Drive device for induction motor

Abstract

The present invention provides a drive device for an induction motor capable of performing sensorless vector control in which an electric constant required for control is set with high accuracy for an induction motor with an unknown electric constant and thereby the induction motor is stably driven from a low speed range to a high speed range. This drive device is provided with an inverter 2 for driving an induction motor 1, a current detector 4 for detecting a current in the induction motor 1, and a controller 5 for reading the current value detected by the current detector 4 and controlling the induction motor 1 via the inverter 2. The controller 5 has speed estimators 7, 7C, 7D, and 7F for estimating and calculating the rotational speed of the induction motor 1, calculates an induced voltage generated by the induction motor 1 by using the voltage applied to the induction motor 1 and the electric constant of the induction motor 1, separately obtains a main magnetic flux direction component Ed of the induced voltage and an orthogonal component Eq of the induced voltage with respect to a main magnetic flux, calculates an error angle Δθ formed between the main magnetic flux direction component Ed and the orthogonal component Eq, adjusts a drive frequency for the induction motor 1 such that the value thereof becomes zero, and estimates and calculates the rotational speed of the induction motor 1.

Description

Drive device for an induction motor

[0001] The present invention relates to a drive device for an induction motor.

[0002] Induction motors are widely used in industries, transportation fields, etc. Induction motors have unified standards as general-purpose motors, and general-purpose inverters for driving them at variable speeds are also sold by various companies. The control technology of general-purpose inverters has also advanced, and it is not limited to variable-speed driving of fans and pumps, but its application to uses that require high torque from low speeds, such as cranes and conveyors, is also expanding.

[0003] As a control technology for high torque of induction motors, speed sensorless vector control is adopted in many products. Speed sensorless vector control can achieve high-precision and high-response control of induction motors, but it is necessary to accurately set the electrical constants of the induction motor to be controlled. Therefore, it is difficult to drive a motor with unknown electrical constants without adjustment. To solve this problem, general-purpose inverters equipped with speed sensorless vector control have an automatic adjustment function for electrical constants, and this adjustment work is carried out before actual operation to set the electrical constants.

[0004] As prior art documents in this technical field, there are Patent Documents 1, 2, and Patent Document 3. In Patent Document 1, a method is described for realizing stable driving of sensorless vector control by calculating and obtaining the speed electromotive voltage of an induction motor and controlling the voltage component of the d-axis to be zero. In Patent Document 2, the rotational speed is estimated and calculated using induction motor constants to realize sensorless vector control. Further, Patent Document 3 describes a method for accurately measuring the minimum electrical constants required to realize sensorless vector control on the premise that the induction motor is locked.

[0005] Japanese Patent Laid-Open No. 4-21387 Japanese Patent Laid-Open No. 6-284771 WO2023132114

[0006] In Patent Document 1, the induced voltage is determined from the terminal voltage of the induction motor or the command voltage inside the controller, using the primary winding resistance and leakage inductance. By controlling the d-axis induced voltage Ed, which is unrelated to the speed electromotive force, to zero, the main magnetic flux is aligned with the d-axis, thereby achieving vector control. However, since the magnitude of the d-axis induced voltage Ed depends on the rotational speed, the value becomes small in the low-speed range, resulting in insufficient gain. Furthermore, near zero speed, the calculation error becomes large, making it difficult to drive stably over a wide speed range.

[0007] Patent Document 2 estimates the rotational speed of an induction motor by calculating the speed electromotive force from electrical constants and dividing the induced voltage by the magnitude of the main magnetic flux. With this method, stable driving can be achieved even in the extremely low speed range if the electrical constants are set accurately. In order to calculate the rotational speed with high accuracy, it is necessary to accurately set the excitation inductance L2 and the mutual inductance M of the induction motor, but in order to accurately measure these, it is necessary to perform drive tests on the induction motor in question. Therefore, when driving an induction motor with unknown constants that is pre-installed in a system, it is necessary to disassemble the system and drive the target induction motor individually, which poses a problem in terms of the amount of work involved.

[0008] Furthermore, Patent Document 3 describes a method for automatically adjusting the electrical constants necessary for realizing sensorless vector control of an induction motor: the second-order time constant T2, the leakage inductance Lσ, and the primary winding resistance R1. While sensorless vector control as described in Patent Document 1 can be realized with these constants alone, the problems during startup and in the low-speed range described above are not solved.

[0009] In view of the above-mentioned background technology and problems, the object of the present invention is to realize an induction motor drive device that enables sensorless vector control, which allows for stable driving from low speed to high speed range by setting the electrical constants necessary for control with high precision for induction motors whose electrical constants are unknown.

[0010] In an induction motor drive system comprising an inverter for driving an induction motor, a current detector for detecting the current of the induction motor, and a controller for reading the current value detected by the current detector and controlling the induction motor via the inverter, the controller has a speed estimator for estimating the rotational speed of the induction motor, the speed estimator calculates the induced voltage generated inside the induction motor using the voltage applied to the induction motor and the electrical constants of the induction motor, separates and obtains the main magnetic flux direction component and the orthogonal component of the induced voltage, calculates the error angle between the main magnetic flux direction component and the orthogonal component, adjusts the driving frequency of the induction motor so that this value becomes zero, and estimates the rotational speed of the induction motor.

[0011] According to the present invention, it is possible to realize a sensorless vector control drive device for an induction motor whose electrical constants are unknown, which enables stable driving from low speed to high speed range by setting the electrical constants necessary for control with high precision.

[0012] Furthermore, based on the measurement of minimal electrical constants, stable speed sensorless vector control is possible, enabling the realization of a robust induction motor drive system.

[0013] This is a diagram of the drive unit for the induction motor in Example 1. This is a diagram of the speed estimator in Example 1. This is a diagram of the error angle calculator in Example 2. This is a diagram of the speed estimator in Example 3. This is a diagram of the speed estimator in Example 4. This is a diagram of the M compensator in Example 5. This is a diagram of the speed estimator in Example 6.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] (Example 1) Figure 1 is a diagram of the configuration of the induction motor drive unit in this Example 1. In Figure 1, the induction motor drive unit is intended to drive a three-phase induction motor 1 (hereinafter abbreviated as induction motor 1), and is broadly composed of an inverter 2, a current detector 4, and a controller 5. Note that in Figure 1, some component names are abbreviated, and the component names with corresponding symbols described below are the official names.

[0016] In Figure 1, the inverter 2 performs switching operations based on the PWM (pulse width modulation) signal output from the controller 5, applying a pulsed voltage to the induction motor 1. The mechanical load 3 is a load device driven by the induction motor 1, and various devices such as fans, pumps, compressors, cranes, and conveyors are envisioned. The current detector 4 is a current sensor that detects the phase current flowing through the induction motor 1.

[0017] Controller 5 is a controller that performs speed sensorless vector control of the induction motor 1. Controller 5 includes a speed command generator 6 that gives the rotational speed command ωrREF to the induction motor 1, a speed estimater 7 that estimates and calculates the rotational speed of the induction motor 1 without using a speed sensor, a speed controller (ASR: Auto Speed ​​Regulator) 8 that makes the rotational speed of the induction motor 1 follow the speed command ωrREF, an Im setter 9 that gives the excitation current command Im to the induction motor 1, and a d-axis current controller (ACR: Auto Current Controller) that controls the current of the d-axis. It consists of a Regulator 10, a q-axis current controller 11 that controls the current in the q-axis, a dq inverse coordinate converter 12 that converts a voltage command on the dq axis into a three-phase AC voltage command, a PWM generator 13 that generates a PWM signal to drive the inverter 2 based on the three-phase AC voltage command, a slip calculator 14 that sets the slip frequency of the induction motor 1, a coordinate axis calculator 15 that calculates the coordinate transformation phase θdc by integrating the drive frequency of the induction motor 1, a dq coordinate converter 16 that converts the current value detected by the current detector 4 into a current value on the dq axis, a pole-to-pole gain converter 17 that converts the rotational speed of the induction motor 1 into an electrical angular frequency, and adders and subtractors 18a, 18b, 18c, 18d, and 18e that perform signal addition and subtraction.

[0018] The speed estimator 7 consists of an induced voltage calculator 71 that calculates the induced voltage of the induction motor 1 based on the current supplied to the induction motor 1, the applied voltage at that time, and the electrical constants of the induction motor 1; an error angle calculator 72 that calculates the error angle of the main magnetic flux inside the induction motor 1 from the induced voltage; a zero setter 73 that sets zero as a command for the error angle Δθ; an adder / subtractor 18e; and a PLL (Phase Locked Loop) controller 74 that adjusts the rotational speed so that the error angle Δθ becomes zero.

[0019] Next, the basic operation shown in Figure 1 will be explained. The speed command generator 6 outputs a rotational speed command ωrREF, and the adder / subtractor 18a calculates the difference between this command and the speed estimate value ωr obtained by the speed estimator 7. The speed controller 8 operates so that this error signal becomes zero, and outputs a torque current command I1qREF. The adder / subtractor 18c calculates the error signal between the torque current command I1qREF and the detected value I1qFB of the q-axis current, and the q-axis voltage command V1q is calculated in the q-axis current controller 11 so that this value becomes zero.

[0020] Similarly, in the adder / subtractor 18b, the error signal between the excitation current command I1dREF and the detected value I1dFB of the d-axis current is calculated, and the d-axis voltage command V1d is calculated in the d-axis current controller 10 so that this value becomes zero.

[0021] The voltage commands V1d and V1q are converted into three-phase voltage commands in the dq inverse coordinate converter 12, and then converted into PWM signals that drive the inverter 2 in the PWM generator 13. The dq coordinate converter 16 converts the phase currents (here, Iu and Iw) detected by the current detector 4 into I1dFB and I1qFB, which are values ​​on the rotating coordinate axis (dq axis). The slip calculator 14 uses the excitation current command I1dREF and the torque current command I1qREF to calculate the slip frequency ωs applied to the induction motor 1 according to the following equation (1): ωs = (1 / T2) * (I1qREF / I1dREF) ... (1)

[0022] Here, T2 is the second time constant (L2 / R2) of the induction motor 1.

[0023] The velocity estimate ωr obtained by the velocity estimator 7 is converted into an electrical angular frequency ωr1 by the pole-logarithmic gain converter 17. This value is then added to the slip frequency ωs obtained by equation (1) (added by the adder / subtractor 18d) to obtain the drive frequency ω1 of the induction motor 1. This drive frequency ω1 is integrated by the coordinate axis calculator 15 to obtain the coordinate transformation phase θdc.

[0024] The above describes the basic operation of the drive unit of the induction motor 1 shown in Figure 1. Furthermore, in order to control the torque with high precision using vector control, it is necessary to appropriately set the slip frequency ωs. Since the "slip" shown in equation (1) above is set using the electrical constant T2, it can be seen that this electrical constant T2 is an extremely important constant for realizing vector control.

[0025] Next, the operation of the velocity estimator 7, which is a characteristic feature of this embodiment 1, will be explained using Figure 2.

[0026] The speed estimator 7 consists of an induced voltage calculator 71, an error angle calculator 72, a zero setter 73, an adder / subtractor 18e, and a PLL controller 74. The error angle calculator 72 is equipped with an arctangent calculator 721. The induced voltage calculator 71 uses the voltages V1d and V1q on the dq coordinate axis, the detected currents I1dFB and I1qFB, and the electrical constants of the induction motor 1, namely the primary winding resistance R1 and leakage inductance Lσ, to calculate the induced voltage Ed (the component of the induced voltage generated inside the induction motor 1 in the direction of the main magnetic flux) and the q-axis induced voltage Eq (the component of the induced voltage generated inside the induction motor 1 orthogonal to the main magnetic flux). Here, since the d-axis is the direction of the main magnetic flux of the induction motor 1, the induced voltage is originally generated only in the q-axis and not in the d-axis. The presence of a value in the d-axis induced voltage Ed means that the phase θdc of the dq axis is shifted from the phase angle θd of the main magnetic flux (secondary magnetic flux Φ2d) inside the actual induction motor 1.

[0027] In Patent Document 1, vector control is achieved by controlling the d-axis induced voltage Ed to become zero. However, since the absolute value of the d-axis induced voltage Ed changes significantly depending on the rotational speed, gain correction according to the speed is necessary.

[0028] To solve this problem, in this embodiment 1, the error angle Δθ, which is the angle between the d-axis induced voltage Ed and the q-axis induced voltage Eq, is defined by the following equation (2) and calculated by the error angle calculator 72. Δθ = tan －１ (Ed / Eq) ...(2)

[0029] Equation (2) converts the rotational speed into an "angular error," which is a physical quantity independent of the rotational speed. This eliminates the need for gain correction according to the rotational speed, simplifies the control system configuration at every stage, and significantly improves the ability to achieve high gain and the instability caused by insufficient gain.

[0030] The Δθ obtained by the error angle calculator 72 is subtracted from the command of the zero setter 73 by the adder / subtractor 18e and controlled to (=0) by the PLL controller 74. The PLL controller 74 is configured with PI control (proportional-integral control) by a proportional controller 741 and an integral compensator 742 (first integral compensator). The output of the proportional controller 741 and the output of the integral compensator 742 are added by the adder 18j and output as the rotational speed. By adjusting the rotational speed so that the error angle Δθ becomes zero, that rotational speed can be used directly as the speed estimate value ωrEST. Since the setting gain of this PLL controller 74 becomes the speed estimation gain, control design becomes extremely easy.

[0031] In constructing the controller 5 shown in Figure 1, the necessary electrical constants are three parameters: the second-order time constant T2 used in the slip calculator 14, and R1 and Lσ used in the induced voltage calculator 71. Patent document 3 shows that these three parameters can be measured under conditions where the induction motor 1 is stopped. Therefore, it is not necessary to rotate the induction motor 1, and the induction motor 1 with unknown constants can be driven by sensorless vector control. Adjustment work is unnecessary for constants other than these three parameters, such as the mutual inductance M and excitation inductances L1 and L2, which are electrical constants of the induction motor 1. This is extremely useful for driving an induction motor with unknown constants that is incorporated into a mechanical system.

[0032] The electrical constants used in calculating the main magnetic flux direction component Ed and the orthogonal component Eq are the values ​​measured with the rotation axis of the three induction motor 1 fixed.

[0033] As described above, sensorless vector control can be achieved using only the electrical constants T2, R1, and Lσ, which are parameters obtainable when the induction motor 1 is stopped, as initial setup requirements. This enables high-precision speed or torque control without the need for rotational drive testing.

[0034] In other words, according to Example 1, it is possible to realize a sensorless vector control drive device for an induction motor that enables stable driving from low speed to high speed range by setting the electrical constants necessary for control with high precision for induction motors with unknown electrical constants.

[0035] (Example 2) The drive device of the induction motor 1 in this Example 2 will be described using Figure 3.

[0036] Figure 3 shows the error angle calculator 72B in this embodiment 2, which is an improvement over the error angle calculator 72 in embodiment 1. The drive device for the induction motor 1 in this embodiment 2 can be realized by replacing the error angle calculator 72 in Figures 1 and 2 with the error angle calculator 72B shown in Figure 3.

[0037] In Figure 3, the error angle calculator 72B comprises an arctangent calculator 721 and a lower limiter 722. The q-axis induced voltage Eq is input to the arctangent calculator 721 via the lower limiter 722. Then, the arctangent calculator 721 executes equation (2) above and calculates the error angle Δθ.

[0038] The drive device of the induction motor 1 in Example 1 can achieve sensorless vector control by using the minimum necessary electrical constants, secondary time constant T2, leakage inductance Lσ, and primary winding resistance R1. However, near zero speed, the magnitude of the induced voltage decreases, and the calculation result of the error angle Δθ becomes unstable.

[0039] As shown in equation (2) above, the error angle Δθ changes significantly because the q-axis induced voltage Eq in the denominator fluctuates between positive and negative values ​​near zero, so countermeasures are necessary.

[0040] In the second embodiment, as a countermeasure, a lower limiter 722 is provided for the magnitude of the q-axis induced voltage (orthogonal component with respect to the main magnetic flux) Eq. As a result, the absolute value of the q-axis induced voltage (orthogonal component with respect to the main magnetic flux) Eq is restricted so as not to become zero, and since the q-axis induced voltage Eq in the denominator is fixed, the variation of the error angle Δθ is suppressed. However, since the d-axis induced voltage Ed in the numerator is used as it is, the calculation result of the error angle Δθ becomes a value smaller than the actual value. Physically, this is equivalent to reducing the PLL control gain, and the responsiveness decreases.

[0041] However, it is effective for the purpose of suppressing the unstable fluctuations during startup, and smooth acceleration characteristics can be obtained. The lower limiter value is set with a value of about 2% to 5% of the rated voltage of the induction motor 1 as a guide. This is because the output voltage accuracy of the inverter 2 has an error of at least about 1%, so at least this order of limitation is necessary.

[0042] As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained, and in addition, it is possible to realize more stable sensorless vector control from startup.

[0043] (Third Embodiment) The drive device of the induction motor 1 in the third embodiment will be described with reference to FIG. 4.

[0044] FIG. 4 shows the speed estimator 7C in the third embodiment, which is an improvement of the speed estimator 7 in the first embodiment. The drive device of the induction motor 1 in the third embodiment can be realized by replacing the speed estimator 7 in FIG. 1 with the speed estimator 7C shown in FIG. 4.

[0045] In FIG. 4, the induced voltage calculator 71, the error angle calculator 72B, the zero setter 73, the adder / subtractor 18e, and the PLL controller 74 are the same as those with the same numbers in FIGS. 1 to 3 described in the previous first and second embodiments.

[0046] In the third embodiment, an induced voltage speed feedforward calculator 75 is newly added in a form including an induced voltage calculator 71, and as its calculation output, in addition to the d-axis induced voltage Ed and the q-axis induced voltage Eq, a speed FF (feedforward) value ωrFF, which is a speed FF value, is calculated and output. Finally, the speed FF value (speed feedforward value) ωrFF output from the induced voltage speed feedforward calculator 75 is added to the speed estimated value ωrEST output from the PLL controller 74 by an adder 18L, and is output as a new speed estimated value ωrEST2, which is utilized as the speed estimated value for sensorless vector control.

[0047] In FIG. 4, the induced voltage speed feedforward calculator 75 includes a calculator 20 that calculates the differential term of the detected value I1qFB of the q-axis current, a first-order lag generator 21 having a time constant of an observer gain, an adder 18j, an adder / subtractor 18k, a first-order lag generator 22 having a time constant of a second-order time constant T2, a mutual inductance gain multiplier 23, an integrator 24, and a KLM gain setter 25C.

[0048] Before the description of the third embodiment, the conventional method disclosed in Patent Document 2 will be described.

[0049] In Patent Document 2, the rotational speed of the induction motor 1 is calculated by the following equation (3). ωrFF = (1 / (1 + T ０ s)) · (L2 / M) · (1 / Φ2d*) · {v1q - ω1 · Lσ · i1dFB - (R1 + Lσ · s) · i1qFB} ... (3)

[0050] Here, To is a speed estimation gain (observer gain), and Φ2d* is a d-axis secondary flux command value.

[0051] In the technique described in Patent Document 2, the calculation of the above equation (3) is realized. However, the d-axis secondary flux command value Φ2d* is actually generated as a first-order lag of the d-axis current command I1dREF by a first-order lag generator 22, and is obtained by multiplying that value by a mutual inductance M (mutual inductance gain) by a mutual inductance multiplier 23.

[0052] Conventional velocity estimators can achieve high accuracy if the electrical constants are precise, but the problem is that errors in setting the electrical constants directly translate into errors in velocity estimation.

[0053] Therefore, the speed estimator 7C according to Embodiment 3 of the present invention is constructed by directly utilizing the Eq output by the induced voltage calculator 71, as shown in Figure 4. Even if the speed FF value ωrFF is slightly off, the PLL controller 74 corrects the error, so it does not pose a problem.

[0054] Furthermore, the KLM gain setter 25C shown in Figure 4 does not accurately reflect the electrical constants of the induction motor 1 in equation (3), but instead uses a fixed value such as "1.05". This is because the ratio of excitation inductance L2 to mutual inductance M is generally slightly greater than "1" in the induction motor 1, and in order to reduce the number of constant settings, it is fixed to a value that does not depend on the induction motor 1. In other words, in the present invention, there is no necessity to set the mutual inductance M and the excitation inductance L2 separately, and even if the value of the excitation inductance L2 is used instead of the mutual inductance M, the speed error will be compensated.

[0055] Furthermore, as mentioned above, the speed estimation error in the extremely low-speed range, which is a problem in Examples 1 and 2, is mitigated by the observer-type speed estimater 7C, resulting in smoother starting.

[0056] In the configuration shown in Figure 4 according to Embodiment 3 of the present invention, it is clear that the set value of the mutual inductance M is important. Although the speed estimation error due to the error in this mutual inductance M is canceled by the PLL controller 74 after startup, the problem is how to set the initial value.

[0057] Therefore, as a method for setting the mutual inductance M, we will use the basic specifications of the induction motor 1 to be driven. In the case of induction motor 1, it can be driven even if a three-phase AC power supply is directly connected, and its specifications are generally listed on the nameplate.

[0058] The relationship between the rated voltage (effective line voltage) V1 [V], rated drive frequency ω [rad / s], excitation current (effective phase current) I1m, and mutual inductance M of induction motor 1 can be approximately expressed by the following equation (4): V1 = ωMI1m ... (4)

[0059] If the excitation current I1m is not specified, it can be roughly considered to be I1 = (√2) * I1m ... (5)

[0060] This will vary depending on the efficiency and capacity of the induction motor 1, but this is how it is set as a guideline for determining the setting value.

[0061] As a result, the initial value of the mutual inductance M can be set as follows: M = (V1 / ω) * ((√2) / I1) ... (6)

[0062] Equation (6) above is an assumed value for the mutual inductance M, and an error of about ±50% is expected, but this is sufficient accuracy for setting as the feedforward value at startup. Furthermore, to avoid the feedforward value ωrFF becoming excessively large, the value of the mutual inductance M can be set to a larger value. For example, if it is set as in equation (7) below, the compensation amount will be a smaller value. M = (V1 / ω) * (2 / I1) ... (7)

[0063] As described above, this embodiment 3 provides the same effects as embodiment 1, and the only electrical constants required for initial setup are the secondary time constant T2, the primary winding resistance R1, and the leakage inductance Lσ. By only provisionally setting the mutual inductance M value from the induction motor specifications, it is possible to achieve sensorless vector control that enables smoother starting.

[0064] Furthermore, the induced voltage-velocity feedforward calculator 75 can also be configured to calculate the velocity feedforward value ωrFF of the induction motor 1 based on the orthogonal component Eq and at least one of the electrical constants of the induction motor 1, namely the mutual inductance M or the excitation inductance L2.

[0065] (Example 4) The drive device of the induction motor 1 in this Example 4 will be described with reference to Figure 5.

[0066] Figure 5 shows the speed estimator 7D in this embodiment, which is an improvement over the speed estimator 7 in Embodiment 1. The drive device for the induction motor 1 in Embodiment 4 can be realized by replacing the speed estimator 7 in Figure 1 with the speed estimator 7D in Figure 5.

[0067] In Figure 5, components with the same numbering as those described in previous examples 1 to 3, such as the induced voltage calculator 71 and the error angle calculator 72B, are the same as those in previous examples 1 to 3. In Example 4, an M compensator (mutual inductance compensator) 76 for correcting the set value of the mutual inductance M, an M initializer 26 for setting the initial value Mini of the mutual inductance M, an adder / subtractor 18n, and a multiplier 19c have been added.

[0068] The M compensator 76 corrects the value of the mutual inductance M, which was provisionally set from the induction motor specifications in Example 3, and compensates it to an accurate value. It consists of a zero setter 73b, an adder / subtractor 18m, and an integral compensator 761 (second integral compensator).

[0069] The velocity estimate ωrESTi output from the PLL controller 74 is subtracted from the command of the zero setter 73b by the adder / subtractor 18m and supplied to the integral compensator 761. Then, ΔM is output from the integral compensator 761 to the adder 18n.

[0070] In other words, the M compensator 76 uses the value of the integral compensator of the PLL controller 74 and adds the output ΔM of the integral compensator 761 to the output from the M initializer 26 (a value initially set based on the rating of the induction motor 1) so that this value becomes zero, thereby correcting the value of the mutual inductance M.

[0071] This operation erases the values ​​stored in the integral compensator 742 (first integral compensator) in the PLL controller 74, and the velocity estimate ωrEST2 is replaced by the velocity FF value ωrFF. By retaining this corrected mutual inductance M value, subsequent startups can be performed based on the observer-type velocity estimater 7D, resulting in extremely stable startups.

[0072] As described above, this embodiment 4 provides the same effects as embodiment 1, and the only electrical constants required for initial setup are the secondary time constant T2, the primary winding resistance R1, and the leakage inductance Lσ. The mutual inductance M can be set to a provisional value from the induction motor specifications, and the motor can be started and then automatically corrected to the accurate value after startup. As a result, sensorless vector control that enables smoother starting can be achieved from the second time onward.

[0073] Furthermore, the induced voltage speed feedforward calculator 75D can be configured to calculate the speed feedforward value ωrFF of the induction motor 1 based on the orthogonal component Eq and at least one of the electrical constants of the induction motor 1, namely the mutual inductance M or the excitation inductance L2.

[0074] (Example 5) The drive device of the induction motor 1 in this Example 5 will be described with reference to Figure 6.

[0075] Figure 6 shows the M compensator 76E in this embodiment 5, which is an improvement over the M compensator 76 in embodiment 4. The drive device for the induction motor 1 in this embodiment 5 can be realized by replacing the M compensator 76 in Figure 5 with the M compensator (mutual inductance compensator) 76E in Figure 6.

[0076] In the M compensator 76E, a switch 762 is placed before the integral controller 761, allowing the input of the integral controller 761 to be switched to "0" as output by the zero setter 73b. When the switch 762 is set to "A", the input of the integral compensator 761 becomes zero, and the output of the integral compensator 761 maintains that value. When the switch 762 is switched to "B", the M compensator 76E continues to operate in such a way that the output value of the integral compensator 742 of the PLL controller 74 is erased. The M compensator operation discriminator (mutual inductance compensator operation discriminator) 763 is a means for determining whether the switch 762 should be set to "A" or "B". The M compensator 76E starts the induction motor 1 and corrects the electrical constants based on the new speed estimate value ωrEST2 obtained by calculation after starting.

[0077] The M compensator 76E is intended to correct the value of the mutual inductance M, and the compensation accuracy increases as the rotational speed increases because the induced voltage increases. Therefore, instead of keeping the M compensator 76E running all the time, it is better to start the compensation operation when the speed of the induction motor 1 reaches a certain level, and conversely, to switch the switch 762 to stop the compensation operation when the rotational speed decreases. Also, the error angle Δθ changes not only due to the setting error of the mutual inductance M but also due to the change in the second-order time constant T2 over time, so in order to separate this correction operation, it is preferable to operate the M compensator 76E under no-load conditions. Such operating conditions can be set in advance in the M compensation operation discriminator 763 of the M compensation discriminator 76E, and the M compensation operation discriminator 763 can switch the switch 762 to operate or stop the compensation according to the operating conditions (speed of the induction motor 1), enabling speed estimation operation and setting of the value of the mutual inductance M according to these ideal conditions.

[0078] As described above, this embodiment 5 provides the same effects as embodiment 1, and it is possible to automatically correct the set value of the mutual inductance M after startup. Furthermore, it is possible to correct the setting value with higher precision by taking into account conditions such as rotational speed and torque.

[0079] (Example 6) The drive device of the induction motor 1 in this Example 6 will be described with reference to Figure 7.

[0080] Figure 7 shows the speed estimator 7F in this embodiment 6, which is an improvement over the speed estimators 7 to 7D in previous embodiments 1 to 5. The drive device for the induction motor 1 in this embodiment 6 can be realized by replacing these previous speed estimators 7 with the speed estimator 7F shown in Figure 7.

[0081] In Figure 7, components with the same part numbers as those described in previous examples 1 to 5, such as the induced voltage calculator 71 and the error angle calculator 72B, are the same as those in previous examples 1 to 5. Example 7 is characterized by the addition of an M map 77 for storing the corrected mutual inductance M for the d-axis current command I1dREF, and a switch 78 for switching whether to use a modified initial value for mutual inductance used in calculating the d-axis secondary magnetic flux command value (Φ2d*) or to use the data stored in the M map 77.

[0082] One of the major features of induction motor 1 is that the magnitude of the main magnetic flux that generates torque can be changed by the excitation current. Therefore, when high torque is not required, it is possible to set a low excitation current command and reduce the magnitude of the main magnetic flux (flux weakening), thereby enabling energy-saving operation and higher rotational speeds.

[0083] However, changing the main magnetic flux can alter the magnetic flux density of the iron core of the induction motor 1, affecting the mutual inductance M and potentially changing its value. In such cases, operating the M compensator 76E according to the present invention allows for the acquisition of an accurate mutual inductance value at all times.

[0084] However, the adjustment operation of the mutual inductance M according to the present invention is gradual and cannot compensate for the mutual inductance M in real time.

[0085] Therefore, the excitation current command I1dREF is first operated at several locations to adjust the mutual inductance value M under several predetermined conditions, and the mutual inductance value M, which is an electrical constant under each condition, is saved as a table in the M map (mutual inductance map) 77. Then, when the excitation current command I1dREF is changed according to the conditions during actual operation, the switch 78 is switched to the "B" side to use the values ​​in the M map 77, thereby enabling highly responsive field weakening control that takes into account fluctuations in the mutual inductance value M. Switching the switch 78 to the "B" side can be performed by any switching means.

[0086] As described above, this embodiment 6 provides the same effects as embodiment 1, and by utilizing the automatic adjustment of mutual inductance M, it is possible to generate a map of mutual inductance M, enabling high-precision, high-response sensorless vector control, including field weakening control.

[0087] Examples 1 to 6 of the present invention have been shown above. The present invention makes it possible to achieve rotation sensorless vector control of induction motor 1 with minimal electrical constants, enabling high starting torque and high-precision torque control.

[0088] Furthermore, the present invention makes it possible to drive the induction motor 1 with high efficiency, reduce carbon emissions, prevent global warming, and contribute to achieving the SDGs (Sustainable Development Goals), particularly item 7, energy.

[0089] Furthermore, the present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0090] 1: Three-phase induction motor (induction motor), 2: Inverter 2, 3: Mechanical load, 4: Current detector, 5: Controller, 6: Speed ​​command generator, 7, 7C, 7D, 7F: Speed ​​estimater, 8: Speed ​​controller, 9: Im setter, 10: d-axis current controller, 11: q-axis current controller, 12: dq inverse coordinate converter, 13: PWM generator, 14: Slip calculator, 15: Coordinate axis calculator, 16: dq coordinate converter, 17: Pole logarithmic gain converter, 18a, 18b, 18c, 18d, 18e, 18k, 18m: Adder / subtractor, 18j, 18L, 18n: Adder, 19c, 21, 22: First-order lag generator, 23: Mutual inductor 24: Gain multiplier, 25C: Subtractor, 71: KLM gain setter, 72, 72B: Error angle calculator, 73: Zero setter, 74: PLL controller, 75: Induced voltage speed feedforward calculator, 76, 76E: M compensator (mutual inductance compensator), 77: M map, 721: Arctangent calculator, 722: Lower limiter, 742, 761: Integral compensator, 762: Switch, 763: M compensator operation discriminator (mutual inductance compensator operation discriminator), T2: Second-order time constant, Lσ: Leakage inductance, M: Mutual inductance, R1: Primary winding resistance

Claims

1. An induction motor drive device comprising: an inverter for driving an induction motor; a current detector for detecting the current of the induction motor; and a controller for reading the current value detected by the current detector and controlling the induction motor via the inverter, wherein the controller has a speed estimator for estimating the rotational speed of the induction motor, and the speed estimator calculates the induced voltage generated inside the induction motor using the voltage applied to the induction motor and the electrical constants of the induction motor, separates and obtains the main magnetic flux direction component and the orthogonal component of the induced voltage, calculates the error angle between the main magnetic flux direction component and the orthogonal component, and adjusts the drive frequency of the induction motor so that the value becomes zero, thereby estimating the rotational speed of the induction motor.

2. The induction motor drive device according to claim 1, wherein the speed estimator comprises a first integral compensator that adjusts the drive frequency of the induction motor based on the error angle.

3. The induction motor drive device according to claim 1, characterized in that the electrical constants used in the calculation of the main magnetic flux direction component and the orthogonal component are values ​​measured with the rotation shaft of the induction motor fixed.

4. The induction motor drive device according to claim 1, characterized in that a lower limiter is provided for the orthogonal component with respect to the main magnetic flux, and the absolute value of the orthogonal component is limited so as not to become zero.

5. An induction motor drive device according to claim 1, wherein the speed estimator comprises an induced voltage speed feedforward calculator that calculates a speed feedforward value of the induction motor based on the orthogonal component and at least one of the mutual inductance or excitation inductance, which are electrical constants of the induction motor, and the speed feedforward value is added to the speed estimate calculated based on the error angle to obtain a new speed estimate.

6. The induction motor drive device according to claim 1, wherein the speed estimator comprises an induced voltage speed feedforward calculator that calculates a speed feedforward value of the induction motor based on the orthogonal component and at least one of the mutual inductance or excitation inductance, which are electrical constants of the induction motor, wherein the mutual inductance or excitation inductance is initially set based on the rated value of the induction motor, and the speed feedforward value obtained by the induced voltage speed feedforward calculator is added to the speed estimate obtained based on the error angle to obtain a new speed estimate.

7. An induction motor drive device according to claim 1, wherein the speed estimator comprises an induced voltage speed feedforward calculator that calculates a speed feedforward value of the induction motor based on the orthogonal component and at least one of the mutual inductance or excitation inductance, which are electrical constants of the induction motor; a mutual inductance compensator that adds the speed estimate obtained by the induced voltage speed feedforward calculator to the speed estimate obtained by adjusting the error angle to start the induction motor with a new speed estimate; and corrects the electrical constants based on the new speed estimate obtained after starting.

8. An induction motor drive device according to claim 7, wherein the mutual inductance compensator is equipped with a mutual intactance compensation operation discriminant that starts or stops the compensation operation according to the operating conditions of the induction motor.

9. An induction motor drive device according to claim 7, characterized in that it includes a mutual inductance map that adjusts the mutual inductance under a plurality of predetermined conditions and stores the mutual inductance under each of the said conditions.

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