Method and apparatus for controlling an electric machine

Abstract

A method of controlling an inverter that powers a permanent magnet alternating current (PMAC) motor having a plurality of phase windings is described. The method includes selecting a first phase winding of the PMAC motor, electrically connecting the first phase winding to a first direct current (DC) link at a first time instant and maintaining the electrical connection between the first phase winding and the first DC link, determining a magnetic flux difference between the first phase winding and a second phase winding of the PMAC motor, selecting a second time instant at which the second phase winding is electrically connected to the first DC link, electrically connecting the second phase winding to the first DC link at the second time instant, and maintaining the electrical connection between the second phase winding and the first DC link. The second time instant is selected based on the determined magnetic flux difference.

Description

Technical Field

[0001] This invention relates to controlling the power supply of motors, and particularly to controlling the power supply of multiphase motors. More specifically, this invention provides an improved means for initiating an active short-circuit mode in a multiphase motor, which can alleviate the problems of existing systems. Background Technology

[0002] Electric motors are used in a variety of machines, primarily in vehicles such as automobiles, but also in other industrial and commercial equipment such as fans, pumps, elevators, and refrigerators. These motors typically have a controller for controlling their operation. Many of these motors are multiphase (e.g., three-phase). Many of these motors are powered by a direct current (DC) voltage source (e.g., battery power). Inverters can be provided to convert the DC voltage to an alternating current (AC) voltage to drive each phase. Summary of the Invention

[0003] The invention is set forth in the independent claims. Preferred features are set forth in the dependent claims.

[0004] This document describes a method for controlling an inverter that supplies power to a permanent magnet alternating current (PMAC) motor having multiple phase windings. The method includes: selecting a first phase winding of the PMAC motor; at a first moment, electrically connecting the first phase winding to a first DC terminal of a DC link circuit and maintaining the connection between the first phase winding and the first DC terminal; determining a flux difference between the first phase winding and a second phase winding of the PMAC motor; selecting a second moment, different from the first moment, for electrically connecting the second phase winding to the first DC terminal, wherein the second moment is selected based on the determined flux difference between the first and second phase windings; and at the second moment, electrically connecting the second phase winding to the first DC terminal and maintaining the connection between the second phase winding and the first DC terminal.

[0005] In some situations, such as motor or power supply failures or accidents (e.g., vehicle collisions), the motor must be reduced to zero torque (or a safe state) or its power output must be reduced relatively quickly. For safety reasons and to prevent (further) damage to equipment, a relatively rapid motor stop is often important. For example, in the event of an accident, it is desirable to stop the wheels of a vehicle as quickly as possible. A motor power failure results in unwanted braking torque, and power outages and battery failures can damage the inverter due to high voltage. Particularly for permanent magnet motors, if the back electromotive force is high, stopping the motor by disconnecting it from the battery can result in a DC link current high enough to damage the inverter. Another method to stop the motor quickly is to turn off the motor's switching devices, such as insulated-gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field-effect transistors (MOSFETs), but this results in natural rectification of the power returning to the DC link and strong motor braking. If the vehicle is turning at high speed, the high braking torque can cause the wheels to lose traction, and the car may, for example, veer off the road.

[0006] Therefore, active short circuit (ASC) mode can be applied to stop the motor without natural rectification and while maintaining low braking torque. The DC link voltage will be reduced safely. (Since no active control is required) Active short circuit is a fairly simple way to reduce these problems and allows energy to dissipate in the motor (therefore, no battery is needed). Using ASC mode prevents large back electromotive force, thereby preventing unwanted braking torque and / or protecting the inverter and motor from damage. In multiphase motors, ASC mode involves short-circuiting all phase windings of the motor, for example, by connecting all phase windings of the motor to the positive or negative connection point of the DC link.

[0007] However, rapidly entering active short-circuit mode in a motor generates large transient currents that can damage the inverter or the motor. Applying ASC can also demagnetize the rotor magnets in the motor and / or damage other components such as switches (e.g., IGBT / MOSFETs) or capacitors. The methods and systems described herein attempt to mitigate these problems, particularly the transient current issue.

[0008] An improved method for enabling ASC mode in a multiphase PMAC motor can be provided by short-circuiting the phase windings at different times based on the magnetic flux in each phase. Advantageously, by applying ASC alternately on each phase based on the magnetic flux difference between phases, the transient currents that occur in the motor when applying ASC can be reduced.

[0009] The inverter may include multiple power output terminals, each of which is switchably connected to two DC terminals of a DC link circuit via switching elements to provide AC power at each power output terminal. Each power output terminal can be used to provide AC power to a corresponding phase winding of a PMAC motor. In active short-circuit mode, a selected switching element can remain in the ON state, such that the multiple power output terminals are electrically connected together.

[0010] Therefore, selecting the first phase winding of the PMAC motor may include selecting a first power output terminal from a plurality of power output terminals, wherein the first power output terminal corresponds to the first phase winding of the PMAC motor.

[0011] Electrically connecting the first phase winding to the first DC terminal of the DC link circuit may include switching a first switching element to the ON state at a first moment, thereby electrically connecting the first phase winding to the first DC terminal of the two DC terminals of the DC link circuit. Maintaining the connection between the first phase winding and the first DC terminal can be achieved by keeping the first switching element in the ON state.

[0012] The second power output terminal among multiple power output terminals may correspond to the second phase winding of the PMAC motor. Electrically connecting the second phase winding to the first DC terminal may include switching a second switching element to the ON state at a second moment to electrically connect the second phase winding to the first DC terminal. Maintaining the connection between the second phase winding and the first DC terminal may include keeping the second switching element in the ON state.

[0013] The magnetic flux difference between the first phase winding and the second phase winding can be the magnetic flux difference between the magnetic flux connected to the multiple windings of the first phase and the magnetic flux connected to the multiple windings of the second phase.

[0014] The method may further include: during the time interval between the first and second moments, electrically connecting the second phase winding to a second terminal of the DC link circuit. The second terminal is one of the two DC terminals of the DC link circuit. By connecting the second phase winding to a DC terminal opposite to the DC terminal connected to the first phase winding, the current in the second phase winding will cause the magnetic flux in the second phase winding to approach the magnetic flux in the first phase winding. Therefore, the time interval between the first and second moments can be selected based on the determined magnetic flux difference between the first and second phase windings and the DC voltage at the second terminal of the DC link.

[0015] In some embodiments, a second moment and / or time interval is selected based on the time required for the flux difference between the first and second phase windings of the PMAC motor to reach zero.

[0016] Preferably, selecting the second moment and / or time interval includes: acquiring motor data at multiple sampling moments, wherein there is a predetermined sampling time period between consecutive sampling moments; calculating multiple corresponding time estimates; each time estimate is an estimate of the time required for the flux difference between the first and second phase windings of the PMAC motor to reach zero, based on the acquired motor data at the sampling moments; comparing each of the multiple time estimates with the predetermined sampling time period; selecting a first time estimate that is less than or equal to the predetermined sampling time period; and selecting the second moment using the selected first time estimate. Preferably, the multiple sampling moments follow the first moment. The motor data may include or relate to the flux in the first and / or second phase windings, and / or may include or relate to the voltage of the DC link (from which the flux in the phase windings and the flux difference between the windings can be obtained). Therefore, the flux difference between the second and first phase windings can be monitored after a short circuit in the first phase winding (at the first moment), and the selection of the second moment can be adjusted to compensate for fluctuations in motor operating conditions that occur after the first moment, thereby improving the reduction of the flux difference between the phases.

[0017] Preferably, the step of connecting the second phase winding to the first DC terminal at the second moment includes: applying a pulse of length equal to a selected time estimate to electrically connect the second phase winding to the first DC terminal at the second moment. Inverters (in normal operation) typically control the AC waveform in each phase winding by using pulse width modulation (PWM) to convert the DC voltage in the inverter into a pulse sequence. Therefore, applying a pulse of time estimate means connecting the second phase to the first DC terminal at an exact (or very close) second moment, without waiting for the next PWM timing. The inverter may have a PWM time base equal to the sampling time period.

[0018] The method may further include: determining the flux difference between the first phase winding and the third phase winding of the PMAC motor; selecting a third time when the third phase winding is electrically connected to the first DC terminal, the third time being different from the first and second times, wherein the third time is selected based on the determined flux difference between the first and third phase windings of the PMAC motor; at the third time, electrically connecting the third phase winding to the first DC terminal and maintaining the connection between the third phase winding and the first DC terminal. A third power output terminal among a plurality of power output terminals may correspond to the third phase winding of the PMAC motor. At the third time, the third power output terminal may be connected to the first DC terminal. The third phase winding can be electrically connected to the first DC terminal by switching a third switching element to the on state at the third time. The connection between the third phase winding and the first DC terminal can be maintained by keeping the third switching element in the on state.

[0019] In some embodiments, selecting a first phase winding of a PMAC motor, or selecting a first power output terminal among a plurality of power output terminals, includes: determining the magnetic flux in each of the plurality of phase windings of the PMAC motor (or each of one or more windings corresponding to each phase in the motor); and selecting the phase winding with the highest magnetic flux value as the first phase winding.

[0020] The method may also include switching multiple switching elements in the inverter to supply AC power to each phase winding before the first moment. This can be achieved by applying PWM.

[0021] In some embodiments, the method may further include: monitoring the magnetic flux in each of the plurality of phase windings of the PMAC motor while switching switching elements to provide alternating current to each phase winding.

[0022] In some embodiments, the magnetic flux difference between the first and second phase windings and / or between the first and third phase windings of the PMAC motor is determined based on the magnetic flux monitored in the first phase winding, the second phase winding, and / or the third phase winding at a first moment.

[0023] The second time point is usually later than the first time point (or after the first time point), and optionally, the third time point is usually later than the first time point (or after the first time point).

[0024] In some embodiments, determining the flux difference between the first and second phase windings of the PMAC motor includes: determining the voltage across the first phase winding as a function of time; determining the voltage across the second phase winding as a function of time; calculating the integral of the voltage across the first phase winding with respect to time; calculating the integral of the voltage across the second phase winding with respect to time; and determining the difference between the integral of the voltage across the first phase winding and the integral of the voltage across the second phase winding. The voltage across the first phase winding can be determined by determining the voltage at the first power output terminal, and the voltage across the second phase winding can be determined by determining the voltage at the second power output terminal.

[0025] In other embodiments, determining the flux difference between the first phase winding and the second phase winding of the PMAC motor includes: determining the voltage on the first phase winding that varies with time; determining the voltage on the second phase winding that varies with time; determining the difference between the voltage on the first phase winding and the voltage on the second phase winding that varies with time; and calculating the integral of the difference between the voltage on the first phase winding and the voltage on the second phase winding over time.

[0026] Preferably, determining the voltage on the first phase winding and the voltage on the second phase winding includes determining one or both of the following: the voltage on the DC link circuit; and the pulse width modulation output from the respective power output terminal.

[0027] In some embodiments, determining the flux difference between the first and second phase windings of the PMAC motor includes, for example, determining the current in the first and second phase windings by measuring using a Hall effect sensor, a sensing resistor, or a giant magnetoresistance (GMR) sensor.

[0028] In some embodiments, determining the flux difference between the first-phase winding and the second-phase winding further includes determining the rotor angle of the motor. This can then be used to identify the flux difference or the flux in the first-phase winding and the second-phase winding based on the current and the rotor angle, using a lookup table. Determining the motor's flux includes using a model that correlates flux with current.

[0029] The method also includes determining the criteria for activating the active short-circuit mode before the first moment (i.e. before enabling ASC mode).

[0030] Preferably, the method further includes: starting a timer when the criteria for activating the short-circuit mode are met; and, after the timer reaches a predetermined time threshold, electrically connecting multiple phase windings to a first DC terminal, such that multiple power output terminals are electrically connected together regardless of whether a first time, a second time, or optionally a third time is reached.

[0031] Preferably, the first moment immediately follows after determining that the criteria for activating the short-circuit mode are met.

[0032] This document also describes a method for controlling an inverter that supplies power to a PMAC motor. The method includes: activating an active short-circuit mode of the inverter, wherein the inverter includes multiple power output terminals, each power output terminal being switchably connected to two DC terminals of a DC link circuit via switching elements to provide AC power at each power output terminal; wherein each power output terminal is used to provide AC power to a corresponding phase winding of a plurality of phase windings of the PMAC motor; and wherein, in the active short-circuit mode, a selected switching element remains in the ON state, such that the plurality of power output terminals are electrically connected together; wherein activating the active short-circuit mode includes: selecting a first power output terminal of the plurality of power output terminals, wherein the first power output terminal corresponds to a first phase winding of the PMAC motor. Phase winding; at a first moment, switching a first switching element to the ON state to electrically connect the first phase winding to the first DC terminal of two DC terminals, and holding the first switching element in the ON state, and determining the flux difference between the first phase winding and the second phase winding of the PMAC motor, wherein the second power output terminal of a plurality of power output terminals corresponds to the second phase winding of the PMAC motor; selecting a second moment to electrically connect the second power output terminal to the first DC terminal, the second moment being different from the first moment, wherein the second moment is selected based on the determined flux difference between the first and second phase windings of the PMAC motor; at the second moment, switching a second switching element to the ON state to electrically connect the second phase winding to the first DC terminal, and holding the second switching element in the ON state.

[0033] This document also describes a computer-readable medium that includes instructions that, when executed by a computer, cause the computer to perform any of the methods described above.

[0034] This document also describes a controller for controlling an inverter supplying power to a PMAC motor having multiple phase windings. The controller includes a processor configured to: select a first phase winding of the PMAC motor; at a first moment, electrically connect the first phase winding to a first DC terminal of a DC link circuit and maintain the connection between the first phase winding and the first DC terminal; determine the flux difference between the first phase winding and a second phase winding of the PMAC motor; select a second moment for electrically connecting the second phase winding to the first DC terminal, the second moment being different from the first moment, wherein the second moment is selected based on the determined flux difference between the first and second phase windings; at the second moment, electrically connect the second phase winding to the first DC terminal and maintain the connection between the second phase winding and the first DC terminal.

[0035] This document also describes a controller for controlling an inverter supplying power to a PMAC motor. The controller includes a processor configured to: enable an active short-circuit mode of the inverter, wherein the inverter includes multiple power output terminals, each power output terminal being switchably connected to two DC terminals of a DC link circuit via switching elements to provide AC power at each power output terminal; wherein each power output terminal is configured to provide AC power to a corresponding phase winding of a plurality of phase windings of the PMAC motor; and wherein, in the active short-circuit mode, a selected switching element remains in the ON state, such that the plurality of power output terminals are electrically connected together; wherein enabling the active short-circuit mode includes: selecting a first power output terminal of the plurality of power output terminals, wherein the first power output terminal corresponds to a phase winding of the PMAC motor. First phase winding; at a first moment, controlling a first switching element to switch to the on state so that the first phase winding is electrically connected to the first DC terminal of the two DC terminals, and controlling the first switching element to remain in the on state, and determining the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor, wherein the second power output terminal of the plurality of power output terminals corresponds to the second phase winding of the PMAC motor; selecting a second moment for electrically connecting the second power output terminal to the first DC terminal, the second moment being different from the first moment, wherein the second moment is selected based on the determined magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor; at the second moment, controlling a second switching element to switch to the on state so that the second phase winding is electrically connected to the first DC terminal, and controlling the second switching element to remain in the on state.

[0036] Each controller can also be used to execute any of the methods described above.

[0037] This document also describes a system comprising: any controller described above; and an inverter for a multiphase permanent magnet motor having a first phase switching circuit and a second phase switching circuit.

[0038] Any system feature described herein can also be used as a method feature, and vice versa. As used herein, a means plus a function feature can be alternatively expressed as the corresponding structure of that feature.

[0039] Any feature in one aspect of the invention may be applied to other aspects of the invention in any suitable combination. Specifically, a method aspect may be applied to a system aspect, and vice versa. Furthermore, any, some, and / or all features in one aspect may be applied to any, some, and / or all features in any other aspect in any suitable combination.

[0040] It should also be understood that specific combinations of the various features described and defined in any aspect of the invention may be implemented, supplied, and used independently. Attached Figure Description

[0041] A method and apparatus for controlling an inverter for a PMAC motor are described by way of example only, in conjunction with the accompanying drawings, wherein:

[0042] Figure 1 An example of an inverter for a permanent magnet motor is shown;

[0043] Figure 2 An example method for activating the active short-circuit mode in a permanent magnet motor is shown;

[0044] Figure 3 A graph showing the voltage and magnetic flux on the phase windings of the motor is shown; and

[0045] Figure 4 A graph showing the voltage, flux, and predicted flux of a motor phase winding is presented. Detailed Implementation

[0046] Figure 1 An exemplary inverter 10 for a permanent magnet motor is shown. In this case, inverter 10 is used to drive motor 20 of an electric vehicle. DC link circuit 30 is connected across power supply 35. The voltage at the negative terminal of the DC link is 0V, and the voltage at the positive terminal of the DC link is V. DC V DC The value can change over time. Inverter 10 includes a three-phase switching circuit. A bridge circuit is provided, including switching elements 40, 42, 44 and switching elements 50, 52, 54, with the switching elements 40, 42, 44 for each phase located in the upper branch connected to the positive terminal of DC link circuit 30, and the switching elements 50, 52, 54 for each phase located in the lower branch connected to the negative terminal of DC link circuit 30. The switching elements 40, 42, 44, 50, 52, 54 can be, for example, IGBTs or MOSFETs. The output of each phase is connected to one of the three phase terminals 60, 62, 64 of motor 20.

[0047] The motor 20 includes a stator 22 and a rotor 24. Figure 1 The rotor 24 is shown as having a single permanent magnet, but rotors typically used in such permanent magnet motors include multiple permanent magnets used to provide a permanent and alternating magnetic field around the rotor 24. The stator 22 includes a yoke surrounding the rotor 24. The stator 22 has windings 70, 72, and 74 arranged around it. Figure 1The diagram shows each phase connected to two windings (phase terminal 60 connected to winding 70, phase terminal 62 connected to winding 72, and phase terminal 64 connected to winding 74). In this example, each winding is located opposite to the other winding of the same phase. Therefore, windings 70, 72, and 74 can be driven by an AC to generate a rotating magnetic field. To effectively drive the motor 20, the excitation timing of each of the three phases is selected based on the rotor position. The phases of the motor can be connected in a delta or star arrangement.

[0048] In this embodiment, a current sensor 80 (e.g., a Hall sensor) is also provided for sensing the current in each phase of the motor, such as the current through each winding or the current in at least one winding of each phase.

[0049] All three phase terminals or drivers 60, 62, and 64 are coupled to receive electrical energy from power supply 35. Each of the phase drivers 60, 62, and 64 is also coupled to a corresponding phase winding of the three phase windings of motor 20. Each phase terminal 60, 62, and 64 is coupled to a different phase winding. Each phase terminal 60, 62, and 64 can be controlled by switching elements 40, 42, 44, 50, 52, and 54 to regulate the electrical energy delivery from power supply 35 to the corresponding phase winding.

[0050] During normal operation, switching elements 40, 42, 44, 50, 52, and 54 operate at different times to provide alternating three phases to drive motor 20. There are three branches connected in parallel with power supply 35 and DC link circuit 30. Each branch has two switching elements; one in the upper branch and the other in the lower branch. The first branch has a first switching element 40 in the upper branch and a second switching element 50 in the lower branch. The two switching elements 40 and 50 operate alternately to provide alternating current to the first phase terminal 60. Therefore, when the first switching element 40 is on / closed, the second switching element 50 will be off / open, and vice versa. The second branch has a first switching element 42 in the upper branch and a second switching element 52 in the lower branch. The two switching elements 42 and 52 operate alternately to provide alternating current to the second phase terminal 62 (i.e., when the first switching element 42 is on / closed, the second switching element 52 will be off / open, and vice versa). The switching of switching elements 42 and 52 on the second branch is 120 degrees out of phase with the switching of switching elements 40 and 50 on the first branch. Similarly, the third branch has a first switching element 44 in the upper branch and a second switching element 54 in the lower branch. The two switching elements 44 and 54 operate alternately to supply AC power to the third phase terminal 64 (i.e., when the first switching element 44 is on / off, the second switching element 54 will be off / on, and vice versa). The switching of switching elements 44 and 54 on the third branch is 120 degrees out of phase with the switching of switching elements on the first and second branches to supply three-phase AC power to the motor 20.

[0051] The switching element can switch at a constant or variable frequency to generate a sinusoidal alternating current (AC) in the motor windings. The frequency of the sinusoidal AC can be around 50 Hz, for example, between 20 Hz and 100 Hz, or between approximately 30 Hz and 70 Hz. In other embodiments, the frequency can be as high as approximately 1 kHz, for example, between 500 Hz and 2000 Hz.

[0052] If motor 20 must be stopped or disabled quickly (e.g., in case of a fault in the motor system), a high back electromotive force (EMF) may occur, causing rectification back to the inverter's DC link circuit 30 or DC power supply 35. This can result in unwanted braking torque. Under worse conditions, the DC link voltage may exceed the operating levels of the capacitors and / or switches, potentially damaging the motor or inverter components.

[0053] Therefore, ASC mode can be applied. This prevents large back EMF on DC link circuit 35, keeping the back EMF level below the trip level to protect inverter 10 and motor 20. In active short-circuit mode, all output terminals 60, 62, 64 are connected to the same DC link terminal (either connected to the positive or negative terminal of DC link circuit 30) by, for example, keeping all switches 40, 42, 44 of the upper branch in the closed (or on) position or by keeping all switches 50, 52, 54 of the lower branch in the closed (or on) position. However, due to, for example, the inductance in the motor windings, the initial application of ASC mode from normal mode operation may cause a significant transient current (e.g., a high current spike) in the motor windings, which may be transferred to inverter 10. This transient current may be sufficient to damage motor 20 and / or inverter 10.

[0054] Therefore, if combined Figure 2 Furthermore, the present invention provides means to prevent or reduce such transient currents when applying ASC mode.

[0055] Figure 2 An exemplary method 2 for activating an active short-circuit mode in a multiphase permanent magnet motor is shown, which can reduce transient current.

[0056] An inverter controller can be provided to control inverter 10, and this inverter controller includes the logic for implementing method 2. Preferably, the same controller that controls the switches 40, 42, 44, 50, 52, and 54 of the inverter in normal operating mode can manage the transition to ASC mode. However, in some embodiments, a parallel hardware set including additional controllers capable of controlling the transition to ASC mode can be provided. The advantage of this approach is that if the main hardware fails, there is a redundant path to apply ASC, although the main controller (used to control the inverter in normal operating mode) typically (but not always) also has this functionality.

[0057] Initially, in step 200, motor 20 operates in normal mode and is driven by three-phase AC power from inverter 10. While motor 20 is operating in normal mode, the magnetic flux in each phase winding is monitored. The magnetic flux in each associated winding can be determined periodically (e.g., at sampling time intervals). The sampling time interval can be, for example, about 30 μs to 500 μs, or about 100 μs to 300 μs.

[0058] Magnetic flux can be determined in several ways. In this example, the magnetic flux is calculated as the integral of the phase voltage (i.e., the voltage at the phase output terminal), for example:

[0059] Flux x (t)=∫V x dt

[0060] Among them, Flux x (t) is the magnetic flux on the x-th phase winding of the motor at time t;

[0061] V x It is the voltage at the x-th phase output terminal that varies with time, for example, the voltage at the corresponding output terminals 60, 62, and 64 of motor 20. The voltage can be measured relative to the negative terminal of the DC link.

[0062] By determining the time-varying output phase voltages on inverter 10 (i.e., the voltages at output terminals 60, 62, and 64), the magnetic flux of each motor phase can be calculated. Therefore, in step 200, the voltages at the output terminals can be measured or otherwise determined during normal operation.

[0063] Preferably, the output phase voltage at each output terminal 60, 62, 64 of the inverter 10 can be determined by measuring the DC link voltage V between the positive and negative terminals of the DC link. DC The voltage readings for that sampling time are then allocated based on the pulse width modulation (PWM) output from the power output terminal. For example, it can be determined whether the output terminal is electrically connected to the positive or negative terminal of the DC link based on which switch is closed, for example, on the inverter branch that supplies power to the output terminal. Other factors, such as a second-order factor for dead time, can also be used to determine the output phase voltage; the second-order factor becomes more relevant at low speeds (e.g., vehicle speeds as low as around 10 km / h).

[0064] Due to the voltage V on the DC bus / link DC The flux may vary over time, so it is sometimes possible to determine the flux in each motor phase more accurately by performing voltage measurements and continuously calculating the flux over time, rather than by predicting from initial measurements and models.

[0065] It is helpful to include an additional damping factor D, which can be used to suppress voltage offset errors or initial offset. The damping factor D typically has a value between 0 and 1, preferably between about 0.9 and 0.99. In this case, the magnetic flux in the x-th phase winding can be calculated as:

[0066]

[0067] The term in the integral related to the damping factor can be considered as a high-pass filter with a time constant τ, which can be approximately 100 ms.

[0068] Therefore, the magnetic flux in each phase-connected winding at each time point can be determined. In some embodiments, the relative magnetic flux in the phase windings is determined rather than the absolute value.

[0069] Adjacent sampling times (e.g., at time t=t) A and time t = t A The change in magnetic flux between +Δt, where Δt is the sampling time, can be given by the following formula:

[0070] Flux x (t A +Δt)=DFlux x (t A )+V x (t A )Δt

[0071] Δt is the sampling time, which is the time interval (in seconds) between subsequent voltage measurements; Δt is typically between about 30 μs and 500 μs.

[0072] V x It is the average voltage at the x-th phase output terminal between time t and Δt.

[0073] Integrals can be calculated using either analog or digital methods.

[0074] The flux value can be recorded in memory during calculation, for example, in the memory of the controller that controls the inverter during normal operation, or in the controller that controls the inverter during transition to ASC mode (in some embodiments, the controller is the same controller). The flux value can be recorded in random access memory; a later flux value can overwrite an earlier flux value.

[0075] In step 202, criteria for activating the ASC mode in motor 20 are determined. Typically, ASC mode needs to be activated for safety reasons, such as if a fault is detected in the motor, inverter, power supply / battery, or other components of the system (e.g., in the vehicle or machine driven by the motor). In one example, the criteria for activating ASC mode include detecting that a vehicle collision has occurred. In another example, the criteria for activating ASC mode include determining that the power supply / battery is overheating. In yet another example, since ASC prevents back electromotive force (EMF) in the towed vehicle caused by motor movement, which could damage the inverter, the criteria for activating ASC mode include receiving an indication that the vehicle is being towed.

[0076] In some embodiments, in step 202, the inverter controller determines, by receiving a signal such as a control signal or message, that a criterion for activating the ASC mode in the motor 20 is met, which instructs the inverter to switch the motor to ASC mode. For example, when the motor is used in an electric vehicle, this signal can be received from the vehicle control unit (VCU).

[0077] In step 204, the first phase to be short-circuited is selected. The first phase is selected for short-circuiting based on the magnetic flux in each motor phase winding (e.g., the magnetic flux in each of the first, second, and third phase windings). The magnetic flux in each set of phase windings is known from the monitoring of the magnetic flux in each set of phase windings in step 200 (as described above).

[0078] In this embodiment, a short circuit is performed by connecting the phase winding to the negative terminal of the DC link. The first phase selected is the phase with the highest magnetic flux through its motor winding. In this example, the phase with the highest magnetic flux is the phase driven by switches 40 and 50 on the first branch of the inverter circuit at the first output terminal 60.

[0079] In step 206, the selected first phase is short-circuited to the negative end of the DC link. The moment when the first phase is short-circuited is called the first moment T1. When the first phase is short-circuited, the first moment T1 is measured and recorded in memory (e.g., in the memory of the controller that manages the transition to ASC mode).

[0080] A phase short circuit is achieved by switching the second switching element 50 on the lower branch of the first branch to the ON state, thereby electrically connecting the output terminal 60 to the negative terminal of the DC link. Simultaneously, the first switching element 40 on the upper branch of the first branch is disconnected. The second switching element 50 remains ON, therefore the voltage at the output terminal 60 drops to and remains at 0V, the voltage at the negative terminal of the DC link.

[0081] In the next step, the goal is to balance the magnetic flux in the remaining phases, which is achieved by making the magnetic flux in all phases as close as possible to the magnetic flux in the first phase.

[0082] In step 208, the other two phases (in this example, the second and third phases) are connected to the positive terminal of the DC link. This is achieved by switching the first switching elements 42 and 44 on the upper branches of the second and third branches of the inverter to the ON state. Simultaneously, the second switches 52 and 54 on the lower branches of the second and third branches of the inverter are disconnected. Therefore, the output terminals 62 and 64 are electrically connected to the positive terminal of the DC link, having a voltage of V. DC .

[0083] Preferably, while connecting the first phase to the negative terminal of the DC link (i.e., at the first moment T1), the remaining two phases are connected to the positive terminal of the DC link.

[0084] In some embodiments, at least one of the first switching elements 42 and 44 on the second and third branches is already in the on state at the first moment, in which case it is simply kept in the on state.

[0085] In step 210, the magnetic flux in each of the second and third phase windings of the motor 20 at the first moment is determined (e.g., the magnetic flux on all motor windings connected to the second and third phases at the first moment). Since the magnetic flux in the phase windings was monitored in step 200, this magnetic flux in the phase windings is known. Therefore, determining the magnetic flux in the second and third phase windings may include recording the magnetic flux in the second and third phase windings at the first moment.

[0086] The magnetic flux in each of the second and third phases can be determined relative to the magnetic flux in the phase with the highest magnetic flux (the first phase in this paper).

[0087] In this example, during monitoring step 200, the magnetic flux in each phase is calculated as an integral of the phase voltage (i.e., the voltage at the phase output).

[0088] The magnetic flux in the second phase relative to the magnetic flux in the first phase can be calculated as follows:

[0089] Flux 2wrt1 (t)=Flux2-Max(Flux1, Flux2, Flux3)=Flux2(t)-Flux1(t)

[0090] Flux 2wrt1 (T1) = Flux2(T1) - Flux1(T1)

[0091] Similarly, the magnetic flux in the third phase relative to the magnetic flux in the first phase is:

[0092] Flux 3wrt1 (T1) = Flux3(T1) - Flux1(T1)

[0093] Since the magnetic flux is highest in the first phase at the first moment in this example, the relative magnetic flux of the other two phases at the first moment will be negative (when the magnetic flux of the first phase is zero).

[0094] In step 212, based on the flux of each phase in the motor at the first moment obtained in step 210, a subsequent moment (i.e., a moment after the first moment) is selected at which each of the other phases is connected to the negative terminal of the DC link. A second moment for connecting the second phase output terminal 62 to the negative terminal of the DC link is calculated, and a third moment for connecting the third phase output terminal 64 to the negative terminal of the DC link is calculated.

[0095] The timing is chosen such that the flux in each of the second and third phase windings matches the flux in the first phase winding before connecting the corresponding phase winding to the negative terminal of the DC link. This balances the flux in the motor and prevents excessive transient currents. Therefore, the timing for connecting that phase to the negative terminal of the DC link is selected based on the flux of each of the second and third phases relative to the flux of the first phase.

[0096] When the first switching elements 42 and 44 on the upper branches of the second and third branches of the inverter are closed in step 208, the voltages at the output terminals 62 and 64 of the second and third phases become V that varies with time. DC Therefore, the second moment T2 when the second phase is connected to the negative DC link can be calculated as follows:

[0097]

[0098] The magnetic flux is calculated relative to the flux in the first phase, where the flux flux Flux1 is zero. Since the first phase is selected as having the highest flux, it is the highest flux. Therefore, the flux in the second and third phases is negative relative to the first phase, thus providing positive timing for connecting the second and third phases to the negative DC link.

[0099] The third time T3 when the third phase is connected to the negative DC link can be calculated as follows:

[0100]

[0101] To simplify the calculation, T1 can be set to zero.

[0102] The first switch 42 on the upper branch of the second branch of the inverter circuit remains on until the calculated second moment. In step 214, at the second moment, the second phase output terminal 62 is connected to the negative terminal of the DC link by closing the second switch 52 on the lower branch of the second branch of the inverter and keeping it on, while simultaneously opening the first switch 42 on the upper branch of the second branch of the inverter circuit.

[0103] The first switch 52 on the upper branch of the third branch of the inverter circuit remains on until the calculated third moment. In step 214, at the third moment, the second switch 54 on the lower branch of the third branch of the inverter is closed and kept on, while the first switch 44 on the upper branch of the third branch of the inverter circuit is opened, thereby connecting the third phase output terminal 64 to the negative terminal of the DC link.

[0104] Inverter 10 operates in ASC mode when all phases are short-circuited by connecting to the first end of the DC link (e.g., to the negative end in this example).

[0105] As a numerical example, when ASC is to be implemented, the magnetic flux in the first, second, and third phases can be:

[0106] Flux1=5Volt-seconds(Vs), Flux2=3Vs, Flux3=1Vs

[0107] Therefore, the relative magnetic flux of each phase in the second and third phases is:

[0108] Flux 2(wrt1) =-2Vs, Flux 3(wrt1) =-4Vs

[0109] If DC voltage V DC If the voltage is 240V, then the delay time for short-circuiting the second and third phases to the negative DC link after the first moment is as follows:

[0110]

[0111] Figure 3 The diagram shows the voltage and magnetic flux on each phase winding in this example. Solid lines represent voltage, and dashed lines represent magnetic flux. The first diagram shows the voltage and magnetic flux in the first phase winding. Before the first moment T1, the switches in the inverter operate in a conventional manner to generate AC current in each phase winding. Initially, the first phase winding is connected to the DC positive terminal, so the voltage of the first phase winding is equal to V. DC At the first moment T1, the system begins to switch to ASC mode. The magnetic flux on the first phase is at its maximum, therefore at the first moment T1, the first phase is connected to the negative DC link, and thus the voltage on the first phase becomes zero. The relative magnetic flux on the first phase is measured relative to the first phase, and is therefore zero.

[0112] Meanwhile, the second and third phase windings are connected to the positive DC link. Figure 3The second and third figures show the voltage and magnetic flux on the second and third phase windings. In this paper, the second phase winding was previously connected to a negative DC link, so the voltage on the second phase winding changes from zero to V at the first moment T1. DC Initially, the third-phase winding is already connected to the positive DC link, therefore the third-phase winding simply remains connected to the positive DC link (voltage is V). DC ).

[0113] The initial relative flux in the second phase winding is -2Vs. When the second phase is connected to the positive DC link, the flux in the positive DC link increases until time T2, at which point the flux in the second phase winding is the same as that in the first phase winding (i.e., the relative flux is zero). At time T2, the second phase is connected to the negative DC link, so the voltage in the second phase winding becomes zero. Afterward, the flux in the second phase winding remains unchanged.

[0114] Similarly, the magnetic flux in the third phase winding also begins to increase from the first moment T1. The magnetic flux in the third phase winding does not match the magnetic flux in the first phase winding until the third moment T3, at which time the third phase is also connected to the negative terminal of the DC link. At this time, the motor is in full ASC mode.

[0115] Although in the embodiment described above, the first phase selected in step 204 is the phase with the highest magnetic flux, in other embodiments, additional selection criteria for the first phase may be used.

[0116] The choice of which phase to short-circuit first in step 204 depends on whether the short-circuit mode is achieved by connecting outputs 60, 62, and 64 to the positive or negative terminal of the DC link circuit 30; that is, whether switches 40, 42, and 44 on the upper branch or switches 50, 52, and 54 on the lower branch are held in the closed position. In an alternative embodiment, the motor output can be connected to the positive terminal of the DC link to achieve ASC mode. In this case, the phase with the lowest magnetic flux or the highest negative magnetic flux can be selected as the first phase in step 204. Typically, in step 208, the other phases are subsequently connected to the DC link terminal opposite to the DC link terminal connected to the first phase in step 206. Therefore, in this alternative embodiment, the other two phases in step 208 will be connected to the negative terminal of the DC link.

[0117] In some embodiments, step 204 of selecting the first phase to be short-circuited first includes selecting whether to connect outputs 60, 62, 64 to the positive or negative terminal of DC link circuit 30. The selection of whether to connect outputs 60, 62, 64 to the positive or negative terminal of DC link circuit 30 can be based on the phase voltage at the transition time; for example, selecting the DC link terminal that minimizes the voltage difference between the first phase and the selected DC link terminal.

[0118] In some embodiments, the phase with the largest magnetic flux is selected as the first phase, for example, the phase with the largest magnetic flux on the phase winding in the motor at the start of the transition to short-circuit mode.

[0119] In an alternative embodiment, step 202 further includes determining the first moment of short-circuiting the first phase before performing the short circuit on the first phase. The timing for implementing ASC mode can also be selected when determining that ASC mode should be implemented, such as the start time of the transition to ASC mode (e.g., the first moment of short-circuiting the first phase of the motor). Typically, the above timing will actually follow immediately after the condition determining that ASC mode should be selected occurs, but occasionally there may be some delay.

[0120] In the embodiment described above, the absolute magnetic flux of each phase is calculated in step 200, and then the relative magnetic flux between phases is determined in step 210. However, in an alternative embodiment, the relative magnetic flux can be calculated during the monitoring phase of step 200.

[0121] For example, given a fixed magnetic flux relative to the first phase, the relative magnetic flux of the second phase is obtained by the following formula:

[0122]

[0123] Among them, Flux 2wrt1 (t) is the magnetic flux in the second phase relative to the magnetic flux in the first phase of the motor at time t;

[0124] Δt is the sampling time, which is the time interval (in seconds) between subsequent voltage measurements; Δt is typically between about 30 μs and 500 μs.

[0125] It is the average voltage at the first phase output terminal 60° between time t and t-Δt; for example, it can be calculated by adding the voltages at the first phase output terminal at time t and time t-Δt and dividing by 2. For example,

[0126] It is the average voltage at the second phase output terminal 62 between time t and t-Δt, for example,

[0127] D is the damping factor, which typically has a value between 0 and 1, preferably between about 0.9 and 0.99.

[0128] Similarly, the magnetic flux of the third phase relative to the first phase can be obtained using the following formula:

[0129]

[0130] Among them, Flux 3wrt1 (t) is the relative magnetic flux on the third phase of the motor at time t; and

[0131] It is the average voltage at the second phase output terminal 62 between time t and t-Δt, for example,

[0132] While a specific method for determining magnetic flux has been used in steps 200, 204, and 210, alternative approaches are available. For example, to calculate the phase flux on one of the motor windings 70, 72, and 74 corresponding to the second phase, the current in motor winding 72 can be measured (e.g., via current sensor 80), and a model that associates the current with the magnetic flux can be used. In another example, the current in motor winding 72 can be measured (e.g., via current sensor 80), and the angle of rotor 24 can be recorded. A lookup table can then be used to associate the motor current and rotor angle with the magnetic flux in the phase. The model or lookup table can be stored in the memory of the inverter controller or in the memory of an additional controller used to manage the transition to ASC mode. For example, the model or lookup table may be motor type-specific and included in the inverter's setup file (mounted on the relevant controller).

[0133] In the embodiment described above, based on the relative magnetic flux in each phase winding of the second and third phase windings at the first moment (i.e., the moment when the first phase is short-circuited), subsequent second and third moments for short-circuiting each of the second and third phases are determined in step 212. However, it may be advantageous to continue monitoring the magnetic flux in the second and third phases and adjust the second and third moments accordingly if the magnetic flux does not change in a predictable manner (e.g., linearly). For example, the voltage of a DC link may fluctuate, so the magnetic flux in each phase may change at a variable rate.

[0134] Therefore, in an alternative embodiment, step 210 involves determining the magnetic flux in the second and third phases at a plurality of sampling times following the first time. The consecutive sampling times may be spaced apart by a predetermined sampling period, or in other words, the sampling times have a predetermined sampling frequency. Step 212 is followed by calculating an estimated subsequent time for short-circuiting each of the other phases, and updating this estimated subsequent time each time the magnetic flux is determined. Therefore, steps 210 and 212 can be performed in parallel. The estimated subsequent time is the moment when the predicted magnetic flux in the other phases matches the magnetic flux in the first phase. When the estimated subsequent time falls within the next sampling period (i.e., earlier than the sampling time immediately following the current sampling time), that estimated subsequent time is selected as the moment to short-circuit the phase winding.

[0135] In some embodiments, the magnetic flux in each phase at each sampling time is determined by estimating the change in magnetic flux in that phase during the sampling period prior to the sampling time. The change in magnetic flux can be estimated by averaging the DC link voltage at the previous sampling time and the DC link voltage at the current sampling time. Therefore, the magnetic flux at the sampling time can be obtained using the following formula:

[0136]

[0137] Here, t represents the current time. It is the sampling period, so It is the previous sampling time, D is the damping factor, and V is the damping factor. DC This is the DC link voltage. (Flux) x It is the magnetic flux in the x-th phase winding.

[0138] The estimated subsequent time can be calculated by estimating the remaining time for the magnetic flux to reach the flux of the first phase winding and adding that remaining time to the current time. To perform this estimation, for example, it can be assumed that the DC link voltage will remain the same as the DC link voltage at the current sampling time. Therefore, the subsequent time can be calculated as follows:

[0139]

[0140] T x This is the moment when the x-th phase winding is short-circuited. The maximum magnetic flux (in this case, the flux of the first phase) will not change because the first phase was short-circuited at the first moment. Therefore, for the case of using relative magnetic flux, the term Max(Flux1,Flux2,Flux3) will only be zero.

[0141] In some embodiments, the sampling time period The sampling time period is approximately 100 microseconds, for example, it can be between approximately 1 microsecond and 10 milliseconds, preferably between 10 microseconds and 1 millisecond, or more preferably between 50 microseconds and 200 microseconds. The sampling time period can be, for example, between approximately 30 μs and 500 μs, or between approximately 100 μs and 300 μs.

[0142] In a preferred embodiment, the sampling frequency is the same as the PWM time base (or minimum PWM switching frequency) of the inverter.

[0143] Typically, the selected time to short-circuit a winding in a phase (connected to the DC positive or negative terminal) is not perfectly aligned with the inverter's PWM time base. In this case, the switching timing can be adjusted by providing a pulse shorter than the normal pulse (i.e., a pulse shorter than the normal minimum PWM switching frequency) to short-circuit the phase winding at the selected time.

[0144] For example, with a PWM time base of 100 microseconds, and if it is estimated that the flux in the second phase will match the flux in the first phase within 73 microseconds, a shorter pulse of 73 microseconds can be provided, so that the second phase winding is connected to the negative terminal of the DC link after 73 microseconds.

[0145] Figure 4 Two graphs are shown showing the voltage and magnetic flux in the second-phase winding when the flux estimate is periodically recalculated at the sampling time period and at the second time point. The sampling period here is 0.005 seconds. The PWM time base is also 0.005 seconds. The lower graph shows the voltage on the second phase and the actual magnetic flux in the second-phase winding. The upper graph shows the estimated flux prediction at consecutive sampling times, with the corresponding estimated second time point marked along the bottom horizontal axis. Both graphs have the same time scale.

[0146] like Figure 3 In the example, the relative magnetic flux in the second phase winding at the first moment is -2Vs, and the initial voltage of the DC link is 240V. Therefore, the first estimate for the second moment (made at the first moment T1) is 0.0083 seconds.

[0147] However, as can be seen from the graph below, the voltage on the DC link decreases during the first sampling period. Therefore, the voltage measured at the second sampling time (t = 0.005 s) is lower. Consequently, the change in magnetic flux is less than initially expected. At the second sampling time, a second magnetic flux prediction is made based on the current magnetic flux and the assumption that the voltage on the DC link will remain constant. A second estimate is then made for the second sampling time. At this new lower voltage, the second estimate for the second sampling time is now greater than 0.015 seconds.

[0148] As shown in the figure below, the voltage increases again between the second sampling time (t = 0.005 s) and the third sampling time (t = 0.010 s). Therefore, the flux change between the second and third sampling times is larger than previously predicted. At the third sampling time, based on the current flux and assuming the voltage of the DC link will remain constant, a third flux prediction is made at the second sampling time. Based on this, a third estimate is made for the second time. The third estimate for the second time is now 0.012 s. This means that the estimated time to switch the second phase to the negative end of the DC link is within the next sampling period (before the fourth sampling time, which is t = 0.015 s). Therefore, the third estimate is now selected as the second time. Then, a short pulse of 0.002 seconds (instead of the normal 0.005-second pulse) is applied, and the second phase winding is connected to the DC link at the selected second time (0.012 seconds). As can be seen from the figure below, the relative flux in the second phase winding is zero at the second time T2.

[0149] Please note that the numbers in this example have been slightly simplified for ease of explanation.

[0150] A similar process can be used to determine the third moment when the third phase is short-circuited to the DC link.

[0151] The embodiments and examples described above should be understood as illustrative. Other embodiments, aspects, or examples are contemplated. It should be understood that any feature described in connection with any embodiment, aspect, or example may be used alone or in combination with other described features, and may also be used in combination with one or more features of any other embodiment, aspect, or example, or in any combination of any other embodiment, aspect, or example. Furthermore, equivalents and modifications not described above may be employed without departing from the scope of the invention, which is defined in the appended claims.

Claims

1. A method for controlling an inverter that supplies power to a permanent magnet alternating current (PMAC) motor having multiple phase windings, the method comprising: Select the first phase winding of the PMAC motor; At the first moment, the first phase winding is electrically connected to the first DC terminal of the DC link circuit, and the connection between the first phase winding and the first DC terminal is maintained. Determine the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor; A second time is selected to electrically connect the second phase winding to the first DC terminal, the second time being different from the first time, wherein the second time is selected based on the determined magnetic flux difference between the first phase winding and the second phase winding; At the second moment, the second phase winding is electrically connected to the first DC terminal, and the connection between the second phase winding and the first DC terminal is maintained.

2. The method according to claim 1, further comprising: During the time interval between the first moment and the second moment, the second phase winding is electrically connected to the second terminal of the DC link circuit.

3. The method according to claim 2, wherein, The time interval between the first moment and the second moment is selected based on the determined flux difference between the first phase winding and the second phase winding and the DC voltage at the second end of the DC link.

4. The method according to any one of claims 2 or 3, wherein, The second moment and / or the time interval are selected based on the time required for the flux difference between the first phase winding and the second phase winding of the PMAC motor to reach zero.

5. The method according to claim 4, wherein, Selecting the second time moment and / or the time interval includes: Motor data is collected at multiple sampling times, with a predetermined sampling time period between consecutive sampling times; Calculate multiple corresponding time estimates; each time estimate is an estimate of the time required for the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor to reach zero, based on the motor data collected at the sampling time. Each of the plurality of time estimates is compared with the predetermined sampling time period; and Select a first time estimate that is less than or equal to the predetermined sampling time period; The second time point is selected using the first time point estimate.

6. The method according to claim 5, wherein, The step of connecting the second phase winding to the first DC terminal at the second moment includes: A pulse of length selected from the first time estimate is applied to electrically connect the second phase winding to the first DC terminal at the second time.

7. The method according to claim 5 or 6, wherein, The inverter has a pulse width modulation time base equal to the sampling time period.

8. The method according to claim 1, further comprising: Determine the magnetic flux difference between the first phase winding and the third phase winding of the PMAC motor; A third time is selected to electrically connect the third phase winding to the first DC terminal, the third time being different from the first time and the second time, wherein the third time is selected based on the determined magnetic flux difference between the first phase winding and the third phase winding of the PMAC motor. At the third moment, the third phase winding is electrically connected to the first DC terminal, and the connection between the third phase winding and the first DC terminal is maintained.

9. The method according to claim 1, wherein, Selecting the first phase winding of the PMAC motor includes: Determine the magnetic flux in each of the plurality of phase windings of the PMAC motor; and The phase winding with the highest magnetic flux value is selected as the first phase winding.

10. The method according to claim 1, further comprising: Before the first moment, Multiple switching elements in the inverter are switched to provide alternating current (AC) to each phase winding.

11. The method of claim 10, further comprising: While switching the switching element to supply the alternating current to each of the phase windings, the magnetic flux in each of the plurality of phase windings of the PMAC motor is monitored.

12. The method according to claim 11, wherein, Based on the magnetic flux detected in the first phase winding, the second phase winding, and / or the third phase winding at the first moment, the magnetic flux difference between the first phase winding and the second phase winding and / or between the first phase winding and the third phase winding of the PMAC motor is determined.

13. The method according to claim 8, wherein, The second time point is later than the first time point, and the third time point is later than the first time point.

14. The method according to claim 13, wherein, Determining the flux difference between the first phase winding and the second phase winding of the PMAC motor includes: Determine the time-varying voltage on the first phase winding; Determine the time-varying voltage on the second phase winding; Calculate the integral of the voltage on the first phase winding with respect to time; Calculate the integral of the voltage across the second phase winding with respect to time; and Determine the difference between the integral of the voltage on the first phase winding and the integral of the voltage on the second phase winding.

15. The method according to claim 13, wherein, Determining the flux difference between the first phase winding and the second phase winding of the PMAC motor includes: Determine the time-varying voltage on the first phase winding; Determine the time-varying voltage on the second phase winding; Determine the difference between the time-varying voltage on the first phase winding and the time-varying voltage on the second phase winding; and Calculate the integral of the difference between the voltage on the first phase winding and the voltage on the second phase winding with respect to time.

16. The method according to claim 14 or 15, wherein, Determining the voltage on the first phase winding and the voltage on the second phase winding includes determining one or both of the following: The voltage on the DC link circuit; and Pulse width modulation output from the corresponding power output terminal.

17. The method according to claim 16, wherein, Determining the flux difference between the first phase winding and the second phase winding of the PMAC motor includes: The current in the first phase winding and the second phase winding is determined by using a Hall effect sensor, a sensing resistor, or a giant magnetoresistance (GMR) sensor.

18. The method according to claim 17, wherein, Determining the flux difference between the first phase winding and the second phase winding further includes: Determine the rotor angle of the motor.

19. The method according to claim 18, wherein, Determining the flux difference between the first phase winding and the second phase winding further includes: Based on the current and the rotor angle, a lookup table is used to identify the magnetic flux difference or the magnetic flux in the first phase winding and the second phase winding.

20. The method according to claim 17 or 18, wherein, Determining the magnetic flux of the motor includes using a model that correlates magnetic flux with current.

21. The method of claim 20, further comprising: The criteria for activating the active short-circuit mode are determined before the first moment.

22. The method of claim 21, further comprising: When the criteria for activating the short-circuit mode are met, the timer is started; as well as After the timer reaches a predetermined time threshold, the plurality of phase windings are electrically connected to the first DC terminal, so that regardless of whether the first time, the second time, or the third time is reached, the plurality of power output terminals are electrically connected together.

23. The method according to claim 21 or 22, wherein, The first moment immediately follows the determination that the criteria for activating the short-circuit mode are met.

24. A method for controlling an inverter that supplies power to a permanent magnet alternating current (PMAC) motor, the method comprising: The inverter is activated in active short-circuit mode, wherein the inverter includes multiple power output terminals, each power output terminal being switchably connected to two DC terminals of a DC link circuit via a switching element to provide alternating current (AC) power at each power output terminal, and Wherein, each power output terminal is used to provide the AC power to a corresponding phase winding among the multiple phase windings of the PMAC motor, and In the active short-circuit mode, the selected switching element among the switching elements remains in the on state, so that the plurality of power output terminals are electrically connected together. Enabling the active short-circuit mode includes: Select the first power output terminal among the plurality of power output terminals, wherein the first power output terminal corresponds to the first phase winding of the PMAC motor; At the first moment, the first switching element is switched to the on state, so that the first phase winding is electrically connected to the first DC terminal of the two DC terminals, and the first switching element is held in the on state. Determine the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor, wherein the second power output terminal among the plurality of power output terminals corresponds to the second phase winding of the PMAC motor; A second time is selected to electrically connect the second power output terminal to the first DC terminal, the second time being different from the first time, wherein the second time is selected based on the determined magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor; At the second moment, the second switching element is switched to the on state so that the second phase winding is electrically connected to the first DC terminal, and the second switching element is held in the on state.

25. A computer-readable medium comprising instructions that, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 23 or 24.

26. A controller for controlling an inverter supplying power to a PMAC motor having multiple phase windings, the controller comprising a processor configured to: Select the first phase winding of the PMAC motor; At the first moment, the first phase winding is electrically connected to the first DC terminal of the DC link circuit, and the connection between the first phase winding and the first DC terminal is maintained. Determine the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor; A second time is selected to electrically connect the second phase winding to the first DC terminal, the second time being different from the first time, wherein the second time is selected based on the determined magnetic flux difference between the first phase winding and the second phase winding; At the second moment, the second phase winding is electrically connected to the first DC terminal, and the connection between the second phase winding and the first DC terminal is maintained.

27. The controller of claim 26 is further configured to perform the method of any one of claims 2 to 24.

28. A controller for controlling an inverter supplying power to a PMAC motor, the controller including a processor for: The inverter is activated in active short-circuit mode, wherein, The inverter includes multiple power output terminals, each of which is switchably connected to two DC terminals of a DC link circuit via a switching element to provide alternating current (AC) power at each power output terminal. Wherein, each power output terminal is used to provide the AC power to a corresponding phase winding among the multiple phase windings of the PMAC motor, and In the active short-circuit mode, the selected switching element among the switching elements remains in the on state, so that the plurality of power output terminals are electrically connected together. Enabling the active short-circuit mode includes: Select the first power output terminal among the plurality of power output terminals, wherein the first power output terminal corresponds to the first phase winding of the PMAC motor; At a first moment, the first switching element is controlled to switch to the on state, so that the first phase winding is electrically connected to the first DC terminal of the two DC terminals, and the first switching element is controlled to remain in the on state. Determine the magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor, wherein the second power output terminal among the plurality of power output terminals corresponds to the second phase winding of the PMAC motor; A second time is selected to electrically connect the second power output terminal to the first DC terminal, the second time being different from the first time, wherein the second time is selected based on the determined magnetic flux difference between the first phase winding and the second phase winding of the PMAC motor; At the second moment, the second switching element is controlled to switch to the conducting state so that the second phase winding is electrically connected to the first DC terminal, and the second switching element is controlled to remain in the conducting state.

29. The controller of claim 28 is further configured to perform the method of any one of claims 2 to 24.

30. A system comprising: The controller according to any one of claims 26 to 29; as well as An inverter for a multiphase permanent magnet motor having a first-phase switching circuit and a second-phase switching circuit.

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