JPH0453179Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a detection device for the rotor bar temperature, which is a factor in changing the secondary resistance, which is an important parameter in vector control of a squirrel cage induction motor.

(Prior art) A vector control method has been proposed as a powerful control method for applying induction motors to torque control, speed control, position (servo) control, etc., and with the advancement of microprocessors, it has been put into practical use and is currently in use. It has many uses.

The vector control method models an induction motor as a DC machine, divides the motor current into two orthogonal vector components, one for torque generation and one for magnetic flux generation, and configures a precise control circuit to control each of these components independently. However, the aim is to obtain a motor torque that is linear and has a fast response to the command torque.

By the way, in order to actually apply this method, many technical problems must be solved, one of which is the problem of changes in motor secondary resistance due to rotor bar temperature. In other words, if the change in the motor secondary resistance is left as is without correction, a. Deviation of the motor torque from the command torque, non-linearity problem b. Deviation from the orthogonal relationship of each vector of the torque component and magnetic flux component, transient characteristics due to interference. Worsening c: Problems such as a decrease in motor output occur due to the difference between the maximum inverter output voltage of the power supply and the motor voltage. Therefore, in order to reduce or eliminate these problems, it is sufficient to detect the rotor bar temperature and correct the secondary resistance value of the control circuit model according to the detected value. It is more widely practiced.

By the way, to detect the temperature of the rotor bar, it is ideal to attach a temperature sensor directly to the rotor bar, but attaching the element to the rotating body requires a complicated mechanism, and the simple structure of the squirrel cage induction motor This impairs the strong feature and is not practical.

For this reason, conventionally, the stator is provided with a temperature measuring element, and the stator temperature is assumed to be substantially equal to the rotor bar temperature, and the stator temperature is substituted for the rotor bar temperature to perform temperature correction of the secondary resistance value.

(Problem to be solved by the invention) In the case of a general squirrel cage induction motor, especially an external fan type,
The structure is such that the heat generated from the stator and rotor is dissipated through the outer skin of the case, and the rotor, which is located deep inside, has a higher thermal resistance to the outside cooling air than the stator, allowing steady, thermally balanced operation. If the rotor is in this state, the rotor is necessarily at a higher temperature than the stator, and the conventional secondary resistance temperature correction assuming that the stator and rotor bar temperatures are approximately equal includes a considerable error. In addition, experimental data shows that at 100% output with a 5.5KW external sector induction motor, the temperature difference between the stator and rotor bar is more than 20℃, and with the conventional secondary resistance temperature correction using the stator temperature,
The deviation of the motor torque from the command torque was 5% or more.

(Means for solving the problem) The stator and rotor bar temperatures differ because a heat flow is generated toward the outer skin, and this creates a temperature gradient in each part of the motor. The present invention is characterized in that the rotor bar temperature is calculated by arranging temperature measuring elements and calculating the data of these temperature measuring elements based on the law of heat conduction.

(Function) Heat flow is generated based on the heat conduction law, and the heat flow, that is, the rotor bar temperature, is estimated by calculating the temperature measurement element data at two or more points on the stator using the heat conduction law. It is possible to obtain a rotor bar temperature that is much more accurate than when the values are equal.

(Example) As an example, a case where the present invention is applied to a totally enclosed external sector squirrel cage induction motor will be shown. In the drawing, 1 is a rotor,
2 is a stator, 3 is a shaft, 4 is a bearing, 5 is an outer skin, 6
7 is a speed detector, 7 is an external fan, and 8 is a wind regulating cover.

Temperature measuring elements are provided at at least two points on the stator 1, that is, in the embodiment, the heat flow is directed toward the outer skin from the inner part of the motor, so that the temperature measuring elements are provided at the outer periphery of the stator 2 near the outer skin 5 and the inner periphery of the stator 2 deep inside. ,
The heat flow is estimated from the temperature difference between the outer and inner circumferential parts of the stator, and the rotor bar temperature is calculated.

That is, from the temperature measurement data T P3 and T _P2 of the temperature measurement point P ₃ on the outer periphery of the stator and the temperature measurement point P ₂ on the inner _periphery , the temperature difference “T _P2 − T _P3 ” between the two is determined, and this Multiply by a predetermined constant K based on the law, K (T _P2 − T _P3 )
is calculated, and the stator inner peripheral temperature T _P2 near the rotor bar is added to obtain the rotor bar temperature T _P1 as T _P1 ≒ T _P2 + K (T _P2 − _{T P3} ). In addition, the constant K depends on the motor structure, material,
It is determined based on the heat conduction law based on the mounting location of the temperature measuring element, etc. Further, in the drawing, reference numeral 10 denotes an arithmetic processing circuit that calculates the rotor bar temperature by processing the temperature measurement element data of the stator based on the heat conduction law.

(Effect of the invention) In vector control of a squirrel-cage induction motor, accurate calculation of the rotor bar temperature allows precise temperature correction of the secondary resistance value of the control circuit model.
It is possible to prevent adverse effects on torque characteristics and transient characteristics, decrease in motor output, etc., and it is possible to always maintain an optimal operating state regardless of the magnitude of the load.

[Brief explanation of the drawing]

The drawing is a block diagram of a rotor bar temperature detection device in a totally enclosed external sector squirrel cage induction motor according to an embodiment. 1...Rotor, 2...Stator, 10...Arithmetic processing circuit, _P2 , _P3 ...Stator temperature measurement point, _P3 ...
Rotor bar temperature point calculated from P ₂ and P ₃ temperature measurement point data.

Claims (1)

[Scope of utility model registration request] Temperature measuring elements are arranged at at least two points on the induction motor stator, one on the inner circumference near the rotor bar and the other on the outer circumference,
A rotor bar temperature detection device characterized by estimating the heat flow from the inner part of the motor toward the outer skin, and adding this estimated value to the data of the inner circumferential temperature measuring element near the rotor bar to obtain the rotor bar temperature.