Motor Control Device

Abstract

To shorten a time from input of an operation command to re-activation of an induction motor by minimizing shock at the time of re-activation even in a case where a residual voltage is attenuated in a configuration where a voltage detector is disposed at an output side of a power converter.SOLUTION: A motor control device comprises: a power converter configured to convert a DC voltage into a three-phase AC voltage of a variable voltage and a variable frequency and supply it to an induction motor; an inter-phase time detection section configured to detect an inter-phase voltage of the induction motor for two or more phase intervals; a current detection section configured to detect a phase current of the induction motor; a current adjustment section configured to calculate a voltage command value so that a component obtained by converting a detected current value onto a synchronous coordinate axis matches a current command value; and a re-activation control section. Therein, the re-activation control section is configured to: when activating the induction motor from a state where an initial velocity is generated, implement an excitation operation for velocity estimation to give a stepwise current command value of a predetermined magnitude to the current adjustment section for a predetermined time; after cutting off output of the power converter, perform convergence arithmetic processing for obtaining a rotation velocity and a rotation speed of the induction motor and a phase of a residual secondary magnetic flux using the detected values of the inter-phase voltages for two or more phase intervals; and restart control of the induction motor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a motor control device that estimates a rotor speed when starting an induction motor from a state in which the induction motor has an initial speed. [Background technology]

[0002] Variable speed motor drives that use power converters to drive electric motors at variable speeds are used in various fields. Among electric motors, induction motors are widely used because of their relatively simple structure and robustness. In addition, they have the advantage that they can be driven by directly connecting to a commercial power source as a backup in the event that the control device breaks down.

[0003] When restarting such an induction motor during a period when the rotor is in a free-running state, such as after a momentary power outage or when switching from commercial operation, it is desirable to acquire the rotor speed and restart the motor by matching the output frequency to the rotor speed in order to reduce mechanical shock at startup.

[0004] One way to obtain the rotor speed during free run is to use the induced voltage generated by the secondary magnetic flux remaining in the rotor. Even if the residual magnetic flux is small, a relatively large induced voltage can be obtained if the rotation speed is high. However, if a long time has passed since the motor stopped operating and the secondary magnetic flux has decreased to near zero, the induced voltage cannot be observed.

[0005] In addition, depending on the installation environment, due to space limitations, a small voltage may be induced in the wiring of the motor due to the influence of wiring of a large-power device located close to the motor to be controlled. If such a voltage is observed to have an amplitude larger than the residual voltage of the motor, it may not be possible to correctly estimate the rotor speed.

[0006] For example, Patent Document 1 discloses a method for obtaining the rotor speed in a free-running state using residual magnetic flux. According to this method, when it is determined that the residual magnetic flux is small and speed estimation is difficult, a direct current is applied to the motor, and the input voltage vector of the induction motor is detected or estimated during the application of the direct current. Then, the secondary magnetic flux is obtained by integrating the result obtained by subtracting the voltage drop due to the primary resistance of the induction motor and the voltage drop due to the leakage inductance from the voltage vector, and the center of the vector is found from the change in the vector at three points, and the rotational angular frequency is estimated from the relationship between the passage of time and the phase.

[0007] In this method, when the rotor is rotating at a low speed, it takes a long time for the vector locus of the secondary magnetic flux to be obtained. During that time, time passes with DC current flowing through the induction motor, which is thought to generate a braking torque proportional to the rotation speed.

[0008] In response to this problem, Patent Document 2 proposes a method for shortening the time for which a DC current is applied by integrating the induced voltage minus the voltage drop due to the primary resistance when a DC current is applied to an induction motor in a free-running state to estimate the secondary magnetic flux, and estimating the rotation speed using the second-order differential value of the estimated q-axis component of the secondary magnetic flux. The second-order differential value of the estimated secondary magnetic flux immediately after the inverter that drives the induction motor starts to operate contains a component that is proportional to the rotation speed. Therefore, the rotation speed can be estimated by dividing the second-order differential value by the product of the excitation inductance, the reciprocal of the secondary time constant, and the excitation current. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 3535735 [Patent Document 2] Patent No. 6447183 Summary of the Invention [Problem to be solved by the invention]

[0010] The methods disclosed in these patent documents all use the amount of magnetic flux generated when a current flows through a motor, and therefore are presumed to assume that the initial residual magnetic flux is close to zero. For example, if these methods are used in a motor with a relatively long secondary time constant when a relatively large amount of magnetic flux remains, such as when the motor is restarted shortly after free running, there is a risk of torque disturbance occurring due to the current applied to obtain magnetic flux information used to estimate the speed and the residual secondary magnetic flux.

[0011] Furthermore, these methods estimate only the rotation speed and rotation direction, and when restarting the motor while the residual magnetic flux is relatively large, there is a risk of a rush current flowing depending on the difference between the induced voltage due to the residual magnetic flux and the initial voltage at the time of restarting the motor.

[0012] When controlling the torque of a motor, it is assumed that the motor will be switched between the operating state and the free-running state relatively frequently, and that it will be restarted in a short time after being placed in the free-running state. In order to suppress current disturbance during restart, it is necessary to apply an output voltage that takes into account the magnitude and phase of the induced voltage due to the residual secondary magnetic flux as the initial value before restarting the motor.

[0013] To obtain the residual voltage accurately without causing torque disturbance, it is desirable to provide a voltage detector on the output side of the power converter. However, as time passes after free-running, the residual voltage attenuates, and when the induced voltage becomes lower than the noise component in the installation environment, it becomes difficult to accurately estimate the speed.

[0014] Therefore, the present invention provides an electric motor control device that has a configuration in which a voltage detector is placed on the output side of a power converter, minimizes the shock at the time of restart even when the residual voltage has attenuated, ensures noise resistance, and shortens the time from when an operation command is input to when the motor is restarted. [Means for solving the problem]

[0015] The motor control device of the embodiment includes: a power converter that converts a DC voltage into a three-phase AC voltage with a variable voltage and variable frequency and supplies the AC voltage to an induction motor; A phase-to-phase voltage detection unit that detects phase-to-phase voltages between two or more phases of the induction motor; A current detection unit that detects a phase current of the induction motor; a current adjusting unit that calculates a voltage command value so that a component obtained by converting the detected value of the phase current onto a synchronous coordinate axis coincides with a current command value; When starting the induction motor from an initial speed state, A speed estimation excitation operation is performed to provide a step-like current command value having a predetermined magnitude to the current adjustment unit for a predetermined period of time; and a restart control unit that, after cutting off the output of the power converter, performs convergence calculation processing to obtain the rotational speed and rotational direction of the induction motor and the phase of the residual secondary magnetic flux using detection values ​​of the phase-to-phase voltage between two or more phases, and restarts control of the induction motor. In addition, the motor control device of the embodiment includes a power converter / current adjustment unit similar to the above, When a request to stop free-run operation is input while the induction motor is in an operating state, or when a main circuit potential of a power converter that drives the induction motor is reduced and it is determined that operation is difficult, and the induction motor transitions to a free-run state, the convergence calculation process is constantly performed; and a restart control unit that, when an operation command is input again or the main circuit potential is restored, restarts control of the induction motor using the rotational speed and rotational direction and the phase of the residual secondary magnetic flux obtained from the convergence calculation process at that time. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a configuration of an electric motor control device according to an embodiment. [Diagram 2] Functional block diagram showing the configuration of the convergence calculation processing unit [Diagram 3] Diagram showing the relationship between rotor magnetic flux and induced voltage [Figure 4] A diagram showing the DQ synchronous coordinate axis and the MT synchronous coordinate axis. [Diagram 5] A diagram explaining how to observe the phase difference between two phase voltages. [Figure 6]Signal waveform diagram showing the state of transition from the stop mode to the initial speed estimation mode [Figure 7] A diagram showing waveforms of phase-to-phase voltage and torque current when an induction motor is restarted from a coasting state. [Figure 8] A waveform diagram showing the change in secondary magnetic flux when a current command value is given for a predetermined time. [Figure 9] Flowchart showing the processing contents of the control device [Figure 10] Timing chart showing the case where the phase-to-phase voltage level judgment is NG in the case of pre-start speed estimation operation: Type 1, speed estimation excitation operation: enabled, and pre-start excitation operation: disabled. [Figure 11] Timing chart showing the case where the phase-to-phase voltage level judgment is NG in the case of pre-start speed estimation operation: Type 1, speed estimation excitation operation: enabled, and pre-start excitation operation: enabled [Figure 12] A timing chart showing a case similar to that shown in FIG. 10 where the phase difference between the phases is judged to be NG. [Figure 13] Flowchart showing the processing contents of the control device [Figure 14] Timing chart showing the cases of pre-start speed estimation operation: Type 2, speed estimation excitation operation: enabled, pre-start excitation operation: enabled DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment will be described below. As shown in Fig. 1, each phase terminal of a three-phase AC power source 1 is connected to an AC input terminal of a full-wave rectifier circuit 2 made of a diode bridge. A smoothing capacitor 3 and a power converter 4 are connected between DC output terminals of the full-wave rectifier circuit 2. Each phase output terminal of the power converter 4, which is an inverter, is connected to each phase winding terminal of an induction motor 5.

[0018] The control device 6, which is a restart control section, controls the power converter 4 to convert the DC voltage into a three-phase AC voltage with variable voltage and variable frequency. Current detection sections 7U and 7W are provided at the U-phase and W-phase output terminals of the power converter 4, and the U-phase and W-phase currents i u ,i w are input to a UVW / dq converter 8. The UVW / dq converter 8 converts the three-phase currents into dq axis currents in vector control and inputs them to a current adjustment unit 9 and a speed estimation processing unit 10.

[0019] Each phase output terminal of the power converter 4 is connected to an input terminal of a phase-to-phase voltage detector 11. The phase-to-phase voltage detector 11 detects a UV phase-to-phase voltage v uv and WV phase-to-phase voltage v wv These are input to a convergence calculation processing unit 12, an interphase voltage level determination unit 13, and an interphase voltage phase difference determination unit 14. The gate drive permission signal is provided to one input terminal of an AND gate 16 via a NOT gate 15, and a speed estimation operation command is provided to the other input terminal of the AND gate 16. The output signal of the AND gate 16 is input to the convergence calculation processing unit 12 as a convergence calculation execution command.

[0020] The convergence calculation processing unit 12 performs a convergence calculation process, which will be described later, on the input interphase voltage to obtain an initial secondary magnetic flux command value φ rd_ref_Init , speed command initial value ω re_ref_Init and the output voltage phase initial value θ re_Init Generate and output the secondary magnetic flux command initial value φ rd_set_Init is input to the magnetic flux / current command generator 17, and the initial speed command value ω re_ref_Init is input to the speed command generating unit 18. The output voltage phase initial value θ re_Init is input to the integrator 27.

[0021] The phase-to-phase voltage level determination unit 13 compares the input phase-to-phase voltage with a threshold and outputs a determination result OK / NG to the restart processing unit 19. The phase-to-phase voltage phase difference determination unit 14 compares the input phase difference between the phase voltages with a threshold and outputs a determination result OK / NG to the restart processing unit 19.

[0022] The magnetic flux / current command generating unit 17 also receives a secondary magnetic flux target value φ rd_set and the initial secondary magnetic flux command value φ rd_ref_Init Based on these input values, the magnetic flux / current command generating unit 17 calculates the d-axis current target value i sd_set , the secondary magnetic flux target value φ rd_set_Filt , the filtered d-axis current target value i sd_set_Filt , and outputs the secondary magnetic flux target value φ rd_set is output as is.

[0023] The speed command generating unit 18 also receives a speed target value ω re_set The speed command generating unit 18 calculates a speed command value ω re_ref The speed controller 20 generates the speed estimation value ω re_est is entered.

[0024] Further, the restart processing unit 19 receives an operation command "ON / OFF", a pre-start speed estimation operation "Type1 / Type2 / disabled", a pre-start speed estimation operation==Type2 operation "enabled / disabled", and a pre-start excitation operation "enabled / disabled". Based on these input signals, the restart processing unit 19 controls the speed estimation excitation operation command "ON / OFF", the pre-start excitation operation command "ON / OFF", the speed control operation command "ON / OFF", the speed estimation operation command "ON / OFF", the speed estimation excitation current setting i mag_1 , switch setting selection, and so on. The speed estimation excitation operation command, pre-start excitation operation command, and speed control operation command are given to input terminals of a three-input OR gate 21. The output signal of the OR gate 21 is input to the power converter 4 and the NOT gate 15 as a gate drive permission signal.

[0025] The two input terminals of the current adjustment unit 9 are connected to the changeover switches 22 and 23, respectively. The movable contact of the changeover switch 22 is switched between the fixed contact AB and the fixed contact CD by the above-mentioned switch setting selection. The fixed contact AB is connected to the speed estimation excitation current setting i mag_1is given, and the fixed contact CD has the d-axis current target value i sd_set i mag_2 The symbols A, B, C, and D attached to the fixed contacts represent the switch contact symbols selected in the processing of the control device shown in Figs.

[0026] The movable contact of the changeover switch 23 is switched between the fixed contacts ABC and D by switch setting selection. A zero value is applied to the fixed contacts ABC, and the output signal of the speed control unit 20 is applied to the fixed contact D. The signals input to the current adjustment unit 9 via the changeover switches 22 and 23 are the D-axis current command i sd_ref , Q-axis current command i sq_ref It becomes.

[0027] Q-axis current command i sq_ref is input to the slip calculation unit 24. The slip calculation unit 24 also receives a secondary magnetic flux command φ rd_ref The slip calculation unit 24 calculates the slip frequency ω of the induction motor 5 based on these input values. slip The adder 25 calculates and outputs the result to the adder 25. The adder 25 is connected to a movable contact of a changeover switch 26, and the movable contact is switched to fixed contacts A, BC, and D by switch setting selection. A zero value is applied to the fixed contact A, and an initial speed command value ω is applied to the fixed contact BC. re_ref_Init is given, and the fixed contact D has the estimated speed ω re_est is given.

[0028] The sum of the adder 25 is the output frequency ω stat The integration result of the integrator 27 is the output voltage phase θ re_c The current adjustment unit 9 receives the D- and Q-axis currents i d ,i q The current adjustment unit 9 adjusts the current i d ,i qThe compensation voltage is generated by, for example, performing a proportional-integral operation on the difference between the compensation voltage and the induction motor, and is output to the voltage calculation unit 29. The voltage calculation unit 29 calculates the compensation voltage and the voltage command v sd_ref ,v sq_ref and outputs it to the dq / UVW converter 28. The dq / UVW converter 28 converts the input voltage command into a three-phase voltage command, and also generates a PWM signal and outputs it to the power converter 4.

[0029] FIG. 2 is a functional block diagram showing the internal configuration of the convergence calculation processing unit 12. uv ,v wv is converted to a three-phase voltage by the UV,WV / UVW converter 31, and is further converted to a d-axis voltage v via the UVW / αβ converter 32 and the αβ / dq converter 33. dc ,q-axis voltage v qc These voltages v dc ,v qc is input to the error calculator 34 and the square sum calculator 35. The error calculator 34 calculates the phase error θ err is calculated. The phase error θ err is given a sign (-) by the encoder 36, and the proportional gain K P_PLL , K I_PLL is multiplied.

[0030] An output terminal of the gain applicator 37P is connected to a START-side fixed contact of a changeover switch 38P, and an output terminal of the gain applicator 37I is connected to a START-side fixed contact of a changeover switch 38I via a Δt applicator 39. A zero value is applied to the STOP side fixed contact of the switch 38. A movable contact of the switch 38P is connected to one input terminal of an adder 41. A movable contact of the switch 38I is connected to the other input terminal of the adder 41 via another adder 40.

[0031] The output signal of the adder 40 is fed back to the sum input of the adder 40 via a unit delay element 42. The changeover of the changeover switch 38 is performed by a convergence calculation execution command signal.

[0032] The output signal of the adder 41 is the estimated speed ω re_est_PLL This is input to the adder 44 via the Δt assigner 43. The output signal of the adder 44 is the estimated phase θ re_est_PLL is input to the αβ / dq converter 33, and the output voltage phase initial value θ re_Init The output signal of the adder 44 is fed back to the adder input via a unit delay element 45. The estimated speed ω re_est_PLL is input to the input B of the divider 46, and the speed command initial value ω re_ref_Init The output signal of the square sum calculator 35 is input to the input A of the divider 46. The divider 46 divides the division result A / B into the secondary magnetic flux command initial value φ rd_ref_Init is output to the outside.

[0033] Next, a speed estimation method in this embodiment will be described. When vector control is performed on the rotor magnetic flux of an induction motor, if the direction of the magnetic flux is defined as the M axis and the phase 90 degrees ahead of that is defined as the T axis as shown in Fig. 3, then an induced voltage is generated in the T axis direction. Actual rotor speed: θ, which corresponds to the electrical angle re The integral value of is the phase; position information representing the M-axis. Since the M-axis is the magnetic flux direction, θ flux Let us assume that.

[0034]

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[0035] In order to estimate the speed and residual flux direction of the rotor with the initial speed, we first define the DQ synchronous coordinate axis that corresponds to the estimated MT synchronous coordinate axis. Figure 4 shows the relationship between the estimated DQ synchronous coordinate axis calculated in the controller and the MT synchronous coordinate axis in the actual motor. The DQ synchronous coordinate axis is expressed as the currently recognized estimated speed ω re_est_PLL , and the estimated phase θ corresponding to the time integral re_est_PLL The direction of is defined as the D axis.

[0036]

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[0037] Observe the induced voltage and estimate the phase θ re_est_PLL The DQ synchronous coordinate system is converted to the DQ synchronous coordinate system using the D and Q axis components v dc , v qc If the MT synchronous axis and the DQ synchronous axis are the same, v qc Since only v dc Speed ​​estimation should be performed so that

[0038] Next, the above calculation process of the convergence calculation processing unit 12 will be described. uv , v wv The detection is performed by detecting the potentials of the U and W phases based on the V phase potential.

[0039]

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[0042] Voltage (v α ,v β ) with the estimated rotor speed ω re_est_PLL Position information θ corresponding to the time integral value of re_est_PLL The voltage value on the synchronous coordinate axis (v dc ,vqc )

[0043]

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[0044] The purpose of this estimation operation is to make the DQ synchronous coordinate axis, which is the estimated MT synchronous coordinate axis calculated in the calculator, coincide with the MT synchronous coordinate axis in the actual motor. re_est_PLL and θ flux If there is no error between the synchronous coordinates, only the Q-axis component of the induced voltage is observed. The DQ synchronous coordinate axis has an error θ err If this occurs, a positive value will be observed as the D-axis component in the controller. re_est_PLL and θ flux If the error is small, the following approximate formula can be used for the induced voltage.

[0045]

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[0046]

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[0047] The PLL (Phase Locked Loop) tracking operation is performed by PI control as shown in Fig. 2. As shown in Fig. 4, the estimated DQ synchronous coordinate axis is θ err Therefore, in order to bring the estimated DQ synchronous coordinate axis closer to the MT synchronous coordinate axis, err The sign of is changed to perform PI compensation.

[0048]

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[0049] In addition, ζ is the damping ratio. The square sum calculator 35 calculates the magnitude of the detected voltage |v dq | is calculated and transmitted to the phase-to-phase voltage level judgment unit 13, and if it is lower than a predetermined voltage judgment value, it is judged that speed estimation using the residual voltage cannot be stably performed and is judged as NG. Note that the magnitude of the voltage may be calculated from the component on the αβ stationary axis.

[0050] Detected phase-to-phase voltage v uv , v wv When an induced voltage caused by residual magnetic flux generated in an induction motor is observed, ideally there is a phase difference of 60 degrees between the phase-to-phase voltages of the two phases. When the amplitude of the induced voltage becomes small and there is no difference with the detected offset amount, or when the amplitude of the induced voltage becomes smaller than the magnitude of the noise, the phase difference becomes a value far removed from 60 degrees. When phase-to-phase voltage phase difference determination unit 14 detects such a state, it determines that speed estimation using the two-phase line voltages cannot be stably estimated, and judges it as NG.

[0051] 5 shows an overview of a method for detecting a phase difference implemented by the interphase voltage phase difference determination unit 14. When the polarity of the WV phase switches, CounterVal is reset. CNT_A: Time difference between the rising timing of WV and UV CNT_B: Time difference between the rising edge between UV and the falling edge between WV If the estimation operation is started by making the initial value of the sign recognition coincident with the sign of the detected voltage value, CounterVal is reset to 0 at the first polarity change of the WV phase as shown in Fig. 5, and the count value up to the second polarity change is stored in CNT_A.

[0052] However, at this time, CNT_B has not yet been saved and has an initial value of 0, so the phase cannot be calculated correctly. At the third polarity switch, "CNT_(A+B)", which corresponds to "CNT_A+CNT_B", is saved, and CNT_B can be calculated using the previously obtained CNT_A. CNT_B=CNT_(A+B)-CNT_A Therefore, the phase from the second polarity change to the third polarity change (between the rising edge of UV and the falling edge of WV) is calculated using the following formula. Phase = 180 × CNT_B / CNT_(A+B)

[0053] At the fourth polarity change, if CNT_B obtained at the third polarity change is used, CNT_(A+B) can be obtained by the following formula: CNT_(A+B)=CNT_A+CNT_B The phase from the third polarity change to the fourth polarity change, that is, the phase from the falling edge of UV to the rising edge of WV, is calculated using the following formula. Phase = 180 × CNT_A / CNT_(A+B) By repeating the above process, the phase difference can be correctly recognized from the third polarity change in the diagram. The third time, 120[deg], the fourth time, 60[deg], the fifth time, 120[deg], and so on.

[0054] Next, we will explain the principle of how secondary magnetic flux is generated by DC excitation of a motor in a free-running state. The mathematical model of the induction motor can be expressed as follows.

[0055]

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[0056] When DC excitation is performed, the control phase θ re = 0, i.e., the phase is fixed, and current control is performed on the DQ synchronous axis. When the rotor is stopped, ω re = 0, and the command value of the applied current is a DC amount given in steps, so the output frequency, the primary frequency ω stat Well, ω stat = 0, ω re =ω stat If i = 0, the slip frequency is also treated as 0. Also, since the response of the current controller is set to be sufficiently faster than the secondary time constant, it can be considered that the voltage command is given so that the current value is the same as the current command value. In other words, the command current i sd is constant.

[0057] Considering the above, the equation of an induction motor when DC excitation is implemented can be expressed as follows:

[0058]

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[0059]

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[0060] The current value is controlled to be a constant value i only on the D axis in a step-like manner, sufficiently fast in response to the change in the secondary magnetic flux. sd From the equation for the D-axis component shown in equation (13), the initial value of the secondary magnetic flux is given as φ rd If we take the Laplace transform with (0)=0, we get the following:

[0061]

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[0062]

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[0063] From this, it can be seen that by applying a current to the D-axis, the secondary magnetic flux proportional to the current value becomes the final value, and rises as a first-order lag response of the secondary time constant. When a current value equivalent to the no-load current is given as the current command, the secondary magnetic flux becomes approximately equivalent to the rated magnetic flux. As for the Q-axis component, since the Q-axis current is controlled to 0, φ rq = 0. If we rearrange the voltage command values ​​at this time from the first and second lines, the D-axis voltage command value is as follows. The command value on the Q-axis side is i sq = 0, so it is omitted.

[0064]

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[0065] From this, the secondary magnetic flux φ rd Mi sd Until the value of R is reached, the second term is a positive value, so the voltage drop due to the winding resistance R s i sd It can be seen that a larger voltage value is applied as the voltage command.

[0066] Next, we will show the case where the rotor has an initial speed. Since the rotor is not stopped, ω re ≠ 0. The command value of the applied current is a DC amount given in steps, so the primary frequency, which is the output frequency, is ω S = 0, and the slip frequency ω slip is considered to be equal in magnitude to the rotor speed and opposite in sign, i.e., ω slip =-ω reIn addition, as in the case of a stopped state, the response of the current controller is set to be sufficiently faster than the secondary time constant, so it can be considered that the voltage command is given so that the current value is the same as the current command value. In other words, the command current i sd is constant.

[0067] Considering the above, the induction motor equation can be expressed as follows:

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[0069]

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[0070]

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[0071] Laplace transform is performed on equation (22). The current value is controlled in a step-like manner in response to the change in the secondary magnetic flux, and a constant value i sd If the rotational speed is assumed to be constant and the initial value of the secondary magnetic flux is set to 0, then the equation can be rearranged as follows:

[0072]

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[0073]

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[0075]

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[0076] If the current application is terminated at time t=t1, the secondary magnetic flux generated in the rotor at that time is expressed as follows:

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[0079]

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[0082] Although the rotor speed is an unknown quantity, the secondary time constant can be obtained by offline tuning, etc., so it is desirable to determine the time to apply the current depending on the secondary time constant. As a guide for the application time, considering the behavior of the magnetic flux when the rotor is stopped, ω re = 0, so

[0083]

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[0084]

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[0085] This coincides with equation (17), which is the behavior of the magnetic flux when the rotor is stopped. It can be seen that the level of magnetic flux generated when the rotor speed is 0 can be adjusted by the applied time and the applied current value. These amounts are preset. Next, a specific method for calculating the initial value of the voltage command value will be described. From equation (11), if only the constant-state terms are used and the voltage is written on the left side,

[0086]

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[0091] When restarting a free-running motor, the rotor angular velocity ω re_est The initial value of the rotor speed command ω re_est_Init and the output voltage phase θ re_c The phase of the secondary magnetic flux θ re_Init is required.

[0092] The magnitude of the induced voltage is calculated from the voltage detection value, and the initial value of the rotor speed command is set to ω re_ref_Init The initial value of the secondary magnetic flux command value φ rd_ref_Init can be obtained as follows:

[0093]

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[0095] In addition, regarding the current value to be applied at startup, if the secondary magnetic flux can be tracked to the D-axis side by the convergence calculation process, the D-axis current i that generates the equivalent of the residual secondary magnetic flux is sd_ref_Init can be calculated as follows: i sd_ref_Init =φ rd_ref_Init / M …(39)

[0096] Using these values, the output voltage command value at restart can be calculated as follows. The torque command immediately after start-up is set to 0, so the torque current i sq is 0, and the slip frequency is also 0, so the output frequency ω stat is the initial speed command value ω re_ref_Init Considering that it is equivalent to the above, it can be given as follows.

[0097]

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[0098] After giving the initial value, if the D-axis current is controlled by the magnetic flux equivalent to the rated magnetic flux of the motor, for example, the leakage time constant T leak Current command i after passing through the corresponding filter sd_set_Filt If the D-axis current is applied at a level that generates the rated magnetic flux, unnecessary vibration elements can be eliminated. The initial value of the filter immediately after restart is i sd_ref_Init It is sufficient to write it as follows. c is the control period.

[0099]

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[0100] Regarding the command value of the secondary magnetic flux, the magnetic flux is not set as the target magnetic flux at the time of restart, so the secondary time constant T r In the case where the magnetic flux command value is to be gradually increased to the rated magnetic flux, the secondary time constant T r Secondary magnetic flux command φ after passing through the corresponding filter rd_set_FiltIf you use φ, unnecessary vibration will not be induced. The initial value of the filter immediately after restart is φ rd_ref_Init It would be fine to say so.

[0101]

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[0102] The voltage command is calculated from the secondary magnetic flux command thus obtained and the D-axis current command. The value equivalent to the rotor speed is ω re_est The initial value of the estimated speed ω re_est_PLL The final value of the speed command initial value ω re_ref_Init Furthermore, when a Q-axis current command is given from a torque command obtained by speed control, the component of the Q-axis current command is also added in the same way as the D-axis current. When the Q-axis current is generated, the primary frequency is the value obtained by adding the slip frequency, ω stat It is necessary to keep it as it is.

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[0104] Figure 7 shows an example of restarting the motor by applying the initial voltage command and subsequent voltage commands as described above. It can be seen that the torque current is not disturbed at all and the motor is restarted without any shock.

[0105] Next, the setting of the current application time will be explained. To obtain the behavior of the secondary magnetic flux when DC excitation is performed, the third line of equation (25) is written as follows:

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[0107] This formula is Mi sd The time constant T r This is the same as the first-order lag filter.

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[0109] In the current regulator 9, i sd The change in magnetic flux when T is controlled to a constant value can be obtained by the following formula. c When expressed in discrete time as the control period, it becomes equivalent to equation (43).

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[0111] As shown in Figure 8, φ rd_set_Filt The initial value of i can be the same as the value shown in equation (38). sd_set While applying the secondary magnetic flux φ rd_set_Filt The calculated value is the secondary magnetic flux command value φ rd_set Time to reach T mag_2 , i sd_set The applied current i sd_set If the no-load current is set to the equivalent, the increase in the secondary magnetic flux requires a time equivalent to the secondary time constant. However, if it is set to be greater than the no-load current, the time it takes for the magnetic flux to reach the target value can be shortened, and the delay until startup can be shortened.

[0112] Next, the operation of this embodiment will be described. The flowchart shown in Fig. 9 shows the process in the restart processing unit when the operation command is switched from OFF to ON and a request for restart is received. The flowchart shown in Fig. 13 shows the process in the restart processing unit when the operation command is switched from ON to OFF and the power converter is in a free run state, that is, the power converter output is OFF.

[0113] In these flowcharts, there are two types of excitation operation for speed estimation. "Excitation operation for speed estimation Type 2" operates so that speed estimation can be performed again by automatically performing excitation operation for speed estimation when it is detected that the phase-to-phase voltage is smaller than the threshold value or the phase difference of the phase-to-phase voltage is smaller than the threshold value in the free-run state after the operation command is turned OFF, and it is determined that speed estimation cannot be performed. On the other hand, "Excitation operation for speed estimation Type 1" does not have the function of Type 2, and when it is determined that speed estimation cannot be performed, it does not automatically perform excitation operation, ends speed estimation, and enters a standby state for the operation command to be turned ON. Excitation operation is performed after the operation command is turned ON.

[0114] The flow when the operation command is switched from OFF to ON will be described with reference to Fig. 9. In the initial state, all commands output by the restart processing unit 19 are OFF. First, the restart processing unit 19 determines whether or not the following condition 1 is satisfied (S1). {(Pre-startup speed estimation operation==Type1)or (Pre-start speed estimation operation == Type2) and (Speed ​​estimation operation counter == 0)} If condition 1 is not met (no), the process proceeds to step S13, and if condition 1 is met (yes), it is determined whether or not the following condition 2 is met (S2). {(Speed ​​estimation excitation operation == enabled) and (Interphase voltage level judgement == NG) or (Interphase voltage phase difference judgement == NG)} Note that NG indicates that each detection is smaller than the threshold.

[0115] If condition 2 is not met (no), the process proceeds to step S8, and if condition 2 is met (yes), the following process A1 is executed (S3). Switch setting selection: A Excitation time setting for speed estimation: Timer=T mag_1 Excitation current setting for speed estimation:i sd_ref =I mag_1 (i sq_ref =0) Excitation operation command for speed estimation: ON Then, in step S6, current application processing is performed (S5) until the timer after Δt is subtracted reaches zero (S4; yes).

[0116] When the timer reaches zero (S4; no), the speed estimation excitation operation command is turned OFF (S7) as process A2, and then the following process B1 is executed (S8). Speed ​​estimation time setting: Timer=T spdest Speed ​​estimation operation command:ON In subsequent steps S9 to S11, similarly to steps S4 to S6, the speed estimation processing unit 10 performs speed estimation processing (S10).

[0117] When the timer reaches zero (S9; no), the following process B2 is executed (S12). Speed ​​command initialization:ω re_ref_Init1 =ω re_ref_Init Control axis phase initialization: θ re_Init1 =θ re_Init1 Secondary magnetic flux calculation initialization: φ r_ref_Init1 =φ r_ref_Init1 Speed ​​command initialization:ω re_ref =ω re_ref_Init1 Control axis phase initialization: θ re_c =θ re_Init1 Secondary magnetic flux calculation initialization: φ r_ref =φ r_ref_Init1 Speed ​​estimation operation command: OFF

[0118] In step S13, the following process B3 is executed. Note that this process is executed when the determination in step S1 is "no," and therefore the pre-start speed estimation operation corresponds to Type 2. Speed ​​command initialization:ω re_ref =ω re_ref_Init2 Control axis phase initialization: θ re_c =θ re_Init2 Secondary magnetic flux calculation initialization: φr_ref =φ r_ref_Init2 After step S12 or S13 is executed, the following condition 3 is judged (S14). {(initial speed command value < threshold) or (pre-start excitation operation == enabled)}

[0119] If condition 3 is not met (no), the process proceeds to step S20, and if it is met (yes), the following process C1 is performed (S15). Switch setting selection: C (Startup) Excitation time setting: Timer=T mag_2 (At startup) Excitation current setting:i sd_ref =I mag_2 Excitation operation command for before startup: ON

[0120] In the following steps S16 to S18, the same processes as in steps S4 to S6 are carried out. Then, when the timer reaches zero (S16; no), the pre-start excitation operation command is turned OFF (S19) as process C2. Then, the switch setting selection is set to D, and the speed control operation command is turned ON to start speed control (S20).

[0121] Next, a flow when the operation command is switched from ON to OFF will be described with reference to Fig. 13. In the initial state, all commands output by the restart processing unit 19 are OFF. The restart processing unit 19 determines whether the following condition 1 is satisfied (S21). (Pre-start speed estimation operation==Type1 or Type2) If condition 1 is not met (no), the process proceeds to step S36, and if condition 1 is met (yes), the following process A1 is executed (S22). Switch setting selection: A Excitation time setting for speed estimation: Timer=T spdest Speed ​​estimation operation counter: Count=0 Speed ​​estimation operation command:ON

[0122] While the operation command is OFF (S23; yes), the speed estimation processing unit 10 performs speed estimation processing (S25) until the Timer, which has been decremented by Δt in step S26, reaches zero (S24; yes). When the timer reaches zero (S24; no), the following process A2 is executed (S27). Speed ​​estimation operation counter: Count+=1 Speed ​​estimation excitation setting: Timer=Δt

[0123] Then, it is determined whether or not the following condition 2 is satisfied (S28). {(phase-to-phase voltage level judgement == NG) or (phase-to-phase voltage phase difference judgement == NG)} If condition 2 is not satisfied (no), the process returns to step S23, and if condition 2 is satisfied (yes), it is determined whether or not the following condition 3 is satisfied (S29). {(Speed ​​estimation excitation operation == Enabled) and (Pre-start speed estimation operation == Type2)}

[0124] If condition 3 is not satisfied (no), the process proceeds to step S36, and if condition 3 is satisfied (yes), the following process B1 is performed (S30). Switch selection setting: B Speed ​​estimation operation command: OFF Excitation time setting for speed estimation: Timer=T mag_1 Excitation current setting for speed estimation:i sd_ref =I mag_1 Excitation operation command for speed estimation: ON

[0125] In the following steps S31 to S33, a current application process is performed similarly to steps S4 to S6 (S32). When the timer reaches zero (S31; no), the following process B2 is executed (S34). Excitation operation command for speed estimation: OFF Excitation time setting for speed estimation: Timer=T spdest Speed ​​estimation operation command:ON Then, return to step S23.

[0126] When the operation command is turned ON (S23; no), the following process C1 is executed (S35) and then the process ends. Speed ​​command initialization:ω re_ref_Init2 =ω re_ref_Init Control axis phase initialization: θ re_Init2 =θ re_Init1 Secondary magnetic flux calculation initialization: φ r_ref_Init2 =φ r_ref_Init1 Speed ​​estimation operation command: OFF

[0127] In step S36, the following process C2 is executed, and then the process ends. Speed ​​command initialization:ω re_ref_Init2 =0 Control axis phase initialization: θ re_Init2 =0 Secondary magnetic flux calculation initialization: φ r_ref_Init2 =0 Speed ​​estimation operation command: OFF

[0128] Fig. 10 to Fig. 12 show an example of operation when using Type 1 of excitation operation for speed estimation. Fig. 10 is a timing chart showing a case where pre-start speed estimation operation: Type 1, excitation operation for speed estimation: enabled, and pre-start excitation operation: disabled, and the phase-to-phase voltage level determination is NG, while Fig. 11 is a timing chart showing a case where pre-start speed estimation operation: Type 1, excitation operation for speed estimation: enabled, and pre-start excitation operation: enabled. Fig. 12 shows a case where the phase-to-phase voltage phase difference determination is NG in the same case as Fig. 10.

[0129] As described above, according to this embodiment, the power converter 4 converts the DC voltage into a three-phase AC voltage with a variable voltage and variable frequency and supplies it to the induction motor 5. The phase-to-phase voltage detection unit 11 detects the phase-to-phase voltage v uv and v wv The current detector 7 detects the phase current i of the induction motor 5. u ,i w The current adjustment unit 9 detects the components of the detected values ​​of the currents of each phase on the DQ synchronous coordinate axis, and calculates the current command value i sd_ref , isq_ref The voltage command value v sd_ref , v sq_ref Calculate the following.

[0130] The control device 6 is configured to constantly perform convergence calculation processing when a coast-run operation stop request is input while the induction motor 5 is in operation, or when the main circuit potential of the power converter 4 that drives the induction motor 5 drops and operation is judged to be difficult, causing the control device 6 to transition to a coast-run state. Then, when an operation command is input again or the main circuit potential is restored, the control device 6 restarts control of the induction motor using the rotation speed and direction of rotation and the phase of the residual secondary magnetic flux obtained from the convergence calculation processing at that time.

[0131] In other words, if the main circuit potential cannot be maintained due to a free-run stop request from a higher-level controller or a momentary power outage, the power converter 4 stops and starts the convergence calculation process when it transitions to a free-run state. By continuing to perform the convergence calculation even during free-running, no matter when an operation command is input or when the momentary power outage state is resolved, the rotation speed estimated at that time can be used as the speed command, making it possible to immediately restart the system.

[0132] In the speed estimation excitation operation Type 1, when it is determined that speed estimation cannot be performed, the speed estimation is terminated and the system is in a standby state for an operation command ON. When the operation command ON is received, the control device 6 performs a speed estimation excitation operation in which a step-like current command value of a predetermined magnitude is given to the current adjustment unit 9 for a predetermined time when starting the induction motor 5 from a state in which the initial speed is generated, and after cutting off the output of the power converter 4, the phase-to-phase voltage v uv and v wv Then, the control of the induction motor 5 is restarted. That is, after performing excitation for speed estimation to bring the residual voltage to a level at which it can be estimated, speed estimation is performed and the induction motor 5 is restarted.

[0133] With this configuration, in which the phase-to-phase voltage detection unit 11 is disposed on the output side of the power converter 4, speed estimation can be performed even when the residual voltage is attenuated, thereby minimizing the shock that occurs at the time of restart, improving noise resistance, and shortening the time from receiving an operation command to actually restarting the motor.

[0134] Furthermore, the control device 6 performs an excitation operation for speed estimation on the condition that the peak value or effective value of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit 11 is determined to be smaller than a predetermined judgment value, and performs a convergence calculation process after cutting off the output of the power converter 4, and restarts the control of the induction motor 5. In other words, by performing excitation for speed estimation when the detected phase-to-phase voltage is smaller than the judgment value, it is possible to appropriately perform speed estimation using voltage detection.

[0135] In addition, when the phase difference between the two phase voltages is determined to be smaller than the determination value by the phase-to-phase voltage phase difference determination unit 14, the control device 6 also performs the excitation operation for speed estimation and restarts the control of the induction motor 5 in the same manner, so that the speed estimation can be performed appropriately in this case as well.

[0136] Furthermore, the control device 6 calculates the rotation speed ω re_est_PLL , the initial value ω of the speed command value from the rotation direction re_ref_Init The phase of the residual secondary magnetic flux obtained by the convergence calculation process is set as the D-axis, and the phase 90 degrees ahead of the D-axis is set as the Q-axis. The DQ synchronous coordinate axes are set as the rotation speed ω re_est_PLL The frequency is based on the voltage command v sd ,v sq The initial value of the secondary magnetic flux φ calculated from the phase-to-phase voltage value and the rotation speed just before the convergence calculation process is completed. re_ref_Init In other words, the direction of the residual secondary magnetic flux, that is, the phase, is determined as the D axis, and the voltage command value v sq The inverter is restarted by adjusting the phase-to-phase voltage and the initial value of the secondary magnetic flux used in torque calculations and voltage command value calculations. This makes it possible to suppress current disturbances at the time of restart.

[0137] The control device 6 determines the application time of the D-axis current command value based on the phase-to-phase voltage value immediately before the end of the convergence calculation process, the deviation between the initial value of the secondary magnetic flux and the command value of the secondary magnetic flux calculated from the rotation speed, and a D-axis current command value of a predetermined magnitude, and the current adjustment unit 9 provides a time for applying a current in the D-axis direction according to the D-axis current command value and its application time. The level of the magnetic flux applied for speed estimation is set to, for example, about 25% of the rated magnetic flux in order to minimize disturbance during application. At the time of restart, the magnetic flux level is further reduced, so if a large torque is requested immediately after start, the magnetic flux is insufficient, so the torque is earned by the current value, and even if the torque command is small, the current may become excessive. Therefore, by setting the magnetic flux level at the time of restart to a state close to the rated state, the increase in current can be suppressed.

[0138] In addition, the control device 6 adjusts the speed estimate value so that the result of transforming the phase-to-phase voltage onto a synchronous axis configured to use the time integral value of the speed estimate value as the phase during coordinate transformation will be only the Q-axis component.

[0139] FIG. 14 is a timing chart showing the cases of pre-start speed estimation operation: Type 2, speed estimation excitation operation: enabled, and pre-start excitation operation: enabled. In pre-start speed estimation operation Type 2, when a coast-run operation stop request is input while the induction motor 5 is in operation, or when the main circuit potential of the power converter 4 that drives the induction motor 5 drops and it is determined that operation is difficult and the induction motor transitions to a coast-run state, the control device 6 performs a convergence calculation process, but when it is determined that the peak value or effective value of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit 11 is smaller than a predetermined determination value, the convergence calculation process is stopped, and when the current adjustment unit 8 is caused to give a step-like current command value of a predetermined magnitude for a predetermined time, the convergence calculation process is resumed. As a result, when speed estimation is continued during a coast-run, if the level of the phase-to-phase voltage becomes small, excitation for speed estimation is performed, and the residual magnetic flux can be maintained at a level at which speed estimation is possible.

[0140] Furthermore, when the control device 6 determines that the phase difference between the two phase-to-phase voltages detected by the phase-to-phase voltage detection unit 11 is smaller than a predetermined determination value while the convergence calculation process is being performed continuously, it stops the convergence calculation process, and when it causes the current adjustment unit 8 to provide a step-like current command value of a predetermined magnitude for a predetermined time, it resumes the convergence calculation process. As a result, even if the phase difference between the phase voltages becomes small while continuing to perform speed estimation during free running, the residual magnetic flux can be maintained at a level at which speed estimation is possible.

[0141] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0142] In the drawing, reference numeral 1 denotes a three-phase AC power supply, 2 denotes a full-wave rectifier circuit, 3 denotes a smoothing capacitor, 4 denotes a power converter, 5 denotes an induction motor, 6 denotes a control device, 7 denotes a current detection unit, 9 denotes a current adjustment unit, 10 denotes a speed estimation processing unit, 11 denotes a phase-to-phase voltage detection unit, 12 denotes a convergence calculation processing unit, 13 denotes a phase-to-phase voltage level determination unit, and 14 denotes a phase-to-phase voltage phase difference determination unit.

Claims

1. a power converter that converts a DC voltage into a three-phase AC voltage with variable voltage and frequency and supplies the AC voltage to an induction motor; A phase-to-phase voltage detection unit that detects phase-to-phase voltages between two or more phases of the induction motor; A current detection unit that detects a phase current of the induction motor; a current adjusting unit that calculates a voltage command value so that a component obtained by converting the detected value of the phase current onto a synchronous coordinate axis coincides with a current command value; When starting the induction motor from an initial speed state, A speed estimation excitation operation is performed to provide a step-like current command value having a predetermined magnitude to the current adjustment unit for a predetermined period of time; and a restart control unit that, after cutting off the output of the power converter, performs convergence calculation processing to obtain the rotational speed and rotational direction of the induction motor and the phase of residual secondary magnetic flux using detection values ​​of the phase-to-phase voltage between two or more phases, and restarts control of the induction motor.

2. 2. The motor control device according to claim 1, wherein the restart control unit performs the speed estimation excitation operation on condition that a peak value or an effective value of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit is determined to be smaller than a predetermined determination value, and performs the convergence calculation process after cutting off the output of the power converter, and restarts control of the induction motor.

3. a phase-to-phase voltage phase difference determination unit that calculates a phase difference between detection values ​​of two or more phases of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit and compares the phase difference with a predetermined determination value; 3. The motor control device according to claim 2, wherein the restart control unit performs the speed estimation excitation operation even when the phase-to-phase voltage phase difference determination unit determines that the phase difference is smaller than the determination value, and performs the convergence calculation process after cutting off the output of the power converter, thereby restarting control of the induction motor.

4. a power converter that converts a DC voltage into a three-phase AC voltage with variable voltage and frequency and supplies the AC voltage to an induction motor; A phase-to-phase voltage detection unit that detects phase-to-phase voltages between two or more phases of the induction motor; A current detection unit that detects a phase current of the induction motor; a current adjusting unit that calculates a voltage command value so that a component obtained by converting the detected value of the phase current onto a synchronous coordinate axis coincides with a current command value; When a request to stop free-run operation is input while the induction motor is in an operating state, or when a main circuit potential of a power converter that drives the induction motor is reduced and it is determined that operation is difficult, and the induction motor transitions to a free-run state, the convergence calculation process is constantly performed; and a restart control unit that, when an operation command is input again or the main circuit potential is restored, restarts control of the induction motor using the rotational speed and rotational direction and the phase of the residual secondary magnetic flux obtained from the convergence calculation processing at that time.

5. 5. The motor control device according to claim 4, wherein the restart control unit stops the convergence calculation process when it is determined that a peak value or an effective value of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit is smaller than a predetermined determination value while the convergence calculation process is being constantly performed, and resumes the convergence calculation process when it causes the current adjustment unit to provide a step-like current command value of a predetermined magnitude for a predetermined time.

6. a phase-to-phase voltage phase difference determination unit that calculates a phase difference between detection values ​​of two or more phases of the phase-to-phase voltage detected by the phase-to-phase voltage detection unit and compares the phase difference with a predetermined determination value; The motor control device according to claim 5 , wherein the restart control unit also stops the convergence calculation process when the interphase voltage phase difference determination unit determines that the phase difference is smaller than the determination value.

7. The restart control unit sets an initial value of a speed command value based on a rotation speed and a rotation direction, a DQ synchronous coordinate axis, in which the phase of the residual secondary magnetic flux obtained by the convergence calculation process is defined as a D axis and a phase 90 degrees ahead of the D axis is defined as a Q axis, is rotated at a frequency based on the rotation speed; 7. The induction motor control device according to claim 1, wherein an initial value of a voltage command is determined using an initial value of a secondary magnetic flux calculated from the interphase voltage value and the rotation speed immediately before the convergence calculation process is completed.

8. the restart control unit determines an application time of the D-axis current command value based on a deviation between an initial value of a secondary magnetic flux and a command value of a secondary magnetic flux, the deviation being calculated from the interphase voltage value and the rotation speed immediately before the end of the convergence calculation process, and a D-axis current command value of a predetermined magnitude; 8. The induction motor control device according to claim 7, wherein the current adjusting unit sets a time for applying a current in the D-axis direction in accordance with the D-axis current command value and its application time.

9. 8. The induction motor control device according to claim 7, wherein the restart control unit adjusts the speed estimation value so that a result of transforming the phase-to-phase voltage onto a synchronous axis configured to use a time integral value of the speed estimation value as a phase during coordinate transformation contains only a Q-axis component.

10. 9. The induction motor control device according to claim 8, wherein the restart control unit adjusts the speed estimation value so that a result of transforming the phase-to-phase voltage onto a synchronous axis configured to use a time integral value of the speed estimation value as a phase during coordinate transformation contains only a Q-axis component.

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