JP2015186346A - induction motor drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve control accuracy of output torque by calculating the slip frequency of an induction motor drive system by using the difference between a torque reference and an output torque.SOLUTION: An induction motor drive system 30a includes: a resolver 12 for detecting the rotational frequency of an induction motor 11; an inverter 5 for performing variable speed control of the induction motor 11; a vector control part 21 for controlling the inverter 5 by using vector control; an output torque calculation part 13a for calculating an output torque; a difference torque calculation part 14 for calculating a difference torque between the calculated output torque and a torque reference; a calculation and memory part 16 for storing a difference torque calculated for each operation condition as torque correction data and calculating a correction torque which compensates for shortage of the output torque; and a slip frequency calculation part 10 for calculating a command value of a slip frequency and outputting it to the vector control part 21.

Description

  The present invention relates to an induction motor drive system having an output compensation function of an induction motor.

  In an induction motor drive system applied to a conventional rolling facility, a deviation in output torque due to a change in motor secondary resistance of the motor is estimated from the temperature of an RTD (Resistance Temperature Detector) provided in the stator winding. And compensated.

  In addition, in the secondary resistance compensation method for induction motors, it is known to compensate for changes in slip angular frequency command values calculated from secondary resistances that change with temperature changes in induction motors (for example, patents). Reference 1).

JP-A-7-303398

For example, FIG. 6 is a block diagram showing a configuration of a conventional induction motor drive system. The induction motor drive system 300 applied to the rolling equipment shown in FIG. 6 employs slip frequency control. The slip frequency (slip angular frequency command value ωs ^* ) is calculated by the time constant of the rotor. included. This time constant includes the secondary resistance of the motor, and since the secondary resistance value of the motor greatly fluctuates due to the temperature change of the induction motor 111, temperature detection is performed on the stator winding of the induction motor 111 as means for correcting this time constant. A vessel 113 and the like are provided.

  In the induction motor drive system 300, the secondary resistance value of the motor is estimated using the detected temperature T_TEMP from the temperature detector 113 for the stator winding. For example, the secondary resistance value of the motor is estimated from the detected temperature T_TEMP by the secondary resistance compensation gain unit 114, the upper and lower limit limit unit 115, and the secondary resistance compensation calculation unit 116, and is further converted into a standard time constant based on the reference temperature. It is corrected by comparison.

  The slip frequency calculation unit 110 performs a slip frequency calculation using the corrected secondary resistance value. However, the detected temperature T_TEMP is not the actual temperature on the rotor side, and since the temperature detection point of the stator winding is one point, the temperature inside the induction motor 111 cannot be grasped as a whole, and the secondary resistance compensation calculation There is a problem that an error occurs in the motor secondary resistance value corrected by the unit 116 and the like, and an error also occurs in the actual output torque.

That is, in order to stabilize the power supply angular frequency ω0, as is apparent in the slip frequency calculation, the motor secondary time constant that is a function of the slip angular frequency command value ωs ^* must be constant. In this operating state, the secondary resistance value of the motor changes as the temperature of the motor rotor changes. Therefore, the detected torque reference current Iq ′ and the slip angular frequency command value ωs ^* are not proportional.

That is, when the secondary resistance value of the motor changes as the temperature of the induction motor 111 changes, the rotational speed (angular frequency ω) of the induction motor 111 changes, and the actual slip angular frequency and the slip angular frequency command value ωs ^* There will be a gap between them. As a result, the torque axis component secondary magnetic flux is generated, and the actual output torque of the induction motor 111 is changed. In the induction motor 111, desired vector control is not performed, and the torque reference (torque command value) is satisfied. The output torque cannot be obtained.

  The problem to be solved by the present invention is to provide an induction motor drive system capable of improving the control accuracy of the output torque by calculating the slip frequency of the induction motor using the difference between the torque reference and the output torque. The purpose is to do.

  In order to solve the above problems, an induction motor drive system according to the present invention includes an induction motor that can be driven by three-phase alternating current, a resolver that detects the number of revolutions of the induction motor, and an inverter that controls the induction motor at a variable speed. And a speed command to obtain a detected speed from the number of rotations detected by the resolver, calculate a speed deviation thereof, detect a three-phase current input to the induction motor, and detect the detected three-phase current And a vector control unit that controls the inverter using a vector control that calculates and controls a torque reference current and a magnetic flux reference current for the induction motor based on the detected speed and a slip frequency command value; and An output torque calculation unit for calculating output torque, and a difference between the calculated output torque and a torque reference obtained from the torque reference current For each operating condition of the induction motor, the calculated differential torque is stored as torque correction data for each operating condition of the induction motor, and the lack of output torque of the induction motor is compensated using the torque correction data A command value for the slip frequency is calculated using a calculation / memory unit for calculating a correction torque for calculating the torque reference current, the magnetic flux reference current and the correction torque, and the command value of the slip frequency is calculated. And a slip frequency calculation unit that outputs to the vector control unit.

  According to the induction motor drive system of the present invention, the control accuracy of the output torque can be improved by calculating the slip frequency of the induction motor using the difference between the torque reference and the output torque.

The block diagram which shows the structure of 1st Embodiment of the induction motor drive system which concerns on this invention. The processing operation figure which shows the differential torque calculation process by the induction motor drive system of FIG. The block diagram which shows the structure of 2nd Embodiment of the induction motor drive system which concerns on this invention. The figure which shows an example of inverter efficiency. The figure which shows an example of motor efficiency. The block diagram which shows the structure of the induction motor drive system of a prior art example.

  Hereinafter, an induction motor drive system according to an embodiment of the present invention will be specifically described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted. Note that the same applies to FIG. 6 described above, and redundant description is omitted. Each of the following embodiments described here will be described by taking an example of an induction motor drive system that controls the induction motor.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a first embodiment of an induction motor drive system according to the present invention. FIG. 2 is a processing operation diagram showing differential torque calculation processing by the induction motor drive system of FIG. Hereinafter, the induction motor drive system of the first embodiment will be described.

  In the induction motor drive system 30a of the first embodiment, the output torque T ′ during no-load acceleration / deceleration during rolling is calculated based on the output torque T of the induction motor 11 at this time from the rotational speed feedback of the resolver 12 as a rotation angle sensor. 'Is calculated, and the difference between the calculation result and the torque reference Tref at that time is obtained. Then, by learning this difference, it is input to the slip frequency calculation unit 10 using the signal converted to the primary frequency, and this value is fed back to the three-phase / two-phase converter 8 so that it can be loaded. A function for compensating the output torque T ′ is provided.

  For this purpose, the induction motor drive system 30a of the first embodiment includes an inverter 5, an induction motor 11, a resolver (SS) 12, an inverter controller 20a, and a phase current detector, as shown in FIG. 51 and an inverter output detector 52.

  The induction motor 11 is an AC motor that is connected to a load such as rolling equipment and drives the load.

  The inverter 5 controls the speed of the induction motor 11 so as to be variable. The inverter 5 is connected to a DC supply source that is a DC power supply source on its input side, and an induction motor 11 that receives supply of AC power is connected to its output side.

  The resolver 12 is a sensor that uses the principle of a transformer, and detects a voltage that deviates to the output winding in accordance with the rotor angle of the induction motor 11. The detected voltage signal is output to the outside of the resolver 12, for example, as an analog signal of a rotation angle, or A / D conversion and calculation, and a digital signal. For example, a signal having the rotation speed rotn is output as an analog signal or a digital signal.

  The inverter control device 20a controls the speed of the induction motor 11 via the inverter 5 so that the speed of the induction motor 11 can be changed and the output torque within a desired range.

The phase current detector 51 detects the three-phase currents I _U , I _V and I _W output from the inverter 5 and input to the induction motor 11, and outputs the detection signal to the inverter control device 20a.

  The inverter output detector 52 is provided on the output side of the inverter 5, for example, and measures the inverter output current Iac and the inverter output voltage Vac. The inverter output detector 52 outputs measured values for the inverter output current Iac and the inverter output voltage Vac to the inverter control device 20a.

  Hereinafter, the inverter control device 20a will be described with reference to FIG. 1 and FIG.

  As shown in FIG. 1, the inverter control device 20 a includes a vector control unit 21, a slip frequency calculation unit 10, an output torque calculation unit 13 a, a differential torque calculation unit 14, a differential torque limiting unit 15, and a calculation / memory unit 16. ing. The vector controller 21 includes a speed controller 1, a q-axis current controller 2, a two-phase / three-phase converter 3, a controller 4, a field weakening controller 6, a d-axis current controller 7, a three-phase / A two-phase converter 8 and a speed detector 9 are provided.

  The vector control unit 21 performs vector control of the induction motor 11 via the inverter 5 and executes variable speed control according to a desired speed command signal ωr. Since the configuration of the vector control unit 21 is a well-known technique, the description thereof will be simplified here. The following mainly describes the slip frequency calculation unit 10, the output torque calculation unit 13a, the differential torque calculation unit 14, and the differential torque limit. Functions of the unit 15 and the arithmetic / memory unit 16 will be described.

  In the vector control unit 21, the speed detection unit 9 converts it into a speed detection signal (referred to as a detection speed) ω based on the detection signal of the rotational speed rotn input from the resolver 12. The speed detector 9 outputs the converted detection speed ω. The output destination is the speed controller 1, the field weakening controller 6, and the like.

  In FIG. 1, a speed deviation Δω = ωr−ω is calculated from an input speed command signal (referred to as a speed command) ωr and a detected speed ω detected by the speed detector 9, and this speed deviation Δω is used for speed control. Input to the device 1.

  The speed controller 1 calculates a q-axis component torque reference current Iq according to the speed deviation Δω. Further, the speed controller 1 calculates a torque reference Tref corresponding to the torque reference current Iq according to the speed deviation Δω.

  The field weakening controller 6 calculates the d-axis component magnetic flux reference current Id according to the detection speed ω.

  Conventionally, in the induction motor drive system 300 shown in FIG. 6, the detection value detected by the temperature detector 113 such as RTD / PT is calculated as the secondary resistance value of the induction motor 111 driven by the inverter 5. , And is fed back to the slip frequency calculation unit 110. The slip frequency calculation unit 110 compensates for the secondary resistance by feeding back to the torque reference current Iq and the magnetic flux reference current Id of the command value based on the calculated secondary resistance value.

In the induction motor drive system 30a shown in FIG. 1, the differential torque ΔT is calculated from the output torque T ′ and the torque reference Tref without performing temperature monitoring for obtaining the secondary resistance value of the induction motor 11, and this differential torque is calculated. By using ΔT, the slip frequency (slip angular frequency command value ωs ^* ) is calculated. Hereinafter, the slip frequency calculation process will be described.

  Also, measured values relating to the rotational speed rotn of the resolver 12, the output voltage Vac detected on the output side of the inverter 5, and the output current Iac are input to the output torque calculator 13a. The output torque calculator 13a calculates the output torque T ′ using the measured values of the rotation speed rotn, the output current Iac of the inverter 5 and the output voltage Vac. The output voltage Vac and the output current Iac are an alternating voltage and an alternating current.

In the output torque calculator 13a, the output torque T ′ is calculated from the following (Equation 1):
T ′ = Kg × P / rotn (Formula 1)
Is required. Kg is a constant corresponding to the unit system.

Moreover, when the motor output P in the induction motor 11 is shown using the output voltage Vac and the output current Iac of the inverter 5,
P = (√3) × Vac × Iac (Expression 2)
It becomes.

  The differential torque calculator 14 determines a differential torque ΔT from the calculated output torque T ′ and the torque reference Tref. The value (calculation result) in the differential torque ΔT is set as a variation of the output torque T ′ due to the influence of the secondary resistance change due to the temperature factor, and the calculation result of the differential torque ΔT is output from the differential torque calculation unit 14 to the differential torque limiting unit 15. To do.

  In the differential torque limiting unit 15, a threshold value for the differential torque ΔT is set in advance, so that an abnormal value is excluded from the calculation result of the differential torque ΔT input to the differential torque limiting unit 15. As a result, only the calculation result of the differential torque ΔT within the normal range is output from the differential torque limiting unit 15.

  The differential torque ΔT detected as described above is input to the calculation / memory unit 16. The calculation / memory unit 16 stores data related to the calculation results of a plurality of differential torques ΔT detected in time series, for example.

  The calculation / memory unit 16 stores the differential torque ΔT as table data related to torque correction data by dividing the differential torque ΔT by operating conditions such as environmental conditions and load conditions, for example.

  In the induction motor drive system 30a, for example, based on the no-load acceleration operation and the no-load deceleration operation, the differential torque ΔT is calculated and stored in the calculation / memory unit 16 together with the torque reference Tref at that time. The calculation / memory unit 16 takes out the stored differential torque ΔT in the on-load operation, corrects the differential torque ΔT by the current torque reference Tref, and obtains the corrected output torque (corrected torque Tx). The calculation / memory unit 16 outputs the calculated value of the correction torque Tx to the slip frequency calculation unit 10.

The slip frequency calculation unit 10 receives the torque reference current Iq (and the corresponding torque reference Tref) and the magnetic flux reference current Id in addition to the correction torque Tx, and based on these inputs, the slip frequency command value (slip angle) The frequency command value ωs ^* ) is calculated. The slip frequency calculation unit 10 corrects the torque reference current Iq according to the correction torque Tx. Thereby, the slip frequency calculation part 10 calculates the command value of a slip frequency using a well-known formula.

The power supply angular frequency ω0 = ωs ^* + ω obtained by adding the slip angular frequency command value ωs ^* output from the slip frequency calculation unit 10 and the detection speed ω is input to the three-phase / two-phase converter 8. .

Further, the three-phase / two-phase converter 8 performs coordinate conversion as a two-phase current as a detection value corresponding to the power supply angular frequency ω0 based on the three-phase currents I _U , I _V , I _W of the inverter output. The dq axis component elements (Id ′, Iq ′) are calculated. The three-phase / two-phase converter 8 feeds back (feeds back) the calculated Id ′ and Iq ′ to the inputs of the d-axis current controller 7 and the q-axis current controller 2, and the magnetic flux reference current Id as a command value, Add to the torque reference current Iq.

  The d-axis current controller 7 multiplies the magnetic flux reference current Id + Id ′ by a predetermined gain and outputs it to the two-phase / three-phase converter 3. In addition, the q-axis current controller 2 multiplies the torque reference current Iq + Iq ′ by a predetermined gain and outputs it to the two-phase / three-phase converter 3. That is, the d-axis current controller 7 and the q-axis current controller 2 perform current control so that the two-phase current of the command value and the two-phase current of the detection value match, and the control output is converted into a two-phase / three-phase converter. To the device 3. The magnetic flux reference current Id + Id ′ and the torque reference current Iq + Iq ′ are shown in an example in which Id ′ and Iq ′ are added and displayed. However, the magnetic flux reference current Id−Id ′ and the torque reference current Iq− Subtraction display may be performed like Iq ′.

  Two-phase currents output from the d-axis current controller 7 and the q-axis current controller 2 are input to the two-phase / three-phase converter 3 and converted into three-phase currents by the two-phase / three-phase converter 3. The two-phase / three-phase converter 3 outputs the converted command value of the three-phase current to the controller 4.

  The controller 4 controls the inverter 5 according to the command value of the three-phase current.

  Hereinafter, a control process for compensating for the variation in the output torque T ′ due to the influence of the secondary resistance change due to the temperature factor will be described.

Regarding the output torque T ′ at the time of rolling, there is a decrease in output torque due to the following factors,
(1) Output torque drop due to _motor loss other than temperature factor: _{TM_loss}
(2) Output torque drop due to mechanical loss: T _{mech_loss}
(3) Output torque drop caused by secondary resistance fluctuation due to temperature factor: _{TR2_loss}
Considering these (1) to (3), when the torque reference Tref is satisfied, the output torque T ′ of the acceleration / deceleration operation under no load is obtained from the following (Equation 3).
T ′ = Tref− _{TM M_loss} −T _{mech_loss} −T _{R2_loss}
... (Formula 3)

  In (Equation 3), if there is no load, (1) output torque decrease due to motor loss other than temperature factor, and (2) output torque decrease due to mechanical loss can be considered constant even if the operating conditions change, so there is no fluctuation. There is (3) a decrease in output torque caused by the influence of secondary resistance fluctuation due to temperature factors. As for the difference from the torque reference Tref, it is only necessary to take into consideration the fluctuation of the output torque drop due to (3).

  Specifically, in the induction motor drive system 30a, before the load operation, for example, a no-load acceleration / deceleration operation at the time of rolling is used, and the differential torque calculation is performed at a timing as shown in FIG. However, in the acceleration / deceleration state as shown in FIG. 2, the speed feedback follows the speed reference (speed command ωr), and the speed reference is satisfied in the state where there is no rolled material (no material biting or slipping out). It shall be.

  In the induction motor drive system 30a, as shown in FIG. 2, for example, the speed command ωr is set to each state of acceleration operation during no load (periods I and III) and deceleration operation during no load (periods V and VII). Input from outside. Here, as shown in FIG. 2, the output torque at this time is classified and described as an unloaded acceleration torque T'ac and an unloaded deceleration torque T'dec. In the periods II, IV and VI, the speed is constant.

  Further, for example, an arithmetic average is performed on the difference between the torque reference Tref acquired in the periods I and III and the no-load acceleration torque T′ac, and the result is set as a differential torque ΔTac. Similarly, for example, an arithmetic average is performed on the difference between the torque reference Tref acquired in the periods V and VII and the no-load deceleration torque T′dec, and the result is defined as a differential torque ΔTdec.

  In order to sequentially store and learn the differential torque ΔT including the differential torque ΔTac and the differential torque ΔTdec, for example, the calculation / memory unit 16 performs the following calculation to obtain the differential torque ΔT (n). Remember. Here, ΔT (n) represents the differential torque obtained by the n-th calculation (n is an integer of 1 or more) (for example, arithmetic average). When the test state such as the first acceleration, deceleration, second acceleration, deceleration, third ... nth, etc. is repeated from the constant speed state, the differential torque ΔT (n) obtained up to the nth is as follows: It is calculated | required by (Formula 4) or (Formula 5).

で示される。 The differential torque ΔT (n) obtained up to the nth acceleration at no load is expressed as ΔT ′ (n),

Indicated by

で示される。 Further, the differential torque ΔT (n) obtained up to the nth deceleration at no load is expressed as ΔT ″ (n),

Indicated by

  As described above, the output torque calculation unit 13a determines the no-load acceleration torque T'ac and the no-load acceleration torque rotn obtained from the resolver 12 and the measured values of the output voltage Vac and the output current Iac of the inverter 5. An output torque T ′ such as a deceleration torque T′dec is calculated.

  The differential torque calculator 14 obtains a differential torque ΔT (differential torque ΔTac, differential torque ΔTdec) from the calculated output torque T ′ and the torque reference Tref. Further, the abnormal value is excluded from the calculation result of the differential torque ΔT input to the differential torque limiting unit 15. As a result, only the calculation result of the differential torque ΔT within the normal range is output from the differential torque limiting unit 15.

  As described above, the calculation / memory unit 16 receives and stores the calculation results of a plurality of differential torques ΔT (n) collected in advance at no load. By repeating the acceleration / deceleration operation under no load, the differential torque ΔT (n) converges, and more accurate torque correction is possible.

  The calculation / memory unit 16 uses the result of convergence of the differential torque ΔT (n) as torque correction data.

  The calculation / memory unit 16 is classified as operating conditions such as environmental conditions (conditions such as ambient temperature and forced air cooling) and load conditions (load levels such as light load and heavy load), and table data relating to torque correction data. Remember.

  As a result, the induction motor drive system 30a extracts torque correction data for the correction torque for correcting the influence of the secondary resistance fluctuation due to the temperature factor from the calculation / memory unit 16 for each operating condition at the time of load. The arithmetic / memory unit 16 corrects the current torque reference Tref using the torque correction data to obtain a corrected torque Tx. The calculation / memory unit 16 outputs the calculated value of the correction torque Tx to the slip frequency calculation unit 10.

  The slip frequency calculation unit 10 calculates a corrected slip frequency command value using the magnetic flux reference, the torque reference Tref, and the correction torque Tx.

  By using the control method described above, the differential torque ΔT is calculated from the output torque T ′ and the torque reference Tref without monitoring the temperature of the induction motor 11, and the correction torque Tx is calculated from the calculated differential torque ΔT. Obtained and used for slip frequency calculation. As a result, it is possible to compensate for fluctuations in the output torque T 'due to the influence of the secondary resistance change due to temperature factors, and to obtain a stable torque output characteristic.

  In other words, the induction motor drive system 30a uses the differential torque ΔT to correct the output torque T ′, thereby reducing the influence of changes in secondary resistance due to temperature changes in various operating conditions of the induction motor 11, Control instability, trips, etc. of vector control can be avoided. Further, the output torque T ′ can be accurately controlled under any operating conditions.

  According to the first embodiment, the control accuracy of the output torque can be improved by calculating the slip frequency of the induction motor using the difference between the torque reference and the output torque.

[Second Embodiment]
FIG. 3 is a block diagram showing the configuration of the second embodiment of the induction motor drive system according to the present invention. FIG. 4 is a diagram illustrating an example of inverter efficiency, and FIG. 5 is a diagram illustrating an example of motor efficiency. Hereinafter, the induction motor drive system according to the second embodiment will be described.

  As shown in FIG. 3, the induction motor drive system 30b according to the second embodiment includes an inverter 5, an induction motor 11, a resolver 12, an inverter control device 20b, a phase current detector 51, and an inverter input detector. (CT · VT) 53.

The phase current detector 51 detects the three-phase currents I _U , I _V and I _W output from the inverter 5 and input to the induction motor 11, and outputs the detection signal to the inverter control device 20b.

  The CT / VT 53 is provided, for example, in the inverter 5 and measures the inverter input current Idc and the inverter input voltage Vdc. The CT / VT 53 outputs the measured values of the inverter input current Idc and the inverter input voltage Vdc to the inverter control device 20b.

  Hereinafter, the inverter control device 20b will be described with reference to FIGS.

  As shown in FIG. 3, the inverter control device 20 b includes a vector control unit 21, a slip frequency calculation unit 10, an output torque calculation unit 13 b, a differential torque calculation unit 14, a differential torque limiting unit 15, and a calculation / memory unit 16. ing. The configuration of the vector control unit 21 is the same as that shown in FIG.

The output torque calculation unit 13b calculates the current motor output P using the inverter input current Idc, the inverter input voltage Vdc, and the previously stored inverter efficiency η _INV and motor efficiency η _MOT . Further, the output torque calculator 13b calculates the current output torque T ′ from the calculation result of the motor output P and the current rotation speed rotn.

For example, units of inverter input current Idc (A), inverter input voltage Vdc (V), inverter efficiency η _INV , motor efficiency η _MOT , output P (W), rotation speed rotn (rpm), output torque T ′ (Nm) In the system, the following (formula 6) and (formula 7) are shown.

P = Idc × Vdc × η _INV × η _MOT (Expression 6)
T ′ = Kg × P / rotn (Expression 7)
Can be converted. Kg is a constant corresponding to the unit system.

The inverter efficiency η _INV and the motor efficiency η _MOT change to, for example, the inverter efficiency η _INV (FIG. 4) and the motor efficiency η _MOT (FIG. 5) due to the load fluctuation of the induction motor 11, and the characteristics of each model It also changes depending on.

In the case of the inverter efficiency η _INV , the difference between the models is mainly the difference in efficiency depending on the power elements used in the inverter 5, for example. That is, the inverter efficiency η _INV differs for each power element used in the inverter 5. The power element (control element) is, for example, an IGBT (Insulated Gate Bipolar Transistor) or a GTO (Gate Turn-Off Thyristor). Further, if the motor efficiency eta _MOT, the motor efficiency eta _MOT varies due design specifications of the induction motor 11 to be used.

The example of FIG. 4 shows the relationship between the load factor for each model of the inverter 5 and the inverter efficiency (also referred to as device efficiency) η _INV . For example, the control element # 1 shown in FIG. 4 is an example using an IGBT, and the control element # 2 is an example using a GTO.

5 shows the relationship between the motor load factor and the motor efficiency (also referred to as device efficiency) η _MOT for each induction motor 11 model. In addition, as for each model of the induction motor 11, examples of the rated speed and the maximum speed of the model A and examples of the rated speed and the maximum speed of the model B are shown.

Here, each efficiency depends on, for example, η _INV = F (x, y, z,...) _{Depending on} the input voltage (x), the input current (y), the rotation speed (z), and others (...). ), Η _MOT = G (x, y, z,...)

In the output torque calculator 13b, as shown in FIGS. 4 and 5, the inverter efficiency η _INV and the motor efficiency η _MOT corresponding to the model of the inverter 5 and the model of the induction motor 11 are stored in advance. By using these, the output torque calculation unit 13b can calculate the current motor output P. These model characteristics of the inverter 5 and the induction motor 11 are factors determined mainly at the time of designing and manufacturing the equipment.

  The differential torque calculation unit 14 obtains a differential torque ΔT between the output torque T ′ and the torque reference Tref output from the speed controller 1, and sets the threshold value of the differential torque ΔT in the differential torque limiting unit 15 based on the calculation result. In this way, abnormal values are excluded, and only normal differences are detected.

  As described above, the calculation / memory unit 16 stores a plurality of differential torques ΔT collected in advance at no load.

  Thereby, the induction motor drive system 30b extracts torque correction data for the correction torque Tx for correcting the influence of the secondary resistance fluctuation due to the temperature factor from the calculation / memory unit 16 for each operation condition at the time of load. The arithmetic / memory unit 16 corrects the current torque reference Tref using the torque correction data to obtain a corrected torque Tx. The calculation / memory unit 16 outputs the calculated value of the correction torque Tx to the slip frequency calculation unit 10.

The slip frequency calculation unit 10 obtains the slip frequency (the slip angular frequency command value ωs ^* after the compensation) using the correction torque Tx, and the three-phase / two-phase converter 8 uses the slip frequency and the three-phase current. The two-phase current of the feedback component is converted into dq axis control and calculated.

  The three-phase / two-phase converter 8 adds this to the inputs of the d-axis current controller 7 and the q-axis current controller 2 as feedback. By using such a control process, a stable torque output characteristic can be obtained without monitoring the temperature of the induction motor 11.

  According to the second embodiment, the control accuracy of the output torque can be improved by calculating the slip frequency of the induction motor using the difference between the torque reference and the output torque.

  Further, for each induction motor model and each inverter model, the output torque can be estimated and calculated using the relationship between the load factor and the efficiency, so that it is possible to cope with various combinations of induction motors and inverters. .

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. For example, the AC motor driving device may control a multiphase (two or more phases) AC motor. For example, the features of the embodiments may be combined. Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Speed controller, 2 ... q-axis current controller, 3 ... Two-phase / three-phase converter, 4 ... Controller, 5 ... Inverter, 6 ... Field weakening controller, 7 ... d-axis current controller, 8 ... three-phase / two-phase converter, 9 ... speed detector, 10, 110 ... slip frequency calculator, 11, 111 ... induction motor, 12 ... resolver (SS), 13a, 13b ... output torque calculator, 14 ... difference Torque calculation unit, 15 ... differential torque limiting unit, 16 ... calculation / memory unit, 20a, 20b, 200 ... inverter control device, 21 ... vector control unit, 30a, 30b, 300 ... induction motor drive system, 51 ... phase current detection , 52 ... Inverter output detector, 53 ... Inverter input detector (CT / VT), 113 ... Temperature detector, 114 ... Secondary resistance compensation gain section, 115 ... Upper / lower limit section, 116 ... Secondary resistance compensation calculation Part

Claims (5)

An induction motor that can be driven by three-phase alternating current;
A resolver for detecting the rotational speed of the induction motor;
An inverter for variable speed control of the induction motor;
A speed command is input to obtain a detected speed from the number of rotations detected by the resolver, a speed deviation thereof is calculated, a three-phase current input to the induction motor is detected, and the detected three-phase current and the A vector control unit for controlling the inverter using vector control for calculating and controlling a torque reference current and a magnetic flux reference current for the induction motor based on a detection speed and a command value of a slip frequency;
An output torque calculator for calculating the output torque of the induction motor;
A differential torque calculator for calculating a differential torque between the calculated output torque and a torque reference obtained from the torque reference current;
A calculation for storing the calculated differential torque as torque correction data for each operating condition of the induction motor and calculating a correction torque for compensating for an insufficient output torque of the induction motor using the torque correction data. A memory section;
Calculating a command value of the slip frequency using the calculated torque reference current and magnetic flux reference current and the correction torque, and outputting the command value of the slip frequency to the vector control unit; An induction motor drive system comprising: The torque correction data is a value obtained by arithmetically averaging the difference between the torque reference and the output torque when at least one of the induction motor during no-load acceleration or no-load deceleration. The induction motor drive system described. The output torque calculation unit inputs measurement values for the output voltage and output current on the output side of the inverter from the inverter, and calculates the output torque using the measurement values and the detected rotation speed. The induction motor drive system according to claim 1 or 2, wherein the induction motor drive system according to claim 1 or 2 is characterized. The output torque calculation unit inputs measurement values for input voltage and input current on the input side of the inverter from the inverter, and uses the measurement value, the detected rotation speed, and a predetermined efficiency to output the output The induction motor drive system according to claim 1 or 2, wherein a torque is calculated. The output torque calculation unit stores the relationship between the load factor and efficiency in advance for the predetermined efficiency for at least one of the induction motor models or the inverter models, and the load factor and The induction motor drive system according to claim 4, wherein the output torque is calculated using a relationship with efficiency.

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