Initial position offset detection apparatus and method for calibrating permanent magnet motors

Abstract

A low cost and efficient method and apparatus for calibrating high performance internal permanent magnet motors that involves starting from an initial estimation of the rotor position and improving the estimation incrementally by successively commanding various current vectors and making adjustments to the estimated initial position according to the rotor's physical reaction to such current vectors.

Claims

1. A method of performing an initial calibration of an internal permanent magnet motor, said method comprising the steps of: A. Assigning the rotor an initial estimated position; B. Assigning the variable .sub.offset an initial value of 0; C. Assigning the variable an initial value positive value greater than 0 and less than or equal to 180; D. Commanding a negative nonzero d-axis current of a magnitude below that which that will excite the bifurcation case for the particular internal permanent magnet motor, and identifying the resultant angular velocity () exhibited by the rotor; E. If the rotor exhibits an angular velocity in a direction opposite as a previous iteration of step D the variable should be reduced; F. If the rotor exhibits negative angular velocity (), reducing the value of the variable .sub.offset by the value of the variable and repeating the method from step D; G. If the rotor exhibits positive angular velocity (), increasing the value of the variable .sub.offset by the value of the variable and repeating the method from step D; H. If the rotor exhibits no angular velocity (), commanding a current d axis of a magnitude below that which that will excite the bifurcation case for the particular internal permanent magnet motor, and identifying the resultant angular velocity () exhibited by the rotor; and I. If the rotor exhibits nonzero angular velocity (), increasing the value of the variable .sub.offset by 180.

2. An apparatus of performing an initial calibration of an internal permanent magnet motor, said apparatus comprising the steps of: a controller in electrical communication with a power supply; and a motion sensor, said controller programmed to execute the steps of the method set forth in claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) The accompanying drawings illustrate various exemplary implementations and are part of the specification. The illustrated implementations are proffered for purposes of example not for purposes of limitation. Illustrated elements will be designated by numbers. Once designated, an element will be identified by the identical number throughout. Illustrated in the accompanying drawing(s) is at least one of the best mode embodiments of the present disclosure. In such drawing(s):

(2) FIG. 1 is an axial diagram illustrating the disparity between the true magnetic flux vector of the rotor (foc) and the estimated magnetic flux vector of the rotor as indicated by the position sensor (.sub.sensor) of an uncalibrated interior permanent magnet motor showing the angle of error (.sub.offset).

(3) FIG. 2 is an axial diagram illustrating the disparity between the true magnetic flux vector of the rotor (.sub.foc) and the estimated magnetic flux vector of the rotor as indicated by the position sensor (.sub.sensor) of a calibrated interior permanent magnet motor showing the angle of error (.sub.offset).

(4) FIG. 3 is a simplified, high-level flow chart indicating the various processing steps and decision steps necessary to perform the presently disclosed calibration method.

(5) FIG. 4 is diagram illustrating the axial orientation of the magnetic flux vector of the rotor of an interior permanent magnet motor in a case where commanding non-zero d-axis current does not result in rotation because the offset error angle is close to 180, thus necessitating the calibration confirmation step of commanding non-zero q-axis current.

(6) FIG. 5 is a diagram of the reluctance torque and the magnetic torque of an internal permanent magnet motor with low current illustrating that when the angle between the current vector and the rotor d axis () is between 0 and 90 and between 2700 and 360 the reluctance torque and the magnetic torque exhibit opposite polarity, but when p is between 90 and 270 the polarities are constructive, thus demonstrating the need for calibration in high performance applications.

(7) FIG. 6 is a diagram of the reluctance torque and the magnetic torque internal permanent magnet motor with current greater than that shown in FIG. 5 but below the level that would excite the bifurcation case demonstrating the increasing effect of the reluctance torque on the total torque distribution.

(8) FIG. 7 is a diagram of the reluctance torque and the magnetic torque of an internal permanent magnet motor with current greater than that shown in FIG. 5 and FIG. 6 demonstrating the bifurcation case to emphasize that the presently disclosed calibration apparatus and method should utilize current lower than that which would excite the bifurcation event.

(9) FIG. 8 is the top half of a detailed flow chart indicating the various processing steps and decision steps necessary to perform the presently disclosed calibration method.

(10) FIG. 9 is the bottom half of the detailed flow chart in FIG. 8 indicating the various processing steps and decision steps necessary to perform the presently disclosed calibration method.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

(11) The above-described drawing figures illustrate an exemplary embodiment of the presently disclosed apparatus and its many features in at least one of its preferred, best mode embodiments, which is further defined in detail in the following description. Those having ordinary skill in the art may be able to make alterations and modifications to what is described herein without departing from its spirit and scope of the disclosure. Therefore, it must be understood that what is illustrated is set forth only for the purposes of example and that it should not be taken as a limitation in the scope of the present apparatus or its many features.

(12) Described now in detail are a series of drawings depicting various features and details for the purpose of further clarifying the presently disclosed apparatus and method.

(13) FIG. 1 is an axial view of the rotor's true magnetic flux vector and the orientation of the rotor's magnetic flux according to the position sensor (.sub.sensor). This is the initial stage of the presently described method when the true rotor position (.sub.foc) is assumed to be equal to the rotor position reported by position sensor (.sub.sensor). However, from the illustration it is apparent that the rotor position as indicated by the position sensor (.sub.sensor) is incorrect by an error angle (.sub.offset).

(14) FIG. 2 is the same axial view; however, in FIG. 2 the true rotor position (.sub.foc) is corrected by the error angle (.sub.offset). This illustration demonstrates that the true rotor position can be calculated by starting with the position according to the position sensor (.sub.sensor) and adding the error angle (.sub.offset) to it. Mathematically, it can be expressed as such: (.sub.foc=.sub.sensor+.sub.offset). The difficulty is determining the correct error angle (.sub.offset). It is this task that the presently disclosed method efficiently achieves through a successive iterative process of making small corrections and observing feedback.

(15) FIG. 3 is a simplified flow chart indicating the various processing steps and decision steps that must be performed to calculate the error angle (.sub.offset). It begins with an initialization phase 200. At this stage, the true rotor position (.sub.foc) is assumed to be the position as indicated by the position sensor (.sub.sensor) and the error angle is assumed to be zero (.sub.offset=0).

(16) Once these initial assumptions are made they must then be tested by commanding a non-zero d-axis current 210 and observing the physical reaction of the rotor 220. The error angle is then adjusted depending of the rotor response 230. If the non-zero d-axis current is negative and it causes the rotor express positive angular velocity (counterclockwise rotation) then the error angle (.sub.offset) will be increased by a pre-selected angle (). If the rotor exhibits negative angular velocity (clockwise rotation) then the error angle (.sub.offset) should be reduced by the value of . If positive non-zero d-axis current is commanded then the opposite polarity adjustments should be made. The variable is assigned an initial pre-selected value between 0 and 180, preferably approximately 30. Each time the rotor expresses opposing angular velocity should be reduced by a set percentage (preferably, approximately 50%) and the iterative process should continue using the newly reduced value of ,

(17) This procedure is repeated until the rotor expresses no motion in response to the commanded d-axis current vector. At which point, either the true position of the rotor's magnetic flux (.sub.foc) has been determined or it is off by exactly 180. To distinguish between the two cases, a non-zero q-axis current is then commanded 250 and the rotor response is, once again, observed 260. If the commanded non-zero q-axis current is positive, then an expression of positive angular momentum (counterclockwise rotation) by the rotor is an indication that the true rotor position (.sub.foc) has been determined and the calibration is complete, whereas an expression of negative angular momentum 270 is the indication that (.sub.foc) should be adjusted by 180. If the non-zero q-axis current is negative rather than positive then the angular velocity of the rotor should be interpreted conversely. FIG. 4 is an illustration of the latter case in which the rotor expressed negative angular velocity in response to a command of positive q-axis current.

(18) FIGS. 5, 6, and 7 illustrate that the reluctance torque and the magnetic torque increasingly engage destructively as the magnitude increases. FIG. 7 illustrates the magnitude that excites the bifurcation case. For the purposes of this presently disclosed apparatus and method the commanded currents should always be of a magnitude less than that which would excite the bifurcation case.

(19) FIGS. 8 and 9 illustrate a more detailed flowchart indicating the various processing steps and decision steps that must be performed to calculate the error angle (.sub.offset).

(20) Beginning with the initialization step 800 in which the error angle (.sub.offset) is assumed to be zero, the presently disclosed procedure instructs to command negative non-zero d-axis current of a magnitude below that which will excite the bifurcation case 810.

(21) The rotor response is then observed and if the rotor expresses positive angular velocity 815 then the error angle (.sub.offset) is increased by 840, if the rotor expresses negative angular velocity 820 then the error angle (.sub.offset) is decreased by 845, and if the rotor exhibits no angular momentum, then the method proceeds to the final step to determine if the error angle (.sub.offset) has determined the true position of the rotor's magnetic flux (.sub.foc) or a position that is 1800 off from the true rotor position 825.

(22) Whether the procedure previously increased or decreased the error angle (.sub.offset), 840 or 845, the procedure instructs to, once again, command non-zero d-axis current 850, 855 and observe the resultant rotor reaction and make new adjustments accordingly 860, 865. This procedure repeats iteratively until the angular velocity of the changes polarity, in which case is reduced by a set percentage, 830 and 835, and the procedure continues once more using the newly reduced value until such time as the rotor expresses no angular velocity, 880 and 885. The set percentage by which is reduced can be any percentage less than 100% but through laboratory testing a percentage in the rage of 50% is recommended for calibration expediency.

(23) Once the rotor exhibites no angular velocity in response to the non-zero d-axis current, the procedure has either properly determined the true position of the rotor's magnetic flux or identified a positon that is exactly 180 off from the true position. To identify which of these two possibilities has been realized, the procedure instructs to command non-zero q-axis current 890 and, once more, observe the rotor's response 895, 900. If the non-zero q-axis current was positive, then an exhibition of positive angular velocity is indicative that the error angle (.sub.offset) has been correctly determined and the true rotor position (.sub.foc) can be found by adding the error angle (.sub.offset) to the position sensor angle (.sub.sensor) 905, if the rotor exhibits negative angular velocity then the error angle (.sub.offset) is off by 180 and should be adjusted accordingly.

(24) The enablements described in detail above are considered novel over the prior art of record and are considered critical to the operation of at least one aspect of the apparatus and its method of use, and to the achievement of the above-described objectives. The words used in this specification to describe the instant embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification: structure, material, or acts beyond the scope of the commonly defined meanings. Thus, if an element can be understood in the context of this specification as including more than one meaning, then its use must be understood as being generic to all possible meanings supported by the specification and by the word(s) describing the element.

(25) The definitions of the words or drawing elements described herein are meant to include not only the combination of elements which are literally set forth, but all equivalent structures, materials or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements described and its various embodiments or that a single element may be substituted for two or more elements in a claim.

(26) Changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalents within the scope intended and its various embodiments. Therefore, substitutions, now or later known to one with ordinary skill in the art, are defined to be within the scope of the defined elements. This disclosure is thus meant to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted, and also what incorporates the essential ideas.

(27) The scope of this description is to be interpreted only in conjunction with the appended claims and it is made clear, here, that each named inventor believes that the claimed subject matter is what is intended to be patented.