阅读说明：本技术 Psm的与温度相关的降额 (Temperature dependent derating of PSM ) 是由 F·比特纳 A·鲁夫 于 2020-11-09 设计创作，主要内容包括：本发明涉及一种用于保护永磁同步电机(PSM)的永磁体免于退磁的方法和一种设备。(The present invention relates to a method and an apparatus for protecting permanent magnets of a permanent magnet synchronous motor (PSM) against demagnetization.)

1. A method for protecting a permanent magnet of a permanent magnet synchronous machine (PSM) in a vehicle against demagnetization, wherein the operation of the PSM is inhibited in the following range of the speed/torque characteristic of the PSM when a predetermined rotor temperature of the PSM is exceeded: in this range, the field strength of the reverse field generated by the active short-circuiting of the PSM exceeds the coercive field strength of the permanent magnet.

2. The method of claim 1, wherein the PSM is inhibited from operating within a range of a speed/torque characteristic of the PSM in which a value of the torque is greater than 70% of a maximum torque of the PSM and a value of the speed is greater than 20% of the maximum speed of the PSM.

3. Method according to claim 1 or 2, characterized in that the range of the speed/torque characteristic of the PSM to be suppressed is defined on the basis of a stored table comprising maximum allowable torques in relation to speed and rotor temperature.

4. Method according to any of claims 1 to 3, characterized in that the temperature of the rotor of the PSM is determined by means of a rotor temperature model.

5. Method according to any of claims 1 to 4, characterized in that the temperature of the rotor of the PSM is determined by means of the temperature of the stator of the PSM.

6. An arrangement for protecting permanent magnets of a permanent magnet synchronous motor (PSM) in a vehicle against demagnetization, said arrangement comprising means for determining the rotor temperature of the PSM and a control unit arranged for adjusting the rotational speed and the torque of the PSM, which control unit is arranged for adjusting the torque and the rotational speed of the PSM when a predetermined rotor temperature is exceeded in such a way that the following ranges of the rotational speed/torque characteristic of the PSM are avoided: in this range, the field strength of the reverse field due to the active short-circuiting of the PSM exceeds the coercive field strength of the permanent magnet.

7. Device according to claim 6, characterized in that the control unit is arranged for, in the event of exceeding a predetermined rotor temperature, adjusting the torque and the rotational speed of the PSM in such a way that a torque value of more than 70% of the maximum torque of the PSM and a rotational speed value of more than 20% of the maximum rotational speed of the PSM do not occur simultaneously.

8. The apparatus according to claim 6 or 7, additionally comprising a memory unit with at least one table in which the maximum allowable torque of the PSM is specified in relation to the rotational speed and the rotor temperature of the PSM.

9. The apparatus according to any of claims 6 to 8, wherein the means for determining the rotor temperature of the PSM comprises a rotor temperature model.

10. The apparatus according to any of claims 6 to 9, additionally comprising means for determining a stator temperature of the PSM.

Technical Field

The present invention relates to a method and an apparatus for protecting permanent magnets of a permanent magnet synchronous motor (PSM) against demagnetization.

Background

In contrast to industrial drives, the electric machine in a motor vehicle is operated not only in the rated point but also over a wide operating range, varying in rotational speed, torque and power. In order to be able to provide better driving performance for a short time, for example within 10 seconds, the electric machine is operated under overload, i.e. greater torque is available than in continuous operation. In order not to damage the components of the electric machine during such overload operation, for example, due to excessive temperatures in the stator windings, a so-called derating function is used in the regulation of the electric machine. In this case, the torque and power permitted for the regulation by the electric machine are limited as a function of the measured or calculated temperature of the stator winding. By limiting the power, a reduction of the power loss and thus a reduction of the heat generation or even a cooling of the electrical machine results.

In permanent magnet synchronous machines (PSMs), in particular the magnets in the rotor are protected from excessive temperatures, since the magnets may be demagnetized in combination with a high reverse field, which permanently reduces the efficiency of the machine. Therefore, in designing a permanent magnet synchronous machine, it is to be noted that the permanent magnets used have a sufficiently high demagnetization strength. Therefore, the value of the coercive field strength/coercive force Hcj of the magnet material must be greater than the expected field strength of the reverse field at the expected maximum operating temperature. This applies both to normal operation and to fault situations.

In the event of a fault, in a drive with a permanent magnet synchronous machine, particularly at high rotational speeds, an active short circuit (AKS) is selected as the safety state. Since the phases of the electric machine are short-circuited here by the power semiconductors in the power electronics/power electronics, no high voltages occur. However, in this case a short-circuit current flows, which can briefly reach a very high value (1.5 to 3 times the maximum current) when transitioning from normal operation to AKS. This large current generates a strong reverse field in the PSM for a short time, which in turn can demagnetize the magnet. The amplitude of this instantaneous short-circuit current and thus the field reversal in the motor depends on the operating state in which the motor is to be operated in the manner of AKS. In operation in the manner of a motor and generator in the maximum torque value range, the highest coercive field strength is required at high rotational speeds, so-called corner points, at the same time.

According to the current state of the art, magnet selection is based on a combination of the expected maximum component temperature and the worst case operating point, i.e. the corner point of generator operation where a fault condition occurs with switching of AKS.

Many magnet materials, such as NdFeB magnets used in PSM for power plant applications in particular, are demagnetized by a combination of high temperature and high reverse field. This results in high requirements for the coercive field strength Hcj for the magnet material. Typically, this requirement is achieved by adding the heavy rare earth elements dysprosium and terbium to the alloy. Therefore, the magnet becomes expensive.

An electric machine with improved short-circuit strength is known from DE 102015218302 a 1. The electric machine is designed as a permanent magnet synchronous machine for vehicles, having permanent magnets which are designed such that the risk of demagnetization is reduced in the event of a short circuit. In particular, separate magnets having different magnetic properties are used.

Document DE 102017220685 a1 discloses a method and a device for operating an electric machine for outputting a predetermined torque and a predetermined rotational speed. The method is used to measure the temperature of the motor and if a temperature threshold is exceeded, an active short circuit is triggered as such. When the temperature threshold is exceeded, the maximum torque is reduced so as to prevent the magnets of the electric machine from demagnetizing.

Document WO 01/10001 a2 describes a demagnetization-resistant, permanent-magnet ship drive. The ship driving apparatus includes a permanent magnet motor, the temperature and current of which are measured, wherein the motor is protected from overcurrent and overheat, and demagnetization in the case of short circuit is prevented by limiting a short-circuit current.

Disclosure of Invention

Against this background, it is an object of the present invention to provide a method and an apparatus with which demagnetization of a permanent magnet of a PSM can be effectively prevented even when the magnet has a low coercive field strength.

According to the invention, this object is achieved by a method having the features of claim 1 and by an apparatus having the features of claim 6. The design and development of the invention result from the dependent claims and the description.

According to the present invention, the maximum allowable torque of the PSM is limited according to the rotor temperature from the predetermined rotation speed, and the AKS causes demagnetization from the predetermined rotation speed. A derating dependent on the rotor temperature is thus achieved for protection against demagnetization in the fault state AKS.

The subject of the invention is a method for protecting permanent magnets of a permanent magnet synchronous machine (PSM) in a vehicle against demagnetization, wherein, when a predetermined rotor temperature of the PSM is exceeded, the PSM is suppressed from operating in a range of the speed/torque characteristic of the PSM in which the field strength of the counter field generated by an active short-circuit of the PSM exceeds the coercive field strength of the permanent magnets.

If the rotor temperature reaches an application-specific limit temperature that is lower than the maximum permissible component temperature, the operating point that requires a high coercive field strength in the case of AKS is avoided by means of deration. As a result, in the case of a fault requiring AKS, only a small reverse field can occur compared to the case without derating. In one embodiment of the method, the defined temperature is 5K to 25K below the maximum allowed component temperature, for example 20K below the maximum allowed component temperature, or 10K below the maximum allowed component temperature. In one embodiment, the maximum allowable component temperature has a value in the range of 60 ℃ to 220 ℃, for example, 80 ℃ to 200 ℃, or 100 ℃ to 180 ℃.

In one embodiment of the method, operation of the PSM is inhibited in a range of a speed/torque characteristic of the PSM in which a value of the torque is greater than 70% of a maximum torque of the PSM and a value of the speed is greater than 20% of the maximum speed of the PSM. Thus, this derating is not achieved by reducing the stator flux, but by adjusting the speed and/or torque, which avoids a critical range of the speed/torque characteristic of the PSM.

Operation at the corner points of the speed/torque characteristic curve, that is to say with maximum torque and maximum power (for example an acceleration from 0km/h to 100km/h in the shortest time, torque vector distribution during dynamic cornering) is required only for dynamic driving operation.

In one embodiment of the method, the range of the speed/torque characteristic of the PSM to be suppressed is defined on the basis of a stored table comprising maximum permissible torques as a function of speed and rotor temperature; that is, the derating is performed based on a stored table in which the maximum allowable torque is specified based on the rotational speed and the rotor temperature.

In one embodiment of the method, the temperature of the rotor of the PSM is determined by means of a rotor temperature model. The temperature of the rotor or the temperature of the permanent magnets of the rotor is calculated using the rotor temperature model. As soon as a specific limit temperature is exceeded, a derating function is activated, which suppresses a specific operating range in the speed/torque characteristic of the PSM. Suitable rotor temperature models are known in principle to the person skilled in the art, for example from the document DE 102015114029 a 1.

In another embodiment of the method, the temperature of the rotor of the PSM is determined by means of the temperature of the stator of the PSM. In one embodiment, the stator temperature is measured by a temperature sensor on the stator.

The subject of the invention also comprises a device arranged for implementing the method according to the invention for protecting the permanent magnets of a permanent magnet synchronous machine (PSM) in a vehicle against demagnetization.

The device according to the invention comprises means for determining the rotor temperature of the PSM and a control unit which is provided for adjusting the rotational speed and the torque of the PSM and which is provided for adjusting the torque and the rotational speed of the PSM when a predetermined rotor temperature is exceeded, such that the following ranges in the rotational speed/torque characteristic of the PSM are avoided: in this range, the field strength of the reverse field due to the active short-circuiting of the PSM exceeds the coercive field strength of the permanent magnet.

In one embodiment of the device, the control unit is configured to adjust the torque and the rotational speed of the PSM when a predetermined rotor temperature is exceeded in such a way that a torque value greater than 70% of the maximum torque of the PSM and a rotational speed value greater than 20% of the maximum rotational speed of the PSM do not occur simultaneously.

Another embodiment of the apparatus additionally comprises a memory unit with at least one table in which a maximum permissible torque of the PSM is defined in relation to the rotational speed and the rotor temperature of the PSM.

In one embodiment of the apparatus, the means for determining the rotor temperature of the PSM comprises a rotor temperature model.

Another embodiment of the apparatus additionally comprises means for determining a stator temperature of the PSM. In one embodiment, the device comprises at least one temperature sensor.

In one embodiment, the permanent magnet of the PSM contains neodymium, iron, and boron, and if necessary dysprosium. The maximum allowable use temperature for NdFeB magnets is not higher than 120 ℃ and not higher than 200 ℃ in the presence of dysprosium.

The advantages of the method according to the invention include: the probability of failure of the PSM is reduced by derating with respect to the rotor temperature. The maximum permissible rotor temperature can also be increased by a derating dependent on the rotor temperature, so that the maximum continuous power of the drive is increased if necessary. The durability of the drive is improved without having to withstand losses in terms of optimum or sustained performance. Depending on the use case, the maximum permissible component temperature is only rarely present over the life of the vehicle, but never present in many drivers. Faults that require a switch to AKS also rarely occur over the life of the vehicle.

In a new development of permanent magnet synchronous machines, it is possible to select a magnet material that requires a smaller coercive field strength and thus a lower cost material.

The efficiency of the drive is limited only in few cases. Vehicle users are already familiar with such behaviors, for example the power behavior of the drive in the case of a cold battery or repeated maximum accelerations.

Other advantages and design aspects of the invention will appear from the description and the accompanying drawings.

It is clear that the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination but also in other combinations or alone without departing from the scope of the invention.

Drawings

The invention is schematically illustrated in the drawings according to one embodiment and is further described with reference to the drawings. The figures show that:

fig. 1 shows a torque-rotation speed characteristic curve in which the coercive field strength and the derating range are recorded.

Detailed Description

Fig. 1 shows, for an exemplary case of a torque-rotational speed characteristic curve, that the magnetic material must have a coercive field strength Hcj in kA/m, so that the magnet does not demagnetize in the case of active short-circuiting (AKS).

As can be seen, in the region of the maximum torque values in which the motor and generator operation is possible, the highest coercive field strength is required at high rotational speeds, the so-called corner points, at the same time.

The derating range 100 recorded in the figure marks a range above 70% of the maximum torque in the case of a rotational speed above 20% of the maximum rotational speed. According to the invention, this range is avoided when a defined limit temperature of the rotor winding is exceeded. As a result, in the case of a fault requiring an active short circuit, only small reverse fields can also occur which do not cause demagnetization of the permanent magnet.

List of reference numerals:

100 derating range