EP1019741A1

EP1019741A1 - Method and device for determining the operating temperature of engines

Info

Publication number: EP1019741A1
Application number: EP98954208A
Authority: EP
Inventors: Reinhard Maier; Paul FRÖHLICH
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1997-09-29
Filing date: 1998-09-21
Publication date: 2000-07-19
Also published as: WO1999017127A1; US6504358B1; DE19743046C1

Abstract

The invention relates to a method enabling determination without sensor of the engine temperature as well as the engine start-up temperature, which involves measuring the engine current and voltage in the start-up phase. Identifying from the current and voltage signals the effective component of the engine impedance and comparing values when the engine is powered off with values for a known temperature enable the engine temperature to be determined. The determination method can be either analog or digital, a computer being needed in the second case.

Description

description

Method and device for detecting the operating temperature of engines

The invention relates to a method for detecting the operating temperature of motors, in which the motor temperature and associated electrical parameters are recorded as calibration values at defined times in a learning phase. In addition, the invention also relates to an associated device.

Overload relays are usually used to protect motors. Such overload relays are either equipped with bimetallic strips or analog or digital evaluation circuits for determining the overload sound. This does indeed meet the requirements of the relevant regulations; however, the engine is not adequately protected. For retrofitting, further parameters, in particular also the operating temperature of the engine, must be recorded, the determination of which is comparatively complex according to the usual methods.

Various devices and circuits for detecting the operating temperature of engines are known from the prior art. A measuring arrangement for determining the winding temperature in electrical devices is described in detail in DE 16 13 879 B1, in which a converter is used to change the resistance by superimposing a direct current in the devices operated with alternating current to separate direct current and alternating current. in the iron circuit of which there is a Hall generator and the alternating flow of the converter is compensated for by another converter which is located in the same circuit. In addition, a thermal overload protection device for an electrical machine is known from DE 25 49 850 C2, in which an overload relay assigned to the machine is able to use of the measured stator current to provide an accurate, thermal image of the motor in normal operation. Furthermore, EP 0 332 568 B1 discloses an operating method and an associated control circuit for start-up monitoring for electrical high-voltage motors with asynchronous start-up, in which

Rotor speed and associated power are recorded and are stored in the heating values, which represent the relative heating state of the motor when it is operated at different speeds and load conditions. Finally, EP 0 414 052 B1 discloses an arrangement of this type in which one or more measuring alternating voltage sources are connected in series in one or more phases to the network supplying the electrical machine, so that one or more non-network-frequency, known voltage components are added. This controls a current at these frequencies through the winding of the machine, which - measured by means of a current transformer - is a measure of the conductance of the winding and thus a measure of its temperature.

In addition to the above prior art, DE 31 11 818 AI discloses a method and an associated device for determining the temperature of an asynchronous motor, in which a value representing the respective motor resistance on the basis of the amplitude of the voltage impressed on the motor, the amplitude of the Motor current, the phase angle between voltage and current and the after-run derived from harmonics of the current flowing in the motor feed lines. In a learning phase, the engine temperature and associated electrical parameters are recorded as calibration values at defined times while the engine is running. By using empirical relationships, the so-called equivalent resistance value is to be converted into a corresponding temperature value and can be used to monitor the engine for an impermissibly high temperature rise. Starting from the above-described prior art, it is the object of the invention to provide an alternative method for sensorless motor temperature detection, with which a simple overload determination of motors is also possible.

The object is achieved in that the motor temperature is determined when the motor is switched on, for which purpose current and voltage are measured at the time the motor is switched on, and in that the motor temperature is determined by determining the active component of the motor impedance and comparing the values of the stationary motor and values, measured at a known temperature. The active component of the motor impedance is preferably determined from the power signal formed by analog multiplication of current and voltage signals. Low-pass filtering can be used to easily determine the active component that is required to determine the temperature.

Current and voltage amplitudes and their phase shift can also be measured to determine the active component of the motor impedance. If the amplitude of the voltage is constant, it is advantageously possible to dispense with its measurement.

In addition to the analog multiplication of the measured variables, it is equally possible to determine the variables digitally. A corresponding computer can be provided for this in a device according to the invention.

With the invention, the problems described at the outset are solved in the simplest way, since the motor temperature when switched on is sensorless, ie without lines or the like. can be done within the engine. Since the dependence of the ohm 'see resistance, ie the effective component of the impedance for the materials used in the motor, for example aluminum and copper, on the temperature is known, one-time Measurement of the stationary engine at a higher temperature, a calibration value can be determined. By comparing these values, it is then possible to determine the temperature from the active component of the motor impedance when the motor is running.

With the invention it is possible that in the case of overload determinations the individual measurements according to the known method, in which e.g. the behavior of a bimetal is simulated in a processor, corrected with the true engine temperature at the beginning of the engine run. A correction can always be made even while the engine is running.

Due to the fact that the temperature measurement is now carried out with the rotor of the motor still stationary, there are considerable simplifications. In this case, the equivalent circuit diagram of the motor is very simple because the secondary circuit is short-circuited and the main inductance and iron losses are no longer measured.

Further details and advantages of the invention result from the following description of the figures of an exemplary embodiment with reference to the drawing. The only figure shows an equivalent circuit diagram for a motor with the rotor stopped.

In the figure, a voltage source 1 for an AC voltage U is provided. This operates an electric motor consisting of a stator and a rotor, the equivalent circuit diagram being simple at the time the motor is switched on. In particular, it consists of resistors connected in series, ie R = R] _ _σ + R '2σ _> ^and inductors, ie = L] _ _σ + L' 2 _σ • R _lσ and L _ισ mean ohmic resistance or Inductance of the stator and R ' _2σ or L' _2σ ohmic resistance or inductance of the rotor, transposed on the stator. The equivalent circuit diagram is therefore sufficiently described for the switched-on motor, while the transformer coupling is added for motor operation. Since the ohmic resistances can be described by a linear temperature behavior, calibration at a single temperature which is higher than room temperature is sufficient. If current and voltage are measured at the time of switching on, it is possible to determine the motor temperature from the determination of the active component of the motor impedance by comparing the “cold value” with the “warm value”. It is then only necessary to determine the active component R = R] _ _σ + R '2σ.

The active component R is determined in a simple manner by multiplying the current and voltage signals with one another. This can be done analogously, for example. The result is a power signal that consists of a DC component on the one hand and an AC component on the other hand, the AC component having twice the mains frequency. The low-pass filtering produces the direct signal P from the complex power signal. Since Lι_ _σ + L'2σ is known for the motor at the time of switching on, the active component R defined above can be determined from the direct signal P. The following applies:

where U = peak voltage; ω = 2τA mean

In a modified method, the flowing current and associated voltage are measured and the phase shift is determined. If the amplitude of the AC voltage supplied by the voltage source is constant, it is not necessary to measure it. In this case, for R:

Ü

R = - C0S ^ 3, where U, I mean the peak values and φ the phase. Instead of the analog multiplications, it is also possible to use digital calculation methods for the determination of the active component of the motor impedance dealt with in detail above. A normal computer is suitable for this.

Claims

claims

1.Procedure for determining the operating temperature of engines, in which the engine temperature and associated electrical parameters are determined as calibration values in a learning phase at defined times with the engine running, so that the engine temperature is determined in the working phase when the engine is switched on,

- what current and voltage are measured at the time the motor is switched on and

- The engine temperature is determined by determining the active component (R) of the engine impedance and comparing the values of the stationary engine and values obtained at a known temperature.

2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that the active component (R), the motor impedance is determined from the power signal formed by analog multiplication of current and voltage signals.

3. The method of claim 2, d a d u r c h g e k e n n z e i c h n e t that the power signal consists on the one hand of a DC component (P) and on the other hand from an AC component of double the network frequency.

4. The method of claim 3, d a d u r c h g e k e n n z e i c h n e t that the DC signal (P) is obtained from the power signal by low-pass filtering.

5. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the effective component of the motor impedance from the relationship

is determined, where U is the peak value of the voltage and applies: ω = 2πf

^{L = L} lσ ^{+ L} '2σ-

6. The method according to any one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that the effective component of the motor impedance from the relationship

R = - cos>,

is determined, where U, I mean the peak values of current and voltage and φ their phase shift.

7. The method according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the voltage amplitude is predetermined constantly.

8. The method according to any one of claims 2 to 7, that the determination of the active component (R) of the motor impedance is carried out by digital calculation.

9. An apparatus for performing the method according to claim 1 or claim 8, a computer for evaluating and calculating the active component of the motor impedance from the current and voltage signals.