JP2004056973A - Method and apparatus for driving ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a torque ripple is increased due to a distortion of an output current waveform without correcting an amount of output voltage deviation due to an ON-delay time or an ON voltage by an incorrect detection of an output current polarity, in an apparatus for driving an AC motor which outputs an arbitrary output by a pulse width modulation. <P>SOLUTION: A method for driving the AC motor for driving the motor by applying arbitrary AC current to the motor by complementarily turning on of off semiconductor switching elements connected in series with each other includes the steps of energizing predetermined offset currents to respective phases of the motor, setting a composite sum of current vectors of the offset currents of the respective phases to a zero, superposing and energizing the AC currents on the offset currents of the respective phases, fixing the superposed currents of the offset currents and the AC currents to a positive or negative current, and driving the motor. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a driving method and a driving apparatus for an AC motor that outputs an arbitrary voltage by controlling on / off of a semiconductor switching element connected in series by a pulse width modulation method.
[0002]
[Prior art]
FIG. 13 shows a schematic configuration diagram of a conventional driving device for an AC motor having a torque control function.
In FIG. 13, 1 is a rectifier for rectifying the AC voltage of the AC power supply 115 to output a DC voltage E, 2 is a smoothing capacitor for smoothing the rectified DC voltage E, and 76 to 81 are both terminals of the smoothing capacitor 2. IGBT transistors connected in series between the IGBT transistors; 82 to 87 are flywheel diodes connected in anti-parallel to the IGBT transistors; 34 is an encoder; 41 is a phase calculator for outputting a motor rotor phase 55; A current command generator 37 generates current commands 43, 44, 45 in accordance with the command 42 and the phase 55 of the rotor of the motor. A voltage command generator for generating 50, 51, 39 is a PWM generator for generating PWM signals 52, 53, 54, 38 is the PWM signal A gate signal generator for generating a gate signal to the IGBT transistor by 2,53,54.
FIG. 14 shows that an on-delay time td, which is a period during which both upper and lower IGBT transistors are turned off, is provided for the gate signal so that the IGBT transistors connected in series to the DC bus are simultaneously turned on and short-circuited. It is a thing. The IGBT transistor is driven by the gate signal to supply power to the motor 33 to drive the motor.
[0003]
In the conventional method, the current commands must be balanced in three phases, and the direction of the current command in each phase can be either positive or negative. When the DC voltage is E, the on-delay time is td, the on-time of the PWM signal before adding the on-delay time (on time of the upper IGBT transistor) is ton, and the switching cycle is T, the current flows to the motor side. And the respective drive unit output average voltages Vopav and Vonav when flowing from the motor side are as follows.
Vopav = (ton-td) / T × E. . . (1)
Vonav = (ton + td) / T × E. . . (2)
Even if ton, T, and E are the same, the driving device output average voltage fluctuates by (2 × td) / T × E according to the direction of the output current.
Therefore, in order to correct such a deviation of the output voltage, generally, the direction in which the current flows is detected by the current detector 40, and in the case where the current flows in the direction of the motor, the PWM is only turned on by the delay time td. On-time of the signal is increased, and when flowing from the motor side, conversely, the on-time of the PWM signal is reduced by the on-delay time td.
[0004]
[Problems to be solved by the invention]
However, in the conventional method, in the vicinity of the zero cross of the output current, the current polarity is erroneously detected due to the influence of the offset shift amount and the switching noise of the current detector, and the output voltage shifts, or the output voltage shifts during a short period of time called an on-delay section. It is difficult to detect the current polarity and correct it, for example, and thus there is a problem that the deviation of the output voltage cannot be corrected.
Further, the output voltage deviation due to the erroneous detection of the current polarity is caused not only in the on-delay section but also in other than the on-delay section.
For example, when the current flows out to the motor side, the output voltage becomes (saturated voltage of the E-IGBT transistor 76) while the upper IGBT transistor 76 is on, but when the current flows in from the motor side, the output voltage becomes The voltage becomes (E + forward voltage of the diode 82), and the polarity of the current is different, so that an output voltage shift (hereinafter, referred to as an ON voltage shift) corresponding to (saturation voltage of the IGBT transistor 76 + forward voltage of the diode 82) occurs. Will be. Although such an output voltage deviation is corrected by current polarity detection, output voltage distortion occurs due to the influence of the erroneous detection.
[0005]
As a result, near the zero cross of the output current, the output current has a distorted waveform as shown in FIG. If the current waveform is distorted, as shown in FIG. 16, an error occurs between the three-phase combined space vector of the drive device output current and the three-phase combined space vector of the current command, and torque ripple occurs. In particular, when the torque command is small, such as when the motor is operating at a constant speed, the current command is also small, and no current is output, and the ratio of distortion to the current command value is large, and the torque ripple is large.
Therefore, the present invention provides an AC motor driving device that outputs an arbitrary voltage by a pulse width modulation method, an ON delay time td and an ON voltage provided for preventing simultaneous ON operations of upper and lower IGBT transistors connected in series. The output voltage waveform distortion caused by the deviation can be eliminated, the command voltage can be matched with the actual output voltage without being affected by the magnitude of the output current, and the actual output current can be matched with the command current. An object of the present invention is to provide a drive device for an AC motor that can suppress torque ripple generated in the motor.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention according to claim 1 drives an AC motor that drives an AC motor by supplying an arbitrary AC current to the AC motor by complementarily turning on and off semiconductor switching elements connected in series. In the method,
An AC current command for each phase for driving the AC motor is determined, and a superimposed sum of the AC current command for each phase is fixed to either a positive current or a negative current, and a combined sum of the current vectors is set. The offset current command of each phase is determined by setting the current of each phase at which the current becomes zero as an offset current command, and the AC current command and the offset current command are superimposed for each phase, and the AC motor is superimposed on the superimposed current command. Are characterized by matching the respective phase currents.
Since the sum of the current vectors by the offset currents of the respective phases is zero, no motor torque is generated by the offset currents. Therefore, the motor torque is generated only by the AC current command among the superimposed current commands. Therefore, the motor torque has no difference from the case where only the AC current command is supplied.
In addition, since the direction of the superimposed current, in other words, the direction of the phase current is fixed in one direction for each, the polarity switching of the output current does not occur.
As a result, the deviation amount of the output voltage or the ON voltage during the on-delay section is known, so that the deviation amount can be easily corrected, and there is no possibility that a correction error due to erroneous detection of the current polarity occurs.
Therefore, no voltage distortion occurs due to the on-delay and the polarity reversal of the output current, and no distortion occurs in the output current, so that the three-phase combined space vector error of the output current does not fluctuate.
In addition, the semiconductor switching element means here includes a diode as described in claims 5 and 6, and is not limited to a transistor.
[0007]
According to a second aspect of the present invention, in the method for driving an AC motor according to the first aspect,
Increase or decrease the magnitude of the offset current command according to the magnitude of the AC current command,
The present invention is characterized in that the combined sum of the current vectors based on the offset current command of each phase during and after the increase / decrease of the offset current command is set to zero.
In the case of torque control, the amplitude of the AC current command increases according to the magnitude of the torque command. When a constant offset current command is added so that the polarity of the output current does not reverse even when the torque command is small or when the torque command is large, an excessive amount of offset current command is added when the torque command is small. . And the power loss increases as the current increases.
Therefore, if the offset current command is small, the offset current command is small, and if the AC current command is large, the offset current command is large, so that the power loss due to the offset current command can be suppressed.
[0008]
Further, in the present invention according to claim 3, an H-bridge circuit in which a DC power supply and two series-connected bodies in which parallel-connected bodies in which a freewheel diode is connected in reverse-parallel to a transistor are connected in series, and the H-bridge circuit are connected in parallel. Are connected in parallel between the positive and negative terminals of the DC power supply by the number of phases of the AC motor, a phase calculator that outputs a rotor phase value of the AC motor, and the rotor phase value as an input, to each phase of the AC motor. A current command generator that outputs an AC current command, and an output current detector that detects an output current to the AC motor,
A voltage command generator that receives an AC current command from the current command generator and a detection value from the current detector and outputs a voltage command, and a PWM that receives the voltage command and outputs a pulse width modulation signal A generator, and a drive device for an AC motor including the pulse width modulation signal as an input and a gate generator that outputs a gate signal to each of the switching elements,
A predetermined offset current command to each phase, wherein a sum of current vectors by the offset current command becomes zero, and a superimposed current of the offset current command and the AC current command is fixed to either positive or negative. The offset current command generator and the voltage command generator receive the AC current command, the offset current command, and the value detected by the current detector, and output a voltage command.
The present invention specifically represents the method invention according to claims 1 and 2 as an apparatus.
[0009]
According to a fourth aspect of the present invention, in the driving device for an AC motor according to the third aspect,
A current command adder that adds the AC current command and the offset current command to obtain an added current command, and outputs the added current command to the voltage command generator instead of the AC current command and the offset current command. It is characterized by:
[0010]
According to a fifth aspect of the present invention, in the driving device for an AC motor according to the third or fourth aspect,
Of the two series-connected bodies constituting the H-bridge circuit, one of the series-connected bodies is replaced with a first series-connected body connected in series with a transistor on the upper side and a diode in the opposite direction on the lower side, and the other series-connected body. The connection body is replaced by a second series connection body in which the transistor is on the lower side and the diode in the opposite direction is on the upper side, and the offset current command generator includes a superimposed current of the offset current command and the AC current command. Is fixed in a direction in which the current flows out of the connection point between the transistor and the diode in the first series connection body and flows into the connection point between the transistor and the diode in the second series connection body.
If the direction of the superimposed current flowing through each phase is fixed in one direction, the current does not flow through both upper and lower transistors connected in series, but flows through one transistor and the reverse diode connected in series to this transistor. Is used to fix the direction in which the current flows, and then remove the transistors and diodes through which no current flows, thereby realizing a compact and low-cost AC motor drive device.
[0011]
According to a sixth aspect of the present invention, in the driving device for an AC motor according to the fifth aspect,
A diode connected in anti-parallel to an upper-stage transistor of the first series-connected body constituting the H-bridge circuit; and a diode connected in anti-parallel to a lower-stage transistor of the second series-connected body. And
In order to prevent the transistor from being damaged by overvoltage when noise or surge voltage enters or occurs, a freewheel diode is connected to the transistor in anti-parallel for overvoltage protection.
Even in this case, only two transistors are required for the H-bridge circuit, so that the effect of reducing the size and cost of the AC motor driving device is provided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart showing an operation process according to the first embodiment of the present invention, and FIG. 2 is a circuit diagram showing the first embodiment of the present invention.
In FIG. 2, IGBT transistors 3 to 6, 11 to 14, 19 to 22 and flywheel diodes 7 to 10, 15 to 18, 23 to 26 anti-parallel to the IGBT transistors are connected in series to both ends of the smoothing capacitor 2. Thus, an arm is formed, and the terminals of the motor windings 30, 31, and 32 wound independently for each phase are connected to the output point of the arm. The output of the power section of the driving device is constituted by H bridges 27, 28 and 29 for each phase. The current command generator 35 generates three-phase balanced AC current commands 43, 44, and 45 according to the torque command 42 and the rotor phase 55 of the motor. The offset current command 56 is added from the offset current command generator 36 to the three-phase balanced AC current commands 43, 44, 45 to generate new current commands 106, 107, 108. The voltage command generator 37 generates three-phase voltage commands 49, 50 and 51 according to the deviation between the new current commands 106, 107 and 108 and the current detection signals 46, 47 and 48. The three-phase voltage commands 49, 50, and 51 are input to the PWM generator 39. The PWM generator 39 generates PWM signals 52, 53 and 54, and a gate signal is generated by the gate signal generator 38. A gate signal is input to the gate of each IGBT transistor, and each IGBT transistor performs an on / off operation according to the gate signal.
[0013]
If the offset current command 56 is set to be larger than the amplitude value of the current command output from the current command device 35, the new current commands 106, 107, 108 Will be fixed.
For this reason, the output voltage during the on-delay section and the deviation amount of the output voltage due to the on-voltage during the on-period section are known, and if this known deviation amount is corrected as it is, the current polarity is inverted with respect to the command voltage. No voltage distortion occurs, and no voltage distortion due to the ON voltage occurs. Therefore, an output voltage that matches the command voltage can be obtained, and the waveform of the actual current can be made without distortion.
Further, as shown in FIG. 3, the three-phase combined space vector of the offset current becomes zero, and thus the current commands 106 and 107 after superimposing the three-phase combined space vector 63 by the AC current commands 43, 44 and 45 and the offset current. , 108 coincide with the three-phase combined space vector 67. This is shown in FIG. 4 and FIG.
Since the three-phase combined space vectors match as described above, the motor output torques also match.
The invention of claim 1 is that the offset current command of each phase is fixed in step 4 of FIG. 1, and the offset current command is increased or decreased according to the magnitude of the torque command that changes every moment. It is an invention. Although not shown in FIG. 1, a microcomputer that outputs the torque command 42 controls the offset current command generator 36 to determine the offset current command value. It can be realized.
[0014]
Next, a second embodiment of the present invention is shown in FIG. The operation principle of FIG. 6 is the same as that of FIG. 2, except that an AC current command from a current command generator 35 and an offset current command from an offset current command generator 36 are added, and the added value is referred to as a voltage command generator. 37 is provided with a current command adder 120 for output.
[0015]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 7 shows the relationship between the torque command, the current command amplitude 68, and the offset current command 69.
In order not to cause distortion in the output current of the driving device, the polarity of the output current only needs to be inverted. That is, it is only necessary that the offset current command 69 to be added is larger than the current command amplitude 68. In the case of torque control, the amplitude 68 of the current command increases in proportion to the torque command. When the offset current command to be added is constant irrespective of the magnitude of the torque command and the current is not distorted when the torque command is large, when the torque command is small, the difference between the current command amplitude and the offset current command is large. Therefore, an unnecessary offset current is added. Since the power loss increases as the current increases, it is desirable that the offset current to be added be small.
Therefore, as shown in FIG. 7, in a range where the offset current command is larger than the current command, the offset current is reduced when the current command is small, and the offset current is reduced when the current command amplitude is large. Even if the current is increased, the current does not reverse, so that no current distortion occurs. FIGS. 8 and 9 show the current command after the offset current command is superimposed when the current command is small and large, respectively.
When the torque command is small, the offset current is small, so that there is an effect that power loss caused by adding the offset current can be suppressed.
[0016]
Next, FIG. 10 shows a fourth embodiment of the present invention. FIG. 10 shows an H bridge composed of two IGBT transistors and two diodes.
The IGBT transistors 3, 11, and 19 are arranged on the upper side and the IGBT transistors 6, 14, and 22 are arranged on the lower side. Diodes 8, 16, 24, 9, 17, and 25 are connected in series to the respective transistors in the reverse direction. I have.
As in the first embodiment, the output current to the motor is fixed in one direction by superposition with the offset current command, but the direction of the output current is fixed in the direction shown in FIG. This is different from the first embodiment irrespective of which direction it is fixed.
Since the IGBT transistors are not vertically connected in series, it is not necessary to provide an on-delay. For example, during the OFF command section of the IGBT transistor 3, the current flows in the direction shown in FIG. It is possible to obtain a predetermined output voltage only by controlling the ON time of the transistor 3.
Further, the output voltage becomes the DC voltage E only during the ON command section to the IGBT transistor 3, and it is obvious that the output current flows through the IGBT transistor 3 only during this section. And the deviation amount of the ON voltage is known, and it is possible to easily obtain an output voltage that matches the command voltage only by correcting the voltage difference between the command voltage and the output voltage according to the above.
[0017]
Next, FIG. 12 shows a fifth embodiment of the present invention. The fifth embodiment differs from the fourth embodiment in that diodes 7 and 10 are connected in anti-parallel to IGBT transistors 3 and 6, respectively.
The diodes 7 to 10 allow the overvoltage to escape by the route shown in FIG. 12 and protect the IGBT transistors 3 and 6 from damage due to the overvoltage even when the overvoltage enters the output terminal.
[0018]
【The invention's effect】
As described above, according to the present invention, in an AC motor driving device that outputs an arbitrary voltage by a pulse width modulation method, an ON-state provided to prevent simultaneous ON operation of both upper and lower IGBT transistors connected in series is provided. The output voltage waveform distortion caused by the delay time td and the deviation of the ON voltage can be eliminated, and the command voltage and the actual output voltage can be matched without being affected by the magnitude of the output current. And the torque ripple generated in the motor can be suppressed.
Further, there is an effect that an increase in power loss due to an offset current for improving torque ripple can be suppressed, and there is also an effect that the number of transistors to be used can be reduced and a drive device can be reduced in size and cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an operation process according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a first embodiment of the present invention.
FIG. 3 is a space vector diagram of an offset current command.
FIG. 4 is a current command space vector diagram before an offset current command is added.
FIG. 5 is a current command space vector diagram after an offset current command is added.
FIG. 6 shows a configuration of a second exemplary embodiment of the present invention.
FIG. 7 is a relationship diagram between a torque command, a current command amplitude, and an offset current command.
FIG. 8 shows a superimposed current command and a power converter output current when the torque command is small.
FIG. 9 shows a superimposed current command and a power converter current when the torque command is large.
FIG. 10 shows a configuration of a fourth exemplary embodiment of the present invention.
FIG. 11 is a diagram showing a current flow during an IGBT transistor off in a fourth embodiment of the present invention.
FIG. 12 shows a configuration of a fifth example of the present invention.
FIG. 13 is a diagram showing a conventional method.
FIG. 14 shows a gate signal and a power converter output voltage waveform.
FIG. 15 shows a current command and a power converter output current in a conventional system.
FIG. 16 is a space vector of a current command and a power converter output current in a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rectifier 2 Smoothing capacitor 3-6, 11-14, 19-22, 76-81 Switching element 7-10, 15-18, 23-26, 82-87 Flywheel diode 27, 28, 29 H bridge circuit 30, 31, 32 Motor winding 33 Motor 34 Encoder 35 Current command generator 36 Offset current command generator 37 Voltage command generator 38 Gate signal generator 39 PWM generator 40 Current detector 41 Phase calculator 42 Torque commands 43, 44, 45 Current commands 46, 47, 48 Power converter output currents 49, 50, 51 Voltage commands 52, 53, 54 PWM signal 55 Motor rotor phase 56 Offset current commands 57, 58, 59 Offset current command vectors 60, 61, 62 Current command vectors 63, 67 Three-phase combined space vectors 64, 65, 66 New current command vector 68 with offset current command added Current command amplitude 69 Offset current command 70, 73 U-phase current command and U-phase output current 71, 74 V-phase current command and V-phase output current 72, 75 W-phase current command And W-phase output current 88 Gate signal waveform 89 of switching element 77 Gate signal waveform 90 of switching element 76 Output voltage 91 when current flows into the motor 91 Power converter output voltage Vopav when current flows into the motor
92 Power converter output voltage when current flows out of motor 93 Power converter output voltage Vonav when current flows out of motor
94 ON delay time td
95 ON time ton before adding ON delay
96 ON time ton before adding ON delay
97 Switching period T
98, 99, 100 Current command space vector 101 Three-phase combined space vector 102, 103, 104 of current command Space vector 105 of power converter output current Three-phase combined space vector 106, 107, 108 of power converter output current Offset current New current command 109 with command added U-phase output current 110 V-phase output current 111 W-phase output current 115 Three-phase AC power supply 120 Offset current command adders 121 and 122 IGBT transistors 123 to 126 Diode

Claims (6)

A method for driving an AC motor that drives an AC motor by supplying an arbitrary AC current to the AC motor by complementarily turning on and off the semiconductor switching elements connected in series,
Determine the AC current command of each phase to drive the AC motor,
Each of the phases is a current for fixing a superimposed sum with the AC current command of each phase to either a positive current or a negative current, and the current of each phase in which the sum of the current vectors becomes zero is defined as an offset current command, Determine the phase offset current command,
For each phase, the AC current command and the offset current command are superimposed,
A method for driving an AC motor, wherein each phase current of the AC motor is matched with the superimposed current command. Increase or decrease the magnitude of the offset current command according to the magnitude of the AC current command,
2. The driving method of an AC motor according to claim 1, wherein the combined sum of the current vectors based on the offset current command of each phase during and after the increase / decrease of the offset current command is set to zero. DC power supply,
An H-bridge circuit in which two series-connected bodies in which parallel-connected bodies in which a freewheeling diode is connected in reverse-parallel to a transistor are connected in series;
The H bridge circuit is connected in parallel between the positive and negative terminals of the DC power supply by the number of phases of the AC motor,
A phase calculator for outputting a rotor phase value of the AC motor,
A current command generator that receives the rotor phase value as input, and outputs an AC current command to each phase of the AC motor,
An output current detector for detecting an output current to the AC motor;
A voltage command generator that receives an AC current command from the current command generator and a detection value from the current detector as inputs and outputs a voltage command,
A PWM generator that receives the voltage command as input and outputs a pulse width modulation signal;
A drive device for an AC motor including the pulse width modulation signal as an input and a gate generator for outputting a gate signal to each of the transistors,
An offset current command to each phase, wherein a sum of current vectors according to the offset current command becomes zero, and a superimposed current of the offset current command and the AC current command is fixed to either positive or negative. An offset current command generator that outputs an offset current command of
A drive device for an AC motor, wherein the voltage command generator receives the AC current command, the offset current command, and a value detected by the current detector and outputs a voltage command. A current command adder that adds the AC current command and the offset current command to generate an added current command, and outputs the added current command to the voltage command generator in place of the AC current command and the offset current command. 4. The driving device for an AC motor according to claim 3, wherein: In the drive device for the AC motor,
Of the two series-connected bodies constituting the H-bridge circuit, one of the series-connected bodies is replaced with a first series-connected body connected in series with a transistor on the upper side and an opposite diode on the lower side. Replacing the series-connected body with a second series-connected body connected in series with the transistor on the lower side and the reverse diode on the upper side,
The offset current command generator outputs a superimposed current of the offset current command and the AC current command from a connection point between a transistor and a diode in the first series connection, and outputs a superimposed current in the second series connection. 5. The driving device for an AC motor according to claim 3, wherein the driving device is fixed in a direction of flowing into a connection point between the transistor and the diode. In the drive device for the AC motor,
A diode connected in anti-parallel to an upper-stage transistor of the first series-connected body constituting the H-bridge circuit; and a diode connected in anti-parallel to a lower-stage transistor of the second series-connected body. The driving device for an AC motor according to claim 5, wherein

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