, wherein the semiconductor switch is turned off when it becomes less than the value.

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