JPH0824438B2 - Induction motor free-run state detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting a free run state of an induction motor, which is executed at the time of restart of an induction motor by an inverter device, restart of the free run, or commercial switching. Is.

[Conventional technology]

FIG. 7 shows a so-called V / f, which controls the ratio of the output voltage V and the output frequency f to a constant value, which has been conventionally used for speed control of a three-phase induction motor (hereinafter referred to as an induction motor).
A circuit for detecting the rotation frequency and the rotation direction of the induction motor in the free running state is added to the constant control type inverter device.

In the figure, (1) is a commercial power supply that outputs three-phase AC,
(2) is a rectifier circuit that converts input 3-phase alternating current into direct current and outputs it, (3) is a smoothing capacitor, (4) is a self-extinguishing element such as a transistor and is connected in antiparallel with this element It consists of a feedback diode, and DC is
It is an inverter part that converts back to phase AC and outputs it.
An induction motor (5) is connected to the AC output terminals composed of U, V and W phases. (6) is a current detector for detecting the output current of the inverter section (4), (7) is a voltage detector including a transformer or the like for detecting the residual voltage of the induction motor (5) in the free-run state, ( 8) is a voltage detector for detecting the voltage of the commercial power source (1). Reference numeral (9) is an instantaneous power failure detection restarting means, which detects an instantaneous power failure of the commercial power source (1) through the voltage detector (8), and supplies it to a free-run state detection unit (10) described later to induce an induction motor (5). ) Output the command signal to detect the free-run frequency F and the rotation direction, and based on the detection result of the free-run state detection unit (10) instead of starting the induction motor (5) from the stopped state. A switching signal is output to a control circuit section (13) described below so that the free-run state is restarted. (10) is a free-running state detection unit, which receives the command signal from the instantaneous blackout detection restart means (9) and inputs the output signal of the voltage detector (7) to free the induction motor (5). The rotation frequency calculation means (11) calculates the run frequency F and outputs it as a voltage signal, and the rotation direction determination means (12) which determines the rotation direction and outputs a determination signal. (13) is a control circuit section for outputting a control signal of the AC output to the inverter section (4), and a speed command unit (14) for outputting a speed command to the induction motor (5), and by inputting the speed command, Acceleration / deceleration limiting means (1) for gradually increasing and outputting a voltage signal according to the speed command so that the induction motor (5) is slowly started.
5), Frequency switching controlled by the switching signal from the instantaneous blackout detection restart circuit (9) to pass the input signal from either the rotational speed computing means (11) or the acceleration / deceleration limiting means (15). Means (16), V / f conversion means (17) for converting the voltage signal input via the frequency switching means (16) to a frequency f corresponding to this signal and outputting the frequency f, acceleration / deceleration limiting means (15) Based on the voltage signal input from the V / f conversion means (17), a normal voltage pattern output means (1 that outputs a voltage command V for which the V / f ratio is constant with respect to the frequency f output by the V / f conversion means (17) is output.
8) Based on the voltage signal input from the rotation speed calculation means (11), the restart voltage reduction pattern output means (19) that gradually increases until the output voltage reaches the normal V / f ratio, the instantaneous power failure detection re-start Switching control is performed according to the output signal of the starting means (9), and voltage switching means (20) for passing an input signal from either the normal voltage pattern output means (18) or the restart reduced voltage pattern output means (19). ), A control signal output means (21) for outputting a control signal of a three-phase sine wave based on the voltage command input through the voltage switching means (20) and the signal input from the V / f conversion means (17), The control signal of the three-phase sine wave is input and converted into a pulse modulation signal, and the inverter unit (4)
The output signals of the PWM circuit (22) and the current detector (6) that are output to the inverter unit (4) as control signals for controlling the AC output of the inverter are monitored, and if an overcurrent exceeding a predetermined value is detected, the inverter unit The overcurrent detection circuit (23) outputs an alarm signal to the PWM circuit (22) so as to stop or limit the AC output of (4). It should be noted that the instantaneous blackout detection restarting means (9) and the free-run detecting section (1
0) and acceleration / deceleration limiting means (15) of the control circuit section (13)
~ The control signal output means (21) is usually constructed by a computer program having such functions as a CPU, a memory and an input / output interface.

Next, the operation will be described. When starting the induction motor (5) when the induction motor (5) is completely stopped, first, the rotation speed of the induction motor (5) is set by the speed commander (14) and the power source (1) is set. Is turned on, the frequency switching means (16) and the voltage switching means (20)
Are set to be switched to the acceleration / deceleration limiting means (15) and the normal voltage pattern output means (18) by the signal from the instantaneous power failure detection restarting means (9), respectively. By inputting the speed command value, the acceleration / deceleration limiting means (15) outputs a voltage signal gradually increasing from zero to the above speed command value for a predetermined time, and this signal is passed through the frequency switching means (16). Is input to the V / f conversion means (17), converted to the frequency f corresponding to the speed command value, and input to the control signal output means (21). On the other hand, the output signal of the acceleration / deceleration limiting means (15) is the normal voltage pattern output means (1
8) and outputs a voltage command V corresponding to the speed command value, that is, a V / f ratio is constant with respect to the output frequency f of the V / f conversion means (17). Is input to the control signal output means (21) through the voltage switching means (20). The control signal means (21) outputs a three-phase sine wave signal corresponding to the speed command by the input of the frequency f and the voltage command V, and the PWM circuit (22) from the inverter unit (4) to the induction motor (5). The input three-phase sine wave signal is converted into a pulse width modulation signal so that three-phase power of a desired frequency is supplied, and the pulse width modulation signal is output as a control signal of the inverter section (4).

Next, the case where the inverter device is stopped and then restarted by power recovery, or the case where the induction device (5) is started from the state in which the induction motor (5) is freely rotated by external force when the inverter device is stopped is explained. To do.

In the above case, the rotational frequency F of the induction motor (5) in the free running state and the output frequency f of the inverter device need to be approximately matched to each other for reacceleration. The reason is that when the induction motor (5) is in a free-run state at a certain rotation speed F, the frequency f and voltage V of the inverter device are gradually increased to a constant V / f ratio as in normal operation. In addition, when the output frequency f of the inverter device approaches the rotation frequency F of the induction motor (5) from below, a large braking torque due to regenerative braking, and conversely, after passing through the synchronous speed, the acceleration torque causes the induction torque (5) to increase. Occurs in. This gives a large torque shock to the load of the induction motor (5). For example, if the load is a blower, a large impact is given to the drive shaft of the blower, and its life is shortened. Therefore, in the V / f constant control type inverter device, it is necessary to know the frequency F in order to match the output frequency f with the free-run frequency F of the induction motor (5) at the time of starting the tachogenerator. The free-run frequency F is obtained by, for example, providing a speed detector, etc., detecting the residual voltage of the induction motor, and calculating from the frequency component thereof.

In FIG. 7, the residual voltage of the induction motor (5) in the free-run state is detected by the voltage detection transformer (7), and the residual speed is calculated by the rotation speed calculation means (11) in the free-run state detection unit (10). The voltage cycle is obtained, the free-run frequency F is estimated from the reciprocal thereof, and the rotation direction discriminating means (12) detects the phase difference of the residual voltage between two different lines such as U-V and V-W. Then, the rotation direction of the induction motor (5) in the free run state is determined. Even if the instantaneous power failure detection restart circuit (9) detects a momentary power failure of the commercial power source (1) via the voltage detection transformer (8), or even during a normal start, the induction motor (5) is in the free running state. When it is detected by the signal input from the free-run state detecting section (10), the frequency switching means (16) and the voltage switching means (20) are respectively set in the free-run state detecting section (10).
Side and the restarting reduced voltage pattern output means (19) side are switched and set, and when the induction motor (5) is restarted,
The voltage signal according to the rotation frequency F in the free run state and the information on the rotation direction are input to the V / f conversion means (17) through the frequency switching means (16), and the rotation frequency F
Is converted to a frequency f that matches the control signal output means (2
Input to 1). On the other hand, the free-run state detection unit (10)
The output signal from is also input to the restart voltage reduction pattern circuit (19), where the voltage command gradually increases until it becomes the normal voltage V corresponding to the input signal, that is, corresponding to the frequency f. Is converted into the above control signal output means (21)
Is input to. Hereinafter, an output control signal is output from the PWM circuit (22) to the inverter section (4) based on the three-phase sine wave signal output by the control signal output means (21), and the induction motor (5) is in a free-run state. Is started according to its rotation frequency F.

[Problems to be solved by the invention]

According to the conventional method of detecting the free running state of the induction motor, the residual voltage of the induction motor is detected as described above, and the rotation frequency of the induction motor in the free running state is obtained from the reciprocal of the cycle of the residual voltage. Since the phase difference of the residual voltage between the two lines is detected to determine the rotation direction in the free-run state, in order to detect the residual voltage of the induction motor, a dedicated voltage detection device such as a voltage detection transformer is used. However, when the induction motor has a small residual voltage, it is difficult to detect the frequency and phase in the free running state.

The present invention has been made to solve the above problems, and is an induction motor capable of detecting the rotation state of the induction motor in the free-run state without having a voltage detector for detecting the residual voltage of the induction motor. An object is to obtain a method for detecting a free run state of an electric motor.

[Means for solving 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 electric power to the induction motor, a current command section that outputs a current command signal when the induction motor is in a free-run state, and the current command. A control signal system for controlling the output current of the inverter unit based on the deviation signal between the current command signal output from the unit and the detection signal that is the detected value of the output current of the inverter unit, and the induction motor is free. In the run state, the current command section outputs a substantially constant command signal as a current command signal in order to forcibly control the induction motor to flow a current, and at this time, it is generated in the control signal system. The ripple component is extracted, and the rotation speed and the rotation direction, which are the rotation states of the induction motor in the free-run state, are obtained.

[Action]

According to the present invention, when the direct current command signal is output from the current command unit when the induction motor is in the free-run state, the control signal system causes the direct current command signal and the output current of the inverter unit to be output. The output current of the inverter section is controlled based on the deviation signal from the detection signal which is the detection value of R, a ripple component is generated in the control signal system at this time, and the ripple component is extracted to be in the free-run state. The rotation speed and the rotation direction, which are the rotation states of the induction motor, are obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit block diagram of an inverter device for realizing the method of detecting the free running state of the induction motor (5) according to the present invention. In the figure, the same reference numerals as those in the conventional example shown in FIG. Indicates the same or equivalent.

In the figure, (10A) is a free-running state detection unit, which receives a command signal from the instantaneous power failure detection restarting means (9) to input orthogonal two-phase current command signals ids ^* (d-axis component),
iqs ^* (q-axis component) and current phase command means (24) as a current command unit that outputs the phase angle θ of the above ids ^* , iqs ^* ,
Function generating means (25) for outputting sine sin θ and cosine cos θ corresponding to the phase angle θ, and a detection signal iu consisting of three phases of the output current of the inverter section (4) detected and output by the current detector (6) , iv, iw are two-phase current ids (d-axis component), iqs
3-phase / 2-phase conversion means (26) for converting into (q-axis component), the current phase command means (24) and 3-phase / 2-phase conversion means (26)
The d-axis components ids ^* and ids of the two-phase current output by and the q-axis components iqs ^* and iqs are compared, and the deviation signal (ids
^* -Ids) output d-axis current comparison means (27) and deviation signal (iqs ^* -iqs) output q-axis current comparison means (2)
8) A two-phase voltage for inputting the deviation signal from the d-axis current comparing means (27) to increase the amplitude and controlling the output current of the inverter section (4) so that the deviation signal becomes zero. D-axis current control means (2 which outputs the d-axis component vds ^* of the command
9) and similarly, the q-axis current control means (30) for inputting the deviation signal from the q-axis current comparison means (28) and outputting the q-axis component vqs ^* of the two-phase voltage command, the above two-phase voltage command vds ^*. , vqs
^The three-phase / two-phase conversion means (31) for converting ^* into three-phase voltage commands vu ^* , vv ^* , vw ^* , and the above-mentioned two-phase voltage commands vds ^* , vqs ^* are input and superposed on these command voltages. Rotation frequency F of the induction motor in the free-run state by extracting the ripple component
And a free-run frequency for calculating the rotation direction and a rotation direction detecting means (32). Reference numeral (13A) is a control circuit section for controlling the output of the inverter section (4), which is controlled by the switching signal from the instantaneous blackout detection restarting means (9) to generate the control signal generating means (21) or the free running state detecting section (13). ) 2 phases
It has output switching means (33) for switching and setting any of the input signals from the / 3 phase conversion means (31) and passing it to the PWM circuit (22) in the subsequent stage. The configuration is similar to that of the control circuit section (13) in the conventional example.

The three-phase / two-phase conversion means (26), current comparison means (27), (2
8), current control means (29), (30) and 2-phase / 3-phase conversion means (31), PWM circuit (22) constituting the control circuit section (13A), inverter section (4), current It forms the main part of the control signal system that detects the free running state of the induction motor (5) from the detector (6).

FIG. 2 shows the free-run frequency rotation direction detecting means (3
It is a block diagram showing the details of 2), and the frequency fn of the ripple component superimposed by inputting the q-axis component vqs ^* of the two-phase voltage command
And a ripple frequency detecting means (32a) for detecting the
The free-run frequency F of the induction motor (5) is obtained by multiplying by, and the free-run frequency calculating means (32b) for outputting a voltage signal corresponding to this frequency F, the vqs ^* , and the d-axis component
A phase comparison means (32c) for inputting vds ^* and comparing the phase difference between the two, and a rotation direction determination means for determining the rotation direction of the induction motor (5) based on the comparison result by the phase comparison means (32c) ( 32d).

The free-run state detecting section (10A), the acceleration / deceleration limiting means (15) to the control signal outputting means (21) and the output switching means (33) of the control circuit section (13A) are instantaneous detection restarting means (9). At the same time, these functions are built on a computer program consisting of a CPU, memory, I / O interface, and so on.

Next, the operation of the inverter device shown in FIG. 1 will be described. With the induction motor (5) completely stopped,
When starting the induction motor (5), the output switching means (33) outputs the output signal of the control signal output means (21) to the PW in response to the switching signal from the instantaneous blackout detection restart circuit (9).
Switching is set to input to the M circuit (22), and the induction motor (5) is started by the same operation as in the case of the conventional example shown in FIG. 7 to control the speed.

Next, the case where the inverter device is stopped and then restarted by power recovery, or the case where the induction device (5) is started from the state in which the induction motor (5) is freely rotated by external force when the inverter device is stopped is explained. To do. In the free-run state detection section (10A), the current phase command means (24) as the current command section detects the instantaneous power failure and both start means (9).
A constant DC signal, for example, is output as the current command signal by the command signal power from the. That is, the two-phase current command ids ^* ,
About iqs ^* and its phase angle θ Is output. The current commands are respectively compared with the two-phase current ids, iqs output by the three-phase / two-phase comparison means (26) by the d-axis current comparison means (27) and the q-axis current comparison means (28), and output. The deviation signal (ids ^* -ids) is input to the d-axis current control means (29) and PI (proportional / integral) controlled to 2
As the d-axis component vds ^* of the phase voltage command, the deviation signal (iqs
^* -Iqs) is input to the q-axis current control means (30), PI controlled, and output as the q-axis component Nqs ^* of the two-phase voltage command. The above two-phase voltage commands vds ^* , vqs ^* are induction motors (5)
Let Rs be the value of the primary resistance equivalent to 1 of It is controlled so that Two-phase voltage command vds ^* , vqs above
^{* Indicates} 3-phase voltage command vu by 2-phase / 3-phase voltage conversion means (31)
Converted to ^* , vv ^* , vw ^* and output via output switching means (33)
It is input to the PWM circuit (22), and the PWM circuit (22) controls the output current to the inverter unit (4) so that a desired current is output from the inverter unit (4) to the induction motor (5). Output a signal. What is the desired current output from the inverter section (4)? Is the direct current given by. The above currents iu, iv, iw are Equation (1), that is, ids ^* = Ids, iqs ^* = 0, θ =
It is calculated by substituting 0.

This current is detected by the current detector (6), converted into two-phase current ids, iqs by the three-phase / two-phase conversion means (26), and d-axis and q-axis current comparison means (27), (28), respectively. Be negatively fed back to.

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

However, in the case where the direct current command of the direct current represented by the above formula (1), that is, ids ^* = Ids (constant), iqs ^* = 0, θ = 0 is input from the current phase command means (24), the control signal system , The two-phase voltage command vds ^* ,
vqs ^* , the output current of the inverter section (4) expressed by the equation (3) and its detected value, the converted two-phase current ids, iq
The ripple component due to the free run of the induction motor (5) is superimposed on s etc., and vds ^* = Rs shown in the above equation (2)
・ Ids, vqs ^* = 0, and iu, iv, iw, etc. shown in the equation (3) indicate the average value.

Next, in the case where the induction motor (5) is in the free-run state, when the DC command signal is output as the current command signal, the reason why the ripple component is superimposed on the control signal system of the current negative feedback system, and the above The ripple frequency and the free-run rotation frequency superimposed on the two-phase voltage commands vds ^* , vqs ^* belonging to the control signal system will be described.

The equation of state of the induction motor (5) on the dq coordinate axes is generally expressed by the following equation.

In equation (6), idr: d-axis secondary current of induction motor iqr: q-axis secondary current of induction motor pωr: rotational angular frequency (electrical angle) of induction motor Rs: 1 equivalent primary resistance Rr: 1 Considerable secondary resistance M: Mutual inductance Ls: Primary self-inductance Lr: Secondary self-inductance σ: Leakage coefficient (σ = 1-M ² / LsLr) P : Differential operator. Expression (6) above is expressed as P i = Ai + Bvs (7) where i = [ids iqs idr iqr] ^T vs = [vds vqs] ^T , and is = Ci ...... (8) where is = [Ids iqs] ^T If the current command is is ^* = [ids ^* iqs ^* ] ^T , the control signal system, that is, the current control system is represented by the block diagram shown in FIG.

In the above block diagram, d-axis and q-axis current control means (2
Since 9) and (30) are for PI (proportional integral) control, their transfer function Gc (s) is And Where Kp is the proportional gain and T is the integration time.

If the PI controller of the above block diagram, that is, the integrated output of the d-axis and q-axis current control means (29), (30) is v _I = [vd _I vq _I ] ^T , the state equation of the closed-loop system in the diagram is It is shown by the following formula.

There are 6 eigenvalues of Eq. (10), that is, there are 6 closed-loop poles. Of these, the poles with eigenfrequency close to the free-running frequency F of the induction motor (5), that is, the representative characteristic root exists on the virtual axis. ， This generates the vibration of the control signal system,
For example, ripples are superimposed on the two-phase voltage commands vds ^* , vqs ^* . From the rotational angular frequency pωr of the induction motor (5), its free-run frequency F Required at.

The above-mentioned representative characteristic root is the constant (Rs, Rr, M, Ls, Lr) of the induction motor (5) in the equation (10), the set value of the free running frequency F of the induction motor (5), the current control circuit (29), ( If the proportional gain Kp and the integration time T in (30) are given, it can be found by numerical calculation, and the natural angular frequency ωn of the representative characteristic root can also be found by calculation. This ωn is the angular frequency of the ripple superimposed on the above vds ^* and vqs ^*. Is generally slightly smaller than the free-run frequency F of the induction motor (5), and varies depending on the constants of the induction motor (5). However, since there is a proportional relationship between the free-run frequency F and the ripple frequency fn, if the ratio between them is previously obtained as a proportional constant r,
The free-run frequency F can be easily calculated by obtaining the ripple frequency fn superimposed on s ^* , vqs ^* and multiplying it by the proportional constant r.

Figures 4 and 5 relate to the results of an experiment using a real machine to determine the free-run frequency F and the direction of rotation of the induction motor (5) from the ripple component superimposed on the voltage commands vds ^* , vqs ^* . FIG. 4 shows the case of forward rotation, and FIG. 5 shows the case of reverse rotation.

The actual machine used in the experiment was a Mitsubishi SF-JR type 3.7Kw 4-pole 3-phase induction motor (rated input voltage 200V) with zero residual voltage of 1,1800r.
As a direct current command to the above induction motor during free running at pm (Rated excitation current), iqs ^* = 0, θ = 0 are given to control the current, and voltage commands vds ^* , vqs ^*, etc. are obtained.

However, in the above experiment, the free run re-input was simulated, the free run state detection was started, and 10 ms later, the phase angle θ of the current command was inverted from 0 to 180 ° to change the polarity of the output current of the inverter unit (4). Flipped. As a result, the amplitude of the ripple component superimposed on the voltage commands vds ^* , vqs ^* is greatly increased, and the peak values of these ripples are the average value of vds ^* Rs · Ids = Almost equal.

The above is an example of an experiment at a free run frequency of 1800 rpm,
It was confirmed that the peak value of ripple component was 2-3V even at 150 rpm (5 Hz).

In FIGS. 4 and 5, vds ^* is displayed by subtracting its average value Rs · Ids, and its ripple component is displayed so that it can be easily compared with the ripple component of vqs ^* . In addition, in FIGS. 4 and 5, vqs
^When comparing the waveforms of ^* , vds ^* and the intersection of the one-dot chain line A-A ', the ripple component of vds ^{* is} the ripple of vqs ^* when the induction motor (5) shown in FIG. The phase is 90 ° ahead of the phase of the component, and conversely in the case of the reverse rotation shown in Fig. 5, it is 90 ° behind or 270 ° ahead of the above phase. The direction of rotation can be determined.

There is no reason why the peak value of the ripple component to be superimposed increases by reversing the polarity of the output current of the inverter unit (4), that is, the input current to the induction motor (5) in the free-run state, during its energization. This is because the stable control signal system is subjected to a disturbance accompanied by a steep current change.

Next, a specific method of detecting the free running frequency F and the rotation direction of the induction motor (5) from the ripple frequency superimposed on the two-phase voltage commands vds ^* , vqs ^* will be described. Vds ^* , above
Since the ripple frequency fn superimposed on vqs ^* is the natural frequency of the representative characteristic root of the equation of state shown in equation (10), vds
Both ^* and vqs ^{* have} the same frequency fn and may be detected from either. However, when ids ^* = Ids ^* (constant) and iqs ^* = 0 are given as the current command as shown in equation (1), the average value of vqs ^* is zero as shown in equation (2), Since it is only AC ripple, the ripple frequency fn is easy to find. Therefore, the ripple frequency detection circuit (32a) in the free-run state detection unit (32) shown in FIG.
On the other hand, by inputting vds ^* , the time between the zero-cross points is obtained as a half cycle of the ripple and the ripple frequency fn is calculated by back calculation as shown in FIG. Next, in the free-run frequency calculation circuit (32b), the above-mentioned fn is multiplied by the proportional constant r (= ωn / ωr) input in advance to obtain the free-run frequency F of the induction motor (5).

Furthermore, two-phase voltage command vds ^*, the phase difference of Ritsupuru superimposed on Vqs ^* varies by the rotation direction of the induction motor (5) as shown in FIG. 5, 90 forward rotation ... vds ^* against Vqs ^*゜ Leading phase Reverse rotation: vds ^* is 90 degrees behind vqs ^* , so input vds ^* and vqs ^* to vqs ^* and (vds ^* -Rsids in phase comparator (32c). ^* ) To obtain the deviation, and the rotation direction discriminating circuit (32d)
When vds ^* -Rsids ^* > 0 when s ^* changes from negative to positive, it is determined to be positive rotation if vds ^* -Rsids <0. Incidentally, RSIDs ^* is the mean value of vds ^* in the above (vds ^* -Rsids ^*) indicates a Ritsupuru component extracted from vds ^*.

In the above embodiment, when the free running frequency F and the rotation direction of the induction motor (5) are detected, the three-phase output current outside the inverter (4) is detected and converted into the currents ids, iqs of the orthogonal two-phase coordinate axis system. Current phase command means (24)
There outputs two-phase current commands ids ^*, iqs ^* and the respective deviations ^{(ids *, ids), (} iqs * -iqs) look, these signals PI (proportional integral) control to 2-phase voltage command vds ^* , Vqs ^*
The control signal system that controls the output of the three-phase voltage command to output the desired current from the inverter unit (4) to the induction motor (5) is not always required. It is not necessary to carry out current control such as PI control, and the same effect can be obtained by giving current commands for three phases and performing current control with the three-phase coordinates unchanged.

Further, in the above embodiment, the example of the PI control is shown as the current control, but the same effect can be obtained by performing the P (proportional) control, the PID (proportional integral, differential) control, or any other control.

Further, in the above embodiment, the ripple component superimposed on the voltage commands vds ^* , vqs ^* was extracted, and the free-run frequency F and the rotation direction were detected from the ripple frequency fn and the phase difference between the two phases. Extraction is voltage command vds
It is not limited to ^* , vqs ^* , but when the induction motor is in a free-run state, it is almost constant as a current command signal from the current command section in order to force the current to flow to the induction motor. Any signal may be used as long as it is a signal of the control signal system in the state of outputting the command signal of, for example, by converting the detected value of the output current of the inverter unit (4) or these currents. The effect can be obtained even by extracting the ripple component superimposed on the obtained two-phase current ids, iqs.

Further, in the experiment by the actual machine shown in FIG. 4 and FIG. 5 in the above-mentioned embodiment, by reversing the polarity of the output current of the inverter (4) in the free running state of the induction motor (5) during energization, Although the amplitude of the ripple component superimposed on the control signal system is increased, the amplitude of the ripple component is increased even if the output current of the inverter unit (4) is sharply changed without reversing the polarity. This has the effect of facilitating the detection of ripple frequency.

In the above embodiment, the free-run state detecting section (10A) that constitutes the main part of the control signal system is provided together with the main part of the control circuit section (13A) that outputs the control signal to the inverter section (4).
Since the software configuration was built on the computer program consisting of CPU memory, input / output interface, etc., the physical size of the inverter device was prevented from increasing due to the addition of the free-run state detection unit (10A). Even when the above free-run state detection unit (10A) is configured with the control circuit unit (13A) as a hardware configuration, the free-run state of the induction motor (5) is so small that residual voltage cannot be detected or does not occur at all. There is a detectable effect.

Although the example of direct current is used as the current command signal, this is only necessary if the ripple component can be extracted.
Signals other than DC are also possible.

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

〔The invention's effect〕

As described above, according to the present invention, when the induction motor is in the free-run state, a substantially constant, for example, direct current command signal is given from the current command section to extract the ripple component generated in the control signal system, Since the rotation state of the induction motor is detected, there is an effect that a method of detecting the free running state of the induction motor can be obtained without detecting the residual voltage of the induction motor.

[Brief description of drawings]

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 a free-run frequency and a rotation direction detecting means of the present invention, and FIG. 3 is an induction motor of the present invention. A block diagram showing a current control system as a control signal system, FIG. 4 shows the induction motor of the present invention in the forward direction.
FIG. 5 is a diagram showing ripple waveforms superimposed on voltage commands vds ^* , vqs ^* during free running at 1800 rpm, FIG. 5 is a diagram corresponding to FIG. 4 when the induction motor is free running in the reverse direction, and FIG. 6 is the present invention. FIG. 7 is a block diagram of a conventional inverter device for explaining the phase relationship between the voltage commands vds ^* and vqs ^* when the induction motor is rotating forward and the ripple cycle T from vqs ^* . In the figure, (1) is a commercial power supply, (2) is a rectifier circuit,
(3) is a smoothing capacitor, (4) is an inverter part,
(5) is an induction motor, (6) is a current detector, (8) is a voltage detector, (9) is an instantaneous power failure detection restarting means, (10A) is a free-run state detection unit, and (13A) is a control circuit. Section, (24) current phase command means as current command section, (25) function generating means, (26) three-phase / two-phase converting means, (27) d-axis current comparing means, (28) q-axis current comparison means, (29) d-axis current control means, (30) q-axis current control means, (31) two-phase
The / 3 phase conversion means, (32) shows the free-run frequency, rotation direction detection means, and (33) shows the output switching means. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An inverter unit for outputting electric power to an induction motor, a current command unit for outputting a current command signal when the induction motor is in a free-run state, and a current command signal output from the current command unit. A control signal system that controls the output current of the inverter unit based on a deviation signal from the detection signal that is the detection value of the output current of the inverter unit,
When the induction motor is in the free run state,
In order to forcibly control the induction motor to flow a current, a substantially constant command signal is output from the current command unit as a current command signal, and the ripple component generated in the control signal system at this time is extracted. A method for detecting a free-run state of an induction motor, comprising: determining a rotation speed and a rotation direction of the induction motor in a free-run state.