JP2012110074A - Current detection device and motor control device - Google Patents

Abstract

Provided is a current detection device capable of reducing a detection error included in a detection current when detecting an output current of a PWM inverter.
A current detection device for detecting an output current of a multiphase inverter using triangular wave pulse width modulation, comprising: a current detection means for detecting a current at a plurality of specific timings during a predetermined period; Adding means 113u and 113w for adding current detection values at a plurality of specific timings during a certain period, and the current detection means is a carrier wave of triangular wave PWM as a plurality of specific timings during the certain period. The current detection is performed at least once each on both the downstream side and the downstream side.
[Selection] Figure 2

Description

  Embodiments relate to a current detection device and a motor control device using the current detection device.

  Conventionally, in a PWM (Pulse Width Modulation) inverter power converter, when detecting an output current of a PWM inverter, current detection is performed a plurality of times in order to reduce signal noise included in the detected current, and the added value is calculated. The detection value method is adopted.

  However, the conventional technique has a problem that a current ripple generated by pulse width modulation (PWM) is picked up and a detection error occurs in the current detection value. Here, the “detection error” represents a deviation of the detected value with respect to the actual current vector, and when the added value is used as the detected value, the average value of the current vector and the average of the added value in the cycle of addition. It is defined as deviation.

  In addition, a multi-phase inverter usually has only one A / D converter due to cost problems, and cannot detect a plurality of phase currents at the same time, and the current detection timing is different for each phase. Yes. If the current detection timing is changed for each phase, there is a problem that, when converted to a current vector, a detection error that differs depending on the position of the vector occurs in the detected current.

Japanese Patent No. 3312472

  The present invention has been made in view of such a problem of the prior art, and an object thereof is to provide a current detection device capable of reducing a detection error included in a detection current and a motor control device using the current detection device.

  The embodiment is a current detection device that detects an output current of a multiphase inverter using triangular wave pulse width modulation, and a current detection unit that detects current at a plurality of specific timings during a predetermined period of time, Adding means for adding current detection values at a plurality of specific timings during the predetermined period, wherein the current detection unit is configured to increase the carrier wave of the triangular wave PWM as the plurality of specific timings during the predetermined period. It is characterized in that current detection is performed at least once on both the side and the downstream side.

1 is a block diagram of a motor control device according to a first embodiment. The block diagram of the electric current detection process part in the motor control apparatus of 1st Embodiment. Explanatory drawing of the relationship between the voltage command vector and PWM output vector in a 3-axis fixed coordinate system. The wave form diagram of the current ripple by an orthogonal voltage component. The vector diagram of the orthogonal voltage component for every voltage command vector. Explanatory drawing of the electric current detection timing in 1st Embodiment. Explanatory drawing of the electric current detection timing in 2nd Embodiment. Explanatory drawing of the electric current detection timing in 3rd Embodiment. Explanatory drawing of the electric current detection timing in 4th Embodiment. Explanatory drawing of the electric current detection timing in 5th Embodiment. Explanatory drawing of the electric current detection timing in 6th Embodiment. Explanatory drawing of the electric current detection timing in 7th Embodiment. Explanatory drawing of the relationship example 1 of the U-phase voltage and U-phase current in triangular wave PWM. Explanatory drawing of the example 2 of a relationship between the U-phase voltage and U-phase current in triangular wave PWM. Explanatory drawing of the electric current detection timing in 8th Embodiment. Explanatory drawing of the electric current detection timing in 9th Embodiment. The wave form diagram of the detection current when the detection delay occurs in the three-phase current. The amplitude diagram of the detection current when the detection delay in the three-phase current occurs. Explanatory drawing of the relationship between the several electric current detection value in the short time, and its average value. Explanatory drawing of the electric current detection timing in 10th Embodiment. Explanatory drawing of the electric current detection timing in 11th Embodiment. The block diagram of the inverter control apparatus of 12th Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a motor control device that uses a synchronous motor 04 common to each embodiment as a load and performs control by sensorless control. This motor control device converts a DC power into an AC power by a PWM gate signal, and also reverses the PWM inverter 02, a synchronous motor 04 that operates by receiving an AC output of the PWM inverter 02, and a PWM inverter 02. Current detectors 03u, 03w for detecting AC currents iu, iw of U, W2 phase among AC currents iu, iv, iw of U, V, W phases of AC power supplied to the motor 04, and PWM inverter 02 In order to perform the gate control, the AC currents iu and iw detected by the current detectors 03u and 03w are A / D converted at predetermined timing, taken as digital current detection values Iu and Iw, and calculated to be voltage commands for each phase. A control device 05 that outputs Vu, Vv, and Vw, and voltage commands Vu, Vv, and Vw of each phase that are output from the control device 05 are expressed by a triangular wave carrier wave. Create a gate command by PWM, and is configured to PWM inverter 02 at the triangular wave PWM modulator 01 to the gate control.

  The synchronous motor 04 generates a magnetic field by three-phase alternating currents iu, iv, iw flowing in the respective excitation phases of the stator, and generates a torque by a magnetic interaction with the rotor.

  The control device 05 is constituted by a microcomputer, but its calculation function is shown by being divided into components, and each of the rotational phase estimators 07, the current controller 08, the 3-axis / 2-axis coordinate converter 09, A 2-axis / 3-axis coordinate converter 10 and a digital current detection processor 11 are included.

  The current detectors 03u and 03w output the current response values of the two phases iu and iw of the three-phase alternating current flowing through the synchronous motor 04 as analog signals. In addition, although the structure which detects the electric current of 2 phases is shown in FIG. 1, the structure which detects the electric current response value of each of U, V, and W3 phase may be sufficient.

  The digital current detection processor 11 inputs the current detection analog signals of the current detectors 03u and 03w at predetermined timings, performs A / D conversion, and adds a predetermined number of times for each phase to detect digital current for each phase. The value is output to the 3-axis / 2-axis coordinate converter 09.

  The rotational phase angle estimator 07 estimates the rotational phase angle θest of the synchronous motor 04 from the current response value converted by the 3-axis / 2-axis coordinate converter 09.

  The 3-axis / 2-axis coordinate converter 09 uses the rotational phase angle θest obtained by the rotational phase angle estimator 07 for the current response values Iu, Iw output from the digital current detection processor 11 to provide a three-phase signal. Three-axis / 2-axis coordinate transformation between the fixed coordinate system and the γδ-axis rotation coordinate system is performed to obtain the two-axis current values Iγres, Iδres from the three-phase current values Iu, Iv, Iw, and the rotational phase angle estimator 07 and the current controller Output to 08. The V-phase current value Iv is obtained by conversion from the detected U-phase and W-phase current values Iu and Iw.

  The current controller 08 compares the 2-axis current response values Iγres, Iδres converted by the 3-axis / 2-axis coordinate converter 09 with the current command values Iγref, Iδref, and determines the biaxial voltage command values Vγ, Vδ.

  The 2-axis / 3-axis coordinate converter 10 converts the 2-axis voltage command values Vγ, Vδ from the current controller 08 into 2-axis / 3-axis coordinates, and converts the 3-phase voltage commands Vu, Vv, Vw into a triangular wave PWM modulator 01. Output to. As described above, the triangular wave PWM modulator 01 generates a gate command by PWMing the three-phase voltage commands Vu, Vv, and Vw with a triangular wave carrier wave, and controls the PWM inverter 02.

  The digital current detection processor 11 has the functional configuration shown in FIG. 2, and includes a multi-input / output channel for A / D converting the analog input signals iu and iw at predetermined timings and outputting them as digital values. A / D converter 111, timing setter 112 for setting the conversion processing timing for this A / D converter 111, digital current detection value output from each output channel of A / D converter 111 is added a predetermined number of times, and current average It consists of adders 113u and 113w that output as values Iu and Iw. The timing setter 112 gives a timing setting channel command to the A / D converter 111 at the current detection timing of each embodiment described later.

  The operation of the motor control device having the above configuration will be described. When a detection error is included in the currents Iu, Iv, and Iw detected by the current detector, vibration is generated at the rotational phase angle θest estimated by the rotational phase angle estimator 07 according to the detection error. For example, when the rotational phase angle estimator disclosed in Japanese Patent No. 312472 is used, a single-phase alternating voltage is applied to the command, and the rotational phase angle is estimated using the current of the orthogonal component. Therefore, the detection current error in the orthogonal direction generated by the inverter becomes the rotation phase angle estimation error as it is.

  Therefore, in the present embodiment, the current detection method is performed as follows to reduce the detection current error generated in the orthogonal direction, improve the estimation accuracy of the rotational phase angle, and realize stable control.

  The triangular wave PWM inverter 02 synthesizes two types of zero vectors and two types of voltage vectors, thereby modulating the voltage vector synthesis during the half cycle of the triangular wave carrier to coincide with the voltage command vector. For example, in the 3-axis fixed coordinate system of U, V, and W phases, the voltage command vector is an error in Fig. 3! The reference source cannot be found. In the position of (U, V, W) = (0, 0, 0), (U, V, W) = (1, 1, 1) and two types of zero vectors (U, V , W) = (1, 0, 0) and (U, V, W) = (1, 1, 0) are combined to output a voltage vector that matches the voltage command vector. At this time, a voltage component Vh orthogonal to the direction of the voltage vector to be output is also output. The orthogonal voltage vector Vh becomes zero if synthesized during a half cycle of the carrier wave (Carrier), but this orthogonal voltage vector generates a current ripple Ih as shown in FIG.

  As shown in FIG. 5, this orthogonal voltage vector vibrates for one cycle every time the voltage command vector rotates by 1/6 period, that is, a current ripple having a frequency six times the carrier frequency is generated.

  Here, from FIG. 4, the current ripple Ih is point-symmetric about the vertex of the carrier wave (Carrier), and the sign is different between the upstream side and the downstream side of the carrier wave. (Actually, the waveform is close to point symmetry although it is not perfectly point symmetric due to the influence of inductance and voltage command vector change.) In FIG. 4, it is point symmetric at the peak on the peak side of the carrier wave. However, point symmetry is similarly applied to the peak on the trough side of the carrier wave. Further, even if the direction and the magnitude of the voltage command vector are different, this tendency is not changed only by switching between the positive and negative of the upstream side and the downstream side or changing the magnitude of the current ripple.

  FIG. 6 shows the current detection timing executed by the control device 05 in the first embodiment. The digital current detection processor 11 performs A / D conversion on the analog current detection signals iu and iw from the current detectors 03u and 03w for each cycle of the carrier wave as one current detection period, and at least on the upstream side. At least once, current detection is performed on the downstream side, the detected values are added, and the added values are output as digital current response values Iu and Iw. Thereby, a positive error and a negative error are added, and the detection error included in the detection current can be reduced.

  In the first embodiment shown in FIG. 6, current detection is performed at a predetermined timing once on the upstream side and twice on the downstream side for each cycle of the carrier wave. If current detection is performed at predetermined timing at least once on the downstream side, detection errors included in the detection value can be reduced.

  Further, since the detection error is always zero with respect to the vertex of the carrier wave, the detection value at the vertex timing may be added as shown in FIG. Second embodiment).

  Further, as shown in FIG. 8, two periods of the carrier wave are set as current detection period units, and current detection is performed at a predetermined timing at least once each on the upstream side and the downstream side of the carrier wave for each current detection period. The added value may be a current response value (third embodiment).

  Further, even when the detection values of less than one cycle of the carrier wave are added as shown in FIG. 9, the current detection may be performed at least once on the upstream side and the downstream side of the carrier wave (fourth embodiment). ). Since the average value of the current ripple Ih is the same on the upstream side and the downstream side of the carrier wave, if the number of current detections is the same on the upstream side and the downstream side, the amount of current ripple Ih that can be canceled increases. According to the current detection method shown in FIG. 9, the detection error is reduced compared to the case where the number of detections is different between the upstream side and the downstream side.

  Furthermore, since the vertex of the carrier wave is not included in the number of times of uplink and downlink, in addition to the detection timing of FIG. 9, for example, the detection value at the vertex may be added as shown in FIG. Embodiment).

  A sixth embodiment will be described with reference to FIG. As described above, the current ripple Ih is symmetric about the vertex of the carrier wave. Therefore, at the timing when the heights of the carrier waves on the upstream side and the downstream side coincide with each other, the current ripples are equal in magnitude and opposite in sign. If the current value is detected at this timing, the current ripple is completely canceled. Therefore, the current value is detected and added at the timing when the carrier heights coincide on the upstream and downstream sides of the carrier. As a result, the current ripple Ih can be effectively canceled and accurate current detection can be achieved.

  Further, since the peak of the carrier wave is not included on either the upstream side or the downstream side, for example, as shown in FIG. 12, the current value is detected at the peak of the carrier wave, and this is detected at another position. (Seventh embodiment). As a result, the current ripple Ih can be effectively canceled and accurate current detection can be achieved.

  According to the sixth and seventh embodiments, not only the detection error included in the current vector but also the detection error included in the three-phase current can be canceled. 13 and 14 show the relationship between the U-phase voltage Vu and the U-phase current iu in PWM. In PWM, the output of the U-phase voltage Vu includes a pattern in which a voltage having the same sign is output (FIG. 13) and a pattern in which a voltage having a different sign is output (FIG. 14). In any of these cases, it is point-symmetric with respect to the vertex of the carrier wave. Therefore, the detection error included in the three-phase current can be effectively canceled by using the current detection method of the present embodiment.

  FIG. 15 shows a current detection method according to the eighth embodiment. One period of the carrier wave is set as an addition period, and the current is detected at the center timing of each equally divided period, and four current detection values are added. As a result, as in the sixth embodiment, the current value can be detected and added at the timing at which the carrier heights coincide on the upstream side and the downstream side of the carrier, and the current ripple Ih is effectively obtained. The current can be detected with high accuracy.

  Further, as described above, since the peak of the carrier wave is not included on either the upstream side or the downstream side, as shown in FIG. 16, the current value is also detected at the peak of the carrier wave, and this is detected at another position. The value is added to the value (9th embodiment). Therefore, in this embodiment, one period of the carrier wave is set as an addition period, and one period is divided into five equal parts, current is detected at the center timing of each equal period, and five current detection values are added. As a result, the current ripple Ih can be effectively canceled and accurate current detection can be achieved. In addition, the current detection methods of the eighth and ninth embodiments have the effect of facilitating mounting on an actual machine because the detection interval is constant while having the effect of canceling the detection error.

  Next, a tenth embodiment will be described. When the fundamental component of the output current in the three-phase inverter is a sine wave as shown in FIG. 17A, if the detection timing is delayed, the phase of the output current is shifted as shown in FIG. 17B. Detected. Then, as shown in FIG. 18, the output current 21 should normally have a constant amplitude, but becomes a detection current 22 that vibrates at twice the output frequency.

  Although the fundamental wave of the inverter output current is sinusoidal, it can be considered that it changes almost linearly in a short time. Therefore, if a current is detected a plurality of times in a short period and the currents are added and averaged, they coincide with the current at the average detection time point (time point when the detection time points are temporally averaged). That is, as shown in FIG. 19, when the current detection values i1, i2, i3 at the respective timings ti, t2, t3 are averaged, iave = (i1 + i2 + i3) / 3. If the timing at which idet = ave is tdet, then tdet = tave = (ti + t2 + t3) / 3.

  For example, in a U, V, W three-phase inverter, if current detection is performed individually for U, V, W phase current at each timing as shown in FIG. 20 and FIG. That is, since tuave = tave = twave, if the detection currents are added and averaged, the current at the average detection time tave is obtained in all the U, V, and W3 phases. In this way, even in a system in which there is only one A / D converter 111 and a plurality of currents cannot be detected simultaneously, current values at substantially the same time for each phase of the U, V, and W phases are obtained. And detection errors can be reduced.

  Further, as shown in FIGS. 13 and 14, since the three-phase current is point-symmetric with respect to the top of the carrier wave, the current detection methods of the sixth and seventh embodiments and the tenth embodiment It is also possible to combine with a current detection method (eleventh embodiment). In this case, the current detection method according to the tenth embodiment eliminates the current detection error due to the fundamental wave, and the current detection method according to the sixth and seventh embodiments eliminates the current detection error due to the current ripple due to PWM. The detection error can be made almost zero. Thereby, the responsiveness of the current control system can be improved.

  In the description so far, the current ripple Ih is completely point-symmetrical around the vertex of the carrier wave. However, as described above, in reality, it is completely point-symmetrical due to the influence of the inductance and the change of the voltage command vector. Therefore, some detection error may occur. Therefore, by making the modulation wave (that is, the voltage command vector) constant within a period in which a plurality of current detection values are added, the current ripple Ih approaches point symmetry with the vertex of the carrier wave as the center, and the reduction effect increases.

  Moreover, although each said embodiment showed the example with respect to a 3-phase PWM inverter, if this invention is a multiphase inverter, all can be utilized.

  Moreover, although the structure which detects U-phase current and W-phase current among three phases, and calculates V-phase current from there was shown, it can also be set as the structure which detects all the electric currents. FIG. 22 shows a general configuration. The inverter control apparatus which generalized the motor control apparatus shown in FIG. 1 is shown. The PWM inverter 02 supplies a three-phase current to the load 04, and the analog current detectors 03u, 03v, 03w detect the three-phase currents for the load 04 and output them to the control device 05. The control device 05 has the same configuration as the control device 05 in the motor control device of the first embodiment. However, the digital current detection processor 11 performs A / D conversion on the analog current detection signals for the U, V, and W phases, and adds them for each phase to obtain a current average value, thereby obtaining a 3-axis / 2-axis coordinate converter 09. It is the structure which outputs to. Even in the configuration of FIG. 22, the current detection can be performed on two of the three phases, and the remaining one-phase current can be calculated therefrom.

  Furthermore, in each embodiment, the example of the load current control by the PWM inverter is shown. However, for example, the present invention can be applied to the control of the power supply current when the load 04 is a power source and the inverter 02 functions as a converter. .

01 ... Triangular wave PWM modulator 02 ... PWM inverter 03u, 03v, 03w ... Current detector 04 ... Synchronous motor (load)
05 ... Control device 07 ... Rotational phase angle estimator 08 ... Current controller 09 ... 3-axis / 2-axis coordinate converter 10 ... 2-axis / 3-axis coordinate converter 11 ... Digital current detection processor 111 ... A / D converter 112 ... Detection timing setter 113u, 113w ... Adder

Claims (7)

A current detection device for detecting an output current of a multiphase inverter using triangular wave pulse width modulation,
Current detection means for detecting current at a plurality of specific timings during a predetermined period of time,
Adding means for adding current detection values for each of a plurality of specific timings during the certain period,
The current detection unit performs current detection at least once each on both the upstream side and the downstream side of the carrier wave of the triangular wave PWM as a plurality of specific timings during the predetermined period. .   2. The current according to claim 1, wherein the current detection unit performs current detection at the same number of times on the upstream side and the downstream side of the carrier wave of the triangular wave PWM as a plurality of specific timings during the predetermined period. Detection device.   The current detection device according to claim 2, wherein the current detection unit performs current detection at a timing at which the height of the carrier wave coincides between the upstream side and the downstream side of the carrier wave of the triangular wave PWM.   The current detection means is configured such that the center of the certain period is set to the peak of the peak of the carrier wave or the peak of the valley, and the timing of the current detection is set to the center of each equally divided period in the period divided into the certain period. The current detection device according to claim 3, wherein   The current detection device according to claim 1, wherein the modulation wave is made constant within the period of addition.   The current detection means performs current detection at a plurality of timings for each of a plurality of phases during the certain period, and the average detection when the plurality of current detection timings of each phase are temporally averaged during the certain period. The current detection device according to claim 1, wherein the timing is set to be equal. The current detection device according to any one of claims 1 to 6,
Rotational phase estimation means for estimating the phase of the motor based on the current values of the three phases detected by the current detection device;
Using the current value detected by the current detection device as the phase estimation value obtained by the rotational phase estimation means, the current in the rotating dq coordinate system with the d axis as the magnetic flux direction of the rotor and the q axis as the axis perpendicular thereto. 3-axis / 2-axis coordinate conversion means for converting coordinates into values;
Current command calculation means for calculating a biaxial voltage command based on a difference between the detected current and the current command converted on the coordinate on the rotation dq coordinate system;
2-axis / 3-axis coordinate conversion means for converting the biaxial voltage command calculated by the current command calculation means into a voltage command of a 3-axis fixed coordinate system using the phase estimation value obtained by the rotational phase estimation means;
Triangular wave PWM modulation means for obtaining a gate signal by PWM-modulating the voltage command of the three-axis fixed coordinate system converted by the two-axis / 3-axis coordinate conversion means with a triangular wave carrier;
A motor control device comprising: a PWM inverter that performs power conversion with a gate signal output from the triangular wave PWM modulation means and outputs the converted signal to the motor.

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