JP2009124872A - V/f control system for synchronous electric motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a V/f control system which does not require an AC current sensor, which can control the reactive power of an electric motor to zero, even if the load is changed. <P>SOLUTION: The V/f control system of a synchronous electric motor has a configuration, in which a synchronous electric motor 1 is driven by a voltage type inverter 4; a stabilization processing section 35 detects the torque ripples from a DC average current of the inverter obtained by a filter average processing section 36, a DC voltage and a frequency command value; and corrects a frequency command value ω<SP>*</SP>so as to suppress the torque ripple component. In the V/f control system, an f/V converter 38 controls a voltage command instantaneous value V<SB>m</SB>of the inverter so that the power factor of the synchronous electric motor has a value of "1", while the DC average current is used, with the DC voltage and a constant of the electric motor as the parameters. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a synchronous motor V / f control device, and more particularly to reactive power control of a motor.

  Permanent magnet synchronous motors usually require the position sensor to detect the magnetic pole position information of the rotor. However, depending on the usage environment, it may be difficult to attach the position sensor, or the position may be reduced in order to reduce costs and avoid position sensor failure. Many sensorless control methods that can be driven without a sensor have been proposed.

  The V / f control method is a method of controlling the primary voltage of the motor to be constant according to the rotation speed, and basically has an open loop configuration in which no position sensor or current sensor is used. However, when the V / f control method is applied to a synchronous motor drive device, the magnetic pole position is not detected, so that an unstable control state is caused by a sudden change in the load, and there is a possibility of stepping out in some cases. high.

  FIG. 5 shows a driving apparatus for a synchronous motor using a general voltage source PWM inverter. In order to stabilize the apparatus without step-out when this apparatus is controlled by the V / f control method, the two-phase current of the synchronous motor 1 is detected by the AC current sensor 2, and the pulsation component included in the motor current is detected by the controller. 3, the control phase of the PWM inverter 4 is corrected. 5 is a DC voltage source of the PWM inverter 4, and 6 is a smoothing capacitor.

  As a stabilization method in this V / f control, the motor current detection value is the inverter voltage reference γδ coordinate (the inverter voltage vector direction is the δ axis, and the orthogonal coordinate of the inverter with the phase delayed 90 degrees from the δ axis as the γ axis) ), And the pulsating component of the γ-axis current is fed back to the frequency command value and stabilized (see, for example, Non-Patent Document 1). This method can cope with load fluctuations by feeding back current.

FIG. 6A is a configuration diagram of the V / f stabilization control of the synchronous motor proposed in Non-Patent Document 1 and the like. The controller 3 that becomes the V / f control device basically obtains the voltage command V ^* that becomes a desired voltage amplitude value from the frequency command value ω ^{* in the} f / V converter 31. This f / V conversion uses the ratio between the rated speed and the rated voltage of the driven synchronous motor. The integrator 32 obtains the phase θ of the inverter voltage command value by integrating the frequency command value ω ^* . The coordinate converter 33 converts the voltage command V ^* (vδ ^* ) and the voltage command vγ ^{* of the} phase θ and γ-axis components into a three-phase voltage command value of the PWM inverter 4. The PWM inverter 4 performs PWM control of the inverter by various PWM methods, for example, a general triangular wave comparison PWM method.

As V / f stabilization control means, the coordinate converter 34 converts the motor currents i _u and i _w detected by the current sensor 2 into coordinates based on the phase information θ of the primary voltage of the PWM inverter, and converts the γ and δ axes. The current is converted into currents iγ and iδ, and the stabilization processing unit 35 obtains the correction frequency Δω using the δ-axis current iδ from the coordinate converter 34, and corrects the frequency command value ω ^* to ω1 ^* with the correction frequency Δω. The stabilization processing unit 35 has, for example, the configuration shown in FIG. 6B, and extracts only the pulsation component (correction frequency Δω) by cutting the component close to direct current with the high-pass filter 35A, and the stabilization gain setting unit 35B. in determining the correction gain K _i.

  When the above-mentioned synchronous motor V / f stabilization method is applied to a low-inertia PM motor, an integrator is inserted in the feedback loop, so overshoot and vibration components remain for load fluctuations and speed fluctuations. It takes time. As another V / f stabilization control method that improves this phenomenon, a method is also proposed in which the pulsation component of the q-axis torque current is directly fed back to the inverter d-axis voltage (proportional term) to achieve a quick response stabilization control. (For example, see Non-Patent Document 2).

As a technique for eliminating the need for a sensor for detecting the motor current, there is a technique for detecting the DC current of the inverter with a shunt resistor or the like and calculating the motor current from the DC current (for example, see Non-Patent Document 3).
Ito, Toyosaki, Osawa “Performance improvement of V / f control of permanent magnet synchronous motor”, D. Theory, Vol. 122, No. 3, 2002 Yamamoto, Ono “V / f control method for low-inertia PM motors”, IEEJ Industrial Application Conference, 1-56, 2005 Fukumoto, Watanabe, Sone, and Hayashi “A Method of AC Current Calculation by Detecting DC Current in a Three-Phase PW Inverter”, Electrical Engineering D, 127, 2, 2007

  In the V / f control device for a permanent magnet synchronous motor, the methods of Non-Patent Documents 1 and 2 described above detect a motor current (at least two phases), extract a pulsation component, and frequency command in a direction to cancel the pulsation. Feedback control is performed to adjust values and voltage command values. This V / f control requires an AC current sensor, but in practice, an AC current sensor in a safety device such as a motor overcurrent protection can be used. However, in applications where low cost and downsizing are important, an alternating current sensor becomes a cause of high cost, and a problem of mounting space also occurs.

  In this respect, the method of Non-Patent Document 3 detects the DC current of the inverter with a single shunt resistor, and can reproduce the three-phase motor current from this DC current. A V / f stabilization control having a block configuration as shown in FIG. In addition, since an AC current sensor is not required, cost reduction can be realized. Furthermore, when overcurrent protection is performed using the voltage across the shunt resistor as DC current information, no additional shunt resistor is required.

  Here, the direct current of the PWM inverter has a waveform including a PWM pulse as shown in FIG. Since this instantaneous pulse current value has information of any phase of the alternating current, it can be grasped from the energization pattern of the PWM inverter. Therefore, in Non-Patent Document 3, A / D conversion is performed at a timing at which the pulse current value can be obtained, and the AC current value of the motor is estimated and reproduced based on the instantaneous current value. For this reason, in order to reproduce the AC three-phase current of the motor from the DC current of the PWM inverter, a high-speed A / D converter and complicated software calculation processing are required.

  In particular, in applications that increase the carrier frequency of PWM control or applications that require high-speed rotation drive, A / D conversion processing must also be performed at high speed, which increases costs and makes it difficult to reproduce motor current. It is predicted that

To solve these problems, average processing is performed using a low-pass filter that removes the PWM carrier component from the pulsed current of the inverter DC bus, and the pulsation component (frequency fluctuation) contained in this DC average current is suppressed. The frequency command value is corrected so that the DC average current is obtained by multiplying the DC average current of the inverter by the DC voltage detection value, and the pulsation component (frequency fluctuation) contained in this DC average power is suppressed. The present applicant has already proposed a V / f control device for correcting the value. In this proposal, the correction value Δω is obtained by lowering the output of the stabilization gain setter 35B as the frequency command value ω ^* increases, or the detected value of DC average current or DC average power is divided by the frequency command value ω ^*. It has also been proposed to correct the frequency command value ω ^* by obtaining a torque estimated value and extracting a pulsation component obtained by cutting a component close to a direct current from the torque estimated value.

FIG. 8A shows a block configuration diagram of the stabilization control based on the DC average power. In place of the AC current sensor 2 in FIG. 6, a DC bus current is detected by a shunt resistor 7, and a filter average processing unit (low-pass filter) from a voltage v _sh proportional to the inverter DC bus current detected by the shunt resistor 7. An averaged current i _dc averaged at 36 is obtained. This averaged current i _dc is an effective current as shown in FIG. The voltage detector 8 detects the DC voltage V _dc of the PWM inverter 4. The three-phase voltage command value generation unit 37 generates a three-phase voltage command V ^* for the PWM inverter 4 from the voltage command V _m and the phase θ. This calculation formula is as follows. Although the switching pattern generation method of a PWM inverter is arbitrary, for example, a PWM signal is generated by comparing a voltage command value and a carrier wave by a carrier comparison method, and the PWM inverter and the electric motor are driven.

As shown in FIG. 8B, the stabilization processing unit 35 multiplies the DC voltage V _dc and the averaged current i _dc by a multiplier 35C to obtain a DC average power, and the DC average power is divided by a divider 35D. By dividing by the frequency command value ω ^* , an estimated torque value (T ^ = P / ω ^* ) is obtained and used as an input to the high-pass filter 35A. This stabilization process calculates the torque estimate value from the DC current / DC voltage detection value and the frequency command value, and corrects the frequency command value so as to suppress the torque pulsation component. Even in the above, stabilization control can always be performed based on torque fluctuations, and more stable V / f control can be realized in the full speed / full load range in accordance with the torque fluctuations of the synchronous motor.

  Here, in order to control the electric motor with high efficiency, it is preferable to control the electric motor to a power factor of 1. For example, when a permanent magnet synchronous motor having no saliency is used in rotation coordinates synchronized with the rotation of the motor (the orthogonal two-axis dq coordinate having the d axis as the permanent magnet magnetic flux direction is defined), the d axis current is set to zero. It is preferable. In other words, the reactive current in the motor is reduced to zero to achieve high efficiency. However, V / f control in a permanent magnet synchronous motor is based on open loop control in which magnetic pole position detection is not performed. For this reason, it is difficult to arbitrarily control the d-axis current at high speed.

  In Non-Patent Document 1, the voltage command values Vγ and Vδ of the estimated dq axis (γδ coordinate) in the controller and the phase of the γδ rotating coordinate system are used to convert the AC current of the motor to Iγ and Iδ. High-efficiency control that makes the reactive power of the motor zero is indirectly realized.

  This approach requires obtaining three-phase current information directly with an alternating current sensor. Instead, reactive power control can be performed by applying, to Non-Patent Document 1, a method of reproducing a three-phase AC current from a DC bus current without an AC current sensor as in Non-Patent Document 3. However, as described above, the technique of Non-Patent Document 3 is difficult to realize when the ultra-high speed driving or the PWM frequency is high.

  In order to solve this problem, when the configuration shown in FIG. 8 is adopted, it is impossible to reproduce the three-phase alternating current, and it becomes difficult to obtain the phase information of the current. Can not. Further, since the V / f conversion ratio is determined from the ratio of the rated voltage and the rated frequency given by the nameplate of the motor or the design value, this conversion ratio directly affects the power factor of the motor, but is a fixed conversion ratio. When reactive power is generated when the load changes (for example, when the load is low) and operation in that state is continued, there is a risk of reducing efficiency.

  An object of the present invention is to provide a V / f control device for a synchronous motor that can control a motor reactive power to zero even when a load changes, in a V / f control device that does not require an alternating current sensor.

In order to solve the above-described problems, the present invention controls the voltage command instantaneous value V _m so that the reactive power of the motor is always zero according to the rotational speed of the synchronous motor and the state of the inverter DC power corresponding to the motor load. As described above, it has the following configuration.

(1) The synchronous motor is driven by a voltage type inverter, and the inverter's DC bus current is averaged by a low-pass filter, and the inverter frequency command value ω ^* is set so as to suppress the pulsation component contained in the DC average current. In the synchronous motor V / f control device including the stabilization processing means for correction,
Using the frequency command value corrected by the stabilization processing means, the DC average current, the inverter DC voltage, and the synchronous motor constant as parameters, the inverter voltage command instantaneous value V _m so that the power factor of the synchronous motor becomes 1. An f / V converter for controlling the above is provided.

(2) The synchronous motor is driven by a voltage type inverter, and the DC bus current of the inverter is averaged by a low-pass filter, and torque pulsation is detected from the DC average current, the inverter DC voltage and the frequency command value, In the synchronous motor V / f control device including the stabilization processing unit that corrects the frequency command value ω ^* so as to suppress the torque pulsation component,
Using the frequency command value corrected by the stabilization processing means, the DC average current, the inverter DC voltage, and the synchronous motor constant as parameters, the inverter voltage command instantaneous value V _m so that the power factor of the synchronous motor becomes 1. An f / V converter for controlling the above is provided.

  (3) The f / V converter is

φ ₀ : maximum value of armature interlinkage magnetic flux by permanent magnets per phase, ω: electrical angular frequency, L: winding inductance value of synchronous motor, V _dc : inverter DC voltage, I _dc : inverter DC average characterized in that the current determining the voltage command instantaneous value V _m.

  (4) The f / V converter is

φ ₀ : maximum value of armature interlinkage magnetic flux by permanent magnet per phase, ω: electrical angular frequency, r: winding resistance of synchronous motor, L: winding inductance value of synchronous motor, V _dc : DC of inverter Voltage, I _dc : The voltage command instantaneous value V _m is obtained from the DC average current of the inverter.

  (5) The f / V converter is

φ ₀ ′: Maximum value of magnetic flux obtained by temperature correction of armature interlinkage magnetic flux by permanent magnet per phase, ω: electrical angular frequency, r ′: resistance obtained by temperature correction of winding resistance of synchronous motor, L: synchronous motor The voltage command instantaneous value V _m is obtained from the winding inductance value of the inverter, V _dc : DC voltage of the inverter, I _dc : DC average current of the inverter.

(6) the stabilizing processing means, characterized in that the gain K _i to lower the correction value Δω as the frequency command value omega ^* is high.

(7) The stabilization processing means extracts a pulsation component obtained by cutting a component close to a direct current from the estimated torque pulsation value to obtain a correction value for the frequency command value ω ^* .

As described above, according to the present invention, the voltage command instantaneous value V _m is controlled so that the reactive power of the motor is always zero according to the state of the inverter DC power corresponding to the rotational speed of the synchronous motor and the motor load. Therefore, in the V / f control device that eliminates the need for an alternating current sensor, the motor reactive power can be controlled to zero even when the load changes.

(Embodiment 1)
FIG. 1 is a block diagram of a V / f control device for a synchronous motor showing the present embodiment. 8 differs from FIG. 8 in that an f / V converter 38 is used in place of the f / V converter 31. FIG.

In addition to the frequency command value ω1 ^* subjected to feedback compensation, the f / V converter 38 uses the DC average current i _{dc obtained} by the filter average processing unit 36, the DC voltage V _dc, and the motor constant as parameters, and the voltage command instantaneous value V _m. Is obtained to control the motor reactive power to 0 (zero). This f / V conversion will be described below.

An equivalent circuit per phase of the electric motor is as shown in FIG. In the figure, terminal voltage effective value: V ₀ , no-load induced voltage effective value: E, winding resistance: r, leakage inductance: l, effective inductance La, armature current effective value: I _0.

  Here, a permanent magnet synchronous motor having no saliency on orthogonal two-axis rotational coordinates is considered, and one-phase inductance values are collectively represented as L shown in the following formula (1).

  The induced voltage effective value E can be expressed by the following equation.

However, phi ₀ is the maximum value of the armature flux linkage ascribable to the permanent magnet per one phase, omega is the electrical angular frequency.

Here, it is assumed that the winding resistance r is sufficiently small. Further, it is assumed that the three-phase current / voltage of the motor is balanced. In order to set the power factor of the motor to 1, the phase of the induced voltage E and the phase of the armature current I ₀ may be matched. FIG. 2B is a vector diagram showing the relationship between current and voltage when the phases match. From this relationship, the voltage command value (instantaneous value) V _m can be obtained by the following equation in the f / V converter 31 of FIG.

Here, the following formula is established from the relationship of the active power when the phases of the induced voltage E and the armature current I ₀ coincide.

V _dc : DC voltage, I _dc : DC average current Therefore, the armature current effective value I ₀ is as follows from the equations (2) and (4).

Substituting Equations (2) and (5) into Equation (3) to obtain V _m yields the following.

Looking at equation (6), the square root is composed of a term of speed electromotive force and a term of DC current (DC power). That is, the reactive power of the motor can be reduced to zero according to the rotational speed (electrical angular frequency ω) and the load by obtaining the voltage command instantaneous value V _m according to the equation (6).

  In the present embodiment, the f / V converter 38 in FIG. 1 performs f / V conversion according to the equation (6), so that the V / f stabilization control without an AC current sensor is performed, and only the rotation frequency is used. In addition, the reactive power can be reduced to zero by performing f / V conversion corresponding to the load state, so that it is possible to control with high efficiency.

(Embodiment 2)
In the first embodiment, assuming that the winding resistance r is sufficiently small, the influence of the voltage drop is ignored. However, when the motor is small and low-inertia, the inductance value L is often small, and when approximating r≈0, the influence of the voltage drop at high load may not be negligible.

Therefore, in this embodiment, it is possible to perform f / V conversion considering the influence of the winding resistance r. The principle is the same as in the first embodiment, and the phase relationship between current and voltage is shown in a vector diagram in FIG. From this relationship, the voltage command value (instantaneous value) V _m can be obtained by the following equation.

  Substituting Equations (2) and (5) into Equation (7) yields Equation (8).

  Therefore, if the conversion formula of the f / V converter 38 in FIG. 1 is replaced with the formula (8), the reactive power 0 can be controlled in consideration of the voltage drop of the winding resistance r.

  According to the present embodiment, since the influence of the voltage drop of the winding resistance r can be taken into consideration, high-efficiency control with zero reactive power can be performed with high accuracy.

(Embodiment 3)
In the first or second embodiment, the reactive power is indirectly set to zero using the parameters of the motor. Among the parameters of the electric motor, in particular, the maximum value φ ₀ of the linkage flux by the winding resistance r and the permanent magnet varies depending on the temperature. Therefore, when used in applications with a wide operating temperature range, the parameters fluctuate and an error occurs in the above-described high efficiency f / V conversion.

  Therefore, in the present embodiment, the parameters are corrected using temperature information obtained by some means such as a temperature sensor installed in the winding of the motor or estimated temperature information. The temperature detection means and the method for obtaining temperature information are not limited. FIG. 4 is an example of the configuration diagram.

4 differs from FIG. 1 in that the temperature detector 39 detects the operating temperature of the electric motor 1, and the temperature coefficient unit 40 uses the temperature information to preset the winding resistance r and the maximum value of the flux linkage. The parameter φ ₀ is corrected, and the corrected parameters r ₀ ′ and φ ₀ ′ are given as motor constants in the f / V converter 38.

For example, the expression (8) in the second embodiment is expressed as the following expression (9) using the corrected r ′ and φ ₀ ′.

  According to the present embodiment, high-efficiency control can be performed with an f / V conversion equation that takes into account the temperature change of the motor parameters.

(Modification)
In the embodiments described above, the V / f of the synchronous motor that detects the torque pulsation from the DC average current of the inverter, the DC voltage detection value, and the frequency command value and corrects the frequency command value so as to suppress the torque pulsation component. In the case of the control device, a V / f control device that averages the DC bus current of the inverter and corrects the frequency command value so as to suppress the pulsation component (frequency variation) included in the DC average current. Applying the same effects.

Similarly, when the output of the stabilization gain setter 35B is applied to a V / f control device that obtains a correction value Δω that is lower as the frequency command value ω ^* is higher, the same effect can be obtained.

In the above embodiments, the f / V converter 38 shows the case where the voltage command instantaneous value V _m is obtained by the calculations of the expressions (6), (8), and (9). The voltage command instantaneous value V _m can be obtained using the table data.

1 is a block configuration diagram of a V / f control device for a synchronous motor showing Embodiment 1. FIG. The equivalent circuit per phase of an electric motor and the current / voltage vector diagram. FIG. 5 is a current / voltage vector diagram including a winding resistance in the second embodiment. FIG. 5 is a block configuration diagram of a synchronous motor V / f control device according to a third embodiment. A synchronous motor drive device using a voltage-type PWM inverter. The conventional block diagram of the V / f stabilization control of a synchronous motor. The DC current waveform of the PWM inverter. The block block diagram of the stabilization control by DC average power. The current waveform figure of filter average processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Synchronous motor 2 AC current sensor 3 Controller 4 PWM inverter 5 DC voltage source 6 Smoothing capacitor 7 Shunt resistor 31, 38 f / V converter 32 Integrator 35 Stabilization processing part 36 Filter average processing part 37 Three-phase voltage command value Generator

Claims (7)

A stable motor that drives a synchronous motor with a voltage-type inverter, averages the DC bus current of the inverter with a low-pass filter, and corrects the inverter frequency command value ω ^* so as to suppress the pulsation component contained in the DC average current In the synchronous motor V / f control device provided with the processing unit,
Using the frequency command value corrected by the stabilization processing means, the DC average current, the inverter DC voltage, and the synchronous motor constant as parameters, the inverter voltage command instantaneous value V _m so that the power factor of the synchronous motor becomes 1. A V / f control device for a synchronous motor comprising an f / V converter for controlling the motor. The synchronous motor is driven by a voltage type inverter, the DC bus current of the inverter is averaged by a low-pass filter, torque pulsation is detected from this DC average current, the DC voltage of the inverter and the frequency command value, and the torque pulsation component In the synchronous motor V / f control device including the stabilization processing means for correcting the frequency command value ω ^* so as to suppress
Using the frequency command value corrected by the stabilization processing means, the DC average current, the inverter DC voltage, and the synchronous motor constant as parameters, the inverter voltage command instantaneous value V _m so that the power factor of the synchronous motor becomes 1. A V / f control device for a synchronous motor comprising an f / V converter for controlling the motor. The f / V converter is

φ ₀ : Maximum value of armature interlinkage magnetic flux by permanent magnets per phase, ω: electrical angular frequency, L: winding inductance value of synchronous motor, V _dc : DC voltage of inverter, I _dc : DC average of inverter The V / f control device for a synchronous motor according to claim 1, wherein the voltage command instantaneous value V _m is obtained from a current. The f / V converter is

φ ₀ : maximum value of armature interlinkage magnetic flux by permanent magnet per phase, ω: electrical angular frequency, r: winding resistance of synchronous motor, L: winding inductance value of synchronous motor, V _dc : DC of inverter voltage, I _dc: V / f control apparatus for a synchronous motor as set forth in the inverter DC average current to claim 1 or 2, characterized in that determining said voltage command instantaneous value V _m. The f / V converter is

φ ₀ ′: maximum value of magnetic flux obtained by temperature correction of armature interlinkage magnetic flux by permanent magnet per phase, ω: electrical angular frequency, r ′: resistance obtained by temperature correction of winding resistance of synchronous motor, L: synchronous motor The voltage command instantaneous value V _m is obtained from the winding inductance value of the inverter, V _dc : DC voltage of the inverter, I _dc : DC average current of the inverter, and V / of the synchronous motor according to claim 1 or 2. f control device. The stabilization means of a synchronous motor according to claim 1, characterized in that the gain K _i to lower the correction value Δω as the frequency command value omega ^* is high V / f control device. The said stabilization processing means extracts the pulsation component which cut | disconnected the component close | similar to direct current | flow from the said torque pulsation estimated value, and obtains the correction value of frequency command value (omega) ^*. A V / f control device for a synchronous motor according to the item.

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