JP2007159235A - Ac motor driving inverter device and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC motor driving inverter device that can stably drive an AC motor in a wide speed range, and its operation method. <P>SOLUTION: The AC motor driving inverter device comprises: a frequency/speed commander 1 that imparts a rotational speed command of the AC motor 6; a V/f controller 4 that inputs therein a speed command outputted from the frequency/speed commander 1, and constantly V/f-controls it; a vector controller 7 that inputs the speed command therein and vector-controls it; and a control method switcher 11 that selects either of an output of the V/f controller 4 and an output of the vector controller 7, and inputs it to a power conversion circuit 5. Each of a switch level setting part 12 that sets a speed command setting value to be compared with the speed command for the actual operation of the motor 6, and a control method switcher 11 is switched to the vector controller 7 when the speed command is smaller than the speed command setting value as the result of the comparison of the speed command and the absolute value of the speed command setting value, and is switched to the V/f-controller 4 when the speed command is not smaller than the speed command setting value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter device for driving an AC motor and an operation method thereof.

  As a conventional method of driving an AC motor, there is a method of determining the output voltage of the inverter according to the output frequency of the inverter using the characteristic that the operation frequency of the motor and the terminal voltage are in a proportional relationship (hereinafter referred to as Prior Art 1). . In general, an inverter outputs an AC voltage having a frequency corresponding to the operation frequency of the target AC motor, and the AC motor rotates in accordance with a phase change of the output voltage (for example, Non-Patent Document 1). ) And the rotation speed and phase of the AC motor and the flow to the AC motor are detected, the magnetic flux phase in the AC motor is obtained from them, and the magnitude of the current that is perpendicular to the phase, that is, the torque component, is controlled. There is vector control to rotate (for example, Non-Patent Document 2: hereinafter referred to as Prior Art 2).

First, the prior art 1 will be described. FIG. 5 is a block diagram (prior art 1) showing a configuration of an inverter device that drives an AC motor by V / f control. In the figure, 1 is a frequency / speed command unit, 2 is a V / f calculator, 3 is a phase calculator, 4 is a V / f controller including the V / f calculator 2 and the phase calculator 3, and 5 is power. A conversion circuit 6 is an AC motor. Based on the command output from the frequency / speed command device 1, the V / f computing device 2 computes the voltage command Vref_vf, and the phase computing device 3 computes the output phase θ_vf of the voltage. The V / f controller 4 is configured by combining the configurations of the V / f calculator 2 and the phase calculator 3 into one. Since the voltage command and this principle are well-known techniques as described in Non-Patent Document 1, description thereof is omitted here. The power conversion circuit 5 supplies an AC voltage to the AC motor 6 based on the voltage command Vref_vf and the voltage output phase θ_vf.
Next, Prior Art 2 will be described. FIG. 6 is a block diagram (prior art 2) showing the configuration of an inverter device for driving an AC motor by vector control. In the figure, 1 is a frequency / speed command device, 5 is a power conversion circuit, 6 is an AC motor, 7 is a vector controller, 8 and 9 are current detectors, and 10 is a speed / phase detector.

  A frequency / speed command device 1 that gives the rotational speed of the AC motor 6, a power conversion circuit 5 that supplies a voltage to the AC motor 6, current detectors 8 and 9 that detect current flowing from the power conversion circuit 5 to the AC motor 6, and AC A speed / phase detector 10 that detects the rotation speed and rotor phase of the electric motor 6 and a vector controller 7 that gives a voltage command Vref_vect and an output voltage phase θ_vect to the power conversion circuit 5. The speed / phase detector 10 is not limited to the detector attached to the AC motor 6 shown in the figure, and estimates the speed / phase using the already known voltage command, current detection value, and AC motor electrical constant. A speed sensorless controller may be used. In the vector controller 7, the magnetic flux axis current command for controlling the magnetic flux of the AC motor and the rotational speed command of the motor given from the frequency / speed command device 1 coincide with the rotational speed of the AC motor detected by the speed / phase detector 10. The torque current component command is created so that the phase of the rotor of the AC motor is based on the current command, the current value detected by the current detector 8 and the current detector 9, and the data detected by the speed / phase detector 10. The voltage command Vref_vect and the output voltage phase θ_vect are calculated and output to the power conversion circuit 5 so that the detected current values of the components of the current command calculated based on The details of the calculation contents are well-known techniques as described in Non-Patent Document 2 and the like, and will not be described here.

Furthermore, as a combination of V / f control and vector control, when driving a synchronous motor without a speed sensor, a speed at which low speed regions where phase estimation is difficult can be operated by V / f control and phase estimation can be performed. In the fast region, there is a method shown in Patent Document 1 (hereinafter referred to as Conventional Technology 3) which is operated by vector control with good control characteristics.
Japanese Patent Laying-Open No. 2004-48886 (page 6-9, FIG. 5) The Institute of Electrical Engineers of the Institute of Electrical Engineers of Japan, Electrical Equipment Studies, 9th Edition, Ohmsha, p. 96 The Institute of Electrical Engineers of the Institute of Electrical Engineers of Japan, Electrical Equipment Studies, 9th Edition, Ohmsha, p. 98-99

In the method based on V / f control of the prior art 1, the control method is simple because the AC motor rotates following the frequency and magnitude of the voltage output from the inverter, but the change in the operating frequency and the load on the AC motor are simple. There is a problem that the responsiveness to the speed fluctuation due to the change of the rotation is poor and the rotational speed cannot be controlled precisely.
Further, in the vector control of the prior art 2, since the rotational speed and phase of the AC motor and the current flowing through the AC motor can be detected and the current of the torque component can be controlled, the response to the speed response is good and the rotational speed accuracy is also good. . However, it is necessary to calculate the detected data according to the phase of the AC motor and to match the output voltage with the phase of the AC motor. For this reason, if the rotation speed of the AC motor is increased, the amount of change in the phase per data sampling interval increases, so the calculation cycle must be increased, and the operating performance deteriorates at high rotation speeds due to restrictions on the performance of the calculator. There are challenges.
Further, the method described in the prior art 3 is to operate a region where vector control cannot be performed at low speed by V / f control, and the above-described vector control that occurs at a higher rotational speed than the rotational speed targeted in the patent document. There were still challenges.
Further, in a machine tool such as a machining center, the rotation speed of the electric motor is switched depending on the processing tool, and a tool that rotates at a low speed requires a higher rotation accuracy than a tool that rotates at a high speed. Conventionally, it is necessary to use within a speed range that can be used in one control method (mode) or to perform setting operation for switching the control method. Furthermore, if the control method is switched based on the actual speed change, the control method may suddenly change due to external factors such as speed fluctuation due to load change, etc., resulting in speed and torque fluctuation at the time of switching, stable operation I could not.

  The present invention has been made in view of such problems, and the user can stably drive the AC motor in a wide speed range without requiring specialized knowledge such as the principle of the control method. An object of the present invention is to provide an inverter device for driving an AC motor and an operation method thereof.

  In order to solve the above problem, the present invention is as follows.

  According to the first aspect of the present invention, a frequency / speed command device (1) for giving a rotational speed command for the AC motor (6), and a speed command output from the frequency / speed command device (1) are inputted, and V / f constant control is performed. A V / f controller (4) for performing the control, a vector controller (7) for performing the vector control by inputting the speed command, an output of the V / f controller (4), and an output of the vector controller (7) In the inverter apparatus for driving an AC motor provided with a control system switch (11) for selecting one of them and inputting it to the power conversion circuit (5), the inverter is compared with a speed command before the AC motor (6) is actually operated. The switching level setting unit (12) that sets the speed command set value and the control method switch (11) compare the absolute values of the speed command and the speed command set value, and the speed command is set to the speed command setting. If the value is smaller, Torr controller to (7), when the speed command is more than the speed command setting value is characterized in that switching to V / f control unit (4).

Further, in the inverter apparatus for driving an AC motor according to claim 1, when the speed command set value of the switching level setting section (12) is changed during operation of the AC motor (6), the speed after the change is changed. The control method switch (11) is switched using a command set value.

  Further, a frequency / speed command device (1) for giving a rotational speed command for the AC motor (6) and a speed command output from the frequency / speed command device (1) are input to perform V / f constant control. f controller (4), vector controller (7) for inputting the speed command to perform vector control, V / f controller (4) output and vector controller (7) output. In an operation method of an inverter apparatus for driving an AC motor provided with a control system switch (11) that is selected and inputted to a power conversion circuit (5), the speed to be compared with a speed command before the actual operation of the AC motor (6) The step of setting the command set value in the switching level setting unit (12) is compared with the absolute value of the speed command and the speed command set value. When the speed command is smaller than the speed command set value, the vector controller Go to (7) If serial speed command is above the speed command setting value is made of a step of switching the controller to the V / f control unit (4).

    Further, in claim 3, when the speed command set value of the switching level setting unit (12) is changed during operation of the AC motor (6), the changed speed command set value is compared with the speed command. It consists of steps to do.

According to the present invention, vector control is automatically performed in a speed range where high-performance vector control is possible by a frequency / speed command, and processing in an inverter that drives an AC motor by V / f control is automatically performed in a high-speed region where vector control is difficult. As a result, the user can stably drive the AC motor in a wide speed range without requiring specialized knowledge such as the principle of the control method.
In addition, since the switching is performed based on the frequency / speed command, the control method is not switched by an external factor such as a speed fluctuation due to a load change or the like, so that stable operation can be performed.
Further, when applied to a machine tool such as a machining center, a setting operation for switching the control method is unnecessary, and a stable operation can be performed.

  Hereinafter, specific examples of the method of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the present invention. In the figure, 1 is a frequency / speed command device, 4 is a V / f controller provided with a V / f calculator 2 and a phase calculator 3, 5 is a power conversion circuit, 6 is an AC motor, 7 is a vector controller, 8 And 9 is a current detector, 10 is a speed / phase detector, 11 is a control system switch, 12 is a switching level setting unit, and 13 is a control unit for controlling the entire inverter device. In the control method switch 11, the switches SW1 and SW2 are both connected to the a side in the case of the V / f control method. In the case of the vector control system, the control system switch 11 has both SW1 and SW2 connected to the b side. When switching from the vector control method to the V / f control method, both the switches SW1 and SW2 are simultaneously switched from the b side to the a side. The same reference numerals are assigned to the same names as those of the prior art, and duplicate descriptions are omitted.
The part in which the present invention is greatly different from the prior art is a part provided with a control system switching unit 11 and a switching level setting unit 12 for comparing with a speed command. That is, the voltage command Vref_vf that is the output of the V / f controller 4, the voltage command Vref_vect that is the output of the vector controller 7, the phase θ_vf of the output voltage that is the output of the V / f controller 4, and the output of the vector controller 7. Is a part provided with a control system switch 11 that switches the absolute value of the frequency / speed command value that is the output of the frequency / speed command device 1 to give to the power conversion circuit 5. When the operation frequency / speed command is set, it is determined whether or not the set value of the operation frequency / speed command value is equal to or greater than a predetermined value. If the operation frequency / speed command value is smaller than the predetermined value, the output Vref_vect and θ_vect of the vector controller 7 The switch of the control method switching unit 11 is switched so that the outputs Vref_vf and θ_vf of the V / f controller 4 are selected as the voltage command Vref and the output voltage phase θ input to the power conversion circuit 5. The control method switch 11 is not limited to a hard switch, and may be a soft switch. The set value of the switching level setting unit 12 can be set as a series of input set value parameters of the inverter.
FIG. 2 is a diagram showing conditions for switching between the two control methods of the present invention. The horizontal axis indicates the frequency / speed command, and the “absolute value” shown in the figure indicates the magnitude of the AC motor, regardless of the direction of rotation, since there are forward and reverse directions. It means that. When the frequency / speed command is 0, that is, when it is at a predetermined switching level from a stopped state, it is operated by vector control, and when it is above the predetermined switching level, it is operated by V / f control.
Since switching is determined by comparing the set value of the switching level with the magnitude (absolute value) of the frequency / speed command, the control method can be switched even if the speed of the AC motor changes during operation due to changes in load conditions, etc. Absent. This switching level is a value determined separately and set in advance, and the determination method is V / f control within a range in which vector control is possible according to current detection in an actual device and sampling / calculation cycle of each controller. Set to switch to.

When the setting of the operation frequency / speed command is changed during the operation of the AC motor, it is determined whether or not the set value of the operation frequency / speed command value is equal to or greater than a predetermined value, and if it is smaller than the predetermined value, the output of the vector controller 7 However, the switch of the control method switching unit 11 is switched so that the output of the V / f controller 4 is given to the power converter 5 if it is equal to or greater than a predetermined value.
FIG. 3 shows the processing method of the first embodiment of the present invention. First, before actually operating the motor, a switching level for switching operation from vector control to V / f control is set as an operation frequency / speed command value (STEP 101). In the inverter calculation process, it is determined whether or not the set value of the operating frequency / speed command value is greater than or equal to a predetermined value (STEP 102) .If the value is smaller than the predetermined value, the control method is set to vector control (STEP 103). If it is equal to or greater than the value, V / f control is performed (STEP 104). When the operation start command is received, the operation is started with the determined control method (STEP 105).

FIG. 4 shows the processing method of the second embodiment of the present invention. Set the operation frequency / speed command (STEP201) and give the operation start command. In the calculation process of the inverter, when the operation start command is received, the operation is started (STEP 202), and whether or not the set value of the operation frequency / speed command value set earlier is equal to or higher than a predetermined value (switching level for operation switching) is compared. If it is smaller than the predetermined value, vector control is selected as the control method (STEP 204). If it is greater than the predetermined value, V / f control is selected (STEP 205) and the operation is continued.
When the setting of the operation frequency / speed command is changed during operation (STEP206), when the inverter calculation process detects that the operation frequency / speed command value has been changed (STEP207), the processing returns to (STEP203) again. Control method switching determination and switching processing are performed.

  As described above, in areas where the current detection sampling time and control calculation cycle are fast with respect to the output voltage frequency, and the vector control is possible, the frequency of the output voltage is difficult to control by operating with high-performance vector control. In the region where the rotational speed is high, the operation to switch to V / f control is determined by the processing in the inverter according to the frequency / speed command. The AC motor can be driven in a wide speed range without requiring knowledge.

The block diagram which shows the structure of this invention The figure which shows the switching condition which is the principal part of this invention The flowchart which shows the process sequence of the Example of this invention. The flowchart which shows the process sequence of the Example of this invention. Block diagram showing configuration of conventional V / f control (conventional technology 1) Block diagram showing configuration of conventional vector control (prior art 2)

Explanation of symbols

1 Frequency / Speed Commander 2 V / f Calculator 3 Phase Calculator 4 V / f Controller 5 Power Conversion Circuit
6 AC Motor 7 Vector Controller 8 Current Detector 9 Current Detector 10 Speed / Phase Detector 11 Control Method Switcher 12 Switching Level Setting Unit 13 Control Unit

Claims (4)

A frequency / speed command device (1) for giving a rotational speed command for the AC motor (6), and a V / f control for inputting a speed command output from the frequency / speed command device (1) and performing V / f constant control. The controller (4), the vector controller (7) for inputting the speed command to perform vector control, the V / f controller (4) output and the vector controller (7) output are selected. In the inverter apparatus for driving an AC motor provided with a control system switching device (11) for inputting to the power conversion circuit (5),
A switching level setting unit (12) that sets a speed command setting value to be compared with a speed command before the actual operation of the AC motor (6);
The control method switching unit (11) compares the absolute values of the speed command and the speed command set value, and if the speed command is smaller than the speed command set value, the control method switch (11) sends the speed command to the vector controller (7). When the command is equal to or higher than the speed command set value, the inverter is switched to the V / f controller (4).   When the speed command setting value of the switching level setting unit (12) is changed during operation of the AC motor (6), the control method switching device (11) is changed using the speed command setting value after the change. 2. The inverter apparatus for driving an AC motor according to claim 1, wherein switching is performed. A frequency / speed command device (1) for giving a rotational speed command for the AC motor (6), and a V / f control for inputting a speed command output from the frequency / speed command device (1) and performing V / f constant control. The controller (4), the vector controller (7) for inputting the speed command to perform vector control, the V / f controller (4) output and the vector controller (7) output are selected. In the operation method of the inverter apparatus for driving an AC motor provided with the control method switching device (11) for inputting to the power conversion circuit (5),
Setting a speed command set value to be compared with a speed command before actual operation of the AC motor (6) in the switching level setting unit (12);
When the absolute value of the speed command and the speed command set value is compared, and the speed command is smaller than the speed command set value, the vector controller (7), and when the speed command is greater than or equal to the speed command set value Is a method for operating an inverter device for driving an AC motor comprising the step of switching the controller to a V / f controller (4).   When the speed command set value of the switching level setting unit (12) is changed while the AC motor (6) is in operation, the speed command set value after the change is compared with the speed command. The operation method of the inverter apparatus for driving an AC motor according to claim 3.

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