Absolute position sensor for field-oriented control of an induction motor

Systems and methods are provided for an automotive drive system using an absolute position sensor for field-oriented control of an induction motor. An automotive drive system comprises an induction motor having a rotor, and a position sensor coupled to the induction motor. The position sensor is configured to sense an absolute angular position of the rotor. A processor may be coupled to the position sensor and configured to determine a relative angular position of the rotor based on a difference between the absolute angular position and an initial angular position obtained when the induction motor is started. A controller may be coupled to the induction motor and the processor and configured to provide field-oriented control of the induction motor based on the relative angular position of the rotor.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally to vehicle drive systems, and more particularly, embodiments of the subject matter relate to absolute position sensing for field-oriented control of induction motors.

BACKGROUND

In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the power usage and complexity of the various electrical systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles. Many of these vehicles use electric motors to provide traction power to the vehicle.

For induction motors, the speed of the rotor and the speed of the rotating magnetic field in the stator must be different, a concept known as slip, in order to induce current. In order to operate the induction motor at its highest efficiency, the slip is controlled using feedback control loops. In conventional control systems, as the rotor speed increases, the rotor approaches a base speed (or rated speed), where the voltage across the motor terminals reaches a value at which no more current can be provided to the motor. In order to operate the motor at higher speeds than the base speed, a technique known as flux weakening, controlled by non-torque generating current is employed.

Accordingly, field-oriented control methods have been developed to control the torque generating current supplied to the induction motor separately from the non-torque generating current. These methods use the relative position and speed of the rotor to maintain a desired relationship between the stator flux and rotor flux. The non-torque generating current is adjusted based on the speed of the rotor and the flux characteristics of the induction motor. By compensating for the undesired flux, field-oriented control can be used to improve efficiency, the motor transient response, and tracking of the torque command at speeds higher than the base speed. As a result of the improved performance, induction motors and drive systems may be appropriately sized for an application, thereby lowering cost and improving overall efficiency.

Most field-oriented control methods for induction motors utilize incremental encoders to measure the relative position and speed of the rotor. Typically, these encoders are either magnetic or optical. For automotive environments, packaging space is often at a premium and the encoders are often exposed to demanding environmental conditions. For example, the operating temperature may range from −40° C. to 150° C., which exceeds the operating temperature ratings for most optical encoders. While magnetic encoders may be able to tolerate automotive temperatures, they often cannot sustain operation when exposed to vibration forces and frequencies encountered in automotive applications. Furthermore, in order to achieve high-levels of accuracy, magnetic encoders must be implemented in a large physical size, which is undesirable from a packaging and automotive design perspective.

BRIEF SUMMARY

An apparatus is provided for an automotive drive system. The automotive drive system comprises an induction motor having a rotor, and a position sensor coupled to the induction motor. The position sensor is configured to sense the absolute angular position of the rotor. A processor may be coupled to the position sensor and configured to determine the relative angular position of the rotor based on a difference between the absolute angular position and an initial angular position obtained when the induction motor is started. A controller may be coupled to the induction motor and the processor and configured to provide field-oriented control of the induction motor based on the relative angular position of the rotor.

An apparatus is provided for a drive system for use in a vehicle. The drive system comprises an induction motor having a rotor, and a position sensor integrated with the induction motor. The position sensor is configured to sense the absolute angular position of the rotor. The position sensor may further comprise a resolver having a resolver rotor coupled to a shaft of the induction motor, and a resolver stator coupled to the induction motor.

A method is provided for controlling an induction motor. The method comprises obtaining an initial angular position of the rotor using an absolute position sensor, wherein the initial angular position of the rotor is obtained when the induction motor is started. The method further comprises obtaining a subsequent angular position of the rotor using the absolute position sensor. The method comprises determining a relative angular position of the rotor based on the initial angular position and the subsequent angular position, and determining a magnetizing current command based on the relative angular position.

DETAILED DESCRIPTION

The following description refers to elements or nodes or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element/node/feature is directly joined to (or directly communicates with) another element/node/feature, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element/node/feature is directly or indirectly joined to (or directly or indirectly communicates with) another element/node/feature, and not necessarily mechanically. Thus, although the schematics shown herein depict exemplary arrangements of elements, additional intervening elements, devices, features, or components may be present in an embodiment of the depicted subject matter. Furthermore, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.

Technologies and concepts discussed herein relate to systems and methods for implementing field-oriented control of induction motors using absolute position sensors. Field-oriented control involves separate current control loops for the torque generating current and the non-torque generating current supplied to the induction motor. The relative position and speed of the rotor is used to maintain a desired relationship between the stator flux and rotor flux to improve motor efficiency, as described in greater detail below. As used herein, subscripts d and q are quantities in the Cartesian frame of reference synchronous with the rotation of a rotor within an induction motor, where the q axis (or quadrature axis) is orthogonal to the rotor pole axis (i.e., torque generating) and the d axis (or direct axis) is parallel to the rotor pole axis (i.e., non-torque generating).

FIG. 1illustrates a vehicle, or automobile100, in accordance with one embodiment, which includes an induction motor102, an energy source104, an inverter assembly106, an electronic control system108, and a drive shaft110. In an exemplary embodiment, the energy source104is in operable communication and/or electrically coupled to the electronic control system108and the inverter assembly106. The inverter assembly106is coupled to the induction motor102, which in turn is coupled to the drive shaft110. The inverter assembly106is in operable communication and/or electrically coupled to the electronic control system108and is configured to provide electrical energy and/or power from the energy source104to the induction motor102as discussed in greater detail below.

Depending on the embodiment, the automobile100may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD). The automobile100may also incorporate any one of, or combination of, a number of different types of engines, such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and alcohol), a fuel cell vehicle engine, a gaseous compound (e.g., hydrogen and natural gas) fueled engine, a combustion/electric motor hybrid engine, or an electric motor.

In the exemplary embodiment illustrated inFIG. 1, the induction motor102may comprise a generator, a traction motor, or another suitable motor known in the art. In an exemplary embodiment, the induction motor102is a multi-phase alternating current (AC) motor and includes a set of windings (or coils), wherein each winding corresponds to one phase of the induction motor102. Although not illustrated inFIG. 1, the induction motor102includes a stator assembly (or stator), and a rotor assembly (or rotor), as will be appreciated by one skilled in the art. In an exemplary embodiment, the induction motor102may also include a transmission integrated therein such that the induction motor102and the transmission are mechanically coupled to at least some of the wheels through one or more drive shafts110.

Depending on the embodiment, the energy source104may comprise a battery, a fuel cell, or another suitable voltage source. It should be understood that althoughFIG. 1depicts an automobile100having one energy source104, the principles and subject matter discussed herein are independent of the number or type of energy source, and apply to vehicles having any number of energy sources.

In an exemplary embodiment, the inverter assembly106includes one or more inverters, each including switches (e.g., semiconductor devices, such as transistors and/or switches) with antiparallel diodes (i.e., antiparallel to each switch), with windings of the induction motor102electrically connected between the switches to provide voltage and create torque in the induction motor102, as will be understood in the art. The electronic control system108is in operable communication and/or electrically connected to the inverter assembly106. Although not shown in detail, the electronic control system108includes various sensors and automotive control modules, or electronic control units (ECUs), such as an inverter control module for controlling the inverter assembly106, and may further include a processor and/or a memory which includes instructions stored thereon (or in another computer-readable medium) for carrying out the processes and methods as described below.

In accordance with one embodiment, the electronic control system108is responsive to commands received from the driver of the automobile100(i.e. via an accelerator pedal) and provides commands to the inverter assembly106to utilize high frequency pulse width modulation (PWM) to manage the voltage provided to the induction motor102by the inverter assembly106, as will be understood. In an exemplary embodiment, the electronic control system108implements a field-oriented control loop to operate the inverter assembly106and improve the efficiency and performance of the induction motor102, as described in greater detail below.

Referring now toFIG. 2, in an exemplary embodiment, an induction motor control system200includes, without limitation, an induction motor102, an energy source104, a controller202, an inverter204, an absolute position sensor206, and a processor208. Some elements ofFIG. 2are similar to their counterpart elements described above in reference toFIG. 1, and such description will not be redundantly repeated in the context ofFIG. 2. The induction motor control system200may be configured to utilize field-oriented control to regulate the induction motor102based on the rotor position, as described in greater detail below. For example, the induction motor control system200may be configured to implement field-oriented control methods, such as those disclosed in U.S. Pat. No. 6,222,335 entitled “METHOD OF CONTROLLING A VOLTAGE-FED INDUCTION MACHINE”, assigned to the assignee of the present invention and incorporated by reference herein, which discloses an exemplary method for implementing field-oriented control based on relative position of a rotor for an induction motor.

Referring again toFIG. 2, in an exemplary embodiment, the energy source104is coupled to the inverter204, which in turn is coupled to the induction motor102. The absolute position sensor206is coupled to the induction motor102. The processor208is coupled between the output of the absolute position sensor206and the controller202. The controller202is coupled to the inverter204, and is configured to provide duty cycle commands to the inverter204. In an exemplary embodiment, the controller202is further coupled to the output of the inverter204and the output of the processor208to create a feedback control loop for implementing field-oriented control as discussed in greater detail below. The three lines between the inverter204and the induction motor102indicate that the induction motor102and the inverter204have three phases, although the subject matter described herein is not limited to a three-phase implementation, and applies to inverters204and induction motors102having any number of phases, as will be appreciated in the art.

In an exemplary embodiment, the absolute position sensor206provides information or signals representative of the absolute angular position of the rotor. The absolute position sensor206may be configured to sense or measure the absolute angular position of the rotor of the induction motor102relative to the stator or some other fixed reference point based on the positioning of the absolute position sensor206. In an exemplary embodiment, the absolute position sensor206is a resolver, although other suitable means for sensing absolute angular position may be used in alternative embodiments. In an exemplary embodiment, a resolver having two pole pairs (e.g., two-pole resolver) is used. In alternative embodiments, multipole resolvers may be used, however, multipole resolvers are generally more costly and require additional mathematical computations to be implemented, which are known in the art and beyond the scope of this disclosure. The resolver is capable of producing accurate position information even while being packaged and designed for compact size. Additionally, resolvers are highly durable and can sustain reliable and accurate operation in the presence of demanding environmental conditions (e.g., automotive temperature and vibration levels).

In an exemplary embodiment, the processor208is coupled to the absolute position sensor206and is configured to convert the signals (analog signals in the case of a resolver) or measurements from the absolute position sensor206to a digital representation (e.g., digital word). The processor208may be a resolver-to-digital converter or another suitable means for processing signals from the absolute position sensor206. The processor208may be configured to perform additional tasks and functions, as described in greater detail below.

In an exemplary embodiment, the induction motor control system200may further include a current calculator210. In an exemplary embodiment, the output of the current calculator210is coupled to an input of the controller202, and the current calculator210is configured to provide a torque producing current command (iq*) to the controller202. The current calculator210may determine the torque producing current command in response to a torque command (Te*) (e.g., provided by the electronic control system108), an estimated rotor flux (Φr), and a commanded rotor flux (Φr*), as described in greater detail below.

In an exemplary embodiment, the controller202is configured to control the voltage provided by the energy source104to the induction motor102by utilizing PWM techniques to regulate the output of the inverter204, as will be understood. The controller202is configured to utilize information regarding the relative position of the rotor of the induction motor102to implement field-oriented control. In an exemplary embodiment, the controller202may further include, without limitation, a speed observer212, a flux reference table214, a magnetizing current estimator216, a synchronous frame current regulator218, a stationary coordinate transformer220, a space vector modulator222, a synchronous coordinate transformer224, a flux estimator and slip angle calculator226, and an adder228. These and other elements may be coupled together to implement field-oriented control of the induction motor102based on the relative rotor position, as described in greater detail below.

Referring now toFIG. 3, in an exemplary embodiment, the induction motor control system200may be configured to perform an induction motor control process300and additional tasks, functions, and operations described below. The various tasks may be performed by software, hardware, firmware, or any combination thereof. For illustrative purposes, the following description may refer to elements mentioned above in connection withFIGS. 1-2. In practice, the tasks, functions, and operations may be performed by different elements of the described system, such as the electronic control system108, controller202or the processor208. It should be appreciated any number of additional or alternative tasks may be included, and may be incorporated into a more comprehensive procedure or process having additional functionality not described in detail herein.

Referring again toFIG. 3, and with continued reference toFIG. 1andFIG. 2, in an exemplary embodiment, the induction motor control process300may be configured to initialize when the induction motor102is started. In an exemplary embodiment, the absolute position sensor206obtains an initial angular position of the rotor when the induction motor102is started (task302). The induction motor control process300may be configured to store the initial angular position (task304). For example, the processor208may be configured to store or maintain the initial angular position in memory. The absolute position sensor206obtains a subsequent angular position of the rotor during operation of the induction motor102as the rotor rotates (task306).

In an exemplary embodiment, the induction motor control process300is configured to determine the relative angular position (θr) of the rotor based on the absolute angular position (task308). The induction motor control process300may determine a relative angular position of the rotor based on a difference between the subsequent angular position and the initial angular position. For example, the processor208may be configured to store the initial angular position of the rotor as an offset, and subtract the initial angular position from each subsequent angular position measurement to produce a relative angular position (e.g., relative to the initial angular position or angular position at startup). In alternative embodiments, the controller202may be configured to receive the absolute angular position and determine the relative angular position. In an exemplary embodiment, the induction motor control process300is configured to provide the relative angular position to a field-oriented control system (e.g., controller202). For example, the output of the processor208may be coupled to an input of the controller202.

In an exemplary embodiment, the induction motor control process300is configured to determine the speed of the rotor (ωr) based on the relative position (task310). For example, the processor208may coupled to and/or provide the relative rotor position information to the speed observer212. The speed observer212may be configured to determine the rotor speed by differentiating the relative rotor position with respect to time. In an exemplary embodiment, the induction motor control process300utilizes the rotor speed to determine a magnetizing current command (id*) to compensate for transient changes in rotor flux based on the rotor speed (task312). For example, the speed observer212may provide the rotor speed to the input of the flux reference table214, which obtains a rotor flux command (Φr*) In accordance with one embodiment, the flux reference table214is a lookup table containing predetermined rotor flux commands (Φr*) based on the rotor speed (ωr), the voltage of the energy source104(VDC), and the flux characteristics of the induction motor102. The output of the flux reference table214may be provided to the magnetizing current estimator216, which is configured to determine the magnetizing current command (id*) to produce the desired rotor flux based on the rotor flux command (Φr*).

In an exemplary embodiment, the induction motor control process300is configured to determine a duty cycle for inverter204based on the relative position of the rotor and the synchronous frame current commands (id*,iq*) (task314). The synchronous frame current regulator218may be coupled to the current calculator210and the magnetizing current estimator216, such that it receives the synchronous frame current commands (id*,iq*). The synchronous frame current regulator218may be coupled to the output of the synchronous coordinate transformer224. The synchronous coordinate transformer224is coupled to the output of the inverter204and configured to measure (or sense) the current in the induction motor102. The synchronous coordinate transformer224performs a coordinate transformation to obtain the value of the measured currents in the synchronous reference frame (id,iq) and provides the measured currents to the synchronous frame current regulator218. The synchronous frame current regulator218is configured to determine synchronous frame duty cycles (dd*,dq*) such that the measured currents (id,iq) track the current commands (id*,iq*).

In an exemplary embodiment, the stationary coordinate transformer220is coupled to the output of the synchronous frame current regulator218and the output of the adder228. The adder228is coupled to the flux estimator and slip angle calculator226, which is configured to receive as inputs the measured current (id,iq) commanded current (id*,iq*), and the rotor flux command (Φr*) and from those inputs determine an estimated rotor flux (Φr) and an optimized slip angle (θslip), as will be appreciated in the art. The adder228is also configured to receive the relative rotor position (θr) and add the relative rotor position and the slip angle (θslip) to produce a transformation angle (θt). In an exemplary embodiment, the stationary coordinate transformer220is configured to convert the synchronous frame duty cycle commands (dd*,dq*) to the stationary frame (dα,dβ) based on the transformation angle (θt). In an exemplary embodiment, the output of the stationary coordinate transformer220is coupled to the input of the space vector modulator222. The space vector modulator222is configured to determine operative duty cycle commands for the switches of the inverter204based on the stationary frame duty cycle commands, such that the inverter204utilizes PWM modulation to provide voltage from the energy source104to operate the induction motor102as desired. In an exemplary embodiment, the loop defined by task306, task308, task310, task312, and task314repeats indefinitely during operation of the induction motor102.

Referring now toFIG. 4, in an exemplary embodiment, an induction motor automotive drive system400includes, without limitation, an induction motor102integrated with an absolute position sensor206.FIG. 4illustrates a cross-sectional view of the induction motor drive system400taken down a center of a rotating shaft. The induction motor102comprises a shaft402concentric with a rotor404encased in a housing406. In an exemplary embodiment, the absolute position sensor206is a resolver having a resolver rotor408and a resolver stator410.

In an exemplary embodiment, the shaft402is mechanically coupled to the rotor404, such that the shaft402rotates synchronously with the rotor404. In an exemplary embodiment, the shaft402has length such that a portion of the shaft402extends beyond the rotor404and through a gap in the housing406. The resolver rotor408is mechanically coupled to the shaft402(e.g., by bolting the resolver rotor408to the shaft402). In an exemplary embodiment, the shaft402is concentric with the resolver rotor408. The resolver stator410may be mechanically coupled to the housing406and concentric with the resolver rotor408. The resolver stator410is configured to sense the absolute angular position of the rotor404based on the angular position of the resolver rotor408, which tracks the angular position of the rotor404via the mechanical coupling to the shaft402, as will be understood in the art.

The systems and/or methods described above provide a field-oriented control system for induction motors using absolute position sensors. Because field-oriented control systems for induction motors are designed for incremental or relative position measurements, implementing an absolute position sensor (such as a resolver) is more complex than using an incremental encoder. However, the space savings exceed the additional implementation costs. Additionally, resolvers are durable can be reliably used in demanding environments where incremental encoders are less reliable. As described above, the performance of the motor is not impaired and the field-oriented control of the induction motor may be achieved without modifying existing control systems, even though a relative position sensor is not used.

Other embodiments may utilize system and method described above in different types of automobiles, different vehicles (e.g., watercraft and aircraft), or in different electrical systems altogether, as it may be implemented in any situation where an induction motor is operated using field-oriented control. Further, the motor and the inverters may have different numbers of phases, and the systems described herein should not be construed as limited to a three-phase design. The basic principles discussed herein may be extended to higher-order phase systems as will be understood in the art.