Method of decoding a resolver

Abstract

A method of decoding a resolver (210) to acquire the position of a rotating shaft, the method being provided with the following steps: - using the output signals (20) of the demodulated resolver (210), generating a trigger signal (90) to be sent to a Phase Locked Loop (260), - processing the trigger signal (90) to generate an output signal (100), and - determining the angular position of the rotating shaft by means of the output signal generated by the Phase Locked Loop (260).

Description

[0001] METHOD OF DECODING A RESOLVER

[0002] D ESCRI PTION

[0003] Technical Field of the Invention

[0004] The present invention relates to a method of decoding a resolver or RDC (Resolver to Digital Converter), i.e., a sensor that provides the angular position of a rotating shaft through variations in an electromagnetic field. The method can be used for any application that uses a resolver, the most common of which is that of vehicles powered by electric motors.

[0005] Background Art

[0006] An electric machine, such as a traction motor for an electric or hybrid vehicle, is traditionally equipped with an angular position sensing device. This device determines the relative angular position between a rotating shaft and a stationary portion of the machine, which corresponds to the relative angular position between a rotor and a stator.

[0007] Typically, the sensing device can be an encoder or, especially for harsh environmental conditions, a resolver.

[0008] Resolvers are therefore very robust angular position sensors that perfectly meet the properties required by safety-critical systems such as aircraft, satellite antennas, and electromechanical braking systems. The resolver is an analog angular position transducer comprising a moving part, associated with the rotor or rotating shaft of the electric machine, and a fixed part, associated with the stator or another stationary portion of the electric machine. In practice, this sensor allows the angular position of a motor shaft to be measured by examining changes in the electromagnetic field between its two constituent elements, the rotor and stator windings.

[0009] Referring to Figure 1, the resolver must be excited by an appropriate carrier signal 1 and produces two analog output signals containing angular position information. A first analog output signal 2 is configured as a sine function, while the second analog output signal 3 is configured as a cosine function of the measured angle, modulated by carrier signal 1. The simplest form of demodulation 4 is performed by subsampling the signals, as illustrated in Figure 1.

[0010] Several ASICs (Application Specific Integrated Circuits) have been developed to obtain angular position from this sensor with high accuracy, but they also have a considerable number of disadvantages:

[0011] - high cost,

[0012] - almost no flexibility and customization of the component, with possible additional constraints on the motor design,

[0013] - significant printed circuit board (PCB) surface area required by the ASIC and the need for additional discrete components,

[0014] - increased exposure to potential component shortages.

[0015] It is also possible to use a microprocessor to perform the aforementioned decoding, reducing the cost of custom hardware, but this solution has the major disadvantage of keeping the processor busy executing algorithmic strategies, thus reducing the residual utilization of the microprocessor itself.

[0016] There is therefore a need to define a resolver decoding method that avoids the aforementioned drawbacks.

[0017] Summary of the Invention

[0018] To substantially solve the technical problems highlighted above, an object of the present invention is a method of decoding a resolver that uses a hardware component, called Phase Locked Loop (PLL), to recover the position from the resolver's demodulated output signals. Since this component is included in most microcontrollers used in the control of traditional automotive traction systems (internal combustion engines), it is possible to avoid separate and dedicated components, such as an ASIC, reducing costs and the occupied surface area of the printed circuit board (PCB).

[0019] Therefore, according to the present invention, a method of decoding a resolver is provided, the method having the features set forth in the independent method claim, appended to this specification.

[0020] According to another aspect, the invention describes a timer platform suitable for implementing the aforementioned method.

[0021] Therefore, according to the present invention, a timer platform is provided having the features set forth in the independent system claim, appended to this specification.

[0022] According to a further aspect, the invention prescribes the use of a Phase Locked Loop or PLL in the aforementioned timer platform to perform the resolver decoding method.

[0023] Therefore, according to the present invention, the use of a Phase Locked Loop in the aforementioned timer platform is provided, having the features set forth in the independent device claim, appended to this specification.

[0024] Further preferred and / or particularly advantageous embodiments of the invention are described according to the features set forth in the appended dependent claims.

[0025] Brief Description of the Drawings

[0026] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting examples of its implementation, in which:

[0027] - Figure 1 is a graphical diagram of the demodulation operation of a resolver according to the known technique. The figure is taken from page 2 of [G. Gross, M. Teixido, A. Sudria, and J. Bergas. «AII-digital resolver-to-digital conversion*. In: 2005 European Conference on Power Electronics and Applications. 2005, 8 pp.-P.8. doi: 10.1109 / EPE.2005.219720]

[0028] - Figure 2 is a schematic diagram of the method of decoding a resolver according to an embodiment of the present invention,

[0029] - Figure 3 illustrates a first step of the method of Figure 2,

[0030] - Figure 4 illustrates a second step of the method of Figure 2, - Figure 5 illustrates a third step of the method of Figure 2, and - Figure 6 illustrates a timer platform suitable for implementing the method of Figure 2.

[0031] Detailed Description

[0032] The resolver is the most widely used sensor for reading the angular position of an electric motor. It is used, for example, in electric cars, electric bicycles, and similar devices.

[0033] The description of the resolver decoding method according to the present invention will therefore refer to the specific case of an electric motor without losing generality.

[0034] The resolver decoding method is based on an approach that reduces or eliminates the use of the microcontroller's CPU for resolver decoding (RDC), i.e., obtaining the angular position from a Phase Locked Loop (PLL), appropriately triggered by a signal derived from the resolver outputs. The Phase Locked Loop can be analog or digital.

[0035] The objective of this element, in fact, is essentially to generate a predefined number of signal pulses within the period between two events of an input "trigger" signal. In the following, for simplicity, the acronym PLL will be used mainly in place of Phase Locked Loop.

[0036] With reference to Figure 2, the solution according to the present invention accepts the demodulated resolver output signals as input, derives the trigger to be sent to the PLL, and recovers the angular position of the rotating shaft from the output generated by the PLL.

[0037] More specifically, Figure 2 illustrates the following logic blocks: - a carrier signal 10,

[0038] - a resolver that, excited by the carrier signal 10, produces two analog output signals 20 containing the angular position information, - sampling and demodulation 30 of the analog output signals, for example, by means of an analog-to-digital converter (ADC) that produces corresponding output signals.

[0039] These steps belong to the previously described state of the art and are not part of the invention.

[0040] According to the present invention, the method of decoding a resolver comprises the following steps:

[0041] - using the demodulated resolver output signals, generating a trigger signal to be sent to the PLL,

[0042] - processing the trigger signal to generate an output signal, and - determining the angular position of the rotating shaft using the output generated by the PLL.

[0043] Referring to Figure 3, the first stage of the method, i.e. generating a trigger signal 90 for the PLL, uses the resolver output signals, i.e. the two analog functions of sine 70 and cosine 80. After obtaining the sin(9) and cos(0) functions from the analog-to-digital converter, these signals are compared with voltage thresholds 75 corresponding to specific angles, derived by dividing 360 degrees by a predetermined number N, and calculated by applying the trigonometric formula together with signal peak detection (a feature often integrated in new generation analog-to-digital converters), depending on the signal characteristics of the real application.

[0044] For example, using N=8, the PLL can be updated every 45° of shaft rotation, considering voltage thresholds 75 corresponding to 0° (= 180°), 45° (= 135°), and 225° (= 315°) degrees, as shown in Figure 3. The voltage thresholds determine specific angles from the sine and cosine signals.

[0045] More specifically, in this case, the comparisons listed are used by the logic expressed below:

[0046] (bsign(sin 0) XOR bsign(cos 0)) XOR bsign(|sin 0| - |cos 0|) where

[0047] bsign(x) is the "binary" sign function (=1 if x> = 0, 0 if x<0), XOR is the logical exclusive disjunction operator.

[0048] Note that the binary sign function would be 1 for x>=0 and -1 for x<0. In order to apply a logical operator such as XOR, the value -1 was considered equal to 0.

[0049] The trigger events 95 are the edges, both rising and falling, of the trigger signal 90 obtained.

[0050] Referring to Figure 4, the second phase of the proposed method, processing the trigger signal, is performed by the PLL. The PLL, starting from the trigger signal90, generates a pulse count 100 (MICRO TICK count) corresponding to the angular position of the shaft. From Figure 4, it can be seen that a difference between the expected and actual period length determines a change in the pulse frequency to follow the given profile.

[0051] Figure 5 illustrates the third phase of the method, which is determining the angular position of the rotating shaft using the output generated by the PLL. Starting from a trigger signal 90 with, for example, a 90° period, the resulting MICROTICK count 100 is related to a 90° rotation of the shaft. Therefore, by counting 100, it is possible to increment the shaft position with respect to the previous reading and obtain the shaft angle. In fact, the MICROTICK count of 100 starts from 0 and increments up to 360, before repeating.

[0052] According to another aspect of the present invention, the method described above can be implemented on hardware modules, for example, on a timer platform integrated into an automotive electronic control unit (ECU). This solution offers all the advantages of a customizable software solution. Referring to Figure 6, a generic timer platform 200 accepts the demodulated resolver output signals as input and recovers the angular position of the rotating shaft from the output generated by the PLL. The timer platform 200 is designed to serve various application domains.

[0053] More specifically, Figure 6 illustrates the following components: - a carrier signal generator 205,

[0054] - a resolver 210 that, excited by the carrier signal, produces two analog outputs containing the angular position information,

[0055] - an analog-to-digital converter 220 for sampling and demodulating the resolver's analog outputs.

[0056] These components belong to the prior art described above and are not part of the invention.

[0057] The timer platform 200 includes several components that are part of the present invention:

[0058] - an internal sequencer 230, also called Multi-Channel Sequencer (MCS), which can be used to apply the necessary logic to the resolver outputs without involving the CPU. Note that the presence of the sequencer is optional. If a microcontroller has only a hardware PLL module, the invention can still be applied by implementing the corresponding calculations performed by the sequencer in the CPU,

[0059] - a timer output module 240,

[0060] - a timer input module 250,

[0061] - a Phase Locked Loop (PLL) 260, the main enabler of the present invention.

[0062] To take advantage of the benefits of this invention, the timer platform must include the PLL and, optionally, the sequencer, to execute the logic upstream of the trigger signal generation. Indeed, the PLL is already present in most microcontrollers used to control traditional automotive traction systems (internal combustion engines), completely eliminating the cost of additional hardware related to the "resolver to digital converter." The control unit will only be used to initialize the hardware module, while, as mentioned, the entire logic is executed within the sequencer.

[0063] Ultimately, the method according to this invention allows:

[0064] - using a more flexible and customizable solution than known solutions (dedicated ASIC), achieving a significant cost reduction;

[0065] - making the processor (CPU) virtually independent of the workload for calculating the angular position of the shaft: in known software-based solutions, the processor workload just for reading the resolver is very high.

[0066] In addition to the embodiment of the invention, as described above, it should be understood that numerous other variations exist. It should also be understood that such embodiments are only exemplary and do not limit either the scope of the invention, nor its applications, nor its possible configurations. On the contrary, although the description above allows the person skilled in the art to implement the present invention at least according to one of its exemplary embodiments, it should be understood that many variations of the described components are possible, without thereby departing from the scope of the invention, as defined in the appended claims, which are interpreted literally and / or according to their legal equivalents.

Claims

CLAI M S1. A method of decoding a resolver (210) to acquire the position of a rotating shaft, the method comprising the following steps:- using the output signals (20) of the demodulated resolver (210), generating a trigger signal (90) to be sent to a Phase Locked Loop (260), - processing the trigger signal (90) to generate an output signal (100), and- determining the angular position of the rotating shaft by means of the output signal generated by the Phase Locked Loop (260).

2. A method according to claim 1, wherein, for the step of generating a trigger signal (90), the output signals (20) of the resolver (210) are the analog functions of sine (70) and cosine (80), obtained from an analog-to-digital converter.

3. A method according to claim 1 or 2, wherein the step of processing the trigger signal (90) is performed by the Phase Locked Loop (260), which starting from the trigger signal (90), generates a count (100) of pulses corresponding to the angular position of the shaft.

4. A timer platform (200) for implementing the method according to anyone of the preceding claims, wherein the platform (200) comprises:- a timer output module (240),- a timer input module (250),- a Phase Locked Loop (260), configured to process the trigger signal (90) to generate an output signal (100).

5. Platform (200) according to claim 4, further comprising an internal sequencer (230), configured to apply the necessary logic to the output signals (20) of the resolver (210).

6. Use of a Phase Locked Loop (260) in a platform (200) according to anyone of claim 4 or 5.

Images