Abstract:
A method of compensating for rotor position error of a rotor of a permanent magnet synchronous generator (PMG) that provides electrical power to a direct current (DC) power generating system, the method including obtaining PMG phase voltages and resolver processed angular position output when the PMG is driven by a prime mover. Once obtained, a PMG fundamental phase voltage waveform is selected by eliminating higher order harmonics. A mechanical angle of the rotor is then converted into an electrical angle, then the electrical angle is aligned within the mechanical angle with a corresponding PMG fundamental phase voltage angle by adjusting offset to the electrical angle. After alignment, a plurality of resolver error offset values associated with the electrical angle are stored and additional values to the compensation table are added by interpolating data between two corresponding resolver error offset values of the plurality of resolver error offset values.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to a direct current power generating system, and more particularly, to a resolver error compensation technique of a PMG-based direct current power generating system and method of operating. 
         [0002]    Permanent magnet synchronous generators (PMG) are used in electric power generating system for electric or hybrid-electric vehicles. A generator control unit (GCU) is used to convert variable alternate current (AC) voltage at the output of the PMG into constant direct current (DC) voltage to supply vehicle loads. GCU contains a pulse-width modulate (PWM) converter (i.e. active rectifier) that may require accurate information about PMG rotor angular positon for proper commutation of active rectifier switches. 
         [0003]    Rotor angle may be detected by a resolver. In high power density applications, the PMG (with a high number of poles) coupled with a frameless two pole resolver may be used. Output of the resolver may be an electrical signal that corresponds to rotor angle. Resolver outputs may be sine and cosine analog signals that, when provided to a resolver-to-digital converter (RDC) may produce a digital output corresponding to the rotor&#39;s absolute angular position. 
         [0004]    Various sources of angle error in the output signal of the resolver may include mechanical misalignment, electrical characteristics and conversion time errors. These errors with a multi-pole PMG may significantly aggravate accuracy of electrical angle that should be within at least one degree to obtain good control of the power generating system. Field oriented control of an active rectifier coupled to the PMG may not be accurately implemented over the entire speed range without knowing the actual position of the PMG rotor. It is therefore desirable to compensate resolver output error caused by misalignment and electrical sources of error. 
       SUMMARY 
       [0005]    A method of compensating for rotor position error of a rotor of a permanent magnet synchronous generator (PMG) that provides electrical power to a direct current (DC) power generating system according to one, non-limiting, embodiment of the present disclosure includes obtaining PMG phase voltages and resolver processed angular position output signals by a resolver-to-digital (R/D) converter of the DC power generating system when the PMG is driven by a prime mover; selecting a PMG fundamental phase voltage waveform by eliminating higher order harmonics; converting a mechanical angle of a rotor into an electrical angle by an electrical angle and frequency derivation component of the DC power generating system; aligning the electrical angle within the mechanical angle with a corresponding PMG fundamental phase voltage angle by adjusting offset to the electrical angle; storing a plurality of resolver error offset values associated with the electrical angle into a computer readable storage medium of a digital signal processor (DSP) component; and adding additional values to the compensation table by interpolating data between two corresponding resolver error offset values of the plurality of resolver error offset values by a computer processor of the DSP component. 
         [0006]    Additionally to the foregoing embodiment, the method includes running the prime mover at a pre-determined speed before obtaining the PMG phase voltages. 
         [0007]    In the alternative or additionally thereto, in the foregoing embodiment, the method includes feeding an excitation signal to a resolver rotor coil; feeding sinusoidal and cosine-shaped signals from respective coils of a resolver associated with a rotor of the PMG; deriving angular and speed values by the R/D converter; and feeding the angular and speed values to the DSP component before running the prime mover. 
         [0008]    In the alternative or additionally thereto, in the foregoing embodiment, the resolver comprises a two-pole resolver. 
         [0009]    In the alternative or additionally thereto, in the foregoing embodiment, the resolver is frameless. 
         [0010]    In the alternative or additionally thereto, in the foregoing embodiment, the PMG includes about twenty-eight poles. 
         [0011]    A vehicle according to another, non-limiting, embodiment includes a prime mover; a PMG including a rotor coupled to the prime mover for rotation; a resolver including an excitation coil, a first coil and a second coil positioned approximately ninety degrees from the first coil, and wherein the excitation coil and the first and second coils are associated with the rotor; a resolver processing and compensation system configured to receive sinusoidal and cosine-shaped analog signals from the respective first and second coils, convert the analog signals to a digital signal corresponding to an absolute angular position of the rotor, and compensate for angular position error; a DC electrical load configured to receive DC power from the resolver processing and compensation system; and a vehicle supervisory controller configured to manage DC power distribution. 
         [0012]    Additionally to the foregoing embodiment, the DC electrical load comprises an electric traction drive. 
         [0013]    In the alternative or additionally thereto, in the foregoing embodiment, the vehicle is an electric automobile. 
         [0014]    In the alternative or additionally thereto, in the foregoing embodiment, the vehicle is a hybrid automobile. 
         [0015]    In the alternative or additionally thereto, in the foregoing embodiment, the prime mover is an internal combustion engine. 
         [0016]    In the alternative or additionally thereto, in the foregoing embodiment, the resolver processing and compensation system includes a computer readable storage medium configured to store a speed compensation table and a position compensation table for storing offset data associated with the angular position error and used by a computer processor of the resolver processing and compensation system to expand the respective speed and position compensation tables by interpolating the stored offset data. 
         [0017]    A DC power generating system according to another, non-limiting, embodiment includes a PMG including a rotor; a resolver including an excitation coil, a first coil and a second coil positioned approximately ninety degrees from the first coil, and wherein the excitation coil and the first and second coils are associated with the rotor; an excitation component configured to electrically excite the excitation coil; a resolver-to-digital converter configured to receive first and second analog signals from the respective first and second coils and convert the first and second analog signals to respective digital rotor angle and digital rotor speed signals; and a digital signal processor component configured to receive the digital rotor angle signal and the digital rotor speed signal, convert to an electrical angle and compensate for angular position error of the rotor. 
         [0018]    Additionally to the foregoing embodiment, the digital signal processor component includes a computer processor, and a computer readable storage medium configured to store a speed compensation table and a position compensation table for storing offset data associated with the angular position error and used by the computer processor to expand the respective speed and position compensation tables by interpolating the stored offset data. 
         [0019]    In the alternative or additionally thereto, in the foregoing embodiment, the angular position error includes a position angle error and a speed angle error. 
         [0020]    The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. However, it should be understood that the following description and drawings are intended to be exemplary in nature and non-limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiments. The drawings that accompany the detailed description can be briefly described as follows: 
           [0022]      FIG. 1  is a schematic of a vehicle including a, non-limiting, embodiment of a power generating system of the present disclosure; 
           [0023]      FIG. 2  is a schematic of the power generating system; 
           [0024]      FIG. 3  is a schematic of generator control unit (GCU) of the power generating system; 
           [0025]      FIG. 4  is a flow chart of a method of initializing a process of a resolver processing and compensation system of the GCU; 
           [0026]      FIG. 5  is a flow chart of a process of compensating for position angle error; and 
           [0027]      FIG. 6  is a flow chart of a process of compensating for speed angle error. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Referring to  FIG. 1 , an exemplary embodiment of an electric power generating system  20  of the present disclosure is illustrated. The electric power generating system  20  may be a DC power generating system and may be applied to vehicles  22  such as, for example, automobiles. The vehicle  22  may be an electrically powered vehicle, a hybrid vehicle and others. As illustrated, the DC power generating system  20  may be driven or powered by a prime mover  24 , and may provide electrical power to various electrical loads  26  of the vehicle  22 . A vehicle supervisory controller  28  (i.e., computer) may monitor the vehicle DC loads  26  and communicate with the power generating system  20  to manage and control power distribution. The DC power generating system  20  may include a permanent magnet synchronous generator (PMG)  30  and a generator control unit (GCU)  32  used to convert variable alternate current (AC) voltage at an output of the PMG  30  into a constant direct current (DC) voltage to supply power to the vehicle loads  26 . Non-limiting examples of the prime mover  24  may include an internal combustion engine (i.e., for hybrid vehicles as one example), and electric motors (i.e., for electric vehicles). Non-limiting examples of vehicle loads  26  may include electric drive pumps, fans, export inverters (i.e., to support 60 Hz and 400 Hz loads, and electric traction drives powered by a high voltage DC bus (not shown). 
         [0029]    Referring to  FIG. 2 , the GCU  32  may include a resolver  34 , a resolver processing and compensation system  36 , an active rectifier  38 , and an active rectifier controller  40 . The resolver and compensation system  36  may include a filter  42  an excitation component  44 , a resolver-to-digital (R/D) converter  46 , and a digital signal processor (DSP) component  50  that may include an electrical angle and frequency derivation component  48 , a computer processor  52  (e.g., microprocessor) and a computer readable storage media or memory  54 . 
         [0030]    The resolver  34  may be located inside a housing (not shown) of the PMG  30 . The resolver  34  and the resolver processing and compensation system  36  are configured to provide position information of a rotor  56  of the PMG  30 . The rotor position information is generally needed for the implementation of a field orientated control algorithm that facilitates the commutating of switches (not shown) of the active rectifier  38 . The resolver  34  may generally be frameless and may be a two-pole resolver. 
         [0031]    The resolver  34  may output an electrical signal that corresponds to rotor angle. The electrical signal output of the resolver  34  may include sine and cosine analog signals (see respective arrows  58 ,  60 ) sent to the R/D converter  46  of the resolver processing and compensation system  36 . The R/D converter  46  outputs a digital output signal corresponding to the absolute angular position of the rotor  56 . The resolver  34  may be a two-pole resolver that corresponds to a mechanical angle from zero (0°) to three hundred sixty degrees (360°) of the rotor  56 . For proper commutation of a multi-pole PMG  30  output, the resolver output is converted into an electrical angle. This conversion is accomplished by multiplying the two-pole resolver output by a pair of PMG poles as follows: where “φ” is the electrical angle, “θ” is the mechanical (rotor) angle, and “P” is the PMG number of poles. One example of a number of poles of the PMG  30  may be about twenty-eight (28). 
         [0032]    The active rectifier  38  of the GCU  32  is coupled to the PMG  30  through contactors  62  and is configured to convert AC power to DC power for the vehicle DC loads  26 . To facilitate field oriented control of the active rectifier  38  and enable and/or achieve efficient power conversion over an entire speed range of the prime mover  24 , the GCU  32  is configured to determine the actual position of the rotor  56  of the PMG  30  and eliminate or minimize (i.e., compensate for) any errors associated with the actual position. Various sources of rotor position error in the output signals  58 ,  60  of the resolver  34  may include mechanical misalignment, electrical characteristics and conversion time errors. These errors with a PMG  30  having multiple poles may aggravate accuracy of the electrical angle that should be within at least a one degree (1°)to obtain good control of the power generating system  20 . 
         [0033]    The active rectifier controller  38  communicates with the vehicle supervisory controller  28  to enable, for example, different operating modes such as built-in-test, engine start, and/or generate mode. The contactors  62  facilitate disconnect of the active rectifier  38  from the PMG  30  during resolver compensating procedure (i.e., the compensation of rotor position error) and/or during fault conditions. Referring to  FIGS. 3 and 4 , a method of initializing the resolver compensating procedure may include a block or step  100  that entails feeding a sinusoidal excitation signal to an excitation coil  64  by the excitation component  44  of the resolver processing and compensation system  36 . At block  102  sinusoidal and cosine-shaped signals are fed to respective stator coils  66 ,  68  (i.e., windings) arranged perpendicular with respect to each other on the stator (not shown). 
         [0034]    At block  104  of the method of initializing the resolver compensating procedure, angular and speed values (see respective arrows  68 ,  70 ) derived by the R/D converter  46  are fed to the electrical angle and frequency derivation component  48  of the DSP component  50 , and the speed value  70  may also be fed directly to the processor component  52  of the DSP component  50 . At block  106 , the prime mover  24  is run at a pre-determined speed. At block  108 , PMG 30 phase voltages (i.e., line to neutral) are obtained and fed to the DSP  50 . At block  110 , higher harmonics are filtered to select a fundamental component of PMG phase A voltage (L-N). At block  112 , an electrical angle is obtained by multiplying a rotor angle by the number of PMG pole pairs. At block  114 , a sine function is applied to the electrical angle. At block  116 , a sector number is defined by assigning each sinusoidal waveform derived from the rotor angle. The sector number may generally be expressed by a sector length that equals 360 degrees divided by the number of pole pairs. In one example, for a PMG having twenty-eight ( 28 ) poles and with a two pole resolver, the sector length is as follows: 
         [0000]      Sector Length=360°/14=25.714°
 
         [0000]    In this example, the total sectors is equal to fourteen ( 14 ). Electrical angle is aligned in each sector with the PMG phase voltage angular position. 
         [0035]    Referring to  FIG. 5 , an exemplary process of compensating position angle error conducted at least in-part via the DSP component  50 , is illustrated. Referring to  FIGS. 3 and 5 , at block  200  position compensation factor(s) are started. At block  202  a counter is reset by leading edge of zero-crossing detector responsive to PMG phase A voltage fundamental component. At block  204  the counter data is latched by leading edge of zero-crossing detector responsive to sin waveform of electrical angle. At block  206 , the processor  52  of the DSP component  50  determines if the counter data is greater than a pre-determined number. If ‘yes,’ then at block  208  an increment is set to a positive offset value; otherwise, at block  210 , the increment is set to a negative offset value. After either of blocks  208 ,  210 , at block  212  the offset is incremented. At block  214 , the incremented offset is added to the electrical angle (see block  112  in  FIG. 4 ). At block  216 , the counter is reset by leading edge of zero-crossing detector responsive to PMG phase ‘A’ voltage fundamental component. At block  218  the counter data is latched by leading edge of zero-crossing detector responsive to sine waveform of electrical angle. At block  220 , the processor  52  of the DSP component  50  determines if the counter data is greater than previous value. If ‘no,’ the process returns to block  212 ; otherwise, at block  222 , the offset is stored in a position compensation table  72  stored in memory  54  of the DSP component  50 . 
         [0036]    At block  224 , the processor  52  of the DSP component  50  determines if the sector number is greater than a maximum value. If “no” then at block  226 , the sector number is incremented and the process returns to block  202 ; otherwise, at block  228 , the position compensation table is expanded by interpolating stored data. 
         [0037]    Referring to  FIG. 6 , an exemplary process of compensating speed angle error is illustrated. Referring to  FIGS. 3 and 6 , at block  300 , the process of compensating speed angle error utilizing speed compensation factors is started. At block  302 , a prime mover  24  speed is set at a minimum pre-determined level. At block  304 , a counter is reset by leading edge of zero-crossing detector responsive to PMG phase ‘A’ voltage fundamental component. At block  306 , counter data is latched by leading edge of zero-crossing detector responsive to a sine waveform of an electrical angle. At block  308 , the processor  52  of the DSP component  50  determines if counter data is greater than a pre-determined number. If ‘yes,’ then at block  310 , a positive offset increment is set; otherwise, at block  312 , a negative offset increment is set. 
         [0038]    At block  314 , the offset is incremented. At block  316  the incremented offset is added to the electrical angle (see block  112  in  FIG. 4 ). At block  318 , the counter is reset by leading edge of zero-crossing detector responsive to PMG phase ‘A’ voltage fundamental component. At block  320 , the counter data is latched by leading edge of zero-crossing detector responsive to sine waveform of electrical angle. At block  322 , the processor  52  of the DSP component  50  determines if the counter data is greater than a previous value. If ‘no,’ then the process returns to block  314 ; otherwise, at  324  the offset is stored to a speed compensation table  74  stored in memory  54  of the DSP component  50 . 
         [0039]    At block  326 , the processor  52  of the DSP component  50  determines if the speed of the prime mover  24  is greater than a maximum pre-determined level. If ‘no,’ then at block  328  the speed of the prime mover  24  is incremented by a pre-determined level and the process returns to block  304 ; otherwise, at block  330  the speed compensation table  64  is expanded by interpolating stored data. 
         [0040]    Benefits of the present disclosure include a DC power generating system  20  with a PMG  30  that contains a large number of poles coupled to a two-pole resolver  34 , improved PMG rotor angular position information by providing the ability to accurately determine position information and to compensate for positional and speed computational errors, a simplified procedure to compensate resolver error due to mechanical misalignment of a frameless resolver with a generator rotor, and an automated procedure that stores corrected resolver position factor data into a resolver error compensation table(s). 
         [0041]    While the present disclosure is described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, various modifications may be applied to adapt the teachings of the present disclosure to particular situations, applications, and/or materials, without departing from the essential scope thereof. The present disclosure is thus not limited to the particular examples disclosed herein, but includes all embodiments falling within the scope of the appended claims.