The invention relates to motor control current sensor loss of assist mitigation for electric power steering (EPS).
EPS systems require the electric motor used to provide steering assist to be operated using a method of torque control. When using a Permanent Magnet Synchronous Machine (PMSM), Field Oriented Control (FOC) is utilized to allow the alternating current (AC) three-phase motor voltage and current signals to be transformed into a synchronously rotating reference frame, commonly referred to as the d/q axis reference frame. In a d/q axis reference frame, the motor voltages and currents become direct current (DC) quantities. The FOC torque control technique is commonly implemented either using feedforward methods of control or a closed loop current feedback control.
When a closed loop current feedback control is used, the ability of the system to regulate the torque is heavily dependent on the measured currents. However, current sensors, just like all sensors, are prone to failures. The most common forms of errors in current measurement are gain and offset errors. Offset errors can be particularly problematic, because depending on the magnitude of the error, the torque ripple caused by the offset error may become large enough to exceed requirements related to maximum steering effort.
A common method for mitigating loss of steering assist due to a current measurement fault is to transition from torque control utilizing a current regulator to achieve the desired motor current (and thus motor torque), to a torque control utilizing a static feedforward (inverse motor model) compensation when the fault is detected. However, a feedforward inverse motor model based torque control typically has much lower bandwidth as compared to a high bandwidth current control loop. The motor torque control loop in an electric power steering system is the actuator for the steering system, therefore should have a bandwidth several times higher than the outer steering assist control loop. The stability compensation for the steering assist control loop is designed in a manner suitable for the higher bandwidth of the torque control when the closed loop current control is active.
A stability compensation designed for the lower bandwidth feedforward inverse motor model based torque control used during a current sensor fault condition would be significantly different than the base stability compensation. This produces the undesirable result during a current sensor fault condition of the overall steering assist control loop being less stable in the faulted condition than in the nominal unfaulted condition.
In accordance with one embodiment, a power steering system comprises a torque modifier module that generates a modified torque command in response to a current sensor fault, a magnitude of the modified torque command changes over a time period, and a feedforward selection module that applies a dynamic feedforward compensation to a motor current command, thereby generating a motor voltage that is applied to a motor of the power steering system, the dynamic feedforward compensation modifies a frequency response of the power steering system, the motor current command is based on the modified torque command.
In accordance with another embodiment, a power steering system comprises a stability compensator selector module that selects a stability compensator of a steering torque control loop of the power steering system when a current sensor fault is detected, the stability compensator generates a compensated torque command, and a torque modifier module that generates a modified torque command from the compensated torque command in response to a current sensor fault, a magnitude of the modified torque command changes over a time period, a motor voltage that is applied to a motor of the power steering system is based on the modified torque command.
In accordance with another embodiment, a method for controlling a power steering system comprises generating a modified torque command in response to a current sensor fault, a magnitude of the modified torque command changes over a time period; and applying a dynamic feedforward compensation to a motor current command, thereby generating a motor voltage that is applied to a motor of the power steering system, the dynamic feedforward compensation modifies a frequency response of the power steering system, the motor current command is based on the modified torque command.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,
The compensation modules GF 202, CP 206 and CI 208, and the plant P(s) of the motor 18 are 2×2 matrices. Signals IR, IE, IP, IA, IM, VP, VI, VC, VFF, VF, VR, VM are vectors with two values each, corresponding to the d and q axes.
The current mode control configuration implemented in
Vd, Vq are the d/q motor voltages (in Volts), Id, Iq are the d/q motor currents (in Amperes), Ld, Lq are the d/q axis motor inductances (in Henries), R is the motor circuit (motor plus controller) resistance (in Ohms), Ke is the motor BEMF coefficient (in Volts/rad/s), ωm is the mechanical motor velocity in (in rad/s), and Te is the electromagnetic motor torque (in Nm).
The torque equation may be nonlinear and may represent a sum of the torque developed by leveraging the magnetic field from the permanent magnets, and the reluctance torque generated by rotor saliency (difference between Ld and Lq) and predefined values of Iq and Id.
Equations 1 and 2 may be rewritten as follows:
Vd=Ldİd+RId+ωeLqIq (Equation 4)
V′q=Vq−Keωm=Lqİq+RIq−ωeLdId (Equation 5)
In the above equations,
is the electrical speed of the machine. To employ standard linear feedback control design techniques, the machine speed is assumed to be a slowly varying parameter. It can be appreciated that due to relatively slow flux dynamics, the quasi-static back-EMF (BEMF) term Keωm can be considered to be essentially constant, which is compensated as a disturbance in the feedforward path. These two assumptions allow linearization of equations 4 and 5 for a fixed speed. Note that the apostrophe in the V′q term is dropped in the equations below.
Equations 4 and 5 can re-written using s-domain representation as follows:
Note that this description translates plant outputs into inputs via the complex frequency transfer matrix Pi(s), and is thus the inverse of the true plant transfer matrix. The block diagram for the above description (with the additional BEMF term also shown) is shown in the block diagram of the motor shown in
The closed loop transfer matrix T relating the reference currents IR to the actual currents IA for the current control system shown in
IA=TIR=(P−1+C)−1(G+C)IR (Equation 8)
By inserting the appropriate compensator matrices in the above expressions, the transfer matrix T may be expressed in equation 9 as follows:
Terms Tdd(s) and Tqq (s) are the direct current to current transfer functions, while Tdq(s) and Tqd (s)represent the cross coupling between the two current loops. For a typical system, the direct transfer functions have extremely high bandwidth.
A block diagram depicting a typical current sensor fault loss of assist mitigation algorithm 400 is shown in
For example, a first ramp waveform as shown in
A second torque ramp return waveform 600 is illustrated in
Although two specific embodiments of torque ramp return waveforms are shown, the torque command modifier may be configured to implement any number of ramp return waveforms, and the subject application is not limited to the waveforms shown in
To compensate for undesirable frequency responses, a stability compensator of the steering control system may be changed at the time the fault occurs. However, a stability compensator would have to be tuned for the motor control loop bandwidth with the static feedforward control configuration. Further, since the stability compensator is a notch filter with various states, when the switching occurs, all the state variables will get re-initialized to zero, causing a lag in response time. Additionally, a modified torque component may be required during the transition.
The system may further include a current sensor fault detector module 920A that detects an operational state of a current sensor (not shown). The current sensor fault detector module 920A may send an enable command to the stability compensator selector module 915A, the torque modifier module 914A, and the feedforward selection module 918A.
In response to the detection of a current sensor fault by current sensor fault detector module 920A, the stability compensator selector module 915A may implement a loss of assist mode in the steering system by selecting a loss of assist mode output from the stability compensator module 913A, and therefore generate a compensated torque command that is sent to the torque command modifier module 913A. The selection of the loss of assist mode output changes a function provided by the stability compensator module 913A upon the detection of the current sensor fault. The stability compensator module 913A may be tuned as a function of the motor control bandwidth, while the static feedforward control configuration implemented in the current loop compensator 925A may not change when the feedforward selection module 918A receives the enable command from the current sensor fault detector module 920A.
The stability compensator module 913A is, in some embodiments, a notch filter that can be programmed with a plurality of states. During the change of the function of the stability compensator module 913A as controlled by the stability compensator selector module 915A, state variables of the stability compensator module 913A may be re-initialized to zero values, and over time, transition to values that represent the actual state of the steering system 900A.
Specifically, the torque modifier module 914A may implement the first and second ramp waveforms as shown in
The torque modifier module 914A may generate a modified torque command in response to a current sensor fault. A magnitude of the modified torque command may change over time and be consistent with the waveforms shown in
Turning to
The system may further include a current sensor fault detector module 920 that detects an operational state of a current sensor (not shown). The current sensor fault detector module 920 may send an enable command to the torque modifier module 914 and to the feedforward selection module 918.
The torque modifier module 914 may implement the first and second ramp waveforms as shown in
The feedforward selection module 918 may select a dynamic feedforward compensation mode that processes a motor current command. The motor current command may be generated by the current reference generator 916 in response to the current reference generator 916 receiving the torque command modifier. The processing of the motor current command may change the voltage commands sent to the electric motor in response to the current sensor fault detection.
The dynamic feedforward compensation algorithm applied by the feedforward selection module 918 may be performed by the dynamic feedforward compensator module 922. The dynamic feedforward compensator module 922 may use a derivative transfer function implemented by a derivative estimation submodule (not shown). The dynamic feedforward compensator module 922 may modify a frequency response of a motor control loop of the power steering system. Ideally, the derivative transfer function is a true derivative that may be denoted by Laplace transform variable s, however in some embodiments, the transfer function may be represented by an approximation of the derivative, {tilde over (s)}, as follows:
The derivative estimation submodule may be a high pass filter in some embodiments, but in other embodiments the derivative estimation submodule may be a discrete time derivative filter with specific magnitude and phase characteristics.
In should be appreciated that although the static feedforward module 922 is shown in
The stability compensator of the steering control module 912 is, in some embodiments, a notch filter that can be programmed with a plurality of states. During the change of the function of the stability compensator as controlled by the stability compensator selector module, state variables of the stability compensator may be re-initialized to zero values, and over time, transition to values that represent the actual state of the steering system.
Specifically, the torque modifier module 1014 may implement the first and second ramp waveforms as shown in
Similar to the description provided in
In addition, a feedforward selection module 1008 enables a dynamic feedforward compensation in the event of a detection of a sensor failure. The feedforward selection module 1008 modifies the torque command sent to the electric motor of the system, which is represented by the PMSM motor electrical plant of the steering system mechanical plant 1018.
For
It can be appreciated from equations 13 and 14 that if the derivative filter were ideal, both the transfer functions would simply become unity. The derivative filter is contained within the derivative estimation module 1110 in
If the current loop has a different configuration, and does not have a complete feedforward compensator during normal operation, then the full dynamic feedforward compensation terms can be calculated continuously, but applied only during the fault condition.
As used above, the term “module” or “sub-module” refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. When implemented in software, a module or a sub-module can be embodied in memory as a non-transitory machine-readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. Moreover, the modules and sub-modules shown in the above Figures may be combined and/or further partitioned.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.
This patent application claims priority to U.S. Provisional Patent Application Ser. No. 62/109,698, filed Jan. 30, 2015, which is incorporated herein by reference in its entirety.
Number | Name | Date | Kind |
---|---|---|---|
4713596 | Bose | Dec 1987 | A |
4733149 | Culberson | Mar 1988 | A |
4920306 | Mard et al. | Apr 1990 | A |
5196778 | Hayashida | Mar 1993 | A |
5223775 | Mongeau | Jun 1993 | A |
5410234 | Shibata et al. | Apr 1995 | A |
5652495 | Narazaki et al. | Jul 1997 | A |
5927430 | Mukai et al. | Jul 1999 | A |
5962999 | Nakamura et al. | Oct 1999 | A |
6002234 | Ohm et al. | Dec 1999 | A |
6021251 | Hammer et al. | Feb 2000 | A |
6104148 | Kumar et al. | Aug 2000 | A |
6152254 | Phillips | Nov 2000 | A |
6161068 | Kurishige et al. | Dec 2000 | A |
6222334 | Tamagawa et al. | Apr 2001 | B1 |
6288515 | Hiti et al. | Sep 2001 | B1 |
6370459 | Phillips | Apr 2002 | B1 |
6465975 | Naidu | Oct 2002 | B1 |
6499559 | McCann et al. | Dec 2002 | B2 |
6605912 | Bharadwaj et al. | Aug 2003 | B1 |
6700342 | Hampo et al. | Mar 2004 | B2 |
6900607 | Kleinau et al. | May 2005 | B2 |
7034493 | Yoshimoto et al. | Apr 2006 | B2 |
7071649 | Kleinau et al. | Jul 2006 | B2 |
7145310 | Ihm et al. | Dec 2006 | B2 |
7199549 | Kleinau et al. | Apr 2007 | B2 |
7207412 | Uryu | Apr 2007 | B2 |
7394214 | Endo et al. | Jul 2008 | B2 |
7548035 | Endo et al. | Jun 2009 | B2 |
7576506 | Kleinau et al. | Aug 2009 | B2 |
7952308 | Schulz et al. | May 2011 | B2 |
8633766 | Khlat et al. | Jan 2014 | B2 |
8896244 | Kleinau | Nov 2014 | B2 |
20020175649 | Reutlinger | Nov 2002 | A1 |
20030076065 | Shafer et al. | Apr 2003 | A1 |
20030146041 | Kanda | Aug 2003 | A1 |
20040095089 | Collier-Hallman | May 2004 | A1 |
20040195993 | Yoshimoto et al. | Oct 2004 | A1 |
20050073280 | Yoshinaga et al. | Apr 2005 | A1 |
20060100766 | Schwarz et al. | May 2006 | A1 |
20070043490 | Yokota et al. | Feb 2007 | A1 |
20070046126 | Sagoo et al. | Mar 2007 | A1 |
20070103105 | Endo et al. | May 2007 | A1 |
20070132446 | Kleinau et al. | Jun 2007 | A1 |
20070177314 | Weng et al. | Aug 2007 | A1 |
20070278032 | Sakaguchi et al. | Dec 2007 | A1 |
20080167779 | Suzuki | Jul 2008 | A1 |
20080191656 | Satake et al. | Aug 2008 | A1 |
20090026994 | Namuduri et al. | Jan 2009 | A1 |
20090027000 | Gallegos-Lopez et al. | Jan 2009 | A1 |
20090069979 | Yamashita et al. | Mar 2009 | A1 |
20090114470 | Shimizu et al. | May 2009 | A1 |
20090189555 | Chen | Jul 2009 | A1 |
20090224710 | Mir | Sep 2009 | A1 |
20090234538 | Ta et al. | Sep 2009 | A1 |
20090267555 | Schulz et al. | Oct 2009 | A1 |
20100153162 | Tam et al. | Jun 2010 | A1 |
20100231148 | Tobari et al. | Sep 2010 | A1 |
20110169432 | Dean | Jul 2011 | A1 |
20110175556 | Tobari et al. | Jul 2011 | A1 |
20110231066 | Ohno et al. | Sep 2011 | A1 |
20120112549 | Perisic et al. | May 2012 | A1 |
20120221208 | Kojo et al. | Aug 2012 | A1 |
20120313701 | Khlat et al. | Dec 2012 | A1 |
20130154524 | Kleinau | Jun 2013 | A1 |
20130187579 | Rozman et al. | Jul 2013 | A1 |
20130261896 | Gebregergis et al. | Oct 2013 | A1 |
20130285591 | Suzuki | Oct 2013 | A1 |
20140191699 | Dixon | Jul 2014 | A1 |
20140239860 | Kleinau | Aug 2014 | A1 |
20140265961 | Gebregergis et al. | Sep 2014 | A1 |
20140265962 | Gebregergis et al. | Sep 2014 | A1 |
20140375239 | Kim et al. | Dec 2014 | A1 |
20150155811 | Merienne | Jun 2015 | A1 |
20150222210 | Kleinau et al. | Aug 2015 | A1 |
Number | Date | Country |
---|---|---|
1675099 | Sep 2005 | CN |
1741368 | Mar 2006 | CN |
101218146 | Jul 2008 | CN |
101399516 | Apr 2009 | CN |
101456429 | Jun 2009 | CN |
101981804 | Feb 2011 | CN |
102570476 | Jul 2012 | CN |
102751936 | Oct 2012 | CN |
1378419 | Jan 2004 | EP |
1768252 | Jan 2006 | EP |
1720242 | Nov 2006 | EP |
1914878 | Apr 2008 | EP |
2003010 | Dec 2008 | EP |
2293428 | Oct 2009 | EP |
2000108916 | Apr 2000 | JP |
2001247049 | Sep 2001 | JP |
2003170850 | Jun 2003 | JP |
2007137272 | Jun 2007 | JP |
2008143200 | Jun 2008 | JP |
2012224258 | Nov 2012 | JP |
2014006329 | Jan 2014 | WO |
Entry |
---|
Jeong et al., “Fault Detection and Fault-Tolerant Control of Interior Permanent-Magnet Motor Drive System for Electric Vehicle”, IEEE Transactions on Industry Applications, vol. 41 No. 1, Jan. 2005, pp. 46-51. |
Chinese Office Action for Chinese Patent Application No. 201310104183.7 dated Jan. 6, 2015. |
English translation of office action issued in related CN Application No. 201400942309, dated Jan. 18, 2016, 14 pages. |
EP Search Report for related EP Application No. EP12196930.7; dated Mar. 22, 2013; 7 pages. |
European Search Report from related Application No. 15171189: dated Jan. 4, 2016; 9 pages. |
Extended European search report for related European application No. 16153434.2, dated Jul. 6, 2016, pp. 8. |
F. Briz, et al., “Analysis and Design of current Regulators Using Complex Vectors”, IEEE Industry Applications Society Annual Meeting, New Orleans, Louisiana; Oct. 5-9, 1997, pp. 1504-1511. |
J. Kirtley, “6.061 Introduction to Electric Power Systems, Class Notes Chapter 12 Permanent Magnet ‘Brushless DC’” Motors, Massachussetts Institute of Technology, Department of Electrical Engineering and Computer Science, Spring 2011. |
L. Harnefors, et al., “Model-Based Current Control of AC Machines Using the Internal Model Control Method”, IEEE Transactions on Industry Applications, vol. 34, No. 1, Jan./Feb. 1998, pp. 133-141. |
Office Action issued in related CN Application No. 201400942309, dated Jan. 18, 2016, 18 pages. |
EP SR dated May 12, 2017 in NXT0018EP. |
Number | Date | Country | |
---|---|---|---|
20160229449 A1 | Aug 2016 | US |
Number | Date | Country | |
---|---|---|---|
62109698 | Jan 2015 | US |