A method and device for controlling no-load back electromotive force of a permanent magnet motor

Abstract

The present invention discloses a method and device for controlling the no-load back electromotive force of a permanent magnet motor. A switch is installed between the motor and the motor control module, and the switch is connected to the switch control module. First, it is determined whether the motor is in a no-load state. Then, according to the determination result, control information is sent to the switch control module to control the switch to open or close. In this way, during the vehicle neutral coasting test, the endurance consistency problem caused by the zero torque deviation of the motor is effectively solved. On the other hand, for four-wheel drive models and distributed drive models, when the vehicle is running normally and the motor is no-loaded, the motor can be prevented from generating back electromotive force, thereby saving battery power and effectively improving the vehicle's endurance.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle development and testing, and in particular to a method and device for controlling no-load back electromotive force of a permanent magnet motor. Background Art

[0002] In the prior art, permanent magnet motors have been widely used in new energy vehicles due to their high power density, high efficiency, etc. However, due to the characteristics of permanent magnet motors, back electromotive force will be generated when the permanent magnet motor runs at no load.

[0003] When a new energy vehicle is coasting in neutral on a test road or drum, if the back electromotive force of the motor is not completely eliminated, torque will be output, which will have an adverse effect on the vehicle's road coasting or drum coasting test, making the test results inaccurate.

[0004] For four-wheel drive vehicles and distributed drive vehicles driven by permanent magnet motors, when one of the magneto motors is in an unloaded state under certain working conditions, the power battery needs to be consumed to eliminate the back electromotive force, resulting in energy waste. In addition, excessive back electromotive force may also damage the motor control module.

[0005] The existing solution to the above shortcomings is to turn off the IGBT, but this solution has certain limitations. When the back electromotive force characteristic of the permanent magnet motor is too large and the matching power battery voltage is too low, in order to ensure that the IGBT is not damaged, the IGBT can only be turned off at certain speeds, but high speeds still cannot solve the zero torque problem caused by the back electromotive force. Summary of the invention

[0006] In view of the above problems, the present invention is proposed to provide a method and device for controlling the no-load back electromotive force of a permanent magnet motor, which can solve the zero torque problem of the motor at all speeds without being limited by voltage or motor speed.

[0007] According to a first aspect of the present invention, a method for controlling no-load back electromotive force of a permanent magnet motor is provided, wherein a switch is installed between the motor and the motor control module, and the switch is connected to the switch control module;

[0008] Methods include:

[0009] Determine whether the motor is in a no-load state;

[0010] According to the judgment result, control information is sent to the switch control module to control the switch to open and close.

[0011] Optionally, there are multiple motors;

[0012] Determine whether the motor is in a no-load state, including:

[0013] Get the throttle opening;

[0014] Determine the driver's required torque based on the throttle opening;

[0015] According to the required torque, the control torque of each motor is determined respectively;

[0016] According to the control torque of each motor, it is determined whether each motor is in a no-load state.

[0017] Optionally, the control torque of each motor is determined separately according to the required torque, including:

[0018] If the required torque is greater than or equal to the torque threshold, the control torque of each motor is greater than 0;

[0019] If the required torque is less than the torque threshold, the control torque of at least one motor is 0.

[0020] Optionally, determining whether each motor is in a no-load state according to the control torque of each motor includes:

[0021] For each motor, if the control torque of the motor is 0, the motor is in a no-load state.

[0022] Optionally, according to the judgment result, control information is sent to the switch control module to control the switch to be turned on or off, including:

[0023] For each motor, if the motor is in a no-load state, no-load information is sent to the switch control module, and the switch control module controls the switch on the motor to be disconnected according to the no-load information.

[0024] Optionally, the number of motors is 2, including a front drive motor and a rear drive motor.

[0025] Optionally, the number of motors is 4, including hub motors on 4 wheels.

[0026] Optionally, determining whether the motor is in a no-load state includes:

[0027] Get the gear status of the vehicle;

[0028] If the gear state is neutral, the motor is in a no-load state.

[0029] Optionally, according to the judgment result, control information is sent to the switch control module to control the switch to be turned on or off, including:

[0030] If the motor is in a no-load state, neutral gear information is sent to the switch control module, and the switch control module controls the switch to be disconnected according to the neutral gear information.

[0031] According to a second aspect of the present invention, a no-load back electromotive force control device for a permanent magnet motor is provided, the device comprising:

[0032] A judgment module, used to judge whether the motor is in a no-load state;

[0033] The control module is used to send control information to the switch control module according to the judgment result to control the switch to open or close.

[0034] The above one or more technical solutions in the embodiments of this specification have at least the following technical effects:

[0035] The embodiment of this specification provides a method and device for controlling the no-load back electromotive force of a permanent magnet motor. A switch is installed between the motor and the motor control module, and the switch is connected to the switch control module. First, it is determined whether the motor is in a no-load state. Then, according to the determination result, control information is sent to the switch control module to control the switch opening and closing. In this way, during the vehicle neutral coasting test, the endurance consistency problem caused by the zero torque deviation of the motor is effectively solved. On the other hand, for four-wheel drive models and distributed drive models, when the vehicle is running normally and the motor is unloaded, the motor can be prevented from generating back electromotive force, thereby saving battery power and effectively improving the vehicle's endurance.

[0036] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] By reading the detailed description of the preferred embodiment below, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only used for the purpose of illustrating the preferred embodiment and are not considered to be limiting of the present invention. Moreover, the same reference figures are used to represent the same parts throughout the accompanying drawings.

[0038] In the attached picture:

[0039] Figure 1 A flow chart of a method for controlling no-load back electromotive force of a permanent magnet motor in an embodiment of the present invention is shown.

[0040] Figure 2 A connection schematic diagram of a permanent magnet motor in an embodiment of the present invention is shown.

[0041] Figure 3 A flow chart showing another method for controlling no-load back electromotive force of a permanent magnet motor in an embodiment of the present invention is shown.

[0042] Figure 4 A block diagram of a no-load back electromotive force control device for a permanent magnet motor in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0046] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] Combination Figure 1 As shown in the flowchart, this embodiment provides a method for controlling no-load back electromotive force of a permanent magnet motor, which is executed by a vehicle controller. The method for controlling no-load back electromotive force of a permanent magnet motor includes steps 101 to 102:

[0048] Step 101: Determine whether the motor is in a no-load state;

[0049] The control method is executed by the vehicle controller, referring to Figure 2 As shown in the connection diagram, the vehicle controller is connected to the switch control module, the switch control module is connected to the switch, and the switch control module controls the switch action. Among them, the switch is connected between the motor and the motor control module, and the switch is connected to the three-phase high-voltage end of the motor. By controlling the opening and closing of the switch, the on and off of the three-phase high-voltage electricity of the motor can be controlled. In other words, when the switch control module controls the normal power supply of the motor when the switch is closed. When the switch control module controls the switch to be disconnected, the power supply circuit of the motor is disconnected.

[0050] The motor refers to the permanent magnet motor in new energy vehicles. When the vehicle is running, the power battery in the vehicle provides electrical energy to the motor to drive the vehicle. When the power battery does not supply power to the motor and the vehicle is still moving, it means that the motor is running at no load. When the motor is running at no load, it will generate back electromotive force, and the higher the no-load speed, the greater the back electromotive force generated, which may break down the motor control module. In order to eliminate the back electromotive force generated by the idling of the motor, the power of the power battery is generally consumed, which inevitably causes power waste, thereby affecting the accuracy of battery life.

[0051] In this embodiment, the no-load operation of the motor generally includes the following situations: one is that the gear state of the vehicle is in neutral and the vehicle is coasting. Another situation is for four-wheel drive vehicles or distributed drive vehicles, when these vehicles are driving normally, at least one motor does not output torque to the outside.

[0052] In detail, when the vehicle is in neutral gear, this situation mostly refers to the neutral gear sliding on the test road and drum when the endurance and energy consumption of new energy vehicles are developed. At this time, the power battery does not supply power to the motor, but the wheels are rotating. In this case, no matter what type of vehicle it is, the motor of the vehicle is in an unloaded state.

[0053] Another case is for four-wheel drive vehicles and distributed drive vehicles. These vehicles have a feature that there are multiple motors in the vehicle. For example, a four-wheel drive vehicle has two motors, namely the front drive motor and the rear drive motor. Distributed drive vehicles have four motors, namely, there is a hub motor on each wheel. For such vehicles with multiple motors, when the vehicle is driving normally, all motors may be running under load, or only some motors may be running under load, and the remaining motors may be running without load. The motor running without load will generate back electromotive force.

[0054] Based on the above, in order to avoid the motor from generating back electromotive force, it is necessary to first determine whether the motor is in an unloaded state. The judgment conditions are different for different situations. For vehicles in neutral coasting tests, the gear status of the vehicle can be used to determine whether the motor is in an unloaded state. For vehicles with multiple motors and running normally, it is necessary to see whether the motor has output control torque.

[0055] Step 102: According to the determination result, control information is sent to the switch control module to control the switch to open or close.

[0056] In this embodiment, there are two results for judging whether the motor is in a no-load state, one result is that the motor is in a no-load state, and the other result is that the motor is not in a no-load state, that is, the motor is in a load operation state. If the motor is not in a no-load state, the motor can drive the wheel movement normally, and there will be no back electromotive force generated in the power-on circuit of the motor. If it is determined that the motor is in a no-load state, it means that when the wheel rotates, it will cause the back electromotive force to be generated in the power-on circuit of the motor. At this time, the vehicle controller will send corresponding switch control information to the switch control module, control the switch to disconnect, and disconnect the power-on circuit of the motor. In this way, even if the wheel rotates, the motor only generates mechanical friction, and will not generate back electromotive force. In this way, during the vehicle neutral coasting test, the endurance consistency problem caused by the zero torque deviation of the motor can be effectively solved. On the other hand, for four-wheel drive models and distributed drive models, when the vehicle is running normally and the motor is unloaded, there is no need to use the power of the power battery to eliminate the back electromotive force, which can save battery power and effectively improve the endurance of the vehicle.

[0057] It is not difficult to find from the above content that the back electromotive force generated by the motor being unloaded can be avoided by simply judging whether the motor is in an unloaded state and then controlling the switch on and off according to the judgment result. In order to facilitate understanding and implementation by those skilled in the art, this embodiment provides a specific implementation method for judging whether the motor is in an unloaded state.

[0058] In an optional implementation, if there are multiple motors on the vehicle, that is, the vehicle is a four-wheel drive model or a distributed drive model. When the vehicle is a four-wheel drive model, there are two motors on the vehicle, namely the front drive motor and the rear drive motor. If the vehicle is a distributed drive model, there are four wheel hub motors on the vehicle. Figure 3 As shown, the step of determining whether the motor is in a no-load state may include steps 201 to 204:

[0059] Step 201, obtaining the throttle opening;

[0060] Among them, the throttle is also called the accelerator pedal, which is used to control the motor torque. The throttle is connected to the vehicle controller, which can also be called the vehicle controller. The throttle pedal is equivalent to a sensor, and the throttle opening refers to the opening of the throttle pedal.

[0061] Step 202: Determine the driver's required torque according to the throttle opening;

[0062] The vehicle controller can obtain the required torque corresponding to different pre-calibrated driving modes by looking up the table based on the obtained accelerator pedal opening, and then obtain the final control torque that needs to be sent to the motor controller after comprehensive strategy restrictions.

[0063] Step 203: Determine the control torque of each motor according to the required torque;

[0064] If the required torque is not large, one motor or part of the motors can meet the torque requirement of the vehicle without turning on all the motors. If the required torque is large, all the motors need to work together. Therefore, there is a torque threshold, and the size of the torque threshold can be determined according to the actual situation and the specific vehicle model. In an optional implementation, the control torque of each motor is determined separately according to the required torque, which may include:

[0065] If the required torque is greater than or equal to the torque threshold, the control torque of each motor is greater than 0;

[0066] If the required torque is less than the torque threshold, the control torque of at least one motor is 0.

[0067] That is to say, if the required torque is greater than or equal to the torque threshold, it means that all motors need to output torque to drive the vehicle to move. If the required torque is less than the torque threshold, it means that not all motors need to output torque, and only one motor or part of the motors need to output torque. For example, when a certain model of four-wheel drive vehicle is operating normally in D gear, if the required torque is 100Nm based on the obtained throttle opening, which is greater than the torque threshold, the control torque of the front drive motor is finally determined to be 50Nm, and the control torque of the rear drive motor is 50Nm. When a certain model of four-wheel drive vehicle is operating normally in D gear, if the required torque is 40Nm based on the obtained throttle opening, which is less than the torque threshold, the control torque of the rear drive motor is finally determined to be 40Nm, the front drive motor is unloaded, and the switch connected to the high-voltage end of the front drive motor is disconnected at the same time to avoid generating back electromotive force.

[0068] Step 204: Determine whether each motor is in a no-load state according to the control torque of each motor.

[0069] Among them, after determining the control torque of each motor, it can be known whether the control torque of each motor is 0. Whether the control torque of the motor is 0 determines whether the motor is in a no-load state. Specifically, for each motor, if the control torque of the motor is 0, the motor is in a no-load state. Correspondingly, if the control torque of the motor is not 0, no matter how large the torque of the motor is, it can be determined that the motor is not in a no-load state.

[0070] After determining the status of each motor, the vehicle control module can determine whether to control the switch to be disconnected. The specific control steps may include:

[0071] For each motor, if the motor is in a no-load state, no-load information is sent to the switch control module, and the switch control module controls the switch on the motor to be disconnected according to the no-load information.

[0072] That is to say, if the motor is in a no-load state, the vehicle control module will send no-load information to the switch control module, and the switch control module will control the switch to be disconnected according to the received no-load information. Of course, if the motor is not in a no-load state, the vehicle control module will not send no-load information to the switch control module, and the switch will remain closed, so that the power circuit of the motor remains unblocked.

[0073] For example, a four-wheel drive vehicle is driving normally on the road in D gear. The driver lightly steps on the accelerator. The vehicle controller determines that the required torque is 30Nm based on the acquired throttle opening. The required torque is small and less than the torque threshold. The vehicle controller sends a control torque value of 30Nm to the front drive motor controller and a control torque value of 0Nm to the rear drive motor controller according to the torque strategy. If the control torque of the rear drive motor is 0, it is judged that the rear drive motor is in an unloaded state. The vehicle controller sends the rear drive unloaded information to the switch controller. The switch controller controls the switch of the rear drive motor to be disconnected according to the rear drive unloaded information. When the driver increases the throttle, that is, the throttle opening increases, the vehicle controller determines that the required torque is 120Nm based on the acquired throttle opening. The required torque is large and greater than the torque threshold. The vehicle controller sends a control torque value of 70Nm to the front drive motor controller and a control torque value of 50Nm to the rear drive motor controller according to the torque strategy. The vehicle controller sends the rear drive non-unloaded information to the switch controller. The switch controller controls the switch of the rear drive motor to be closed according to the rear drive non-unloaded information.

[0074] In another optional implementation, if a neutral coasting test is performed on a vehicle, when determining whether the motor is in an unloaded state, it is not necessary to consider the vehicle model, and only the gear state of the vehicle when in motion needs to be determined. The specific steps may include:

[0075] Get the gear status of the vehicle;

[0076] If the gear state is neutral, the motor is in a no-load state.

[0077] In this embodiment, the gear state of the vehicle generally includes four types, namely, the parking gear P gear, the forward gear D gear, the reverse gear R gear and the neutral gear N gear. Only when the gear state of the vehicle is neutral gear, it can be determined that the motor is in the no-load state.

[0078] When it is determined that the gear state of the vehicle is neutral, the vehicle controller sends neutral information to the switch control module to control the switch to open or close. The specific steps may include:

[0079] If the motor is in a no-load state, neutral gear information is sent to the switch control module, and the switch control module controls the switch to be disconnected according to the neutral gear information.

[0080] It should be noted that the neutral gear information and the aforementioned no-load information are consistent in function, both of which control the switch to be disconnected.

[0081] For example, when a vehicle is undergoing a drum test, the vehicle is placed on a test bench, and then the vehicle is ignited and started. After the gear state of the vehicle is in neutral, the drum test begins, and the wheels begin to rotate. The vehicle controller obtains that the gear state of the vehicle is neutral, and the vehicle controller sends neutral information to the switch controller. The switch controller controls the motor switch to be disconnected according to the neutral information. During the test, the wheels rotate, and the motor only generates mechanical friction, and since the electrical circuit inside the motor is disconnected, no back electromotive force is generated. When the vehicle completes the drum test, the gear state of the vehicle is in P gear. The vehicle controller obtains the gear state of the vehicle. After determining that it is not neutral, the vehicle controller sends non-neutral information to the switch control module. The switch controller controls the motor switch to be closed according to the received non-neutral information, so that the power circuit of the motor remains unobstructed.

[0082] In summary, the embodiment of this specification provides a method for controlling the no-load back electromotive force of a permanent magnet motor, by installing a switch between the motor and the motor control module, and the switch is connected to the switch control module; first, determine whether the motor is in a no-load state; then, according to the determination result, send control information to the switch control module to control the switch opening and closing. In this way, during the vehicle neutral coasting test, the endurance consistency problem caused by the zero torque deviation of the motor is effectively solved. On the other hand, for four-wheel drive models and distributed drive models, when the vehicle is running normally and the motor is unloaded, the motor can be prevented from generating back electromotive force, thereby saving battery power and effectively improving the vehicle's endurance.

[0083] Based on the same inventive concept, Figure 4 As shown in the block diagram, this embodiment provides a permanent magnet motor no-load back electromotive force control device, which includes a judgment module and a control module.

[0084] The judgment module is used to judge whether the motor is in a no-load state;

[0085] The control module is used to send control information to the switch control module according to the judgment result to control the switch to open or close.

[0086] In an optional implementation, the judgment module is further used to:

[0087] Determine whether the motor is in a no-load state, including:

[0088] Get the throttle opening;

[0089] Determine the driver's required torque based on the throttle opening;

[0090] According to the required torque, the control torque of each motor is determined respectively;

[0091] According to the control torque of each motor, it is determined whether each motor is in a no-load state.

[0092] In an optional implementation manner, the judgment module is further used to:

[0093] If the required torque is greater than or equal to the torque threshold, the control torque of each motor is greater than 0;

[0094] If the required torque is less than the torque threshold, the control torque of at least one motor is 0.

[0095] In an optional implementation manner, the judgment module is further used to:

[0096] For each motor, if the control torque of the motor is 0, the motor is in a no-load state.

[0097] In an optional implementation, the control module is further configured to:

[0098] For each motor, if the motor is in a no-load state, no-load information is sent to the switch control module, and the switch control module controls the switch on the motor to be disconnected according to the no-load information.

[0099] Optionally, the number of motors is 2, including a front drive motor and a rear drive motor.

[0100] Optionally, the number of motors is 4, including hub motors on 4 wheels.

[0101] In an optional implementation manner, the judgment module is further used to:

[0102] Get the gear status of the vehicle;

[0103] If the gear state is neutral, the motor is in a no-load state.

[0104] In an optional implementation, the control module is further configured to:

[0105] If the motor is in a no-load state, neutral gear information is sent to the switch control module, and the switch control module controls the switch to be disconnected according to the neutral gear information.

[0106] In summary, the embodiment of this specification provides a permanent magnet motor no-load back electromotive force control device, by installing a switch between the motor and the motor control module, the switch is connected to the switch control module; first determine whether the motor is in a no-load state; then send control information to the switch control module according to the judgment result to control the switch opening and closing. In this way, during the vehicle neutral coasting test, the endurance consistency problem caused by the zero torque deviation of the motor is effectively solved. On the other hand, for four-wheel drive models and distributed drive models, when the vehicle is running normally and the motor is unloaded, the motor can be prevented from generating back electromotive force, thereby saving battery power and effectively improving the vehicle's endurance.

[0107] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, the specific working process of the permanent magnet motor no-load back electromotive force control device described above can refer to the corresponding process in the aforementioned method, and will not be elaborated here.

[0108] The above are only various embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for controlling no-load back electromotive force of a permanent magnet motor, characterized in that: A switch is installed between the motor and the motor control module, and the switch is connected to the switch control module; The method comprises: Determine whether the motor is in a no-load state; According to the judgment result, control information is sent to the switch control module to control the switch to open or close; There are multiple motors; the step of determining whether the motor is in a no-load state comprises: Get the throttle opening; determining the driver's required torque according to the throttle opening; Determining the control torque of each motor according to the required torque; According to the control torque of each motor, it is determined whether each motor is in a no-load state.

2. The method according to claim 1, characterized in that The step of determining the control torque of each motor according to the required torque comprises: If the required torque is greater than or equal to the torque threshold, the control torque of each motor is greater than 0; If the required torque is less than the torque threshold, the control torque of at least one motor is 0.

3. The method according to claim 1 or 2, characterized in that: The step of determining whether each motor is in a no-load state according to the control torque of each motor includes: For each motor, if the control torque of the motor is 0, the motor is in a no-load state.

4. The method according to claim 1, characterized in that: The step of sending control information to the switch control module according to the judgment result to control the switch to be turned on or off includes: For each motor, if the motor is in a no-load state, no-load information is sent to the switch control module, and the switch control module controls the switch on the motor to be disconnected according to the no-load information.

5. The method according to claim 1, characterized in that The number of the motors is 2, and the motors include a front drive motor and a rear drive motor.

6. The method according to claim 1, characterized in that The number of the motors is 4, and the motors include hub motors on 4 wheels.

7. A permanent magnet motor no-load back electromotive force control device, characterized in that: Using the method for controlling no-load back electromotive force of a permanent magnet motor according to any one of claims 1 to 6, the device comprises: A judgment module, used to judge whether the motor is in a no-load state; By obtaining the throttle opening; determining the driver's required torque according to the throttle opening; determining the control torque of each motor according to the required torque; and determining whether each motor is in an unloaded state according to the control torque of each motor; The control module is used to send control information to the switch control module according to the judgment result to control the switch to be turned on and off.

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