The present invention relates to a method for detecting a short circuit of a resolver signal line of the sine or cosine receiver coil to ground or to the operating voltage, and a circuit for implementing this method.
Resolvers are used for ascertaining the angular position of a rotating object, for example, the drive shaft of a motor. There are various types of resolvers in the prior art. Generally, a changing magnetic field is generated by means of at least one coil, and this field is detected by means of at least one additional coil, wherein the strength of the coupling between the coils varies as a function of the position or angular position to be measured. In the case of the variable reluctance resolver (VR resolver), for example, only one excitation coil is used, and there are two measuring coils which generate position-dependent signals. German patent application DE 10 2011 078 583 A1 discloses, for example, an evaluation of resolver sensor signals in a vehicle. For this purpose, a resolver picks up a rotational movement of a rotor, and a processor element processes the sine-shaped and cosine-shaped output signals of the resolver.
The present invention is directed to such a resolver, wherein the excitation signal is sinusoidal and typically has a frequency of 10 kHz. The two measurement coils are generally positioned orthogonally with respect to one other and are referred to as the sine coil and the cosine coil. The angle of the measured object may be unambiguously determined via the two measurement signals.
The excitation signal for the excitation coil may, for example, be provided via two push-pull output stages, one each for the two terminals of the excitation coil. The output signals of the two output stages are then phase-shifted by 180° with respect to one other, and the excitation signal which is effective for the excitation coil is the differential voltage between the outputs of the two output stages.
However, there is also the possibility of driving the excitation coil via only one output stage. The second terminal of the excitation coil is then set to a fixed potential, for example, ground potential, either directly or via a capacitor.
An AC voltage signal having the same frequency as the excitation signal results at the receiver coils, the amplitude of said signal, however, being modulated according to the rotor position, wherein the signal at the cosine coil is phase-shifted by 90° with respect to the signal at the sine coil.
Resolvers are often used for controlling permanently excited synchronous machines (PSMs) and electrically excited synchronous machines (ESMs), which, for example, are used as the drive for hybrid and electric vehicles. For such control, knowledge of the instantaneous rotor angle position is necessary. For controlling asynchronous machines (ASMs), knowledge of the instantaneous frequency of the drive is required.
Because of their robustness, resolvers are preferably used in motor vehicles for these purposes, even if there are alternative sensors, for example, digital angle sensors or sensors based on the eddy-current effect.
For sensors in the automobile sector, diagnostic options for ascertaining possible faults are desirable. In the case of resolvers which are the subject matter of the present application, a possible fault to be diagnosed is a short circuit of a resolver signal line to ground or to the operating voltage UB. Hereinafter, a short circuit will be understood to mean merely an undesirable electrical connection of one of the signal lines to ground or to the operating voltage UB, wherein the diagnosis is also intended to determine which of these potentials forms the undesirable connection.
In the prior art, such a fault is diagnosed in that it triggers clipping (overdriving) of the corresponding A/D converter. However, such a diagnosis is not sufficient, because A/D converter clipping may also have other causes.