JP3442982B2 - Motor drive system using speed sensorless vector controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for connecting and controlling a plurality of induction motors driven by speed sensorless vector control, and particularly relates to a stable starting characteristic. The purpose is to obtain. 2. Description of the Related Art FIG. 2 shows a diagram of a motor drive system using a conventional speed sensorless vector control device, and the prior art will be described based on the diagram. FIG. 2 is a block diagram showing an example in which four speed sensorless vector controllers are used. In FIG.
1 to 14 are speed sensorless vector control devices and 21 to 2
4 is an induction motor having a double shaft structure, 3 is a gear box, 4 is a load machine driven by using the present system, 5 is a speed detector for detecting the rotation speed N, and 6 is a rotation speed command N * rotation speed N This is an external speed controller that calculates the torque command T * based on the deviation from. The induction motors 21 to 24 have a double-shaft structure, and each is directly connected to an output shaft. The load machine 4 is driven by a rotating shaft output from the gear box 3. The external speed controller 5 receives the rotation speed command N * and the rotation speed N output from the speed calculator 6, and outputs a torque command T * such that the rotation speed follows the rotation speed command. The torque command T * is input to the speed sensorless vector controllers 11 to 14. The speed sensorless vector controllers 11 to 14 perform speed sensorless vector control so that the output torque of the induction motors 21 to 24 follows the input torque command. Next, a speed sensorless vector control device 1
1 will be described. 111 is an output voltage detector 113
And a speed calculator for calculating the calculation speed Nc based on the output voltage and output current detected by the output current detector 114. The torque controller 112 controls the voltage using the calculation speed Nc so that the output torque of the induction motor 21 follows the input torque command T *.
Output to Here, the speed sensorless vector control device 11 has been described, but the speed sensorless vector control devices 12 to 14 are completely the same. FIG. 3 shows an equivalent circuit of an induction motor. As can be seen from this circuit diagram,
When the frequency of the input voltage V1 is zero, ω = 0 and the inductances L1 and L2 are all equal to 0. Therefore, the input current I1 depends only on the primary resistance R1, and the resistance R
2 and the rotational angular frequency ωm proportional to the rotational speed N are not affected at all. In other words, near the zero frequency, it is impossible to determine the rotational speed from the input voltage and the input current.
In the speed sensorless vector control, when starting the induction motor, the rotation speed is set to N = 0, and the output frequency is equal to the slip frequency command. Since the slip frequency command is proportional to the torque command, when the torque command is small, the output frequency becomes close to 0, and the rotation speed cannot be calculated as described above, so that normal starting cannot be performed. As shown in FIG. 2, when the load is light in a system in which a plurality of induction motors are driven by the same torque command by one speed controller, the start of starting one of the plurality of motors is delayed. However, when the rotation speed reaches the rotation speed command at the time of starting by another electric motor, the torque command decreases. As a result, a small torque command is also input to the speed sensorless vector control device that drives the electric motor whose start start is delayed, so that it may not be possible to start only one vehicle whose start start is delayed. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and aims to solve these disadvantages. Even when the start of one of a plurality of electric motors is delayed, the start of the start is prevented. It is an object of the present invention to provide a motor drive system using a speed sensorless vector control device that can obtain a stable starting characteristic without preventing a delayed one from starting. [0008] That is, a means for achieving the object is an induction motor and a speed calculator for estimating or calculating the rotation speed of the motor from an input current and an input voltage of the motor. An internal speed controller for inputting a speed command for instructing the rotation speed of the electric motor and an output rotation speed of the speed calculator and outputting an internal torque command such that the rotation speed follows the command; And a plurality of speed sensorless vector control devices each comprising a torque controller for inputting the rotation speed of the output of the speed calculator and supplying electric power to the motor so that the output torque of the motor follows the torque command. When starting the motor drive system using a speed sensorless vector control device that drives and connects the output shafts of the motor to each other , the drive system The rotation speed output from the speed detector attached to the motor and the external torque command obtained by inputting the rotation speed command to the external speed controller are input to all of the plurality of speed sensorless controllers, The internal torque command obtained by inputting the minimum rotation speed command and the rotation speed of the output of the speed calculator to the speed calculator is compared with the input external torque command, and the larger torque command is subjected to the torque control. It is configured to be the input of a vessel. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reference numerals 11 to 14 denote speed sensorless vector control devices, which control induction motors 21 to 24 respectively. Drive. The induction motors 21 to 24 have a double-shaft structure, and the shafts are directly connected to each other. 3
Is a gear box for transmitting the output of the shafts of the induction motors 21 to 24 to the load machine 4. Reference numeral 5 denotes a speed detector which detects the rotation speed N of the induction motors 21 to 24. Reference numeral 6 denotes an external speed controller, which controls the external torque command T1 * such that the rotation speed N detected by the speed detector 5 follows the speed command N *. Next, the speed sensorless vector control device 1
1 will be described. 111 is an output voltage detector 113
And a speed calculator for calculating the calculation speed Nc based on the output voltage and the output current detected by the output current detector 114. Reference numeral 115 denotes a minimum rotation speed setting device, which sets a minimum rotation speed in this drive system in advance. The internal speed controller 116 is the minimum rotation speed setting device 1
The internal torque command T2 * is controlled so that Nc follows the minimum rotation speed command Nc * set by the control unit 15. The priority circuit 117 selects the larger one of the output T1 * of the external speed controller 6 and the internal speed controller T2 * and outputs it as a torque command T *. The torque controller 112 controls the voltage so that the output torque of the induction motor 21 follows the torque command T * using the calculation speed Nc as in the related art, and outputs the voltage to the induction motor 21. Here, the speed sensorless vector control device 11 has been described, but the speed sensorless vector control devices 12 to 14 are completely the same. When the engine is operating normally and the calculated rotational speed Nc can be calculated correctly, the minimum rotational speed command Nc * is always smaller than Nc. Therefore, the internal torque command T2 * of the internal speed controller 116 is a negative value. It becomes. Therefore, the priority command 117 sets the torque command T * to T * =
Since T1 * is selected, the speed of the present drive system is controlled by the external speed controller 5 to be the speed command N. On the other hand, when starting with a light load, the start of the speed sensorless vector control device 11 is delayed. Become smaller. However, in this case, the output Nc of the speed calculator 111 is 0, and to accelerate to the minimum rotation speed Nc *,
The internal speed controller 116 increases the internal torque command T2 * in the positive direction. Therefore, the priority circuit 117
As a result, T * = T2 * is selected, so that a torque command large enough for starting is given to the torque controller 112, and starting is possible. As described above, according to the present invention, a system in which a plurality of induction motors are driven by a single speed controller under the same torque command, and one of the plurality of motors is used. Even if the start of the start is delayed, stable starting characteristics can be obtained without preventing the start of only one of the units whose start of the start is delayed, which is extremely useful in practical use.

[Brief description of the drawings] FIG. 1 is a configuration diagram showing one embodiment of the present invention. FIG. 2 is a configuration diagram of an example showing a conventional technique. FIG. 3 is an equivalent circuit diagram of the induction motor. [Explanation of symbols] 3 Gearbox 4 Load machine 5 Speed detector 6 External speed controller 11-14 Speed sensorless vector controller 21-24 Induction motor 111 Speed calculator 112 Torque controller 113 Voltage detector 114 current detector 115 Minimum rotation speed setting device 116 Internal speed controller 117 Priority circuit

Claims (1)

(57) [Claims] 1. An induction motor and an input current of the motor.
Estimating or calculating the rotation speed of the motor from the input voltage
Speed calculator and speed commanding the rotation speed of the motor
Input the command and the rotation speed of the output of the speed calculator and rotate
Outputs an internal torque command so that the speed follows that command
Internal speed controller, and the torque command and the speed calculator
By inputting the output rotation speed, the output torque of the
Supply electric power to the motor so as to follow the torque command
Speed sensorless vector control device consisting of torque controller
And the output shafts of the motors are connected to each other.
Using a speed sensorless vector controller
Motivation drive systemAt the start of Output from a speed detector attached to the drive system
Input the rotation speed and speed command to the external speed controller.
And the external torque command obtained by
Input to each of the sensorless control devices,
A minimum rotation speed command and the speed calculation to the internal speed controller;
Internal obtained by inputting the rotation speed of the vessel output
Comparing the torque command with the input external torque command,
The larger torque command is input to the torque controller.
Using a speed sensorless vector controller configured as
Motor drive system.