JP2012010513A - Motor driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize iron loss of a motor with no use of complicated control mechanism and calculation circuit at the time when driving the motor by supplying an AC power to the motor by PWM control.SOLUTION: The carrier frequency within such range as corresponds to the iron loss between a minimum value and 1.04 times the value (1.02 times is preferred), in the relationship between iron loss of a motor M and carrier frequency, is taken as a carrier frequency of triangular wave generated by a triangular wave generating part 72. Based on a PWM signal S which corresponds to the result of comparison between a voltage command signal and triangular wave of the carrier frequency, the operation of an inverter 50 (IGBT) that supplies AC power to the motor M is controlled.

Description

  The present invention relates to a motor drive device, and is particularly suitable for driving a motor with AC power generated by performing PWM (Pulse Width Modulation) control.

  As a power supply device for driving a motor of a train, a hybrid vehicle, a home appliance, etc., an inverter of a PWM control system that can easily control the speed is used. Such an inverter determines the width of a pulse signal (time for turning on a pulse) by comparing a carrier signal (for example, a triangular wave) and a voltage command signal, and according to the generated pulse signal, a switching element (for example, an IGBT (Insulated Gate)). By turning on / off the Bipolar Transistor)), the input DC power is converted to AC power having a frequency necessary for motor speed control and supplied to the motor. Here, the frequency of the carrier signal is called the carrier frequency, and the generated pulse signal is called the PWM signal.

In an electric device equipped with a motor, the motor consumes most of the total electric power, and increasing the efficiency of the motor is an important issue.
Therefore, Patent Document 1 prepares table data in which the relationship between the carrier frequency that minimizes the total loss of the motor and the PWM control inverter and the electrical angular frequency of the motor (frequency of the current that excites the motor) is set, A technique for driving an inverter by operating an inverter at a carrier frequency corresponding to a detected value of an electrical angular frequency of the motor is disclosed.
Also, iron loss (loss generated in the motor core), which is one of the main losses in the motor, consumes electric power as heat, which causes the motor temperature to rise and the efficiency to decrease. It is important to reduce iron loss. Therefore, in Patent Document 2, the voltage loss command is calculated so that the iron loss suppression superimposed current is calculated based on the motor current value, and the motor current value follows the sum of the current command value and the iron loss suppression superimposed current. A technique for generating a signal and sending it to a PWM generator is disclosed.
In Patent Document 3, the iron loss and the copper loss of the motor are calculated, respectively, and the d-axis current and the amplitude of the output voltage with respect to the armature winding are set so that the sum of the iron loss and the copper loss is minimized. A technique for controlling the phase is disclosed.

JP 2007-282298 A JP 2008-72832 A JP 2008-236948 A

However, in the technique described in Patent Document 1, the loss of the motor becomes constant as the carrier frequency increases, but this knowledge is not accurate as will be described later. Therefore, Patent Document 1 does not have a clear basis for obtaining a carrier frequency that minimizes motor loss. In the technique described in Patent Document 1, it is necessary to change the carrier frequency depending on the electrical angular frequency of the motor.
Further, the technique described in Patent Document 2 requires a control mechanism that superimposes the iron loss suppressing superimposed current on the current command value. In Patent Document 2, it is necessary to preliminarily determine the superimposed current waveform for suppressing iron loss by electromagnetic field analysis. This determination is performed by repeatedly performing electromagnetic field analysis while correcting the superimposed current waveform for suppressing iron loss. Since it is executed, there is a risk that a great deal of time and labor may be required.
The technique described in Patent Document 3 requires an arithmetic circuit for calculating the iron loss, copper loss, and the like of the motor.
As described above, the conventional technique has a problem that a complicated control mechanism and arithmetic circuit are required when the motor is driven with less loss by performing AC control and supplying AC power to the motor.
The present invention has been made in view of such problems, and uses complex control mechanisms and arithmetic circuits when driving a motor by performing PWM control to generate AC power and supplying it to the motor. It aims at minimizing the iron loss of the motor without.

  The motor drive device of the present invention is a motor drive device that drives a motor by a PWM (Pulse Width Modulation) control method, and the relationship between the iron loss of the motor and the carrier frequency of the PWM control is 1 from the minimum value. A carrier frequency within a range corresponding to iron loss up to .04 times is used.

  According to the present invention, the carrier frequency within the range corresponding to the iron loss from the minimum value to 1.04 times the minimum is used as the carrier frequency for PWM control in the relationship between the iron loss of the motor and the carrier frequency for PWM control. Therefore, the iron loss of the motor can be minimized without using a complicated control mechanism or arithmetic circuit.

It is a figure which shows embodiment of this invention and shows an example of schematic structure of a motor drive device. It is a figure which shows embodiment of this invention and shows an example of the relationship between the iron loss ratio of a motor, and a carrier frequency. It is a figure which shows embodiment of this invention and shows the value of each point of the graph shown in FIG. 2 in a table format.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a schematic configuration of a motor driving device.
In the present embodiment, the motor M is an IPM (Interior Permanent Magnet) motor (three-phase synchronous motor) in which a permanent magnet is built in a rotor.

  In FIG. 1, a motor driving apparatus for driving such a motor M includes an AC power source 10, a rectifier circuit 20, an electrolytic capacitor 30, a voltage sensor 40, an inverter 50, current sensors 61 to 63, And a control device 70.

The AC power supply 10 supplies AC power having a commercial frequency (50 Hz / 60 Hz).
The rectifier circuit 20 is a full-wave rectifier circuit composed of, for example, four diodes, and converts AC power into DC power.
The electrolytic capacitor 30 removes the pulsating flow of the DC power output from the rectifier circuit 20.

The voltage sensor 40 measures a DC input voltage Vi input to the inverter 50.
The inverter 50 is, for example, a circuit including six IGBTs constituting a three-phase full bridge. The inverter 50 drives the motor M (for example, speed control) with the input DC power by turning on / off an IGBT which is an example of a switching element based on the PWM signal S output from the control device 70. Is converted into AC power having a frequency necessary for the motor M and output to the motor M.
The current sensors 61 to 63 are, for example, CT (Current Transformer), and measure AC motor currents Iu, Iv, and Iw flowing through the windings of the phases u, v, and w of the motor M, for example.

The control device 70 includes an applied voltage calculation unit 71, a triangular wave generation unit 72, a comparison unit 73, and a PWM signal output unit 74. The control device 70 can be realized by using, for example, a microcomputer or an arithmetic circuit.
The applied voltage calculation unit 71 outputs an externally output speed (number of rotations of the motor M) command value, an input voltage Vi measured by the voltage sensor 40, and motor currents Iu and Iv measured by the current sensors 61 to 63. , Iw are input, and based on these, the voltage applied to each phase of the motor M is calculated, and a voltage command signal indicating the voltage is generated.
The triangular wave generator 72 generates a triangular wave that is an example of a carrier signal in PWM control. At this time, the triangular wave generation unit 72 generates a triangular wave having a carrier frequency set in advance for the triangular wave generation unit 72. The carrier frequency determination method according to this embodiment will be described later.
The comparison unit 73 compares the voltage command signal generated by the applied voltage calculation unit 71 with the triangular wave (carrier signal) generated by the triangular wave generation unit 72.
The PWM signal output unit 74 outputs a pulse signal corresponding to the comparison result in the comparison unit 73 to the inverter 50 as the PWM signal S. As described above, the inverter 50 turns on / off the IGBT based on the PWM signal S, converts the input DC power into AC power, and outputs the AC power to the motor M.

Here, a method for determining a carrier frequency according to the present embodiment will be described. The inventors of the present application investigated the influence of the carrier frequency on the iron loss of the motor M. The specifications of the motor M used here are as follows.
Number of phases: 3
Number of poles: 12
Stator outer diameter: 135mm
Stator inner diameter: 87mm
Number of stator slots: 18 (concentrated winding)
Stator material: Non-oriented electrical steel sheet rotor outer diameter: 85 mm
Rotor thickness: 30mm
Magnetic flux of permanent magnet; 1.1T

The excitation frequency of the motor M (frequency of current for exciting the motor) is 400 Hz (torque; 0.5 N · m (constant)), 800 Hz (torque; 0.5 N · m (constant)), 1000 Hz (torque; 0.1 N · m (constant)), and in each case, the iron loss ratio at each carrier frequency when the iron loss of the motor M when the carrier frequency was 5 kHz was set to 1 was obtained.
FIG. 2 is a diagram illustrating an example of the relationship between the iron loss ratio of the motor M and the carrier frequency. FIG. 3 is a table showing the values of the points in the graph shown in FIG. 2 and 3, the iron loss ratio [−] at the carrier frequency f is expressed by the following equation (1).
Iron loss ratio = (iron loss of motor M when carrier frequency is f) / (iron loss of motor M when carrier frequency is 5 kHz) (1)

As shown in FIG. 2, the inventors of the present application have a graph showing the relationship between the iron loss ratio of the motor M and the carrier frequency when the iron loss ratio of the motor M is the vertical axis and the carrier frequency is the horizontal axis. It has been found for the first time that the peak has a convex peak and one minimum value is obtained for the iron loss ratio (ie, iron loss).
Increasing the carrier frequency concentrates the magnetic flux on the surface of the electrical steel sheet due to the skin effect, increases the effective resistance and reduces the eddy current loss generated in the iron core of the motor M. Therefore, the iron of the motor M increases as the carrier frequency increases. The loss is expected to decrease. On the other hand, if the carrier frequency is further increased, the magnetic flux density excited in the iron core of the motor M shifts to the high frequency side, so that the iron loss due to the magnetic flux density corresponding to this high frequency increases. It is considered that the iron loss of the motor M increases as the value increases.

  From the above, it is most desirable to adopt the carrier frequency corresponding to the minimum value of the iron loss as the carrier frequency of the triangular wave generated by the triangular wave generator 72 in relation to the iron loss of the motor M and the carrier frequency. Become. Here, “7.2.2 Iron loss measurement” of “JIS C 2556” states that the reproducibility of the test apparatus is about 2% standard deviation for non-oriented electrical steel sheets. ing. Taking this standard deviation into account, it can be considered that up to 1.02 times the minimum value is equivalent to the minimum value of iron loss. Therefore, the carrier frequency within the range corresponding to the iron loss from the minimum value to 1.02 times that of the iron loss of the motor M and the carrier frequency is adopted as the carrier frequency of the triangular wave generated by the triangular wave generator 72. It can be said that it is desirable.

  Furthermore, the relationship between the iron loss of the motor M and the carrier frequency, the range of the carrier frequency corresponding to the iron loss from the minimum value to 1.02 times thereof is obtained for each of the plurality of excitation frequencies of the motor M. Of the ranges, it is more desirable to employ the carrier frequency within the overlapping range as the carrier frequency of the triangular wave generated by the triangular wave generator 72. This is because if the carrier frequency is in such a range, the iron loss is minimized (can be regarded as the minimum) regardless of the excitation frequency of the motor M. In addition, since the carrier frequency that minimizes the iron loss is employed regardless of the excitation frequency, even in the motor M having a different number of poles, the effect that the iron loss is minimized can be obtained. Here, the plurality of excitation frequencies of the motor M are, for example, a predetermined plurality of excitation frequencies within the range of the specification of the motor M (for example, a plurality of excitation frequencies including an upper limit and a lower limit of the specification). The number of excitation frequencies to be selected is arbitrary, but by selecting as many excitation frequencies as possible within the specification range, it is possible to accurately determine the carrier frequency range in which the iron loss is minimized (considered to be the minimum). It becomes possible.

  The specification of the excitation frequency of the motor M in the present embodiment is a lower limit of 400 Hz and an upper limit of 1000 Hz. In the example shown in FIG. 2, three excitation frequencies of 400, 800, and 1000 Hz that are within the specification range are iron with respect to the carrier frequency. The loss ratio results are shown. The range of the carrier frequency corresponding to the iron loss ratio from the minimum value of the iron loss ratio to 1.02 times is the range filled in gray in FIG. The range is 7 kHz or more and 10 kHz or less. Since the range from the minimum value of the iron loss ratio to 1.02 times thereof coincides with the range from the minimum value of the iron loss to 1.02 times thereof, in the example shown in FIG. 2, the carrier frequency is 7 kHz or more and 10 kHz or less. Is preferably set in the triangular wave generator 72.

Assuming that the distribution of a plurality of data of iron loss of the motor M at a certain carrier frequency is a normal distribution, 95.44% of the data is in the range of ± 2σ (σ: standard deviation) of their average values. Will be included. Therefore, in practice, the data within this range is regarded as normal, and is 4% which is twice the standard deviation of 2% shown in “7.2.2 Iron loss measurement” of “JIS C 2556”, that is, the minimum It can be said that up to 1.04 times the value may be regarded as equivalent to the minimum value of iron loss. Therefore, the carrier frequency within the range corresponding to the iron loss from the minimum value to 1.04 times that of the iron loss of the motor M and the carrier frequency is adopted as the carrier frequency of the triangular wave generated by the triangular wave generator 72. May be.
Further, in the relationship between the iron loss of the motor M and the carrier frequency, the range of the carrier frequency corresponding to the iron loss from the minimum value to 1.04 times is set to each of a plurality of excitation frequencies within the range of the specification of the motor M. Of these ranges, the carrier frequency within the overlapping range may be adopted as the carrier frequency of the triangular wave generated by the triangular wave generator 72.

In the example shown in FIG. 2, the range of the carrier frequency corresponding to the iron loss ratio (iron loss) from the minimum value to 1.04 times that is the region filled with gray in FIG. The range of the carrier frequency that overlaps with the frequency is 7 kHz or more and 15 kHz or less. Therefore, in the example shown in FIG. 2, a carrier frequency of 7 kHz or more and 15 kHz or less may be set in the triangular wave generator 72.
In the example shown in FIG. 3, the values of the measurement points are used as the carrier frequency at which the iron loss ratio (iron loss) is minimized and the upper and lower limits of the carrier frequency range. For this reason, 7.0 kHz is adopted as the lower limit of the carrier frequency, and 15 kHz (preferably 10 kHz) is adopted as the upper limit of the carrier frequency. However, this is not always necessary. For example, the value of the iron loss ratio at the carrier frequency between two measurement points on the graph shown in FIG. 2 is obtained by linear interpolation, and the value of the carrier frequency at that point is obtained. May be employed as the upper and lower limits of the carrier frequency range. In addition, from the measurement point of the iron loss ratio and the carrier frequency, a fitting curve (approximation function) that has one peak protruding downward when the iron loss ratio of the motor M is the vertical axis and the carrier frequency is the horizontal axis is obtained. The value of this fitting curve may be used to obtain the carrier frequency that minimizes the iron loss ratio (iron loss) and the upper and lower limits of the carrier frequency range.

  The above carrier frequency range can also be applied to an AC motor driven by a PWM control type inverter other than the present embodiment. That is, a sawtooth wave instead of a triangular wave may be used as a PWM control type carrier signal. Further, as an AC motor, for example, an induction motor and a synchronous motor (including a brushless DC motor having the same structure) can be applied. Furthermore, the present invention can also be applied to cases where soft magnetic materials other than non-oriented electrical steel sheets (such as dust cores and amorphous materials) are used as the stator material. In the first approximation, each frequency component included in the current generated by the inverter determines each frequency component of the magnetic flux density excited in the iron core of the motor. Is the integrated value of iron loss corresponding to the magnetic flux density of each frequency component, and therefore the carrier frequency at which the iron loss is minimized exists in the same way regardless of the type of carrier signal, AC motor model, and iron core material. (In other words, the iron loss in a motor having such a drive system and structure is excited in the iron core regardless of the type of the carrier signal of the inverter, the shape and number of poles, and the material of the motor iron core. This is because the minimum value of iron loss similarly exists because it is caused by the magnetic flux density).

  As described above, in the present embodiment, the carrier frequency within a range corresponding to the iron loss from the minimum value to 1.04 times (preferably 1.02 times) in relation to the iron loss of the motor M and the carrier frequency. Is the carrier frequency of the triangular wave generated by the triangular wave generating unit 72, and the inverter 50 (supplies AC power to the motor M based on the PWM signal S according to the comparison result between the triangular wave of this carrier frequency and the voltage command signal. The operation of IGBT) was controlled. Therefore, the iron loss of the motor M can be minimized without using a complicated control mechanism or arithmetic circuit. As a result, the output of the motor M can be made highly efficient, and an equivalent output can be achieved with a smaller input power, so that the capacity of the power source for driving the motor M can be reduced.

  In the present embodiment, the range of the carrier frequency corresponding to the iron loss from the minimum value to 1.04 times (preferably 1.02 times) in the relationship between the iron loss of the motor M and the carrier frequency is set to the motor M. Each of the plurality of excitation frequencies is determined, and among those ranges, the carrier frequency within the overlapping range is adopted as the carrier frequency of the triangular wave generated by the triangular wave generating unit 72. Therefore, even if the excitation frequency of the motor M changes, the iron loss of the motor M can be minimized (if the excitation frequency is within the range of the plurality of excitation frequencies).

  It should be noted that the embodiments of the present invention described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 10 AC power supply 20 Rectification circuit 30 Electrolytic capacitor 40 Voltage sensor 50 Inverter 61-63 Current sensor 70 Control apparatus 71 Applied voltage calculating part 72 Triangular wave generation part 73 Comparison part 74 PWM signal output part

Claims (2)

A motor driving device that drives a motor by a PWM (Pulse Width Modulation) control method,
A motor driving device using a carrier frequency in a range corresponding to an iron loss from a minimum value to 1.04 times the relationship between the iron loss of the motor and the carrier frequency of the PWM control.   The relationship between the iron loss of the motor and the carrier frequency, the carrier frequency range corresponding to the iron loss from the minimum value to 1.04 times, each of a plurality of excitation frequencies within the range of the specification of the motor 2. The motor drive device according to claim 1, wherein a carrier frequency within an overlapping range is used in a range of carrier frequencies obtained for.

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