Electric motor control

Abstract

A method for controlling an alternating current (AC) electric motor by means of a voltage inverter having a plurality of electrical switches having on-off states which collectively define a plurality of non-zero vectors arranged angularly with respect to a common origin, the method includes calculating, by one or more controllers, a rotating voltage reference vector for application to the AC electric motor by a voltage inverter. The method further includes calculating, by one or more controllers, a voltage inverter switching time using a first subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and not including adjacent non-zero vectors. Further, the method includes applying, by the voltage inverter, the rotating voltage reference vector to the AC electric motor.

Description

[0001] introduction The present disclosure belongs to the field of electric motor control.

[0002] Electric motors are used in many applications, including generating traction power for propelling electric vehicles. In the control of AC electric motors, particularly high voltage electric motors, significant unintended leakage currents generated during motor operation may reduce the efficiency of the motor. In addition, unintended leakage currents may travel through various components of the motor, such as its bearings, which may affect the durability of the motor. Therefore, a motor control method that reduces unintended leakage currents may be advantageous. Summary of the invention

[0003] A method for controlling an AC (alternating current) electric motor via a voltage inverter having a plurality of electrical switches with on-off states that collectively define a plurality of non-zero vectors angularly disposed about a common origin, the method comprising: calculating, via one or more controllers, a rotating voltage reference vector to be applied to the AC electric motor via the voltage inverter. The method further comprises: calculating, via one or more controllers, a switching time of the voltage inverter using a first subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors. Additionally, the method comprises: applying, via the voltage inverter, the rotating voltage reference vector to the AC electric motor.

[0004] As an additional feature, the method may further include: calculating, by one or more controllers, a switching time of a voltage inverter using a second subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the second subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors, wherein the second subset of the plurality of non-zero vectors is different from the first subset of non-zero vectors; and applying, by the voltage inverter, the rotating voltage reference vector to the AC electric motor. The first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors may have no common members.

[0005] The AC electric motor may be a three-phase electric motor and the voltage inverter may be an H-bridge two-level voltage inverter having six electrical switches and six non-zero vectors. Alternatively, the voltage inverter may be a multi-level voltage inverter having 24 non-zero vectors.

[0006] Furthermore, applying the rotating voltage reference vector to the AC electric motor may include applying the voltage reference vector via pulse width modulation, and the pulse width modulation may be a state vector pulse width modulation.

[0007] As an alternative, each non-zero vector in the first subset of the plurality of non-zero vectors may produce a first resulting voltage at the neutral point of the AC electric motor. As yet another alternative, each non-zero vector in the second subset of the plurality of non-zero vectors may produce a second resulting voltage at the neutral point of the AC electric motor. The first resulting voltage may be different from the second resulting voltage. The method may also include: changing from using the first subset of non-zero vectors to using the second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

[0008] A second method for controlling an AC electric motor via a voltage inverter having a plurality of electrical switches with on-off states that collectively define a plurality of non-zero basis vectors angularly disposed about a common origin, the method comprising: calculating, via one or more controllers, a rotational state vector to be applied to the AC motor via the voltage inverter. The method further comprises: controlling, via the one or more controllers, switching of the voltage inverter using a first subset of the plurality of non-zero basis vectors to synthesize the rotational state vector, the first subset including less than all of the plurality of non-zero basis vectors and excluding adjacent non-zero basis vectors. Still further, the method comprises: applying, via the voltage inverter, the rotational state vector to the AC electric motor via pulse width modulation.

[0009] The method may additionally include: controlling, by one or more controllers, switching of a voltage inverter using a second subset of the plurality of non-zero base vectors to synthesize a rotating state vector, the second subset including less than all of the plurality of non-zero base vectors and excluding adjacent non-zero base vectors, wherein the second subset of the plurality of non-zero base vectors is different from the first subset of non-zero base vectors; and applying, by the voltage inverter, the rotating state vector to the AC electric motor by pulse width modulation. The first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors may have no common members.

[0010] In addition, the method may include: calculating, by one or more controllers, a voltage inverter switching time using all non-zero basis vectors to synthesize a rotating state vector; and applying, by the voltage inverter, the rotating state vector to the AC electric motor by pulse width modulation. A first subset of the non-zero basis vectors may be used in a first AC electric motor operating condition, and all of the non-zero basis vectors may be used in a second AC electric motor operating condition. The first AC electric motor operating condition may be a lower motor speed or lower motor torque condition than the second AC electric motor operating condition.

[0011] In the method for controlling an AC electric motor, each non-zero vector in a first subset of the plurality of non-zero vectors may generate a first resulting voltage at a neutral point of the AC electric motor, and each non-zero vector in a second subset of the plurality of non-zero vectors may generate a second resulting voltage at a neutral point of the AC electric motor. The first resulting voltage may be different from the second resulting voltage. Additionally, in response to a voltage of a shaft of a rotor of the AC electric motor, use of the first subset of non-zero vectors may be changed to use of the second subset of the plurality of non-zero vectors.

[0012] A motor vehicle includes a source of stored electrical energy and an AC electric motor. The motor vehicle also includes a voltage inverter coupled to the source of stored electrical energy and the AC electric motor to provide switched electrical energy from the source of stored electrical energy to the AC electric motor, the voltage inverter having a plurality of electrical switches having on-off states that collectively define a plurality of non-zero vectors angularly disposed about a common origin. The motor vehicle additionally includes one or more controllers. The one or more controllers are collectively programmed with instructions to: calculate a rotating voltage reference vector to apply to the AC electric motor through the voltage inverter; calculate switching times of the voltage inverter using a first subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors; and apply the rotating voltage reference vector to the AC electric motor through the voltage inverter.

[0013] The one or more controllers may additionally be collectively programmed with the following instructions: using a second subset of the plurality of non-zero vectors to calculate, by the one or more controllers, a switching time of the voltage inverter to synthesize a rotating voltage reference vector, the second subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors, wherein the second subset of the plurality of non-zero vectors is different from the first subset of non-zero vectors; and applying, by the voltage inverter, the rotating voltage reference vector to the AC electric motor.

[0014] The first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors may have no common members. Each non-zero vector in the first subset of the plurality of non-zero vectors may produce a first resulting voltage at a neutral point of the AC electric motor, and each non-zero vector in the second subset of the plurality of non-zero vectors may produce a second resulting voltage at a neutral point of the AC electric motor. The first resulting voltage may be different from the second resulting voltage.

[0015] The one or more controllers may be further programmed with instructions to change from using a first subset of non-zero vectors to using a second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

[0016] The present disclosure provides the following embodiments: 1. A method for controlling an AC electric motor by a voltage inverter having a plurality of electrical switches having on-off states, the on-off states collectively defining a plurality of non-zero vectors angularly disposed about a common origin, the method comprising: calculating, by one or more controllers, a rotating voltage reference vector for application to the AC electric motor via a voltage inverter; calculating, by the one or more controllers, a switching time of the voltage inverter using a first subset of the plurality of non-zero vectors to synthesize the rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors; and A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter.

[0017] 2. The method according to embodiment 1, further comprising: calculating, by one or more controllers, a switching time of a voltage inverter using a second subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the second subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors, wherein the second subset of the plurality of non-zero vectors is different from the first subset of non-zero vectors; and A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter.

[0018] 3. The method of embodiment 2, wherein the first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors have no common members.

[0019] 4. The method of embodiment 1, wherein: The AC electric motor is a three-phase electric motor; and The voltage inverter is an H-bridge two-level voltage inverter with six electrical switches and six non-zero vectors.

[0020] 5. The method of embodiment 1, wherein: The AC electric motor is a three-phase electric motor; and The voltage inverter is a multi-level voltage inverter with 24 non-zero vectors.

[0021] 6. The method of embodiment 1 wherein the step of applying a rotating voltage reference vector to the AC electric motor comprises applying the voltage reference vector via pulse width modulation.

[0022] 7. The method of embodiment 6, wherein the pulse width modulation is state vector pulse width modulation.

[0023] 8. The method of embodiment 2, wherein each non-zero vector in the first subset of the plurality of non-zero vectors produces a first resulting voltage at a neutral point of the AC electric motor.

[0024] 9. The method of embodiment 8, wherein each non-zero vector in the second subset of the plurality of non-zero vectors produces a second resulting voltage at a neutral point of the AC electric motor, wherein the first resulting voltage is different from the second resulting voltage.

[0025] 10. The method of embodiment 2, comprising changing from using a first subset of non-zero vectors to using a second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

[0026] 11. A method for controlling an AC electric motor by a voltage inverter having a plurality of electrical switches having on-off states, the on-off states collectively defining a plurality of non-zero basis vectors angularly disposed about a common origin, the method comprising: calculating, via one or more controllers, a rotational state vector for application to an AC motor via a voltage inverter; controlling, by one or more controllers, switching of a voltage inverter using a first subset of the plurality of non-zero basis vectors to synthesize a rotating state vector, the first subset including less than all of the plurality of non-zero basis vectors and excluding adjacent non-zero basis vectors; and The rotating state vector is applied to the AC electric motor via a voltage inverter by pulse width modulation.

[0027] 12. The method according to embodiment 11, further comprising: controlling, by one or more controllers, switching of a voltage inverter using a second subset of the plurality of non-zero base vectors to synthesize a rotating state vector, the second subset including less than all of the plurality of non-zero base vectors and excluding adjacent non-zero base vectors, wherein the second subset of the plurality of non-zero base vectors is different from the first subset of non-zero base vectors; and applying, by the voltage inverter, the rotating state vector to the AC electric motor by pulse width modulation; wherein The first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors have no common members.

[0028] 13. The method according to embodiment 12, further comprising: calculating, by one or more controllers, voltage inverter switching times using all non-zero basis vectors to synthesize a rotating state vector; and A rotating state vector is applied to an AC electric motor via a voltage inverter by pulse width modulation; wherein a first subset of the non-zero basis vectors are used in a first AC electric motor operating condition and all of the non-zero basis vectors are used in a second AC electric motor operating condition; and The first AC electric motor operating condition is a lower motor speed or lower motor torque condition than the second AC electric motor operating condition.

[0029] 14. The method of embodiment 12, wherein: Each non-zero vector in a first subset of the plurality of non-zero vectors produces a first resulting voltage at a neutral point of the AC electric motor; and Each non-zero vector in a second subset of the plurality of non-zero vectors produces a second resulting voltage at a neutral point of the AC electric motor; wherein The first resulting voltage is different from the second resulting voltage.

[0030] 15. The method of embodiment 12, comprising changing from using the first subset of the non-zero vectors to using the second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

[0031] 16. A motor vehicle comprising: the source of the stored electrical energy; AC electric motor; a voltage inverter coupled to the source of stored electrical energy and the AC electric motor to provide switched electrical energy from the source of stored electrical energy to the AC electric motor, the voltage inverter having a plurality of electrical switches having on-off states that collectively define a plurality of non-zero vectors angularly disposed about a common origin; and One or more controllers are collectively programmed using the following instructions: calculating a rotating voltage reference vector for application to an AC electric motor via a voltage inverter; calculating a switching time of a voltage inverter using a first subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors; and A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter.

[0032] 17. The motor vehicle of embodiment 16, wherein the one or more controllers are further collectively programmed with the following instructions: calculating, by one or more controllers, a switching time of a voltage inverter using a second subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the second subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors, wherein the second subset of the plurality of non-zero vectors is different from the first subset of non-zero vectors; and A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter.

[0033] 18. The motor vehicle of embodiment 17 wherein the first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors have no common members.

[0034] 19. The motor vehicle of embodiment 18, wherein: Each non-zero vector in a first subset of the plurality of non-zero vectors produces a first resulting voltage at a neutral point of the AC electric motor; and Each non-zero vector in the second subset of the plurality of non-zero vectors produces a second resulting voltage at a neutral point of the AC electric motor, wherein the first resulting voltage is different than the second resulting voltage.

[0035] 20. The motor vehicle of embodiment 17 wherein the one or more controllers are further programmed with instructions to change from using a first subset of non-zero vectors to using a second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

[0036] The above summary of the invention does not represent every embodiment or every aspect of the present disclosure. The above features and advantages of the present disclosure and other possible features and advantages will become apparent from the following detailed description of the embodiments and best modes for implementing the present disclosure when considered in conjunction with the accompanying drawings and the appended claims. In addition, the present disclosure expressly includes combinations and sub-combinations of the elements and features presented above and above. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A motor vehicle and an electric motor control system therefor are shown.

[0038] Figure 2 It is a vector diagram showing the control mode of the electric motor.

[0039] Figure 3 Shows Figure 1 The cross-section of the electric motor and the specific current associated with the electric motor.

[0040] Figure 4 A vector diagram is shown representing an alternative control mode for an electric motor.

[0041] Figure 5A vector diagram is shown representing another alternative control mode for an electric motor.

[0042] Figure 6 Resulting waveforms of a switching voltage associated with a voltage inverter and an induced voltage on a shaft of an electric motor coupled to the voltage inverter are illustrated.

[0043] Figure 7 A multilevel inverter is illustrated.

[0044] Figure 8 The diagram shows Figure 7 Vector of switching elements of a multilevel inverter.

[0045] Fig. 9 The diagram shows the use of a multi-level inverter (such as Figure 7 The electric motor control strategy of the inverter is as follows. DETAILED DESCRIPTION

[0046] The present disclosure allows for embodiments in many different forms. Representative examples of the present disclosure are shown in the accompanying drawings and are described in detail herein as non-limiting examples of the disclosed principles. For this reason, elements and limitations described in the abstract, introduction, summary, and detailed description, but not explicitly set forth in the claims, should not be incorporated into the claims individually or collectively by implication, inference, or otherwise.

[0047] For the purposes of this description, unless specifically disavowed, the use of the singular includes the plural, and vice versa, the terms "and" and "or" shall be both conjunctive and disjunctive, "any" and "all" shall mean both "any and all", and the words "include", "comprising", "including", "having", etc. shall mean "including but not limited to". In addition, approximate words (such as "approximately", "almost", "substantially", "substantially", "approximately", etc.) may be used herein in the sense of "at, close to, or nearly at", or "within 0-5% of...", or "within acceptable manufacturing tolerance", or their logical combinations.

[0048] First reference Figure 1, a motor control system 12 is illustrated. The motor control system 12 may be used in an electric vehicle 10. The motor control system 12 may include a traction battery 20, a power inverter module (PIM) 22, an electronic control unit (ECU) 24, and an electric motor 26. The traction battery 20 may include one or more batteries or battery cells. The electric vehicle 10 may be a vehicle that uses an electric motor for at least a portion of vehicle propulsion, and may be an all-electric or hybrid electric vehicle. In addition, the electric vehicle 10 may be any style of vehicle, such as a car, truck, sport utility vehicle, motorcycle, bicycle, all-terrain vehicle, etc. The electric motor 26 may be a motor that provides traction power for propulsion of the electric vehicle 10.

[0049] The power inverter module 22 may include six switching elements - switching element 30, switching element 31, switching element 32, switching element 33, switching element 34 and switching element 35. The switching elements may have various technologies for the purposes of the present disclosure, including insulated gate bipolar transistors (IGBTs) and field effect transistors (FETs). Switching element 30, switching element 31, switching element 32, switching element 33, switching element 34 and switching element 35 may also be collectively referred to as switching elements 30-35 hereinafter.

[0050] The electronic control unit 24 may control the switching of the switching elements 30-35 for the purpose of controlling and providing voltage to the electric motor 26. The electronic control unit 24 is understood to have appropriate electronic resources (microprocessor, software, memory, inputs, outputs, etc.) to perform the functions attributed to the electronic control unit 24 herein. The electronic control unit 24 may be a stand-alone controller, may be integrated with the power inverter module 22, or may be integrated with other controllers on the electric vehicle 10 including the motor control system 12. The electronic control unit 24 may also be networked with other controllers and share responsibility for performing the functions laid out herein.

[0051] The electric motor 26 may be an alternating current (AC) motor. The electric motor 26 may be, for example, a permanent magnet motor (and further, a permanent magnet synchronous motor) or an induction motor. For simplicity, the electric motor 26 is Figure 1 In the embodiment, the stator windings are represented by stator windings 40, 42 and 44, wherein Figure 1 The rotor of the electric motor 26 is omitted in FIG. The stator windings may be connected together at a neutral point 48. The electric motor 26 may have a conductive housing 46.

[0052] exist Figure 1Various leakage capacitors may exist in the illustrated motor control system, including a leakage capacitor C between the negative rail N (negative rail) of the power inverter module 22 and the ground 49 (GND). S1 , the leakage capacitance C between the housing 46 of the electric motor 26 and the ground 49 S2 , and the leakage capacitance C between the neutral point 48 of the stator winding of the electric motor 26 and the housing 46 of the electric motor 26 S3 .

[0053] The electric motor 26 can be controlled by so-called field oriented control (FOC). In FOC, the current entering the stator winding of the electric motor 26 is decomposed into two orthogonal currents - the flux induction component i and the flux induction component i. d and the torque induction component i q , which form the basis for the signal provided for commanding the electric motor 26. In conjunction with FOC, as well as other situations, the so-called Clarke transformation can be used to reduce multi-phase quantities in a balanced three-phase system to two-dimensional quantities in the alpha-beta domain.

[0054] In an implementation of FOC control, a rotating voltage reference vector in the α-β domain may be calculated at high speed (i.e., much higher than the speed at which the electric motor operates) for providing a three-phase voltage to the electric motor in order to generate a desired mechanical output (torque / speed) from the electric motor. The rotating voltage reference may be applied by the power inverter module 22 to the electric motor 26, such as by pulse width modulation (PWM), including state vector PWM (SVPWM), where the rotating voltage reference vector may be referred to as a “state vector”.

[0055] Figure 2 The implementation of SVPWM is described. SVPWM can be operated under the assumption that the switching elements in any branch of the power inverter module 22 (e.g., the leftmost branch including switching element 30 and switching element 31, the middle branch including switching element 32 and switching element 33, or the rightmost branch including switching element 34 and switching element 35) have complementary states (i.e., one switching element is closed and one switching element is open). Under this assumption, there are eight states, defining eight vectors, in which the switching elements 30-35 can be commonly located.

[0056] For convenience, these eight vectors can be labeled by three binary digits. The first digit can identify the state of switching element 30 ("1" = closed, "0" = open), which is the upper switching element in the leftmost branch of the power inverter module 22. When switching element 30 is closed, switching element 31 is therefore open. The second binary digit can identify the state of switching element 32 ("1" = closed, "0" = open), which is the upper switching element in the central branch of the power inverter module 22. When switching element 32 is closed, switching element 33 is therefore open. The third digit can identify the state of switching element 34, which is the upper switching element in the rightmost branch of the power inverter module 22. When switching element 34 is closed, switching element 35 is therefore open (recall that any two switching elements in a branch of a power inverter module have complementary states).

[0057] The eight different vectors of the switching elements 30 - 35 of the power inverter module 22 are correspondingly explained with reference to the following table: Vector Inverter switching status CMV value M0 000 0 M1 100 <![CDATA[V PN / 3]]> M2 110 <![CDATA[2V PN / 3]]> M3 010 <![CDATA[V PN / 3]]> M4 011 <![CDATA[2V PN / 3]]> M5 001 <![CDATA[V PN / 3]]> M6 101 <![CDATA[2V PN / 3]]> M7 111 <![CDATA[V PN / 3V]]> .

[0058] Vectors M0 to M7 may be referred to as "base" vectors. Vectors M1-M6 may be referred to as "non-zero" vectors, considering that they have magnitudes greater than zero. Vectors M0 and M7 may be referred to as "zero" vectors, considering that they have zero magnitudes (i.e., they are located at the origin of the α-β plane). Vectors M1-M6 may be described as being "angled" about a common origin 51 in the α-β plane.

[0059] The vector labeled M0 (000) may represent that all upper switching elements (i.e., switching element 30, switching element 32, and switching element 34) are open. The vector labeled M7 (111) may represent that all upper switching elements (i.e., switching element 30, switching element 32, and switching element 34) are closed. Vectors M1 to M6 may represent vectors in which one or two of switching element 30, switching element 32, and switching element 34 (i.e., upper switching elements in power inverter module 22) are closed.

[0060] Continuing with reference to the table above, the resulting common mode voltage (CMV) at the neutral point 48 of the electric motor 26 and associated with vectors M0 through M7 is shown. For vector M0, the resulting CMV at the neutral point 48 is zero because all switching elements 30, 32, and 34—switching elements coupled to the positive rail P—are open, and all switching elements 31, 33, and 35—switching elements coupled to the negative rail N—are closed. For vector M7, the resulting CMV at the neutral point 48 is V PN, the voltage between the positive rail P and the negative rail N, because all upper switching elements are closed (ie, connected to the positive rail P) and all lower switching elements are open.

[0061] For vector M1, switching element 30, switching element 33, and switching element 35 are open. Therefore, the resulting CMV at the neutral point 48 of the electric motor 26 is V PN / 3, where V PN is the DC voltage between the positive rail P and the negative rail N of the power inverter module 22 and the traction battery 20. For vectors M3 and M5, the resulting CMV at the neutral point 48 is also V PN / 3, one of the upper switching elements (switching element 32 and switching element 34 respectively) is closed.

[0062] For vector M2, switching element 30, switching element 32 and switching element 35 are closed. Therefore, the resulting CMV at the neutral point 48 of the electric motor 26 is 2V PN / 3. This is also true for vector M4 and vector M6.

[0063] The unintended leakage current generated in the electric motor 26 can be attributed to, and is a function of, the time rate of change of the CMV of the electric motor 26. This can be illustrated by the fact that for a capacitor, the current i through the capacitor is i=Cdv / dt, where C is the capacitance and dv / dt is the time rate of change of the voltage across the capacitor. Therefore, reducing the time rate of change of the voltage across the capacitor will reduce the current therethrough.

[0064] As an example of SVPWM modulation, consider V ref - rotating voltage reference vector, which will be applied by the power inverter module 22 to the electric motor 26 - in Figure 2 The position in the α-β plane shown. To create this voltage vector, a combination of vector M1, vector M2 and vector M0 and / or vector M7 can be used. During the PWM duty cycle, a sufficient fraction of the period of the carrier signal can apply M1, M2 and M0 and / or M7 to result in a vector sum (magnitude and direction) of V ref However, in this case, the resulting CMV at the neutral point 48 of the electric motor 26 will be between the vectors M1 and M2, i.e., at V PN / 3 vs 2V PN / 3. This will tend to cause dv / dt in the CMV which results in leakage current.

[0065] Additional references Figure 3. Therein, a stator 50 and a rotor 56 are illustrated, along with a housing 46 of the electric motor 26 and bearings 52 and 54 of the electric motor 26. The rotor 56 is mounted on a shaft 58 for rotation therewith. A gearbox 70 is also schematically illustrated, the gears of which may be driven by the electric motor 26. Various currents resulting from dv / dt in the CMV are illustrated, including leakage current 60, leakage current 62, and leakage current 64 (which together result in leakage current i leakage ), together with the circulating current 66.

[0066] However, considering Figure 4 An alternative control strategy is shown. In this control strategy, the use of vectors M2, M4 and M6 can be omitted. The voltage reference vector V ref can be generated as a vector sum using only vectors M1, M3, and M5. Recall from the table above that in each of vectors M1, M3, and M5, the resulting common mode voltage (CMV) at the neutral point 48 of the electric motor 26 is V PN / 3. Thus, using only vectors M1, M3, and M5 will reduce or eliminate the rate of change of CMV of electric motor 26 and the resulting i=Cdv / dt current associated with the time rate of change of CMV. Figure 4 It is obvious that vector M1, vector M3 and vector M5 are used - the non-adjacent non-zero vectors obtained by omitting vector M2, vector M4 and vector M6. In other words, the adjacent non-zero vectors are not used.

[0067] exist Figure 4 In the illustrated variation of the control strategy, reference is now made to Figure 5 Here, the voltage reference vector V ref can be generated using only vectors M2, M4, and M6. Recall from the table above that in each of vectors M2, M4, and M6, the resulting common mode voltage at the neutral point 48 is 2V. PN / 3. Thus, using only vectors M2, M4, and M6 will reduce or eliminate the time rate of change of CMV of electric motor 26 and the resulting i=Cdv / dt current between neutral point 48 and ground 49 associated with the time rate of change of CMV. Figure 4 It is obvious that vector M2, vector M4 and vector M6 are used - the non-adjacent non-zero vectors obtained by omitting vector M1, vector M3 and vector M5. In other words, the adjacent non-zero vectors are not used.

[0068] As noted above, the voltage reference vector Vref is a rotating vector. However, regardless of which part of the α-β plane Vref is in, Vref can be synthesized using the vector sum of vectors M1, M3, and M5 (at the appropriate PWM duty ratios of these three vectors), or by using the vector sum of vectors M2, M4, and M6 (again, at the appropriate PWM duty ratios of these three vectors).

[0069] It is also contemplated that the switching of the switching elements 30-35 may induce a common mode voltage on the shaft 58 of the electric motor 26. An example may be Figure 6 It is shown in Figure 6 The common mode voltage (CMV) associated with the switching of the switching elements 30-35 of the power inverter module 22 may induce a common mode voltage on the shaft 58 of the electric motor 26. The waveform 80 associated with the switching of the switching elements 30-35 may be reflected in the waveform 82, which shows the voltage V measured at the shaft 58 of the electric motor 26. sft The induced common mode voltage at shaft 58 may accumulate over time and may become large enough to exceed the breakdown voltage of the oil film in bearing 52. This induced voltage may travel on path 72 through bearing 52, which represents a significant potential for fretting due to electrical discharge machining (EDM). The current traveling on path 72 may also travel through gearbox 70, which similarly causes damage.

[0070] However, the absolute voltage level on the shaft 58 of the electric motor 26 may be measured, such as by using a conductive brush carried on the shaft 58 of the electric motor 26. If the voltage level on the shaft 58 of the electric motor 26 is observed to be increasing, then Figure 5 The control strategy shown (i.e., using vectors M2, M4, and M6) can be transformed to Figure 4 The control strategy shown (ie, using vectors M1, M3 and M5) is to counteract the accumulation of common mode voltage of the shaft of the electric motor 26. A reverse direction can also be adopted (from Figure 4 The control strategy changes to Figure 5 control strategy).

[0071] The motor control method and system thus described may be useful when the electric motor 26 is operated at relatively low or moderate speeds, where the fullest voltage capacity of the power inverter module 22 is not required.

[0072] Reference now Figure 7 Here, an alternative inverter is illustrated. The inverter 300 can be connected between two rails V DC / 2 and -V DC / 2. Here, inverter 300 includes three branches, branch 302, branch 304, and branch 306, and three phase outputs, output 308, output 310, and output 312, which can be connected to the stator windings of electric motor 26. In the multi-level configuration shown for inverter 300, each of output 308, output 310, and output 312 can present three different voltages. As an illustration, it is assumed that switching element 320 and switching element 322, as well as switching element 324 and switching element 326 are turned off. In this case, output 308 presents a voltage V DC / 2. If switching element 324 and switching element 326 are turned on, and switching element 320 and switching element 322 are turned off, output 308 exhibits a voltage of -V DC If switching element 322 and switching element 324 are turned on, and switching element 320 and switching element 326 are turned off, output 308 exhibits a voltage of 0V (zero volts).

[0073] Figure 8 A vector diagram of the vector for the inverter 300 is shown in FIG. Figure 3 The voltage applied to the electric motor 26 may have 27 vectors, compared to the eight vectors shown. Figure 8 In each vector shown, the voltage state (P = V DC / 2, N = -V DC / 2, and O = 0V). For vectors 300a, 300b, 300c, 300d, 300e, and 300f, the resulting voltage at the neutral point 48 is + / -V DC / 2. For vector 302a, vector 302b, vector 302c, vector 302d, vector 302e, and vector 302f, the resulting voltage applied at neutral point 48 is + / -V DC / 3. For vector 304a, vector 304b, vector 304c, vector 304d, vector 304e, and vector 304f, the resulting voltage at neutral point 48 is + / -V DC / 6. Finally, for vector 307, the resulting voltage at neutral point 48 is zero volts. Obviously, Figure 8 24 non-zero vectors are illustrated.

[0074] In the case of modulation using the inverter 300, in various torque-speed regions ( Fig. 94 (illustrated in FIG. 4 ) can be performed by selecting vectors that produce the same common mode voltage at the neutral point 48 of the electric motor 26. For example, operation in region 320a, region 320b, and region 320c can be performed by selecting vector 300a, vector 300b, vector 300c, vector 300d, vector 300e, and vector 300f to exclude vectors 302a-302f and vectors 304a-304f. In addition, operation in regions 322a and 322b can be performed by selecting vector 304a, vector 304b, vector 304c, vector 304d, vector 304e, and vector 304f. Finally, operation in region 324 can be performed by selecting vector 302a, vector 302b, vector 302c, vector 302d, vector 302e, and vector 302f.

[0075] As a way of boosting the voltage available for controlling the electric motor 26 , so-called third-harmonic injection may be used.

[0076] The motor control method and system disclosed in the present disclosure can reduce leakage current in the electric motor 26 by reducing the time rate of change of the common mode voltage at the neutral point 48 of the electric motor 26. Additionally, electrical discharge machining (EDM) currents that can damage the bearings of the electric motor 26 and the gears within the gearbox 70 can be reduced.

[0077] The motor control methods and systems disclosed herein may result in a reduced need for common mode chokes that might otherwise be used to suppress common mode currents.

Claims

1. A method for controlling an AC electric motor by a voltage inverter having a plurality of electrical switches having on-off states, the on-off states collectively defining a plurality of non-zero vectors angularly disposed about a common origin, the method comprising: calculating, via one or more controllers, a rotating voltage reference vector for application to the AC electric motor via a voltage inverter; calculating, by one or more controllers, a switching time of a voltage inverter using a first subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the first subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors; as well as A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter.

2. The method according to claim 1, further comprising: calculating, by one or more controllers, a switching time of a voltage inverter using a second subset of the plurality of non-zero vectors to synthesize a rotating voltage reference vector, the second subset including less than all of the plurality of non-zero vectors and excluding adjacent non-zero vectors, wherein the second subset of the plurality of non-zero vectors is different from the first subset of non-zero vectors; as well as A rotating voltage reference vector is applied to the AC electric motor via a voltage inverter. 3 . The method of claim 2 , wherein the first subset of the plurality of non-zero vectors and the second subset of the plurality of non-zero vectors have no common members.

4. The method according to claim 1, wherein: The AC electric motor is a three-phase electric motor; and The voltage inverter is an H-bridge two-level voltage inverter with six electrical switches and six non-zero vectors.

5. The method according to claim 1, wherein: The AC electric motor is a three-phase electric motor; and The voltage inverter is a multi-level voltage inverter with 24 non-zero vectors.

6. The method of claim 1 wherein the step of applying a rotating voltage reference vector to the AC electric motor comprises applying the voltage reference vector via pulse width modulation.

7. The method of claim 6, wherein the pulse width modulation is state vector pulse width modulation. 8 . The method of claim 2 , wherein each non-zero vector in the first subset of the plurality of non-zero vectors produces a first resulting voltage at a neutral point of the AC electric motor. 9 . The method of claim 8 , wherein each non-zero vector in the second subset of the plurality of non-zero vectors produces a second resulting voltage at a neutral point of the AC electric motor, wherein the first resulting voltage is different from the second resulting voltage.

10. The method of claim 2, comprising changing from using a first subset of non-zero vectors to using a second subset of the plurality of non-zero vectors in response to a voltage of a shaft of a rotor of the AC electric motor.

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