JP5055835B2 - Synchronous motor drive - Google Patents

Description

  The present invention relates to a synchronous motor drive device such as a surface magnet type permanent magnet motor (also simply referred to as a motor), and more particularly to a synchronous motor drive device that does not have a rotor position or phase current detector.

  As a control method for a permanent magnet type synchronous motor having no rotor position or phase current detector, for example, as shown in Patent Document 1, a synchronous motor is based on a detection value of only a DC current detector provided on an inverter bus. Some control the motor by adjusting the voltage and frequency applied to the motor. This method is characterized by a simple configuration and easy control.

FIG. 3 is a block diagram showing the method disclosed in Patent Document 1.
In the figure, 10 is a DC bus, 11 is a three-phase inverter, 12 is a permanent magnet type synchronous motor (motor), 13 is a frequency commander, 14 is a frequency / voltage (f / v) converter, and 15 is a pulse width ( PWM) modulator, 17 is a current detector, 18 is a low-pass filter that passes low-frequency components, 19 is an effective current calculator, 20 is a high-pass filter that passes high-frequency components, 21 is a proportional calculator, and 22 is a proportional calculator. An adder / subtractor 23 is an integrator.

  The frequency command device 13 is set with the synchronous speed (frequency command f *) of the motor 12 from the host controller, and the f / v converter 14 outputs a voltage command v * corresponding to the frequency command f *. The integrator 23 integrates the deviation between the frequency command f * and the frequency correction amount Δf * obtained by the proportional calculator 21 and calculates the phase θ * of the voltage applied to the stator winding of the synchronous motor 12. The pulse width modulator 15 performs pulse width modulation (PWM) based on the voltage command v * and the phase θ * to generate a drive pulse, and controls the switching element of the three-phase inverter 11 to be turned on / off. The three-phase inverter 11 outputs a three-phase AC voltage whose pulse width is controlled, and this voltage is applied to the winding of the motor 12 to generate a rotating magnetic field.

  The current detector 17 detects an input DC current (also referred to as a bus current) of the inverter. Since the inverter bus current becomes a pulse current by switching of the pulse width modulator 15, the high frequency band component is removed from the inverter bus current detection signal Idc 0 obtained from the current detector 17 by the low-pass filter 18, and the inverter bus current average is obtained. The value Idc is obtained. The effective current calculator 19 calculates an effective current iδ from the inverter bus current average value Idc. How to find it is as follows.

The inverter output power Winv is represented by the following equation (1), where Edc is the inverter DC voltage.
Winv = Edc · Idc (1)
The electric power Wmot input to the motor is expressed by the following equation (2).
Wmot = 3 · Irms · (v * / √2) · cosφ (2)
Irms: Effective value of motor phase current equivalent to 1 v *: Command value of voltage amplitude given to inverter

Φ is a power factor angle and is given by the following equation (3).
cosφ = iδ / Irms (3)
Since the inverter output power Winv and the power Wmot input to the motor are equal,
From the above formulas (1) and (2),
iδ = √2 · Idc · Edc / (3 · v *) (4)
Thus, the effective current iδ is obtained from the inverter bus current average value Idc.

  The effective current iδ becomes a direct current amount in a steady state, but if a deviation of the synchronization speed from the steady state occurs, a vibration without attenuation occurs in iδ and the system becomes unstable. Therefore, the variation Δiδ of iδ is obtained by removing the DC component from iδ by the high-pass filter 20, and the frequency correction amount Δf * is obtained by multiplying Δiδ by a predetermined gain by the proportional computing unit 21, and the previous frequency command f Negative feedback to *. As a result, the fluctuation of iδ is reduced, the system state is brought close to the steady state, and the control system is stabilized.

  By the way, in the control of the motor, if the deviation between the phase of the applied voltage and the phase of the motor rotor position becomes excessive, the motor may not be controlled and a so-called step-out state may occur. At this time, in a system having a motor rotor position detector or an electrical angle detector, this step-out state can be easily detected. However, in the method of detecting only the bus current as described above, although the deviation between the phase of the applied voltage and the phase of the motor rotor position can be reduced and stable driving can be performed, it is possible to detect the phase deviation itself. Can not. That is, no countermeasures against step-out due to unexpected disturbance such as sudden load application are not taken.

  When a step-out occurs, immediately after that, the output voltage of the inverter is maintained at substantially the same frequency as before the step-out. On the other hand, the motor cannot maintain the torque due to step-out. Since the motor is driven to withstand normal loads, the rotational speed decreases due to the disappearance of torque. Therefore, the output voltage of the inverter and the induced voltage of the motor become asynchronous, which becomes a disturbance and disturbs the phase current of the motor, which appears as a vibration component in the inverter DC bus current.

In view of such a point, the inverter DC bus current is filtered, and it is detected that the bus current exceeds a predetermined threshold value due to vibration, or the value obtained by extracting and integrating the vibration component by the filter is the predetermined threshold value. The applicant has already proposed a method of detecting motor step-out by detecting exceeding (see Japanese Patent Application No. 2005-119398: also referred to as a proposed method).
JP 2005-218273 A

However, in the proposed method, since the threshold value of the current serving as a reference for detection is obtained by experiment, another problem arises that it is necessary to conduct another experiment when driving different types of motors. In addition, when extracting vibration components with a filter, if the filter is configured by software of an arithmetic processing unit such as a CPU in order to suppress an increase in the number of parts, the current sampling frequency of the arithmetic processing unit is limited, so at least from the sampling frequency. Since it is necessary to pass through a low-pass filter having a small cut-off frequency, there is a problem that the detected current becomes small and detection is difficult particularly at low speeds.
Accordingly, an object of the present invention is to make it possible to reliably detect step-out with a simple and inexpensive configuration.

In order to solve such a problem, in the invention of claim 1, in a synchronous motor drive device that drives a synchronous motor via an inverter that converts direct current into alternating current,
Based on a value obtained by dividing the voltage applied by the inverter to the synchronous motor by the impedance of the synchronous motor electrical circuit composed of the resistance of the synchronous motor winding and the inductance at the frequency at which the inverter drives the synchronous motor. A calculating means for calculating a reference current value is provided, and when the detected value of the inverter output current exceeds the reference current value, the synchronous motor is determined to be out of step.

In the invention of claim 2, in the synchronous motor drive device that drives the synchronous motor via an inverter that converts direct current to alternating current,
Based on a value obtained by dividing the voltage applied by the inverter to the synchronous motor by the impedance of the synchronous motor electrical circuit composed of the resistance of the synchronous motor winding and the inductance at the frequency at which the inverter drives the synchronous motor. An arithmetic means for calculating a reference current value and a timer for measuring the time when the detected value of the inverter output current exceeds the reference current value are provided, and the synchronous motor is activated when the time measured by the timer exceeds a predetermined reference time. It is characterized by determining a step out.

In the invention of claim 1 or 2, the detected value of the inverter output current can be obtained from the peak value of the current flowing through the inverter DC bus (invention of claim 3). In the invention of claim 3, A peak hold circuit for detecting the peak value of the current can be provided (invention of claim 4).
In the invention according to any one of claims 1 to 4, the reference current value can be obtained from a table or an approximate function using the frequency of the voltage applied to the synchronous motor by the inverter as a parameter (invention of claim 5). In the invention of any one of claims 1 to 5, the voltage applied from the inverter to the synchronous motor so that the current difference between the reference current value and the inverter output current during normal driving is equal to or greater than a certain value. Voltage control means for controlling the above can be provided (invention of claim 6).

According to the first aspect of the invention, the inverter is applied to the synchronous motor in a system capable of detecting only the bus current and reducing the difference between the phase of the applied voltage and the phase of the motor rotor position to enable stable driving. The reference current value for step-out determination is determined from the value obtained by dividing the voltage to be divided by the impedance of the synchronous motor electrical circuit consisting of the resistance and inductance of the synchronous motor winding at the frequency at which the inverter drives the synchronous motor. Since the detected value of the inverter output current is obtained from the peak value of the bus current and the detected value exceeds the reference current value, it is determined that the step-out has occurred, so that it can be easily applied to different types of motors. .
Further, according to the invention of claim 2, it is possible to detect the step-out more reliably.

FIG. 1 is a block diagram showing an embodiment of the present invention.
This can be said to be characterized by the addition of the step-out detection means 32 and the peak hold circuit 33 to that shown in FIG. The step-out detection means 32 is also installed in the previous proposed method, but it goes without saying that its specific configuration or function is different from that of the proposed method. Hereinafter, differences from the conventional example will be mainly described.

First, consider the relationship that holds for the current and voltage of the system shown in FIG.
The equation of state of the motor in this system is as follows:
vδ = (R + pL) iγ−ω ₁ Liδ + ω _M Ψmsin δ = 0 (5)
vγ = ω ₁ Liγ + (R + pL) iδ + ω _M Ψmcos δ = V ^* (6)
I ² = iγ ² + iδ ² (7)

The meaning of each symbol is as follows. Here, the motor type is a surface magnet type permanent magnet motor.
vγ, vδ: γ, δ-axis voltage iγ, iδ: γ, δ-axis current I: Inverter output current (instantaneous value) L: Phase inductance of motor winding R: Phase resistance of motor winding Ψm: Maximum armature linkage Magnetic flux ω ₁ : Drive frequency command ω _M : Motor shaft electrical angular velocity V ^* : Inverter output voltage command δ: Load angle p: Differential operator

  Here, the orthogonal coordinate γ-δ axis is a coordinate system in which the δ axis is the direction of the inverter output voltage. The load angle δ is an angle formed by the inverter output voltage and the motor induced voltage. Here, the currents and voltages on the γ and δ axes are converted so that the amplitude is the same as the inverter output current and voltage. These relationships are shown in FIG.

Using the superposition theorem, the out-of-step current in the system of FIG.
(1) Only the voltage from the power source is applied and there is no induced voltage, that is, the current when the motor shaft is stopped,
(2) the current when no voltage is applied from the power supply and only the induced voltage is applied;
Can be thought of as a composite.

Considering the γ and δ axes, in the case of (1) above, the applied voltage is a DC voltage, and therefore the γ and δ axis currents are DC values. In the case of the above (2), only a sinusoidal induced voltage having a phase difference of 90 degrees is applied to the stopped γ and δ axes, and this current becomes a vibration component at the time of step-out.
In the case of (1) above, ω _M = 0, iγ = const, and iδ = const. Therefore, i? At this time, i?, Respectively I i? _D, i? _D, when put between I _D, from (5) to (7), as follows (8) to (10) below.

iγ _D = ω ₁ LV ^* / (ω ₁ ² L ² + R ² ) (8)
iδ _D = RV ^* / (ω ₁ ² L ² + R ² ) (9)
I _D = V ^* / √ (ω ₁ ² L ² + R ² ) (10)

When the currents (1) and (2) are combined,
iγ = Asin (ωαt + α) + iγ _D (11)
iδ = Acos (ωαt + α) + iδ _D (12)
δ = ωαt + β (13)
Can be expressed as However,
t: Time A: Amplitude for current vibration ωα: Angular frequency for current vibration α: Initial value of current phase β: Initial value of load angle

Substituting equations (11) to (13) into equations (5) to (7),
A = ω _M Ψm / √ (ω _M ² L ² + R ² ) (14)
^{I = √ {A 2 + 2A√} (iγ D 2 + iδ D 2) sin (ωαt + α + θ) + iγ D 2 + iδ D 2}
However, θ = tan ⁻¹ (iδ _D / iγ _D ) (15)
Is obtained.

Therefore, the maximum value Imax of I is
^{Imax = {A 2 + 2A√ (} iγ D 2 + iδ D 2) + iγ D 2 + iδ D 2} 1/2
= A + I _D = ω _M Ψm / √ (ω _M ² L ² + R ² ) + V ^* / √ (ω ₁ ² L ² + R ² ) (16)
It becomes.

Therefore, from equation (16), it can be said that a current of I _D = V ^* / √ (ω ₁ ² L ² + R ² ) flows at least when the motor steps out.
On the other hand, the inverter output current Is at the time of non-step-out is calculated from the equations (5) to (7) as ω ₁ = ω _M.
Is = √ {(V ^* −ω ₁ Ψm cos δ) ² + (ω ₁ Ψ m sin δ) ² } / √ (ω ₁ ² L ² + R ² )
... (17)
It is required as follows. For a load that can be stably driven, Is is usually smaller than I _D.

From the above, if _ID is used as a reference current for step-out detection and the inverter output current is detected and compared, step-out can be detected without leakage. Here, the numerator of _ID is the impedance of the motor electric circuit composed of the resistance R and the inductance L of the motor winding at the frequency ω _{1 at} which the inverter drives the motor. Therefore, the reference current value for step-out detection can be determined if the resistance and inductance of the motor winding are known.
In the above, the type of motor is a non-salient pole machine (surface magnet type permanent magnet motor). However, even in a salient pole machine such as an embedded magnet type permanent magnet motor, the current is affected by the saliency. Although it becomes more vibrant than the case, the step-out detection can be performed in the same manner as described above.

The inverter output current is detected as follows.
That is, the peak value Ip of the inverter DC bus current is detected from the Idc detected by the current detector 17. This peak value can be obtained from the sampling value by software or by a peak hold circuit. Idc becomes a pulsed current by PWM switching. The amplitude of the pulsed current of Idc is always equal to the instantaneous value of any one of the three phases, and its peak value Ip is the peak value of the three-phase current. be equivalent to.

Therefore, the inverter output current effective value Irms can be obtained from the peak value Ip of Idc. That is,
Irms = Ip / √2 (18)
It is. Thus, the inverter output current can be obtained only from the current detector 17 on the inverter DC bus 10.

In addition, when calculating the reference current value _ID for step-out detection, there is a case where an inexpensive arithmetic unit is burdensome. Here, when V / f control is performed in the control of the inverter, an applied voltage is determined with respect to the motor frequency, and _ID is also determined with respect to the motor frequency. Therefore, if this value is obtained in advance and stored in a memory or the like as a table, for example, _ID for the motor frequency can be easily obtained. Alternatively, _ID with respect to the motor frequency may be approximated by a simple arithmetic expression. In this way, even with an inexpensive calculator, I _D can be obtained with a light calculation load.

By the way, the inverter output current Ip is increased rapidly due to the application of electrical noise to the control device or the sudden disturbance of the motor or a load driven by the motor, and the step-out is erroneously detected. Can be considered. Therefore, the time when the detected output current Ip exceeds the reference current value _ID is measured, and the step-out is detected more reliably by detecting the step-out when the measured time exceeds a predetermined reference time. It becomes possible. Note that, as the time when the output current Ip exceeds the reference current value _ID , attention may be paid to the sum of the time exceeding the predetermined time.

In addition, the control of the magnitude of the voltage applied to the motor of the inverter is inappropriate, and the current difference between the reference current value I _D and the detected output current Ip becomes extremely small depending on the motor load and speed conditions, and the step-out determination is made It is assumed that this is difficult. Therefore, the applied voltage is controlled so that the current difference becomes equal to or greater than a certain value, and the output current of the inverter during steady driving is reduced, so that erroneous detection can be prevented and reliable step-out detection can be performed. Can do.

Configuration diagram showing an embodiment of the present invention Relational diagram of inverter output current and its γ-axis and δ-axis components Configuration diagram showing a conventional example

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... DC bus line, 11 ... Inverter, 12 ... Permanent magnet type synchronous motor (motor), 13 ... Frequency command device, 14 ... f / v converter, 15 ... Pulse width modulator, 17 ... AC current detector, 18 ... Low-pass filter, 19 ... active current calculator, 20 ... high-pass filter, 21 ... proportional calculator, 22 ... adder / subtractor, 23 ... integrator, 32 ... step-out detection means, 33 ... peak hold circuit.

Claims (6)

In a synchronous motor drive device that drives a synchronous motor via an inverter that converts direct current to alternating current,
Based on a value obtained by dividing the voltage applied by the inverter to the synchronous motor by the impedance of the synchronous motor electrical circuit composed of the resistance of the synchronous motor winding and the inductance at the frequency at which the inverter drives the synchronous motor. An apparatus for driving a synchronous motor, characterized in that an arithmetic means for calculating a reference current value is provided, and when the detected value of the inverter output current exceeds the reference current value, the synchronous motor is determined to be out of step. In a synchronous motor drive device that drives a synchronous motor via an inverter that converts direct current to alternating current,
Based on a value obtained by dividing the voltage applied by the inverter to the synchronous motor by the impedance of the synchronous motor electrical circuit composed of the resistance of the synchronous motor winding and the inductance at the frequency at which the inverter drives the synchronous motor. An arithmetic means for calculating a reference current value and a timer for measuring the time when the detected value of the inverter output current exceeds the reference current value are provided, and the synchronous motor is activated when the time measured by the timer exceeds a predetermined reference time. A synchronous motor driving device characterized in that step-out is determined.   3. The synchronous motor drive device according to claim 1, wherein the detected value of the inverter output current is obtained from a peak value of a current flowing through the inverter DC bus.   4. The synchronous motor drive device according to claim 3, further comprising a peak hold circuit that detects a peak value of the current.   5. The synchronous motor drive device according to claim 1, wherein the reference current value is obtained from a table or an approximate function using a frequency of a voltage applied by the inverter to the synchronous motor as a parameter. The voltage control means for controlling the voltage applied from the inverter to the synchronous motor is provided so that a current difference between the reference current value and the inverter output current during normal driving is equal to or greater than a certain value. 5 synchronous motor driving device according to any one of.

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