Methods, systems and apparatus for synchronous current regulation of a five-phase machine

Methods, systems and apparatus are provided for controlling operation of and regulating current provided to a five-phase machine when one or more phases has experienced a fault or has failed. In one implementation, the disclosed embodiments can be used to synchronously regulate current in a vector controlled motor drive system that includes a five-phase AC machine, a five-phase inverter module coupled to the five-phase AC machine, and a synchronous current regulator.

TECHNICAL FIELD

Embodiments of the present invention generally relate to multi-phase systems, such as those that implement five-phase machines, and more particularly relate to techniques for controlling operation of and regulating current provided to a five-phase machine when one or more phases has experienced a fault or failed.

BACKGROUND OF THE INVENTION

Electric machines are utilized in a wide variety of applications. For example, hybrid/electric vehicles (HEVs) typically include an electric traction drive system that includes an alternating current (AC) electric motor which is driven by a power converter with a direct current (DC) power source, such as a storage battery. Motor windings of the AC electric motor can be coupled to inverter sub-modules of a power inverter module (PIM). Each inverter sub-module includes a pair of switches that switch in a complementary manner to perform a rapid switching function to convert the DC power to AC power. This AC power drives the AC electric motor, which in turn drives a shaft of HEV's drivetrain. Traditional HEVs implement a three-phase pulse width modulated (PWM) inverter module, which drives a three-phase AC machine (e.g., AC motor).

Many modern high performance AC motor drives use the principle of field oriented control (FOC) or “vector” control to control operation of the AC electric motor. In particular, vector control is often used in variable frequency drives to control the torque applied to the shaft (and thus finally the speed) of an AC electric motor by controlling the current fed to the AC electric motor. In short, stator phase currents are measured and converted into a corresponding complex space vector. This current vector is then transformed to a coordinate system rotating with the rotor of the AC electric motor.

Recently, researchers have investigated the possibility of using multi-phase machines in various applications including electric vehicles. As used herein, the term “multi-phase” refers to more than three-phases, and can be used to refer to electric machines that have three or more phases. One example of a multi-phase electric machine is a five-phase AC machine. In a five-phase system, a five-phase PWM inverter module drives one or more five-phase AC machine(s). While the possibility of using five-phase systems (e.g., five-phase inverter and motor configurations) in HEVs is being explored, a lot of work remains to be done before these inverter and motor configurations can actually be implemented.

In certain circumstances, one or more of the five-phases of a five-phase system can fail or experience a fault condition. For example, in some situations, a connection between the inverter module and its corresponding motor phase can fail. This can happen, for example, due to a disconnection of a wire to/in the five-phase AC motor. For instance, the connection between the PWM inverter module and the AC motor can be “open.” Such open-circuit situations can be due to a problem with a connector or cable between a pole of the five-phase PWM inverter module and a winding of the motor, damage in one of the motor stator windings, etc. Such open-circuit situations cause improper current control of the five-phase AC motor.

In other scenarios, one or more of the switches in the five-phase PWM inverter module may be operating a faulty manner, which can lead to improper current control of the five-phase AC motor, such as abnormal operation of one or more of the switches in the five-phase PWM inverter module. For example, a partial phase fault happens when a switch in one of the inverter sub-modules fails or when a gate drive circuit that generates gate drive signals malfunctions.

Nevertheless, a five-phase machine can still operate and provide torque/power when only three or four of its five phases are operational even though the system operates at a lower power rating as a three-phase or four-phase system. In such situations, it is important to maintain proper current regulation, while maintaining machine torque linearity, to limit torque and power when one or more of the five phases fails or experiences a fault condition

In conventional five-phase systems, a torque-to-current mapping table is used to generate ia*, ib*, ic*, id*, ie* current commands. These ia*, ib*, ic*, id*, ie* current commands are regulated in the stationary reference frame. In particular, one stationary reference frame current regulator is used to regulate each of the ia*, ib*, ic*, id*, ie* current commands. Each stationary reference frame current regulator consists of a summing junction that subtracts a feedback stator current from the corresponding current command to generate a current error signal for that phase. The current error signal is applied to a proportional-integrator control module that generates a stationary reference frame voltage command signal based on the current error signal.

Regulating current commands in the stationary reference frame can be very cumbersome since five current commands are regulated independently of one another. These current commands are AC signals and there is a phase lag, which can be significant at medium/high motor speeds and therefore PI control modules are subject to errors when generating voltage command signals. To avoid this problem electric machines can be controlled with synchronous current regulator instead. System designers need to generate torque-to-current mapping or control tables that will optimize power and efficiency of the five-phase machine, and this requires an accurate characterization of machine parameters. This becomes particularly problematic when using stationary current regulators in the event one of the phases experiences a fault or failure condition. To maintain current regulation in such scenarios, separate torque-to-current mapping tables must be developed for each failure scenario. For example, a torque-to-current mapping tables that is used to when phase A fails would not be applicable in the situation where phase B fails. In addition, because a five-phase system can still operate when two phases fail, even further torque-to-current mapping tables must be generated to handle different combinations of two failed phases. Again, for each torque-to-current mapping table the system designer must characterize the behavior of the machine for that particular failure/fault scenario and develop a separate torque-to-current mapping table that will work in that scenario.

As such, improved techniques are needed for regulating current to control operation of a five-phase AC machine when one or more of the phases experiences a fault/failure condition.

Accordingly, it is desirable to provide methods, systems and apparatus for controlling operation of a five-phase AC machine when one or more phases has experienced a fault or failed. It is also desirable to provide methods, systems and apparatus for regulating current that controls a five-phase AC machine when one or more of its phases has experienced a fault or failed. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background

SUMMARY

Embodiments of the present invention relate to methods, systems and apparatus for controlling operation of and regulating current provided to a five-phase machine when one or more phases has experienced a fault or has failed.

According to one embodiment methods are provided for synchronously regulating current in a vector controlled motor drive system that includes a five-phase AC machine, a five-phase inverter module coupled to the five-phase AC machine, and a synchronous current regulator.

The five-phase inverter module generates five-phase stationary reference frame stator currents. Based on measured five-phase stationary reference frame stator currents, it can be determined whether a phase fault condition exists with respect to one or more of the five phases (e.g., one or more phase(s) is experiencing a phase fault condition), and if so, the system generates a fault signal that includes information that indicates which particular phases are presently experiencing fault condition(s).

Based on the particular phases indicated in the fault signal, a five phase-to-two phase transformation can be performed. This transformation transforms particular ones of the five-phase stationary reference frame stator currents that correspond to non-faulting phases to two-phase stationary reference frame stator currents. However, particular ones of the five-phase stationary reference frame stator currents that correspond to faulting phases that are experiencing fault condition(s) are excluded from the five phase-to-two phase transformation. This way, only the particular ones of the five-phase stationary reference frame stator currents that correspond to non-faulting phases are used to generate two-phase stationary reference frame stator currents. In some implementations, a particular combination of four stationary reference frame stator currents (e.g., that correspond to four non-faulting phases) are transformed to two-phase stationary reference frame stator currents, whereas in other implementations, a particular combination of three stationary reference frame stator currents (e.g., that correspond to three non-faulting phases) are transformed to two-phase stationary reference frame stator currents.

The synchronous current regulator generates synchronous reference frame voltage command signals based on synchronous reference frame feedback current signals and synchronous reference frame current commands. To explain further, two-phase stationary reference frame feedback stator currents along with a rotor angular position, can be used to generate synchronous reference frame feedback current signals, which can be used (along with current commands) to generate synchronous reference frame voltage command signals, which can in turn be used to generate two-phase stationary reference frame voltage command signals.

Based on the particular phases indicated in the fault signal, a two phase-to-five phase transformation can be performed that transforms the two-phase stationary reference frame voltage command signals to generate either three or four five-phase stationary reference frame voltage command signals that correspond to the particular non-faulting phases In other words, in some implementations, two-phase stationary reference frame voltage command signals are transformed into four particular five-phase stationary reference frame voltage command signals (e.g., that correspond to four particular non-faulting phases), whereas in other implementations, the two-phase stationary reference frame voltage command signals are transformed into three five-phase stationary reference frame voltage command signals (e.g., that correspond to three particular non-faulting phases).

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the present invention relate to methods and apparatus for regulating current in a five-phase system when one or more phases has experienced a fault or failed. The disclosed methods, systems and apparatus for controlling operation of a five-phase system and regulating current provided to a five-phase machine can be implemented in operating environments such as a hybrid/electric vehicle (HEV). However, it will be appreciated by those skilled in the art that the same or similar techniques and technologies can be applied in the context of other systems in which it is desirable to control operation of a five-phase system and regulate current provided to a five-phase machine in that system when one or more phases has experienced a fault or failed. In this regard, any of the concepts disclosed here can be applied generally to “five-phase alternating current (AC) machines,” and, and as used herein, the term “AC machine” generally refers to “a device or apparatus that converts electrical energy to mechanical energy or vice versa.” AC machines can generally be classified into synchronous AC machines and asynchronous AC machines. Synchronous AC machines can include permanent magnet machines and reluctance machines. Permanent magnet machines include surface mount permanent magnet machines (SMPMMs) and interior permanent magnet machines (IPMMs).

FIG. 1is a block diagram of one example of a vector controlled motor drive system100. The system100controls a five-phase AC machine120via a five-phase pulse width modulated (PWM) inverter module110coupled to the five-phase AC machine120so that the five-phase AC machine120can efficiently use a DC input voltage (Vdc) provided to the five-phase PWM inverter module110by adjusting current commands that control the five-phase AC machine120. In one particular implementation, the vector controlled motor drive system100can be used to control torque in an HEV.

In the following description of one particular non-limiting implementation, the five-phase AC machine120is described as a five-phase AC powered motor120, and in particular a five-phase, interior permanent magnet synchronous AC powered motor (or more broadly as a motor120); however, it should be appreciated that the illustrated embodiment is only one non-limiting example of the types of AC machines that the disclosed embodiments can be applied to, and further that the disclosed embodiments can be applied to any type of multi-phase AC machine that includes five or more phases.

The five-phase AC motor120is coupled to the five-phase PWM inverter module110via five inverter poles and generates mechanical power (Torque×Speed) based on five-phase sinusoidal voltage signals received from the PWM inverter module110. In some implementations, the angular position of a rotor (θr) of the first five-phase AC motor120or “shaft position” is measured using a position sensor (not illustrated), and in other implementations, the angular position of a rotor (θr) of the first five-phase AC motor120can be estimated without using a position sensor by using sensorless position estimation techniques.

Prior to describing operation details of the system100, a more detailed description of one exemplary implementation of the five-phase voltage source inverter110will be provided (including how it is connected to the five-phase AC motor120) with reference toFIG. 2.FIG. 2is a block diagram of a portion of a motor drive system including a five-phase voltage source inverter110connected to a five-phase AC motor120. It should be noted that the five-phase voltage source inverter110and the five-phase motor120inFIG. 1are not limited to this implementation; rather,FIG. 2is merely one example of how the five-phase voltage source inverter110and the five-phase motor120inFIG. 1could be implemented in one particular embodiment.

As illustrated inFIG. 2, the five-phase AC motor120has five stator or motor windings120a,120b,120c,120d,120econnected to motor terminals A, B, C, D, E, and the five-phase PWM inverter module110includes a capacitor180and five inverter sub-modules115-119. In this embodiment, in phase A the inverter sub-module115is coupled to motor winding120a, in phase B the inverter sub-module116is coupled to motor winding120b, in phase C the inverter sub-module117is coupled to motor winding120c, in phase D the inverter sub-module118is coupled to motor winding120d, and in phase E the inverter sub-module119is coupled to motor winding120e. The motor windings A, B, C, D, E (120a,120b,120c,120d,120e) that are coupled together at a neutral point (N). The current into motor winding A120aflows out motor windings B-E120b-120e, the current into motor winding B120bflows out motor windings A, C, D, E120aand120c-e, the current into motor winding C120cflows out motor windings A, B, D, E120a,120b,120d,120e, the current into motor winding D120dflows out motor windings A, B, C, E120a-cand120eand the current into motor winding E120eflows out motor windings A-D120a-d.

The resultant phase or stator currents (Ia-Ie)122,123,124,125,126flow through respective stator windings120a-e. The phase to neutral voltages across each of the stator windings120a-120eare respectively designated as Van, Vbn, Vcn, Vdn, Ven, with the back electromagnetic force (BEMF) voltages generated in each of the stator windings120a-120erespectively shown as the voltages Ea, Eb, Ec, Ed, Eeproduced by ideal voltage sources, each respectively shown connected in series with stator windings120a-120e. As is well known, these back EMF voltages Ea, Eb, Ec, Ed, Eeare the voltages induced in the respective stator windings120a-120eby the rotation of the permanent magnet rotor. Although not shown, the motor120is coupled to a drive shaft.

The inverter110includes a capacitor180, a first inverter sub-module115comprising a dual switch182/183,184/185, a second inverter sub-module116comprising a dual switch186/187,188/189, a third inverter sub-module117comprising a dual switch190/191,192/193, a fourth inverter sub-module118comprising a dual switch194/195,196/197, and a fifth inverter sub-module119comprising a dual switch198/199,200/201. As such, the inverter110has ten solid state controllable switching devices182,184,186,188,190,192,194,196,198,200and ten diodes183,185,187,189,191,193,195,197,199,201to appropriately switch compound voltage (VDC) and provide five-phase energization of the stator windings120a,120b,120c,120d,120eof the five-phase AC motor120.

Although not illustrated, a closed loop motor controller can receive motor command signals and motor operating signals from the motor120, and generate control signals for controlling the switching of solid state switching devices182,184,186,188,190,192,194,196,198,200within the inverter sub-modules115-119. Examples of these switching vectors used to construct these control signals will be described below. By providing appropriate control signals to the individual inverter sub-modules115-119, the closed loop motor controller controls switching of solid state controllable switching devices182,184,186,188,190,192,194,196,198,200within the inverter sub-modules115-119and thereby control the outputs of the inverter sub-modules115-119that are provided to motor windings120a-120e, respectively. The resultant stator currents (Ia . . . Ie)122-126that are generated by the inverter sub-modules115-119of the five-phase inverter module110are provided to motor windings120a,120b,120c,120d,120e. The voltages as Van, Vbn, Vcn, Vdn, Ven, Ea, Eb, Ec, Ed, Eeand the voltage at node N fluctuate over time depending on the open/close states of switches182,184,186,188,190,192,194,196,198,200in the inverter sub-modules115-119of the inverter module110, as will be described below.

Referring again toFIG. 1, the vector control motor drive system100includes a torque-to-current mapping module140, a synchronous (SYNC.) frame current regulator module170, a synchronous-to-stationary (SYNC-TO-STAT.) transformation module102, a two-phase-to-five-phase transformation module106, a Space Vector (SV) PWM module108, a five-phase PWM inverter110, a five-phase-to-two-phase transformation module127, a stationary-to-synchronous (STAT-TO-SYNC.) transformation module130, a current measurement and fault detection module210and an optional output module216.

The torque-to-current mapping module140receives a torque command (Te*)136, angular rotation speed (ωr)138of the shaft, and the DC input (or “link”) voltage (Vdc)139as inputs. In one implementation, the angular rotation speed (ωr)138of the shaft can be generated based on the derivative of a rotor/shaft position output (θr)121. Depending upon implementation the torque-to-current mapping module140may also receive a variety of other system parameters. The torque-to-current mapping module140uses the inputs to map the torque command (Te*)136to a fundamental d-axis current command signal (Id1*)142, a third harmonic d-axis current command signal (Id3*)143, a fundamental q-axis current command signal (Iq1*)144, a third harmonic q-axis current command signal (Iq3*)145, and a zero sequence current command signal (10*)146. These current command signals will cause the motor120to generate the commanded torque (Te*) at speed (ωr)138. The synchronous reference frame current command signals142-146are DC commands that have a constant value as a function of time during steady state operation. Because the current commands are DC signals in the synchronous reference frame it is easier to regulate current commands

The five-to-αβ phase transformation module127receives measured five-phase stationary reference frame feedback stator currents (Ia . . . Ie)122-126that are feedback from motor120.FIG. 3Ais a graph showing measured five-phase stationary reference frame feedback stator currents (Ia . . . Ie)122-126when the five-phase PWM inverter110and five-phase motor120are operating correctly and there is no fault or failure condition.

The five-to-αβ phase transformation module127uses these five-phase stationary reference frame feedback stator currents122-126and performs an abcde reference frame-to-αβ reference frame transformation to transform the five-phase stationary reference frame feedback stator currents122-126into αβ stationary reference frame feedback stator currents128,129. During normal operation, the five-to-five phase transformation can be performed using the matrices defined in equation (1) below. In equation (1) the column vector that represents the five-phase stationary reference frame feedback stator currents122-126is multiplied by a transformation matrix and scaling factor to generate a column vector that represents the αβ stationary reference frame feedback stator currents. With respect to this equation (1), it is noted that the αβ stationary reference frame stator currents (Iα3, Iβ3)128-2,129-2can be, for example, third (or other) harmonic currents. In a system that functions normally when all five phases are operating correctly (e.g., not faulting or failing), these stationary reference frame feedback stator currents Iα3, Iβ3and I0can be regulated and controlled since a five-phase machine has an extra degree of freedom compared to a three-phase machine. However, when one or more phases fails/faults, the extra degree of freedom is lost, and the stationary reference frame feedback stator currents Iα3, Iβ3and I0can no longer be controlled/regulated. Thus, when one or more phases faults/fails for some reason, the equation (1) that is normally implemented at the five-phase to five-phase transformation module127for generating stationary reference frame feedback stator currents will not be accurate, as will be described in more detail below.

FIG. 3Bis a graph showing two-phase stationary reference frame feedback stator currents (Iα, Iβ)128-1,129-1computed by the five-to-αβ phase transformation module127based on the measured five-phase stationary reference frame feedback stator currents (Ia . . . Ie)122-126.

The stationary-to-synchronous transformation module130receives the two-phase stationary reference frame feedback stator currents128,129and the rotor angular position (θr)121. The rotor position angle (θr)121can be measured or estimated based on information from the motor120. The stationary-to-synchronous transformation module130generates (e.g., processes or converts) these two-phase stationary reference frame feedback stator currents128,129to generate a fundamental synchronous reference frame d-axis current signal (Id1)132, a third harmonic synchronous reference frame d-axis current signal (Id3)133, a fundamental synchronous reference frame q-axis current signal (Iq1)134, a third harmonic synchronous reference frame q-axis current signal (Iq3)135and a synchronous reference frame zero sequence current signal (I0)136. The process of stationary-to-synchronous conversion is well-known in the art and for sake of brevity will not be described in detail.

The synchronous frame current regulator module170receives the fundamental synchronous reference frame d-axis current signal (Id1)132, the third harmonic synchronous reference frame d-axis current signal (Id3)133, the fundamental synchronous reference frame q-axis current signal (Iq1)134, the third harmonic synchronous reference frame q-axis current signal (Iq3)135, the synchronous reference frame zero sequence current signal (I0)136, the fundamental d-axis current command signal (Id1*)142, the third harmonic d-axis current command signal (Id3*)143, the fundamental q-axis current command signal (Iq1*)144, the third harmonic q-axis current command signal (Iq3*)145, the zero sequence current command signal (I0*)146, and uses these signals to generate a fundamental d-axis voltage command signal (Vd1*)172, a third harmonic d-axis voltage command signal (Vd3*)173, a fundamental q-axis voltage command signal (Vq1*)174, a third harmonic q-axis voltage command signal (Vq3*)175, and a zero sequence voltage command signal (V0*)176. The voltage command signals172-176are also synchronous reference frame signals and are therefore DC commands that have a constant value as a function of time. The process of current to voltage conversion can be implemented as a Proportional-Integral (PI) controller, which is well-known in the art and for sake of brevity will not be described in detail.

Regulating the d-axis and q-axis current commands (Id1*, Iq1*)142,144in the synchronous reference frame has a number of advantages especially in the event that one of the motor phases A, B, C, D, E experiences a fault/failure condition. For instance, because current commands are regulated in the synchronous reference frame, and not in the stationary reference frame, only two DC current commands need to be regulated. Because the current commands are DC signals in the synchronous reference frame it is easier to regulate synchronous current commands. Moreover, to handle phase fault/failure scenarios, there is no need for system designers to develop separate torque-to-current mapping tables. Instead, the same one can be used regardless of the fault/failure scenario and current regulation can still be maintained. For example, the same torque-to-current mapping table would be used when no phases fail, or when one phase fails or when two phases fail. This eliminates the need for system designers to characterize the behavior of the five-phase machine for each particular failure/fault scenario and develop a separate torque-to-current mapping table that will work in that scenario. As will be described more detail below, by regulating the d-axis and q-axis current commands (Id1*, Iq1*)142,144in the synchronous reference frame, system designers only need to change equations used at the αβ-to-five phase transformation module106and five-to-αβ phase transformation module127to handle phase fault/failure conditions yet still maintain current regulation. No other blocks or modules inFIG. 1need to be changed to handle phase fault/failure conditions.

As its inputs the synchronous-to-stationary transformation module102receives the synchronous reference frame voltage command signals172-176from the synchronous frame current regulator module170, and the rotor position output (θr)121. In response to these inputs, the synchronous-to-stationary transformation module102performs a dq-to-αβ transformation based on these signals to generate a fundamental a-axis stationary reference frame voltage command signal (Vα1*)104-1, a fundamental β-axis stationary reference frame voltage command signal (Vβ1*)105-1, a third harmonic a-axis stationary reference frame voltage command signal (Vα3*)104-2, a third harmonic β-axis stationary reference frame voltage command signal (Vβ3*)105-2, and a zero sequence voltage command signal (V0*)103. These voltage command signals are in the stationary reference frame and therefore have values that vary as a sine wave as a function of time. The process of synchronous-to-stationary transformation is well-known in the art and for sake of brevity will not be described in detail.

The αβ-to-five phase transformation module106receives the stationary reference frame voltage command signals (Vα*, Vβ*, Vα3*, Vβ3*, V0*)103-105generated by the synchronous-to-stationary transformation module102, and based on these signals, generates five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107that are sent to the Space Vector Pulse Width Modulation (SVPWM) module200. The five-to-five phase transformation can be using the matrices defined in equation (2) below. Note that V0is assumed to be equal to zero.

In equation (2) the column vector that represents the stationary reference frame voltage command signals (Vα*, Vβ*, Vα3*, Vβ3*, V0*)103-105is multiplied by a transformation matrix and scaling factor to generate a column vector that represents the five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107

The SVPWM module108is used for the control of pulse width modulation (PWM). The five-phase PWM inverter module110is coupled to the SVPWM module108. The SVPWM module108receives the five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107as inputs, and uses these signals to generate switching vector signals (Sa . . . Se)109, which it provides to the five-phase PWM inverter module110. The particular SV modulation algorithm implemented in the SV PWM module108can be any known SV modulation algorithm. The switching vector signals (Sa . . . Se)109control the switching states of switches in PWM inverter110to generate five-phase voltage commands. The five-phase PWM inverter module110receives the DC input voltage (Vdc) and switching vector signals (Sa . . . Se)109, and uses them to generate five-phase alternating current (AC) voltage signal waveforms at inverter poles that drive the five-phase AC machine/motor120at varying speeds.

The five-phase interior permanent magnet synchronous motor120receives the five-phase voltage signals generated by the PWM inverter110and generates a motor output at the commanded torque Te*136. In this one particular implementation, the motor120comprises a five-phase interior permanent-magnet synchronous motor (IPMSM)120. The measured feedback stator currents (Ia-Ie) are sensed, sampled and provided to the five-to-two phase transformation module127as described above.

Although not illustrated inFIG. 1, the system100may also include a gear coupled to and driven by a shaft of the five-phase AC machine120.

Synchronous Current Regulation of a Five-Phase Machine with at Least One Faulted/Failed Phase

FIG. 3Cis a graph showing measured five-phase feedback stator currents (Ia . . . Ie)122-126when the five-phase PWM inverter110or five-phase motor120are not operating correctly and there is a fault or failure condition in phase A (e.g., current Ia122is not present).

In the event of a phase-fault or failure (i.e. when one or more phases fail), the standard equation (1) that is normally used to make the five-to -αβ phase transformation does not apply and produces inaccurate results. Likewise, the standard equation (2) that is normally used to make the αβ-to-five phase transformation does not apply and produces inaccurate results. According to an embodiment, these equations are not used to regulate current in the synchronous frame.

In accordance with the disclosed embodiments, methods, systems and apparatus are provided for synchronous current regulation of a five-phase machine when one or more phase(s) are experiencing a fault/failure condition. As will be described below with reference toFIGS. 1 and 6, when the current measurement and fault detection module210detects a phase fault (or phase failure), the disclosed embodiments are designed to mitigate performance issues that may otherwise occur at the αβ-to-five phase transformation module106, and the five-to-αβ phase transformation module127that are described above.

FIG. 4is a flowchart illustrating a method400in accordance with some of the disclosed embodiments, and will be described below with reference toFIG. 1. Method400begins at step405, when the current measurement and fault detection module and an output module210receives currents (Ia . . . Ie) that are fedback from the five-phase AC motor120.

In this particular embodiment, the current measurement and fault detection module210comprises a current measurement module212that measures amplitude of the five-phase stationary reference frame stator currents (Ia . . . Ie)122-126generated by the inverter sub-modules115-119(step410). In other embodiments, current measurement module212can measure other characteristics of the five-phase stationary reference frame stator currents (Ia . . . Ie)122-126that can be used to determine whether there is a fault. Examples would include, for instance, RMS measurement, FFT, signal faults from gate drive, and the like. The current measurement and fault detection module210also includes a fault detection module214that receives current measurements from the current measurement module212and processes them to determine whether a fault condition or failure condition exists with respect to one or more of the phases (step420).

In this regard, the fault detection module214can be used to detect abnormal operation of a five-phase PWM inverter module due to, for example: (1) a malfunction of the power electronics system (e.g., when one or more switching devices of the five-phase PWM inverter module is turned off due to problem in power electronics circuit), (2) a physical disconnection involving the five-phase PWM inverter module (e.g., when there is a physical disconnection between a wire/line/cable that connects a pole of the five-phase PWM inverter module to a motor winding of the motor), (3) a problem with an inverter connector, (4) damage to motor stator winding, or (5) a problem with a connection to a grid of a converter application, etc. For example, in one implementation, the fault detection module214can detect an actual physical open circuit condition involving a five-phase PWM inverter module110. In some implementations, the fault detection module214can also detect a “malfunction of” or “abnormal operation of” the five-phase PWM inverter module110(e.g., when one or more of the switches in the five-phase PWM inverter module110are off or not operating properly). In general, “operating properly” as used here can mean that an inverter sub-module is working properly (e.g., that the switches that generate the five-phase stationary reference frame stator current (Ia)122are generating a current and operating normally, and that with respect to phase A there is cable connection between the inverter sub-module115and the phase A motor winding).

When the fault detection module214detects a phase fault or phase failure based on the measured five-phase stationary reference frame currents (Ia . . . Ie)122-126, the fault detection module214generates a fault signal220(step430) and sends it to the five-to-αβ phase transformation module127to indicate that a fault/failure condition has been detected with respect to one (or more) phase(s). The fault signal220includes information that indicates which particular phases are presently experiencing a fault condition or have failed. In some implementations, when the current measurement and fault detection module210detects a phase fault or phase failure it also provides a fault indicator signal215to the output module216, which can include for example a display, indicator light and/or speaker used to indicate the detected fault to an observer (e.g., an operator of the vehicle).

The five-to-αβ phase transformation module127in accordance with the disclosed embodiments is designed to identify, select and modify equations (1) and (2) (above) that are necessary for current regulation in the synchronous frame when one (or more) phase(s) fails in five-phase machine. In response to the fault signal220, the five-to-αβ phase transformation module127selects (step440), based on the particular phases that are identified as being faulty or in failure, the appropriate modified variation of equation (3) (below) for transforming non-faulting ones of the five-phase stationary reference frame currents (Ia . . . Ie)122-126to two-phase stationary reference frame feedback stator currents128-1,129-1, by zeroing out columns that correspond to the faulting/failing phase by setting a phase coefficient (δi) for that faulting/failing phase equal to zero (0). The five-to-αβ phase transformation module127then uses the appropriate equation to transform non-faulting ones of the five-phase stationary reference frame currents (Ia . . . Ie) 122-126 to αβ-phase stationary reference frame feedback stator currents128-1,129-1(step450).

Thus, the five-to-αβ phase transformation module127in accordance with the disclosed embodiments uses the fault signal220to modify equation (3) as necessary for current regulation in the synchronous frame such that the “healthy” or non-faulting stationary frame currents can be transformed to alpha and beta stationary frame currents.

For instance, when the fault detection module214detects a phase fault or phase failure based on the measured five-phase stationary reference frame current signal (Ia)122, the fault detection module214generates a fault signal220and sends it to the five-to-αβ phase transformation module127to indicate that a fault/failure condition has been detected with respect to five-phase stationary reference frame current signal (Ia)122of phase A. The fault signal220includes information that indicates that phase A is presently experiencing a fault condition or failure. In response to the fault signal220, the five-to-αβ phase transformation module127modifies equation (3) as shown below in equation 3A, and computes values for αβ-phase stationary reference frame feedback stator currents (Iα, Iβ)128-1,129-1that may better provide current regulation in the synchronous frame when phase A has faulted/failed.

In equation (3A), the first column of the second transformation matrix has zero values such that the five-phase stationary reference frame current signal (Ia)122corresponding to phase A is not considered when converting non-faulting ones of the five-phase stationary reference frame current signals (Ib . . . Ie)123-126to two-phase stationary reference frame stator current signals (Iα, Iβ)128-1,129-1. Thus, the five-to-αβ phase transformation module127can modify equation (3) to generate the appropriate equation for computation of two-phase stationary reference frame stator current signals (Iα, Iβ)128-1,129-1such that only the “healthy” or non-faulting stationary reference frame five-phase current signals (Ib . . . Ie)123-126are transformed to two-phase stationary reference frame stator current signals (Iα, Iβ)128-1,129-1. This helps ensure more accurate current regulation in the synchronous frame.

Consider another example when the fault detection module214detects a phase fault or phase failure based on the measured five-phase stationary reference frame current signal (Ia)122and the measured five-phase stationary reference frame current signal (Ib)123. Here, the fault detection module214generates a fault signal220and sends it to the five-to-two phase transformation module127to indicate that a fault/failure condition has been detected with respect to five-phase stationary reference frame current signal (Ia)122corresponding to phase A and the five-phase stationary reference frame current signal (Ib)123corresponding to phase B. The fault signal220includes information that indicates that phases A and B are presently experiencing a fault condition or failure. In response to the fault signal220, the five-to-two phase transformation module127modifies equation (3) as per equation (3B) below to provide improved current regulation in the synchronous frame when both phases A and B have faulted/failed.

In equation (3B), the first and second columns of the second transformation matrix have zero values such that the five-phase stationary reference frame current signal (Ia)122corresponding to phase A and the five-phase stationary reference frame current signal (Ib)123corresponding to phase B are not considered when converting non-faulting ones of the five-phase stationary reference frame current signals (Ic . . . Ie)124-126to αβ-phase stationary reference frame current signals (Iα, Iβ)128-1,129-1. Thus, the five-to-two phase transformation module127can modify equation (3) as appropriate for computation of stationary frame feedback stator currents (Iα, Iβ)128-1,129-1such that only the “healthy” or non-faulting stationary frame five-phase stationary reference frame current signals (Ic . . . Ie)124-126are transformed to alpha (α) and beta (β) stationary reference frame current signals (Iα, Iβ)128-1,129-1.

It will be appreciated that equation (3) can be modified as appropriate to generate similar equations (not shown) at the five-to-αβ phase transformation module127that can be used to compute stationary reference frame feedback stator current signals (Iα, Iβ)128-1,129-1when any one of the other phases B, C, D, E are experiencing a fault condition. In such cases, the columns of the second transformation matrix that correspond to non-faulting phases would have the values indicated in the corresponding columns of the transformation matrix in equation (1), and the columns of the second transformation matrix that correspond to the faulting phase will have zero values such that the five-phase stationary reference frame current signals (Ib . . . Ie)123-126corresponding to the particular faulting phase is not considered when converting non-faulting ones of the five-phase currents to stationary reference frame feedback stator currents (Iα, Iβ)128-1,129-1.

Similarly, it will be appreciated that similar equations (not shown) can be used at the five-to-two phase transformation module127to compute stationary frame feedback stator currents (Iα, Iβ)128-1,129-1when any combination of two-phases are experiencing a fault condition. Two columns of the transformation matrix that correspond to the faulting phases will include zero values such that the five-phase currents corresponding to the particular faulting phases are not considered and the other columns will use the values indicated in equation (3) above when converting non-faulting ones of the five-phase currents to stationary frame feedback stator currents (Iα, Iβ)128-1,129-1.

Similar considerations apply with respect to the transformations by the αβ-to-five phase transformation module106. As mentioned above, the αβ-to-five phase transformation module106receives the αβ-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1, and based on these signals, generates a five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107. The standard equation (2) that is used to perform the αβ-to-five phase transformation should not be used when one or more of the phases is experiencing a fault/failure condition.

Thus, when the fault detection module214detects (at step420) a phase fault or phase failure based on the measured five-phase stationary reference frame currents (Ia . . . Ie)122-126, the fault detection module214generates a fault signal220(step430) and sends it to αβ-to-five phase transformation module106to indicate that a fault/failure condition has been detected with respect to one (or more) phase(s). The fault signal220includes information that indicates which particular phases are presently experiencing a fault condition or have failed.

The αβ-to-five phase transformation module106in accordance with the disclosed embodiments is designed to identify/select and modify an appropriate equation that is necessary for current regulation in the synchronous frame when one (or more) phase(s) fails. In response to the fault signal220, the αβ-to-five phase transformation module106identifies/selects (step460) equation (4) or (5) below, based on the particular phases that are identified as being faulty or in failure, and modifies the selected equation to generate an appropriate equation for transforming the αβ-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107.

For example, when the fault signal indicates that one phase has faulted/failed, the αβ-to-five phase transformation module106identifies/selects (step460) equation (4) below, and modifies the selected equation (4), based on the particular phases that are identified as being faulty or in failure, to generate an appropriate modified version of equation (4) for transforming the αβ-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107. In particular, the αβ-to-five phase transformation module106modifies equation (4) by setting phase coefficient (δi) for the faulted/failed phase equal to zero (0) to zero out the row that corresponds to the faulting/failing phase. Table 1 ofFIG. 5shows various combinations of the phase coefficients (δi) and the phase shifting differential (Δφi) for various fault scenarios in which equation (4) can apply.

where Table 1 ofFIG. 5indicates which phase has faulted via setting phase coefficient (δi) for that phase equal to zero (0).

For instance, when the fault detection module214detects a phase fault or phase failure based on the measured five-phase stationary reference frame current signal (Ia)122, the fault detection module214generates a fault signal220and sends it to the αβ-to-five phase transformation module106to indicate that a fault/failure condition has been detected with respect to five-phase stationary reference frame current signal (Ia)122that corresponds to phase A. The fault signal220includes information that indicates that phase A is presently experiencing a fault condition or failure. In response to the fault signal220, the αβ-to-five phase transformation module106identifies/selects equation (4) and modifies it as indicated in equation (4A) below to provide improved current regulation in the synchronous frame when phase A has faulted/failed.

In equation (4A) the first row of the transformation matrix has zero values such that phase A is not considered when converting the two-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107.

Thus, the αβ-to-five phase transformation module106can apply the appropriate equation for computation of the five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107such that only the “healthy” or non-faulting phases are taken into account during the transformation. This helps ensure more accurate current regulation in the synchronous frame. Although equation (4A) above assumes that phase A is in a fault condition, it will be appreciated that similar equations (not shown) can be used at the αβ-to-five phase transformation module106to compute non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107when one of the other phases B, C, D, E are experiencing a fault condition. In such cases, the columns of the transformation matrix in equation (4) that correspond to the non-faulting phases would have the same values as indicated in equation (4), and any columns of the transformation matrix that correspond to faulting phase(s) would be replaced with zero values such that the particular faulting phase(s) is/are not considered when converting the two-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107.

The αβ-to-five phase transformation module106then transforms, based on the modified equation, the αβ-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107(step460). Thus, in accordance with the disclosed embodiments, the αβ-to-five phase transformation module106uses the fault signal220to select the appropriate equation that may better provide current regulation in the synchronous frame.

The general equation (2) can also be modified when two phases are experiencing a fault/failure condition. For instance, when the fault signal indicates that phase D, for example, is healthy and that two of the other phases have faulted/failed, the αβ-to-five phase transformation module106identifies/selects (step460) equation (5) below, and modifies the selected equation (5), based on the particular phases that are identified as being faulty or in failure and corresponding entries in Table 2 ofFIG. 6, to generate an appropriate modified version of equation (5) for transforming the αβ-phase stationary reference frame voltage command signals (Vβ* , Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals107. Table 2 ofFIG. 6shows various combinations of the phase scaling coefficients (ki) and the phase shifting differential (Δφi) for various fault scenarios in which equation (5) can apply.

[Vas*Vbs*Vcs*Vds*Ves*]=[ka⁢cos⁡(Δφa)ka⁢sin⁡(Δφa)kb⁢cos⁡(Δφb-2⁢π5)kb⁢sin⁡(Δφb-2⁢π5)kc⁢cos⁡(Δφc-4⁢π5)kc⁢sin⁡(Δφc-4⁢π5)kd⁢cos⁡(Δφd+4⁢π5)kd⁢sin⁡(Δφd+4⁢π5)ke⁢cos⁡(Δφe+2⁢π5)ke⁢sin⁡(Δφe+2⁢π5)]×[Vα*Vβ*],(5)where Table 2 ofFIG. 6indicates which phase has faulted via setting phase coefficient (ki) for that phase equal to zero (0).

It is noted that the equation (5) applies to the specific example when phase D is not faulting along with any two of the other phases. Similar equations can be produced for the other phases A, B, C, E when that phase is not faulting along with any two of the other phases. For sake of brevity, examples of these equations will not be described. In general, the equation (5) can be modified so that it applies to other specific examples when phase A, B, C or E are always healthy (i.e., not faulting/failing) along with any two of the other phases by rotating the transformation matrix by plus/minus seventy-two degrees (72°) or by plus/minus one-hundred forty-four degrees (144°). For example, if phase E is always healthy (i.e., not faulting/failing) along with any two of the other phases, the transformation matrix is rotated by seventy-two degrees (72°) because there are 72 degrees between phases D and E. Similarly, if phase C is always healthy (i.e., not faulting/failing) along with any two of the other phases, the transformation matrix is rotated by negative seventy-two degrees (−72°) because there are 72 degrees between phases C and D. By contrast, if phase A is always healthy (i.e., not faulting/failing) along with any two of the other phases, the transformation matrix is rotated by one-hundred forty-four degrees (144°) because there are 144 degrees between phases A and D. Likewise, if phase B is always healthy (i.e., not faulting/failing) along with any two of the other phases, the transformation matrix is rotated by negative one-hundred forty-four degrees (−144°) because there are 144 degrees between phases B and D.

Consider an example where the fault detection module214detects a phase fault or phase failure based on the measured five-phase stationary reference frame current signal (Ia)122and the measured five-phase stationary reference frame current signal (Ib)123. Here, the fault detection module214generates a fault signal220and sends it to the αβ-to-five phase transformation module106to indicate that a fault/failure condition has been detected with respect to phase A and phase B. The fault signal220includes information that indicates that phases A and B are presently experiencing a fault condition or failure. In response to the fault signal220, the two-to-five phase transformation module106identifies/selects equation (5) above and modifies it to generate equation (5A) below.

In equation (5A), the first and second rows of the transformation matrix have zero values such that phase A and phase B are not considered when converting the two-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vcs* . . . Ves*)107. Using equation (5A) to compute non-faulting five-phase stationary reference frame voltage command signals (Vcs* . . . Ves*)107when both phases A and B have faulted/failed can provide better provide current regulation in the synchronous frame. Thus, the αβ-to-five phase transformation module106can select the appropriate equation and modify it such that only the “healthy” or non-faulting phases are transformed to five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107.

Although equation (5A) above assumes that phases C, D, E are healthy, and that phases A and B are in a fault condition, it will be appreciated that similar equations (not shown) can be used at the αβ-to-five phase transformation module106to compute non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107when any combination of two-phases are experiencing a fault condition. For sake of brevity these are not shown. In all such cases, however, two columns of the transformation matrix that correspond to the faulting phases will include zero values such that the particular faulting phases are not considered when converting the two-phase stationary reference frame voltage command signals (Vα*, Vβ*)104-1,105-1to non-faulting five-phase stationary reference frame voltage command signals (Vas* . . . Ves*)107.

Thus, the disclosed embodiments can provide for fault tolerant synchronous current regulation of a five-phase machine when one (or more) of its phase(s) is faulted. By regulating current in the synchronous reference frame, more accurate current regulation can be achieved. For example, in contrast to current regulation in the stationary phase, the disclosed synchronous frame current regulation techniques do not suffer from phase lag, and therefore, may have faster transient response. In this regard, current regulation may be more robust. In addition, the control tables that convert torque command to current commands (block140inFIG. 1) do not need to be changed for every phase failure case. The disclosed embodiments may also help to maintain optimum torque and power control when the motor operates at high speeds in field-weakening region. In the context of a HEV application, if one of the phases of a five-phase system fails, then the system can still operate on a lower power rating during the phase fault, and the disclosed techniques allow for current regulation to be maintained to provide torque and power and allow the vehicle operator to continue driving, and, for example, to reach their destination or get to a shop for fault diagnostic.

Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Some of the embodiments and implementations are described above in terms of functional and/or logical block components (or modules) and various processing steps. However, it should be appreciated that such block components (or modules) may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions.

To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. For example, an embodiment of a system or a component may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments described herein are merely exemplary implementations.