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 stopped state or a coasting state in speed sensorless control. [Background technology]

[0002] In the field of railway vehicles, the low running resistance of trains is utilized to achieve energy-efficient operation by accelerating under powered running, stopping the power converter (inverter), and extending the coasting period. On the other hand, from the perspective of reducing maintenance, there are an increasing number of applications of speed sensorless control, which does not use a speed sensor.

[0003] In speed sensorless control, a speed estimate is obtained from the motor current. Therefore, during coasting when the inverter operation is stopped, a speed estimate cannot be obtained because no motor current flows. When restarting the inverter from a coasting state, the speed estimate must first be converged and then torque control can be started.

[0004] However, for example, when the inverter is restarted during high-speed coasting to apply the brakes, the braking distance will be extended by the time required for the speed estimate to converge. Therefore, from the perspective of safe operation, it is necessary to converge the speed estimate quickly. However, if the speed estimate does not converge sufficiently and a large error remains, an excessive current will flow in the motor, which may cause a torque shock.

[0005] In view of this, the techniques disclosed in Patent Documents 1 and 2 are known as techniques (initial speed estimation methods) for quickly converging a speed estimate value when restarting from a coasting state. Patent Document 1 discloses a technique in which the initial value of the speed estimation value is first set to the maximum value of the speed range, and then the frequency is swept (speed search) in the direction of zero speed, and the speed search is terminated at the point where the polarity of the q-axis current reverses (zero crossing) to obtain a speed estimation value.

[0006] Patent Document 2 discloses a technique in which, when restarting from a coasting (free-running) state, the initial value of the speed estimation value is first set within the range from the median value 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 becomes zero, and the output of the PI controller is used as the speed estimation value. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-106461 A [Patent Document 2] JP 2022-60914 A Summary of the Invention [Problem to be solved by the invention]

[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 upon restart. In the worst case scenario, the frequency sweep (speed search) is performed up to the minimum value of the speed range (typically a speed of zero), which takes time to obtain a speed estimate.

[0009] In addition, the technology disclosed in Patent Document 2 states that the initial value of the speed estimate at restart is set to between the median and maximum values ​​of the speed range, but does not specifically disclose the detailed manner in which this is done.

[0010] For example, if the initial value is set to the maximum value of the speed range, it takes time for the speed estimation value to converge, as in 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 estimation value can be shortened, but the risk of speed estimation failure 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 estimated speed and the actual speed, so the speed estimate can be converged quickly using PI control. However, if the actual speed is significantly different from the estimated speed, the q-axis current value that flows according to the difference between the actual speed and the estimated speed becomes very small, and it takes time for the estimated speed to converge.

[0012] In particular, immediately after restart, there is a period during which the q-axis current flows in the opposite direction to its normal direction, and if the PI control is set to high response in order to shorten the convergence time, there is a risk that speed estimation will fail.

[0013] In addition, the resistance value of an induction motor varies greatly depending on the operating temperature, and the q-axis current value varies greatly depending on this resistance value. If the polarity of the q-axis current is reversed due to this resistance value, this will lead to a failure of speed estimation.

[0014] Therefore, an object of the present invention is to provide a technology that enables speed estimation at restart to converge in as short a time as possible within a wide speed range, and prevents failure of speed estimation due to temperature fluctuation of the resistance value of the induction motor. [Means for solving the problem]

[0015] In order to solve the above problems, a representative induction motor control device of the present invention includes a rotating coordinate conversion unit that converts an AC current flowing through the induction motor into a d-axis current and a q-axis current in a rotating coordinate system; a rotational angular frequency estimator that determines an estimate of the rotational angular frequency of the induction motor based on a deviation between a q-axis current command and the q-axis current using an initial value of the estimate; a voltage command calculation unit that determines a voltage command for a power converter that supplies AC power to the induction motor based on the estimated value of the rotational angular frequency, the d-axis current command, and the q-axis current command; a rotational angular frequency command generation unit that generates a rotational angular frequency command at the time of restarting the power converter based on a maximum value of the rotational angular frequency; and a rotational angular frequency range division unit that divides the range of rotational angular frequencies based on the d-axis current and q-axis current at the time of restarting, wherein the rotational angular frequency command generation unit starts operation immediately after the power converter is restarted, the rotational angular frequency range division unit divides the range of rotational angular frequencies when the operation of the rotational angular frequency command generation unit ends, and the rotational angular frequency estimator sets an initial value based on the range of rotational angular frequencies divided by the rotational angular frequency range division unit after the operation of the rotational angular frequency command generation unit ends. Effect of the Invention

[0016] According to the present invention, it is possible to cause speed estimation to converge in as short a time as possible when restarting a power converter within a wide speed range, and to prevent estimation failure due to temperature fluctuations of an induction motor. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0017] [Figure 1] 1 is a block diagram showing an example of a control device for an induction motor according to the present invention; [Diagram 2] FIG. 4 is a diagram illustrating an example of a detailed configuration of a rotor angular frequency range dividing unit in the embodiment. [Diagram 3] FIG. 13 is a diagram showing details of a rotor angular frequency range map in an area map provided in a rotor angular frequency range dividing unit. [Figure 4]FIG. 11 is a diagram showing an example of characteristics of the d-axis current and the q-axis current of an induction motor with respect to a rotor angular frequency command when the present invention is applied. [Diagram 5] FIG. 11 is a diagram showing an example of characteristics of the d-axis current and the q-axis current of an induction motor with respect to a rotor angular frequency command when the present invention is not applied. [Figure 6] FIG. 11 is a diagram showing waveforms of the d-axis current and the q-axis current at the time of restart when the actual rotor angular frequency ωr=ωrmax. [Figure 7] FIG. 13 is a diagram showing waveforms of the d-axis current and the q-axis current at the time of restart when the actual rotor angular frequency ωr=0. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals. EXAMPLES

[0019] FIG. 1 is a block diagram showing an example of a control device for an induction motor according to the present invention. Filter (smoothing) capacitor 1 smoothes 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. 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 an induction motor 8, and a current sensor 9 is provided to detect the output currents (iu, iv and iw) from the AC output terminals to the induction motor 8.

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

[0022] The above-described power converter and induction motor 8 are mounted on, for example, a railway vehicle together with a control device 10, which will be described later.

[0023] The control device 10 (the portion enclosed in a dashed line frame in FIG. 1) is made up 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 a d-axis voltage command Vd* and a q-axis voltage command Vq* from the d-axis current command Id*, the q-axis current command Iq*, and the inverter angular frequency command ω1. Integrator 16: Integrates the inverter angular frequency command ω1 to generate the fundamental wave phase θ Rotation / stationary coordinate conversion 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: Inputs 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 phases. Stationary / rotating coordinate conversion unit 17: Generates a d-axis current Id and a 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 generator 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, the q-axis current Iq, the d-axis current command target value Id0*, and the rotor angular frequency command ωrc. Rotor angular frequency estimator 18: Obtains rotor angular frequency estimate ωre from q-axis current command Iq*, q-axis current Iq, and frequency range division information Area. Selection switch 21: Inputs rotor angular frequency command ωrc and rotor angular frequency estimate ωre, and outputs inverter angular frequency command ω1

[0024] Here, assuming that the value of primary resistance R1 of induction motor 8 at the minimum motor temperature in the specifications is a and the value of secondary resistance R2 is b, rotor angular frequency command generating unit 19 generates rotor angular frequency command ωrc for the maximum actual rotor angular frequency value ωmax in the specifications from the following equation. ωrc=ωmax×(a+b / 2) / (a+b) Here, when the values ​​of the primary resistance R1 and the secondary resistance R2 can be considered to be substantially equal, the rotor angular frequency command ωrc may be simply generated by the following equation. ωrc=ωmax×(3 / 4)

[0025] Rotor angular frequency estimator 18 starts operation after rotor angular frequency command generator 19 and rotor angular frequency range divider 20 finish their operations. Based on frequency range division information Area from rotor angular frequency range divider 20, the upper limit or intermediate value of the divided frequency range, or a value between the intermediate value and the upper limit, is set as the initial value of rotor angular frequency estimate value ωre. Thereafter, based on the deviation between q-axis current command value Iq* and q-axis current Iq, rotor angular frequency estimate value ωre is calculated by proportional integral control (PI control).

[0026] The selection switch 21 outputs the rotor angular frequency command ωrc as the inverter angular frequency command ω1 immediately after restart, and outputs the rotor angular frequency estimated value ωre after the rotor angular frequency command generating unit 19 and the rotor angular frequency range dividing unit 20 finish operating.

[0027] FIG. 2 is a diagram showing an example of a detailed configuration of the rotor angular frequency range dividing unit 20 in the embodiment. The on / off switch 30 is turned on only during a period T from the end of the operation period of the rotor angular frequency command generating unit 19 (on period T), and is turned off otherwise.

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

[0029] The area map 33 receives the d-axis current average value Ida and the q-axis current average value Iqa as input, and outputs frequency range division information Area at the end of the operating period.

[0030] FIG. 3 is a diagram showing details of a rotor angular frequency range map in the area map 33 included in the rotor angular frequency range dividing unit 20. As shown in FIG. (1) First area (Area 1) When the d-axis current average value Ida is smaller than the d-axis current threshold value Idth, it is determined to be in a 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 in the range shown in the following equation. ωrc-Δωlmax<ωr<ωrc+Δωhmax Here, ωrc-Δωlmax is the lower limit of the first range (Area 1) when the motor temperature is at its lowest, and ωrc+Δωhmax is the upper limit of the first range (Area 1) when the motor temperature is at its highest.

[0031] (2) Second area (Area 2) When the d-axis current average value Ida is equal to or greater than the d-axis current threshold value Idth and the q-axis current average value Iqa is negative, the area is determined to be a 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) when the motor temperature is at its maximum.

[0032] (3) Third Area (Area 3) When the d-axis current average value Ida is equal to or greater than the d-axis current threshold value Idth and the q-axis current average value Iqa is positive, the range is determined to be a third range (Area 3). 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 in the following equation. ωr<ωrc-Δωlmin Here, ωrc-Δωlmin is the upper limit of the third range (Area3) when the motor temperature is at its lowest.

[0033] FIG. 4 is a diagram showing an example of characteristics of the d-axis current Id and the q-axis current Iq of an induction motor relative to a rotor angular frequency command when the present invention is applied. The upper graph in FIG. 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 being zero, and the rotor angular frequency command ωrc.

[0034] When the motor temperature is at its lowest in the specifications, the value of the primary resistance R1 of the induction motor 8 is a and the value of the secondary resistance R2 is b. For the maximum actual rotor angular frequency value ωmax in the specifications, the rotor angular frequency command ωrc is given by the following equation. ωrc=ωmax×(a+b / 2) / (a+b) From the graph, it can be seen that the following relationship holds regardless of the 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 or smaller than the rotor angular frequency command ωrc. If the motor temperature is x and the intermediate value between the value of Iq when ωr = 0 and the value of Iq when ωr = ωmax is the q-axis current threshold value Iqth(x), then as can be seen from the graph, Iqth(x) is always 0 regardless of the motor temperature (in FIG. 4, Iqth(Tmax) = Iqth(Tmin) = 0).

[0036] Comparing the q-axis current Iq at the maximum motor temperature Tmax and the minimum motor temperature Tmin, it is found that the current Iq is smaller at the minimum motor temperature Tmin (solid line graph), and the margin for the q-axis current threshold Iqth is small. For this reason, the required current detection accuracy is designed according to the minimum motor temperature Tmin.

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

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

[0039] The angular frequency range is divided according to the magnitude relationship between the d-axis current Id and the d-axis current threshold Idth. As shown in the angular frequency ranges (Area1 to Area3) shown at the bottom of the graph in the bottom of Fig. 4, when 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 can change depending on the motor temperature (Tmin to Tmax).

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

[0041] In FIG. 5, in order to explain the effect of the present invention, the rotor angular frequency command ωrc=ωmax / 2 is set, which is intentionally different from the value determined by the present invention (when the present invention is not applied). If the motor temperature x is the q-axis current threshold Iqth(x), which is the intermediate value 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 smaller than the rotor angular frequency command ωrc, this is extremely difficult to handle because the q-axis current threshold Iqth varies depending on the motor temperature.

[0043] In particular, the q-axis current threshold value Iqth(Tmax) at the maximum temperature Tmax has a portion that intersects with the q-axis current characteristics at the minimum temperature Tmin, and using Iqth(Tmax) may result in an erroneous range determination.

[0044] On the other hand, when the q-axis current threshold Iqth(Tmin) at the minimum temperature Tmin is used, the characteristic does not intersect with the q-axis current characteristic, but the distance between the two is closer than that shown in Figure 4, so the margin for current detection is smaller. In Figure 5, the margin is halved.

[0045] In addition, in the characteristics of the q-axis current Iq shown in the upper graph of FIG. 5, when the actual rotor angular frequency ωr is in the vicinity of the rotor angular frequency command ωrc, the following relationship holds: 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 a range far away from the rotor angular frequency command ωrc, When Iq>Iqth(Tmin), ωr<ωrc Iq<Iqth(Tmin)のときωr> ωrc Again, as described in the explanation of FIG. 4, the range selected can change depending on the motor temperature, so if the q-axis current threshold Iqth to be determined differs, the number of cases in which the range is determined incorrectly increases.

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

[0048] Therefore, we will derive the conditions for the rotor angular frequency command ωrc that has such characteristics. If the input to the induction motor is constant in frequency and voltage, and the steady-state values ​​of the dq-axis vectors of the voltage and current are Vd, Vq, Id, and Iq, then Vd and Vq are expressed 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} In the primary-conversion T-type equivalent circuit of the induction motor, the primary resistance is R1, the secondary resistance is R2, the leakage inductance is Lσ, the excitation inductance is M, the resistance is Rσ (=R1+R2), and the secondary time constant is T2=M / R2. Also, the difference between the inverter angular frequency ω1 and the actual rotor angular frequency ωr is ωs (=ω1-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 between the minimum value (ωr = 0) and the maximum value (ωr = ωmax) of the actual rotor angular frequency ωr within the operating range. Then, with |ωs·T2|≫1, the coefficients D and N can be regarded as in the following equations. D=R1+R2·ω1 / ωs N=ω1·Lσ

[0050] Furthermore, as the d-axis current command Id*, the d-axis voltage Vd and the q-axis voltage Vq are given as shown in the following equation. Vd = R1c Id* Vq=ω1·(Lσ+M)·Id* Here, since the primary resistance R1 varies more greatly due to temperature changes than the other constants Lσ and M, the setting value of the primary resistance R1 in the control device is set to R1c.

[0051] Furthermore, if the inverter angular frequency ω1 is sufficiently large, ω1·Lσ≫R1, so 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 where the sum of the q-axis current when the actual rotor angular frequency ωr within the operating range is at its minimum value (ωr = 0) and its maximum value (ωr = ωmax) becomes zero, the inverter angular frequency ω1 is expressed by the following equation. ω1=ωmax×(R1+R2 / 2) / (R1+R2)

[0053] The values ​​of primary resistance R1 and secondary resistance R2 can vary depending on the motor temperature, so if the temperature coefficients of primary resistance R1 and secondary resistance R2 are K1 and K2 at absolute temperature x, the primary resistance R1 and secondary resistance R2 are expressed by the following equations. R1 = K1 x R2=K2·x

[0054] Then, the inverter angular frequency ω1 is expressed by the following equation, which is found to hold regardless of the motor temperature (absolute temperature x). ω1=ωmax×(K1+K2 / 2) / (K1+K2)

[0055] Inside the motor, the temperature of the primary resistor and the temperature of the secondary resistor are strongly correlated, but do not strictly coincide. However, as explained in the explanation of Figure 4, as the motor temperature rises, the motor resistance value always increases, the q-axis current value also increases, and the current detection margin also increases. Therefore, it is preferable to design using the most severe conditions, that is, the resistance value at the minimum motor temperature Tmin.

[0056] In addition, in the case of 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, taking into consideration the difference in resistance value between the primary resistance R1 and the secondary resistance R2, the inverter angular frequency ω1 may be set between the maximum value (ωmax) of the actual rotor angular frequency ωr and ½ of the maximum value (ωmax).

[0058] FIG. 6 is a diagram showing the waveforms of the d-axis current and the q-axis current at the time of restart when the actual rotor angular frequency ωr=ωrmax. When the actual rotor angular frequency ωr = ωrmax, the q-axis current command Iq* is set to zero, the d-axis current command Id* is set to its target value Id0*, and the induction motor is driven with the rotor angular frequency command ωrc = ωrmax × (3 / 4), which shows the d-axis current Id (graph above) and the q-axis current Iq (graph below).

[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 distinguish the positive or negative polarity (especially of the q-axis current) in this form, the values ​​are shown for reference after passing them through a low-pass filter (LPF) (Id (LPF), Iq (LPF)).

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

[0061] Here, as is clear from the characteristics of Iq(LPF), the q-axis current Iq swings to the positive side immediately after startup, but swings to the negative side after time t1, so the range can be correctly determined. The rotor angular frequency command generating unit 19 and rotor angular frequency range dividing unit 20 shown in Fig. 1 only need to operate from time t0 to t2.

[0062] FIG. 7 is a diagram showing waveforms of the d-axis current and the q-axis current at the time of restart when the actual rotor angular frequency ωr=0. When the actual rotor angular frequency ωr = 0, the q-axis current command Iq* is set to zero, the d-axis current command Id* is raised to its target value Id0*, and the rotor angular frequency command ωrc = ωrmax × (3 / 4) is set to drive the induction motor, as shown in the graph above for the d-axis current Id (top graph) and the q-axis current Iq (bottom graph).

[0063] As in Figure 6, the instantaneous values ​​of the d-axis current and the q-axis current are shown as Id (raw value) and Iq (raw value), and the d-axis current and the q-axis current passed through a low-pass filter (LPF) are shown as Id (LPF) and Iq (LPF). Unlike the characteristics shown in FIG. 6, it can be seen that the q-axis current Iq swings in the correct direction (positive side) from the beginning.

[0064] The following describes the effects of the embodiments of the present invention. As described above, the technology disclosed in Patent Document 2, when restarting from coasting (free running), first sets the initial value of the speed estimation value within the range from the median value 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 becomes zero, and uses the output of the PI controller as the speed estimation value.

[0065] However, as shown in Fig. 6, immediately after restart, there is a period during which the q-axis current flows in the opposite direction to its normal direction, and if the PI control is set to high response to shorten the convergence time, there is a risk that speed estimation will fail.

[0066] In addition, when the actual rotor angular frequency ωr and the rotor angular frequency command ωrc are close to each other, the slip angular frequency ωs = ωrc - ωr and the q-axis current Iq are in an almost proportional relationship as shown in Fig. 4. Therefore, the speed estimation value can be quickly converged by the PI control.

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

[0068] Therefore, in the present invention, before starting the operation of PI control for speed estimation, the induction motor 8 is first driven for a predetermined period at a predetermined fixed frequency. If the value of the primary resistance R1 of the induction motor 8 when the motor temperature is at its minimum according to the specifications is a and the value of the secondary resistance R2 is b, then the rotor angular frequency command ωrc is given by the following equation for 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 (ωr=0) of the actual rotor angular frequency ωr 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 value Iqth when determining whether the actual rotor angular frequency ωr and the rotor angular frequency command ωrc are larger or smaller by referring to the q-axis current becomes just zero.

[0070] As long as the motor resistance is proportional to temperature, the q-axis current threshold Iqth remains zero even if the motor temperature fluctuates. Even if the motor resistance is not strictly proportional to temperature, as the motor temperature rises, the motor resistance always increases and the q-axis current value also increases, so the margin for current detection also increases. For this reason, even if the motor temperature fluctuates, it is possible to accurately determine the magnitude relationship between the actual rotor angular frequency ωr and the rotor angular frequency command ωrc by determining the polarity of the q-axis current.

[0071] After this, the rotor angular frequency estimator 18 starts operating, sets the initial value of the rotor angular frequency estimate ωre to the upper limit, intermediate value, or between the intermediate value and the upper limit of the three divided ranges (frequency ranges), and performs PI control so that the deviation between the q-axis current command Iq* and the q-axis current Iq becomes zero, thereby making the rotor angular frequency estimate ωre converge.

[0072] In the present invention, the wide frequency range is divided into three ranges (first range (Area 1) to third range (Area 3)), of which the third range (Area 3) is the widest (lower diagram in FIG. 4), and its frequency range occupies about half of the whole. By limiting the frequency range in this way, it is possible to shorten the convergence period of the speed estimate value at the time of restart.

[0073] According to the above-mentioned embodiment, the present invention includes at least the following aspects. <Aspect 1> The control device for an induction motor includes a rotating coordinate conversion unit that converts the AC current flowing through the induction motor into a d-axis current and a q-axis current in a rotating coordinate system; a rotational angular frequency estimator that determines an estimate of the rotational angular frequency of the induction motor based on the deviation between a q-axis current command and the q-axis current using an initial value of the estimate; a voltage command calculation unit that determines a voltage command for a power converter that supplies AC power to the induction motor based on the estimated value of the rotational angular frequency, the d-axis current command, and the q-axis current command; a rotational angular frequency command generation unit that generates a rotational angular frequency command at the time of restarting the power converter based on a maximum value of the rotational angular frequency; and a rotational angular frequency range division unit that divides the range of the rotational angular frequency based on the d-axis current and q-axis current at the time of restarting. The rotational angular frequency command generation unit starts operation immediately after the restart of the power converter, and the rotational angular frequency range division unit divides the range of the rotational angular frequency when the operation of the rotational angular frequency command generation unit ends, and the rotational angular frequency estimator sets an initial value based on the range of the rotational angular frequency divided by the rotational angular frequency division unit after the operation of the rotational angular frequency command generation unit ends.

[0074] <Aspect 2> In the control device for the induction motor according to the first aspect, the rotational angular frequency command generating unit sets the rotational angular frequency command between a maximum value of the rotational angular frequency and 1 / 2 of the maximum value.

[0075] <Aspect 3> In the control device for the induction motor described in the above aspect 1, the rotational angular frequency command generating 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, and multiplies the rotational angular frequency command by (a+b / 2) / (a+b) times the maximum value of the rotational angular frequency.

[0076] <Aspect 4> In the control device for the induction motor according to the third aspect, the rotational angular frequency command generating unit sets the rotational angular frequency command to 3 / 4 times the maximum value of the rotational angular frequency, assuming that the primary resistance value and the secondary resistance value are equal.

[0077] <Aspect 5> In the control device for an induction motor according to any one of the above aspects 1 to 4, the frequency range division unit obtains d-axis current average value and q-axis current average value by integrating the d-axis current and the q-axis current over a period that is an integer multiple of the reciprocal of the rotational angular frequency command, and divides the range of the rotational angular frequency into a first range when the d-axis current average value is smaller than the d-axis current threshold, a second range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is negative, and a third range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is positive, using the d-axis current average value and the q-axis current average value.

[0078] <Aspect 6> In the control device for an induction motor according to any one of the above aspects 1 to 5, the induction motor and the power converter are mounted on a railway vehicle.

[0079] <Aspect 7> The control device for an induction motor according to any one of the above-mentioned first to sixth aspects is mounted on a railway vehicle.

[0080] <Aspect 8> The control method for the induction motor includes converting the AC current flowing through the induction motor into d-axis current and q-axis current in a rotating coordinate system, determining a rotational angular frequency command at the time of restart based on the maximum value of the rotational angular frequency of the induction motor immediately after restarting a power converter that supplies AC power to the induction motor, dividing a range of rotational angular frequencies based on the d-axis current and q-axis current at restart when the rotational angular frequency command at restart is determined, setting an initial value for an estimate of the rotational angular frequency of the induction motor based on the divided range of rotational angular frequencies, determining an estimate of the rotational angular frequency based on the deviation between the q-axis current command and the q-axis current using the set initial value, and determining a voltage command for the power converter based on the determined estimate of the rotational angular frequency, the d-axis current command, and the q-axis current command.

[0081] <Aspect 9> In the control method for the induction motor according to the eighth aspect, the rotational angular frequency command is set between the maximum value of the rotational angular frequency and 1 / 2 of the maximum value.

[0082] <Aspect 10> A control method for an induction motor according to the eighth aspect, wherein the primary resistance and secondary resistance at the lowest temperature within the operating range of the induction motor are a and b, and 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> In the control method for the induction motor according to the tenth aspect, the primary resistance value and the secondary resistance value are equal to each other, and 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 according to any one of the above aspects 8 to 11, wherein when dividing the range of rotational angular frequency based on the d-axis current and q-axis current at restart, the d-axis current and the q-axis current are integrated over a period that is an integer multiple of the reciprocal of the rotational angular frequency command to obtain an average d-axis current and an average q-axis current, and the range of rotational angular frequency is divided into a first range when the average d-axis current is smaller than the d-axis current threshold, a second range when the average d-axis current is equal to or greater than the d-axis current threshold and the average q-axis current is positive, and a third range when the average d-axis current is equal to or greater than the d-axis current threshold and the average q-axis current is negative.

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

[0086] 1 Filter (smoothing) capacitor, 2~7 Semiconductor switching element, 8 induction motor, 9 current sensor, 10 control device, 11, 12 low pass filter, 13 voltage vector generation unit, 14 rotation / stationary coordinate conversion unit, 15 PWM control unit, 16 integrator, 17 stationary / rotating coordinate conversion unit, 18 rotor angular frequency estimator, 19 rotor angular frequency command generating unit, 20 rotor angular frequency range dividing unit, 21 selector switch, 30 on / off switch, 31,32 integrator, 33 Area Map

Claims

1. a rotating coordinate conversion unit that converts the AC current flowing through the induction motor into a d-axis current and a q-axis current in a rotating coordinate system; a rotational angular frequency estimating unit that obtains an estimate of a rotational angular frequency of the induction motor based on a deviation between a q-axis current command and the q-axis current by using an initial value of the estimate; a voltage command calculation unit that calculates a voltage command for a power converter that supplies AC power to the induction motor based on the estimated value of the rotational angular frequency, a d-axis current command, and the q-axis current command; a rotational angular frequency command generating unit configured to generate a rotational angular frequency command at the time of restarting the power converter based on the maximum value of the rotational angular frequency; a rotational angular frequency range division unit that divides the range of the rotational angular frequency based on the d-axis current and the q-axis current at the time of the restart; Equipped with the rotational angular frequency command generating unit starts operation immediately after the power converter is restarted, the rotational angular frequency range division unit divides the range of the rotational angular frequency when the operation of the rotational angular frequency command generation unit ends, the rotational angular frequency estimation unit sets the initial value based on the range of the rotational angular frequency divided by the rotational angular frequency range division unit after the operation of the rotational angular frequency command generation unit is completed.

2. A control device for an induction motor comprising:

2. The control device for an induction motor according to claim 1, The rotational angular frequency command generating unit sets the rotational angular frequency command between a maximum value of the rotational angular frequency and 1 / 2 of the maximum value.

2. A control device for an induction motor comprising:

3. The control device for an induction motor according to claim 1, The rotational angular frequency command generating unit sets the rotational angular frequency command to (a+b / 2) / (a+b) times the maximum value of the rotational angular frequency, where a is a primary resistance value and b is a secondary resistance value at the lowest temperature within the operating range of the induction motor.

2. A control device for an induction motor comprising:

4. The control device for an induction motor according to claim 3, The rotational angular frequency command generating unit sets the rotational angular frequency command to 3 / 4 times the maximum value of the rotational angular frequency, assuming that the primary resistance value and the secondary resistance value are equal.

2. A control device for an induction motor comprising:

5. The control device for an induction motor according to any one of claims 1 to 4, The rotational angular frequency range division unit integrating the d-axis current and the q-axis current over a period that is an integer multiple of the reciprocal of the rotational angular frequency command to obtain a d-axis current average value and a q-axis current average value; Using the d-axis current average value and the q-axis current average value, the range of the rotational angular frequency is divided into a first range when the d-axis current average value is smaller than a d-axis current threshold, a second range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is negative, and a third range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is positive.

2. A control device for an induction motor comprising:

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

2. A control device for an induction motor comprising:

7. A railway vehicle equipped with the control device for an induction motor according to claim 6.

8. The AC current flowing through the induction motor is converted into the d-axis current and q-axis current of the rotating coordinate system, determining a rotational angular frequency command at the time of restart based on a maximum value of the rotational angular frequency of the induction motor immediately after restarting a power converter that supplies AC power to the induction motor; When the rotational angular frequency command at the time of restart is obtained, a range of the rotational angular frequency is divided based on the d-axis current and the q-axis current at the time of restart; setting an initial value of the estimated value of the rotational angular frequency of the induction motor based on the divided range of the rotational angular frequency; Using the set initial value, an estimate of the rotational angular frequency is obtained based on a deviation between a q-axis current command and the q-axis current; A voltage command for the power converter is calculated based on the estimated value of the rotational angular frequency, the d-axis current command, and the q-axis current command. A method for controlling an induction motor comprising the steps of:

9. A control method for an induction motor according to claim 8, comprising the steps of: The rotational angular frequency command is set between the maximum value of the rotational angular frequency and 1 / 2 of the maximum value. A method for controlling an induction motor comprising the steps of:

10. A control method for an induction motor according to claim 8, comprising the steps of: The primary resistance value and secondary resistance value at the lowest temperature within the operating range of the induction motor are a and b, and the rotational angular frequency command is set to (a+b / 2) / (a+b) times the maximum value of the rotational angular frequency. A method for controlling an induction motor comprising the steps of:

11. A method for controlling an induction motor according to claim 10, comprising the steps of: Assuming that the primary resistance value and the secondary resistance value are equal, the rotational angular frequency command is set to 3 / 4 times the maximum value of the rotational angular frequency. A method for controlling an induction motor comprising the steps of:

12. A control method for an induction motor according to any one of claims 8 to 11, comprising: When dividing the range of the rotational angular frequency based on the d-axis current and the q-axis current at the time of the restart, integrating the d-axis current and the q-axis current over a period that is an integer multiple of the reciprocal of the rotational angular frequency command to obtain a d-axis current average value and a q-axis current average value; Using the d-axis current average value and the q-axis current average value, the range of the rotational angular frequency is divided into a first range when the d-axis current average value is smaller than a d-axis current threshold, a second range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is positive, and a third range when the d-axis current average value is equal to or greater than the d-axis current threshold and the q-axis current average value is negative. A method for controlling an induction motor comprising the steps of:

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