Patent Description:
To drive a permanent magnet synchronous motor (PMSM), the rotor position is needed to allow field oriented control (FOC). A rotor position sensor such as resolver, hall sensor, GMR sensor, or optical encoder can provide the rotor position information, but it is usually costly.

There have been a lot of researches on sensorless control topic which have intended to use the <NUM>-phase current information to extract the rotor position information and therefore to relieve the system from rotor position or angular position sensors so that total cost is reduced and system reliability is improved.

Specifically, in a situation without rotor position sensor, the rotor position can be estimated by extracting the position information from the measured phase currents. Typical extraction methods include non-linear observer method, or sliding-mode observer method.

However, most of the methods involve low-pass filter and there are delay times involved. When the rotational speed is very high (typically more than 6000rpm), the delay time will be comparable to the electrical rotational cycle. The deficiencies of the conventional techniques may be clearly understood from <FIG>, which shows the delay time between actual speed ωm and expected speed ω̂m from the test result when sensorless control is applied. In this case the sensorless control algorithm has limit to extract the rotor position information in the rotational cycle when the speed is up to a level of more than 6000rpm typically for a pole pair of <NUM> and the limit level would be lower if pole pair is bigger.

Prior art researches or inventions such as <CIT>, <CIT> or <CIT> have addressed the problems when the e-machine is at standstill or at low speed when the sensorless control strategy has few limits or accuracy issues, but no prior arts have taken high speed issues into consideration.

As mentioned above, with the wider and wider application of the sensorless control algorithm in e-scooters and even in electrical vehicles, there comes the response time limit of sensorless control algorithm due to its inherent filters. Therefore, due to the deficiencies of the conventional sensorless control techniques, there is a need to provide an improved method and sensor for addressing this issue with low cost solution at high speed regions.

To this end, the inventors of the present invention found that at high speed regions as the revolutions are fast and it is not required to be high accuracy of the angular position, there is a need to design a low cost angular position sensor with rough accuracy.

The invention is to be found in the appended claims, and provides an optical sensor and methods for estimating positions of rotors in a motor as recited in the independent claims. Various aspect helpful for understanding the invention will be described in the following.

Therefore, in accordance with an aspect of the present invention, it proposes an optical sensor for estimating positions of rotors in a motor, which further has stators and is used for e-machines. The optical sensor comprises an optical source mounted on the surface of one rotor where the air gap is big enough to not block magnetic flux between the rotors and the stators; and a plurality of photo detectors arranged evenly around the stator tooth slots and configured to detect light emitted by the optical source and output parameters which are used to estimate the positions of rotors.

Furthermore, in accordance with another aspect of the present invention, it proposes a method for estimating positions of rotors by utilizing the sensorless control algorithm and the optical sensor together.

In one embodiment, it proposes a method for estimating positions of rotors in a motor, the motor further having stators and being used for e-machines, the motor comprising the optical sensor mentioned above, the method comprising:.

In this way, the proposed low cost optical sensor measures the angular position of rotating e-machine when sensorless control algorithm is applied but limited by response time at high speed region. The optical sensor only adds small cost and provides rotor position information with enough accuracy for FOC control at high rotational speed.

In another embodiment, it proposes a method for estimating positions of rotors in a motor, the motor further having stators and being used for e-machines, the motor comprising the optical sensor mentioned above, the method comprising:.

Compared with the first method, the second method provides a smooth switch-over between sensorless control and control with optical sensor, which is typically a hysteresis to avoid frequent switch between the two control modes at the critical speed.

Furthermore, in accordance with another aspect of the present invention, it proposes a motor comprising the optical sensor for estimating positions of rotors, and an e-machine comprising the motor.

Various aspects and features of the disclosure are described in further detail below.

The present invention will be described and explained hereinafter in more detail in combination with embodiments and with reference to the drawings, wherein:.

The same reference signs in the figures indicate similar or corresponding feature and/or functionality.

As mentioned above, an optical sensor is proposed as a low cost rotor position sensor solution and is used only at high speed region.

<FIG> shows the placement of the optical sensor. As shown, the optical sensor consists of an optical source <NUM> and a few photo detectors <NUM> displaced evenly within the slots between the stator teeth <NUM>. The optical source <NUM> can be mounted on the rotor surface where the air gap is relatively big not to block magnetic flux between rotor and stator.

The optical source <NUM> can be powered by an external power supply either wired or wireless. If the power supply is wired, the wiring has to be placed along the rotor shaft so that it will not be wound during the rotations. If the power supply is wireless, the energy transmitter could be radio waves, microwaves, infrared or visible light waves et al. Energy transmitter such as electric fields, magnetic fields shall be taken special precautions to avoid EMC issues.

An LED is utilized as the optical source <NUM>. The LED is insensitive to the EMI generated by the rotor magnets <NUM> and can be placed within or very near the electromagnet <NUM> of the rotor. Further, the optical sensor possesses characteristics of long term stability and high resolution.

In one embodiment, the number of the photo detectors <NUM> can be N*<NUM>*p, where p is the number of rotor pole pair, N can be any natural number. The more N is, the better accuracy the optical sensor has. If N is <NUM>, then the accuracy of the electrical rotor position is <NUM>°. If N is <NUM>, then the accuracy of the electrical rotor position is <NUM>°, and so on. The photo detectors <NUM> are evenly placed on the top of the stator winding (with insulations inbetween) inside each of the tooth slots. The reason of placing the photodetectors inside the slots is, firstly not to reshape the air gap flux. Secondly the stator teeth crown which partially blocks the LED light beam happens to be at a place between the LED and photo detector. As viewed by the photo detector the space between the teeth crowns appears to be a slit. Therefore it is possible for the photo detector to detect the position of the LED as well as the rotor position when the rotor turns to the place where the LED and the photo detector face one another, the maximal light energy reaches the photo detector and their axes are aligned.

The optical sensor with the LED/photodetector pair provides the absolute rotor positions at the positions where the photo detector is placed. The rotor position inbetween the photodetectors can be calculated from θ<NUM> + ωt, θ<NUM> is the position read from the photodetector, and ω is the estimated speed from the different photodetector readings. The estimated rotor position is then refreshed once the rotor turns and aligns to the next photodetector.

This optical sensor shall only be used at high speed operations because at high speed region, ω is high and the estimation time is small so that accumulated error would be small than that at low speed regions. This is the theoretical background of why the optical sensor shall be used at high speed and sensorless control algorithm at low and middle speed operations.

In accordance with another aspect of the present invention, it proposes a method for estimating positions of rotors by utilizing the sensorless control algorithm and the optical sensor together. In other words, it proposes a combined control strategy with sensorless control and with optical sensor.

When the motor starts to operate, the rotational speed n of the motor could be monitored and estimated continuously in accordance with any method well-known in the prior art.

Then, the rotational speed n is compared with a predetermined speed nsw, which is the mode switching speed and typically <NUM> rpm. Usually, at this time, since the motor just starts and operates in a low or middle speed region, the rotational speed n is lower than the predetermined speed nsw. In this case, the control strategy utilizes the sensorless control and the positions of rotors are estimated based on the measured phase currents.

When the rotational speed n increases as time goes by and exceeds the predetermined speed nsw, the control strategy would change to the control with optical sensor. In other words, in this case, the positions of rotors are estimated based on the parameters output by the plurality of photo detectors.

In another embodiment, it further proposes an improved combined control strategy. The improved combined control strategy with sensorless control and with optical sensor is shown in <FIG>.

As shown in <FIG>, there is a smooth switch-over between sensorless control and control with optical sensor, which is typically a hysteresis to avoid frequent switch between the two control modes at the critical speed. When the control mode is sensorless control and the speed is higher than nsw + nhyst, the rotor position starts to use θ̂ + ωt until the first photodetector detects the LED energy and outputs the absolute rotor position θ. θ̂ is the last estimated rotor position from sensorless control strategy. When the control mode is now with optical sensor and the speed is now lower than nsw - nhyst, the control mode is switched to sensorless control. nsw is the mode switching speed and typically <NUM> rpm, and nhyst is the hysteresis speed typically <NUM> rpm.

<FIG> is a flow chart of the method for estimating positions of rotors according to an embodiment of the present invention, which is running throughout the torque control or speed control mode for e-scooter or electrical vehicle applications.

As shown in <FIG>, at step a, usually when the motor starts to operate, since the motor just starts and operates in a low or middle speed region, the control strategy utilizes the sensorless control, and the positions of rotors are estimated based on the measured phase currents.

Next, at step b, the rotational speed n of the motor is estimated. Then, at step c, the estimated speed n is compared with a predetermined speed nsw plus a hysteresis speed nhyst, and it is determined whether the rotational speed n exceeds the sum. Then, see step d1, if the result of determination is NO, the flowchart would go back to step a. However, see step d2, if the result of determination is YES, the control strategy would change to the control with optical sensor, and the positions of rotors would then be estimated based on the parameters output by the plurality of photo detectors. In other words, if the rotational speed n exceeds a predetermined speed nsw plus a hysteresis speed nhyst, the control strategy would change from the sensorless control to the control with optical sensor.

At step e, the rotational speed n of the motor is estimated again. Then, at step f, the estimated speed n is compared with the predetermined speed nsw minus the hysteresis speed nhyst, and it is determined whether the rotational speed n is lower than nsw - nhyst. Then, see step g1, if the result of determination is NO, the flowchart would go back to step d2. However, see step g2, if the result of determination is YES, the flowchart would go back to step a, and the positions of rotors would then be estimated based on the measured phase currents. In other words, if the rotational speed n is lower than the predetermined speed nsw minus the hysteresis speed nhyst, the control strategy would change back to the sensorless control and the positions of rotors are estimated based on the measured phase currents.

According to a further aspect of the present application, the above proposed optical sensor may be incorporated in a motor. In this way, the positions of rotors in the motor may be estimated based on any one of the above mentioned two methods. Furthermore, the e-machine in the prior art may comprise the motor with the optical sensor to make advantage of the novel rotor position estimation approach.

Furthermore, as can be easily understood by the skilled in the art, in the apparatus claim enumerating several means, several of these means can be embodied by one and the same item of hardware.

Claim 1:
An optical sensor for estimating positions of rotors in a motor, the motor further having stators and being used for electrical machines, the optical sensor comprising:
an optical source (<NUM>) mounted on the surface of one rotor where the air gap is big enough to not block magnetic flux between the rotors and the stators, wherein the optical source (<NUM>) is an LED; and
a plurality of photo detectors (<NUM>) arranged evenly within stator tooth slots between stator teeth and configured to detect light emitted by the optical source (<NUM>) and output parameters which are used to estimate the positions of rotors;
characterized in that
a stator teeth crown is arranged at a place between the LED and the photo detectors (<NUM>) and is configured to partially block the LED light beam; and
the photo detectors (<NUM>) are configured to detect a position of the LED as well as a rotor position when the rotor turns to a place where the LED and the photo detector face one another, the maximal light energy reaches the photo detector and their axes are aligned.