JPH033694A - Method of detecting freely running state of induction motor - Google Patents

Abstract

PURPOSE:To detect the freely running state of an induction motor by extracting a ripple component generated in a control signal system according to a predeter mined command signal to obtain a rotating state of the motor of freely running state. CONSTITUTION:If an induction motor 5 is rotated in a freely running state, when DC current command signals ids*, iqs* are output from a current instruc tion unit 24, the output current of an inverter 4 is controlled based on a devia tion signal between the signals ids*, iqs* and a detection signal of an output current detected value of the inverter 4 by a control signal system, and a ripple component is generated in the system. The component is extracted to obtain the rotating state of the motor 5 of the freely running state. Thus, the freely running state of the motor 5 can be detected without detecting the remaining voltage of the motor 5.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for detecting a coasting state of an induction motor, which is carried out by an inverter device when restarting an induction motor after a momentary power failure, restarting it from coasting, or switching to commercial power. It is.

[Conventional technology]

The diagram in FIG. 7 has been conventionally used to control the speed of a three-phase induction motor (hereinafter referred to as induction motor). Output voltage V
and the output frequency f are controlled to be constant. So-called V/f
This is a constant control type inverter device with a circuit for detecting the rotational frequency and direction of rotation of the induction motor in a free running state.

In the figure, (1) is a commercial power supply that outputs three-phase AC.

(2) is a rectifier circuit that converts input three-phase AC into DC and outputs it, (3) is a smoothing capacitor, and (4) is a self-extinguishing element such as a transistor connected in antiparallel to this element. Consists of a return diode, which converts direct current into three frequencies of any frequency.
This is an inverter section that inversely converts phase alternating current to output, and an induction motor (5) is connected to the alternating current output terminal consisting of U, V, and W phases. (6) is a current detector that detects the output current of the inverter section (4), and () is a voltage detector that includes a transformer and the like that detects the residual voltage of the induction motor (5) in a free-running state.

(8) is a voltage detector that detects the voltage of the commercial power source (1). (9) is an instantaneous power failure detection restart means, which detects an instantaneous power failure of the commercial power supply (1) via the voltage detector (8).

Free run state detection unit (11 to be described later) Induction motor (5)
A command signal is output to detect the free run frequency F and rotation direction of
Based on the detection result, a switching signal is output to the control circuit unit 0, which will be described later, so as to restart from the free run state. The member is a free run state detection section, and when a command signal is given from the instantaneous power failure detection restart means (9), the voltage detector (7)
Input the output signal of and calculate the free run frequency F of the induction motor (5).

It consists of a rotation speed calculation means t111 which outputs a voltage signal and a rotation direction determination means (13) which determines the rotation direction and outputs a 0 determination signal. a3 is an inverter section (4).
) A control circuit unit that outputs a control signal of the umbilical alternating current output, and a speed command unit that outputs a speed command to the induction motor (5) by inputting the above speed command.

The acceleration/deceleration limiting means αS gradually increases and outputs a voltage signal according to the speed command so that the induction motor (5) is slowly started, and is controlled by a switching signal from the instantaneous power failure detection restart circuit (9). Frequency switching means ae that passes an input signal from either one of the rotational speed calculating means αDi and the acceleration/deceleration limiting means aS, converting the voltage signal inputted through this frequency switching means qe into a frequency f corresponding to this signal. Based on the voltage signal inputted from the V/f converting means +lη and the acceleration/deceleration limiting means α, the v/f converting means α
Normal voltage pattern output means α to output a voltage command V with a constant V/f ratio for the frequency f output by η Based on the voltage signal input from the α/revolution speed calculation means αυ, the output voltage is normal. The restart reduced voltage pattern output means α port gradually increases until the V/f ratio is reached, and the switching is controlled by the output signal of the instantaneous power failure detection restart means (9).1 Normal voltage pattern output means α3 or the restart reduced voltage pattern Output means α
Voltage switching means (■) that passes an input signal from either one of the voltage switching means (9), converting the voltage command inputted through this voltage switching means (■) and V/ to the voltage command inputted through the voltage switching means (3) based on the signal input from the converting means (α).
control signal output means QD for outputting a phase sine wave control signal;
The three-phase sine wave control signal is input, converted into a pulse modulation signal, and outputted to the inverter section (4) as a control signal for controlling the AC output of the inverter section (4).
WM circuit 4.

The output signal of the current detector (6) is monitored, and if an overcurrent exceeding a predetermined value is detected, an alarm signal is output to the PWM circuit 4 to stop or limit the AC output of the inverter section (4). It consists of an overcurrent detection circuit (to). In addition, the instantaneous power failure detection restart means (9), the free-run detection section (II), and the acceleration/deceleration limiting means (15 to control signal output means c!D) of the control circuit section 0 usually have the functions of the CPU, memory, It is built on a computer program consisting of input/output interfaces, etc.

Next, the operation will be explained. When starting the induction motor (5) in a state where the induction motor (5) has completely stopped, first the induction motor (5) is started using the speed command α4.
When the rotational speed of 5) is set and the power source (1) is turned on, the frequency switching means 1 and the voltage switching means (■) each control the acceleration/deceleration limiting means αj by the signal from the instantaneous power failure detection restarting means (9). and normal voltage slam output means 119 side, and by inputting the speed command value from the speed command device I, the acceleration/deceleration limiting means (19 gradually adjusts the speed command value from zero over a predetermined period of time). A voltage signal raised to V is output, and this signal is passed through frequency switching means 0,
/f is input to the α force converting means, where it is converted to a frequency f according to the speed command value, and is input to the control signal output means CfJ. On the other hand, the output signal from the acceleration/deceleration limiting means α is input to the normal voltage pattern output means αe, and corresponds to the speed command value. That is, it outputs a voltage command V that makes the V/f ratio constant with respect to the output frequency f of the V/f conversion means αη, and this voltage command V is input to the control signal output means QTJ via the voltage switching means ■. be done. Control signal means c!
D outputs a three-phase sine wave signal according to the speed command by inputting the frequency f and voltage command V, and connects the PWM circuit (
2) converts the input three-phase sine wave signal into a pulse width modulation signal so that three-phase power of a desired frequency is supplied from the inverter section (4) to the induction motor (5), and 4) is output as the control signal.

Next, after a momentary power outage occurs and the inverter equipment stops,
A case will be described in which the induction motor (5) is restarted due to power restoration or is started from a state where the induction motor (5) is freely rotating due to an external force when the inverter device is stopped.

In the above case, it is necessary to make the rotational frequency F of the induction motor (5) in the free running state coincide with the output frequency f of the inverter device, and to accelerate the motor again. The reason for this is that when the induction motor (5) is free-running at a certain rotation speed F, if the frequency f and voltage V of the inverter device are gradually increased at a constant ratio of V/ as in normal operation. When the output frequency f of the inverter device approaches the rotational frequency F of the induction motor (5) from below, a large braking torque due to regenerative braking is generated, and after passing the synchronous speed, an acceleration torque is applied to the induction motor (5). ) occurs.

This will not give a large torque shock to the load of the induction motor (5).9 For example, if the load is a proar, a large impact will be given to the drive shaft of the proar, shortening its life. Therefore, in an inverter device using a constant V/f control method, at the time of starting the inverter device, the above output frequency f
In order to match the free-run frequency F of the induction motor (5), it is necessary to know the frequency F. In this case, it is necessary to know the frequency F, or to install a speed detector such as a tacho generator, or to detect the residual voltage of the induction motor and calculate its frequency component. The above-mentioned free run frequency F is obtained by calculating from .

In Fig. 7, the induction motor (
5) is detected by the voltage detection transformer (7), and the rotation speed calculation means (I
In step 11, the period of the residual voltage is determined, and the free run frequency F is estimated from its reciprocal. Induction motor (5) in free running state after detecting phase difference
) to determine the direction of rotation. If the instantaneous power failure detection restart circuit (9) detects an instantaneous power failure of the commercial power supply (1) via the voltage detection transformer (8), or even if the startup is normal, the induction motor (5) will be in a coast-to-coast state. When it is detected by the signal input from the free run state detection unit (11), the 0 frequency switching means αe and the voltage switching means When the induction motor (5) is restarted, a voltage signal corresponding to the rotational frequency F in the free running state and information on the rotational direction are set to V/Lllllll via the frequency switching means (161).
The signal is inputted to the f conversion means aη, converted into a frequency f that matches the rotational frequency FK, and inputted to the control signal output means c2D. On the other hand, the output signal from the free run state detection member is also input to the restart voltage reduction pattern circuit (19), where it responds to the input signal.In other words, it gradually increases until it reaches the normal voltage V corresponding to the frequency fK. The output voltage is converted into a voltage command and inputted to the control signal output means Qυ.

The following is based on the three-phase sine wave signal output by the control signal output means.

An output control signal is output from the PWM circuit (2) to the inverter section (4), and the induction motor (5) is in a free running state.
is started at its rotational frequency F.

[Problem that the invention seeks to solve]

According to the conventional induction motor free run state detection method, 1
As described above, the residual voltage of the induction motor is detected, the rotational frequency of the induction motor in the free running state is determined from the reciprocal of the period of the residual voltage, and the phase difference of the residual voltage between two different lines is detected. Since the direction of rotation in the free-run state is determined by using the motor, a dedicated voltage detector such as a voltage detection transformer is required to detect the residual voltage of the induction motor, which increases the size of the inverter device. In addition, when the residual voltage of the induction motor is small, there is a problem that it is difficult to detect the frequency 9 phase etc. in the free running state.

This invention was made in order to solve the above-mentioned problems, and it is an induction motor that can detect the rotational state of the induction motor in a free running state without having a voltage detector for detecting the residual voltage of the induction motor. The purpose of this invention is to obtain a method for detecting the free running state of an electric motor.

[Means to solve the problem]

A method for detecting a free run state of an induction motor according to the present invention includes: an inverter section that outputs a current to the induction motor; and a current command section that outputs a current command signal.

a control signal system that controls the output current of the inverter section based on a deviation signal between the current command signal output from the current command section and a detection signal that is a detected value of the output current of the inverter section; When the motor is in a free run state, the current command section outputs a nearly constant command signal as a current command signal, and at this time, the ripple component generated in the control signal system is extracted, and the motor is in the free run state. This is to determine the rotational state of the induction motor.

[Effect]

According to this invention, when the induction motor is in a free running state, when a DC current command signal is output from the current command section, the control signal system outputs the DC current command signal and the inverter section. The output current of the inverter section is controlled based on the deviation signal from the detection signal, which is the detected value of the output current, and at this time, a ripple component is generated in the control signal system, and this ripple component is extracted to maintain the free run state. The rotational state of the induction motor at .

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to FIGS. 1 to 6. Figure 1 is a circuit block diagram of an inverter device for realizing the method for detecting a free running state of an induction motor (5) according to the present invention.

The same reference numerals as in the conventional example shown in FIG. 7 indicate the same or equivalent elements as in the conventional example.

In the figure, (10A) is a free-run state detection unit, which receives orthogonal two-phase current command signals tcr2 (a-axis component) and iq'' ( q-axis component) and the above ids.

Current phase command means @ as a current command unit that outputs the phase angle θ of Iqs, sine gin corresponding to the above phase angle θ
Function generating means (to) outputting θ and cosine caIS.

The inverter section (4) which the current detector (6) detects and outputs
) detection signal consisting of three phases of output current fu, iv
, fv fc 2-phase current 1ds (d-axis component), 1q
3-phase/2-phase conversion means (to) for converting into s (q-axis component);
The d-axis component ta of the two-phase current output by the current phase command means (■) and the three-phase/two-phase conversion means (to)? and ida
and the d-axis current comparison means (b) which compares the q-axis components iq2 and iq@ and outputs the deviation signal (id"-ids), and the deviation signal (iq"-1qs).
), inputs and amplifies the deviation signal from the d-axis current comparison means (product), and also inputs and amplifies the deviation signal from the inverter section (4) so that the deviation signal becomes zero.
), which outputs the d-axis component ma d2 of the two-phase voltage command for controlling the output current of Q-axis current control means (to) that outputs the q-axis component vqs of the command.

The above two-phase voltage command ma d2. VQ Homare 3-phase voltage command record.

3-phase/2-phase conversion means Gυ for converting into VV, VW, and the 2-phase voltage command vd2. Input vq2 and extract the ripple component superimposed on this command voltage.

It consists of a free-run frequency one-rotation direction detection means (to) that calculates the rotational frequency F and one-rotation direction of the induction motor in a free-run state. (13A) is a control circuit section that controls the output of the inverter section (4).

A switching signal from the instantaneous power failure detection restart means (9) causes the control signal generation means Qυ or the free run state detection section a3 to be activated.
It has an output switching means (to) that switches and sets any of the input signals from the phase/three-phase conversion means OD and passes it to the subsequent PWM circuit @, and the other configuration of this control circuit section (13A) is conventional. This is the same as the control circuit section 0 in the example.

In addition, the three-phase/two-phase conversion means (c), the current comparison means (3), which constitute the free run state detection section (10A), @.

Current control means -, (to) and 2-phase/3-phase conversion means OD
and a PWM circuit wire that constitutes the control circuit section (13A).

Free running state of induction motor (5) from inverter section (4) and current detector (6)? It forms the main part of the control signal system to be detected.

Figure 2 shows the free run frequency rotation direction detection means (2).
It is a block diagram showing details of the ripple component frequency fn to be superimposed by inputting the q-axis component vqs of the two-phase voltage command.
A ripple frequency detection means (32 m) for detecting inputs the ripple frequency fn, multiplies it by a proportionality constant r that has been input in advance, calculates the free run frequency F of the induction motor (5), and calculates the free run frequency F corresponding to this frequency F. Free-run frequency calculation means (32b) that outputs a voltage signal, phase comparison means (32c) that inputs the d-axis component vd2 together with the V paste and compares the phase difference between the two, and the phase comparison means (52c). The rotational direction determining means (32d) determines the rotational direction of the induction motor (5) based on the comparison result.

In addition, the free run state detection section (10A), the acceleration/deceleration limiting means +is to the control signal output means t2D and the output switching means (to) of the control circuit section (13A), together with the instantaneous detection restart means (9), etc. The functions of CPU, memory,
It is built on a computer program consisting of input/output interfaces, etc.

Next, the operation of the inverter device shown in FIG. 1 will be explained. When starting the induction motor (5) when the induction motor (5) has completely stopped, the output switching means (to) is controlled by the switching signal from the instantaneous power failure detection restart circuit (9). PWM the output signal of the signal output means Qυ
The switching setting is made so that the input is input to circuit 4.
5) Start and speed control.

Next, after a momentary power outage occurs and the inverter equipment stops,
A description will be given of a case where the induction motor (5) is restarted due to power restoration, or when the induction motor (5) is restarted from a state where it is freely rotating due to an external force when the inverter device is stopped. In the free-run state detection section (10A), current phase command means 4 as a current command section receives a command signal input from the instantaneous detection restart means (9).

A constant, for example, DC signal is output as a current command signal. That is, a two-phase current command, iqs, and its phase angle θ are output. The above current commands are determined by the d-axis current comparison means gradient and the q-axis current comparison means, respectively In the means (to), the three phases are compared with the two-phase currents ids and iqg outputted by the comparison means (e), respectively, and the output deviation signal (id" - ids) is
is input to the d-axis current control means (to) and subjected to PI (proportional/integral) control as the d-axis component ma d2 of the two-phase voltage command.
Further, the deviation signal (1q11-1q11) is input to the q-axis current control means (to), subjected to PI control, and output as the q-axis component Nqs of the two-phase voltage command. The above two-phase voltage command v
d2, vq'? : If the value of the primary resistance per phase of the induction motor (5) is Rs.

is the direct current given by . The above currents iu, iv,
iw is controlled to satisfy the following equation. The above two-phase voltage command v d2
.

vqs is converted into three-phase voltage commands vu, vv, vw by the two-phase/three-phase voltage conversion means 6υ, and is inputted to the PWM circuit ■ via the output switching means (to).
A) outputs a signal to the inverter section (4) to control the output current so that a desired current is output from the inverter section (4) to the induction motor (5). The desired current output from the inverter section (4) is (1
) formula, i.e. id book = Ids, iq = 0゜0
; Calculated by substituting 0.

This current is detected by the t photodetector (6), converted into two-phase currents ids and iqs by the three-phase/two-phase conversion means (to), and negatively returns to the d-axis and q-axis current comparison means and @, respectively. It is surrounded.

The above ids and iqs are calculated by the following formula.

However, from the current phase command means (goods), the DC current command shown in the above (Equation 11, i.e., id%':=Ids
(constant), +qa=0. In the control signal system when θ=0 is input. The two-phase voltage commands va2, vq2, +3) shown in equation (2), the output current of the inverter section (4) and its detected value, the converted two-phase currents ids, iqs, etc. Ripple components due to free run of the induction motor (5) are superimposed,
yd'F= Rs ・Ida shown in the above formula (2)
, vq"= O, iu, i shown in equation (3)
v, iw, etc. indicate their average values.

Next, when the induction motor (5) is in a free running state and a DC command signal is output as the current command signal, the reason why a ripple component is superimposed on the control signal system of the current negative feedback system will be explained.

and a two-phase voltage command vdn belonging to the control signal system.

The ripple frequency and free run rotation frequency that are superimposed on the magnification will be explained.

The equation of state of the induction motor (5) in the a-q coordinate axes is generally expressed by the following equation.

In equation (6).

idr: d-axis secondary current of the induction motor iqr: q-axis secondary current of the induction motor pcdr: rotational angular frequency (4 angles of current) of the induction motor Rs
:Primary resistance per unit Rr:Secondary resistance per unit M:Mutual inductance L+s:Primary self-inductance Lr:Secondary self-inductance σ:Leakage coefficient (σ=1-M2/LsLr)
P: Differential operator. The above equation (6) is converted to pi=Ai+Bvs, where i=[:ids iqs idr i
qr]'vs = (vd+s vqa)τ...(7), and further 1s=ci However, i@= [tda iqa]"...(8
) is expressed in the block diagram shown.

In the above block diagram, since the d-axis and q-axis current control means (to) and (to) perform PI (proportional-integral) control, their transfer function G c (s) is set as follows. However, K
p represents the proportional gain, and T represents the integration time.

The PI control section in the above block diagram, that is, the d axis.

The integral output of the q-axis current control means (c) and (7) is expressed as V = [
[Mad engineering vq engineering] 7 Then, the equation of state of the closed loop system in Figure 1 is expressed by the following equation.

Expressing the current command as I = (i/'iq")"
Then, the control signal system, ie? ! The flow control system is shown in Figure 3. There are six eigenvalues of the -1 fII equation, that is, six closed loop poles, and the free run frequency F of the induction motor (5) is
A pole with a natural frequency close to , that is, a representative characteristic root exists on the imaginary axis, and this generates vibration in the control signal system.9For example, the two-phase voltage command vd2. Superimpose Ripple on the enemy. In addition, the rotational angular frequency pωr of the induction motor (5) and its free run frequency Fpωr are determined by F=-.

2π The above representative characteristic root is expressed in equation 01 as the constant (R
s, Rr, M, Ls, Lr) The set value of the free run frequency F of the induction motor (5), the proportional gain Kp of the current control circuit w, C31), and the integral time T, the system can be found by numerical calculation. , Furthermore, the natural angular frequency ωn of the representative characteristic root is calculated. This ωn is the angular frequency of the ripple superimposed on the above vci2 and vq2, and the ripple frequency fn
=- is generally slightly smaller than the frequency F of the induction motor (5), and differs depending on the constants of the induction motor (5), etc. but.

Since there is a proportional relationship between the free run frequency F and the ripple frequency fn, if the ratio between the two is determined in advance as the proportionality constant r, the above vdn.

By finding the ripple frequency fn superimposed on vqa and multiplying it by the proportionality constant r, the free run frequency F can be easily calculated.

Figures 4 and 5 show the results of an experiment using an actual machine to determine the free run frequency F and rotation direction of the induction motor (5) from the ripple components superimposed on the voltage commands vd'' and vq''. , FIG. 4 shows the case of forward rotation, and FIG. 5 shows the case of reverse rotation.

The actual machine used in the experiment is Mitsubishi 5F-JR type 17Kw 4-pole 3
It is a phase induction motor (rated input voltage 200V), and the above induction motor is free-running at 1800 rpm with zero residual voltage. As a DC current command, id = taiA (rated excitation current) * 'q = 0
Current control is performed by giving 020, and voltage commands such as vd and vq are determined.

However, in the above experiment, we simulated free run re-injection,
Free run state detection was started, and 10 m5 later, the phase angle θ of the current command was reversed from 0 to 1800, and the polarity of the output current of the inverter section (4) was reversed. As a result, the amplitude of the ripple components superimposed on the voltage commands Md and VQ2 increases greatly, and the peak values of these ripple components increase to the above Vd! Average value of 1 Rs-Ids=o, 433(g)xtaff prisoner-,
16(v) is equal to y.

Although the above is an experimental example at a free run frequency of t800 rpm, it was confirmed that even at 150 rpm (5 Hz), a ripple component peak value of 2 to 3 V was obtained.

In addition, in FIGS. 4 and 5, vdR is displayed by subtracting its average [Rs·Ids.

The ripple component is displayed so that it can be easily compared with the ripple component of vqs. In addition, in FIGS. 4 and 5, the waveforms of vq and vd2 and the dashed line A-
Comparing the intersection with the induction motor shown in Figure 4 (
5) When rotation is positive, the ripple component of vd%' is vq
It is 90° ahead of the phase of the ripple component of s, and conversely, in the case of reverse rotation as shown in Figure 5, the phase is delayed by 90° or 2706 times ahead of the above phase, and this phase difference is detected. The direction of rotation of the induction motor can be determined by

The reason why the peak value of the superimposed ripple component increases by reversing the polarity of the output current of the inverter section (4), that is, the input current to the induction motor (5) in the free-running state during the current flow. This is due to the unstable control signal system being subjected to disturbances accompanied by steep current changes.

Next, two-phase voltage command vd2. A specific method for detecting the free run frequency F and rotational direction of the induction motor (5) from the ripple frequency superimposed on "vq" will be described.

The ripple frequency fn superimposed on the above ma d% and maq parable is a
Since it is the natural frequency of the representative characteristic machine of the state equation shown in equation 1, both vd2 and VQ': have the same frequency f
It may be detected from either n or n. However, as a current command (as shown in equation 11 < , fd" = fd
” (constant), when 1qs=o is given, as shown in equation (2), the average value of the above vqs is zero and there is only AC ripple, so it is easy to find the ripple frequency fn.Therefore, the ripple frequency fn is easy to find. Free run state detection section C shown in Figure 2
The above-mentioned vd'' is input to the ripple frequency detection circuit (32a) in 3, and as shown in FIG. 6, the time between the zero crossing points is determined as 1/2 period of the ripple.
Find the ripple frequency fn by calculating backwards. Next, in the free run frequency calculation circuit (32b), the above fn is multiplied by the proportionality constant r (=ωn/ωr) inputted in advance.
Find the free run frequency F of the induction motor (5).

Further, as shown in FIG. 5, the phase difference of the ripples superimposed on the two-phase voltage command ve vq' varies depending on the rotation direction of the induction motor (5).

During forward rotation...the phase of the magnet d2 is 90' ahead of the v tape.When rotating in the opposite direction...the phase of the magnet n is 90 degrees behind the v tape, so the 1st phase comparator circuit (52c) calculates the above Inputs ma d2 and vq', compares ma q honor and (vd2-Rs1d2), finds the deviation, and 1 rotation direction discrimination circuit (S2a)
When vqs changes from negative to positive, vd': -Rs fd2) If 0, it is determined as forward rotation vd 脣 -Rsids (If 0, it is determined as reverse rotation. In addition, in the above, RgfdR is the average value of vd change. (Mad''-Ra i person) indicates the ripple component extracted from vd Homare.

In the above embodiment, the free run frequency F of the induction motor (5)
In the case of detecting the rotation direction, the three-phase output current from the outside of the inverter (4) is detected and converted into the current id@, iqs of the orthogonal two-phase coordinate axis system, and 1 is output by the flow phase command means Q4. Phase current command i intelligence.

The respective deviations from iqs (fd change - 1da), (iq
Parable -1qa) and convert these signals into PI (proportional integral)
control to obtain the two-phase voltage command mad% and vq%, and further
Although the control signal system converts it into a phase voltage command and controls it so that the desired current is output from the inverter section (4) to the induction motor (5), it is not necessarily necessary to perform px control etc. in a two-phase coordinate system. It is not necessary to carry out current control, and the same effect can be obtained even if three-phase current commands are given and current control is carried out using the three-phase coordinates.

Further, in the above embodiment, an example of PI control was shown as the current control, but similar effects can be obtained by performing P (proportional) control, PID (proportional integral, differential) control, or other control.

Furthermore, in the above embodiment, the voltage command vd2. Extract the ripple component superimposed on vqR, and calculate this ripple frequency fn
, and the free run frequency F and the rotation direction from the phase difference between the two phases.However, the extraction of the ripple component is not limited to the voltage commands vdR, vq'', and as long as it is a signal of the control signal system, Any signal may be used.
For example, the detected value of the output current of the inverter section (4) or the two-phase currents ida and iqs obtained by converting these currents.
The effect can also be obtained by extracting the ripple component superimposed on the

First, in the experiment using the actual machine shown in FIGS. 4 and 5 in the above embodiment, the polarity of the output current of the inverter (4) was reversed during the energization when the induction motor (5) was in a free running state.

Although we attempted to increase the amplitude of the ripple component superimposed on the control signal system, the inverter section (
4) Even if the output current is changed rapidly.

This has the effect of increasing the amplitude of the ripple component and making it easier to detect the ripple frequency.

In the above embodiment, the free-run state detection section (10A) constituting the main part of the control signal system is connected to the CPU memory, along with the main part of the control circuit section (1) that outputs the control signal to the inverter section (4). Since the software configuration was built on a computer program consisting of input/output interfaces, etc., an increase in the physical dimensions of the inverter device due to the addition of the above-mentioned free-run state detection section (10A) was prevented. Even when the detection section (IQA) is configured as a hardware together with the control circuit section (13A).

This has the effect of detecting a free running state of the induction motor (5) in which the residual voltage is too small to be detected or does not occur at all.

Although the explanation has been given using an example of direct current as the current command signal, it is only necessary that ripple components can be extracted, and signals other than direct current may also be used.

For example, it is clear from the description of the above embodiments that a low frequency signal or an intermittent signal that outputs a command signal of a substantially constant value for a sufficiently longer period of time than the frequency of the free run state may be used.

〔Effect of the invention〕

As described above, according to the present invention, when the induction motor is in a free running state, a substantially constant current command signal of, for example, DC is applied from the current command section.

Since the ripple component generated in the control signal system is extracted and the rotational state of the induction motor is detected, a method that can detect the free running state of the induction motor without detecting the residual voltage of the induction motor can be obtained. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an inverter device for realizing an embodiment of the present invention, FIG. 2 is a block diagram of free-run frequency 0 rotation direction detection means of the present invention, and FIG. 3 is an induction motor of the present invention. FIG. 4 is a block diagram showing a current control system as a control signal system of the present invention.
, Fig. 5 is a drawing corresponding to Fig. 4 when the induction motor is free-running in the reverse direction, and Fig. 6 shows the voltage when the induction motor of this invention rotates in the forward direction. Command vd2, vq? and the above v
FIG. 7, which is an explanatory diagram for determining the ripple period T from the q change, is a block diagram of a conventional inverter device. In the figure, (1) is a commercial power supply, (2) is a rectifier circuit, (
3) is the smoothing capacitor, (4) is the inverter section, (5)
is an induction motor, (6) is a current detector, (8) is a voltage detector, (9) is an instantaneous power failure detection restart means, (IOA) is a coast-to-coast state detection unit, (1) is a control circuit unit,・M is current phase command means as a current command section, (C) is function generation means, (1) is 3-phase/2-phase conversion means, @ is d-axis current comparison means, @ is q-axis current comparison means, Kan (7) is the d-axis current control means, (7) is the q-axis current control means, and 0υ is the 2-phase/3-phase conversion means. (To) is a free-run frequency 9 rotation direction detection means, (To)
indicates the output switching means. In addition, in FIG. 1, the same reference numerals indicate the same or corresponding parts. Figure 4 Figure 5 N = -1800hiP L

Claims (1)

[Claims] An inverter section that outputs current to the induction motor, a current command section that outputs a current command signal, and a deviation between the current command signal output from the current command section and the detection signal that is the detected value of the output current of the inverter section. a control signal system that controls the output current of the inverter section based on the signal, and outputs a substantially constant command signal as a current command signal from the current command section when the induction motor is in a free run state; A method for detecting a free run state of an induction motor, characterized in that a ripple component generated in the control signal system at this time is extracted, and a rotational state of the induction motor in the free run state is determined.