Description Title of Invention: ELEVATOR CONTROL DEVICE
Technical Field
[0001] The present invention relates to an elevator control device, and more particularly, to an elevator control device, which is configured to reduce a start shock, which occurs when an elevator starts running.
Background Art
[0002] In general, in a rope type elevator, a car and a counterweight are suspended with a rope via a sheave connected to a motor. At rest, the car is held stationary by a brake, but when starting to run, the car raises and lowers by opening a brake and rotating the sheave by the motor.
[0003] At this time, along with the opening of the brake, an unbalance torque, which is a difference in weight between the car and the counterweight, is transferred to the motor via the sheave. In view of speed control of the motor, the unbalance torque acts as step-like disturbance. Therefore, when a brake is opened under a state in which a motor torque is zero, the motor (sheave) is affected by the step-like disturbance, and a variation in acceleration (hereinafter referred to as "start shock") of the car and rollback of the car occur. The start shock and the rollback deteriorate ride comfort, and hence countermeasures are required.

[0004] In view of the above, in order to reduce the start shock and the rollback of the car, there is generally adopted a start control method involving detecting a live weight of the car, estimating the unbalance torque, and further generating, by the motor, a torque (torque offset current) for canceling the unbalance torque, to thereby open a brake.
[0005] This method requires a load detection device for detecting the live weight of the car, and leads to an increased cost. Further, it is required to mount and adjust the load detection device at the time of installation.
Therefore, there has been proposed a control method for reducing a start shock and rollback without using the load detection device (see Patent Literature 1, for example).
In Patent Literature 1, angle information of a motor encoder is subjected to second-order differentiation to obtain angular acceleration information, and an unbalance torque at startup is further calculated with the use of information on a total inertia moment (total sum of moments of inertia of car, sheave, counterweight, rope, and the like) applied on a motor. The calculated unbalance torque is used as a torque bias command value and added to a torque command value to control a motor configured to drive an elevator.
Citation List Patent Literature

[0006] [PTL 1] JP 2005-132541 A
Summary of Invention Technical Problem
[0007] In the related-art elevator control device, the encoder information of the motor is quantized, and hence when differentiation is performed under an environment that is discretized by calculation means, for example, a microcomputer, there is a problem in that a value of discretization timing is significantly miscalculated.
[0008] To address the above-mentioned problem, in Patent Literature 1, the differentiation is performed not at intervals of the motor encoder but for every predetermined number of encoder pulses.
Therefore, a rollback amount becomes several millimeters to ten millimeters in principle, and when the unbalance torque is large, there has been a problem in that the start shock and the rollback of the car are not sufficiently reduced.
[0009] The present invention has been made to solve the above-mentioned problems, and therefore has an object to provide an elevator control device, which is capable of stably reducing a start shock and rollback of a car by estimating and correcting, in a short period of time, an unbalance torque after a brake is opened.

Solution to Problem
[0010] In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided an elevator control device, including: a current detection unit configured to detect a drive current of a motor configured to drive a sheave to rotate, the sheave having a car and a counterweight suspended therefrom with a rope; a speed calculation unit configured to output a speed signal of the motor based on an output from a rotation amount detection unit configured to detect a rotation amount of the motor; a speed command generation unit configured to generate a speed command signal for the motor; a speed control unit configured to output a torque current command signal based on the speed command signal and the speed signal; a current control unit configured to drive the motor so that the drive current responds to the torque current command signal; an unbalance torque estimator configured to estimate an unbalance torque, which is a difference in weight between the car and the counterweight, based on the drive current or the torque current command signal and the speed signal; a switching unit configured to select whether to output, as a torque offset current command signal, a signal obtained by adding an output signal from the unbalance torque estimator and a value proportional to the speed signal, or the output signal from the unbalance torque estimator after a brake configured to brake rotation of the motor is released; and an addition unit configured to add the torque offset current command signal, which is output

from the switching unit, to the torque current command signal to be input to the current control unit.
Advantageous Effects of Invention
[0011] According to the present invention, the unbalance torque, which is the difference in weight between the car and the counterweight, is estimated by the unbalance torque estimator based on a motor drive current or the torque current command signal of the motor and a detected speed signal of the motor, and the elevator control device includes: the switching unit configured to select whether to output, as the torque offset current command signal, a signal obtained by adding the estimated unbalance torque and a value proportional to the speed signal, or to output, as the torque offset current command signal, the estimated unbalance torque after the brake configured to brake rotation of the motor is released; and the addition unit configured to add the torque offset current command signal, which is output from the switching unit, to the torque current command signal to be input to the current control unit. Therefore, even in a case where there is an unbalance torque when the brake is opened, the elevator can be started under a stable state by accurately estimating and correcting the unbalance torque in the short period of time, and car vibration can be suppressed and sped up in convergence, with the result that there is provided an effect that the rollback can be stably reduced.

Brief Description of Drawings
[0012] FIG. 1 is a block diagram for illustrating an elevator control device according to a first embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram obtained by modeling a disturbance observer illustrated in FIG. 1.
FIG. 3 is a block diagram for illustrating a configuration of a pass/hold switching unit illustrated in FIG. 1.
FIG. 4 is a complex plane graph for showing movement of pole assignment of the disturbance observer illustrated in FIG. 1 and FIG. 2.
FIGS. 5 are waveform graphs, in which FIG. 5 (b) is waveform graphs for showing effects obtained when feedback control is performed using an estimated disturbance signal as a torque offset current signal in the elevator control device according to the first embodiment of the present invention, and FIG. 5 (a) is waveform graphs without the above-mentioned feedback control.
FIGS. 6 are waveform graphs, in which FIG. 6 (b) is waveform graphs for showing effects of speed feedback control in the elevator control device according to the first embodiment of the present invention, and FIG. 6 (a) is waveform graphs without the above-mentioned speed feedback control.
FIGS. 7 are waveform graphs, in which FIG. 7 (b) is waveforms for showing effects of the change in pole assignment of the disturbance observer in the elevator control device according to

the first embodiment of the present invention, and FIG. 7 (a) is waveform graphs without the change in pole assignment.
FIG. 8 is a specific time axis waveform graph of the change in pole assignment of the disturbance observer illustrated in FIG. 1 and FIG. 2.
FIGS. 9 are waveform graphs, in which FIG. 9 (b) is waveform graphs for showing effects obtained by holding a waveform of the torque offset current signal illustrated in FIG. 1, and FIG. 9 (a) is waveform graphs without the above-mentioned holding of the waveform.
FIGS. 10 are enlarged time axis graphs of FIGS. 9, and are waveform graphs for showing a timing to hold the waveform.
FIG. 11 is a block diagram for illustrating an elevator control device according to a second embodiment of the present invention.
FIG. 12 is an equivalent circuit diagram obtained by modeling a disturbance observer illustrated in FIG. 11.
FIGS. 13 are time axis waveform graphs for showing a difference in behavior depending on a timing to stop speed feedback control in a third embodiment of the present invention.
FIG. 14 is a block diagram for illustrating a configuration of a pass/hold switching unit in the third embodiment of the present invention.
FIGS. 15 are graphs for showing a timing to change a magnification of a speed feedback gain in the third embodiment of

the present invention.
FIG. 16 is an equivalent circuit diagram obtained by modeling a disturbance observer in a fourth embodiment of the present invention.
FIG. 17 is a time axis waveform graph for specifically showing a change in cutoff frequency of a band-limiting filter in FIG. 16.
Description of Embodiments
[0013] Now, an elevator device according to each embodiment of the present invention is described in detail with reference to the accompanying drawings.
[0014] First Embodiment
In an elevator control device according to a first embodiment of the present invention, which is illustrated in FIG. 1, a sheave 2 is connected to a rotary shaft of a motor 1. A rope 3 is hung around the sheave 2 , which has one end from which a car 4 is suspended, and another end from which a counterweight 5 is suspended via the rope 3. On the motor 1, a pulse encoder 11 configured to detect an angle is mounted, and speed control, which is to be described below, is executed on the basis of the angle information. A detected motor angle signal, which is an output of the pulse encoder 11, is input to a speed calculation unit 12.
[0015] The speed calculation unit 12 has a function of converting the detected motor angle signal into an angular velocity signal of the motor 1 to output a speed signal co. Processing of

subtracting the speed signal co from a speed command signal co_ref, which is an output of a speed command generation unit 13, is performed by a subtraction unit 14 to obtain a speed error signal co_err. This speed error signal co_err is input to a speed control unit 15, and the speed control unit 15 outputs a speed control signal iq_co_cont, which is a result of performing proportional (P) , integral (I), differential (D) calculation such that the speed control provides stable and predetermined performance. [0016] An addition unit 16 is configured to generate a torque current command signal iq_t*, which is obtained by adding the speed control signal iq_co_cont and a torque offset current signal iq_t*_off, which is to be described later. The torque current command signal iq_t* is input to a current control unit 9. The current control unit 9 is configured to perform control such that a motor drive current signal iq from a current detection unit 10 becomes the torque current command signal iq_t*, which is input from the addition unit 16. Therefore, the current control unit 9 supplies such the motor drive current iq as to become the torque current command signal iq_t* to the motor 1.
With the above-mentioned configuration, there is achieved a
speed control system, which functions so that the speed co of the
motor 1 responds to the speed command signal co_ref with the speed
error signal co_err being a predetermined value or less.
[0017] A brake 6 has states of braking and brake releasing
(hereinafter referred to as "opening") with respect to the motor

1, and is shifted in state with a brake control command signal BK_cont from a controller 7 via a brake control unit 8. When the car 4 is moved from the current floor to a predetermined floor, the brake 6 is shifted from a braking state to an open state, and the above-mentioned speed control system is further shifted from an OFF state to an ON state at a brake opening timing. The speed command signal co_ref at the time when the speed control system is shifted to the ON state is set to zero.
[0018] When a torque difference from both ends of the rope 3, which is hung around the sheave 2, is zero, a torque from the rope 3, which is applied to the sheave 2 when the brake 6 is opened, is matched, and hence there is no start shock or rollback. [0019] When there is the torque difference (hereinafter referred to as "unbalance torque") from the both ends of the rope 3, which is hung around the sheave 2, the torque from the rope 3, which is applied to the sheave 2 when the brake 6 is opened, is not matched, which is equivalent to so-called "step-like disturbance" acting for the speed control system. As a result, the rollback and the start shock occur, and car vibration occurs in some cases in a period until a response operation of the speed control system becomes static.
[0020] As countermeasures for the rollback and the start shock, a disturbance observer 17 configured to estimate the unbalance torque and a pass/hold switching unit 18 are provided. The pass/hold switching unit 18 generates the torque offset current signal

iq_t*_off on the basis of the unbalance torque estimated by the disturbance observer 17, the torque offset current signal iq_t*_off which has a function of generating a torque for canceling the unbalance torque.
[0021] The torque offset current signal iq_t*_off is generated as follows.
First, a method of estimating the unbalance torque is described.
The unbalance torque is estimated by the disturbance observer 17. The disturbance observer 17 receives the motor drive current iq and the speed signal co as inputs, and outputs an estimated disturbance signal Di^. Moreover, this is a configuration in which pole assignment, which is a parameter that determines an estimated frequency characteristic (disturbance estimation band) of the disturbance observer 17, is changed by the brake control command signal BK_cont.
[0022] In FIG. 2, an equivalent circuit obtained by modeling the disturbance observer 17 is illustrated, and the disturbance observer 17 corresponds to a portion enclosed by a dotted line. Blocks 200 to 203 are obtained by modeling and expressing the current control unit 9, the motor 1, and the sheave 2 of FIG. 1 by transfer functions, in which a coefficient KT of the block 200 indicates a force constant for converting the motor drive current iq into a torque, and Di is an unbalance torque, which is transferred from the rope 3 hung around the sheave 2, and which is applied to the

motor 1 as the step-like disturbance when the brake 6 is opened. [0023] In the block diagram, the block 201 expresses addition of the unbalance torque Di. In the block 202, 1/J indicates an amount with which the torque is converted into an angular acceleration, and J is defined by a sum of a moment of inertia of the motor 1 and a moment of inertia of the sheave 2. The block 203 is an integrator configured to convert the angular acceleration into an angular velocity. A block 204 is obtained by modeling the pulse encoder 11 and the speed calculation unit 12 illustrated in FIG. 1, and is obtained by modeling an encoder resolution characteristic of the pulse encoder 11 and a calculation characteristic for calculating the angular velocity co based on the speed calculation unit 12.
[0024] The disturbance observer 17 is a disturbance observer of a minimum-order type, has the above-mentioned blocks 200 to 203 as internal models, and is configured to define the unbalance torque Di as a state to be able to estimate the unbalance torque Di. The configuration of the disturbance observer 17 may be of a full-order type. A block 171 is obtained by modeling the block 200 as a coefficient Kin corresponding to the coefficient KT, a block 172 is an addition block, a block 173 gives a coefficient having a coefficient Jn, which is obtained by modeling the sum J of the moment of inertia of the motor 1 and the moment of inertia of the sheave 2, and an eigenvalue X(t) of the disturbance observer as parameters, a block 174 is a first-order low-pass filter having the eigenvalue

X(t) as a parameter, and a block 175 is an addition block. The eigenvalue X(t) is defined as a time-dependent function, and corresponds to the above-mentioned pole assignment. [0025] In an internal configuration of the pass/hold switching unit 18 illustrated in FIG. 3, the estimated disturbance signal Di^ is multiplied by a reciprocal of the coefficient Kin in a coefficient block 181 to be input to a sample-and-hold unit 182 and input to an addition block 185 . The speed signal co is multiplied by a in a coefficient block 184 to be input to the addition block 185, and a result of being added to the output of the coefficient block 181 is given as one input signal of a switch unit 183. [0026] Signal holding control of the sample-and-hold unit 182 and switch changeover control of the switch unit 183 are performed on the basis of a signal obtained by delaying the brake control command signal BK_cont by a predetermined time (Tl) in a delay unit 186 . An output of the switch unit 183 is output as the torque offset current signal iq_t*_off to the addition unit 16 illustrated in FIG. 1.
[0027] With the above-mentioned configuration, there is achieved a switching function for selecting, by the switch unit 183, whether to use, as the torque offset current signal iq_t*_off, a signal A obtained by adding, by the addition block 185, a signal obtained by multiplying the estimated disturbance signal Di^ by 1/Kin and a signal obtained by multiplying the speed signal co by a, or a signal B obtained by sampling and holding, by the

sample-and-hold unit 182, the signal obtained by multiplying the estimated disturbance signal Di^ by 1/Kin at a timing that is delayed, by the delay unit 186, from the brake opening timing in accordance with the brake control command signal BK_cont by the predetermined time (Tl).
[0028] The selection by the switch unit 183 is performed by a signal obtained by delaying, by the delay unit 186 , a brake opening signal in accordance with the brake control command signal BK_cont by the predetermined time (Tl) . Therefore, the pass/hold switching unit 18 has the function of selecting, by the switch unit 183, whether to pass, for the predetermined time (Tl) from the brake opening, the signal A obtained by adding the signal obtained by multiplying the estimated disturbance signal Di^ by 1/Kin and the signal obtained by multiplying the speed signal co by a, or the signal B obtained by sampling and holding the signal obtained by multiplying the estimated disturbance signal Di^ by 1/Kin at the timing that is delayed, by the delay unit 186, from when the brake is opened in accordance with the brake control command signal BK_cont by the predetermined time (Tl).
[0029] A basic configuration of the present invention has been described above. Now, meanings and effects of this configuration are described.

A pole (eigenvalue) of the disturbance observer 17 is the time-dependent function X(t) . A disturbance estimation

characteristic of the disturbance observer 17 is determined by assignment of the pole on a complex plane.
[0030] In the first embodiment, the disturbance observer 17 is required of function as an unbalanced torque estimator. Therefore, it is required to estimate the unbalance torque Di, which acts as step disturbance when seen from the speed control system, accurately and at high speed. The estimation characteristic of the disturbance observer 17, which is configured to estimate the unbalance torque Di, may be set to a wide band within a range that is allowed by stability of the system. In other words, in the first embodiment, the eigenvalue X(t) of the disturbance observer 17 is assigned, as shown in FIG. 4, to a point XI on a real axis that is far from an origin 0 in a left half of the complex plane. [0031]
In FIG. 5 (b) , in order to observe the effects obtained when only feedback control with the estimated disturbance signal Di^ in the first embodiment is performed, there is shown a result of setting a coefficient a of the coefficient block 184 of the pass/hold switching unit 18 to zero in FIG. 3, and further disabling the sample-and-hold unit 182 and the switch unit 183 so as to set only the signal obtained by multiplying the estimated disturbance signal Di^ by 1/Kin as the torque offset current signal iq_t*_off.
For comparison, a waveform without the feedback control with the estimated disturbance signal Di^ is also shown in FIG. 5 (a) .

[0032] In each of FIG. 5 (a) and FIG. 5 (b) , an upper waveform indicates a variation with time of a car acceleration, and a lower waveform indicates the estimated disturbance signal ( = torque offset current signal). As shown in FIG. 5 (a), without the feedback control with the estimated disturbance signal Di^, when the brake is opened, a peak occurs in the car acceleration, and it can be seen that a large start shock occurs. Moreover, rollback as large as about 4 cm occurs.
[0033] When the feedback control with the estimated disturbance signal Di^ is performed, as shown in FIG. 5 (b), a step-like waveform simulating the unbalance torque Di is applied as the torque offset current signal iq_t*_off, with the result that the start shock after the brake is opened is significantly reduced, and that a rollback amount is also reduced to less than 1 mm.
[0034] However, car acceleration vibration (upper side) after the brake is opened continues, and is problematic in terms of ride comfort. This is ascribable to the fact that, although the disturbance observer 17 has the function of estimating mechanical resonance of the car 4 and the counterweight 5 (caused by elasticity in a stretching direction of the rope 3) as disturbance, resonant vibration of the car 4 is not observed and cannot be controlled. A countermeasure against the resonant vibration is taken by a change in pole assignment, which is to be described later.
[0035]
In FIG. 6 (a) and FIG. 6 (b) , there are shown waveforms for

describing the effects of reducing the start shock, which occurs when the feedback control with the estimated disturbance signal Di^ is performed, by speed feedback control.
In FIG. 6 (a), there are shown waveforms under the same conditions as those of FIG. 5 (a) , which are displayed in enlargement in a vertical axis direction. In FIG. 6 (b) , there are shown waveforms in a case where a of the coefficient block 184 is set to a predetermined value (in this case, -16 times) . It can be seen that an amplitude (start shock) of the car acceleration is reduced with the feedback of the speed co, but persistent vibration remains. Moreover, the torque offset current signal iq_t*_off, which is macroscopically a step-like waveform, is also a waveform on which high-frequency vibration is superimposed. [0036]
In FIG. 7 (a) and FIG. 7 (b) , there are shown waveforms for describing the effects in a case where the assignment of the pole (eigenvalue) of the disturbance observer 17 in the complex plane is changed with time.
In FIG. 7 (a), there are shown waveforms under the same conditions as those of FIG. 6 (a) and in a case where the pole of the disturbance observer 17 is fixed to XI in FIG. 4, and the large start shock occurs. In FIG. 7 (b) , there are shown waveforms in a case where the pole of the disturbance observer 17 is moved to (3X1 after TO [sec] from the brake opening timing as shown in FIG. 8. In this example, (3 is a coefficient that is 0 or more and less

than 1, and it is shown that (3X1 is obtained by moving XI to the origin side on the real axis in the left half (lower half in FIG. 8) of the complex plane.
[0037] In FIG. 8, there is shown the waveform for showing an example of a time-axis characteristic of the eigenvalue X(t) of the disturbance observer 17. The eigenvalue X(t) in FIG. 8 is defined as the following expressions.
[0038] When 0
In FIG. 9 (a) and FIG. 9 (b) , there are shown waveforms for showing the effect of sampling and holding the waveform by the sample-and-hold unit 182 in the torque offset current signal iq_t*_off.
In FIG. 9 (a), there are shown waveforms under the same conditions as those of FIG. 7 (b), which are the same waveforms as those of FIG. 7 (b) , and are waveforms in a case where the sampling and holding of the waveform of iq_t*_off is not performed. In FIG. 9 (b), there are shown waveforms when the sampling and holding of iq_t*_off is performed. The sampling and holding of the waveforms is performed after the delay time Tl [sec] from the brake opening timing by the delay unit 186. This delay time Tl is selected as a timing at which iq_t*_off takes a converged value of a step-like waveform.
[0042] In FIG. 10 (a) and FIG. 10 (b) , there are shown waveforms obtained by enlarging the time axis of FIGS. 9. A relationship between the timing (TO) of the change in pole assignment and the timing (Tl) of sampling and holding the waveform is additionally shown.
[0043] As described above, the predetermined time TO at which the pole (eigenvalue) is moved from the brake opening timing has a function of suppressing a vibration component of iq_t*_of f, which

has been vibrating. Therefore, it is desirable that the delay time Tl be set to a timing after the vibration is suppressed at TO. A relationship between TO and Tl in this case is expressed as the following expression.
T1>T0 Expression (2)
[0044] As shown in FIG. 9 (b) , the torque offset current signal iq_t*_off is sampled and held after the time Tl from the brake opening timing, and the amplitude of the car acceleration is reduced. Moreover, it can be observed that the vibration converges, and that the low-frequency vibration is eliminated. [0045] initialization of Output of Disturbance Observer>
It is required for the disturbance observer 17 to function as an estimator for the unbalance torque Di. The disturbance observer 17 includes the integral element (block 174) therein as illustrated in FIG. 2, and hence holds past information. Therefore, when the brake 6 performs braking after the car is moved, and when previous information remains in the integral element at next startup, accurate estimation is inhibited.
[0046] In order to avoid the above-mentioned situation, when the brake 6 performs the braking operation after the car 4 is moved, outputs of the disturbance observer 17 and the pass/hold switching unit 18 may be initialized.
When the initialization is performed before the startup, the disturbance observer 17 can estimate the unbalance torque Di accurately, and an accurate torque offset current signal iq_t*_off

is output, with the result that the start shock and the rollback can be suppressed to low levels.
[0047] With the above-mentioned configuration, with the disturbance observer 17 estimating the step-like unbalance torque, which acts on the speed control after the brake is opened, at high speed and with accuracy, and by generating and feeding back the torque offset current signal on the basis of the estimated disturbance signal Di*", the speed signal co, and the brake control command signal in order to cancel the unbalance torque, the start shock and the rollback amount can be suppressed to the low levels. [0048] Second Embodiment
In the first embodiment described above, the motor drive current signal iq has been used as the input signal to the disturbance observer 17, but the torque current command signal iq_t* may be used instead as illustrated in FIG. 11. With this configuration, the calculation of the disturbance observer 17 consists only of internal signals in the calculation unit, and hence the system can be built more simply.
[0049] The disturbance observer 17 in this case is as illustrated in FIG. 12. The configuration is the same as in the first embodiment, which is illustrated in FIG. 1 and FIG. 2, except that an input signal to the disturbance observer 17 is changed from the motor drive current signal iq to the torque current command signal iq_t*, and effects similar to those of the first embodiment are also obtained.

[0050] In the first and second embodiments described above, the disturbance observer 17 is described and explained as an analog system, but may be digitized and formed using a digital computing element, for example, a digital signal processor or a microcomputer.
[0051] Third Embodiment
A third embodiment of the present invention enables operation with higher performance and stability by limiting a timing to end speed feedback control.
[0052] Specifically, in FIG. 1, the speed of the motor 1 is determined by inputting detected information of the pulse encoder 11, which is configured to detect a rotation angle of the motor 1, to the speed calculation unit 12. This pulse encoder 11 is configured to perform the detection by outputting a waveform of one pulse every time the rotation angle of the motor 1 takes a predetermined value. With this configuration, when a rotation speed of the motor 1 becomes lower, that is, when the change in rotation angle becomes slower, a pulse detection period of the pulse encoder 11 becomes longer. Therefore, a period at which the detected motor angle signal, which is the input signal to the speed calculation unit 12, is detected and updated becomes longer, and hence a detection time delay occurs for the speed signal co, which is the output of the speed calculation unit 12.
[0053] Then, when the speed of the motor 1 approaches zero, the detection time delay of the speed signal co becomes larger, and stability of the speed feedback control on the basis of the speed

signal co may be lost. This tendency becomes more significant as a speed feedback gain (absolute value of a of the coefficient block 184 illustrated in FIG. 3) is set larger. Meanwhile, there is a relationship in which, as the speed feedback gain is set larger, a start shock becomes smaller, and the stability and the start shock have had a trade-off relationship.
Therefore, in the third embodiment, a description is given of a configuration in which the stability and the suppression of the start shock are both achieved.
[0054] In FIG. 13 (a) , there are shown, in order to reduce the start shock immediately after the brake is opened, transient behaviors in a case where the speed feedback gain is set to be large in the configuration described in the first or second embodiment of the present invention. From the waveform at the top, time axis waveforms of the car acceleration, the torque offset current signal, and the motor speed co are shown.
[0055] Although the car acceleration immediately after the brake is opened is suppressed to be small, the amplitude of the car acceleration is increased in a period from the brake opening timing to TO, which is the timing to move the pole. This is because, as shown in the waveform at the bottom in FIG. 13 (a), the motor speed co becomes zero and the speed feedback control is destabilized, with the result that the motor speed co vibrates, and that the torque offset current signal iq_t*_off also vibrates. [0056] Those vibrations are the result of the stability of the

control being lost because the speed of the motor 1 becomes lower, and hence because the detection time delay of the motor speed co becomes larger. Therefore, as a countermeasure for the vibrations, the speed feedback control may be stopped before the stability of the control is lost. Therefore, in the third embodiment, there is adopted a configuration in which the speed feedback control is stopped at a timing at which the speed co of the motor 1 is converged to around zero.
[0057] The configuration of the pass/hold switching unit 18 in the third embodiment, which is illustrated in FIG. 14, is different from the configuration described with reference to FIG. 3 in the first or second embodiment of the present invention in a signal path of the speed signal co.
[0058] Specifically, the speed signal co is multiplied, by the coefficient block 184, by a to be input to a second switch unit 187. The second switch unit 187 is turned ON/OFF with an output signal from a second delay unit 188.
[0059] In FIGS. 15, there are shown time waveforms for showing a relationship between a delay amount T2 of the second delay unit 188 and the delay amount TO that determines the timing to move the pole of the disturbance observer 17. An input to the second delay unit 188 is the brake control command signal BK_cont and is a signal delayed from the brake opening timing by TO as shown in FIG. 15 (a) . [0060] The second switch unit 187 outputs, as shown in FIG.

15 (b) , the speed signal co having a gain a of the coefficient block 184 until the period T2 elapses from the brake opening timing, and the speed signal co is added, by the addition block 185, to the output from the coefficient block 181. Then, the second switch unit 187 sets the speed signal co to zero at a time point when the period T2 has elapsed. Then, the output of the addition block 185 is supplied as one input signal A of the switch unit 183.
Other components are the same as, and perform operations similar to, those illustrated in FIG. 3, and hence a description thereof is omitted.
[0061] With the above-mentioned configuration, there is achieved a function of selecting, by the switch unit 183 and the second switch unit 187, whether to use, as the torque offset current signal iq_t*_off, the signal A obtained by adding, by the addition block 185, the signal obtained by multiplying the estimated disturbance signal Di^ by l/Kin and the signal obtained by multiplying the speed signal co by a, to use, as the torque offset current signal iq_t*_of f, the signal A obtained by multiplying the estimated disturbance signal Di^ by l/Kin, or to use, as the torque offset current signal iq_t*_off, the signal B obtained by sampling and holding, by the sample-and-hold unit 182, the signal obtained by multiplying the estimated disturbance signal Di^ by l/Kin at the timing that is delayed, by the delay unit (first delay unit) 186, from the brake opening timing in accordance with the brake control command signal BK_cont by the predetermined time (Tl).

[0062] The selection by the switch unit 183 and the second switch unit 187 is performed by a signal obtained by delaying the brake opening signal in accordance with the brake control command signal BK_cont by predetermined times (Tl and T2).
[0063] The speed feedback control is set so as to function faster than response time of the disturbance observer 17 to the disturbance, and hence convergence time of step response becomes shorter than convergence time of the disturbance observer 17. Therefore, a relationship between both of the delay amounts is expressed by the following expression.
T2