JP2005218273A - Control device of permanent magnet synchronous motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably control a permanent magnet synchronous motor without the use of position detectors and AC current detectors. <P>SOLUTION: In performing a control using an inverter 11 by making a direct proportional relationship between a voltage and its frequency applied on the winding of a permanent magnet synchronous motor 12, it is so designed as to determine frequency corrections Δf* for establishing the stabilization of the control through a negative-feedback to numeric command values of frequencies f* of applied voltages of the electric motor given to the inverter 11, by the use of a current detector 24, a low path filter 25 and an effective current arithmetic device 26, etc. As a result, the position detectors and AC current detectors that are needed conventionally are eliminated, and the costs will be reduced accordingly. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for a synchronous motor (also simply referred to as an electric motor), particularly a permanent magnet type synchronous motor.

  This type of control method includes controlling the voltage and current of the synchronous motor based on position information obtained from a position detector attached to the rotating shaft of the motor, and estimating the rotor position from the voltage and current of the motor. There are those that do not require a position detector (sensorless vector control), and those that control the voltage and frequency applied to the motor approximately in proportion (constant V / f control). Such V / f control is disclosed in, for example, Patent Document 1, and has a feature that a position detector is unnecessary and control is simple.

FIG. 2 is a block diagram showing an example of V / f constant control described in Patent Document 1. In FIG.
In the figure, 11 is a three-phase inverter, 12 is a permanent magnet synchronous motor, 13 is a frequency commander, 14 is a frequency / voltage (f / v) converter, 15 is a pulse width modulator, and 16 and 17 are alternating currents. Detector, 18 is a vector calculator, 19 is a high-pass filter that passes high-frequency components, 20 is a proportional calculator, 21 is an adder / subtractor, and 22 is an integrator.

The frequency command device 13 is set with the synchronous speed (frequency command f *) of the synchronous motor 12, and the f / v converter 14 outputs a voltage command v * corresponding to the frequency command f *. The integrator 22 integrates the frequency command f * and calculates the phase θ of the voltage applied to the stator winding of the synchronous motor 12. The pulse width modulator 15 generates a drive pulse by performing pulse width modulation (PWM) based on the voltage command v * and the phase θ, and controls the switching element of the three-phase inverter 11 on and off.
The three-phase inverter 11 outputs a three-phase AC voltage whose pulse width is controlled, and this voltage is applied to the windings of the synchronous motor 12 to generate a rotating magnetic field.

Two phases out of the three-phase current supplied to the synchronous motor 12, for example, iu and iw are detected by the AC current detectors 16 and 17, and converted into an orthogonal coordinate system by the vector calculator 18, thereby being effective. The current iδ is obtained from the relationship of the following equation (1).
iδ = [(− 1 / √3) sin θ + cos θ] iu + [(− 2 / √3) sin θ] iw
... (1)

By the way, the effective current iδ becomes a direct current amount in the steady state, but if the synchronization speed deviates from the steady state, a transient change occurs in iδ and the system becomes unstable. This has been confirmed by analysis and experiment as in Non-Patent Document 1, for example.
Therefore, the variation Δiδ of iδ is obtained by removing the direct current component from iδ by the high-pass filter 19, and is obtained as a frequency correction amount Δf * by multiplying Δiδ by a predetermined gain by the proportional calculator 20, and the previous frequency command f * Negative feedback is made. As a result, the fluctuation of iδ can be reduced, the system state can be brought close to the steady state, and the control system can be stabilized.

JP 2000-236694 (page 3-4, FIG. 1) IEEJ Transactions D, Vol.122, No.3, 2002, pp. 253-259 "Performance improvement of V / f control of permanent magnet synchronous motor"

As described above, those using a rotor position detector hinder downsizing of the equipment, and there are problems in reliability, workability, price, etc. because multiple wiring and receiving circuits for transmitting detector signals are required. Moreover, there is a problem that what detects the position of the rotor from the information on the voltage and current of the motor without using the position detector requires complicated and high-speed arithmetic processing.
On the other hand, even in the conventional V / f constant control described with reference to FIG. 2, at least two AC current detectors for detecting the phase current of the electric motor are required, resulting in high cost.
Therefore, an object of the present invention is to enable stable control with a simple configuration without using a position detector or an alternating current detector.

In order to solve such a problem, in the first aspect of the invention, the power applied to the permanent magnet type synchronous motor winding is controlled by the power converter that converts direct current to alternating current in a substantially proportional manner. In the control device for the magnet synchronous motor,
Current detecting means for detecting a direct current flowing through the power converter, filter means for performing a filtering process on the detected direct current, and a frequency correction amount generated based on an output signal from the filter means, to the power converter Feedback means for negative feedback to the frequency command of the applied motor applied voltage is provided.

  In the invention of claim 1, the filter means can have means for obtaining an average value of the detection current by excluding a high frequency band from the detection current (invention of claim 2). In the invention, the frequency correction amount is obtained from the detected current or an average value thereof, a command value or detected value of the electric motor applied voltage, and a command value or detected value of a DC voltage applied to the power converter. (Invention of claim 3).

  According to the present invention, there is an advantage that the permanent magnet type synchronous motor can be stably controlled without requiring a position detector, an alternating current detector, or a complicated and high-speed arithmetic processing device.

FIG. 1 is a block diagram showing a first embodiment of the present invention.
As is apparent from FIG. 1, this example omits the AC current detectors 16 and 17 and the vector calculator 18 from the conventional example of FIG. 2, and instead uses a current detector 24, a low-pass filter 25, and an effective current calculator. 26 is added. Hereinafter, the difference will be mainly described.

The current detector 24 detects the inverter DC current. As the current detector 24, a Hall element, a magnetoresistive element, a magnetoimpedance element, or a shunt resistor and a voltage detector can be used. Since the inverter DC current becomes a pulsed current by switching of the pulse width modulator 15, the high-frequency band component is removed from the inverter DC current detection signal Idc ₀ obtained from the current detector 24 by the low-pass filter 25, and the inverter DC An average current value Idc is obtained.

Next, the effective current calculator 26 calculates an effective current iδ from the inverter DC current average value Idc. How to find it is as follows.
The inverter output power Winv is represented by the following equation (2), where Edc is the inverter DC voltage.
Winv = Edc · Idc (2)

The electric power Wmot input to the synchronous motor is represented by the following equation (3).
Wmot = 3 · Irms · (v * / √2) · cosφ (3)
Irms: Effective value of motor phase current equivalent to 1 v *: Command value of voltage amplitude given to inverter In addition, φ is a power factor angle and is given by the following equation (4).
cosφ = iδ / Irms (4)

Since the inverter output power Winv and the power Wmot input to the synchronous motor are equal,
From the above equations (2) and (3),
iδ = √2 · Idc · Edc / (3 · v *) (5)
Thus, the effective current iδ is obtained from the inverter DC current average value Idc. Note that the inverter modulation factor λ represented by the equation (6) can also be used, and the calculation can be simplified.
λ = 2 · v * / Edc (6)
In the following, the DC component is removed from i δ by the high-pass filter 19 in the same manner as in the prior art, the variation is obtained, and the proportional calculator 20 multiplies Δi δ by a predetermined gain to obtain the frequency correction amount Δf *. By negatively feeding back to the command f *, the control system can be stabilized.

  As described above, by using the inverter DC current, stable control can be performed without a phase current detector. Further, by filtering the inverter DC current, the average value of the effective current of the synchronous motor can be calculated as described above. Note that the inverter DC voltage used in the calculation may be the detection value Edc or its command value. Similarly, the inverter applied voltage may be the detected value v instead of the command value v *, and the modulation factor λ may be used.

Configuration diagram showing an embodiment of the present invention Configuration diagram showing a conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... DC bus line, 11 ... Inverter, 12 ... Permanent magnet type synchronous motor, 13 ... Frequency command device, 14 ... f / v converter, 15 ... Pulse width modulator, 16, 17 ... AC current detector, 18 ... Vector An arithmetic unit, 19 ... a high-pass filter, 20 ... a proportional calculator, 21 ... an adder / subtractor, 22 ... an integrator, 24 ... a current detector, 25 ... a low-pass filter, 26 ... an effective current calculator.

Claims (3)

In the control device for a permanent magnet type synchronous motor that controls the voltage applied to the winding of the permanent magnet type synchronous motor by a power converter that converts direct current to alternating current and the frequency thereof in substantially proportion,
Current detecting means for detecting a direct current flowing through the power converter, filter means for performing a filtering process on the detected direct current, and a frequency correction amount generated based on an output signal from the filter means, to the power converter A control device for a permanent magnet type synchronous motor, comprising feedback means for negatively feeding back to a frequency command of an applied motor applied voltage.   2. The control device for a permanent magnet synchronous motor according to claim 1, wherein the filter means includes means for obtaining an average value of the detected currents by excluding a high frequency band from the detected current. The frequency correction amount is obtained from the detected current or an average value thereof, a command value or detected value of the motor applied voltage, and a command value or detected value of a DC voltage applied to the power converter. The control device for a permanent magnet type synchronous motor according to claim 1 or 2.

Images