Motor control device

Abstract

To provide a motor control device capable of performing sensor-less control of an induction motor in a low speed range.SOLUTION: A motor control device includes: a sensor-less control unit configured to calculate a parameter for calculating a speed estimation value of an induction motor based on a current output to the induction motor, and to perform speed control of the induction motor based on the speed estimation value and a speed reference; a material information setting unit in which attribute information used for calculation of speed of a load driven by the induction motor is set when the induction motor is in a free-run operation; a deceleration time calculation unit configured to calculate a deceleration rate in the case of free-run operation based on the attribute information to output the deceleration rate to the sensor-less control unit as the speed reference within a low speed range when the speed reference is within the low speed range set in advance; and a reset command unit configured to output a reset command for resetting the parameter to the sensor-less control unit when the speed reference is within the low speed range.SELECTED DRAWING: Figure 1

Description

【Technical Field】 【0001】 Embodiments of the present invention relate to a motor control device for sensorless control of an induction motor. 【Background Art】 【0002】 In the sensorless control of an induction motor, current detection of the current output to the induction motor may not work well in the very low speed range near zero speed, particularly at the speed zero cross where the polarity of the speed reverses. In that case, the calculation of the control parameters using the current value of the induction motor also does not show correct values. Therefore, there is a problem that the induction motor stalls at the speed zero cross and eventually the control device trips due to overcurrent. 【0003】 Regarding such a problem, Patent Document 1 describes a technique for correcting a speed reference in order to prevent out-of-step at the speed zero cross. More specifically, the speed reference is corrected so that the relationship between the speed reference and the slip frequency is outside the unstable region. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2010-271850 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 In sensorless speed control, a speed estimate is used to correct the speed reference, and the current value output to the induction motor is used to calculate the speed estimate. As mentioned above, in the extremely low speed range, the current value may not be detected properly, so there is a problem that the calculated speed estimate is not an appropriate value. In addition, in general sensorless control systems, a function is often provided to temporarily suspend sensorless control in the extremely low speed range, taking into account that current detection may not work well at extremely low speeds, but the method described in Patent Document 1 has the problem that it cannot be applied to such sensorless control. 【0006】 The present invention was made to solve the above problems, and aims to provide an electric motor control device that can stably control an induction motor without sensors in the low-speed range. [Means for solving the problem] 【0007】 Embodiments of the present invention include: a sensorless control unit connected to an induction motor, which detects the output current output to the induction motor, calculates parameters for calculating an estimated speed of the induction motor based on the output current, calculates the estimated speed based on the output current and the parameters, and controls the speed of the induction motor based on the calculated estimated speed and a first speed reference; a load information setting unit that outputs information about the load driven by the induction motor; a deceleration calculation unit that calculates the deceleration rate of the induction motor when the induction motor is in free-run operation based on the load information; a reset command unit that outputs a reset command to the sensorless control unit to reset the parameters when the first speed reference is within a preset low-speed range; and a unit that receives a speed command, calculates a second speed reference corresponding to the speed command, and when the second speed reference is within the Outside low speed range In that case, the second speed reference is output to the sensorless control unit as the first speed reference, and the second speed reference is Outside low speed rangeWhen the speed falls within the low speed range, the speed calculated by the deceleration rate is used as the third speed reference in calculations, and the third speed reference is output to the sensorless control unit as the first speed reference from the time the speed falls within the low speed range until the time the third speed reference becomes 0, and the second speed reference is used from the time the third speed reference becomes 0 Outside low speed range The sensorless control unit includes a speed reference calculation unit that outputs the second speed reference as the first speed reference to the sensorless control unit until the point in time when the first speed reference is Outside low speed range In this case, the induction motor is speed-controlled so that the estimated speed follows the first speed reference, and the first speed reference is Outside low speed range If the speed falls within the low speed range, the induction motor shall be put into free-running operation until the first speed standard becomes 0, and from the point when the first speed standard becomes 0, the first speed standard shall be Outside low speed range The induction motor's speed is controlled according to the first speed standard until that point is reached. [Effects of the Invention] 【0008】 According to one embodiment, an electric motor control device is provided that can stably control an induction motor without sensors in the low-speed range. [Brief explanation of the drawing] 【0009】 [Figure 1] This is a schematic block diagram illustrating an electric motor control device according to the first embodiment. [Figure 2] Figure 2(a) is a schematic graph illustrating the operation of the motor control device according to the first embodiment. Figure 2(b) is a schematic graph illustrating the operation of the motor control device according to a comparative example. [Figure 3] This is a schematic block diagram illustrating an electric motor control device according to the second embodiment. [Figure 4] This is a schematic graph illustrating the operation of the electric motor control device according to the second embodiment. [Modes for carrying out the invention] 【0010】 The embodiments will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate. 【0011】 (First embodiment) Figure 1 is a schematic block diagram illustrating an electric motor control device according to the first embodiment. As shown in Figure 1, the motor control device 10 comprises a sensorless control unit 13, a material information setting unit 21, a deceleration time calculation unit 22, a reset command unit 23, and a speed reference calculation unit 24. The motor control device 10 is connected to n induction motors 1-1 to 1-n and controls the speed of the induction motors 1-1 to 1-n sensorlessly so as to follow the speed reference calculated by the speed reference calculation unit 24. Here, "n" is an integer (natural number) of 2 or more. In the example in Figure 1 and the example in Figure 3 described later, the motor control device controls the speed of n induction motors, but of course, the motor control device can control the speed of just one induction motor. 【0012】 The sensorless control unit 13 detects the output current IM output to the induction motors 1-1 to 1-n, calculates various parameters for sensorless control, and uses the calculated parameters to calculate a speed estimate. The calculated parameters include, for example, the slip frequency ωs and the motor secondary voltages E2q and E2d. When the speed reference falls within a preset low-speed range, the sensorless control unit 13 resets the various parameters calculated by the sensorless control unit 13 and operates the induction motors 1-1 to 1-n in free-run mode. In addition, under normal operating conditions, the sensorless control unit 13 controls the speed of the induction motors 1-1 to 1-n so that the speed estimate follows the speed reference. Normal operating conditions refer to operating conditions where the speed reference is outside the preset low-speed range. 【0013】 Regarding sensorless speed control, various methods have been proposed for calculating the estimated speed using different parameters. In this embodiment and the second embodiment described in relation to Figures 3 and 4, it is possible to apply any sensorless speed control method, and the sensorless control unit 13 can have a well-known configuration. 【0014】 The material information setting unit 21 acquires material information such as loads driven by induction motors 1-1 to 1-n, sensor information, and setting data from a master control unit and a higher-level computer (not shown), and sets these various data. Material information such as loads refers to, for example, data on the material and weight of steel products etc. transported through the plant by the operation of induction motors 1-1 to 1-n. Sensor information refers to, for example, data on the output signals of sensors that provide information for detecting which process and position the transported steel products etc. are at. Setting data refers to, for example, data on the rated output and rotational speed of the motors that drive the table rollers, and data on mechanical constants such as the diameter of the table rollers that transport the steel products etc., GD2, and mechanical loss. This data is used to calculate the deceleration time, deceleration speed, and deceleration rate when induction motors 1-1 to 1-n are allowed to run free. 【0015】 The material information etc. setting unit 21 is connected to the output of the speed reference calculation unit 24. The output of the material information etc. setting unit 21 is connected to the deceleration time etc. calculation unit 22. The material information etc. setting unit 21 inputs the speed reference ωr* output from the speed reference calculation unit 24, and at that time, outputs material information such as load when the induction motors 1-1 to 1-n are in free-run operation, sensor information, and setting data etc. to the deceleration time etc. calculation unit 22. 【0016】 The deceleration time etc. calculation unit 22 is connected to the output of the speed reference calculation unit 24. The output of the deceleration time etc. calculation unit 22 is connected to the reset command unit 23. The deceleration time etc. calculation unit 22 uses the value of the speed reference ωr* output from the speed reference calculation unit 24 and the data of material information etc. set in the material information etc. setting unit 21 to calculate the deceleration time, deceleration speed, and deceleration rate when the induction motors 1-1 to 1-n are in free-run operation at that time. The deceleration time etc. calculation unit 22 outputs the calculated deceleration time, deceleration speed, and deceleration rate to the speed reference calculation unit 24 and the reset command unit 23. 【0017】 The reset command unit 23 is connected to the output of the deceleration time etc. calculation unit 22. The output of the reset command unit 23 is connected to the sensorless control unit 13. The reset command unit 23 sets a reset timer based on the deceleration rate output from the deceleration time etc. calculation unit 22. The reset command unit 23 outputs a reset command RST for resetting the parameters of the sensorless control unit 13 to the sensorless control unit 13. The reset command RST continues for the time of the reset timer set in the reset command unit 23. The reset timer is a period for outputting the reset command RST when the speed reference ωr* is within the low-speed range preset in the deceleration time etc. calculation unit 22. 【0018】 The speed reference calculation unit 24 is connected to the output of the deceleration time calculation unit 22, etc. The output of the speed reference calculation unit 24 is connected to the sensorless control unit 13. Although not shown, the speed reference calculation unit 24 inputs, for example, a speed command generated by the main control device, and calculates a speed reference based on the speed command. During normal operation, the speed reference calculation unit 24 outputs the speed reference calculated based on the speed command to the sensorless control unit 13. Normal operation means that the calculated speed reference is outside the range of the preset low-speed range. When the calculated speed reference is within the preset low-speed range, the speed reference calculation unit 24 uses the deceleration time, deceleration speed, and deceleration rate output from the deceleration time calculation unit 22, etc., to calculate the speed reference in the low-speed range and outputs it to the sensorless control unit 13. 【0019】 The operation of the motor control device 10 according to this embodiment will be described. FIG. 2(a) is a schematic graph for explaining the operation of the motor control device according to the first embodiment. In FIG. 2(a), the values of the speed ωr of the induction motors 1-1 to 1-n with respect to time t are plotted. The vertical axis of the graph is the speed ωr, and the horizontal axis is the time t. In each graph, the solid-line plot represents the speed reference ωr*, and the dashed-line plot represents the speed estimated value ωre calculated by the sensorless control unit 13. The same applies to the graphs in the description of the operation of the motor control device according to the comparative example described in relation to FIG. 2(b) and the motor control device according to the second embodiment described in relation to FIG. 4. 【0020】 As shown in FIG. 2(a), in the motor control device 10 according to this embodiment, a low-speed range is preset. In FIG. 2(a), the low-speed range is shown as a ratio with respect to the speed reference ωr* of the induction motor, and is -A% to +A% of the speed reference ωr*. Here, "A" is an arbitrary real number. For example, the low-speed range is within ± several% of the speed reference ωr*. "A" is set to an appropriate value, for example, according to the detection accuracy of the output current output from the motor control device 10 to the induction motor. In the graph, the range of the low-speed range ±A% is shown shaded. 【0021】 In this embodiment, the motor control device 10 monitors the speed reference ωr* supplied from the master control device, etc. When the speed reference ωr* falls below +A%, the speed during free-running operation of the induction motor is applied as the speed reference ωr*. When the speed during free-running operation reaches 0, the speed reference ωr* for normal operation is applied. 【0022】 Specifically, in Figure 2(a), the speed standard ωr* decreases over time, reaching +A% at time t1. From time t1 to time t2, the speed calculated by the deceleration rate α during free-running, calculated by the deceleration time calculation unit 22, is applied as the speed standard ωr*. At time t2, when the speed standard ωr* reaches 0, the speed standard ωr* for normal operation is applied. 【0023】 The reset timer time calculated by the reset command unit 23 continues the reset command RST until the speed reference ωr* reverses and falls below -A% of the speed reference. In other words, in Figure 2(a), the reset timer time is calculated as the sum of the period from time t1 to time t2 and the period from time t2 to time t3. As described above, the period from time t1 to time t2 is calculated based on the deceleration rate during free-running calculated by the deceleration time calculation unit 22. The period from time t2 to time t3 is calculated by the deceleration time calculation unit 22 as the period until the normal speed reference ωr* reaches -A% of the speed reference. 【0024】 The reset command unit 23 continuously outputs the reset command RST to the sensorless control unit 13 within the time of the reset timer. The reset command RST resets the parameters used to calculate the slip frequency ωs, motor secondary voltages E2q and E2d, etc. Therefore, the speed estimate value ωre calculated by the sensorless control unit 13 is approximately 0 within the time of the reset timer. After time t3, the reset command RST is released, and the speed estimate value ωre is calculated based on the detected output current IM output from the motor control device 10 to the induction motors 1-1 to 1-n. After time t3, the output current IM to the induction motors 1-1 to 1-n is appropriately detected, so each parameter is calculated appropriately, and the speed estimate value ωre is controlled to follow the speed reference ωr*. Note that the parameters to be reset may be all parameters, or appropriate parameters may be selected according to the control method adopted by the sensorless control unit 13. 【0025】 Figure 2(b) is a schematic graph illustrating the operation of the motor control device according to the comparative example. In the motor control device of the comparative example, the estimated speed value ωre is calculated by detecting the current output to the induction motor even in the low-speed range, which is within ±A% of the speed reference ωr*. After time t11, the speed reference ωr* becomes +A% or less, so the current output to the induction motor is not detected properly. As a result, the estimated speed value ωre, which is calculated based on a detection value with a large error, may not yield an appropriate result. Therefore, as shown in Figure 2(b), the estimated speed value ωre may be a value that differs significantly from the speed reference ωr*. Even if the output current is detected normally and the parameters are calculated at time t13, if the calculation result of the estimated speed value ωre during the preceding period is an inappropriate value, for example, overcurrent protection may be activated, causing the induction motor to stop or the induction motor's speed control to stall. 【0026】 The effects of the motor control device 10 according to this embodiment will be explained. The motor control device 10 according to this embodiment includes a material information setting unit 21, a deceleration time calculation unit 22, a reset command unit 23, and a speed reference calculation unit 24. The material information setting unit 21 calculates the deceleration speed, deceleration rate, and deceleration time when the induction motor is in free-run operation, based on the attributes and position of the products being transported on the line. The induction motor is stopped without control based on the deceleration rate during free-run operation, and then the induction motor is reversed by the normal speed reference ωr* supplied by the speed reference calculation unit 24 to escape the low-speed range. 【0027】 Within the low-speed range of the speed reference ωr*, a reset command RST is output to the sensorless control unit 13 for the duration of the reset timer. The reset command RST resets the parameters used in the sensorless control unit 13 to calculate the estimated speed value ωre. As a result, the estimated speed value ωre becomes approximately 0, preventing the overcurrent protection from activating or the induction motor from stalling, and allowing the motor control device 10 to stably control the induction motor. 【0028】 (Second embodiment) Figure 3 is a schematic block diagram illustrating an electric motor control device according to the second embodiment. As shown in Figure 3, the motor control device 210 according to this embodiment includes a sensorless control unit 13, a speed reference output unit 224, and a start command unit 225. The motor control device 210 may further include a stop monitoring unit 226. The motor control device 210 according to this embodiment includes a sensorless control unit 13 similar to that of the motor control device 10 according to the first embodiment, and a detailed description of the sensorless control unit 13 is omitted. 【0029】 The speed reference output unit 224 is connected to, for example, a master control unit (not shown), and calculates the speed reference ωr* based on the speed command supplied from the master control unit. The speed reference output unit 224 outputs the calculated speed reference ωr* to the sensorless control unit 13 and the start command unit 225. 【0030】 The start command unit 225 is connected to the output of the speed reference output unit 224. In the example in Figure 3, the start command unit 225 is also connected to the output of the stop monitoring unit 226. The output of the start command unit 225 is connected to the sensorless control unit 13. The start command unit 225 monitors the speed reference ωr* output from the speed reference output unit 224, and if it determines that the speed reference ωr* is within the low-speed range, it stops the output of the start command EXT for the duration of the stop timer. The start command EXT is a command that specifies the conditions for allowing the induction motor to start. In other words, when the sensorless control unit 13 receives the start command EXT, it takes the value of the speed reference ωr* output from the speed reference output unit 224 as input and operates according to the speed reference ωr*. When the input of the start command EXT is stopped, the sensorless control unit 13 stops operating regardless of the input of the speed reference ωr*. In this case, the sensorless control unit 13 stops operating by setting the speed reference ωr* to 0. 【0031】 The stop timer duration may be set to a fixed value in advance, or it may be set by calculation based on the deceleration rate before the speed reference ωr* enters the low-speed range. Alternatively, the stop timer duration may be calculated using the time at which the speed reference ωr* calculated by the speed reference output unit 224 during normal operation becomes 0. 【0032】 The stop monitoring unit 226 is connected to the sensorless control unit 13. The output of the stop monitoring unit 226 is connected to the start command unit 225. The stop monitoring unit 226 monitors the current value of the current output to the induction motors 1-1 to 1-n of the sensorless control unit 13. In addition to the output current value to the induction motors 1-1 to 1-n, or instead of the output current value, the stop monitoring unit 226 may also monitor material information, sensor information, etc. The stop monitoring unit 226 monitors the output current value of the induction motors 1-1 to 1-n and determines the operating status of the induction motors 1-1 to 1-n. The stop monitoring unit 226 outputs an interlock command to the start command unit 225 until it determines that the operation of the induction motors 1-1 to 1-n has stopped. In other words, if the induction motors 1-1 to 1-n do not stop once during zero-cross deceleration, the stop monitoring unit 226 stops the output of the start command EXT from the start command unit 225. 【0033】 The operation of the motor control device 210 according to this embodiment will be described. Figure 4 is a schematic graph illustrating the operation of the motor control device 210 according to this embodiment. In Figure 4, as in Figures 2(a) and 2(b), the velocity ωr is set to a low-speed range of ±A%. 【0034】 As shown in Figure 4, the start command unit 225 monitors the speed reference ωr* output from the speed reference output unit 224, and stops outputting the start command EXT when the speed reference ωr* falls below +A%. For example, the stop timer time is calculated and set by the start command unit 225 by applying the deceleration rate just before the speed reference ωr* reaches +A%. 【0035】 At time t21, the start command unit 225 determines that the speed reference ωr* is less than or equal to +A%. The start command unit 225 calculates and sets the time for the stop timer and stops outputting the start command EXT to the sensorless control unit 13. If the start command unit 225 exceeds time t22, when the speed reference ωr* becomes 0, it outputs the speed reference ωr* for normal operation, which is output by the speed reference output unit 224. In other words, during the period from time t21 to time t22, the start command unit 225 effectively sets the speed reference ωr* to 0 for the sensorless control unit 13. 【0036】 During the period from time t22 to time t23, the speed estimation calculation is started. However, after time t23, the speed reference ωr* becomes a value smaller than -A% (large in absolute value), and the estimated speed ωre is calculated based on the appropriately detected output current. The sensorless control unit 13 then controls the speed so that the estimated speed ωre follows the speed reference ωr*. 【0037】 The effects of the motor control device 210 according to this embodiment will be explained. In the motor control device 210 according to this embodiment, the start command unit 225 monitors the speed reference ωr* and outputs a start command EXT to the sensorless control unit 13 when the speed reference ωr* is within the low speed range. Therefore, during the time of the stop timer when the start command EXT is not output, the speed reference ωr* is set to 0. As a result, the estimated speed value ωre can be forcibly set to 0, and stall of the induction motor can be prevented. 【0038】 The stop monitoring unit 226 monitors other parameters within the sensorless control unit 13 besides the speed reference ωr* and interlocks the activation of the sensorless control unit 13. This makes it possible to perform sensorless speed control more safely. 【0039】 The start command unit 225 is a function that is incorporated into many systems related to starting and stopping in motor control devices to which the sensorless control unit 13 is applied. The motor control device 210 according to this embodiment has the advantage of being able to achieve stable control in the low-speed range with few modifications to these existing functions. 【0040】 Specific examples in each of the embodiments described above may be implemented using a computer device or programmable controller that reads a program stored in a memory device and executes each step of the program sequentially. When an electric motor drive device is implemented using a computer device or the like, it is possible to implement some or all of the above-described parts using one or more steps that constitute a program. 【0041】 In this way, it is possible to realize an electric motor control device that can stably control induction motors without sensors in the low-speed range. 【0042】 While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols] 【0043】 1-1~1-n…Induction motor, 10, 210…Motor control device, 13…Sensorless control unit, 21…Material information setting unit, 22…Deceleration time calculation unit, 23…Reset command unit, 24…Speed ​​reference calculation unit, 224…Speed ​​reference output unit, 225…Start command unit, 226…Stop monitoring unit

Claims

[Claim 1] A sensorless control unit connected to an induction motor detects the output current output to the induction motor, calculates parameters for calculating an estimated speed of the induction motor based on the output current, calculates the estimated speed based on the output current and the parameters, and controls the speed of the induction motor based on the calculated estimated speed and a first speed reference. A load information setting unit that outputs information about the load driven by the induction motor, A reduction calculation unit calculates the reduction rate of the induction motor when the induction motor is in free-run operation based on the load information, A reset command unit outputs a reset command to the sensorless control unit to reset the parameter when the first speed standard is within a preset low speed range, A speed reference calculation unit receives a speed command, calculates a second speed reference corresponding to the speed command, outputs the second speed reference as the first speed reference to the sensorless control unit if the second speed reference is outside the low-speed range, calculates the speed calculated by the deceleration rate as the third speed reference if the second speed reference moves from outside the low-speed range to within the low-speed range, outputs the third speed reference as the first speed reference to the sensorless control unit from the point when it becomes within the low-speed range until the point when the third speed reference becomes 0, and outputs the second speed reference as the first speed reference to the sensorless control unit from the point when the third speed reference becomes 0 until the point when the second speed reference is outside the low-speed range. Equipped with, The sensorless control unit controls the speed of the induction motor so that the estimated speed follows the first speed reference when the first speed reference is outside the low speed range, and when the first speed reference moves from outside the low speed range to within the low speed range, it allows the induction motor to run free until the first speed reference becomes 0, and controls the speed of the induction motor in accordance with the first speed reference from the time the first speed reference becomes 0 until the time the first speed reference moves outside the low speed range. [Claim 2] A sensorless control unit connected to an induction motor detects the output current output to the induction motor, calculates parameters for estimating the speed of the induction motor based on the output current, calculates the estimated speed based on the output current and the parameters, and controls the speed of the induction motor based on the calculated estimated speed and speed reference. A speed reference calculation unit receives a speed command, calculates the speed reference corresponding to the speed command, and outputs the speed reference to the sensorless control unit, A startup command unit enables the operation of the sensorless control unit by inputting a startup command to the sensorless control unit, and stops the operation of the sensorless control unit by stopping the input of the startup command to the sensorless control unit. Equipped with, The start command unit stops outputting the start command during the period from when the speed standard moves from outside the predetermined low-speed range to within the predetermined low-speed range until the speed standard becomes 0. The sensorless control unit controls the speed of the induction motor so that the estimated speed follows the speed reference when the speed reference is outside the low-speed range, stops operation in response to the cessation of the input of the start command when the speed reference moves from outside the low-speed range to within the low-speed range, starts operation in response to the input of the start command after the speed reference becomes 0, and controls the speed of the induction motor in accordance with the speed reference until the speed reference moves outside the low-speed range. [Claim 3] The motor control device according to claim 2, further comprising a stop monitoring unit that outputs an interlock command to the start command unit to stop inputting the start command to the sensorless control unit after the start command unit has stopped inputting the start command to the sensorless control unit, until the induction motor stops operating.

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