Assembly for monitoring a winding threshold temperature

Abstract

A temperature monitoring device for protecting the winding of an electronically commutated electric motor from being heated over a specified limit temperature T.sub.G regardless of the rotational speed includes a phase current detection device for detecting the phase current I.sub.Winding for the motor windings, an overcurrent switch-off device for switching off the electric motor if a maximum permissible phase current I.sub.Shutdown is exceeded, and an overcurrent monitoring device, which is connected to the overcurrent switch-off device, in order to transmit to it a switch-off signal if the detected phase current I.sub.Winding exceeds the maximum permissible phase current I.sub.Shutdown ascertained by a detection and computing device, wherein an algorithm in which the measured ambient temperature T.sub.U is incorporated is used when ascertaining the maximum permissible phase current I.sub.Shutdown.

Claims

1. A method for temperature monitoring of an electric motor having at least one winding regardless of the rotational speed with a temperature monitoring device; the method comprising the following steps: a) providing the temperature monitoring device comprising: a phase current detection device for detecting a phase current I.sub.Winding for the motor windings, an overcurrent switch-off device for switching off the electric motor if a maximum permissible phase current I.sub.shutdown is exceeded, and an overcurrent monitoring device, which is connected to the overcurrent switch-off device, in order to transmit to it a switch-off signal if the detected phase current I.sub.Winding exceeds the maximum permissible phase current I.sub.Shutdown ascertained by a detection and computing device, wherein an algorithm in which the measured ambient temperature T.sub.U is incorporated is used when ascertaining the maximum permissible phase current I.sub.Shutdown; b) measuring the phase current with the phase current detection device during a predetermined time interval t; c) performing a Clark-Park transformation of the measured phase current to obtain a d-winding current component and a q-winding current component in a dq-pointer system; d) calculating a geometrical sum of the d-winding current and the q-winding current by the following formula:
I.sub.Winding=√{square root over (Id.sup.2+Iq.sup.2)} e) detecting ambient temperature, and f) calculating the switch-off current by the following algorithm:
I.sub.Shutdown=I.sub.Limiting*K.sub.TU where I.sub.Shutdown: is the switch-off current, i.e., the mean value of the winding current at which the motor is switched off, I.sub.Limiting: Is the maximum permissible mean value of the winding current I.sub.Winding, and K.sub.TU: is a correction factor, being determined as follows: $\begin{array}{cc}{K}_{\mathrm{TU}}=1& \mathrm{for}{T}_U<T_Z\\ K_{\mathrm{TU}}=1-\left(\frac{\mathrm{Tu}-T\max }{T\max }\right)& \mathrm{for}{T}_U>T_Z\end{array}$ where  T.sub.U: is the ambient temperature,  T.sub.Z: is the maximum ambient temperature specified for the motor, and  T.sub.max: is the maximum permissible excess temperature for the motor.

2. The method according to claim 1, wherein the calculation in step f) is done by means of the detection and computing device.

3. The method according to claim 1, wherein a comparator compares the detected phase current I.sub.Winding with the maximum permissible phase current I.sub.Shutdown and the overcurrent switch-off device switches off the electric motor or interrupts the commutation when I.sub.Winding>I.sub.Shutdown.

4. The method according to claim 3, wherein an automatic motor starting occurs upon expiration of a defined dead time after a switch-off process or an interruption process.

5. The method according to claim 2, wherein a comparator compares the detected phase current I.sub.Winding with the maximum permissible phase current I.sub.shutdown and the overcurrent switch-off device switches off the electric motor or interrupts the commutation when I.sub.Winding>I.sub.shutdown.

6. The method according to claim 1, wherein a readable storage device provides target value data to the detection and computing device; wherein the target value data comprises at least T.sub.z, T.sub.max, and I.sub.Limiting.

7. The method according to claim 6, wherein the target value data is entered into the readable storage device via a data entry device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 shows a table representing the relationship between the insulation classes or the respective temperature values and the particular permissible temperature rise,

(3) FIG. 2 shows a function graph of the correction factor in dependence on the ambient temperature;

(4) FIG. 3 shows a block diagram of an embodiment of a temperature monitoring device of an electric motor, and

(5) FIG. 4 shows a flow chart of the method according to the present disclosure.

(6) The drawings are provided herewith for purely illustrative purposes and are not intended to limit the scope of the present invention.

DETAILED DESCRIPTION

(7) The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description, corresponding reference numerals indicate like or corresponding parts and features.

(8) Within this specification, embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.

(9) In the following, one aspect of the present disclosure shall be explained more closely with the aid of an embodiment with reference to FIGS. 1 to 4, where the same references are used for the same functional and/or structural features.

(10) FIG. 1 shows a table representing the relationship between the insulation classes or the corresponding temperature values 105° (class A) to 250° and the respective permissible temperature rise in Kelvin. The temperature rise is determined here as the difference between the winding temperature and the ambient temperature.

(11) FIG. 2 shows a function graph of the correction factor K.sub.TU in dependence on the ambient temperature T.sub.U with the designations T.sub.U, T.sub.Z, T.sub.max already explained in the context of the general description of the invention.

(12) $\begin{array}{cc}{K}_{\mathrm{TU}}=1& \mathrm{for}{T}_U<T_Z\\ K_{\mathrm{TU}}=1-\left(\frac{\mathrm{Tu}-T\max }{T\max }\right)& \mathrm{for}{T}_U>T_Z\end{array}$

(13) The correction factor K.sub.TU diminishes in linear fashion with increasing ambient temperature T.sub.U from the maximum ambient temperature specified for the motor until the maximum excess temperature is reached. The motor can be operated in this range with diminished power.

(14) FIG. 3 shows a block diagram of an embodiment of a temperature monitoring device 1 of an electric motor. The temperature monitoring device 1 is designed to protect the winding of an electronically commutated electric motor 10 against heating above a particular limit temperature T.sub.G regardless of the rotational speed with a phase current detection device 11 for detecting the phase current I.sub.Winding for the motor windings. Moreover, an overcurrent switch-off device 12 is provided for switching off the electric motor 10 upon exceeding a maximum permissible phase current I.sub.Shutdown.

(15) The overcurrent switch-off device 12 is connected to an overcurrent monitoring device 11 in order to obtain from the latter a switch-off signal upon occurrence of the switch-off condition, namely, when the detected phase current I.sub.Winding exceeds the maximum permissible phase current I.sub.Shutdown.

(16) In order to determine or calculate the maximum permissible phase current I.sub.Shutdown, a detection and computing device 14 is provided, which is connected to the overcurrent monitoring device 11.

(17) Further, it can be recognized that the detection and computing device 14 is connected to devices for the obtaining of target values T.sub.Z, T.sub.max, I.sub.Limiting as well as the ambient temperature T.sub.U. The ambient temperature is determined or measured with a device 18 for detection of the ambient temperature.

(18) The phase current detection device 11 is connected to the commutation controller 15 and this in turn is connected to the inverter 16 for energizing the motor windings 17 of the electric motor E.

(19) FIG. 4 shows a flow chart in order to explain the method according to the present disclosure. In order to increase the motor torque, there occurs an increasing of the winding current, which is measured. After this, the already described steps are carried out until a comparator compares the detected phase current I.sub.Winding with the maximum permissible phase current I.sub.Shutdown and, when I.sub.Winding>I.sub.Shutdown, the overcurrent switch-off device 12 switches off the electric motor E or the commutation controller 15 interrupts the commutation. Otherwise, the normal operation is detected.

(20) The present disclosure is not limited in its scope to the above indicated embodiments. Rather, a number of variants are conceivable, which make use of the represented solution even with fundamentally different configurations. Thus, as shown in the embodiment of FIG. 4, an automatic restarting of the motor may occur after expiration of a defined dead time after a switching off of the electric motor E.

(21) While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.