Patent Application
20190235025
The subject matter disclosed herein generally relates to a motors and motor control and, more particularly, to detecting faults in three-phase sine drive motors and the wiring connected to them.
Aircraft systems commonly include a variety of motor controlled systems. For example, actuation systems for control surfaces, aircraft components environmental control systems and the like. In some systems, such as actuation systems for control surfaces, detection of motor faults, or interconnect wiring faults, is very important to the proper operation of the system in the aircraft.
Conventional methods for detection of motor wiring faults have classically been limited to a non-real-time test signal injection, and phase-by-phase continuity checks, or limited, real-time, current monitoring, and summation (for a three-phase motor, the three phase currents should add to zero). While the phase-by-phase continuity check can be very thorough, it cannot be performed under operational conditions such as when a motor is being commanded in flight. The current sum monitor can be performed in flight, however, its fault detection capability is limited (i.e., phase-to-phase shorts and singular open phases cannot be detected).
Accordingly for at least the above discussed reasons, as well as others, there is a desire to provide improved control and fault detection methods for motors.
According to one embodiment described herein is a method of detecting a fault in a sinusoidally driven or field oriented controlled (FOC) permanent magnet synchronous motor (PMSM). The method includes receiving a first rotor reference frame current demand, the first rotor reference frame current demand based on a current control for the PMSM and receiving a first rotor reference frame current feedback, the first rotor reference frame current feedback corresponding to the first rotor reference frame current demand received. The method also includes computing a first error of the rotor reference frame current based on the first rotor reference frame current demand and the first rotor reference frame current feedback and identifying a fault of the sinusoidally controlled PMSM if the first error exceeds a first selected threshold for a first selected duration.
In addition to one or more of the features described above, or as an alternative, further embodiments may include receiving a second rotor reference frame current demand, the second rotor reference frame current demand based on a current control for the PMSM, receiving a second rotor reference frame current feedback, the second rotor reference frame current feedback corresponding to the second rotor reference frame current demand received, computing a second error of the rotor reference frame current based on the second rotor reference frame current demand and the second rotor reference frame current feedback and identifying a fault of the sinusoidally driven PMSM if the second error exceeds a second selected threshold for a second selected duration.
In addition to one or more of the features described above, or as an alternative, further embodiments may include identifying a fault of the sinusoidally driven PMSM if the second error exceeds a second selected threshold for a second selected duration.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first rotor reference frame current demand is the quadrature axis current (Iq).
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second rotor reference frame current demand is the direct axis current (Id).
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first selected threshold is based on at least the first rotor reference frame current demand.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first selected threshold is based on a magnitude of the first rotor reference frame current demand.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first selected duration is based on at least a characteristic of at least one component of a control system operably connected to the PMSM.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first selected duration is based on a dynamic characteristic of the PMSM.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second selected threshold is based on at least the second rotor reference frame current demand.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second selected threshold is based on a magnitude of the second rotor reference frame current demand.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second selected duration is based on a characteristic of at least one component of a control system operably connected to the PMSM.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the second selected threshold is based on a dynamic characteristic of the PMSM.
In addition to one or more of the features described above, or as an alternative, further embodiments may include controlling the PMSM based on the identifying of a fault of the sinusoidally driven PMSM.
Also described herein in an embodiment is a system for detecting a fault in a sinusoidally driven permanent magnet synchronous motor (PMSM). The system includes a sinusoidally driven PMSM and a controller operably connected to the PMSM. The controller is configured to receive a first rotor reference frame current demand, the first rotor reference frame current demand based on a current control for the PMSM, and receive a first rotor reference frame current feedback, the first rotor reference frame current feedback corresponding to the first rotor reference frame current demand received. The controller is also configured to compute a first error of the rotor reference frame current based on the first rotor reference frame current demand and the first rotor reference frame current feedback and identify a fault of the sinusoidally driven PMSM if the first error exceeds a first selected threshold for a first selected duration.
Also described herein in and embodiment is motor drive system configured for detecting a fault in a sinusoidally driven permanent magnet synchronous motor (PMSM). The system including an excitation source, a drive system operably connected to the excitation source and configured to provide motor command signals to the PMSM, and a controller operably connected to the PMSM. The controller is configured to receive a first rotor reference frame current demand, the first rotor reference frame current demand based on a current control for the PMSM and receive a first rotor reference frame current feedback, the first rotor reference frame current feedback corresponding to the first rotor reference frame current demand received. The controller is also configured to compute a first error of the rotor reference frame current based on the first rotor reference frame current demand and the first rotor reference frame current feedback and identify a fault of the sinusoidally driven PMSM if the first error exceeds a first selected threshold for a first selected duration.
The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. It should be understood, however, that the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.
The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Faults in an electric machine can occur for numerous reasons, including mechanical vibration, thermal cycling, thermal shock, manufacturing defects and improper maintenance. Applications of permanent magnet synchronous machines (PMSMs) are proliferating due to power density, efficiency gains, and simplicity in control algorithms. Field Oriented Control (FOC) is one control algorithm applied towards the control of PMSMs due to simplicity. However even with FOC some faults can impact performance, result in reductions in torque or force, or m some instances complete loss of functionality. Some typical faults that can occur in a PMSM drive system include winding failures, open circuits in the motor windings or wiring harness, short circuits of the motor windings internally, to each other, or to ground, and mechanical faults. A winding short in a rotating PMSM can result in induced voltages generating a current flow in a low resistance path. Currents beyond the rated current for the winding can then circulate in the loop of the conductor even at low speeds due to low resistance. Exceeding the rated current of the winding can cause overheating of the machine and can lead to potentially harmful circumstances. The rapid detection of such a winding fault will prevent damage to the machine, the drive electronics, and other equipment.
Embodiments described herein are directed to a monitoring mechanism and methodology that can detect motor phase open circuits and short circuits to ground. In one embodiment, the methods can also detect difficult to detect phase-to-phase short circuits within the motor windings or harness wiring. The described embodiments leverage the fact that the motor winding faults, under most conditions, result in larger than normal errors between commanded and actual quadrature current (Iq) and direct (Id) current feedback signals. The described embodiments incorporate a fault detection mechanism with a time based persistence on the Iq and Id error. Thus, providing the ability to detect motor winding faults while operating or even commanded to stop and thereby facilitating enhanced failure/fault detection capability in operation, and particularly flight operations).
For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended. The following description is merely illustrative in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term controller refers to processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, an electronic processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable interfaces and components that provide the described functionality.
Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms “a plurality” are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term “connection” can include an indirect “connection” and a direct “connection”.
The illustrated drive 20 also includes an inverter 50 to convert the DC voltage on the DC bus 34 to multiphase, AC drive motor command signals 15. Motor command signals 15 from the inverter 50 of the drive system 20 are supplied to a multiphase machine 14. For example, a motor 16 to impart motion to a control surface, power an environmental control system, and the like. In an exemplary embodiment, machine 14 includes, but is not limited to a multiphase, permanent magnet synchronous motor 16. It should also be appreciated, that while the embodiments herein are described primarily with reference to an aircraft electrical system and application, this description is for example only. The embodiments described here are readily applied to any application employing a three phase drive with a multiphase phase sine drive motor power application including motor controls, environmental control, control surface actuation, and any other power system and motor control application.
According to one or more embodiments, both rectifier/converter 30 (if an active type) and inverter 50, are controlled by a controller 60. In an alternative embodiment, converter 30 and inverter 50 may be controlled by separate drive controllers, 60. As stated above controller(s) 60 provides control signals 62 and in to the switching devices of the inverter 50 to control generation of the of the motor command signals 15. Likewise the controller 60 may provide control signals 62 to the active rectifier or converter 30 to control generation and maintenance of the DC voltage on the DC bus 34. Drive controller 60 may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, drive controller 60 may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software.
In operation, in embodiments employing an active converter 30, the controller 60 develops a DC current command for the converter 30 based on the operation the motor 16 and the inverter 50 generating the motor command signals 15. The DC current command is then employed to formulate the PWM control commands 62 for the switching devices (not shown) of the converter 30 to provide a DC output current to the DC bus 34 accordingly. In addition, the controller 60 receives various input signals or values, including set point signals or values for desired output operation, such as DC bus voltage, motor speed, position, torque, etc., as well as feedback signals or values representing operational values of various portions of the motor drive 20. In another embodiment, a passive rectifier configuration for the converter 30 is employed and no PWM commands from the controller 60 are needed. While such a configuration is advantageous because of its simplicity for employing passive rectifiers to supply the DC bus 34, other configurations with an active converter 30 may be desirable for improved current and electromagnetic interference (EMI) control. Likewise, the controller 60 develops a command for the inverter 50 based on the operation the motor 16 e.g., speed, torque, and the like and the inverter 50 generating the motor command signals 15. The command is then employed to formulate the PWM control commands 64 for the switching devices of the inverter 50 to formulate the motor command signals 15 accordingly.
Conventionally a pulse width modulation (PWM) control scheme is employed to command the switching devices of the converter 30 to supply the DC bus and the inverter 50 to generate and control the motor command signals 15 to the motor 16. Conventionally, such a PWM control scheme employs space vector pulse width modulation SVPWM techniques. Moreover, conventionally the SVPWM for the converter 30 (if active) and inverter 50 would be operated at the same frequency and synchronized. Synchronization of the PWM for both the converter 30 and the inverter 50 improves functions and reduces generated EMI from the operation of the switching devices of the converter 30 and inverter 50).
However, in some applications, other PWM techniques may be employed to address the advantages and constraints imposed by the construction or particular implementation of the converter 30 or inverter 50. For example, conventional discontinuous (DPWM) or even hybrid SVPWM techniques. Hybrid SVPWM is effectively a combination or hybrid of SVPWM and DPWM techniques. Moreover, while it is well known that increasing switching frequency facilitates reductions in the size of magnetics, filters, improves acoustics, and the like, though it does result in increased switching losses in the switching devices for the converter 30 or for the switching devices of the inverter 50. Therefore, in some embodiments, particularly where an active converter 30 is employed it may be advantageous to operate the converter 30 at a different PWM frequency than those of the inverter 50 or with a different PWM scheme than the inverter 50. However, increased operating frequencies also results in increased switching losses in the switching devices reducing efficiency and potentially causing the switching devices to overheat. As a result, while SVPWM is effective for most applications though it is less efficient, employing conventional discontinuous (DPWM) or hybrid SVPWM improves efficiency. Conversely, DPWM or hybrid SVPWM in applications where emitter side current sensing is employed makes current sensing more difficult. Therefore, employing DPWM, or a hybrid SVPWM results improved efficiency at the expense of current sensing quality. Finally, for the inverter 50, in applications where torque/current control are important, low current distortion (and thereby low torque ripple) is commonly desired. As such, continuous SVPWM or hybrid SVPWM techniques are conventionally employed to ensure good motor response. In the embodiments as described herein conventional SVPWM techniques are employed.
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The motor 16, in one embodiment, is a permanent magnet motor that operates using the voltages provided by the inverter 50. The motor 16 in a rotary configuration, includes a rotor with magnets embedded in or connected to the rotor. The motor 16 also includes a stator with multiple teeth around which conductive windings are wound. The windings are selectively energized and de-energized based on the signals from the inverter 50, which creates a rotating magnetic field that causes the rotor to rotate. The motor 16 drives a machine 14. The motor 16 can drive the machine 14 with, for example, a drive shaft and one or more gears. Likewise, in linear applications the stator is linearly arranged once again selectively energized and de-energized based on signals from the inverter 50, which causes a translation of forces that moves the secondary.
The position control function 110, velocity control function 120 and current control function 130, the rotor reference frame voltage to phase voltage transformation unit 140, and the PWM generation unit 160 together control the operation of the inverter 50 to thereby control the operation of the motor 16. For example, the PWM generation unit 160 generates PWM signals that drive the transistor switches in the inverter 50. By controlling the duty cycles of the PWM signals, the PWM generation unit 160 controls the three-phase voltages provided by the inverter 50 to the motor 16. For example, in one embodiment, the velocity control function may receive as input a commanded speed signal, which identifies a desired speed of the motor 16. The velocity control function 120 receives as feedback measured or estimated motor speed, optionally rotor position, or other characteristic(s) of the motor 16. The PWM generator 160 uses the inputs to generate PWM signals for driving the transistor switches in the inverter 50.
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In an embodiment, the system 10 also includes a fault detection function 214. The fault determination function 138 detects an existence of a fault in the permanent magnet motor 16 by executing a detection algorithm based on a rotor reference frame current errors 128,129 due to machine imbalance caused by the fault. Advantageously, because the detection is based on the characteristics of the motor rotor reference frame currents, and more specifically the errors, the detection of faults can be made essentially real-time, while the motor 16 is under command and operating. For example, for control purposes, an electric machine e.g., motor 16 is conventionally considered a balanced three phase machine. That is, the total current entering and leaving the phase windings of the motor 16 must sum to zero. An FOC algorithm relies on a balanced machine that is controlled with a balanced set of three phase currents.
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The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The present embodiments may be a system, a method, and/or a computer program product at any possible technical detail level of integration. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.
The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.
