System and method for protecting motor magnets during a three-phase short circuit

Abstract

Systems and methods for protecting motor magnets during a three-phase short circuit operating condition are provided herein. One system includes a power electronics configured to provide current to a three-phase electric motor using a plurality of switches; and a control circuit configured to transition the three-phase electric motor to a three-phase short circuit operating condition using the plurality of switches, and alternate between the three-phase short circuit operating condition and a three-phase open circuit operating condition using the plurality of switches based on a transient current of the three-phase electric motor. In some embodiments, the transition from the three-phase short circuit operating condition to the three-phase open circuit operating condition is in response to the transient current exceeding a threshold. In some embodiments, the transition to a three-phase short circuit operating condition is in response to at least one switch of the plurality of switches being damaged.

Description

[0001] introduction

[0002] This disclosure relates to systems and methods for switching an electric motor to a three-phase short-circuit condition. More specifically, this disclosure relates to protecting the motor during a three-phase short-circuit condition by alternating between a three-phase short-circuit condition and a three-phase open-circuit condition based on the motor's transient current. Summary of the Invention

[0003] The operation of an electric motor (e.g., within an electric vehicle) may include various fail-safe procedures. These procedures should be able to protect the motor, including the motor's magnets and the battery coupled to the electric motor. In some cases, the motor driver switch may malfunction (e.g., get stuck in an open or closed position) and generate a voltage imbalance. To prevent this voltage imbalance from causing excessive current to flow to the battery, other motor switches may be controlled to create a short-circuit condition across the motor (which may have been preceded by an open-circuit condition). However, this short-circuit condition may cause excessive current to flow through the electric motor and demagnetize the motor's magnets. An open-circuit condition may be introduced before the short-circuit condition to reduce excessive current, but this approach may not protect the magnets when faced with relatively large voltage imbalances. According to embodiments of this disclosure, alternating short-circuit and open-circuit conditions (i.e., a short-circuit condition followed by at least one instance of alternation between an open-circuit and short-circuit condition) are considered as a fail-safe method for protecting the motor magnets in response to voltage imbalances. In some implementations, the corresponding time amounts associated with each short-circuit condition and each open-circuit condition are determined based on the motor temperature, motor speed, characteristics of the motor magnets, voltage imbalance, or any combination thereof.

[0004] According to embodiments of this disclosure, systems, methods, and electric vehicles are provided for protecting motor magnets during a three-phase short circuit. One system includes power electronic devices configured to supply current to a three-phase electric motor using a plurality of switches. The system also includes control circuitry configured to switch the three-phase electric motor to a three-phase short-circuit condition using the plurality of switches, and to alternate between the three-phase short-circuit condition and a three-phase open-circuit condition based on transient currents of the three-phase electric motor. One method includes operating the control circuitry to achieve the aforementioned switching and alternation. The electric vehicle includes a three-phase electric motor coupled to one or more wheels, as well as the power electronic devices and the control circuitry.

[0005] In some implementations, the control circuit is configured to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition by switching the three-phase electric motor from the three-phase short-circuit condition to the three-phase open-circuit condition in response to the transient current exceeding a threshold.

[0006] In some implementations, the control circuit is configured to determine the threshold based on the temperature associated with the three-phase electric motor.

[0007] In some implementations, the control circuit is configured to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition by switching the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition based on the transient current and steady-state three-phase short-circuit current of the three-phase electric motor.

[0008] In some implementations, the control circuit is configured to determine the steady-state three-phase short-circuit current based on the motor speed.

[0009] In some implementations, the control circuit is configured to switch the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition when the distance between the vector associated with the transient current and the steady-state three-phase short-circuit current is less than a threshold distance.

[0010] In some implementations, the control circuit is further configured to determine whether the transient current meets the steady-state three-phase short-circuit current condition, and to terminate the alternation in response to the transient current meeting the steady-state three-phase short-circuit current condition.

[0011] In some implementations, the control circuit is further configured to determine whether one of the plurality of switches is damaged, and in response to determining that one of the plurality of switches is damaged, to switch the three-phase electric motor to the three-phase short-circuit condition.

[0012] In some implementations, the plurality of switches includes a first switch, a second switch, and a third switch respectively coupled to the first, second, and third phases of the three-phase electric motor, and the control circuit is configured to switch the three-phase electric motor to the three-phase short-circuit condition by closing the first switch, the second switch, and the third switch. Attached Figure Description

[0013] The above and other objects and advantages of this disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein similar reference characters always refer to similar parts, and wherein:

[0014] Figure 1 An exemplary block diagram of components of a three-phase electric motor system according to some embodiments of the present disclosure is shown;

[0015] Figure 2 This is an exemplary graph showing the temperature-dependent characteristics of a magnet based on the current applied to both ends of a motor including a magnet, according to some embodiments of the present disclosure;

[0016] Figure 3This is the first example of an indicative plot showing the transient current distribution associated with a three-phase short-circuit condition;

[0017] Figure 4 This is a second example of an indicative plot showing the transient current distribution associated with a three-phase short-circuit condition;

[0018] Figure 5 This is a third example of an indicative plot showing the transient current distribution associated with a three-phase open-circuit condition and a subsequent three-phase short-circuit condition;

[0019] Figure 6 This is an exemplary flowchart of a method for switching a motor to a three-phase short-circuit condition by alternating between a three-phase short-circuit condition and a three-phase open-circuit condition, according to some embodiments of this disclosure.

[0020] Figure 7 This is a fourth exemplary graph showing the current distribution associated with a method for protecting motor magnets during a three-phase short circuit, according to some embodiments of this disclosure; and

[0021] Figure 8 This is an exemplary flowchart of a method for protecting a motor during a transition to a three-phase short-circuit condition, according to some embodiments of this disclosure. Detailed Implementation

[0022] An electric motor system (e.g., as part of an electric vehicle) may include a three-phase motor (e.g., including magnetic materials), a motor driver (e.g., including three pairs of switches, each coupled to a corresponding phase of the three-phase motor), and a power source (e.g., a battery). The electric motor system can use electricity to rotate driven components (e.g., including a drivetrain and wheels).

[0023] During operation of an electric motor system, a portion of the motor drive (e.g., any of the three pairs of switches) may fail, potentially causing large transient currents to flow into other components, such as the battery. These large transient currents can damage other components. To protect other components from potential damage, a short-circuit condition can be implemented across all three phases of the three-phase motor. This short-circuit condition causes large transient currents to flow through the motor instead of into other components (e.g., the battery).

[0024] Applying a short-circuit condition to protect the battery can lead to demagnetization of the magnetic materials in a three-phase motor when a large transient current flows through it. To protect the motor and other components, a temporary open-circuit condition can be applied across the three-phase motor before implementing a short-circuit condition. However, this temporary open-circuit condition may not protect the magnets from demagnetization when the transient current is too large.

[0025] According to some embodiments of this disclosure, in response to the presence of transient current in the electric motor system, the control circuit implements alternating short-circuit and open-circuit conditions across the three-phase motor. For example, alternating short-circuit and open-circuit conditions may refer to implementing two corresponding short-circuit conditions, with an open-circuit condition occurring between these two short-circuit conditions. These alternating short-circuit and open-circuit conditions protect the magnetic materials of the motor from demagnetization, while also protecting, for example, the battery of the electric motor system from exposure to transient current. Furthermore, these alternating short-circuit and open-circuit conditions are configured to terminate when a steady-state short-circuit current flows through the motor.

[0026] In some implementations, the control circuitry determines the transition to a three-phase short-circuit condition and implements alternating conditions based on transient currents (e.g., non-steady-state currents) associated with the electric motor. For example, the transient current may be generated in response to at least one switch failure in the electric motor system and / or in response to an electromotive force (e.g., applied by the three-phase motor) on the electric motor's battery exceeding a threshold. The control circuitry performs the transition by implementing a short-circuit condition across the motor and then alternating between an open-circuit condition and a short-circuit condition until the short-circuit condition causes the transient current to meet the condition associated with the steady-state current (e.g., the transient current stabilizes to or is sufficiently close to a steady-state value). In some implementations, during the transition, the control circuitry limits the transient current below a threshold (e.g., based on protective devices for the electric motor system, including preventing demagnetization of the electric motor's magnets).

[0027] In some implementations, the control circuitry determines the current across the electric motor and compares this current with a current limit or threshold associated with the motor (e.g., where the limit may be based on a model of the magnet's susceptibility to demagnetization). Based on this limit and the transient current amplitude, the control circuitry determines the duration for each of the alternating short-circuit and open-circuit conditions, and the number of times each condition is performed, to protect the motor and other components such as the battery.

[0028] In an illustrative example, an electric vehicle is operated at a relatively high speed (e.g., on a highway). During this operation, a switch in the electric vehicle's motor driver fails (e.g., malfunctions). A failed switch can cause the voltage across the motor terminals to exceed the voltage across the battery terminals used to drive the motor. This voltage imbalance can cause unregulated current to flow back from the motor to the battery. To protect the battery from this unregulated current flow, the control circuitry determines to apply a short-circuit condition across the motor. However, applying only a short-circuit condition (which may or may not precede only an open-circuit condition) risks demagnetizing the motor's magnets. Therefore, the control circuitry implements alternating short-circuit and open-circuit conditions to protect the battery while limiting the amount of current flowing through the motor's magnets.

[0029] Therefore, as described above and further described in detail below, a method and corresponding system for protecting motor magnets using control circuitry during three-phase short-circuit conditions are provided.

[0030] Figure 1 A motor driver 110, a motor 120, a driven component 130, and a DC power supply 150 (e.g., including a battery and optionally supporting a power converter and other power electronic devices) are illustrated according to some embodiments of this disclosure. Any one or more of the illustrative motor driver 110, motor 120, and DC power supply 150, including their respective components, may be referred to as power electronic devices. In some embodiments, the power electronic devices are included within an electric vehicle 105. The motor driver 110 includes switches S1-S6, which may be IGBT devices as shown, or any other suitable switches. In some embodiments, diodes D1-D6 are arranged across the corresponding switches S1-S6 to provide a flyback current path.

[0031] DC power supply 150 provides energy to a phase of motor 120 (e.g., a three-phase motor, as shown) driven by motor driver 110. Motor driver 110 includes control circuitry 112 configured to provide control signals to open or close switches S1-S6. Control circuitry 112 is operable on switches S1-S6 (e.g., using pulse width modulation or other suitable switching schemes) to convert a DC input voltage (e.g., provided by DC power supply 150) into an AC output voltage and AC output current to drive motor 120. During this operation, one or more switches may malfunction (e.g., become stuck in the open or closed position). In response to a switch malfunction, there is a possibility that a high voltage is generated across motor 120 and a back electromotive force (EMF) is presented on DC power supply 150. To prevent the back EMF from driving an unregulated current through DC power supply 150 without damaging motor 120, control circuitry 112 may use one or more methods of this disclosure (e.g., as described above, and at least in combination). Figures 6 to 8 As shown and described, alternating short-circuit and open-circuit conditions are achieved at both ends of motor 120.

[0032] Control circuitry 112 may be coupled to sensor 180 and memory 190 to implement alternating open-circuit and short-circuit operating conditions across motor 120. For example, control circuitry may rely on one or more sensors 180 to determine the current across motor 120, the corresponding operating condition of switches S1-S6 (e.g., whether the switches are faulty), and / or the electromotive force applied to DC power supply 150. In some embodiments, the current sensor is based on measuring the three-phase current output of motor driver 110 (e.g., as shown in the image). Figure 1The current flowing between the positive (+) and negative (-) terminals of the motor 120 can be determined by the memory 190 (e.g., based on susceptibility to demagnetization). The control circuit 112 can rely on the memory 190 (e.g., based on susceptibility to demagnetization) to determine the maximum current level that can flow through the motor 120 (e.g., as in conjunction with...). Figure 2 (Further shown and described). The control circuit 112 may rely on both the sensor 180 and the memory 190 to determine the duration of each open-circuit condition and each short-circuit condition when alternating open-circuit and short-circuit conditions are achieved at both ends of the motor 120.

[0033] As used herein, a short-circuit condition can refer to any configuration of switches S1-S6, wherein the three-phase terminals of motor 120 (e.g., ...) Figure 1 The circuit nodes “A”, “B”, and “C” in the annotations are electrically connected to each other. For example, a short-circuit condition may include having all three switches S1-S3 in the closed position or all three switches S4-S6 in the closed position. Under certain conditions, including some conditions described in conjunction with this disclosure, current may flow through the motor during a short-circuit condition.

[0034] As used herein, an open condition (i.e., an open-circuit condition) can refer to any configuration of switches S1-S6 in which there is no path for current to flow into and out of motor 120. For example, an open condition could include having all six switches S1-S6 in the open position.

[0035] In some embodiments, sensor 180 includes one or more current sensors, voltage sensors, torque sensors, temperature sensors, sensors configured to sense any other suitable characteristic or changes thereof, any other suitable sensors, or any combination thereof. For example, sensor 180 may include an optical encoder, a magnetic encoder, a potentiometer, or other suitable device for determining (e.g., the rotational position or speed of a magnet in motor 120). In some embodiments, sensor 180 includes features for measuring or determining... Figure 1 Temperature sensors (e.g., thermocouples, resistance temperature detectors, thermistors, optical thermal sensors) are used to measure the temperature of any one or more of the components shown. In some embodiments, sensor 180 includes a voltage sensor for determining the back electromotive force (e.g., the back electromotive force applied to DC power supply 150 by motor 120).

[0036] Considering the aforementioned power electronic devices as part of the electric vehicle 105, the motor 120 may be coupled to the driven component 130 (e.g., including a drivetrain) to rotate multiple wheels 135 (e.g., two or four wheels). The motor 120 may be coupled to the driven component 130 to rotate the wheels 135 using energy provided by the DC power supply 150 based on a signal provided by the motor driver 110. That is, the motor 120 may be coupled to one or more wheels 135 via one or more driven components 130.

[0037] Figure 2 This is an illustrative graph showing the temperature-dependent characteristics of a magnet based on the current applied to both ends of a motor, which includes a magnet. Figure 2 The vertical axis indicates the magnetic flux density, which represents the magnetic properties of the magnet. Figure 2 The horizontal axis shows the magnetic field strength at both ends of the magnet, based on the current applied to the motor and the magnet. In some embodiments, the magnetic field strength may be related to the motor speed (e.g., the magnetic field strength is greater at relatively high speeds of the electric vehicle 105 than at relatively slow speeds). A set of curves labeled from 20°C to 180°C represents an illustrative temperature correlation between magnetic flux density and magnetic field strength.

[0038] The above set of curves shows the threshold temperature (e.g., for Figure 2 The data shown above 120°C (this is merely illustrative) illustrates how a magnet deviates from the linear relationship between magnetic flux density and magnetic field strength within a possible range of magnetic field strengths. Specifically, the curves at 120°C, 140°C, and 180°C show that the linear relationship drops to an almost vertical line at the corresponding magnetic field strengths of approximately -760 kA / m, -580 kA / m, and -325 kA / m. This drop indicates a degradation of the magnet's magnetic flux density (e.g., which may be referred to as a demagnetizing condition or demagnetizing region). In other words, as shown in path 202, if the magnet is exposed to operating conditions in the dropping region, the magnetic flux density will not return to its pre-exposure level when the magnitude of the magnetic field strength is reduced; that is, the magnet has been demagnetized (e.g., partially demagnetized). Conversely, at 20°C, for example, the coupled magnetic field strength increases to -1000 kA / m, and when that field strength is reduced back to 0, the magnetic flux density will recover to ~1.24 T, as... Figure 2 The rightmost limit is shown.

[0039] based on Figure 2 The trend is to limit the current applied across the motor terminals so that, for a given operating temperature, the magnetic field strength does not increase into the demagnetizing region. It needs to be reiterated that... Figure 2 The curves depicted are merely illustrative and will depend at least on the magnetic material of the magnet. For a given magnet (e.g., the magnet of motor 120), memory 190 may store information related to... Figure 2 The data corresponds to the data. The control circuit 112 can rely on this data to establish one or more thresholds associated with achieving a three-phase short-circuit condition, achieving a three-phase open-circuit condition, and alternating between those conditions to prevent demagnetization of the magnet.

[0040] Figure 3 This is a first example indicative graph showing the transient current distribution associated with a three-phase short-circuit condition. For example, this distribution could represent the transient current flowing through motor 120 in response to control circuit 112 implementing a three-phase short-circuit condition. After implementing the three-phase short-circuit condition (e.g., Figure 3 (To the right of the origin shown), transient current 302 (i.e., I) d (t) evolves into an oscillating current within a decaying envelope having an upper current limit 304 and a lower current limit 306. The oscillating current is within the characteristic current 308 (i.e., I). char ) oscillate around. If given enough time (although this is in...) Figure 3 If (not shown in the figure), then the transient current 302 will stop oscillating (i.e., it will transition from a transient current to a steady-state current) and will reach a steady-state value equal to the characteristic current 308. As shown in note 309, the amplitude of the envelope 306 at time t = 0 can be relative to I. char Defined, and can be equal to or less than I. char The value of [I] d (t=0)+I char The amplitude of envelope 306 depends on the motor speed. That is, the higher the motor speed, the larger the amplitude of transient current oscillation and the larger the amplitude of steady-state current.

[0041] The attenuation envelope can be monitored or determined by control circuit 112, and the attenuation rate can be determined by e. -Rt / L Given, where R and L are the resistance and impedance associated with the motor (e.g., motor 120), respectively. The oscillation rate of the current 302 in the decay envelope can also be monitored or determined by the control circuit 112, and can be determined by 1 / ω. r Given, where ω r It is the rotational angular frequency associated with the motor (e.g., motor 120).

[0042] Figure 4 This is a second example of an indicative plot showing the transient current distribution associated with a three-phase short-circuit condition. Figure 4 The graph includes the current component I. q The vertical axis and the current component I d The horizontal axis. In some embodiments, current 402 is shown as a first component (e.g., an in-phase component, which may be represented as I). d ) and the second component (e.g., the orthogonal component, which can be represented as I) qThe sum of the currents 302 and 402. Therefore, the spiral progression of the current 402, which has a directionality indicated by the annotated arrow, can correspond to the time progression of the current 302.

[0043] Figure 4 The demagnetizing current limit 404 is shown, which can be a threshold associated with current 402 (e.g., based on current component I). d (Limited amplitude). If the current component I of current 402 d If the demagnetizing current limit 404 is exceeded, the magnet (e.g., a magnet included in motor 120) can be demagnetized. That is, if the current component I of current 402... d If the demagnetizing current limit 404 is exceeded, the magnetic field strength at both ends of the magnet associated with current 402 can be in the following state: Figure 2 The descending region shown.

[0044] In an exemplary example, a three-phase short-circuit condition is implemented, and current 402 flows from I... dq (t=0) indicates the initial value changes to, as indicated by I char The indicated steady-state characteristic current value (e.g., corresponding to) Figure 3 I char Because this illustrative example does not include alternating three-phase short-circuit and three-phase open-circuit conditions, current 402 exceeds the demagnetizing current limit 404. Before (or when) implementing the three-phase short-circuit condition, the distance 406 between the steady-state characteristic current value and the initial transient current value (e.g., which may correspond to distance 309) can be used (e.g., as a threshold, for example, by control circuit 112) to determine alternation between the three-phase short-circuit and three-phase open-circuit conditions.

[0045] Figure 5 This is a third exemplary plot showing the transient current distribution associated with a three-phase open-circuit condition and a subsequent three-phase short-circuit condition. The transient current 502 comprises two parts, wherein transient current part 502a corresponds to the three-phase open-circuit condition and transient current part 502b corresponds to the three-phase short-circuit condition.

[0046] In some implementation schemes, Figure 5 This indicates the progression of the transient current 502 after control circuit 112 determines that a three-phase short-circuit condition has been achieved. Specifically, Figure 5 This indicates the progression of the transient current 502 after the control circuit 112 implements a three-phase open-circuit condition and then a three-phase short-circuit condition. For example, based on the distance 503 between the initial value of the transient current 502 and the characteristic current 508, the control circuit 112 can implement the open-circuit condition before the short-circuit condition to reduce the risk that the transient current 502 will exceed the demagnetizing current limit 506.

[0047] exist Figure 5 In this method, which can be described as switching the motor to a three-phase short-circuit condition using an intermediate three-phase open-circuit condition, the control circuit 112 determines that the initial amplitude of the transient current 502 exceeds a threshold, implements the intermediate three-phase open-circuit condition until the transient current 502 decreases to zero, and then implements the three-phase short-circuit condition until the transient current 502 reaches its steady-state value (e.g., the transient current 502 stabilizes to the characteristic current 508). However, as shown in section 506 of the transient current 502, the transient current passes through the demagnetizing region 510. Therefore, when the initial transient current amplitude is higher than the threshold, Figure 5 This method does not protect the motor magnets.

[0048] According to some implementation schemes disclosed herein Figure 6 This is an exemplary flowchart of a method 600 for switching a motor to a three-phase short-circuit condition by alternating between a three-phase short-circuit condition and a three-phase open-circuit condition. Figure 7 This is a fourth exemplary graph showing the current distribution associated with a method for protecting motor magnets during a three-phase short-circuit condition. For illustrative and non-limiting examples, method 600 can be implemented to provide... Figure 7 Current distribution.

[0049] In some embodiments, the control circuit 112 implements method 600 by controlling switches S1-S6 of the motor driver 110. In some embodiments, the control circuit 112 implements method 600 to protect both the motor 120 (e.g., to prevent demagnetization of the magnets of the motor 120) and the DC power supply 150 (e.g., to prevent current from flowing back to the battery of the DC power supply 150).

[0050] At point 602, a three-phase short-circuit transition process is initiated. As used herein, the three-phase short-circuit transition process may refer to a transition between a first operating mode and a second operating mode (e.g., in the first operating mode, switches S1-S6 are controlled to drive motor 120 (e.g., to accelerate or decelerate electric vehicle 105 according to desired torque), and in the second operating mode, switches S1-S6 are controlled to protect power electronic devices (e.g., to provide steady-state three-phase short-circuit current across motor 120).

[0051] In some embodiments, control circuit 112 determines to initiate a three-phase short-circuit transition process at 602 because at least one of the multiple switches (e.g., any one of switches S1-S6) is determined to be faulty. In some embodiments, control circuit 112 determines to initiate a three-phase short-circuit transition process at 602 because the electromotive force (EMF) on a DC power source (such as DC power source 150) (e.g., the EMF generated by a motor (such as motor 120)) exceeds a threshold. In some embodiments, control circuit 112 determines to initiate a three-phase short-circuit transition process at 602 because the current across a motor including a magnet (e.g., motor 120) exceeds a threshold.

[0052] At point 604, a three-phase short-circuit condition is achieved. For example, a three-phase short-circuit condition can be achieved by closing all three switches in switches S1-S3 or all three switches in switches S4-S6. In any case, achieving a three-phase short-circuit condition involves creating a short-circuit connection across each phase of the three-phase motor. In response to achieving the three-phase short-circuit condition, transient currents (e.g., transient currents 302, 402, 502b, 702a) flow through motor 120.

[0053] At 606, the components of the transient current are determined (e.g., I as described above). d Whether the transient current is approaching the demagnetization limit. The demagnetization limit can be estimated or determined based on the motor's speed, temperature, and / or characteristics. Furthermore, it can be determined that the transient current is approaching the demagnetization limit based on whether the transient current is, for example, 50%, 60%, 70%, 80%, 85%, 90%, 95%, 99%, or any other suitable fraction of the demagnetization limit. For an illustrative example, it can be determined that the transient current 702a is within 5% of the demagnetization limit 709, and therefore there is a risk of demagnetizing the motor magnets if no further action is taken. Therefore, it can be determined that a three-phase open-circuit condition is required to prevent current 702 from passing through the demagnetization region 710.

[0054] If the component of the transient current is determined to be close to the demagnetization limit at 606, then a three-phase open-circuit condition is achieved at 608. For example, in the first iteration of the process of method 600, the three-phase open-circuit condition allows the transient current 702 to flow according to the path shown by the transient current portion 702b. Similarly, the transition between the three-phase short-circuit condition at 604 and the three-phase open-circuit condition at 608 can correspond to... Figure 7 The time period is depicted in 704 places.

[0055] At 610, the difference between the transient current amplitude and the characteristic current amplitude is monitored (e.g., this difference is based on or equal to a distance, as described below). In some embodiments, the operation at 610 includes determining the characteristic current amplitude I. char(For example, based on motor speed). In some implementations, monitoring the difference includes monitoring the transient current as comprising two components (e.g., I as described above). d and I q The transient current vector (or phase component and quadrature component) is the difference between the peak of the vector and the characteristic current (e.g., I as described above). char This can also be described as being monitored by the distance between the steady-state three-phase short-circuit currents. For example, control circuit 112 can monitor time-dependent coordinates such as (I0, I ...) representing transient currents. d ,I q ) and static coordinates representing characteristic steady-state currents, such as (I char The distance between ,0).

[0056] At 612, determine whether the distance or difference monitored at 610 meets the threshold condition. For example, when I dq The amplitude and I char The difference between the amplitudes is less than a threshold (e.g., based on I during the corresponding three-phase short-circuit condition). dq initial value, I char The value and demagnetizing current limit, such as I demag The threshold condition is satisfied when the distance is the minimum distance between the transient current amplitude and the characteristic current amplitude (e.g., 1%, 5%, 10%, or any other suitable percentage greater than the minimum distance). The threshold condition is also satisfied when the distance is a predetermined amount based on the minimum distance between the transient current amplitude and the characteristic current amplitude (e.g., 1%, 5%, 10%, or any other suitable percentage greater than the minimum distance). Furthermore, the threshold condition is satisfied if the transient current amplitude is less than the characteristic steady-state current amplitude.

[0057] If it is determined at 612 that the threshold condition is not met, the three-phase open-circuit condition is maintained and the operations at 608, 610, and 612 are repeated. However, if it is determined at 612 that the threshold condition is met, the three-phase short-circuit condition is implemented during the operation at 604 in method 600 and subsequent operations. For example, the operation at 604 in method 600 could correspond to... Figure 7 The transition described in 706 places is the time, and / or in Figure 7 The transition is depicted at 711 points in time.

[0058] As mentioned, method 600 includes implementing a first three-phase short-circuit condition at 604, a three-phase open-circuit condition at 608, and a second three-phase short-circuit condition at a subsequent iteration of 604. Therefore, method 600 includes switching the electric motor to the first three-phase short-circuit condition (e.g., based on the first three-phase short-circuit condition) and then alternating between the three-phase short-circuit condition and the three-phase open-circuit condition (e.g., based on implementing at least one three-phase open-circuit condition in one or more iterations of 608 and based on implementing a corresponding number of three-phase short-circuit conditions in subsequent iterations of 604).

[0059] Returning to 606, if it is determined that the component of the transient current is not approaching the demagnetization limit, then at 614, it is determined whether a steady-state three-phase short-circuit current condition has been reached. In some implementations, the steady-state three-phase short-circuit current condition includes the characteristic current across the motor (e.g., as...). Figures 3 to 5 and Figure 7 The I shown char The steady-state flow of the transient current is determined at 614. If a steady-state three-phase short-circuit current condition is determined at 614, the three-phase short-circuit transition process is terminated at 616. That is, in response to the transient current satisfying the steady-state three-phase short-circuit current condition (e.g., the transient current has stabilized to a steady-state current, or is sufficiently close to a steady-state current), the alternation between the three-phase short-circuit condition and the three-phase open-circuit condition is terminated. For example, determining that the transient current has satisfied the steady-state condition at 614 may include measuring the rate of change of the transient current and determining that the rate of change is below a threshold (e.g., the rate of change is sufficiently close to zero). As another example, determining that the transient current has satisfied the steady-state condition at 614 may include determining that the transient current amplitude is within a threshold range (e.g., at I...). char The duration of the threshold time is between 90% and 110%, 98% and 102%, or any other suitable approximate range. However, if it is determined at 614 that the steady-state three-phase short-circuit current condition has not been reached, method 600 returns to the operation at 604.

[0060] Figure 7 A specific implementation of method 600 is illustrated. Note that... Figure 7 The curve and Figures 4 to 5 The graphs are arranged similarly, but depict different methods for transitioning to a three-phase short-circuit condition.

[0061] exist Figure 7At the initial time 701, a three-phase short-circuit condition is achieved (e.g., corresponding to the operations at 602 and 604), and transient current 702 flows as shown in transient current portion 702a. While transient current portion 702a flows, the operation at 606 can be performed. Then, at the first alternation time 704, it is determined that transient current 702 is approaching demagnetization limit 709. In some embodiments, demagnetization limit 709 includes an error margin to ensure that the current does not reach the limit. That is, it can be determined that demagnetization occurs at a first current value, and demagnetization limit 709 can then be established as a fraction of that first current value (e.g., 99%, 95%, 90%, or any other suitable fraction).

[0062] Therefore, a three-phase open-circuit condition is achieved (e.g., corresponding to the operation at 608), and the transient current 702 flows as shown in the transient current portion 702b. Since the three-phase open-circuit condition is achieved at the transition time 704, the transient current 702 does not enter the demagnetization region 710. While the transient current portion 702b is flowing, the operations at 610 and 612 can be performed. Then, at the second alternation time 706, it is determined that the transient current amplitude has been sufficiently reduced (e.g., the transient current amplitude is less than the characteristic current amplitude, or the distance between the transient current amplitude and the characteristic current amplitude is at or appropriately close to the minimum distance).

[0063] Therefore, a three-phase short-circuit condition is achieved (e.g., corresponding to the operation at 604), and the transient current 702 flows as shown in transient current section 702c. This transient current section 702c again approaches the demagnetization limit 709. Therefore, the above-described operation occurs at alternation time 708, alternating to the second three-phase open-circuit condition (as shown by transient current section 702d), and at alternation time 711, alternating to the third three-phase short-circuit condition (as shown by transient current section 702e).

[0064] Finally, the transient current portion 702e stabilizes at time 712 to the steady-state three-phase short-circuit current (i.e., the characteristic current I). char Stability at time 712 corresponds to operation at 614 and 616.

[0065] Based on the first example of the indicative transient current vector 720a and the second example of the indicative transient current vector 720b, in Figure 7 The diagram illustrates the relationship between transient current vector 720 and transient current 702. As transient current 702 changes, the base position of transient current vector 720 remains at I... char At the coordinates, the tip of the transient current vector 720 follows the current value of the transient current 702.

[0066] During the execution of method 600 or any equivalent method for alternating between a three-phase short-circuit condition and a three-phase open-circuit condition, the length of the transient current vector 720 (e.g., equal to the distance between the transient current and the steady-state three-phase short-circuit current vector) can be monitored (e.g., by control circuitry 112). Control circuitry 112 can be configured to switch between the three-phase open-circuit condition and the three-phase short-circuit condition (e.g., at the transition between steps 612 and 604) when the length of the transient current vector 720 is sufficiently small (i.e., as determined at step 612, it is “sufficiently short”, it is at its minimum, or it is otherwise below a threshold that can be defined relative to the minimum).

[0067] According to some implementation schemes disclosed herein Figure 8 This is an exemplary flowchart of a method 800 for protecting a motor during transition to a three-phase short-circuit condition. Method 800 may include some or all of methods 600 and may produce results similar to those in method 600. Figure 7 Some or all of the exemplary current distributions shown are similar to the current distributions in the illustration.

[0068] At an optional operation point 802, multiple switches (e.g., switches S1-S6) (e.g., by control circuit 112 or motor driver 110) are used to supply current to an electric motor (e.g., motor 120). For example, current can be provided to accelerate an electric vehicle driven by the motor.

[0069] At point 804, (e.g., by control circuitry) it is determined that the electric motor will be switched to a three-phase short-circuit condition using multiple switches. In some embodiments, the multiple switches include a first switch, a second switch, and a third switch respectively coupled to a first phase, a second phase, and a third phase of the three-phase electric motor, and switching the motor to the three-phase short-circuit condition includes closing the first switch, the second switch, and the third switch. In some embodiments, it is determined whether one of the multiple switches is damaged, and in response to determining that at least one of the multiple switches is damaged, the switch to the three-phase short-circuit condition occurs.

[0070] At point 806, multiple switches are used to alternate the motor's operating conditions between a three-phase short-circuit condition and a three-phase open-circuit condition based on transient currents associated with the motor. In some embodiments, the alternation occurs in response to a transient current exceeding a threshold. In some embodiments, the threshold is based on the temperature associated with the three-phase motor, at least one magnetic characteristic associated with the three-phase motor, or both. In some embodiments, the threshold is determined based on a comparison of the transient current with the steady-state three-phase short-circuit current associated with the three-phase motor. In some embodiments, the steady-state three-phase short-circuit current associated with the three-phase motor is based on one or more of the motor speed, at least one magnetic characteristic of the three-phase motor, or the temperature associated with the three-phase motor.

[0071] For example, one or more of the following factors—motor speed, motor magnetic properties, or temperature associated with the motor—can affect the motor's susceptibility to demagnetization. More specifically, any one or more of those characteristics can indicate and combine with... Figure 2 , Figure 4 , Figure 5 and Figure 7 The current level associated with the demagnetized region is depicted and described.

[0072] In some implementations, the alternation at 806 includes a transition from a three-phase open-circuit condition (e.g., as implemented at 806) to a three-phase short-circuit condition (e.g., as implemented at 804) based on transient current. For example, the transition from a three-phase open-circuit condition to a three-phase short-circuit condition may occur when the transient current is less than the steady-state three-phase short-circuit current, or when the difference between the transient current amplitude and the steady-state three-phase short-circuit current amplitude is at (or close to) a minimum distance.

[0073] In some implementations, the alternation at 806 includes a transition from a three-phase short-circuit condition (e.g., as implemented at 804, or as implemented after any subsequent alternation) to a three-phase open-circuit condition based on transient current (e.g., based on monitoring the transient current vector or otherwise monitoring the distance between the transient current and the steady-state three-phase short-circuit current). For example, a transition from a three-phase open-circuit condition to a three-phase short-circuit condition may occur when the transient current vector is sufficiently short. Specifically, the distance between the transient current vector and the steady-state three-phase short-circuit current is below a threshold distance. The threshold distance may be defined based on a demagnetizing current limit associated with the magnets of a three-phase motor, which may be further based on the motor's temperature, motor speed, voltage imbalance across the motor, or any combination thereof.

[0074] Note that in illustrative cases where a transient current comprises multiple parts (e.g., including transient current part 702a, transient current part 702b, etc.), each of these multiple parts may indicate a corresponding instance of applying one of a three-phase open-circuit condition or a three-phase short-circuit condition. When describing a transient current, reference may be made to the shared basic reference numerals applied to each of these current parts (e.g., as used in conjunction with transient current 702).

[0075] Note that, as used herein, transient current refers to a current having at least one time-dependent characteristic. That is, at least one aspect of the current changes over time. In some embodiments, transient current is described in contrast to steady-state current (e.g., where steady-state current may be referred to as characteristic current).

[0076] The processes described above are intended to be illustrative and not restrictive. Those skilled in the art will recognize that the steps of the processes described herein can be omitted, modified, combined, and / or rearranged, and any additional steps can be performed without departing from the scope of the invention.

[0077] The foregoing description is merely illustrative of the principles of this disclosure, and various modifications can be made by those skilled in the art without departing from the scope of this disclosure. The above embodiments are presented for illustrative purposes and not for limitation. This disclosure may also take many forms other than those expressly described herein. Therefore, it should be emphasized that this disclosure is not limited to the methods, systems, and apparatus expressly disclosed, but is intended to include variations and modifications thereof, which are within the spirit of the appended claims.

Claims

1. A system comprising: A power electronic device configured to supply current to a three-phase electric motor using multiple switches; and Control circuit, the control circuit being configured to: The three-phase electric motor is switched to a three-phase short-circuit condition using the plurality of switches; and Based on the transient current of the three-phase electric motor, the plurality of switches are used to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition.

2. The system of claim 1, wherein the control circuit is configured to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition by switching the three-phase electric motor from the three-phase short-circuit condition to the three-phase open-circuit condition in response to the transient current exceeding a threshold.

3. The system of claim 2, wherein the control circuit is configured to determine the threshold based on the temperature associated with the three-phase electric motor.

4. The system of claim 1, wherein the control circuit is configured to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition by switching the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition based on the transient current and steady-state three-phase short-circuit current of the three-phase electric motor.

5. The system of claim 4, wherein the control circuit is configured to determine the steady-state three-phase short-circuit current based on the motor speed.

6. The system of claim 4, wherein the control circuit is configured to switch the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition when the distance between the vector associated with the transient current and the steady-state three-phase short-circuit current is less than a threshold distance.

7. The system of claim 1, wherein the control circuit is further configured to: Determine whether the transient current meets the steady-state three-phase short-circuit current condition; and The alternation is terminated in response to the transient current satisfying the steady-state three-phase short-circuit current condition.

8. The system of claim 1, wherein the control circuit is further configured to: Determine whether one of the plurality of switches is damaged; and In response to determining that one of the plurality of switches is faulty, the three-phase electric motor is switched to the three-phase short-circuit condition.

9. The system according to claim 1, wherein: The plurality of switches includes a first switch, a second switch, and a third switch respectively coupled to the first phase, the second phase, and the third phase of the three-phase electric motor; and The control circuit is configured to switch the three-phase electric motor to the three-phase short-circuit condition by closing the first switch, the second switch and the third switch.

10. A method, the method comprising: Using a control circuit, multiple switches are used to switch the three-phase electric motor to a three-phase short-circuit condition. as well as Using the control circuit, the plurality of switches are used to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition based on the transient current of the three-phase electric motor.

11. The method of claim 10, wherein alternating between the three-phase short-circuit condition and the three-phase open-circuit condition comprises switching the three-phase electric motor from the three-phase short-circuit condition to the three-phase open-circuit condition in response to the transient current exceeding a threshold.

12. The method of claim 11, further comprising determining the threshold based on the temperature associated with the three-phase electric motor.

13. The method of claim 10, wherein alternating between the three-phase short-circuit condition and the three-phase open-circuit condition comprises switching the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition based on the transient current and steady-state three-phase short-circuit current of the three-phase electric motor.

14. The method of claim 13, further comprising determining the steady-state three-phase short-circuit current based on motor speed.

15. The method of claim 13, further comprising switching the three-phase electric motor from the three-phase open-circuit condition to the three-phase short-circuit condition when the distance between the vector associated with the transient current and the steady-state three-phase short-circuit current is less than a threshold distance.

16. The method according to claim 10, further comprising: Determine whether the transient current meets the steady-state three-phase short-circuit current condition; as well as The alternation is terminated in response to the transient current satisfying the steady-state three-phase short-circuit current condition.

17. The method according to claim 10, further comprising: Determine whether one of the plurality of switches is damaged; as well as In response to determining that one of the plurality of switches is faulty, the three-phase electric motor is switched to the three-phase short-circuit condition.

18. The method of claim 10, wherein the plurality of switches comprises a first switch, a second switch, and a third switch respectively coupled to a first phase, a second phase, and a third phase of the three-phase electric motor; wherein: Switching the three-phase electric motor to the three-phase short-circuit condition includes closing the first switch, the second switch, and the third switch.

19. An electric vehicle, the electric vehicle comprising: A three-phase electric motor, the three-phase electric motor being coupled to one or more wheels; A power electronic device configured to supply current to the three-phase electric motor using multiple switches; and Control circuit, the control circuit being configured to: The three-phase electric motor is switched to a three-phase short-circuit condition using the plurality of switches; and Based on the transient current of the three-phase electric motor, the plurality of switches are used to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition.

20. The electric vehicle of claim 19, wherein the control circuit is configured to alternate between the three-phase short-circuit condition and the three-phase open-circuit condition by switching the three-phase electric motor from the three-phase short-circuit condition to the three-phase open-circuit condition in response to the transient current exceeding a threshold.

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