Induction motor drive unit

Abstract

This invention realizes a sensorless vector control drive system for induction motors that enables stable operation from low to high speeds by precisely setting the electrical constants required for control of induction motors with unknown electrical constants. [Solution] The drive device includes an inverter 2 for driving the induction motor 1, a current detector 4 for detecting the current of the induction motor 1, and a controller 5 that reads the current value detected by the current detector 4 and controls the induction motor 1 via the inverter 2. The controller 5 has speed estimators 7, 7C, 7D, and 7F for estimating the rotational speed of the induction motor 1. The controller 5 calculates the induced voltage generated by the induction motor 1 using the voltage applied to the induction motor 1 and the electrical constants of the induction motor 1, separates and obtains the main magnetic flux direction component Ed and the orthogonal component Eq of the induced voltage, calculates the error angle Δθ between the main magnetic flux direction component Ed and the orthogonal component Eq, adjusts the drive frequency of the induction motor 1 so that this value becomes zero, and estimates the rotational speed of the induction motor 1.

Description

Technical Field

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

Background Art

[0002] Induction motors are widely used in industries and transportation fields. 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 only limited to variable-speed driving of fans and pumps, but also the application to uses that require high torque from low speeds, such as cranes and conveyors, is 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 for realizing stable driving of sensorless vector control is described by calculating and obtaining the speed electromotive force of an induction motor and controlling the voltage of the d-axis component to be zero. In Patent Document 2, the rotational speed is estimated and calculated using induction motor constants, and sensorless vector control is realized. Also, in Patent Document 3, a method for accurately measuring the minimum necessary electrical constants for realizing sensorless vector control on the premise that the induction motor is locked is described.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-21387 [Patent Document 2] Japanese Patent Application Publication No. 6-284771 [Patent Document 3] WO2023132114 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Patent Document 1 describes how to determine the induced voltage using the terminal voltage of an induction motor or the command voltage inside the controller, along with 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, calculation errors become 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 induction motors: the secondary 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 art 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. [Means for solving the problem]

[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. [Effects of the Invention]

[0011] According to the present invention, 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 whose electrical constants are unknown.

[0012] In addition, based on the measured values of the minimum electrical constants, stable sensorless vector control is possible, and a drive device for an induction motor with robustness can be realized.

Brief Description of the Drawings

[0013] [Figure 1] It is a configuration diagram of a drive device for an induction motor in Example 1. [Figure 2] It is a configuration diagram of a speed estimator in Example 1. [Figure 3] It is a configuration diagram of an error angle calculator in Example 2. [Figure 4] It is a configuration diagram of a speed estimator in Example 3. [Figure 5] It is a configuration diagram of a speed estimator in Example 4. [Figure 6] It is a configuration diagram of an M compensator in Example 5. [Figure 7] It is a configuration diagram of a speed estimator in Example 6.

Mode for Carrying Out the Invention

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

Embodiment

[0015] (Example 1) FIG. 1 is a configuration diagram of a drive device for an induction motor in this Example 1. In FIG. 1, the drive device for an induction motor is for driving a three-phase induction motor 1 (hereinafter abbreviated as induction motor 1), and roughly includes an inverter 2, a current detector 4, and a controller 5. In FIG. 1, there are also parts described in abbreviated form for each component name, and the component name corresponding to the reference numeral of each component described below is the official name.

[0016] In FIG. 1, the inverter 2 performs a switching operation based on a PWM (pulse width modulation) signal output from the controller 5, and applies 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 a fan, a pump, a compressor, a crane, and a conveyor are assumed. The current detector 4 is a current sensor that detects the phase current flowing through the induction motor 1.

[0017] The controller 5 is a controller that performs speed sensorless vector control of the induction motor 1. The controller 5 includes a speed command generator 6 that gives a rotational speed command ωrREF of the induction motor 1, a speed estimator 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 causes the rotational speed of the induction motor 1 to follow the speed command ωrREF, an Im setter 9 that gives an excitation current command Im to the induction motor 1, a d-axis current controller (ACR: Auto Current Regulator) 10 that controls the current on the d-axis, a q-axis current controller 11 that controls the current on the q-axis, a dq inverse coordinate converter 12 that converts the voltage commands on the dq axes into three-phase AC voltage commands, a PWM generator 13 that generates a PWM signal for driving the inverter 2 based on the three-phase AC voltage commands, a slip calculator 14 that sets the slip frequency of the induction motor 1, a coordinate axis calculator 15 that integrates the drive frequency of the induction motor 1 to calculate the coordinate conversion phase θdc, a dq coordinate converter 16 that converts the current value detected by the current detector 4 into the current values on the dq axes, a pole pair 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, 18e that perform addition and subtraction of signals.

[0018] The speed estimator 7 includes 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 and 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 speed estimator 7 calculates the difference between this command and the estimated speed value ωr obtained by the speed estimator 18a. 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 current controller 11 calculates the q-axis voltage command V1q 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. In addition, 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). Furthermore, the slip calculator 14 uses the excitation current command I1dREF and the torque current command I1qREF to calculate the slip frequency ωs to be 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 using 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 induction motor 1 shown in Figure 1. Furthermore, in order to control torque with high precision as a 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, as well as 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 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] Patent Document 1 achieves vector control 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 only electrical constants required are the second-order time constant T2 used in the slip calculator 14, and the 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 using sensorless vector control. Adjustment of other constants, such as the mutual inductance M and excitation inductances L1 and L2 of the induction motor 1, is unnecessary, making this method extremely useful for driving an induction motor with unknown constants that is integrated 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 induction motor drive device 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 mechanism of the induction motor 1 in this embodiment 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, equation (2) above is executed in the arctangent calculator 721 to calculate 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 becomes small, 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 this second embodiment, as a countermeasure, a lower limiter 722 is provided for the magnitude of the q-axis induced voltage (component orthogonal to the main magnetic flux) Eq. This limits the absolute value of the q-axis induced voltage (component orthogonal to the main magnetic flux) Eq so that it does not become zero, and since the denominator of the q-axis induced voltage Eq is fixed, the variation in the error angle Δθ is suppressed. However, since the numerator, the d-axis induced voltage Ed, is used as is, the calculated result of the error angle Δθ will be smaller than the actual value. Physically, this acts equivalently to lowering the PLL control gain, and the responsiveness decreases.

[0041] However, it is effective in suppressing unstable fluctuations during startup, resulting in smooth acceleration characteristics. The lower limiter value is generally set at approximately 2% to 5% of the rated voltage of the induction motor 1. This is because the output voltage accuracy of the inverter 2 has an error of at least 1%, requiring a limit of this order of magnitude.

[0042] In summary, this embodiment 2 provides the same effects as embodiment 1, and also enables more stable sensorless vector control from startup.

[0043] (Example 3) The drive mechanism of the induction motor 1 in this embodiment 3 will be described using Figure 4.

[0044] Figure 4 shows the speed estimator 7C in this embodiment 3, which is an improvement over the speed estimator 7 in embodiment 1. The drive device for the induction motor 1 in this embodiment 3 can be realized by replacing the speed estimator 7 in Figure 1 with the speed estimator 7C shown in Figure 4.

[0045] In Figure 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 numbered in Figures 1 to 3 described in the previous Examples 1 and 2.

[0046] In Example 3, an induced voltage-velocity feedforward calculator 75 is newly added, encompassing the induced voltage calculator 71. As its calculation output, in addition to the d-axis induced voltage Ed and the q-axis induced voltage Eq, it calculates and outputs the velocity FF (feedforward) value ωrFF. Finally, the velocity estimate ωrEST output by the PLL controller 74 is added to the velocity FF value (velocity feedforward value) ωrFF output by the induced voltage-velocity feedforward calculator 75 using an adder 18L to output a new velocity estimate ωrEST2, which is used as the velocity estimate for sensorless vector control.

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

[0048] Before describing Example 3, we will explain the conventional method disclosed in Patent Document 2.

[0049] In Patent Document 2, the rotational speed of the induction motor 1 is calculated by the following equation (3). ωrFF=(1 / (1+T0s))·(L2 / M)·(1 / Φ2d*)·{v1q-ω1·Lσ·i1dFB-(R1+Lσ·s)·i1qFB} ···(3)

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

[0051] In the technology described in Patent Document 2, the calculation of equation (3) above is realized, but the d-axis secondary magnetic flux command value Φ2d* is actually generated by the first-order lag generator 22 as a first-order lag of the d-axis current command I1dREF, and this value is obtained by multiplying it by the mutual inductance M (mutual inductance gain) using the 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 using 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) above, 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 estimator 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 lies in 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 that will 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 value of line voltage) V1 [V], rated drive frequency ω [rad / s], excitation current (effective value of 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 given by the following equation (5), using the relationship between the rated current I1 (phase current) and the excitation current Ilm. 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: (6) M=(V1 / ω)·((√2) / I1)···(6)

[0062] Equation (6) above is an assumed value for mutual inductance M, and an error of about ±50% is expected, but this is sufficient accuracy for setting as a feedforward value at startup. Also, in order to avoid ωrFF becoming an excessive value as a feedforward value, the value of mutual inductance M can be set to be larger, so 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 mechanism of the induction motor 1 in this embodiment 4 will be explained using 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 numbers as those described in Examples 1 to 3, such as the induced voltage calculator 71 and the error angle calculator 72B, are the same as those in 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 the 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 value stored in the integral compensator 742 (first integral compensator) in the PLL controller 74, and the velocity estimate ωrEST2 is then taken over 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 startup.

[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 mechanism of the induction motor 1 in this embodiment 5 will be described using 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 under ideal conditions.

[0078] In summary, according to this embodiment 5, the same effects as in embodiment 1 can be obtained, and the set value of the mutual inductance M can be automatically corrected 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 mechanism of the induction motor 1 in this embodiment 6 will be described using 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 system 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 numbering 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 key 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, the excitation current command can be set low, reducing the magnitude of the main magnetic flux (flux weakening), which enables 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 enables the induction motor 1 to be driven with high efficiency, thereby reducing carbon emissions, preventing global warming, and contributing to the achievement of Sustainable Development Goals (SDGs), 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. [Explanation of Symbols]

[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 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 that estimates and calculates the rotational speed of the induction motor. The induction motor drive device is characterized in that 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 determines the main magnetic flux direction component and the component perpendicular to the main magnetic flux of the induced voltage, calculates the error angle between the main magnetic flux direction component and the perpendicular component, and adjusts the drive frequency of the induction motor so that this value becomes zero, thereby estimating the rotational speed of the induction motor.

2. In the induction motor drive device according to claim 1, The induction motor drive device is characterized in that the speed estimator includes a first integral compensator that adjusts the drive frequency of the induction motor based on the error angle.

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

4. In the induction motor drive device according to claim 1, The induction motor drive device is characterized by providing a lower limit limiter for the orthogonal component with respect to the main magnetic flux, thereby limiting the absolute value of the orthogonal component so that it does not become zero.

5. In the induction motor drive device according to claim 1, The induction motor drive device is characterized in that 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. In the induction motor drive device according to claim 1, The induction motor drive device is characterized in that the speed estimator includes 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, 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. In the induction motor drive device according to claim 1, The induction motor drive device is characterized in that the speed estimator includes 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; the speed estimate obtained by the induced voltage speed feedforward calculator is added to the speed estimate obtained by adjusting the error angle to start the induction motor with a new speed estimate; and the induction motor drive device includes a mutual inductance compensator that corrects the electrical constants based on the new speed estimate obtained after starting.

8. In the induction motor drive device according to claim 7, The induction motor drive device is characterized in that the mutual inductance compensator includes a mutual intactance compensation operation discriminator that starts or stops the compensation operation according to the operating conditions of the induction motor.

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

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