Abstract:
Disclosed is a technique for compensating for an abnormal output of a resolver. More specifically, a central processing unit (CPU) sets a current motor position angle before compensation θ n,ORG  as a current motor position angle θ n  and obtains a motor position change Δθ n [rad] between a current sampling [n] and a previous sampling [n−1] and a motor position change Δθ n-1 [rad] between the previous sampling [n−1] and a more previous sampling [n−2]. Subsequently, a variable A is calculated based on the above angles. The CPU determines whether to perform the compensation by comparing the calculated variable A and a calibration variable K and calculates a current motor position angle for compensation θ n [rad]. Finally, the CPU compensates for the absence of motor rotor position information with the calculated current motor position angle for compensation θ n [rad].

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2011-0130669 filed Dec. 8, 2011, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    (a) Technical Field 
         [0003]    The present invention relates to a technique for compensating for an abnormal output of a resolver for an environmentally friendly vehicle. More particularly, it relates to a method for compensating for an abnormal output of a resolver for an environmentally friendly vehicle, which prevents the occurrence of errors in the rotor position angle and speed estimation of a motor due to an abnormal AD conversion error in a resolver-to-digital converter (RDC). 
         [0004]    (b) Background Art 
         [0005]    Typically, a drive motor for converting electrical energy into mechanical energy and an inverter for controlling the operation of the drive motor are mounted in environmentally friendly vehicles such as hybrid vehicles, electric vehicles, hydrogen fuel cell vehicles, etc. 
         [0006]    As shown in  FIG. 3 , the inverter  100  includes: a power module  101  (e.g., an insulated gate bipolar transistor, IGBT) which transmits electrical energy between a battery  110  and an interior permanent magnet synchronous motor (IPMSM)  120 . A direct current (DC) link capacitor  102  absorbs the ripple component of DC voltage caused by the operation of the inverter  100  to prevent the ripple component from being transmitted to the battery  110 . A DC link voltage sensor  103  measures the DC voltage of the inverter  100 , i.e., the voltage at both ends of the DC link capacitor  102  to be used to control the inverter  100 . A DC link voltage sensing circuit  104  processes the output of the DC link voltage sensor  103  to have a magnitude capable of being input to an analog/digital (AD) converter and, at the same time, prevents the occurrence of a voltage measurement error due to noise, etc. 
         [0007]    A current sensor  105  measures the alternating current of the inverter  100  to be used to control the inverter  100  and a current sensing circuit  106  processes the output of a current sensor in a current sensor module to have a magnitude capable of being input to the AD converter and, at the same time, prevents the occurrence of a current measurement error due to noise, etc. A central processing unit (CPU)  107  is equipped with a software program stored on a computer readable medium that is executed by a processor to control the inverter  100  and the overall operation of the inverter  100  by using measured physical parameters received from the sensors  103  and  105 . A control/gate board  108  is equipped with the above-described circuits and components used to control the inverter  100 . 
         [0008]    More specifically, however, a resolver  122  in automotive applications detects the speed of the motor and the angle of a rotor that is used in the synchronous motor  120 . Thus, the sensing and failure detection of the resolver  122  is one of the most important factors in controlling the motor effectively. 
         [0009]    At present, as shown in  FIG. 4 , the occurrence of a failure in the resolver  122  is conventionally detected as follows. In the event of a failure in input signals (i.e., excitation signals, EXT+, EXT−) or output signals (i.e., basic signals for measuring the speed, S 1 -S 3 , S 2 -S 4 ) of the resolver  122 , a FAULT signal is generated by a resolver-to-digital converter (RDC)  124 , and the digital FAULT signal transmitted to the CPU  107  is input to a CPU, e.g., a motor controller, thereby detecting the occurrence of a failure in the resolver  122 . 
         [0010]    However, when the voltage margin is reduced by the maximum torque operation of the motor at high temperature and at low speed and during overmodulation, the occurrence of an abnormal AD conversion error in the RDC causes errors in the rotor position angle and speed estimation of the motor, which are used to control the motor. Therefore, due to the absence of resolver position information, the temperature of the motor is increased, the controllability of the motor current is reduced, and an overcurrent occurs in the motor. As a result, the hybrid function of a hybrid vehicle may be disabled. Even worse, in some instances the operation of the electric vehicle and the hybrid vehicle may be disabled completely unnecessarily. 
         [0011]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE DISCLOSURE 
       [0012]    The present invention provides a technique for compensating for an abnormal output of a resolver for an environmentally friendly vehicle, which increases the reliability of the hybrid function of a hybrid vehicle and the operation of an electric vehicle by accurately compensating for the current position of a motor rotor in the event of absence of motor rotor position information due to an AD conversion error in a resolver-to-digital converter (RDC) or due to noise, considering that it is necessary to accurately determine the position of the motor rotor in order to control the motor of hybrid and electric vehicles. 
         [0013]    In one aspect, the present invention provides a method for compensating for an abnormal output of a resolver for an environmentally friendly vehicle. In particular, a current motor position angle is set before compensation θ n,ORG  as a current motor position angle θ n . A motor (e.g., rotor) position change Δθ[rad] between a current sampling [n] and a previous sampling [n−1] and a motor (rotor) position change Δθ n-1 [rad] between the previous sampling [n−1] and a more previous sampling [n−2] is then obtained by a CPU. A variable A expressed as a difference between the motor (e.g., rotor) position change Δθ n [rad] between the current sampling [n] and the previous sampling [n−1] and the motor (rotor) position change Δθ n-1 [rad] between the previous sampling [n−1] and the more previous sampling [n−2] is then calculated. The CPU then determines whether to perform the compensation by comparing the calculated variable A and a calibration variable K and calculates a current motor position angle for compensation θ n [rad]. Finally, the CPU compensates for the absence of motor rotor position information with the calculated current motor position angle for compensation θ n [rad]. 
         [0014]    Other aspects and exemplary embodiments of the invention are discussed infra. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying to drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0016]      FIG. 1  is a flowchart illustrating a method for compensating for an abnormal output of a resolver for an environmentally friendly vehicle in accordance with an exemplary embodiment of the present invention; 
           [0017]      FIGS. 2A and 2B  are waveform diagrams illustrating the simulation results before and after applying the method for compensating for an abnormal output of a resolver for an environmentally friendly vehicle in accordance with an exemplary embodiment of the present invention; 
           [0018]      FIG. 3  is a schematic diagram illustrating the configuration of a conventional inverter system for an environmentally friendly vehicle; and 
           [0019]      FIG. 4  is a schematic diagram illustrating the signal transmission of a resolver for detecting the speed of a motor and the angle of a rotor. 
       
    
    
       [0020]    Reference numerals set forth in the Drawings includes reference to the following elements as further discussed below:
         100 : inverter     101 : power module     102 : DC link capacitor     103 : DC link voltage sensor     104 : DC link voltage sensing circuit     105 : current sensor     106 : current sensing circuit     107 : CPU     108 : control/gate board     110 : battery     120 : interior permanent magnet synchronous motor     122 : resolver     124 : resolver-to-digital converter       
 
         [0034]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
         [0035]    In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
       DETAILED DESCRIPTION 
       [0036]    Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0037]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
         [0038]    The above and other features of the invention are discussed infra. 
         [0039]    First, the configuration and function of a resolver will be briefly described for a better understanding of the present invention. For vector control of a synchronous motor or an induction motor used in a hybrid electric vehicle (HEV) or a pure electric vehicle (EV), it is necessary to set a coordinate system in synchronization with the flux position of the motor. To this end, it is necessary to read the absolute position of a rotor of the motor, and thus the resolver is used to detect the absolute position (i.e., rotation angle) of the rotor. 
         [0040]    As such, each phase of the rotor is accurately measured by the resolver, and a resolver-to-digital converter (RDC), which includes a synchronous rectifier for rectifying the measurement value and a voltage control oscillator (VCO) for outputting the rectified voltage at a desired oscillation frequency, transmits the measured phase of the rotor. Therefore, to the illustrative embodiment of the present invention accurately controls the motor speed and the motor torque required for the operation of the HEV or EV without unnecessary failures. 
         [0041]    Differential signals (S 1 -S 3 , S 2 -S 4 ) output from the resolver may have a frequency of about 10 kHz and an AC voltage of about 1 to 4 V in a normal state. However, if outside this range, i.e., in the event of a failure in input signals (i.e., excitation signals, EXT+, EXT−) or output signals (i.e., basic signals for measuring the speed, S 1 -S 3 , S 2 -S 4 ) of the resolver, a FAULT signal is generated by the RDC and this FAULT signal is transmitted to a CPU, thereby indicating to the CPU that a failure in the detection of the rotor position of the resolver has occurred. 
         [0042]    The present invention aims at ensuring the reliability of the hybrid function of a hybrid vehicle and the operation of an electric vehicle by estimating the current rotor position information from the motor speed and rotor position information at the previous sampling in the event of absence of motor rotor position information due to an AD conversion error in the RDC or due to noise. 
         [0043]    More specifically, a method for compensating for an abnormal output of a resolver for an environmentally friendly vehicle in accordance with an exemplary embodiment of the to present invention will be described with reference to  FIG. 1 . In order to obtain a current motor position angle for compensation θ n [rad], a current motor position angle before compensation θ m,ORG  is set as a current motor position angle θ n  (S 101 ). For reference, it should be noted that the reason the current motor position angle for compensation is expressed as θ n  and the current motor position angle is also expressed as θ n  is that they cannot be expressed in a different manner based on the programming flow of the software. 
         [0044]    Next, a motor (rotor) position change Δθ n [rad] between a current sampling [n] and a previous sampling [n−1] according to the output of the RDC is obtained based on the current motor position angle θ n . Simultaneously, a motor (rotor) position change Δθ n-1  [rad] between the previous sampling [n−1] and the more previous sampling [n−2] is also obtained (S 102 ). 
         [0045]    That is, the motor (rotor) position change Δθ n [rad] between the current sampling [n] and the previous sampling [n−1] is obtained by subtracting the previous motor position angle θ n-1  from the current motor position angle θ n . The motor (rotor) position change Δθ n-1  [rad] between the previous sampling [n−1] and the more previous sampling [n−2] is obtained by subtracting the more previous motor position angle θ n-2  from the previous motor position angle θ n-1 . These values may be obtained by periodically sampling the measurement signals of the motor position angle of the resolver output from the RDC. 
         [0046]    Then, a variable A, i.e., a difference between the position change Δθ n [rad] between the current sampling [n] and the previous sampling [n−1] and the position change Δθ n-1 [rad] to between the previous sampling [n−1] and the more previous sampling [n−2] is calculated by the following formula 1 (S 103 ): 
         [0000]        A =Bound2 PI (|Δθ n −Δθ n-1 |)  [Formula 1]
 
         [0047]    In formula 1, the function “| |” is a function that outputs an absolute value of an input and the function of “Bound 2 PI” is a function that limits the input to 0 to 2π(rad). Here, when the sample period is taken at a given point in time, the difference between the motor (rotor) position changes Δθ n [rad] and Δθ n-1 [rad], which indicate the position changes according to time, may be seen as a difference between the current sampling rate and the previous sampling rate, and this variable A may be expressed as an instantaneous acceleration change. 
         [0048]    Next, the variable A calculated in the above manner is compared with a calibration variable K to determine whether to perform the compensation (S 104 ). The calibration variable K is a constant that represents a physical limit. Accordingly, when the instantaneous acceleration change, i.e., the variable A is greater than the calibration variable K and smaller than 2π−K, the compensation for the motor rotor position is determined. 
         [0049]    In other words, if the variable A is greater than the calibration K and, at the same time, the variable A is smaller than 2π−K, it is determined that the motor rotor position information is omitted, and thus the compensation for the motor rotor position is determined. Accordingly, the current motor position angle for compensation θ n [rad] is calculated by the to following formula 2 (S 105 ): 
         [0000]      θ n =Bound2 PI (Δθ n-1 +ω rEstOld   ×T   s )  [Formula 2]
 
         [0050]    In formula 2, ω rEstOld  is an estimated speed at the previous sampling (e.g., a position change at the previous sampling rate), T s  represents the control period (us), and the function “Bound 2 PI” is a function that limits the current motor position angle for compensation to 0 to 2π(rad). As a result, the calibration value, i.e., the current motor position angle for compensation θ n [rad] is a sum of the previous sampling position θ n-1  and a position change ω rEstOld  at the previous sampling rate. Therefore, the absence of the motor rotor position information is compensated with the current motor position angle for compensation θ n [rad]calculated by formula 2, thereby continuously ensuring the current of the motor and the torque control performance. 
         [0051]    In more detail, as shown in  FIG. 2A , when the motor rotor position information is omitted during a certain sampling during RDC output and, at the same time, a current ripple (e.g., 350 Apk) larger than an abnormal output command current (e.g., 312 Apk) of the resolver is generated at the corresponding period, the omitted motor rotor position information is compensated with the current motor position angle for compensation θ n [rad] calculated by formula 2 as shown in  FIG. 2B , thereby continuously ensuring the current of the motor and the torque control performance. 
         [0052]    Meanwhile, after the compensation for the omitted motor rotor position information with the current motor position angle for compensation θ n [rad] during the RDC output, new motor rotor position information is output at the next sampling period, and thus a process (S 106 ) of assigning and storing the previous motor position angle θ n-1  as the more previous motor position angle θ n-2 , a process (S 107 ) of assigning and storing the current motor position angle for compensation θ n  as the previous motor position angle θ n-1  and, at the same time, assigning and storing an estimated speed to ω rEst [rad/sec] at the current sampling [n] as an estimated speed ω rEstOld [rad/sec] at the previous sampling are performed based on the programming constructed in, e.g., a computer readable medium. 
         [0053]    Furthermore, the control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN). 
         [0054]    Advantageously, in the event of absence of the rotor position information due to an AD conversion error in the RDC or due to noise, the illustrative embodiment of the present invention accurately determines the current motor rotor position through the compensation method of the present invention, thereby ensuring the current of the motor and the torque control performance. 
         [0055]    Moreover, according to the compensation method of the present invention, the reliability and stability of the motor/inverter system, the hybrid function of the hybrid vehicle, and the operation of the electric vehicle is increased, thereby reducing the costs for ensuring the reliability of the resolver signal. 
         [0056]    The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.