Control device of induction motor

Abstract

To provide a control device of an induction motor which can prevent a start failure resulting from torque shortage even when the induction motor is started with high load and at low speed.SOLUTION: A control device comprises: a rotational speed acquisition unit which acquires rotational speed of an induction motor; a Q-axis current command setting unit which sets a Q-axis command as a torque command to the induction motor on the basis of deviation between the acquired rotational speed and a speed command; and a D-axis current command setting unit which sets a D-axis current command as an excitation command to the induction motor. The D-axis current command setting unit comprises: a D-axis current command calculation unit which calculates a D-axis current command; and a D-axis current command compensation unit which increases the D-axis current command calculated by the D-axis current command calculation unit to be compensated in start of the induction motor.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a control device for an induction motor, and more particularly to a control device for controlling an induction motor for transporting a material to be rolled in a rolling line. [Background technology]

[0002] Known methods of controlling an induction motor include sensorless vector control, sensor-equipped vector control, and V / F control. A control device for driving an induction motor by vector control is disclosed in, for example, Patent Document 1.

[0003] The control device includes a means for calculating a magnetizing current command for the induction motor, a speed adjustment means for calculating a torque command such that the deviation between the rotation speed of the induction motor and the speed command is zero, and a means for calculating a torque current command from the torque command. The control device further includes a speed calculation means for estimating the rotation speed of the induction motor, and a speed detection means for detecting the rotation speed of the induction motor. By selecting either the estimated rotation speed or the detected rotation speed, it is possible to select either sensorless vector control or sensor-equipped vector control.

[0004] The induction motor is installed to drive a table (hot rolling table) that transports the material to be rolled in the rolling line. In the roughing mill installed in the rolling line, the induction motor performs an oscillation operation in which it rotates forward and backward at a low speed repeatedly. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5445933 Summary of the Invention [Problem to be solved by the invention]

[0006] When a material to be rolled (slab) is placed on the table, a high load is applied to the induction motor. When the induction motor is switched between forward and reverse rotation in this state, the induction motor is started at a low speed. When the induction motor is started at such a low speed, a torque shortage is likely to occur. When a torque shortage occurs, the rotation speed of the induction motor does not increase, and the deviation between the rotation speed and the speed command becomes large. As a result, the torque command (Q-axis current command) becomes stuck at the upper limit value (see the conventional control shown on the left side of Figure 3), and eventually the current is limited, which leads to the induction motor being judged to have tripped (serious failure), and the rolling line is shut down. Such an induction motor trip is particularly likely to occur in the case of sensorless vector control.

[0007] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a control device for an induction motor that can prevent start-up failure caused by insufficient torque even when starting an induction motor at a high load and low speed. [Means for solving the problem]

[0008] A first aspect of the present disclosure relates to a control device for an induction motor. The control device controls an induction motor for transporting a material to be rolled on a rolling line. The control device includes a rotation speed acquisition unit that acquires the rotation speed of the induction motor by measuring or estimating the rotation speed, a Q-axis current command setting unit that sets a Q-axis current command, which is a torque command for the induction motor, based on the deviation between the rotation speed acquired by the rotation speed acquisition unit and a speed command, and a D-axis current command setting unit that sets a D-axis current command, which is an excitation command for the induction motor. The D-axis current command setting unit includes a D-axis current command calculation unit that calculates the D-axis current command, and a D-axis current command compensation unit that increases and compensates the D-axis current command calculated by the D-axis current command calculation unit when the induction motor is started. In the present disclosure, when the induction motor is started, it is assumed that the start of the induction motor includes not only the start of the start of the induction motor, but also a low-speed region from the start of the start until the rotation speed of the induction motor reaches a predetermined reference value.

[0009] The second aspect has the following features in addition to the first aspect: A D-axis current command compensation unit increases the D-axis current command until the rotation speed acquired by the rotation speed acquisition unit reaches a reference value.

[0010] The third aspect has the following features in addition to the second aspect: The D-axis current command compensation unit has a compensation amount calculation unit that calculates a compensation amount for the D-axis current command, and a compensation amount addition unit that adds the compensation amount calculated by the compensation amount calculation unit to the D-axis current command, and the compensation amount calculation unit calculates the compensation amount such that the compensation amount decreases as the rotation speed acquired by the rotation speed acquisition unit increases. Effect of the Invention

[0011] According to the present disclosure, by providing a D-axis current command compensation unit, the D-axis current command is raised when the induction motor is started. This makes it possible to ensure sufficient torque when the induction motor is started, and prevents the induction motor from failing to start due to insufficient torque. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram for explaining a system configuration of a rolling line. [Diagram 2] 1 is a schematic diagram showing a configuration of a control device for an induction motor according to an embodiment; [Diagram 3] FIG. 13 is a diagram for explaining compensation of a D-axis current command during a low-speed startup of an induction motor. [Figure 4] 2 is a conceptual diagram illustrating an example of a hardware configuration of a processing circuit included in a control device. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, common or corresponding elements are denoted by the same reference numerals, and descriptions thereof will be simplified or omitted.

[0014] Fig. 1 is a schematic diagram showing the configuration of a rolling line 1. The rolling line 1 rolls steel or other metal material as a rolled material M into a plate shape by hot rolling. The rolling line 1 is equipped with a heating furnace 2, a roughing mill 3, a crop shear 4, a finishing mill 5, a cooling device 6, and a winder 7 as its main equipment.

[0015] The heating furnace 2 is configured to heat a slab, which is a material M to be rolled before rolling, to a predetermined temperature.

[0016] The roughing mill 3 has at least one, usually one to three, rolling stands, and is configured to roll the material M heated in the heating furnace 2 in a forward direction (from the upstream side to the downstream side of the rolling line) and a reverse direction (from the downstream side to the upstream side of the rolling line) in multiple passes. The roughing mill 3 is also provided with at least one induction motor IM that drives a table (not shown) that transports the material M. For this reason, the roughing mill 3 performs an oscillation operation in which the induction motor IM repeats forward and reverse rotation at a low speed.

[0017] The crop shear 4 is configured to cut off any defective shape portions at the leading or trailing end of the rolled material M using upper and lower blades, based on the shape measured by a shape detector 81 described later.

[0018] The finishing mill 5 is, for example, a hot tandem rolling mill. The finishing mill 5 has a plurality of (seven in this embodiment) rolling stands F1 to F7 arranged in parallel in the conveying direction of the material M to be rolled. Each of the rolling stands F1 to F7 has two work rolls 51, one above the other, two backup rolls 52, one above the other, and an electric motor 53 for rotating the rolls. The backup rolls 52 are provided with a screw down device 54, which is configured to be able to adjust the roll gap between the upper and lower work rolls 51. The rolling load of each of the stands F1 to F7 is measured by a rolling load sensor 55. The rolling load sensor 55 is, for example, a load cell. The roll gap of each of the rolling stands F1 to F7 can be measured by a magnet scale (not shown). The finishing mill 5 is also provided with at least one induction motor IM for driving a table (not shown) for conveying the material M to be rolled.

[0019] The cooling device 6 is configured to be able to cool the material M by injecting water onto the material M using a cooling bank. The cooled material M is wound into a coil by a winder 7.

[0020] Various sensors are installed at key points in the rolling line 1 as various measuring instruments. The key points in the rolling line 1 are, for example, the outlet side of the heating furnace 2, the outlet side of the roughing mill 3, the outlet side of the finishing mill 5, and the inlet side of the winder 7. Various sensors may also be installed between the rolling stands F1 to F7 of the finishing mill 5. The various sensors include a shape detector 81 capable of measuring the shape (including the width) of the material M to be rolled at the outlet side of the roughing mill 3, a thermometer 82 measuring the surface temperature of the material M to be rolled at the upstream side of the finishing mill 5, a thickness gauge 83 measuring the actual thickness of the material M to be rolled at the outlet side of the finishing mill 5, and the rolling load sensor 55 measuring the rolling load at each of the rolling stands F1 to F7. In addition, a speed sensor for measuring the rotation speed may be provided on the rotating shaft of the induction motor IM. The various sensors successively measure the condition of the rolled material M and each piece of equipment.

[0021] The rolling line 1 is operated by a control system using a computer. The computer includes a host computer 10 and a process control computer 11, which are connected to each other via a network. An interface screen 12, which is an operation screen for an operator, is connected to the process control computer 11 via the network. The operator can perform operations such as inputting control conditions on the interface screen 12.

[0022] The process control computer 11 executes setting calculations and control of control targets in a series of rolling processes. The process control computer 11 also has a function of correcting the roll gaps of each of the rolling stands F1 to F7. Product information is input to the process control computer 11 from the host computer 10. The product information includes target information (product target) such as the target plate thickness (product plate thickness) and target plate width of the rolled material M heated by the heating furnace 2, and the steel type.

[0023] The process control computer 11 appropriately controls each piece of equipment based on the target information and the control conditions provided from the interface screen 12. When the material M to be rolled is transported to a predetermined position in the rolling line 1, the process control computer 11 calculates the settings of each piece of equipment that can achieve the target information, and operates the actuators and motors of each piece of equipment based on these setting values. The process control computer 11 also sends a speed command SP_REF for the induction motor IM to the control device 20, which will be described later.

[0024] The rolling line 1 includes a control device 20 that controls an induction motor IM installed in a roughing mill 3. Fig. 2 is a schematic diagram showing a configuration of the control device 20 for the induction motor IM according to an embodiment. The control device 20 includes a rotation speed acquisition unit 21, a Q-axis current command setting unit 22, and a D-axis current command setting unit 23.

[0025] The rotation speed acquisition unit 21 acquires the rotation speed SP_FBK of the induction motor IM by estimation calculation. The acquired rotation speed SP_FBK is fed back to the Q-axis current command setting unit 22 and a compensation amount calculation unit 233 described later. A known method can be used to calculate the rotation speed SP_FBK, so a detailed description will be omitted here. The rotation speed acquisition unit 21 may be configured to acquire and feed back the rotation speed SP_FBK measured by a speed sensor (not shown) such as a pulse generator provided on the rotating shaft of the induction motor IM.

[0026] The Q-axis current command setting unit 22 sets a Q-axis current command IQ_R, which is a torque command for the induction motor IM, based on the deviation between the rotation speed SP_FBK acquired (feedback) by the rotation speed acquisition unit 21 and the speed command SP_REF (by multiplying the deviation by a proportional gain). A known method can be used to set the Q-axis current command IQ_R, and therefore a detailed description thereof will be omitted here.

[0027] D-axis current command setting unit 23 sets a D-axis current command ID_R which is an excitation command for induction motor IM. In this embodiment, D-axis current command setting unit 23 is configured as follows to avoid torque shortage during low-speed startup of induction motor IM. That is, D-axis current command setting unit 23 includes a D-axis current command calculation unit 231 which calculates a D-axis current command in response to a speed command SP_REF, and a D-axis current command compensation unit 232 which increases and compensates for the D-axis current command calculated by D-axis current command calculation unit 231 during low-speed startup of induction motor IM. As will be apparent from the following description, D-axis current command compensation unit 232 is different from known slip compensation and multiple-unit drive control compensation.

[0028] The D-axis current command compensation unit 232 has a compensation amount calculation unit 233 and a compensation amount addition unit 234. The compensation amount calculation unit 233 calculates a compensation amount A for the D-axis current command. The compensation amount addition unit 234 adds the compensation amount A calculated by the compensation amount calculation unit 233 to the D-axis current command ID_R calculated by the D-axis current command calculation unit 231.

[0029] Here, the rotation speed SP_FBK acquired by the rotation speed acquisition unit 21, and the preset maximum compensation amount Amax and compensation effective speed B are input to the compensation amount calculation unit 233. The maximum compensation amount Amax can be set, for example, so as not to exceed the rated current of the induction motor IM. The compensation effective speed B can be set, for example, to a speed that is considered to eliminate the torque shortage through simulation, experiment, or the like. The compensation amount calculation unit 233 calculates a compensation amount (boost compensation amount) A to be added until the time (time t2 described later) when the rotation speed SP_FBK reaches the compensation effective speed B. After the rotation speed SP_FBK reaches the compensation effective speed B, the compensation amount A is calculated to be zero. The compensation amount A is calculated so that the compensation amount A decreases as the rotation speed SP_FBK increases. That is, the compensation amount A is calculated so that the compensation amount A decreases in a tapered or linear manner as the rotation speed SP_FBK increases.

[0030] The D-axis current command ID_R to which the compensation amount A calculated by the compensation amount calculation unit 233 has been added is set as the D-axis current command ID_R for the induction motor IM.

[0031] Next, compensation of the D-axis current command when the induction motor IM is started will be described taking as an example a case where the induction motor IM of the roughing mill 3 is started at a low speed. Fig. 3 is a diagram for explaining compensation of the D-axis current command when the induction motor IM is started at a low speed.

[0032] At time t1 shown in Fig. 3, when the induction motor IM is started (started) at a low speed, the speed command SP_REF rises. Here, in the conventional technology shown on the right side of Fig. 3, the rise of the rotation speed SP_FBK is delayed with respect to the speed command SP_REF due to a torque shortage, and as a result, the Q-axis current command IQ_R, which is a torque command, is stuck to the upper limit value IQ_LMT.

[0033] On the other hand, in this embodiment, at the start-up start time t1, the compensation (flag) of the D-axis current command by the D-axis current command compensation unit 232 is turned ON. As a result, the compensation amount A calculated by the compensation amount calculation unit 233 is added to the D-axis current command ID_R calculated by the D-axis current command calculation unit 231, and the D-axis current command ID_R is raised. As a result, during the low-speed start-up of the induction motor IM, the torque increases by the amount that the magnetic flux becomes stronger, and sufficient torque can be secured. As a result, the rise of the rotation speed SP_FBK becomes faster, and the Q-axis current command IQ_R does not stick to the upper limit value IQ_LMT. This makes it possible to prevent the induction motor IM from failing to start due to insufficient torque.

[0034] At time t2 when the rotation speed SP_FBK reaches the compensation effective speed B, which is a predetermined reference value, the compensation (flag) of the D-axis current command by the D-axis current command compensation unit 232 is turned OFF. This prevents excessive compensation of the D-axis current command. Also, by calculating the maximum compensation amount A at time t1 and then calculating the compensation amount A so that it gradually decreases until time t2, it is possible to realize appropriate compensation of the D-axis current command according to the rotation speed SP_FBK.

[0035] As described above, according to this embodiment, the D-axis current command ID_R is increased when the induction motor IM is started by providing the D-axis current command compensation unit 232. This makes it possible to ensure sufficient torque when the induction motor IM is started, and prevents the induction motor IM from failing to start due to insufficient torque.

[0036] Next, a specific structure of the control device 20 will be described. The specific structure of the control device 20 is not limited, but may be as follows, for example. FIG. 4 is a conceptual diagram showing a hardware configuration example of a processing circuit included in the control device 20. The rotation speed acquisition unit 21, the Q-axis current command setting unit 22, the D-axis current command setting unit 23, the D-axis current command calculation unit 231, the D-axis current command compensation unit 232, the compensation amount calculation unit 233, and the compensation amount addition unit 234 indicate some of the functions included in the control device 20, and each function is realized by the processing circuit. For example, the processing circuit includes at least one processor 201 and at least one memory 202. For example, the processing circuit includes at least one dedicated hardware 203.

[0037] When the processing circuit includes the processor 201 and the memory 202, each function of the control device 20 is realized by software, firmware, or a combination of software and firmware. At least one of the software and firmware is written as a program. At least one of the software and firmware is stored in the memory 402. The processor 201 realizes each function by reading and executing the program stored in the memory 202. The processor 201 is also called a CPU (Central Processing Unit), central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or DSP. For example, the memory 202 is a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, or an EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD, or the like.

[0038] When the processing circuitry includes dedicated hardware 203, the processing circuitry may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. For example, each function is realized by a processing circuit. For example, each function is realized collectively by a processing circuit. Also, each function may be realized partially by dedicated hardware 203 and the other part by software or firmware. In this way, the processing circuitry realizes each function by hardware 203, software, firmware, or a combination thereof.

[0039] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and can be modified in various ways without departing from the spirit of the present disclosure. For example, the above embodiments have been described with reference to an example of controlling the induction motor IM installed in the roughing mill 3, but the present disclosure can also be applied to a case where the induction motor IM installed in the finishing mill 5 is controlled. That is, for example, by applying the present disclosure to a case where the induction motor IM of the finishing mill 5 is started at a low speed after manual intervention is performed, it is possible to prevent a start failure caused by a lack of torque.

[0040] Furthermore, in the above embodiment, sensorless vector control has been described as an example, but the present disclosure can also be applied to sensor-equipped vector control and V / F control.

[0041] Furthermore, when the number, quantity, amount, range, etc. of each element is mentioned in the above embodiments, the present disclosure is not limited to the mentioned number unless specifically stated or clearly specified in principle to that number. [Explanation of symbols]

[0042] 1... rolling line, 20... control device, 21... rotational speed acquisition unit, 22... Q-axis current command setting unit, 23... D-axis current command setting unit, 231... D-axis current command calculation unit, 232... D-axis current command compensation unit, 233... compensation amount calculation unit, 234... compensation amount addition unit, IM... induction motor, M... rolled material

Claims

1. A control device for an induction motor for transporting a material to be rolled in a rolling line, A rotation speed acquisition unit that acquires a rotation speed of the induction motor by measuring or estimating the rotation speed; a Q-axis current command setting unit that sets a Q-axis current command, which is a torque command for the induction motor, based on a deviation between the rotation speed acquired by the rotation speed acquisition unit and a speed command; a D-axis current command setting unit that sets a D-axis current command that is an excitation command for the induction motor, The D-axis current command setting unit is a D-axis current command calculation unit for calculating the D-axis current command; a D-axis current command compensation unit that increases and compensates for the D-axis current command calculated by the D-axis current command calculation unit when starting the induction motor.

2. The control device for an induction motor according to claim 1 , wherein the D-axis current command compensation unit increases the D-axis current command until the rotation speed acquired by the rotation speed acquisition unit reaches a reference value.

3. the D-axis current command compensation unit includes a compensation amount calculation unit that calculates a compensation amount for the D-axis current command, and a compensation amount addition unit that adds the compensation amount calculated by the compensation amount calculation unit to the D-axis current command, The control device for an induction motor according to claim 2 , wherein the compensation amount calculation unit calculates the compensation amount such that the compensation amount decreases as the rotation speed acquired by the rotation speed acquisition unit increases.

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