Control device and control method for induction motor

Abstract

To settle a speed estimation within a short period when reactivating a power converter and prevent an estimation failure with respect to a temperature fluctuation of an induction motor.SOLUTION: A control device for an induction motor comprises: a rotation coordinate conversion section for converting an AC current of an induction motor into currents of a (d) axis and a (q) axis; a rotation angle frequency estimation section for calculating an estimate of a rotation angle frequency from an initial value on the basis of a deviation between a current command and the current of the (q) axis; a voltage command calculation section for calculating a voltage command of a power converter based on the estimate and current commands of the (d) axis and the (q) axis; a rotation angle frequency command generation section for generating a rotation angle frequency command at the time of reactivation based on a maximum value of the rotation angle frequency; and a rotation angle frequency range division section for dividing a range of the rotation angle frequency based on the currents of the (d) axis and the (q) axis at the time of reactivation. The rotation angle frequency command generation section starts operating just after the reactivation, the rotation angle frequency range division section divides the range of the rotation angle frequency at the end of the operation of the rotation angle frequency command generation section, and the rotation angle frequency estimation section sets the initial value of the rotation angle frequency on the basis of the divided range after the operation of the rotation angle frequency command generation section ends.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device and a control method for an induction motor, and is particularly suitable for control during restart from a stop state or a coasting state in sensorless speed control.

Background Art

[0002] In the field of railway vehicles, by taking advantage of the fact that the running resistance of a train is small, after power running acceleration, the power converter (inverter) is stopped and the coasting period is lengthened, so as to perform energy-efficient operation. On the other hand, from the perspective of maintenance reduction, etc., the application examples of sensorless speed control without using a speed sensor are increasing.

[0003] In sensorless speed control, since the speed estimated value is obtained from the motor current, during coasting when the operation of the inverter is stopped, no motor current flows, so the speed estimated value cannot be obtained. When restarting the inverter from the coasting state, first, the speed estimated value is converged and then torque control is started.

[0004] However, for example, when restarting the inverter from high-speed coasting and applying brakes, the braking distance will increase by the time required for the convergence of the speed estimated value. Therefore, from the perspective of safe operation, it is necessary to quickly converge the speed estimated value. However, if the convergence of the speed estimated value is insufficient and a large error remains, an excessive current may flow through the motor, causing a torque shock.

[0005] Therefore, as a technique (initial speed estimation method) for quickly converging the speed estimated value during restart from the coasting state, the techniques disclosed in Patent Document 1 and Patent Document 2 are known. Patent Document 1 discloses a technique in which first, the initial value of the speed estimated value is set to the maximum value of the speed range, and the speed search is terminated at the point where the polarity of the q-axis current is reversed (zero crossing) while performing frequency sweep (speed search) in the zero speed direction to obtain the speed estimated value.

[0006] Patent Document 2 discloses a technique in which, when restarting from a coasting (free-running) state, the initial value of the speed estimate is first set within the range from the median to the maximum value of the speed range, and a proportional-integral (PI) controller is used such that the deviation between the q-axis current detection value and the q-axis current command value is zero, and the output of the PI controller is used as the speed estimate. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-106461 [Patent Document 2] Japanese Patent Publication No. 2022-60914 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the technology disclosed in Patent Document 1, the initial value of the speed estimate is set to the maximum value of the speed range when restarting. In the worst case, this results in a frequency sweep (speed search) being performed down to the minimum value of the speed range (typically speed zero), which takes time to obtain the speed estimate.

[0009] Furthermore, while the technology disclosed in Patent Document 2 states that the initial value of the speed estimate during restart is set between the median and maximum values ​​of the speed range, it does not specifically disclose the detailed aspects of this method.

[0010] For example, if the initial value is set to the maximum value of the speed range, it will take time for the speed estimate to converge, similar to the technology disclosed in Patent Document 1. On the other hand, if the initial value is set to the median value of the speed range, the convergence time of the speed estimate can be shortened, but the risk of failure in speed estimation increases.

[0011] If the actual speed is close to the initial value of the speed estimate, the q-axis current flows in proportion to the difference between the speed estimate and the actual speed, so the speed estimate can be converged quickly using PI control. However, if the actual speed deviates significantly from the speed estimate, the q-axis current value that flows in accordance with the difference between the actual speed and the speed estimate becomes very small, and it will take a long time for the speed estimate to converge.

[0012] In particular, immediately after restarting, there is a period when the q-axis current flows in the opposite direction to its normal direction. If the PI control is set to high response to shorten the convergence time, there is a risk that velocity estimation will fail.

[0013] Furthermore, the resistance of an induction motor varies greatly with operating temperature, and the q-axis current value also varies greatly with this resistance. If the polarity of the q-axis current is reversed due to this resistance, it can lead to a failure in speed estimation.

[0014] Therefore, the object of the present invention is to provide a technology that converges the speed estimation during restart as quickly as possible within a wide speed range, and prevents failure of speed estimation due to temperature fluctuations in the resistance value of the induction motor. [Means for solving the problem]

[0015] To solve the above problems, one of the representative induction motor control devices of the present invention is: Driven by a power converter A rotational coordinate transformation unit that converts the alternating current flowing through an induction motor into d-axis current and q-axis current in a rotational coordinate system, The estimated rotational angular frequency of an induction motor, Based on the deviation between the q-axis current command and the q-axis current that rotational angular frequency A rotational angular frequency estimation unit that uses the initial value of the estimated value to determine the rotational angular frequency. , of the induction motor Maximum value of rotational angular frequency and the internal resistance value of the induction motor A rotational angle frequency command generation unit generates a rotational angle frequency command for restarting the power converter based on the above. 、d Axial current 、 q-axis current and the rotational angular frequency command at restart A rotational angular frequency range division unit that divides the range of rotational angular frequencies based on the following, Based on the rotational angular frequency command, d-axis current command, and q-axis current command for the power converter using the rotational angular frequency command or estimated rotational angular frequency at restart electric A voltage command calculation unit that obtains a voltage command for the power converter, The rotational angular frequency command generation unit starts operating immediately after the power converter is restarted.outputs the rotational angular frequency command at restart The rotation angle frequency range dividing unit divides the range of the rotation angle frequency at the end of the operation of the rotation angle frequency command generation unit, and the rotation angle frequency estimation unit is the rotation angle frequency command generation unit and each of the rotational angular frequency range division units After the operation ends to Based on the range of the rotation angle frequency divided by the rotation angle frequency range dividing unit of the estimated rotational angular frequency Set the initial value and thereafter, obtains the estimated rotational angular frequency by proportional-integral control based on the deviation between the q-axis current command and the q-axis current That's what it is.

Advantages of the Invention

[0016] According to the present invention, within a wide speed range, the speed estimation at the restart of the power converter can be converged in as short a time as possible, and the estimation failure due to the temperature fluctuation of the induction motor can be prevented. Problems, configurations, and effects other than those described above will be clarified by the description in the following embodiments for implementation.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Implementing the Invention

[0018] The following describes embodiments for carrying out the present invention with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, in the drawings, identical parts are denoted by the same reference numerals. [Examples]

[0019] Figure 1 is a diagram showing an example of an induction motor control device according to the present invention in block configuration. The filter (smoothing) capacitor 1 smooths the DC power supplied by a DC voltage source (not shown). Semiconductor switching elements 2 and 3 (u-phase), semiconductor switching elements 4 and 5 (v-phase), and semiconductor switching elements 6 and 7 (w-phase) are connected in series to form a three-phase bridge circuit. The filter (smoothing) capacitor 1 is connected in parallel to this three-phase bridge circuit to form a power converter.

[0020] The AC output terminals of the three-phase bridge circuit are connected to the induction motor 8, and a current sensor 9 is provided to detect the output currents (iu, iv, and iw) from these AC output terminals to the induction motor 8.

[0021] The switching state (on and off) of the semiconductor switching elements 2-7 is controlled by the gate signals Gpu, Gnu, Gpv, Gnv, Gpw, and Gnw.

[0022] The power converter and induction motor 8 described above, together with the control device 10 described later, are installed, for example, in a railway vehicle.

[0023] The control device 10 (the part enclosed by the dashed frame in Figure 1) consists of the following components. • Low-pass filter 11: Inputs the d-axis current command target value Id0* and generates the d-axis current command Id*. • Low-pass filter 12: Inputs the q-axis current command target value Iq0* and generates the q-axis current command Iq*. • Voltage vector generation unit 13: Generates d-axis voltage command Vd* and q-axis voltage command Vq* from d-axis current command Id*, q-axis current command Iq*, and inverter angular frequency command ω1. • Integrator 16: Integrates the inverter angular frequency command ω1 to generate the fundamental wave phase θ. • Rotation / stationary coordinate transformation unit 14: Generates u~w phase voltage commands vu*, vv*, and vw* from the d-axis voltage command Vd*, the q-axis voltage command Vq*, and the fundamental wave phase θ. • PWM control unit 15: Takes input to u~w phase voltage commands vu*, vv*, and vw*, and generates gate signals Gpu, Gnu, Gpv, Gnv, Gpw, and Gnw for the upper and lower arms of the u~w phase. • Stationary / rotating coordinate transformation unit 17: Generates the d-axis current Id and the q-axis current Iq based on the u~w phase currents iu, iv, and iw detected by the current sensor 9 and the fundamental wave phase θ. • Rotor angular frequency command generation unit 19: Generates a rotor angular frequency command ωrc from the actual rotor angular frequency maximum value ωmax. • Rotor angular frequency range division unit 20: Generates frequency range division information Area from the d-axis current Id, q-axis current Iq, d-axis current command target value Id0*, and rotor angular frequency command ωrc. • Rotor angular frequency estimation unit 18: From the q-axis current command Iq*, q-axis current Iq, and frequency range division information Area, it calculates the rotor angular frequency estimate ωre. • Selection switch 21: Inputs rotor angular frequency command ωrc and rotor angular frequency estimate ωre, and outputs inverter angular frequency command ω1.

[0024] Here, the rotor angular frequency command generation unit 19 generates the rotor angular frequency command ωrc from the following equation, where a is the value of the primary resistance R1 and b is the value of the secondary resistance R2 of the induction motor 8 at the lowest specified motor temperature, and ωmax is the maximum actual rotor angular frequency specified. ωrc = ωmax × (a + b / 2) / (a ​​+ b) If the values ​​of the primary resistor R1 and the secondary resistor R2 can be considered to be approximately equal, the rotor angular frequency command ωrc may be simply generated using the following equation. ωrc = ωmax × (3 / 4)

[0025] The rotor angular frequency estimation unit 18 starts operating after the rotor angular frequency command generation unit 19 and the rotor angular frequency range division unit 20 have completed their respective operations. Based on the frequency range division information Area from the rotor angular frequency range division unit 20, the unit sets the upper limit, the middle value, or the value between the middle and upper limits of the divided frequency range as the initial value of the rotor angular frequency estimation value ωre. Thereafter, the rotor angular frequency estimation value ωre is determined by proportional-integral control (PI control) based on the deviation between the q-axis current command value Iq* and the q-axis current Iq.

[0026] The selection switch 21 outputs the rotor angular frequency command ωrc as the inverter angular frequency command ω1 immediately after restarting, and outputs the rotor angular frequency estimated value ωre after the rotor angular frequency command generation unit 19 and the rotor angular frequency range division unit 20 have finished operating.

[0027] Figure 2 shows an example of a detailed configuration of the rotor angular frequency range division unit 20 in the embodiment. The on / off switch 30 is turned on only during the last period T of the operating period of the rotor angular frequency command generation unit 19 (on period T), and is turned off at all other times.

[0028] The integrator 31 integrates the d-axis current Id during the ON period T of the ON / OFF switch 30 and outputs the average value Ida of the d-axis current at the end of the operating period. Similarly, the integrator 32 integrates the q-axis current Iq during the ON period T of the ON / OFF switch 30 and outputs the average value Iqa of the q-axis current at the end of the operating period. Here, the ON period T is an integer multiple of the reciprocal of the rotor angular frequency command ωrc (fundamental wave period).

[0029] Area map 33 takes the average current value Ida on the d axis and the average current value Iqa on the q axis as inputs and outputs frequency range division information Area at the end of the operating period.

[0030] Figure 3 shows the details of the rotor angular frequency range map in the area map 33 provided by the rotor angular frequency range division unit 20. (1) First area (Area 1) When the average value of the d-axis current Ida is less than the d-axis current threshold Idth, this is considered the first range (Area 1). In this first range (Area 1), the actual rotor angular frequency ωr is in the vicinity of the rotor angular frequency command ωrc and is within the range shown by the following equation. ωrc-Δωlmax<ωr<ωrc+Δωhmax Here, ωrc - Δωlmax is the lower limit of the first range (Area1) when the motor is at its lowest temperature, and ωrc + Δωhmax is the upper limit of the first range (Area1) when the motor is at its highest temperature.

[0031] (2) Second area (Area 2) When the average d-axis current Ida is greater than or equal to the d-axis current threshold Idth, and the average q-axis current Iqa is negative, this is defined as the second range (Area 2). In this second range (Area 2), the actual rotor angular frequency ωr is greater than the rotor angular frequency command ωrc and is within the range shown by the following equation. ωr>ωrc+Δωhmin Here, ωrc + Δωhmin is the lower limit of the second range (Area2) at the motor's maximum temperature.

[0032] (3) Third area (Area 3) A third range (Area 3) is defined as the case where the average d-axis current Ida is greater than or equal to the d-axis current threshold Idth, and the average q-axis current Iqa is positive. In this third range (Area 3), the actual rotor angular frequency ωr is smaller than the rotor angular frequency command ωrc and is within the range shown by the following equation. ωr<ωrc-Δωlmin Here, ωrc - Δωlmin is the upper limit of the third range (Area 3) at the motor's lowest temperature.

[0033] Figure 4 shows an example of the characteristics of the d-axis current Id and q-axis current Iq of an induction motor in response to a rotor angular frequency command when the present invention is applied. The upper graph in Figure 4 shows the steady-state value of the q-axis current Iq when the induction motor 8 is driven with the d-axis current command target value Id0*, the q-axis current command set to zero, and the rotor angular frequency command ωrc.

[0034] When the motor temperature of the induction motor 8 is at its lowest specified temperature, let the value of the primary resistance R1 be a and the value of the secondary resistance R2 be b. Then, the rotor angular frequency command ωrc is given by the following equation for the maximum actual rotor angular frequency ωmax specified in the specifications. ωrc = ωmax × (a + b / 2) / (a ​​+ b) The graph shows that the following relationship holds true regardless of motor temperature. When Iq > 0, ωr < ωrc When Iq=0, ωr=ωrc When Iq < 0, ωr > ωrc

[0035] In other words, by looking at the polarity of the q-axis current Iq, it is possible to determine whether the actual rotor angular frequency ωr is greater than or less than the rotor angular frequency command ωrc. Here, if we let the motor temperature be x, and define the q-axis current threshold Iqth(x) as the midpoint between the value of Iq when ωr=0 and the value of Iq when ωr=ωmax, then as can be seen from the graph, Iqth(x)=0 is always true regardless of the motor temperature (shown as Iqth(Tmax)=Iqth(Tmin)=0 in Figure 4).

[0036] Comparing the q-axis current Iq at the motor's maximum temperature Tmax and minimum temperature Tmin, we can see that the current Iq at the minimum temperature Tmin is smaller (solid line graph), indicating a smaller margin for the q-axis current threshold Iqth. Therefore, the required current detection accuracy should be designed to match the motor's minimum temperature Tmin.

[0037] The lower graph in Figure 4 shows the steady-state value of the d-axis current Id under the same conditions as the upper graph described above. The d-axis current Id coincides with the d-axis current command target value Id0* (Id=Id0*) only when the rotor angular frequency command ωrc matches the actual rotor angular frequency ωr (ωrc=ωr), and as the difference between the two widens, the d-axis current Id asymptotically approaches the maximum value of the d-axis current Idmax.

[0038] The value of the maximum d-axis current Idmax is given by the following equation in the primary-reduced T-type equivalent circuit of an induction motor, where Lσ is the leakage inductance and M is the excitation inductance. Idmax = Id0 * × (Lσ + M) / Lσ Comparing the d-axis current Id at the motor's maximum temperature Tmax and minimum temperature Tmin, the drop at ωr=ωrc is steeper at the minimum temperature Tmin (solid line graph). As a guideline, the d-axis current threshold Idth should be set to approximately 0.8 to 0.9 times the maximum d-axis current Idmax.

[0039] The angular frequency range is divided based on the relationship between the d-axis current Id and the d-axis current threshold Idth. As shown in the angular frequency range (Area1 to Area3) at the bottom of the graph in Figure 4, if the actual rotor angular frequency ωr is within the range of ωrc-Δωlmax < ωr < ωrc-Δωlmin (section "α" shown in the figure) or ωrc+Δωhmin < ωr < ωrc+Δωhmax (section "β" shown in the figure), the range selected may change depending on the motor temperature (Tmin to Tmax).

[0040] Figure 5 shows an example of the characteristics of the d-axis current Id and q-axis current Iq of an induction motor in response to a rotor angular frequency command when the present invention is not applied. The graph in Figure 5 shows the steady-state values ​​of the d-axis current Id and q-axis current Iq when an induction motor is driven with the d-axis current command target value Id0*, the q-axis current command set to zero, and the rotor angular frequency command ωrc.

[0041] In Figure 5, to illustrate the effects of the present invention, the rotor angular frequency command ωrc = ωmax / 2 is deliberately deviated from the value defined by the present invention (in cases where the present invention is not applicable). If we let the motor temperature be x, and define the q-axis current threshold Iqth(x) as the midpoint between the value of Iq when ωr=0 and the value of Iq when ωr=ωmax, then Iqth(Tmax)>Iqth(Tmin)>0.

[0042] Furthermore, when comparing the q-axis current Iq with the q-axis current threshold Iqth to determine whether the actual rotor angular frequency ωr is greater than or less than the rotor angular frequency command ωrc, the q-axis current threshold Iqth fluctuates depending on the motor temperature, making the process extremely difficult.

[0043] In particular, the q-axis current threshold Iqth(Tmax) at the maximum temperature Tmax intersects with the q-axis current characteristics at the minimum temperature Tmin, and using Iqth(Tmax) may lead to incorrect range determination.

[0044] On the other hand, using the q-axis current threshold Iqth(Tmin) at the lowest temperature Tmin, the characteristics do not intersect with the q-axis current characteristics, but compared to the characteristics shown in Figure 4, the distance between the two approaches, resulting in a smaller margin for current detection. In Figure 5, this margin is halved.

[0045] Furthermore, in the characteristics of the q-axis current Iq shown in the upper graph of Figure 5, the following relationship holds when the actual rotor angular frequency ωr is near the rotor angular frequency command ωrc. When Iq > 0, ωr < ωrc When Iq=0, ωr=ωrc When Iq < 0, ωr > ωrc

[0046] In other words, the q-axis current threshold Iqth for speed discrimination is zero. On the other hand, in the range far from the rotor angular frequency command ωrc, When Iq > Iqth(Tmin), then ωr < ωrc · Iq<Iqth(Tmin)のときωr> ωrc This is the relationship. Here again, as explained in Figure 4, the range selected can change depending on the motor temperature, so if the q-axis current threshold Iqth to be determined is different, the number of cases in which the range determination is incorrect increases.

[0047] Therefore, in order to prevent range determination failures, it is required that the q-axis current threshold Iqth does not fluctuate regardless of the motor temperature, and that the q-axis current threshold Iqth is consistent across the entire range of the actual rotor angular frequency ωr.

[0048] Therefore, we derive the conditions for a rotor angular frequency command ωrc with these characteristics. Assuming that the input to the induction motor is constant in frequency and voltage, and that the steady-state values ​​of the voltage and current dq axis vectors are Vd, Vq, Id, and Iq, then Vd and Vq are given by the following equations. Vd = D·Id - N·Iq Vq = N·Id + D·Iq Here, the coefficients D and N in the above equation are defined as follows. D = Rσ - R² / {1 + (ωs·T²)} 2}+ωr·M·ωs·T2 / {1+(ωs·T2) 2} N=ω1·Lσ+ω1·M / {1+(ωs·T2) 2} Here, in the primary-reduced T-type equivalent circuit of the induction motor, let the primary resistance be R1, the secondary resistance be R2, the leakage inductance be Lσ, the excitation inductance be M, the resistance be Rσ (= R1 + R2), and the secondary time constant be T2 = M / R2. Also, let ωs (= ω1 - ωr) be the difference between the inverter angular frequency ω1 and the actual rotor angular frequency ωr.

[0049] We focus on the range where the actual rotor angular frequency ωr is significantly different from the inverter angular frequency ω1, specifically the range of the minimum value (ωr=0) and maximum value (ωr=ωmax) of the actual rotor angular frequency ωr within the operating range. Then, assuming |ωs·T2|≫1, the coefficients D and N can be considered as follows. D = R1 + R2·ω1 / ωs N=ω1·Lσ

[0050] Furthermore, the d-axis current command Id* is given by the d-axis voltage Vd and q-axis voltage Vq as follows: Vd = R1c·Id* Vq = ω1·(Lσ+M)·Id* Here, since the primary resistance R1 fluctuates more significantly with temperature changes compared to the other constants Lσ and M, the set value of the primary resistance R1 in the control device was set to R1c.

[0051] Furthermore, if the inverter angular frequency ω1 is sufficiently large, then ω1·Lσ≫R1, and the q-axis current Iq can be simplified as follows. Iq=(R1+R2・ω1 / ωs)×(Lσ+M) / Lσ×Id* / (ω1・Lσ)

[0052] Considering the condition under which the sum of the q-axis current at the minimum value (ωr=0) and the q-axis current at the maximum value (ωr=ωmax) of the actual rotor angular frequency ωr within the operating range is zero, the inverter angular frequency ω1 is given by the following equation. ω1 = ωmax × (R1 + R2 / 2) / (R1 + R2)

[0053] Since the values ​​of the primary resistance R1 and secondary resistance R2 can vary depending on the motor temperature, let K1 and K2 be the temperature coefficients for the primary resistance R1 and secondary resistance R2, respectively, at absolute temperature x. Then the primary resistance R1 and secondary resistance R2 are given by the following equations. R1 = K1·x R² = K²·x

[0054] Then, the inverter angular frequency ω1 is given by the following equation, and it can be seen that this holds true regardless of the motor temperature (absolute temperature x). ω1 = ωmax × (K1 + K2 / 2) / (K1 + K2)

[0055] While there is a strong correlation between the primary and secondary resistance temperatures within the motor, they do not strictly coincide. However, as explained in Figure 4, as the motor temperature increases, the motor resistance value always increases, the q-axis current value also increases, and the current detection margin increases. Therefore, it is preferable to design using the resistance value at the most severe condition, i.e., the lowest motor temperature Tmin.

[0056] Furthermore, in most induction motors, the primary resistance R1 and secondary resistance R2 can be considered as R1 ≈ R2, so the inverter angular frequency ω1 can be simplified to the following equation. ω1 = ωmax × 3 / 4

[0057] Furthermore, considering the difference in resistance values ​​between the primary resistor R1 and the secondary resistor R2, the inverter angular frequency ω1 may be set between the maximum value (ωmax) of the actual rotor angular frequency ωr and half of the maximum value (ωmax).

[0058] Figure 6 shows the waveforms of the d-axis current and q-axis current during restart when the actual rotor angular frequency ωr = ωrmax. The graphs above show the d-axis current Id (upper graph) and q-axis current Iq (lower graph) when an induction motor is driven with a rotor angular frequency command ωrc = ωrmax, where the q-axis current command Iq* is set to zero and the d-axis current command Id* is set to its target value Id0*, and the rotor angular frequency command ωrc = ωrmax × (3 / 4).

[0059] Note that the instantaneous values ​​of the d-axis current and q-axis current are shown as raw values ​​(Id(raw value), Iq(raw value)). However, since it is difficult to determine the polarity (especially for the q-axis current) in this raw value, the values ​​after passing through a low-pass filter (LPF) are shown for reference (Id(LPF), Iq(LPF)).

[0060] As shown in the figure, pulsating components are observed in both the d-axis current and the q-axis current, which are the rotor angular frequency command ωrc components. To eliminate the influence of such pulsating components, the average values ​​of the d-axis current Ida and q-axis current Iqa, obtained using integrators 31 and 32 shown in Figure 2, are used for range determination. The period during which the on / off switch 30 shown in Figure 2 is turned on is the period T shown in Figure 6. In this embodiment, this period T is set to two cycles of the reciprocal of the rotor angular frequency command ωrc (fundamental wave period).

[0061] As is clear from the characteristics of Iq (LPF), the q-axis current Iq initially swings to the positive side immediately after startup, but swings to the negative side from time t1 onwards, allowing for correct range determination. The rotor angular frequency command generation unit 19 and the rotor angular frequency range division unit 20 shown in Figure 1 only need to be operated from time t0 to t2.

[0062] Figure 7 shows the waveforms of the d-axis current and q-axis current during restart when the actual rotor angular frequency ωr = 0. The graphs above show the d-axis current Id (upper graph) and q-axis current Iq (lower graph) when an induction motor is driven with the rotor angular frequency command ωrc = ωrmax × (3 / 4), with the q-axis current command Iq* set to zero and the d-axis current command Id* set to its target value Id0*, assuming an actual rotor angular frequency ωr = 0.

[0063] Similar to Figure 6, the instantaneous values ​​of the d-axis current and q-axis current are shown as Id (raw value) and Iq (raw value), respectively, and the values ​​obtained by passing the d-axis current and q-axis current through a low-pass filter (LPF) are shown as Id (LPF) and Iq (LPF). Unlike the characteristics shown in Figure 6, it can be seen that the q-axis current Iq is swinging in the correct direction (positive side) from the beginning.

[0064] The following describes the effects and benefits of the embodiments of the present invention. As described above, the technology disclosed in Patent Document 2, when restarting from coasting (free run), first sets the initial value of the speed estimate within the range from the median to the maximum value of the speed range, configures a proportional-integral (PI) controller such that the deviation between the q-axis current detection value and the q-axis current command value is zero, and uses the output of the PI controller as the speed estimate.

[0065] However, as shown in Figure 6, immediately after restarting, there is a period in which the q-axis current flows in the opposite direction to its original direction. If the PI control is set to high response to shorten the convergence time, there is a risk that velocity estimation will fail.

[0066] Furthermore, as shown in Figure 4, when the actual rotor angular frequency ωr and the rotor angular frequency command ωrc are close together, the slip angular frequency ωs = ωrc - ωr and the q-axis current Iq are approximately proportional. Therefore, the speed estimate can be quickly converged by PI control.

[0067] However, when the actual rotor angular frequency ωr and the rotor angular frequency command ωrc are far apart, the q-axis current Iq actually decreases as the slip angular frequency ωs increases. Therefore, it takes time for the velocity estimate to converge.

[0068] Therefore, in this invention, before starting the operation of PI control for speed estimation, the induction motor 8 is first driven at a predetermined fixed frequency for a predetermined period of time. The rotor angular frequency command ωrc at this time is given by the following equation, where a is the value of the primary resistance R1 and b is the value of the secondary resistance R2 of the induction motor 8 when the motor temperature is at its lowest according to the specifications, and the maximum value ωmax of the actual rotor angular frequency ωr according to the specifications. ωrc = ωmax × (a + b / 2) / (a ​​+ b)

[0069] As a result, the sum of the steady-state value of the q-axis current at the minimum value of the actual rotor angular frequency ωr (ωr=0) and the steady-state value of the q-axis current at the maximum value (ωr=ωmax) becomes zero. This means that the q-axis current threshold Iqth, which is used to determine the relative magnitudes of the actual rotor angular frequency ωr and the rotor angular frequency command ωrc by referring to the q-axis current, is exactly zero.

[0070] As long as the motor's resistance is proportional to temperature, the q-axis current threshold Iqth remains zero and does not change even if the motor temperature fluctuates. Even if the motor's resistance is not strictly proportional to temperature, as the motor temperature rises, the motor's resistance will always increase, and the q-axis current will also increase, thus increasing the margin for current detection. Therefore, even if the motor temperature fluctuates, the relationship between the actual rotor angular frequency ωr and the rotor angular frequency command ωrc can be accurately determined by judging the polarity of the q-axis current.

[0071] Next, the rotor angular frequency estimation unit 18 starts operating and sets the initial value of the rotor angular frequency estimate ωre to the upper limit, the middle value, or between the middle and upper limits of the three previously divided ranges (frequency ranges). PI control is then performed so that the deviation between the q-axis current command Iq* and the q-axis current Iq becomes zero. This aims to converge the rotor angular frequency estimate ωre.

[0072] In this invention, a wide frequency range is divided into three ranges (the first range (Area1) to the third range (Area3)), of which the third range (Area3) has the widest range (lower diagram in Figure 4), and its frequency range accounts for approximately half of the total. By limiting the frequency range in this way, it is possible to shorten the convergence period of the speed estimate during restart.

[0073] According to the embodiments described above, the present invention encompasses at least the following aspects. <Aspect 1> As a control device for induction motors, 0]Driven by a power converter A rotational coordinate transformation unit that converts the alternating current flowing through an induction motor into d-axis current and q-axis current in a rotational coordinate system, The estimated rotational angular frequency of an induction motor, Based on the deviation between the q-axis current command and the q-axis current that rotational angular frequency A rotational angular frequency estimation unit that uses the initial value of the estimated value to determine the rotational angular frequency. , of the induction motor Maximum value of rotational angular frequency and the internal resistance value of the induction motor A rotational angle frequency command generation unit generates a rotational angle frequency command for restarting the power converter based on the above. 、d Axial current 、 q-axis current and the rotational angular frequency command at restart A rotational angular frequency range division unit that divides the range of rotational angular frequencies based on the following, Based on the rotational angular frequency command, d-axis current command, and q-axis current command for the power converter using the rotational angular frequency command or estimated rotational angular frequency at restart electric The rotational angular frequency command generation unit starts operating immediately after the power converter is restarted. A voltage command calculation unit that obtains a voltage command for the power converter, The rotation angular frequency range division unit divides the range of rotation angular frequencies when the rotation angular frequency command generation unit finishes operating, and the rotation angular frequency estimation unit divides the range of rotation angular frequencies when the rotation angular frequency command generation unit finishes operating. outputs the rotational angular frequency command at restart After the operation is complete and each of the rotational angular frequency range division units Based on the range of rotational angular frequencies divided by the rotational angular frequency division unit to Set initial value of the estimated rotational angular frequency .

[0074] <Aspect 2> The control device for the induction motor described in Embodiment 1 above, wherein the rotational angular frequency command generation unit is: and thereafter, obtains the estimated rotational angular frequency by proportional-integral control based on the deviation between the q-axis current command and the q-axis current The rotational angular frequency command is set to a value between the maximum rotational angular frequency and half of that maximum value.

[0075] <Aspect 3> The control device for an induction motor described in Embodiment 1 above, wherein the rotational angular frequency command generation unit sets the primary resistance value and secondary resistance value at the lowest temperature within the operating range of the induction motor as a and b, At restart The rotational angular frequency command is set to (a+b / 2) / (a+b) times the maximum value of the rotational angular frequency.

[0076] <Aspect 4> The control device for an induction motor described in embodiment 3 above, wherein the rotational angular frequency command generation unit assumes that the primary resistance value and the secondary resistance value are equal, At restart The rotational angular frequency command is set to 3 / 4 times the maximum value of the rotational angular frequency.

[0077] <Aspect 5> A control device for an induction motor as described in any of the above embodiments 1 to 4, wherein the frequency range division unit comprises the d-axis current and the q-axis current At restart The average d-axis current and q-axis current are calculated by integrating over a period that is an integer multiple of the reciprocal of the rotation angular frequency command. Using these average d-axis and q-axis currents, the range of rotation angular frequency is divided into three ranges: a first range when the average d-axis current is less than the d-axis current threshold, a second range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is negative, and a third range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is positive.

[0078] <Aspect 6> A control device for an induction motor as described in any of the above embodiments 1 to 5, wherein the induction motor and power converter are mounted on a railway vehicle.

[0079] <Aspect 7> A control device for an induction motor, as described in any of the above embodiments 1 to 6, is installed in the railway vehicle.

[0080] <Aspect 8> As a control method for induction motors, the AC current flowing through the induction motor is converted into d-axis and q-axis currents in a rotating coordinate system, and immediately after restarting the power converter that supplies AC power to the induction motor, the maximum value of the rotational angular frequency of the induction motor is set.At restart Based on and the internal resistance value of the induction motor When the rotational angular frequency command at startup is determined, and the rotational angular frequency command at restart is determined, 、d Axial current 、 q-axis current at re The range of rotational angular frequencies is divided based on this, and the rotational angular frequency of the induction motor is determined based on the divided range of rotational angular frequencies. and the rotational angular frequency command at restart A fixed initial value is set, and the deviation between the q-axis current command and the q-axis current is calculated using the set initial value. number est Rotational angular frequency by proportional-integral control Determine the constant value, number est The rotational angle frequency that was determined The rotational angular frequency command at restart obtained Based on the constant value, the d-axis current command, and the q-axis current command, the voltage command for the power converter is determined.

[0081] <Pattern 9> The induction motor control method described in the above embodiment 8, number est The rotational angular frequency command is set to a value between the maximum rotational angular frequency and half of that maximum value.

[0082] <Aspect 10> A control method for an induction motor as described in embodiment 8 above, wherein the primary resistance value and secondary resistance value at the lowest temperature within the operating range of the induction motor are a and b, At restart The rotational angular frequency command is set to (a+b / 2) / (a+b) times the maximum value of the rotational angular frequency.

[0083] <Aspect 11> The induction motor control method described in the above embodiment 10, wherein the primary resistance value and the secondary resistance value are equal, At restart The rotational angular frequency command is set to 3 / 4 times the maximum value of the rotational angular frequency.

[0084] <Aspect 12> A control method for an induction motor as described in any of embodiments 8 to 11 above, wherein when dividing the range of rotational angular frequencies based on the d-axis current and q-axis current at restart, the d-axis current and q-axis current At restart At restartThe average d-axis current and q-axis current are calculated by integrating over a period that is an integer multiple of the reciprocal of the rotation angular frequency command. Using these average d-axis and q-axis currents, the rotation angular frequency range is divided into three ranges: a first range when the average d-axis current is less than the d-axis current threshold, a second range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is positive, and a third range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is negative.

[0085] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0086] 1. Filter (smoothing) capacitor, 2-7. Semiconductor switching elements, 8 induction motor, 9 current sensor, 10 control device, 11,12 low-pass filter, 13 Voltage vector generation unit, 14 Rotation / stationary coordinate transformation unit, 15 PWM control unit, 16 Integrator, 17 Stationary / Rotational Coordinate Transformation Unit, 18 Rotor Angular Frequency Estimation Unit, 19 Rotor angular frequency command generation unit, 20 Rotor angular frequency range division unit, 21 Selector switch, 30 On / Off switch, 31, 32 Integrator, 33 Area Map

Claims

1. A rotational coordinate transformation unit that converts the alternating current flowing through an induction motor driven by a power converter into d-axis current and q-axis current of a rotational coordinate system, A rotational angular frequency estimation unit that determines the rotational angular frequency of the induction motor based on the deviation between the q-axis current command and the q-axis current, using an initial value of the rotational angular frequency estimation unit, A rotational angular frequency command generation unit generates a rotational angular frequency command for restarting the power converter based on the maximum rotational angular frequency of the induction motor and the internal resistance value of the induction motor. A rotation angular frequency range division unit divides the range of the rotation angular frequency based on the d-axis current, the q-axis current, and the rotation angular frequency command at the time of restart, A voltage command calculation unit that determines a voltage command for the power converter based on the rotational angular frequency command for the power converter, the d-axis current command and the q-axis current command, using the rotational angular frequency command or the rotational angular frequency estimate value used during the restart. Equipped with, The rotational angular frequency command generation unit starts operating immediately after the power converter is restarted and outputs the rotational angular frequency command at the time of the restart. The rotation angular frequency range division unit divides the range of the rotation angular frequency when the operation of the rotation angular frequency command generation unit is completed. After the rotation angular frequency estimation unit and the rotation angular frequency range division unit have completed their respective operations, the rotation angular frequency estimation unit sets an initial value of the rotation angular frequency estimation value based on the rotation angular frequency range division unit, and thereafter determines the rotation angular frequency estimation value by proportional-integral control based on the deviation between the q-axis current command and the q-axis current. A control device for an induction motor, characterized by the following features.

2. A control device for an induction motor according to claim 1, The rotational angular frequency command generation unit sets the rotational angular frequency command for restart to be between the maximum value of the rotational angular frequency and half of that maximum value. A control device for an induction motor, characterized by the following features.

3. A control device for an induction motor according to claim 1, The rotational angular frequency command generation unit sets the rotational angular frequency command at restart to (a + b / 2) / (a ​​+ b) times the maximum value of the rotational angular frequency, with a and b being the primary and secondary resistance values ​​at the lowest temperature within the operating range of the induction motor. A control device for an induction motor, characterized by the following features.

4. A control device for an induction motor according to claim 3, The rotational angular frequency command generation unit assumes that the primary resistance value and the secondary resistance value are equal, and sets the rotational angular frequency command at the time of restart to 3 / 4 times the maximum value of the rotational angular frequency. A control device for an induction motor, characterized by the following features.

5. A control device for an induction motor according to any one of claims 1 to 4, The rotational angular frequency range division unit is, The average values ​​of the d-axis current and the q-axis current are obtained by integrating the d-axis current and the q-axis current over a period that is an integer multiple of the reciprocal of the rotation angular frequency command at the time of restart. Using the average d-axis current and the average q-axis current, the range of rotational angular frequency is divided into three ranges: a first range when the average d-axis current is less than the d-axis current threshold, a second range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is negative, and a third range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is positive. A control device for an induction motor, characterized by the following features.

6. A control device for an induction motor according to claim 5, The induction motor and the power converter are to be mounted on a railway vehicle. A control device for an induction motor, characterized by the following features.

7. A railway vehicle equipped with the control device for an induction motor as described in claim 6.

8. The alternating current flowing through the induction motor is converted into d-axis and q-axis currents in a rotating coordinate system. Immediately after restarting the power converter that supplies AC power to the induction motor, the rotational angular frequency command at the time of restart is determined based on the maximum value of the rotational angular frequency of the induction motor and the internal resistance value of the induction motor. When the rotational angular frequency command at the time of restart is determined, the range of the rotational angular frequency is divided based on the d-axis current, the q-axis current, and the rotational angular frequency command at the time of restart. Based on the divided range of rotational angular frequencies, an initial value is set for the estimated rotational angular frequency of the induction motor. Using the set initial value, the rotational angular frequency estimate is obtained by proportional-integral control based on the deviation between the q-axis current command and the q-axis current. Based on the rotational angular frequency command obtained during the restart or the estimated rotational angular frequency, the d-axis current command, and the q-axis current command, a voltage command for the power converter is determined. A control method for an induction motor characterized by the following features.

9. A method for controlling an induction motor according to claim 8, The rotational angular frequency command during the restart is set to be between the maximum value of the rotational angular frequency and half of that maximum value. A control method for an induction motor characterized by the following features.

10. A method for controlling an induction motor according to claim 8, Let a and b be the primary and secondary resistance values ​​at the lowest temperature within the operating range of the induction motor, and set the rotational angular frequency command during restart to (a + b / 2) / (a ​​+ b) times the maximum value of the rotational angular frequency. A control method for an induction motor characterized by the following features.

11. A method for controlling an induction motor according to claim 10, Assuming that the primary resistance value and the secondary resistance value are equal, the rotational angular frequency command during restart is set to 3 / 4 times the maximum value of the rotational angular frequency. A control method for an induction motor characterized by the following features.

12. A method for controlling an induction motor according to any one of claims 8 to 11, When dividing the range of rotational angular frequencies based on the d-axis current and the q-axis current, The average values ​​of the d-axis current and the q-axis current are obtained by integrating the d-axis current and the q-axis current over a period that is an integer multiple of the reciprocal of the rotation angular frequency command at the time of restart. Using the average d-axis current and average q-axis current, the range of rotational angular frequency is divided into three ranges: a first range when the average d-axis current is less than the d-axis current threshold, a second range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is positive, and a third range when the average d-axis current is greater than or equal to the d-axis current threshold and the average q-axis current is negative. A control method for an induction motor characterized by the following features.

Images