JP2008072832A - Controller for ac motor, and method of calculating superimposition current for suppression of iron loss - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for AC motor which can surely reduce iron loss by simple control mechanism. <P>SOLUTION: This controller is equipped with a superimposition current computer 9 which calculates superimposition currents id+ and iq+ for suppression of iron loss, based on the current detected values iu, iv, and iw of a three-phase motor 1, and a current controller 7 makes voltage commands vd* and vq* so that the current detected values id and iq of the three-phase motor 1 may follow the sum of current commands id* and iq*, and id+ and iq+, and sends them to a PWM generator 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an AC motor such as a synchronous motor, and more particularly to a technique for reducing the iron loss by a control means.

For example, Patent Document 1 discloses a motor control device that reduces distortion of a phase current flowing in a stator winding of an AC motor and reduces generation of torque ripple and electromagnetic noise.
The motor control device includes a voltage command value creating unit that creates a voltage command value to be applied to the motor based on the current command value and the current detection value, and a drive unit that applies a voltage to the motor based on the voltage command value. The voltage command value creating means has learning value creating means for creating a learning value used for correcting the voltage command value.

JP 2000-324879 A (refer to claim 1 and FIG. 1)

As described above, the motor control device of Patent Literature 1 suppresses torque ripple by correcting the voltage command value using the learning value.
By the way, the torque ripple is a quadratic function with respect to the current, and hence the magnetic flux, and is a time function (or a function of the rotor position) obtained by spatially integrating the torque received by each part of the motor around the gap part. However, the iron loss is the time average of one rotation of a value obtained by spatially integrating the hysteresis loss, which is a linear function of current, and hence magnetic flux, and the eddy current loss, which is a quadratic function of magnetic flux, with the motor core and magnet. Therefore, the effect on current differs between torque and iron loss.

As described above, the conventional motor control device requires a complicated control mechanism that corrects the voltage command value using the learning value, and the phenomenon of iron loss generation is more complicated than the phenomenon of torque ripple generation. Yes, applying it for the purpose of reducing iron loss makes the control mechanism more complicated and the effect cannot be expected.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an AC motor that can reliably reduce iron loss with a simple control mechanism.

Control of an AC motor provided with a power converter that converts a DC voltage into an AC voltage and supplies the AC motor, and a current controller that controls the power converter so that the detected current value of the AC motor follows the current command value A device,
In order to reduce the iron loss generated in the AC motor by superimposing it on the current command value, the current controller includes a superimposed current calculation means for calculating the iron loss suppression superimposed current based on the detected current value of the AC motor, The power converter is controlled so that the detected current value of the AC motor follows the sum of the current command value and the superimposed current from the superimposed current calculation means.

  The control apparatus for an AC motor according to the present invention is a conventional control mechanism that controls a power converter, and only superimposes the above-described iron loss suppression superimposed current on the current command value, thereby reducing the iron loss generated in the AC motor. It can be surely reduced.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a synchronous motor control apparatus according to Embodiment 1 of the present invention. In FIG. 1, a three-phase motor 1 that is a synchronous motor is connected to a PWM inverter 2 that is a power converter. The PWM inverter 2 generates electric power of variable voltage and variable frequency by a control signal generated by an amplifier 3 that is a control device, and sends it to the three-phase motor 1. The amplifier 3 receives the torque command value Te * 4 according to the load connected to the three-phase motor 1, and generates the current command values id * and iq * in the torque command device 5. The adders 12 and 13 add the iron loss suppression superimposed currents id + and iq + described later to the current command values id * and iq *, and send them to the current controller 7.

The three-phase motor currents iu, iv, iw detected by the current detector 11 are converted into actual currents id, iq by the dq converter 6 based on the rotor position θ and sent to the current controller 7.
For example, the PI controller controls the voltage command values vd * and vq * so that the actual currents id and iq follow the current obtained by adding the superimposed currents id + and iq + to the current command values id * and iq *. Create Based on the voltage command values vd * and vq *, the PWM generator 8 generates a gate drive signal and sends it to the PWM inverter 2.

  Here, the superimposed currents id + and iq + are extracted from the waveform data set in the superimposed current calculator 9 according to the load, that is, the motor currents iu, iv and iw, and converted into id + and iq + by the dq converter 10. To use.

FIG. 2 is a diagram showing the iron loss of the three-phase motor 1 under a certain operating condition, comparing the case of driving with a sine wave current and the case of driving with an inverter current. The vertical axis is normalized as 1 when driven by a sine wave current. The iron loss in the inverter drive is about 1.2 times the iron loss in the sine wave drive.
In the case of inverter driving, as shown in FIG. 3, the current waveform deviates from a sine wave and includes distortion components of low-order harmonics such as the fifth and seventh orders. A carrier component by PWM drive is also included. Of these, the distortion component mainly leads to an increase in hysteresis loss, and the carrier component mainly leads to eddy current loss. That is, the increase during the inverter driving in FIG. 2 is a hysteresis loss due to the fifth-order seventh-order component of the current waveform and an eddy current loss due to the carrier component.

FIG. 4 shows an example of the fifth, seventh and carrier components of the inverter current waveform. FIG. 5A is a bar graph display in which the fifth and seventh current amplitudes are integrated in order from the bottom. FIG. 4B shows the phases of the fifth and seventh currents in the same format.
FIG. 4C shows the current amplitudes of the orders fcn−2, fcn + 2, fcn × 2-1, and fcn × 2 + 1, where fcn is the carrier wave order of PWM (carrier wave frequency fcarr / fundamental frequency fo). The bar graph is displayed in the form of integration in order from the bottom. FIG. 4D shows the phase of the same order current in the same format.

It is thought that iron loss can be reduced by canceling these current components, and superposition current waveform data for iron loss suppression using superposition components of the same amplitude and opposite phase as the harmonic currents shown in FIG. The loss could be reduced to 1.05, which is almost the same as that in the sinusoidal current driving in FIG.
That is, the control apparatus for an AC motor according to the first embodiment of the present invention is a simple one in which the superimposed currents id + and iq + are added to the current command values id * and iq * created by the torque commander 5 of the amplifier 3. With the configuration, iron loss, particularly its harmonic components, can be greatly reduced.

Embodiment 2. FIG.
FIG. 5 is a diagram showing a synchronous motor control apparatus according to Embodiment 2 of the present invention. 1 is different from FIG. 1 of the first embodiment in that it includes a superimposed current calculator 9A for setting current waveform data for torque ripple suppression in addition to the superimposed current calculator 9 for setting current waveform data for suppressing iron loss. Furthermore, a mode selector 14 that selects either of them and outputs it to the dq converter 10 is provided.

  Here, the superposed currents id + and iq + are preliminarily stored in the amplifier 3 memory according to the mode selected by the mode selector 14 according to the user setting, that is, either the torque ripple suppression control priority mode or the iron loss suppression control priority mode. The waveform corresponding to the load, that is, the motor currents iu, iv, iw is extracted from the torque ripple suppressing superimposed current waveform data (9) or the iron loss suppressing superimposed current waveform data (9A) stored in the dq converter 10 is used after being converted into superimposed currents id + and iq +.

As described above, in the control apparatus for an AC motor according to Embodiment 2 of the present invention, both the torque ripple suppressing superimposed current waveform data and the iron loss suppressing superimposed current waveform data are stored in the memory in the amplifier 3; Since it is now possible to set which condition to prioritize torque ripple suppression or iron loss suppression, a synchronous motor drive system with performance according to the application can be used for products with a wide operating range such as servo motors. Realized with the same amplifier.
In other words, depending on the application, when the reduction of torque ripple is prioritized, the current waveform for torque ripple suppression is switched by user setting so that the current waveform for iron loss suppression is superimposed when priority is given to iron loss suppression. As a result, an AC motor control device having performance according to the application can be obtained.

  Further, generally, when the torque ripple is large, the servo performance is deteriorated, and in the low speed range where the torque ripple is large, the problem of hindering constant speed control and constant load control is often highlighted. On the other hand, in the high-speed range, the problem of iron loss, particularly eddy current loss becoming large and lowering efficiency is often highlighted. In such a case, a control apparatus for an AC motor having appropriate performance in a wide area can be obtained by performing a setting in which priority is given to torque ripple reduction in the low speed range and priority is given to iron loss suppression in the high speed range.

  In addition, operating conditions where torque ripple suppression and iron loss suppression superimposed current waveforms are almost the same are obtained from the suppression data in advance, and an operating range that provides two performances of low torque ripple and low iron loss is recommended. It is also possible to increase the product value by setting the operating conditions.

Embodiment 3 FIG.
Next, a method of creating the iron loss suppressing superimposed current waveform data (9) and the torque ripple suppressing superimposed current waveform data (9A) will be described as a third embodiment.
First, FIG. 6 is a diagram showing a creation flow of the superimposed current waveform data for iron loss suppression. In FIG. 6, after first determining the shape by motor design (S1), electromagnetic field analysis is performed with a sine wave current based on this shape. The no-load induced voltage and cogging torque are obtained by analysis at the time of external drive and no energization, and the rotor position dependency of the torque and inductance is obtained with respect to the load condition of the operation range, that is, the current condition, speed condition, and current phase condition (S2) . A motor model including these pieces of information is created, and the motor model is incorporated into a control (circuit) simulator having the same control loop as the actual PWM inverter (S3). Again, a control (circuit) simulation is performed under conditions within each operation range to obtain a current waveform (S4).

In the first embodiment, the current waveform is frequency-analyzed to obtain the in-phase and out-of-phase superimposed current for each component. However, even when the reduction of the harmonic iron loss is insufficient with this method, the following According to the method described in FIG. 6, it is possible to obtain a current waveform that can sufficiently reduce the iron loss by calculation.
That is, the iron loss is calculated again by electromagnetic field analysis using the obtained current waveform, and the harmonic iron loss portion A is obtained (S5). Next, a current waveform having a provisionally determined low-order harmonic component is superimposed on the current waveform, and an iron loss B is obtained by electromagnetic field analysis (S6). The condition for comparing the iron loss A and B is determined (S7), and until the harmonic iron loss B due to the superimposed waveform is sufficiently smaller than the original harmonic iron loss A and approaches 0, The superimposed current waveform is corrected (S8), and when the conditions in S7 are satisfied, the superimposed current waveform data is determined (S9).

  The motor characteristics used in S2 and S3 in FIG. 6 include the rotor position dependency of the induced voltage due to the magnet magnetic flux of the motor, and also include the rotor position dependency and current dependency of the inductance. The effect of saturation is also taken into consideration, and the characteristics are close to those of the actual machine. Furthermore, since the current waveform when the motor is rotated while feedback control is performed by an actual PWM inverter is calculated using this motor characteristic, the current waveform is almost the same as the actual measurement. In this way, since the iron loss is calculated using the same current waveform as the actual measurement, the iron loss value takes into account the effects of PWM control, magnetomotive force harmonics, and slot harmonics. A superimposed current waveform for loss suppression can be obtained.

Next, a method of creating torque ripple suppressing superimposed current waveform data will be described with reference to FIG.
Conventionally, when torque ripple suppression control is performed, the torque ripple at constant speed rotation using the current fundamental wave component, that is, the sine wave current, is used, or the torque ripple is generated by creating an actual machine. The measured data was used. However, since an actual motor is driven by an inverter and performs feedback control, torque ripple occurs in a state accompanied by speed fluctuation, and the torque ripple data obtained by electromagnetic field analysis cannot sufficiently suppress the effect.
In addition, a prototype is manufactured and the torque ripple and iron loss are measured in detail for each operating condition, and the database is used to perform torque ripple suppression control and maximum efficiency control. In this case, there is a problem that the measurement has to be carried out and the development cost and time are required.
Therefore, in order to improve the prediction accuracy by calculating the torque ripple, a calculation method based on the flow shown in FIG. 7 was used.
In FIG. 7, first, after determining the shape by motor design (S10), electromagnetic field analysis is performed with a sine wave current based on this shape. The no-load induced voltage and cogging torque are obtained by analysis at the time of external drive and no energization, and the rotor position dependency of the torque and inductance is obtained with respect to the load condition of the operation range, that is, the current condition, speed condition, and current phase condition (S11). . A motor model including these pieces of information is created, and the motor model is incorporated into a control (circuit) simulator having the same control loop as the actual PWM inverter (S12). Again, a control (circuit) simulation is performed under conditions within each operating range to obtain torque ripple (S13), and a superimposed current waveform for torque ripple suppression is calculated from torque ripple data.

  The motor characteristics used in S11 and S12 in FIG. 7 include the rotor position dependency of the induced voltage due to the magnet magnetic flux of the motor, and also include the rotor position dependency and current dependency of the inductance. The effect of saturation is also taken into consideration, and the characteristics are close to those of the actual machine. Furthermore, since the torque ripple when the motor is rotated with the actual control flow using this motor characteristic is calculated by the control (circuit) simulator, the control response by the feedback loop is reflected and the speed fluctuation is also reproduced. The torque ripple under the condition is calculated, and the phase information is also the same data as in actual operation.

As described above, in this third embodiment, torque ripple or iron loss equivalent to that of the actual machine is predicted by calculation without producing a prototype, and the superimposed current waveform for suppression is obtained from these, so that development cost and The effect that a period can be shortened is also acquired.
Furthermore, by using this flow when designing the motor, the torque ripple and iron loss can be reduced by devising the motor shape so that the operating range where the superimposed current waveforms for torque ripple suppression and iron loss suppression are almost the same is as wide as possible. It becomes possible to obtain a motor in which both can be reduced.

  In each of the embodiments described above, the case of controlling a synchronous motor has been described. However, the present invention can be widely applied to AC motors such as induction motors, and has the same effects.

  Moreover, in each modification of this invention, when a power converter is comprised with a PWM inverter, a superimposition current calculating means is a superposition current for iron loss suppression so that the harmonic component of the iron loss which generate | occur | produces in an AC motor may be reduced. Is calculated based on the harmonic component of the detected current value of the AC motor, so that the iron loss based on the harmonic generated due to the operation of the PWM inverter is effectively reduced.

  The superimposed current calculating means calculates the superimposed current for iron loss suppression and the superimposed current for torque ripple suppression so as to reduce the torque ripple generated in the AC motor by superimposing the current on the current command value. Depending on the output current, either the superposition current for iron loss suppression or the superposition current for torque ripple suppression is selected and output, and the current controller determines whether the current command value and the superposition current selected by the superposition current calculation means Since the power converter is controlled so that the current detection value of the AC motor follows the sum, even with an AC motor having a wide operating range, the same control device can provide optimum operating characteristics according to the characteristics of the AC motor. .

  Since the superimposed current calculation means selects and outputs the torque ripple suppressing superimposed current in the low speed region below the rated speed of the AC motor, and selects and outputs the iron loss suppressing superimposed current in the high speed region exceeding the rated speed. An AC motor control device having suitable performance in a wide area can be obtained.

A method of calculating a superposition current for suppressing iron loss in a superposition current calculation means of a control device for an AC motor,
The first step of determining the shape of the motor, and the rotor position dependency and torque of the induced voltage and the rotor position dependency and current dependency of the inductance are calculated by electromagnetic field analysis based on the shape determined in the first step A second step of performing a circuit simulation under the same control as that of an actual power converter using the characteristics of the motor calculated in the second step, and calculating a current waveform for each operating condition. The fourth step of calculating the harmonic component A of the iron loss by electromagnetic field analysis based on the current waveform calculated in the step of step 4, the harmonic current component tentatively defined in the current waveform calculated in the third step The fifth step of calculating the harmonic component B of the iron loss by electromagnetic field analysis based on the superimposed current waveform, and comparing the harmonic components A and B of the iron loss. Meet the condition to be small The fifth step is repeated by correcting the superimposed current waveform until the above condition is satisfied, and the sixth step of outputting the superimposed current waveform as the iron loss suppressing superimposed current when the above condition is satisfied is provided. Since the superposed current waveform for suppressing iron loss is obtained by calculation without manufacturing, the effect of shortening the development cost and period can be obtained.

It is a figure which shows the control apparatus of the alternating current motor in Embodiment 1 of this invention. It is a figure which shows the measurement result of the iron loss before applying Embodiment 1 of this invention. It is a figure which shows the current waveform before applying Embodiment 1 of this invention. It is a figure which shows the distortion component of the current waveform before applying Embodiment 1 of this invention. It is a figure which shows the control apparatus of the alternating current motor in Embodiment 2 of this invention. In Embodiment 3 of this invention, it is a figure which shows the preparation flow of the superimposed current waveform data for iron loss suppression. In Embodiment 3 of this invention, it is a figure which shows the creation flow of the superimposed current waveform data for torque ripple suppression.

Explanation of symbols

1 Three-phase motor, 2 PWM inverter, 3 amplifier, 5 torque command device,
7 current controller, 8 PWM generator, 9, 9A superimposed current calculator, 11 current detector,
12, 13 Adder, 14 mode selector.

Claims (5)

An AC motor comprising a power converter that converts a DC voltage into an AC voltage and supplies the AC motor, and a current controller that controls the power converter so that a current detection value of the AC motor follows a current command value. A control device of
Superimposing current calculating means for calculating a superimposing current for iron loss suppression based on a current detection value of the AC motor so as to reduce iron loss generated in the AC motor by being superimposed on the current command value, The controller controls the power converter so that the current detection value of the AC motor follows the sum of the current command value and the superimposed current from the superimposed current calculation means. apparatus. When the power converter is composed of a PWM inverter, the superimposition current calculation means converts the iron loss suppression superimposition current of the AC motor so as to reduce a harmonic component of iron loss generated in the AC motor. 2. The AC motor control apparatus according to claim 1, wherein the calculation is performed based on a harmonic component of the current detection value. The superimposed current calculating means calculates the iron loss suppressing superimposed current and the torque ripple suppressing superimposed current so as to reduce the torque ripple generated in the AC motor by being superimposed on the current command value, According to the operating condition of the AC motor, either the iron loss suppressing superimposed current or the torque ripple suppressing superimposed current is selected and output, and the current controller calculates the current command value and the superimposed current calculation. The control apparatus for an AC motor according to claim 2, wherein the power converter is controlled so that a current detection value of the AC motor follows a sum of the superimposed current selected by the means. The superimposed current calculation means selects and outputs the torque ripple suppressing superimposed current in a low speed range below the rated speed of the AC motor, and selects the iron loss suppressing superimposed current in a high speed range exceeding the rated speed. 4. The control apparatus for an AC motor according to claim 3, wherein A calculation method of the iron loss suppressing superimposed current in the superimposed current calculation means of the control device for an AC electric motor according to any one of claims 2 to 4,
The first step of determining the shape of the motor, and the rotor position dependency and torque of the induced voltage and the rotor position dependency and current dependency of the inductance are calculated by electromagnetic field analysis based on the shape determined in the first step A second step of performing a circuit simulation under the same control as that of an actual power converter using the characteristics of the motor calculated in the second step, and calculating a current waveform for each operating condition. A fourth step of calculating the harmonic component A of the iron loss by electromagnetic field analysis based on the current waveform calculated in the step, and a harmonic current component provisionally defined in the current waveform calculated in the third step. The fifth step of calculating the harmonic component B of the iron loss by electromagnetic field analysis based on the current waveform superimposed with the above, the harmonic components A and B of the iron loss are compared, and compared with A, the B The condition to be small enough A sixth step of correcting the superimposed current waveform until it is completed, repeating the fifth step, and outputting the superimposed current waveform as the iron loss suppressing superimposed current when the condition is satisfied. A method for calculating a superimposed current for suppressing iron loss, which is characterized by the above.

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