WO2013171866A1 - Ac motor control device and on voltage correction method - Google Patents

Description

AC motor control device and ON voltage correction method

The present invention relates to an AC motor control device that variably drives an AC motor and an ON voltage correction method.

The AC motor control device includes a control unit that generates a voltage command of arbitrary amplitude and frequency for variably driving the AC motor, and a power converter that supplies drive power to the AC motor according to the voltage command generated by the control unit. However, the voltage command generated by the control unit and the power converter are supplied to the AC motor by the voltage (hereinafter referred to as “ON voltage”) generated by the current flowing through the power device element that is a component of the power converter. An error occurs in the actual output voltage. This error is called an ON voltage error. The control unit of the AC motor control device has an ON voltage correction function for correcting this ON voltage error by software processing.

This ON voltage correction function is realized by a process for determining the magnitude of the ON voltage correction voltage (hereinafter referred to as “ON voltage correction amount”) and a process for determining the polarity of the ON voltage correction voltage. Since the ON voltage correction amount depends on the absolute value of the flowing current, the processing for obtaining the ON voltage correction amount is described in the data sheet of the power device element using the output current value captured by the current detector. The current-voltage characteristics are reproduced and created inside the software. In addition, since the polarity of the ON voltage correction voltage matches the polarity of the output current, in the process for obtaining the polarity of the ON voltage correction voltage, a process for making the same as the polarity of the output current captured by the current detector is performed.

By the way, when the polarity of the ON voltage correction voltage is erroneously detected, the voltage error due to the ON voltage is amplified and the control performance deteriorates. Improving the accuracy of determining the polarity switching timing is one of the important issues.

This is because the absolute value of the output current is small in the vicinity of the current zero cross where the polarity of the output current switches, so the influence of the current detection error by the current detector and the ripple component of the output current due to switching of the power converter It is a problem caused by receiving. Polarity detection in the vicinity of the zero crossing of the output current is performed not only in ON voltage correction but also in dead time compensation, and various proposals have conventionally been made regarding polarity detection methods (eg, Patent Documents 1 and 2). ).

That is, in Patent Document 1, the polarity switching timing determination of the ON voltage correction voltage is performed using the AC current commands iu *, iv *, and iw * instead of the output current, and the AC current command is smaller than the reference current iδ. An example (hereinafter referred to as “first example”) is disclosed in which erroneous detection in the vicinity of the output current zero cross is prevented by setting the compensation voltage to zero.

In Patent Document 2, the voltage correction amount is created as a constant value in a range where the magnitude of the current command is larger than a certain threshold value Id, and is created as an amount proportional to the current command in a range smaller than the certain threshold value Id. Thus, an example (hereinafter referred to as “second example”) for preventing erroneous polarity detection near the output current zero cross in the dead time compensation is disclosed.

Further, when the output current falls below a certain threshold value ΔI, the phase Δθ until polarity switching is estimated from the threshold value ΔI and the output current effective value by calculation, and the correction is made when the output phase advances by the estimated phase Δθ. An example (hereinafter referred to as “third example”) is known in which the polarity of the voltage is switched to prevent erroneous detection in the vicinity of the output current zero cross.

JP-A-6-62580 JP-A-9-84385

However, since the correction amount depends on the absolute value of the output current, the correction voltage polarity switching method shown in the first example in which the correction voltage is zero when the current command is smaller than the reference current iδ is ideal. Correction cannot be performed.

In the ON voltage correction, the magnitude of the ON voltage correction voltage is not an amount proportional to the output current. Therefore, when the current command is smaller than a certain threshold value Id, the ON voltage correction voltage is an amount proportional to the current command. In the polarity switching method of the ON voltage correction voltage shown in the second example, ideal correction cannot be performed.

In short, in the ON voltage correction, since the ideal magnitude of the ON voltage correction voltage can be obtained from the data sheet, the method of reducing the influence of the erroneous polarity detection by changing the magnitude of the ON voltage correction voltage, It is not an optimal solution. Therefore, in order to improve the ON voltage correction accuracy, it is necessary to obtain an ideal current polarity switching timing. In this regard, the third example is notable.

However, in the third example, since the calculation of the phase Δθ until the polarity is switched is performed on the assumption that the output current is a sine wave, the AC motor has a characteristic that the output current captured by the current detection circuit does not become a sine wave. When applied to the above, there is a problem that the calculation error of the phase Δθ becomes large.

The present invention has been made in view of the above, and it is an object of the present invention to obtain an AC motor control device and an ON voltage correction method capable of improving the determination accuracy of the polarity switching timing of the correction voltage used in the ON voltage correction realized by software processing. Objective.

In order to solve the above-described problems and achieve the object, the present invention provides a control unit that generates a voltage command of arbitrary amplitude and frequency for variably driving an AC motor, and the AC command according to the voltage command generated by the control unit. In an AC motor control device including a power converter that supplies driving power to an electric motor, the control unit corrects an error between a voltage command applied to the power converter and an actual output voltage of the power converter. As a configuration for performing correction, calculation is performed based on the effective value of the current command on two orthogonal axes rotating the phase Δθ from the threshold value set for the envelope of the three-phase current command to the zero cross point of the envelope and the threshold value. A first means for determining a time point when an output voltage phase advances by the phase Δθ after the three-phase current command generated by performing coordinate conversion from the current command on two orthogonal axes enters the threshold value; 2 Means, wherein said second means comprises a third means for switching the polarity of the correction voltage used in the ON voltage correction at the time of the determination.

According to the present invention, focusing on the point that each envelope of the three-phase current command is sinusoidal, a threshold is set for each envelope to give a calculation start point of phase Δθ until polarity switching, Since the calculation of Δθ is performed using the threshold value and the effective value of the rotating orthogonal two-axis current command, the calculation error of the phase Δθ can be extremely reduced, and the polarity of the correction voltage used in the ON voltage correction can be changed. There is an effect that the determination accuracy of the switching timing can be improved.

FIG. 1 is a block diagram showing a configuration of an ON voltage correction voltage creating unit provided in a control unit of an AC motor control apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining the processing procedure of the polarity determiner shown in FIG. FIG. 3 is a diagram for explaining the relationship between the envelope of the correction target phase current command processed in the procedure shown in FIG. 2 and the correction voltage polarity determined.

Hereinafter, embodiments of an AC motor control device and an ON voltage correction method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a block diagram showing a configuration of an ON voltage correction voltage creating unit provided in a control unit of an AC motor control apparatus according to an embodiment of the present invention. In FIG. 1, the ON voltage correction voltage generator included in the controller of the AC motor control apparatus according to this embodiment includes a two-phase → three-phase coordinate converter 1, a current effective value calculator 2, and a Δθ calculator 3. , Polarity determination unit 4, correction amount calculation means 5, and multipliers 6a, 6b, 6c.

The ON voltage correction voltage generating unit includes a threshold ΔI, an output voltage phase θout, and two rotating orthogonal axes (d) from a control unit that generates and outputs a voltage command of arbitrary amplitude and frequency to the power converter (not shown). D-axis current command Id * and q-axis current command Iq * which are current commands on the (axis and q-axis) are input. Here, the threshold value ΔI is not a threshold value for the three-phase output current taken in by the current detection circuit, but is converted from two-phase to three-phase coordinate conversion from the current commands Id * and Iq * on the rotating orthogonal two axes. This is a threshold value commonly defined for the envelopes of the phase current commands Iu *, Iv *, and Iw *.

The two-phase → three-phase coordinate converter 1 is configured to convert the two-phase → three-phase coordinates based on the output voltage phase θout input from the control unit to the d-axis current command Id * and the q-axis current command Iq * input from the control unit. By applying the conversion, three-phase current commands Iu *, Iv *, and Iw * are converted and generated.

The current command effective value calculation unit 2 applies the d-axis current command Id * and the q-axis current command Iq * input from the control unit to the equation (1), and generates current commands Id * and Iq * on two orthogonal axes. Current command effective value Irms * is obtained.

The Δθ calculation unit 3 applies the threshold value ΔI defined in the envelope of the three-phase current command input from the control unit and the current command effective value Irms * input from the current command effective value calculation unit 2 to the equation (2). Then, the phase Δθ from the threshold value ΔI to the zero cross point of the envelope of the three-phase current command is obtained. In order to obtain the phase Δθ from sin (Δθ), it is necessary to perform sin ⁻¹ calculation. However, from the viewpoint of increasing the calculation efficiency, the expression (2) is obtained when the phase Δθ is sufficiently small with respect to the AC cycle. Assuming that the phase Δθ is approximated by sin (Δθ). Needless to say, there is no problem even if Δθ is calculated by sin ⁻¹ calculation as theoretically.

The polarity determination unit 4 includes the threshold value ΔI and the output voltage phase θout input from the control unit, the three-phase current commands Iu *, Iv *, Iw * converted by the two-phase → three-phase coordinate converter 1, and Δθ. From the phase Δθ from the threshold value ΔI obtained by the calculation unit 3 to the zero cross point of the envelope of the three-phase current command, the correction voltage polarities SGNu, SGNv, SGNw for three phases are obtained by the procedure shown in FIG. Ask for. These polarities are “+1” for positive and “−1” for negative.

The correction amount calculation means 5 calculates the three-phase ON voltage correction amounts | Vcu |, | Vcv |, | Vcw | from the current-voltage characteristics described in the data sheet of the power device element.

The multipliers 6a, 6b, and 6c are three-phase correction voltage polarities SGNu, SGNv, and SGNw obtained from the polarity determiner 4, and a three-phase ON voltage correction amount | Vcu | The phases corresponding to | Vcv | and | Vcw | are multiplied to generate final three-phase ON voltage correction voltages Vcu, Vcv, and Vcw, which are output to a control unit (not shown). A control unit (not shown) performs ON voltage correction by adding the obtained ON voltage correction voltage for each phase to a three-phase voltage command and outputting the voltage command to a power converter (not shown).

Next, the operation of the polarity determiner 4 will be specifically described with reference to FIG. FIG. 2 is a flowchart for explaining the processing procedure of the polarity determiner shown in FIG. The polarity judgment unit 4 performs the processing shown in FIG. 2 for each of the three-phase current commands Iu *, Iv *, and Iw * input from the two-phase → three-phase coordinate converter 1 at every control calculation cycle by software processing. For each phase. In FIG. 2, the correction target phase among the three phases is represented by x. That is, x = u, v, w. In FIG. 2, the step indicating the processing procedure is abbreviated as ST.

In FIG. 2, in ST1, in response to the start of the control calculation cycle, first, the absolute value | Ix * | of the current command Ix * of the correction target phase x and the envelope of the current command Ix * are determined. The threshold value ΔI (see FIG. 3) is compared to determine whether the current command Ix * is equal to the threshold value ΔI or whether the current command Ix * is inside or outside the threshold value ΔI.

In ST1, when the current command Ix * is not equal to the threshold value ΔI and is outside the threshold value ΔI (ST1: Yes), the processing of ST2 to ST4 is performed to end this procedure, and the arrival of the next control calculation cycle. Monitor. In ST2, the sign SGNx of the ON voltage correction voltage is replaced with a function sign (Ix *) that represents the sign of the current command Ix *. The function sign (Ix *) shown in ST2 is a function that returns +1 if the current command Ix * is positive and returns -1 if the current command Ix * is negative. In ST3 and ST4, the initial flag and the polarity switching flag used for processing when the current command Ix * is within the threshold value ΔI are set to OFF.

On the other hand, when the current command Ix * is within the threshold value ΔI in ST1 (ST1: No), the output voltage phase θout is changed from the threshold value ΔI to the envelope of the current command Ix * to be corrected by the processing of ST5 to ST15. A process for determining the polarity of the ON voltage correction voltage is executed depending on whether or not the phase Δθ has advanced to the point.

First, the phase advance amount θl after the current command Ix * enters the threshold value ΔI is calculated by the processing of ST5 to ST9. That is, in order to know whether or not the current command Ix * is within the threshold value ΔI for the first time this time, it is determined whether or not the initial flag is OFF (ST5). If the initial flag is OFF (ST5: Yes) Then, the output voltage phase (initial phase θout_1st) at that time is stored as the output voltage phase θout (ST6), the initial flag is set to ON (ST7), and the process proceeds to ST9.

On the other hand, when the initial flag is set to ON in ST5 (ST5: No), the output voltage phase at this time (current phase θout_1st) is stored as the output voltage phase θout (ST8), and the process of ST9 is performed. Do.

In ST9, the phase advance amount θl from the first time when the current command Ix * enters the threshold value ΔI for the first time is obtained by Expression (3). In Equation (3), θout is the current output voltage phase, and θout_1st is the output voltage phase (that is, the stored output phase) of the number of times that has entered the threshold ΔI.
θl = θout−θout — 1st (3)

Next, it is determined whether or not the output voltage phase θout has advanced by a phase Δθ indicating that the envelope of the current command Ix * has reached the zero cross point by the processing of ST10 to ST14, and the output voltage phase θout has advanced by a phase Δθ. Switches the polarity of the correction voltage.

That is, in ST10, the phase advance amount θl and the phase Δθ are compared, and it is determined whether or not the phase advance amount θl and the phase Δθ are equal or whether the phase advance amount θl is larger than the phase Δθ.

In ST10, if θl <Δθ (ST10: No), since the output voltage phase θut has not yet advanced the phase Δθ indicating the arrival of the zero cross point of the envelope of the current command Ix *, the process proceeds to ST11 and the correction voltage polarity SGNx is set. This procedure is terminated with the same correction voltage polarity SGNx as the previous time, and the arrival of the next control calculation cycle is monitored.

On the other hand, in ST10, if θl ≧ Δθ (ST10: Yes), the process proceeds to ST12 and it is determined whether or not the polarity switching flag is ON. Here, the polarity switching flag is a flag used to determine whether or not the output voltage phase θout has already advanced a phase Δθ indicating the arrival of the zero cross point of the envelope of the current command Ix *.

Therefore, if the polarity switching flag is OFF (ST12: No), it is determined that it is the polarity switching timing, and the calculation of “SGNx = −1 * previous SGNx” is performed to obtain the correction voltage polarity SGNx from the previous correction voltage polarity SGNx. Invert (ST13), set the polarity switching flag to ON (ST14), end this procedure, and monitor the arrival of the next control calculation cycle.

On the other hand, when the polarity switching flag is set to ON in ST12 (ST12: Yes), since the polarity has been switched, the correction voltage polarity SGNx is made the same as the previous correction voltage polarity SGNx (ST15), and this procedure is performed. And the arrival of the next control calculation cycle is monitored. The polarity switching flag is turned off in ST4 when the determination in ST1 is affirmative (Yes).

Next, FIG. 3 is a diagram for explaining the relationship between the envelope of the correction target phase current command processed in the procedure shown in FIG. 2 and the correction voltage polarity determined. In FIG. 3, a threshold value “+ ΔI” is set on the positive electrode side and a threshold value “−ΔI” is set on the negative electrode side with respect to the envelope 7 of the current command Ix * of the correction target x phase with reference to the zero cross point. . Then, the phase Δθ from the point where the envelope 7 descends from the top dead center and crosses the threshold value “+ ΔI” to the zero cross point on the way to the zero cross point is obtained by the Δθ computing unit 3 and output to the polarity determiner 4. Are held together with a threshold value ΔI. The correction voltage polarity SNGx is “+1” for the positive polarity and “−1” for the negative polarity. FIG. 3 shows how the correction voltage polarity SNGx is switched at the zero cross point when the envelope 7 changes from the positive electrode side to the negative electrode side.

Since the current command Ix * is within the threshold “+ ΔI” in the section 10 on the positive polarity side of the envelope 7, the process of ST 15 shown in FIG. 2 is performed. In section 11, since current command Ix * is outside the threshold “+ ΔI”, the processing of ST1 (Yes) to ST4 shown in FIG. 2 is performed. In the section 12, since the current command Ix * falls within the threshold “+ ΔI”, the processing of ST10 (No) to ST11 shown in FIG. 2 is performed. At the zero cross point 13 where the envelope 7 switches from the positive polarity side to the negative polarity side, the processing of ST10 (Yes) to ST12 (No) to ST13 to ST14 shown in FIG. 2 is performed.

Since the current command Ix * is within the threshold “−ΔI” in the section 14 on the negative polarity side of the envelope 7, the process of ST 15 shown in FIG. 2 is performed. In the section 15, since the current command Ix * is outside the threshold “−ΔI”, the processing of ST1 (Yes) to ST4 shown in FIG. 2 is performed. In the section 16, since the current command Ix * falls within the threshold “−ΔI”, the processing of ST10 (No) to ST11 shown in FIG. 2 is performed.

Thus, according to this embodiment, paying attention to the point that each envelope of the three-phase current command (Iu *, Iv *, Iw *) becomes a sine wave, the polarity is switched to each envelope. The threshold value “± ΔI” that gives the calculation start point of the phase Δθ until is set, and the effective value of the orthogonal biaxial current command (Id *, Iq *) that rotates with the threshold value “± ΔI” The calculation error of the phase Δθ can be made extremely small, and the determination accuracy of the timing for switching the polarity of the ON voltage correction voltage can be improved.

Therefore, in the example shown in FIG. 3, when the current command Ix * of the correction target phase becomes the threshold value “+ ΔI”, when the output phase θout of the current command Ix * advances by the phase Δθ, that is, at the zero cross point. The correction voltage polarity SGNx can be switched.

As described above, the AC motor control apparatus and the ON voltage correction method according to the present invention can improve the determination accuracy of the polarity switching timing of the correction voltage used in the ON voltage correction realized by software processing. This is useful as a correction method.

DESCRIPTION OF SYMBOLS 1 Two-phase-> three-phase coordinate converter 2 Current command effective value calculating unit 3 Δθ calculating unit 4 Polarity determining unit 5 Correction amount calculating means 6a, 6b, 6c Multiplier 7

Claims (2)

In an AC motor control device comprising: a control unit that generates a voltage command of arbitrary amplitude and frequency for variably driving an AC motor; and a power converter that supplies driving power to the AC motor according to the voltage command generated by the control unit. ,
The controller is
As a configuration for performing ON voltage correction for correcting an error between a voltage command given to the power converter and an actual output voltage of the power converter,
A first means for calculating based on the effective value of the current command on two orthogonal axes rotating the phase Δθ from the threshold value determined for the envelope of the three-phase current command to the zero cross point of the envelope and the threshold value;
A second means for determining when the output voltage phase has advanced by the phase Δθ after the three-phase current command generated by performing coordinate conversion from the current command on the two orthogonal axes enters the threshold;
An AC motor control device comprising: third means for switching the polarity of the correction voltage used in the ON voltage correction at the time point determined by the second means. In an AC motor control device comprising: a control unit that generates a voltage command of arbitrary amplitude and frequency for variably driving an AC motor; and a power converter that supplies driving power to the AC motor according to the voltage command generated by the control unit. ,
An ON voltage correction method for correcting an error between a voltage command given to the power converter and an actual output voltage of the power converter, which is performed by the control unit,
A first step of calculating based on the effective value of the current command on the two orthogonal axes rotating the phase Δθ from the threshold value set for the envelope of the three-phase current command to the zero cross point of the envelope and the threshold value;
A second step of determining when the output voltage phase has advanced by the phase Δθ after the three-phase current command generated by performing coordinate conversion from the current command on the two orthogonal axes enters the threshold;
And a third step of switching the polarity of the correction voltage used in the ON voltage correction at the time point determined in the second step. An ON voltage correction method in an AC motor control device, comprising:

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