Method and apparatus to determine rotational position of an electrical machine

A control system and method to determine position of a rotor relative to a stator for a synchronous multipole electrical machine is presented, including one for application on a fuel/electric hybrid powertrain for a vehicle. The machine includes a stator, a rotor, and a rotor position sensing mechanism. The control system controls the electrical machine, in conjunction with an electrical storage device and an inverter, using algorithms and calibrations which derive a rotor position based upon a sensorless position sensing technique, and determine an offset from a sensed rotor position. Electrical output from the inverter to the machine is controlled based the offset, which is stored non-volatile memory. A rotor position is derived based upon a sensorless position sensing technique during initial machine operation after startup of the machine, and includes operation in a torque-generative mode and in an electrical energy-generative mode.

TECHNICAL FIELD

This invention pertains generally to control of an electrical machine, and more specifically to a control system for an electric machine to determine rotational position to optimize energy usage to supply motive torque in a vehicle propulsion system.

BACKGROUND OF THE INVENTION

Control systems for electrical motors typically include a feedback device such as a position sensor to provide data to measure position and rotational velocity of the motor. On a three-phase multipole synchronous electrical motor, precise and accurate measurement of position of a rotor relative to each of the poles of a stator is important to achieve efficient transmission of electrical energy. Rotor position is typically measured using the position sensor to determine position of the resolver. Position of the resolver relative to the machine rotor is subject to error due to factors including manufacturing variations and tolerances. Electrical motor manufacturers have attempted to correct errors in resolver position measurement using adjustments and post-assembly calibrations. Manufacturers have also attempted to correct sensor-related errors by introducing sensorless techniques for determining rotor position by monitoring and analyzing electromagnetic characteristics of the motor.

Vehicle propulsion systems comprising hybrid powertrains are known for managing the input and output torques of various torque-generative devices, most commonly internal combustion engines and electric machines. One hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving torque from a torque-generative source, e.g. an internal combustion engine, and an output member for delivering motive torque from the transmission to a vehicle driveline. Motive torque is transmitted to the transmission from first and second electrical machines operatively connected to an energy storage device for interchanging electrical power therebetween. A controller is provided for regulating the electrical power interchange between the energy storage device and the electrical machines.

The electrical machines preferably comprise known permanent magnet synchronous motor/generator machines, each constructed of a multi-pole electrical stator and a rotor device. Such machines are preferable for powertrain and vehicle applications because they exhibit high torque-to-inertia ratios, high efficiency, and high power density. In such machines, the controller requires accurate and precise information regarding position of the rotor device relative to the stator in order to optimize electrical energy efficiency, thus leading to improved fuel economy.

Prior art systems utilize such techniques as tight machine tolerances and assembly methods, coupled with multiple position sensing devices to ensure accurate measurement of rotor position relative to the stator.

When using PM synchronous machines, absolute position (within one pole pair pitch) is required. Also, the accuracy of this position measurement is critical, as it will affect the performance of the motor control, most noticeably in torque production and linearity. Using a resolver can provide precise position measurement. However, the accuracy of the measurement is directly affected by the initial alignment of the resolver during installation. The installation of the resolver and mechanical alignment can be difficult to control in production.

It is therefore desirable to use a self-aligning start-up algorithm in the motor control.

There is a need to provide an improved method and system to precisely and accurately determine position of a rotor device in a stator for an electrical machine, especially one for application on a fuel/electric hybrid powertrain for a vehicle.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a control system for an electric machine which precisely and accurately determines position of a rotor device relative to a stator for the electrical machine, especially one comprising a synchronous multipole electrical machine, including one for application on a fuel/electric hybrid powertrain for a vehicle.

In accordance with the present invention, a sensorless motor control system is used to estimate rotor position during powertrain start-up. The estimated angle is compared to the measured resolver angle. A correcting offset is added to the resolver signal. After start-up, the control system uses the corrected resolver signal for position feedback and control. In this manner, the installation alignment requirements for the resolver are greatly reduced.

Thus, in accordance with the invention, a control system and a method for controlling an electric machine comprising a multi-phase multipole motor having a stator, a rotor, and a rotor position sensing mechanism is provided. The control system comprises an inverter operable to transmit electrical energy between the stator of the electrical machine and an electrical storage device, and a controller. The controller includes executable algorithms and predetermined calibrations which derive a rotor position based upon a sensorless position sensing technique, and determine an offset parameter between the derived rotor position and a sensed rotor position. The inverter is controlled based upon the sensed rotor position and the offset parameter. The offset parameter is stored in a non-volatile memory device of the control system for future reference.

These and other aspects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same,FIGS. 1 and 2depict a system comprising an engine14, transmission10, control system, and driveline which has been constructed in accordance with an embodiment of the present invention.

Mechanical aspects of exemplary transmission10are disclosed in detail in commonly assigned U.S. Pat. No. 6,953,409 entitled TWO-MODE, COMPOUND-SPLIT, HYBRIDELECTRO-MECHANICALTRANSMISSIONHAVINGFOURFIXEDRATIOS, which is incorporated herein by reference. The exemplary two-mode, compound-split, electro-mechanical transmission embodying the concepts of the present invention is depicted inFIG. 1, and is designated generally by the numeral10. The transmission10has an input shaft12preferably directly driven by an engine14. A transient torque damper20is incorporated between the output shaft18of the engine14and the input member12of the transmission10. The transient torque damper20preferably comprises a torque transfer device77having characteristics of a damping mechanism and a spring. The transient torque damper20permits selective engagement of the engine14with the transmission10. The torque transfer device77is not utilized to change, or control, the mode in which the transmission10operates. The torque transfer device77preferably comprises a hydraulically operated friction clutch, referred to as clutch C5.

The engine14may be any of numerous forms of internal combustion engines, such as a spark-ignition engine or a compression-ignition engine, readily adaptable to provide a torque output to the transmission10at a range of operating speeds, from idle, at or near 600 revolutions per minute (RPM), to over 6,000 RPM. Irrespective of the means by which the engine14is connected to the input member12of the transmission10, the input member12is connected to a planetary gear set24in the transmission10.

Referring specifically now toFIG. 1, the transmission10utilizes three planetary-gear sets24,26and28. The first planetary gear set24has an outer ring gear member30which circumscribes an inner, or sun gear member32. A plurality of planetary gear members34are rotatably mounted on a carrier36such that each planetary gear member34meshingly engages both the outer gear member30and the inner gear member32.

The second planetary gear set26has an outer ring gear member38, which circumscribes an inner sun gear member40. A plurality of planetary gear members42are rotatably mounted on a carrier44such that each planetary gear42meshingly engages both the outer gear member38and the inner gear member40.

The third planetary gear set28has an outer ring gear member46, which circumscribes an inner sun gear member48. A plurality of planetary gear members50are rotatably mounted on a carrier52such that each planetary gear50meshingly engages both the outer gear member46and the inner gear member48.

The three planetary gear sets24,26and28each comprise simple planetary gear sets. Furthermore, the first and second planetary gear sets24and26are compounded in that the inner gear member32of the first planetary gear set24is conjoined through a hub plate gear54to the outer gear member38of the second planetary gear set26. The conjoined inner gear member32of the first planetary gear set24and the outer gear member38of the second planetary gear set26are continuously connected to a first electrical machine comprising a motor/generator56, referred to as Motor A or “MA”.

The planetary gear sets24and26are further compounded in that the carrier36of the first planetary gear set24is conjoined through a shaft60, to the carrier44of the second planetary gear set26. As such, carriers36and44of the first and second planetary gear sets24and26, respectively, are conjoined. The shaft60is also selectively connected to the carrier52of the third planetary gear set28, through a torque transfer device62which, as will be hereinafter more fully explained, is employed to assist in the selection of the operational modes of the transmission10. The carrier52of the third planetary gear set28is connected directly to the transmission output member64.

In the embodiment described herein, wherein the transmission10is used in a land vehicle, the output member64is operably connected to a driveline comprising a gear box90or other torque transfer device which provides a torque output to one or more vehicular axles92or half-shafts (not shown). The axles92, in turn, terminate in drive members96. The drive members96can be either front or rear wheels of the vehicle on which they are employed, or they may be a drive gear of a track vehicle. The drive members96may have some form of wheel brake94associated therewith. The drive members each have a speed parameter, NWHL, comprising rotational speed of each wheel96which is typically measurable with a wheel speed sensor.

The inner gear member40of the second planetary gear set26is connected to the inner gear member48of the third planetary gear set28, through a sleeve shaft66that circumscribes shaft60. The outer gear member46of the third planetary gear set28is selectively connected to ground, represented by the transmission housing68, through a torque transfer device70. Torque transfer device70, as is also hereinafter explained, is also employed to assist in the selection of the operational modes of the transmission10. The sleeve shaft66is also continuously connected to a second electrical machine comprising a motor/generator72, referred to as MB.

All the planetary gear sets24,26and28as well as the two electrical machines56and72are coaxially oriented, as about the axially disposed shaft60. Electrical machines56and72are both of an annular configuration which permits them to circumscribe the three planetary gear sets24,26and28such that the planetary gear sets24,26and28are disposed radially inwardly of the electrical machines56and72. This configuration assures that the overall envelope, i.e., the circumferential dimension, of the transmission10is minimized.

A torque transfer device73selectively connects the sun gear40with ground, i.e., with transmission housing68. A torque transfer device75is operative as a lock-up clutch, locking planetary gear sets24,26, electrical machines56,72and the input to rotate as a group, by selectively connecting the sun gear40with the carrier44. The torque transfer devices62,70,73,75are all friction clutches, respectively referred to as follows: clutch C170, clutch C262, clutch C373, and clutch C475. Each clutch is preferably hydraulically actuated, receiving pressurized hydraulic fluid from a pump when a corresponding clutch control solenoid is actuated. Hydraulic actuation of each of the clutches is accomplished using a known hydraulic fluid circuit having a plurality of clutch-control solenoids, which is not described in detail herein.

The transmission10receives input motive torque from the torque-generative devices, including the engine14and the electrical machines56and72, as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (ESD)74. The ESD74typically comprises one or more batteries. Other electrical energy and electrochemical energy storage devices that have the ability to store electric power and dispense electric power may be used in place of the batteries without altering the concepts of the present invention. The ESD74is preferably sized based upon factors including regenerative requirements, application issues related to typical road grade and temperature, and propulsion requirements such as emissions, power assist and electric range. The ESD74is high voltage DC-coupled to transmission power inverter module (TPIM)19via DC lines or transfer conductors27. The TPIM19is an element of the control system described hereinafter with regard toFIG. 2. The TPIM19communicates with the first electrical machine56by transfer conductors29, and the TPIM19similarly communicates with the second electrical machine72by transfer conductors31. Electrical current is transferable to or from the ESD74in accordance with whether the ESD74is being charged or discharged. TPIM19includes the pair of power inverters and respective motor controllers configured to receive motor control commands and control inverter states therefrom for providing motor drive or regeneration functionality.

In motoring control, the respective inverter receives current from the DC lines and provides AC current to the respective electrical machine, i.e. MA and MB, over transfer conductors29and31. In regeneration control, the respective inverter receives AC current from the electrical machine over transfer conductors29and31and provides current to the DC lines27. The net DC current provided to or from the inverters determines the charge or discharge operating mode of the electrical energy storage device74. Preferably, MA56and MB72are three-phase AC machines and the inverters comprise complementary three-phase power electronics.

Referring now toFIG. 2, a schematic block diagram of the control system, comprising a distributed controller architecture, is shown. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and are operable to provide coordinated system control of the powertrain system described herein. The control system is operable to synthesize pertinent information and inputs, and execute algorithms to control various actuators to achieve control targets, including such parameters as fuel economy, emissions, performance, driveability, and protection of hardware, including batteries of ESD74and MA and MB56,72. The distributed controller architecture includes engine control module (‘ECM’)23, transmission control module (‘TCM’)17, battery pack control module (‘BPCM’)21, and Transmission Power Inverter Module (‘TPIM’)19. A hybrid control module (‘HCP’)5provides overarching control and coordination of the aforementioned controllers. There is a User Interface (‘UI’)13operably connected to a plurality of devices through which a vehicle operator typically controls or directs operation of the powertrain, including the transmission10. Exemplary vehicle operator inputs to the UI13include an accelerator pedal, a brake pedal, transmission gear selector, and, vehicle speed cruise control. Each of the aforementioned controllers communicates with other controllers, sensors, and actuators via a local area network (‘LAN’) bus6. The LAN bus6allows for structured communication of control parameters and commands between the various controllers. The specific communication protocol utilized is application-specific. By way of example, one communications protocol is the Society of Automotive Engineers standard J1939. The LAN bus and appropriate protocols provide for robust messaging and multi-controller interfacing between the aforementioned controllers, and other controllers providing functionality such as antilock brakes, traction control, and vehicle stability.

The HCP5provides overarching control of the hybrid powertrain system, serving to coordinate operation of the ECM23, TCM17, TPIM19, and BPCM21. Based upon various input signals from the UI13and the powertrain, including the battery pack, the HCP5generates various commands, including: an engine torque command, clutch torque commands, TCL—Nfor the various clutches C1, C2, C3, C4of the transmission10; and motor torque commands, TAand TB, for MA and MB, respectively.

The ECM23is operably connected to the engine14, and functions to acquire data from a variety of sensors and control a variety of actuators, respectively, of the engine14over a plurality of discrete lines collectively shown as aggregate line35. The ECM23receives the engine torque command, TE—CMD, from the HCP5, and generates a desired axle torque, and an indication of actual engine torque, TI, input to the transmission, which is communicated to the HCP5. For simplicity, ECM23is shown generally having bi-directional interface with engine14via aggregate line35. Various other parameters that are sensed by ECM23include engine coolant temperature, engine input speed (NI) to shaft12leading to the transmission, manifold pressure, ambient air temperature, and ambient pressure. Various actuators that are controlled by the ECM23include fuel injectors, ignition modules, and throttle control modules.

The TCM17is operably connected to the transmission10and functions to acquire data from a variety of sensors and provide command signals to the transmission. Inputs from the TCM17to the HCP5include estimated clutch torques, TCL—N—EST, for each of the clutches C1, C2, C3, and, C4and rotational speed, NO, of the output shaft64. Other actuators and sensors may be used to provide additional information from the TCM to the HCP for control purposes.

The BPCM21is signally connected one or more sensors operable to monitor electrical current or voltage parameters of the ESD74to provide information about the state of the batteries to the HCP5. Such information includes battery state-of-charge, battery voltage, VBAT, and available battery power, PBAT—MINand PBAT—MAX.

The Transmission Power Inverter Module (TPIM)19includes a pair of power inverters and motor controllers configured to receive motor control commands and control inverter states therefrom to provide motor drive or regeneration functionality. The TPIM19is operable to generate torque commands for MA56and MB72, TAand TB, based upon input from the HCP5, which is driven by operator input through UI13and system operating parameters. The motor torque commands for MA and MB, i.e. TAand TB, are implemented by the control system, including the TPIM19, to control MA and MB. Individual motor speed signals, NAand NBfor MA and MB respectively, are derived by the TPIM19from the motor phase information or conventional rotation sensors. The TPIM19determines and communicates motor speeds, NAand NB, to the HCP5. The electrical energy storage device74is high-voltage DC-coupled to the TPIM19via DC lines27. Electrical current is transferable to or from the TPIM19in accordance with whether the ESD74is being charged or discharged.

Each of the aforementioned controllers is preferably a general-purpose digital computer generally comprising a microprocessor or central processing unit, storage mediums comprising read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. Each controller has a set of control algorithms, comprising resident program instructions and calibrations stored in ROM and executed to provide the respective functions of each computer. Information transfer between the various computers is preferably accomplished using the aforementioned LAN6.

Algorithms for control and state estimation in each of the controllers are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units and are operable to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the respective device, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.

In response to an operator's action, as captured by the UI13, the supervisory HCP controller5and one or more of the other controllers determine required transmission output torque, TOat shaft64. Selectively operated components of the transmission10are appropriately controlled and manipulated to respond to the operator demand. For example, in the exemplary embodiment shown inFIGS. 1 and 2, when the operator has selected a forward drive range and manipulates either the accelerator pedal or the brake pedal, the HCP5determines an output torque for the transmission, TO, which affects how and when the vehicle accelerates or decelerates. Final vehicle acceleration is affected by other factors, including, e.g., road load, road grade, and vehicle mass. The HCP5monitors the parametric states of the torque-generative devices, and determines the output of the transmission required to arrive at the desired torque output. Under the direction of the HCP5, the transmission10operates over a range of output speeds from slow to fast in order to meet the operator demand.

The two-mode, compound-split, electro-mechanical transmission, includes output member64which receives output power through two distinct gear trains within the transmission10, and operates in several transmission operating modes, described with reference now toFIG. 1, and Table 1, below.

The various transmission operating modes described in the table indicate which of the specific clutches C1, C2, C3, C4are engaged or actuated for each of the operating modes. Additionally, in various transmission operating modes, MA and MB may each operate as electrical motors to generate motive torque, or as a generator to generate electrical energy. A first mode, or gear train, is selected when the torque transfer device70is actuated in order to “ground” the outer gear member46of the third planetary gear set28. A second mode, or gear train, is selected when the torque transfer device70is released and the torque transfer device62is simultaneously actuated to connect the shaft60to the carrier52of the third planetary gear set28. Other factors outside the scope of the invention affect when MA and MB56,72operate as motors and generators, and are not discussed herein.

The control system, shown primarily inFIG. 2, is operable to provide a range of transmission output speeds, NO, of shaft64from relatively slow to relatively fast within each mode of operation. The combination of two modes with a slow-to-fast output speed range in each mode allows the transmission10to propel the vehicle from a stationary condition to highway speeds, and meet various other requirements as previously described. Additionally, the control system coordinates operation of the transmission10so as to allow synchronized shifts between the modes.

The first and second modes of operation refer to circumstances in which the transmission functions are controlled by one clutch, i.e. either clutch C162or C270, and by the controlled speed and torque of the electrical machines56and72, which can be referred to as a continuously variable mode. Certain ranges of operation are described below in which fixed ratios are achieved by applying an additional clutch. This additional clutch may be clutch C373or C475, as shown in the table, above.

When the additional clutch is applied, fixed ratio of input-to-output speed of the transmission, i.e. NI/NO, is achieved. The rotations of machines MA and MB56,72are dependent on internal rotation of the mechanism as defined by the clutching and proportional to the input speed, NI, determined or measured at shaft12. The machines MA and MB function as motors or generators. They are completely independent of engine-to-output power flow, thereby enabling both to be motors, both to function as generators, or any combination thereof. This allows, for instance, during operation in Fixed Ratio1that motive power output from the transmission at shaft64is provided by power from the engine and power from MA and MB, through planetary gear set28by accepting power from the energy storage device74.

The transmission operating mode can be switched between Fixed Ratio operation and continuously variable Mode operation by activating or deactivating one the additional clutches during Mode I or Mode II operation. Determination of operation in fixed ratio or mode control is by algorithms executed by the control system, and is outside the scope of this invention. The modes of operation may overlap the ratio of operation, and selection depends again on the driver's input and response of the vehicle to that input. RANGE1falls primarily within mode I operation when clutches C170and C475are engaged. RANGE2falls within mode I and mode II when clutches C262and C170are engaged. A third fixed ratio range is available primarily during mode II when clutches C262and C475are engaged, and a fourth fixed ratio range is available during mode II when clutches C262and C373are engaged. It is notable that ranges of operation for Mode I and Mode II typically overlap significantly.

Referring again toFIG. 1, and with reference now toFIG. 8, the electric machines MA and MB56,72are known three-phase AC electrical machines and the inverters comprise known complementary three-phase power electronics. MA and MB are coaxially oriented about the axially disposed shaft60. MA and MB are both of an annular configuration permitting them to circumscribe the three planetary gear sets24,26and28such that the planetary gear sets24,26and28are disposed radially inwardly of MA and MB. Each machine includes a stator, a rotor, and a resolver assembly80, shown also with reference toFIG. 8. The motor stator for each machine is grounded to outer transmission housing68, and includes a stator core with coiled electrical windings extending therefrom. The rotor for MA56is supported on a hub plate gear54that is operably attached to output shaft60via carrier36. The rotor for MB72is attached to sleeve shaft hub66. Each motor resolver assembly80is appropriately positioned and assembled on one of MA and MB, such that a notch88is oriented at magnetic, or true north. Each resolver assembly80of this embodiment comprises a known variable reluctance device including a resolver stator82, operably connected to the stator for each machine, and a resolver rotor84, operably connected to the rotor for each machine described above. Each resolver80comprises a sensing device operable to sense rotational position of the resolver stator relative to the resolver rotor, and identify the rotational position relative to notch88. Each resolver stator82comprises a series of inductive coils assembled thereon which receive an electrical excitation signal from the TPIM19, and a pair of sensing, or pickup, coils which provide an electrical signal output to the TPIM19. Each resolver rotor84comprises a rotating device having a plurality of lobes86, or eccentricities, located on the outer circumference. In the exemplary system shown inFIG. 8there are three lobes shown, but the system is operative using various quantities of lobes86. In operation, the resolver rotor84rotates with the motor rotor. The pickup coils are excited by the excitation signal and return a signal to the TPIM at the same frequency as the excitation frequency and having a voltage level that is dependent upon the proximity of the of the lobed resolver rotor84to the resolver stator82. The resolver80operates by sensing relative position and motion of the resolver rotor rotating within the resolver stator. The control system is able to interpret the signal returned through the resolver stator to determine rotor position, as is described herein. The variable reluctance device for the resolver80is one of several known technologies useable to determine position.

The invention, described with reference to the embodiment described above, comprises utilizing elements of the distributed control system to operate MA and MB, to provide motive torque and regenerative torque for the vehicle powertrain system. The overall control system operates the TPIM19to transmit electrical energy between the stator of each electrical machine and the ESD74. The TPIM operates to measure a position of the resolver rotor and hence the machine rotor, using the resolver stator device, measured relative to notch88of the rotor84, including known signal processing methods. The TPIM acts to derive a position of the machine rotor using a sensorless position sensing technique, described hereinbelow. The derived position of the machine rotor is a true position of the machine rotor. The TPIM determines an offset parameter, comprising an angular difference between the derived position of the machine rotor and the measured position of the resolver rotor. The TPIM operates to control electrical energy input to each of the coils of the stator for the three-phase multipole motor, using the offset parameter. The offset parameter is preferably stored in a non-volatile memory device within the TPIM or other element of the control system, for use in future operation. An alternative control system preferably includes an on-board algorithm that provides statistical analysis of a plurality of offset parameters calculated over subsequent starting events, using such known techniques as exponentially weighted moving averages. A parametric value for the offset is preferably determined once during each operation of the engine or vehicle. The control system preferably operates to derive the rotor position during initial machine operation, i.e. at engine startup or immediately thereafter. The control system is preferably operable to determine the offset parameter when the machine is operating in a motive torque-generative mode and when operating in an electrical energy-generative mode.

One exemplary method for sensorless position sensing comprises injecting a high frequency signal into the stator of the electrical machine at low operating speed, during initial machine operation; and, detecting a position of the rotor based upon the injected high frequency signal. This includes determining a north/south polarity of the resolver rotor prior to, or simultaneously with determining its position, in systems wherein this is necessary. The technique is described as below.

Referring now toFIGS. 3,4, and5, a diagrammatic drawing of an embodiment of the exemplary sensorless position sensing scheme110, for execution as a coded algorithm in the distributed control system described hereinabove, is now described. The position sensing scheme110is illustrated as a sequence of block diagrams that represent software executed in the distributed control system, to control one of electrical machines MA and MB56,72. Alternate embodiments of electric machines which may employ the control system described herein include motor technologies such as, synchronous reluctance motors, and interior permanent magnet motors. In operation, the HCP5generates input torque command TI, previously described. The torque command TIis processed by a torque linearization model114to generate a corresponding stator current Isrequired to develop the desired electromagnetic torque in the machine. The stator current generated at block114is then passed to an optimum torque per amp block116. Block116processes the commanded stator current and decomposes it into the respective D and Q axis components of current command (Idse1and Iqse) to provide the maximum torque for the given stator current amplitude.

The current command Idse1is added to a field weakening component Idse—fwgenerated at summing junction118to generate the final D axis current command Idse. The field weakening component Idse—fwis generated by a field weakening block120using the measured DC link voltage Vdc, commanded output voltages Vqssand Vdss, and rotor angular velocity ωr. Summing junction122subtracts the feedback current Iqse—fbfrom the Q axis current command Iqseto obtain the error of the Q axis current regulator. Summing junction124subtracts the feedback current from Idse—fbfrom the D axis current command Idseto obtain the error of the D axis current regulator. The errors generated by the summing junctions122and124are used by a synchronous current regulator block126to control the synchronous frame voltage commands Vdseand Vqse.

Block128uses the estimated rotor angular position θrto convert the synchronous frame voltage commands Vdseand Vqseto the stationary frame voltage commands Vdss1and Vqss1. The high frequency voltage signals Vdss—injand Vqss—injare added to the stationary reference frame voltage commands by the summing junctions130and132, resulting in the final voltage commands Vdssand Vqss. The voltage source inverter134processes the final voltage commands Vdssand Vqssto generate the actual phase voltages applied the motor56. The phase currents are measured and processed by a three-phase to two-phase transformation block136. The outputs of the block136are stationary frame currents Idssand Iqss. A stationary to rotating frame transformation block140uses the stationary frame currents Idssand Iqssand the estimated rotor angular position θrto generate synchronous reference frame feedback currents Idse—fband Iqse—fb.

The present invention includes sensorless control of the rotor speed and position that includes: a low speed rotor angular position estimation method/observer at block142; an initial rotor polarity detection method at block143, when needed; a high speed rotor angular position estimation method/observer at block144; and a transition algorithm at block146to seamlessly merge the low and high speed estimation methods, when the high speed rotor angular position estimation method is utilized.

Block142ofFIG. 3represents the low speed estimation method of the present invention.FIG. 4shows a detailed block diagram implementation of block142to estimate rotor electrical position during low-speed operations as described above. The low speed estimation method is used to estimate rotor electrical position during zero and low-speed operations (preferably <10% of rated machine speed but any machine speed is considered within the scope of the low speed estimation method of the present invention). The estimation of the rotor electrical position is performed by injecting a high frequency voltage signal on an estimated D axis of the machine. The fluctuating high frequency signal in a synchronously rotating reference frame with the fundamental stator frequency is used to detect an asymmetry of the spatial impedance in an AC machine. An asymmetry of the spatial impedance is caused by salient construction of the rotor of the machine or induced magnetic saturation in the machine.

When the high frequency voltage signal is injected on the estimated D axis, the orthogonal component of the current measured at the estimated reference frame can be used as an error signal as shown by Eq. 1.

wherein yavg=(zqe+zde)/2zdezqeand ydiff=(zqe−zde/2zdezqe. If the voltage signal is injected on the estimated D-axis (vdsim=Vinjsin ωht and vqsim=0) then in the Q-axis current signal the diagonal component disappears and the off-diagonal component appears as shown in Eq. 2. If resistive components are much smaller than inductive components (rde, rqe<<xde, xqe) at the high frequency and also the impedance difference of the reactive component is much larger than that of the resistive component (|xde−xqe|>>|rde−rqe|), then Eq. 2 can be simplified as shown in Eq. 3 in quasi-steady-state.

Multiplying the orthogonal signal with respect to the injected signal results in the DC quantity of the error signal for the tracking controller. After low-pass filtering the DC quantity can be obtained as shown in Eq. 4:

Referring toFIG. 4, block150converts the stationary frame currents Iqssand Idssto the estimated synchronous reference frame current Iqsm. Block152comprises a second order band pass filter to allow only the injection high frequency signal (preferably in the range 500 to 1000 Hz) to be processed at multiplying junction154. Junction154multiplies the output of the BPF of block152by the term −cos(ωinjt) to extract the DC component of the error signal. Block156comprises a second order low pass filter to remove high frequency harmonics from the signal and output the term Iqm. Iqmis an error signal defined in Eq. 4.

Block158is a third order position observer that processes the error term Iqm. Iqmis processed by proportional control block160, integral control block162, and feed-forward control block164to generate outputs. The integral and proportional outputs of blocks160and162are summed at summing junction166and processed by block168to generate and estimate speed ωr—low. The output of the feed-forward gain block164is processed by a limiter block170and then fed-forward to summing junction172to be added to the speed output of block168. Block174processes ωr—lowto generate the term θr—lowwhich is the estimated angular position of the rotor at low speed.

FIG. 5is a detailed block diagram implementation of the block143used to detect initial rotor magnet polarity, for north/south polarity determination. The stationary to rotating reference frame block180converts the stationary frame currents Idssand Iqssto the synchronous reference frame currents Idseand Iqseusing θr. Only the D axis current Idseis used in the initial rotor polarity detection method. Idseis passed through a band-pass filter182which filters out all but the second harmonic of the injection frequency of the Idsecurrent. The output of the band-pass filter182is Idse—bp. The signal Idse—bpis demodulated by multiplying it with the term sin(2ωinjt−φ) using the multiplier block184. The resultant signal Id1contains a DC component and a high frequency component. The low-pass filter block186filters out the high frequency component of Id1, leaving only the DC portion Id. The signal Idcontains the information on the polarity of the rotor magnet with respect to the estimated machine D axis. Condition block188determines the polarity of the estimated position using the sign of the signal Id. This condition is evaluated once during the start-up sequence. If the sign of Idis negative, 180 degrees is added to the estimated rotor position.

Referring now toFIG. 6, an algorithm, executed in the control system to control the exemplary powertrain shown with reference toFIGS. 1 and 2, is described which implements the exemplary method for sensorless position sensing described hereinabove with reference toFIGS. 3,4, and5. The method comprises injecting a high frequency signal into the stator at low operating speed during initial machine operation to detect position of the rotor based upon the injected high frequency signal. The algorithm includes measuring the resolver position using the resolver sensor (S1). When the rotational speed is greater than a calibrated maximum (nmax), (S2) a previously stored offset value is used by the control system, or alternatively, the algorithm waits until the speed drops below the calibrated maximum (nmax) (S3′). When the rotational speed is less than the calibrated maximum (nmax) switching is enabled (S3), the high frequency (‘HF’) signal is injected, and estimation of the rotor electrical position is performed (S4). The system converges on a value (S5), and the offset is computed (S6). The offset is validated, and filtered (S7), and the high frequency injection and estimation is disabled for the remainder of the operating cycle (S8). The powertrain system operates (S9) using the resolver sensor position and the learned offset. At shutdown, the data is stored in a non-volatile memory storage device of the control system, such as one of the electrically programmable read only memory (EPROM) devices of one of the controllers.

Referring now toFIG. 7, data for the exemplary system is shown. The plotted data comprises a plot of magnitude of resolver error, in electrical degrees. Line A is a representation of the actual resolver error, in this instance comprising a worst-case error created during system assembly, having a magnitude of ten degrees electrical rotation. The data points shown as C in the plot comprise raw algorithm learn values for resolver position, corrected using the invention described herein. In all instances, the magnitude of error of the corrected resolver position is less than two degrees electrical rotation. Line B comprises a filtered, or statistically analyzed resolver learn value, which has an initial offset of ten degrees electrical rotation, which converges to less than two degrees after forty observations, and converges to near zero after eighty observations, thus demonstrating the capability of the method described herein to learn and correct for resolver error.

The invention has been described with specific reference to the preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention.