Method and device for detecting fluid that has entered an electrical machine

Abstract

Device for detecting fluid ingress into a housing (22) of an electric machine (2), comprising an evaluation unit (6) for monitoring a parasitic capacitance between an electrically controllable winding (21) of the electric machine (2) and the housing (22) and for detecting fluid ingress depending on a detected change in the parasitic capacitance, wherein the evaluation unit (6) is configured to monitor a frequency of a resonant circuit formed with the parasitic capacitance, and wherein the evaluation unit (6) is configured to detect a characteristic frequency of a motor current and to infer fluid ingress depending on a change in the characteristic frequency of the motor current.

Description

Technical field

[0001] The invention relates to electrical machines, in particular electric motors, used in applications where a fluid, especially water, can penetrate the interior of the electrical machine, such as in washing machines and the like. In particular, the invention relates to methods for detecting a fluid that has penetrated an electrical machine. State of the art

[0002] Depending on the application, electrical machines may be used in environments near water. This often exposes them to the risk of flooding and water ingress into the machine's housing. This can cause electrical short circuits, which can damage or destroy system components.

[0003] To prevent damage and destruction of components, water detection is typically implemented. This system shuts down the electric motor or other components upon detecting water ingress. Electrodes are often placed in a lower area of ​​the machine's housing to detect water penetration by measuring and monitoring the electrical resistance between the electrodes. This is possible because the electrical resistance of water or other fluids is significantly lower than that of air.

[0004] However, arranging electrodes for water detection is complex, as the electrodes must be shaped and placed close to the electric motor inside the housing. Furthermore, additional evaluation electronics are required, which adds to the complexity.

[0005] Against this background, a device for detecting fluid that has penetrated into a housing of an electric machine is known from DE 23 437 52 A1, wherein a parasitic capacitance between an electrically controllable winding of the electric machine and the housing is monitored by means of an evaluation unit and, depending on a detected change in the parasitic capacitance, intruded fluid is detected.

[0006] The object of the present invention is to provide a method and a device with which water that has penetrated the electric machine can be detected with less component effort and less assembly effort. Disclosure of the invention

[0007] This problem is solved by the device according to claim 1 as well as by the system and the method according to the dependent claims.

[0008] According to one aspect, a device is provided for detecting fluid ingress into the housing of an electric machine. The device includes an evaluation unit to monitor a parasitic capacitance between an electrically controlled winding of the electric machine and the housing, and to detect fluid ingress depending on a detected change in the parasitic capacitance.

[0009] One aspect of the invention is to evaluate the parasitic capacitance between a winding of the electric machine and the machine's housing for the detection of fluid ingress. This parasitic capacitance changes due to the fluid's different dielectric constant compared to air when a fluid has penetrated the housing and is thus at least partially located between the current-carrying windings and the housing. This allows fluid ingress to be detected without the need for additional electrodes or other measures within the electric machine's housing.

[0010] Furthermore, the evaluation unit is designed to monitor the frequency of a resonant circuit formed with the parasitic capacitance. The inductance of the electrical machine's winding typically forms one or more resonant circuits with the parasitic capacitance, so that a change in the capacitance value can be detected by monitoring the resonant circuit frequency. If a change in capacitance is detected, it can then be concluded that water has infiltrated the system.

[0011] Furthermore, the evaluation unit is designed to record a characteristic frequency of a motor current and to infer the presence of fluid depending on a change in the characteristic frequency of the motor current.

[0012] According to another aspect, a system is provided. The system comprises an electric machine with a housing that is at least partially electrically conductive and an electrically controllable winding, as well as the device mentioned above.

[0013] According to another aspect, a method for detecting fluid ingress into the housing of an electrical machine comprises the following steps: - Monitoring of parasitic capacitance between a winding of the electric machine and the housing, - Detection of infiltrated fluid when a change in parasitic capacity has been detected. Brief description of the drawings

[0014] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a motor system with a multi-phase electric motor; Fig. 2. An equivalent circuit diagram for detecting a change in the parasitic capacitance of one or more phase windings of the electric motor. Fig. 1. Description of embodiments

[0015] Fig. Figure 1 shows a motor system 1 with an electric motor 2, which is operated via a driver circuit 3. The driver circuit 3 is controlled by a control unit 4 in order to drive the electric motor 2 appropriately.

[0016] The electric motor 2 is preferably designed as a multiphase electronically commutated electric machine, in particular as a multiphase, e.g., three-phase synchronous motor. For example, the electric machine 2 has a stator with several stator windings 21, which are assigned to the individual phases of the electric machine 2. The stator is located in a housing 22 that is at least partially conductive and is preferably grounded or connected to a predefined potential.

[0017] The individual stator windings are connected in delta or star configurations, or combinations thereof, and are controlled via their respective inverter circuits 31 of the driver circuit 3. The inverter circuits 31 have electronic switches 32 in the form of semiconductor switches. Each inverter circuit 31 comprises a pull-high switch and a pull-low switch connected in series between supply potentials V H , V L are switched on.

[0018] Between the supply potentials V H , V L A capacitor 8 is provided, which reduces the effects of the switching operations on the supply lines.

[0019] Depending on control signals provided by the control unit 4 according to a preset value V, one of the pull-high switches of the inverter circuits 31 is closed (conducting) for a predetermined time window, while the others are open (non-conducting), and simultaneously the pull-low switch of one of the remaining inverter circuits 31 is closed, while the remaining pull-low switches are open. This allows motor current to flow through two selected stator windings 21 of the electric machine 2.

[0020] The driver circuit 3 can also have other configurations; in particular, each of the stator windings of the electric machine 2 can be controlled via suitable H-bridges.

[0021] The electrical machine is not limited to a synchronous machine; in principle, any electrical machine with current-carrying windings is conceivable.

[0022] The housing 22 of the electric machine 2 is generally not waterproof, so depending on the application of the electric motor 2, water from the surrounding environment can penetrate it. The water initially collects in a lower area of ​​the housing 22 and is thus located in a partial area between the stator windings 21 and the housing 22.

[0023] The parasitic capacitance of an electric motor 2 is generally largely determined by the capacitance between the stator windings and the housing. If a medium, such as water, is present in a section between a stator winding 21 and the housing 22, the parasitic capacitance is significantly altered due to the medium's different dielectric constant compared to air (dielectric constant of water ε). r =80).

[0024] In Fig.Figure 2 shows an equivalent circuit diagram of the current flowing at a specific time. It can be seen that in a state where one of the pull-high switches is closed, the inductance L x the associated stator winding 21 with a first supply potential V H is connected and has a further connection to the parasitic capacitance C Phase_Gehäuse such that a resonant circuit is formed by the inductance of the stator winding 21 and the capacitance of the parasitic capacitance. If there is also water in a lower area of ​​the housing 22, this acts like a series connection of two parasitic capacitances. The first parasitic capacitance C Wasser The first parasitic capacity is determined by the water level, and the second parasitic capacity is determined by the capacity C. Phase_Gehäuse between the relevant stator winding 21 and the lower area of ​​the housing 22 or, in the case of water ingress, the water surface.

[0025] The inductance of the stator winding 21 and the series connection of the aforementioned capacitors form a series resonant circuit, the frequency of which can be detected by a suitable evaluation circuit 6. The excitation of the resonant circuit is achieved by the continuous switching of the inverter circuits 31 in the driver circuit 3.

[0026] The frequency f r The resonant circuit is calculated according to: fr=12πLxC and C(CWater)=CPhase_HousingCWaterCPhase_Housing+CWater

[0027] The resulting frequency can be evaluated using a frequency detector 61, which is provided in the evaluation unit 6. Frequency detectors are well known in the prior art. For example, the frequency can be determined using a counter that counts the oscillations within a predetermined time window and calculates the frequency by dividing the number of detected oscillations by the duration of the defined time window.

[0028] The evaluation unit 6 can be provided separately from the control unit 4 or integrated into the control unit 4. The evaluation unit 6 can have a frequency filter 62, such as a high-pass filter, to filter out the switching frequencies of the semiconductor switches 32, which are determined by the switching behavior of the control unit 4.

[0029] If the frequency of the received electrical signal corresponds to a predetermined or previously established reference for an electrical machine into which no water has penetrated, then proper functioning can be confirmed. If the signal, which depends on the parasitic capacitance, deviates from the predetermined reference, then water ingress can be inferred.

[0030] The evaluation unit 6 can, for example, detect the frequency of a motor current, which is measured via a measuring resistor 7. The evaluation unit 6 also has an output for sending a display signal indicating whether the monitored frequency has changed.

[0031] The invention is generally applicable to any type of electrical machine in which a measurable parasitic capacitance exists between the windings provided in the electrical machine and the surrounding housing. However, it is advantageous if the windings of the electrical machine are designed as stator windings of a stator. If these are located in the rotor, the position of the coil winding relevant for monitoring the parasitic capacitance must be taken into account. For example, it can be provided that the measurement is only carried out at certain positions of the rotor of the electrical machine.

[0032] Instead of measuring the frequency response of the series resonant circuit formed with the parasitic capacitance, other methods can be used to measure the parasitic capacitance between the stator winding and the housing. The essential point is to obtain a signal dependent on the parasitic capacitance for further analysis. This signal can then be monitored. A change in the signal can then be interpreted as the ingress of a medium into the housing.

Claims

[1] Device for detecting fluid ingress into a housing (22) of an electric machine (2), comprising an evaluation unit (6) for monitoring a parasitic capacitance between an electrically controllable winding (21) of the electric machine (2) and the housing (22) and for detecting fluid ingress depending on a detected change in the parasitic capacitance, wherein the evaluation unit (6) is configured to monitor a frequency of a resonant circuit formed with the parasitic capacitance, and wherein the evaluation unit (6) is configured to detect a characteristic frequency of a motor current and to infer fluid ingress depending on a change in the characteristic frequency of the motor current. [2] System (1) comprising: an electric machine (2) with an electrically conductive housing (22) and an electrically controllable winding (21); a device according to claim 1. [3] Method for detecting fluid that has entered a housing (22) of an electric machine (2), comprising the following steps: - Monitoring a parasitic capacitance between a winding (21) of the electrical machine (2) and the housing (22), wherein a frequency of a resonant circuit formed with the parasitic capacitance is monitored, - Detection of fluid ingress when a change in parasitic capacitance has been detected, whereby a characteristic frequency of a motor current is recorded and inferences about fluid ingress are made depending on a change in the characteristic frequency of the motor current.

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