Low acoustic noise open-loop motor starting

Abstract

A method and apparatus for open loop starting of a three phase motor that reduces acoustic noise. During rotor alignment of the motor, a maximum level of phase current to the motor exists. After rotor alignment, open loop motor starting is performed during which the phase current has a first slope. At a selected time, such as when the frequency of the phase current reaches a first threshold, the phase current transitions to a second slope.

Description

【Background Art】 【0001】 Various circuits for controlling and driving brushless DC (BLDC) electric motors are known. In conventional BLDC motor control techniques, back electromotive force (BEMF) information may be used for position estimation, but BEMF information is not available at zero speed, such as at the start of the motor. Another conventional starting technique is to drive the motor in an open loop without performing position estimation (e.g., alignment and go), which may cause reverse rotation at startup. Furthermore, this technique may result in a long startup time when a relatively conservative startup profile is selected, or unreliable motor startup when an aggressive startup profile is selected. 【0002】 Among the starting techniques for three-phase BLDC motors, some are known to be able to use hall sensors. In other techniques, sensorless control is used. Various starting techniques may have advantages and disadvantages. For example, a conventional hall effect sensor-based starting configuration typically has three hall elements, one for each phase. The hall effect sensor configuration can provide relatively reliable starting, high-speed starting, and adaptation to different motor and load conditions without changing the parameters of the controller. However, typical hall effect sensor starting techniques generate a rectangular current with a relatively non-smooth phase change of the current, which causes acoustic noise. 【0003】 Conventional sensorless motor starting control is open-loop in order to obtain sufficient torque to rotate the motor from static friction because the starting torque needs to be higher than the normal operating current of the sensorless operation. In such a system, the starting current needs to be high enough to ensure starting. However, conventional controllers generate acoustic noise from the motor due to the large current at startup. 【0004】 In the automotive industry, motor control is shifting towards sensorless control from the perspectives of reliability and cost. Furthermore, quiet motor operation is required for electric vehicles (EVs) and hybrid electric vehicles (HEVs). Acoustic noise generated by motors in internal combustion engines is less problematic than in electric vehicles. However, quiet motor operation, especially when the internal combustion engine is stopped, is particularly important. [Overview of the project] 【0005】 Embodiments of this disclosure provide a method and apparatus for a BLDC motor controller that adjusts the phase current to the motor during open-loop starting in order to reduce acoustic noise during startup compared to conventional systems. Low acoustic noise during motor starting is useful in vehicles such as electric vehicles. 【0006】 In exemplary embodiments, the motor controller uses position open-loop control with current limiting operation. A first gradient of the starting current determines the downward trend ratio of the phase current limit. A second gradient determines the upward trend of the phase current limit. For example, when the drive frequency of the motor drive signal changes, the gradient of the starting current transitions from the first current gradient to the second current gradient. Various parameters described herein, such as current gradient and drive frequency, can be selected to meet the needs of a particular application. When the open-loop endpoint of the phase current level coincides with the required drive current using sensorless control, phase lead errors are minimized, and acoustic noise from the motor is also minimized. 【0007】 In one embodiment, the method includes the step of starting a three-phase BLDC motor in an open loop, wherein the step is performed by allowing the phase current to the motor to have a maximum starting amplitude during rotor alignment of the motor; performing an open-loop motor start after rotor alignment while the amplitude of the phase current has a first gradient; and transitioning the amplitude of the phase current to a second gradient. 【0008】 The method may further include one or more of the following features: a step of transitioning the phase current to a second gradient when the frequency of the phase current reaches a first threshold that defines a transition frequency, the first gradient being negative, the second gradient being positive, the rate of change of the second gradient being greater than the rate of change of the first gradient, the phase current gradient being equal to 1 when the amplitude of the phase current reaches the second threshold, a step of receiving a value for the transition frequency from a user, rotor alignment moving the rotor to a known position, the phase current being at its maximum starting amplitude at the start of open-loop starting, and / or the transition frequency corresponding to a predetermined speed of the motor. 【0009】 In another embodiment, the motor controller includes a circuit configured to start a three-phase BLDC motor in an open loop, the start being performed by allowing a maximum starting amplitude in the phase current to the motor during the motor's rotor alignment, and after the rotor alignment, performing an open-loop motor start while the amplitude of the phase current has a first gradient, and then transitioning the amplitude of the phase current to a second gradient. 【0010】 The motor controller may further include one or more of the following features: the circuit is further configured to transition the phase current to a second gradient when the frequency of the phase current reaches a first threshold determining a transition frequency; the first gradient is negative; the second gradient is positive; the rate of change of the second gradient is greater than the rate of change of the first gradient; when the amplitude of the phase current reaches the second threshold, the gradient of the phase current is equal to 1; the circuit is further configured to receive a value for the transition frequency from the user; rotor alignment moves the rotor to a known position; the phase current is at its maximum starting amplitude at the start of open-loop starting; the transition frequency corresponds to a predetermined speed of the motor; and / or the motor controller includes a BLDC motor controller IC package. 【0011】 In a further embodiment, the motor controller IC package includes an output terminal for supplying a signal to drive a three-phase BLDC motor, and means for starting the three-phase BLDC motor by performing an open-loop motor start while the amplitude of the phase current has a first gradient, and then transitioning the amplitude of the phase current to a second gradient when the frequency of the phase current reaches a first threshold that determines a transition frequency. 【0012】 The aforementioned features of the present invention and the invention itself can be better understood from the following description of the drawings. [Brief explanation of the drawing] 【0013】 [Figure 1] This is a schematic diagram of a motor controller that controls the phase current to the motor in open-loop starting to reduce acoustic noise, according to an exemplary embodiment of the present disclosure. [Figure 2] Figure 1 shows an exemplary IC package embodiment of the controller. [Figure 3] This is an exemplary waveform diagram of phase currents to a three-phase motor for reducing acoustic noise during startup, according to an exemplary embodiment of the present disclosure. [Figure 4] This flowchart shows an example sequence of steps for controlling the phase current to a three-phase motor to reduce acoustic noise during startup, according to an exemplary embodiment of the present disclosure. [Figure 5] This is a schematic diagram of an exemplary computer capable of performing at least some of the processes described herein. [Modes for carrying out the invention] 【0014】 Figure 1 shows an exemplary motor control circuit 102 coupled to an electric motor 104 to provide BLDC motor starting with low acoustic noise open-loop starting, according to an exemplary embodiment of the present disclosure. The phase current is controlled during open-loop motor starting to reduce acoustic noise, as will be described in more detail below. 【0015】 Motor 104 is shown to include three windings 104a, 104b, and 104c, which can each be drawn as an equivalent circuit having an inductor in series with a resistor and a back electromotive force (BEMF) voltage source. For example, winding A104a is shown to include an inductor in series with a back electromotive force voltage source VA136 and a resistor 131. 【0016】 The motor control circuit 102 includes a speed request generator 107 coupled to receive an external speed request signal 106 from outside the motor control circuit 102. The external speed request signal 106 can be one of several forms. Generally, the external speed request signal 106 indicates the speed of the motor 104 requested from outside the motor control circuit 102. 【0017】 The speed request generator 107 is configured to generate a speed request signal 107a. The pulse width modulation (PWM) generator 108 is coupled to receive the speed request signal 107a and is configured to generate a PWM signal having a duty cycle controlled by the speed request signal 107a. The PWM generator 108 is also coupled to receive a modulated waveform from the modulation signal generation module 146. The PWM signal is generated having modulation characteristics (i.e., a relatively time-varying duty cycle) corresponding to the modulated waveform. 【0018】 The motor control circuit 102 also includes a gate driver circuit 110 configured to generate PWM gate drive signals 110a, 110b, 110c, 110d, 110e, and 110f for driving six transistors 112, 114, 116, 118, 120, and 122, which are coupled to receive a PWM signal and arranged as three half-bridge circuits 112 / 114, 116 / 118, and 120 / 122. The six transistors 112, 114, 116, 118, 120, and 122 operate in saturation state, supplying three motor drive signals VoutA, VoutB, VoutC, 124, 126, and 128 to nodes 102d, 102c, and 102b, respectively. It should be understood that any suitable configuration of switching elements can be used to supply the motor drive signals. 【0019】 The motor control circuit 102 can also include a signal processing module 143 for processing signals from the sensor module 147. In an embodiment, the signal processing module 143 can include a start module 149 for controlling the start of the motor. The sensor module 147 can be configured to receive a back electromotive force signal (e.g., coupled to receive one or more of the motor drive signals 124, 126, 128 including a back electromotive force signal that can be directly observed when the motor windings 104a, 104b, 104c are not being driven and the respective winding currents are zero). 【0020】 The signal processing module 143 is configured to generate a position reference signal indicating the rotational reference position of the motor 104. The modulation signal generation module 146 is coupled to receive the position reference signal and is configured to change the phase of the modulation waveform supplied to the PWM generator 108. 【0021】 The motor control circuit 102 can be coupled to receive the motor voltage VMOT, or simply VM, at node 102a, and this voltage is supplied to the motor through the transistors 112, 116, 120 during the time that the upper transistors 112, 116, 120 are turned on. It will be appreciated that there can be a small voltage drop (e.g., 0.1 volts) through the transistors 112, 116, 120 when the transistors 112, 116, 120 are on and supplying current to the motor 104. 【0022】 It is understood that embodiments of the present disclosure are applicable to a wide range of applications where low acoustic noise during motor startup is desirable. Examples of vehicle applications include battery cooling fans, radiator fans, fuel control, oil pumps, and the like. 【0023】 FIG. 2 shows an exemplary BLDC motor controller IC package 200 according to an exemplary embodiment of the present disclosure. A power input terminal VBB may be coupled to a voltage power supply to which a charge pump input VCP may also be coupled. Capacitors may be coupled across charge pump inputs CP1, CP2. The motor controller 200 generates gate driver signals for a three-phase motor MOT. In the illustrated embodiment, the motor controller 200 generates high-side GHx and low-side GLx gate driver signals for controlling bridge transistors that drive the three phases of the motor MOT. 【0024】 Embodiments of the controller 200 provide a three-phase, sensorless, brushless DC (BLDC) motor driver (gate driver) for low acoustic noise during open-loop startup. In an embodiment, the controller 200 can include a field-oriented control (FOC) module for efficiency and acoustic noise performance. The motor speed may be controlled by pulse-width modulation (PWM). 【0025】 In an embodiment, the controller 200 receives a start command and checks for a BEMF signal. If the motor is rotating in reverse, the controller can apply a brake until the brake current disappears. If the motor is rotating forward, the controller 200 synchronizes the drive frequency and enters full sensorless control. If the motor is stopped, the controller 200 can apply rotor alignment and start motor control. The controller 200 performs rotor alignment of the motor and confirms that the rotor has stopped at a known position. 【0026】 When rotor alignment is complete, an open-loop startup process is executed and the amplitude of the phase current is adjusted to provide stable torque. The drive frequency increases until a stable BEMF condition is achieved. When open-loop startup is complete, the controller 200 may operate in sensorless FOC control mode. 【0027】 Open-loop starting controls phase current ramp-up to minimize acoustic noise from open-loop starting to sensorless control. Maintaining an appropriate phase lead depends on the current amplitude at any given drive speed and load. The appropriate current level depends on the motor characteristics and connected load. For reliable starting, the starting current must be sufficient to rotate the motor. To achieve a quieter transition, the current towards the end of the open-loop starting period can be reduced, if load conditions allow. As the current level approaches the level required by the feedback control, transition noise can be minimized. 【0028】 Figure 3 shows the phase current I for one of the phases of a three-phase motor to reduce acoustic noise during open-loop starting, according to an exemplary embodiment of the present disclosure. PHASE An exemplary waveform diagram is shown. During rotor alignment 300, the phase current I PHASE It has a maximum amplitude 302, which is indicated as the starting current. When the motor is commanded to rotate, the controller performs rotor alignment of the motor to ensure that the rotor is stopped in a known position. After alignment is complete, the open-loop start 304 process begins. During the open-loop start 304, the phase current I PHASE It has a first slope 306, which is shown as I_limit_slope_1 (I_limit_slope_1) that determines the downward trend ratio of the phase current. PHASE If the frequency is greater than the selected threshold, the phase current I PHASE When entering the feedback control phase 310, it transitions to a second gradient 308, indicated as I_limit_slope_2 (I_limit_slope_2). Phase current I PHASE The amplitude increases until it reaches the rated current level 312. In the embodiment, the frequency of the drive signal increases until it reaches a selected frequency. 【0029】 As can be seen from the exemplary embodiment, the phase current I PHASEThe system starts an open-loop start 304 with a starting current amplitude 302, and the amplitude decreases with a first gradient 306 until the frequency of the phase current increases beyond a predetermined threshold corresponding to Speed_1. Thereafter, the phase current I PHASE The amplitude increases with a second gradient 308 until the rated current is reached in the feedback control phase 310d. 【0030】 If the open-loop endpoint of the phase current level coincides with the required drive current using sensorless control, the phase lead error will be minimized. Consequently, acoustic noise from the motor will also be minimized. 【0031】 As used herein, open-loop motor control refers to an operating mode in which the control algorithm does not use information regarding the rotor position. 【0032】 In some embodiments, the absolute value of the first gradient 306 is smaller than the absolute value of the second gradient 308. That is, the rate of change of the phase current amplitude in the second gradient 308 is greater than the rate of change in the first gradient 306. In some embodiments, the first gradient may be 1, which is a horizontal line. 【0033】 It is understood that the first and second gradients 306, 308 and the transition frequency depend on the motor characteristics. The transition frequency may be based, for example, on an internally estimated frequency (actual drive frequency). When the drive frequency exceeds a threshold, the current amplitude is determined by the second gradient 308. In embodiments, the transition at the end of open-loop starting is determined by a selected frequency value of the starting phase current. In embodiments, the transition frequency value is selected by the user. The phase current frequency increases at a certain rate until the desired motor speed is reached, and the current amplitude is limited by the first gradient 306, then the second gradient 308, and then the rated current 312. 【0034】 It should be understood that the values ​​of the first and second gradients are determined to satisfy the desired operating characteristics for a given motor. In the embodiment, the values ​​of the first gradient, the second gradient, and / or the transition frequency can be selected by the user or others as configuration parameters. 【0035】 Figure 4 shows an example sequence of steps for controlling the phase current to the motor during open-loop starting to reduce acoustic noise. In step 400, the motor controller enters open-loop starting. For example, after rotor alignment, the controller can transition to open-loop starting. In step 402, the controller controls the phase current amplitude to have a first gradient. In embodiments, the first gradient is negative so that the amplitude decreases. In step 404, it is determined that the frequency of the phase current is greater than or equal to a selected threshold, and the controller transitions to the feedback control phase. In step 406, the controller controls the phase current amplitude to have a second gradient. In embodiments, the second gradient is positive so that the current amplitude increases. In step 408, the controller controls the frequency of the phase current to achieve a selected frequency. In step 410, the phase current is limited to a selected amplitude, which can be called the rated current. 【0036】 Figure 5 shows an exemplary computer 500 capable of performing at least some of the processes described herein, such as controlling the phase current amplitude as shown in Figure 3. The computer 500 includes a processor 502, volatile memory 504, non-volatile memory 506 (e.g., a hard disk), an output device 507, and a graphical user interface (GUI) 508 (e.g., a mouse, keyboard, and display). The non-volatile memory 506 stores computer instructions 512, an operating system 516, and data 518. In one embodiment, computer instructions 512 are executed by the processor 502 from the volatile memory 504. In one embodiment, article 520 includes non-transient computer-readable instructions. 【0037】 The processing may be carried out in hardware, software, or a combination of both. Each processing may also be carried out in a computer program executed on a programmable computer / machine that includes a processor, a storage medium or other manufactured item readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and one or more output devices. The program code can be applied to data input using the input device to perform processing and generate output information. 【0038】 This system can perform processing, at least partially, via computer program products (e.g., in machine-readable storage devices) for execution by data processing devices (e.g., programmable processors, computers, or multiple computers) or for controlling the operation of data processing devices. Each such program may be implemented in a high-level procedural programming language or an object-oriented programming language for communication with the computer system. However, the program may also be implemented in assembly language or machine language. The language may be a compiled language or an interpreted language, and may be deployed in any form, such as a standalone program, or as modules, components, subroutines, or other units suitable for use in a computing environment. The computer program may run on a single computer, on multiple computers at one site, or distributed across multiple sites and interconnected by a communication network. The computer program may be stored on a storage medium or device (e.g., a CD-ROM, hard disk, or magnetic diskette) that is readable by a general-purpose or dedicated programmable computer to configure and operate the computer when the storage medium or device is read by a computer. The process can also be carried out using a machine-readable storage medium composed of computer programs, in which case the computer operates when the instructions of the computer program are executed. 【0039】 The processing may be performed by one or more programmable processors that run one or more computer programs to perform the functions of the system. All or part of the system may be implemented as dedicated logic circuits (e.g., FPGAs (Field-Programmable Gate Arrays) and / or ASICs (Application-Specific Integrated Circuits)). As used herein, circuitry refers to any implementation of hardware, firmware, and / or software that includes at least one transistor, i.e., is not software itself. 【0040】 As used herein, the term “magnetic field sensing element” is used to describe various electronic elements capable of sensing a magnetic field. A magnetic field sensing element may be, but is not limited to, a Hall effect element, a magnetoresistive element, or a magnetotransistor. As is well known, there are various types of Hall effect elements, such as planar Hall elements, vertical Hall elements, and circular vertical Hall (CVH) elements. Also, as is well known, there are various types of magnetoresistive elements, such as semiconductor magnetoresistive elements such as indium antimonide (InSb), colossal magnetoresistive (GMR) elements, such as spin valves, anisotropic magnetoresistive (AMR) elements, tunnel magnetoresistive (TMR) elements, and magnetic tunnel junctions (MTJs). A magnetic field sensing element may be a single element or may include two or more magnetic field sensing elements arranged in various configurations, such as a half-bridge or a full (Wheatstone) bridge. Depending on the type of device and other application requirements, the magnetic field sensing element may be made of a Group IV semiconductor material such as silicon (Si) or germanium (Ge), or a Group III-V semiconductor material such as gallium arsenide (GaAs) or an indium compound, such as indium antimony (InSb). 【0041】 As is well known, some of the magnetic field sensing elements described above tend to have a maximum sensitivity axis parallel to the substrate supporting the magnetic field sensing element, while others tend to have a maximum sensitivity axis perpendicular to the substrate supporting the magnetic field sensing element. In particular, planar Hall elements tend to have a sensitivity axis perpendicular to the substrate, while metal-based or metal magnetoresistive elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have a sensitivity axis parallel to the substrate. 【0042】 In this specification, the term “magnetic field sensor” is generally used to refer to a circuit that uses a magnetic field sensing element in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but are not limited to, angle sensors that sense the angle of direction of a magnetic field, current sensors that sense a magnetic field generated by an electric current carried by a current-carrying conductor, magnetic switches that sense the proximity of ferromagnetic materials, and rotation detectors that sense passing ferromagnetic articles, such as magnetic domains of a ring magnet or ferromagnetic targets (such as the teeth of a gear). Magnetic field sensors are used in combination with back-bias magnets or other magnets to sense the magnetic field density of a magnetic field. 【0043】 While exemplary embodiments of the present invention have been described, it will become apparent to those skilled in the art that other embodiments incorporating these concepts can also be used. The embodiments included herein should not be limited to those disclosed, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. 【0044】 Elements of different embodiments described herein may be combined to form other embodiments not specifically defined above. Furthermore, various elements described in the context of a single embodiment may be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also included in the following claims.

Claims

[Claim 1] A method comprising the step of starting a three-phase BLDC motor in an open loop, wherein the step is: During the rotor alignment of the motor, the step of allowing the maximum starting amplitude in the phase current supplied to the motor, The steps include: performing an open-loop motor start after the rotor alignment, while the amplitude of the phase current has a first gradient that is negative; A step of transitioning the amplitude of the phase current to a second gradient that is positive. A method performed by [a specific method]. [Claim 2] The method according to claim 1, further comprising the step of transitioning the phase current to the second gradient when the frequency of the phase current reaches a first threshold that determines the transition frequency. [Claim 3] The method according to claim 1, wherein the rate of change of the second gradient is greater than the rate of change of the first gradient. [Claim 4] The method according to any one of claims 1 to 3, wherein when the amplitude of the phase current reaches a second threshold, the gradient of the phase current becomes equal to 1. [Claim 5] The method according to claim 2, further comprising the step of receiving the value of the transition frequency from a user. [Claim 6] The method according to claim 1, wherein the rotor alignment moves the rotor to a known position. [Claim 7] The method according to claim 1, wherein the phase current is at its maximum starting amplitude at the start of the open-loop start. [Claim 8] The method according to claim 2, wherein the transition frequency corresponds to a predetermined speed of the motor. [Claim 9] It is a motor controller, Includes a circuit configured to start a three-phase BLDC motor in open-loop mode, The start-up in question is, During the rotor alignment of the motor, the maximum starting amplitude is allowed for the phase current supplied to the motor. After the rotor alignment, the open-loop motor start is performed while the amplitude of the phase current has a first gradient that is negative. The amplitude of the phase current is transitioned to a second gradient that is positive. A motor controller that operates by doing so. [Claim 10] The motor controller according to claim 9, wherein the circuit is further configured to transition the phase current to the second gradient when the frequency of the phase current reaches a first threshold that determines the transition frequency. [Claim 11] The motor controller according to claim 9, wherein the rate of change of the second gradient is greater than the rate of change of the first gradient. [Claim 12] The motor controller according to any one of claims 9 to 11, wherein when the amplitude of the phase current reaches a second threshold, the gradient of the phase current becomes equal to 1. [Claim 13] The motor controller according to claim 10, wherein the circuit is further configured to receive the value of the transition frequency from the user. [Claim 14] The motor controller according to claim 9, wherein the rotor alignment moves the rotor to a known position. [Claim 15] The motor controller according to claim 9, wherein the phase current is at its maximum starting amplitude at the start of the open-loop start. [Claim 16] The motor controller according to claim 10, wherein the transition frequency corresponds to a predetermined speed of the motor. [Claim 17] The motor controller according to claim 9, wherein the motor controller includes a BLDC motor controller IC package. [Claim 18] An output terminal that supplies a signal to drive a 3-phase BLDC motor, A means for starting a three-phase BLDC motor by performing an open-loop motor start while the amplitude of the phase current has a first gradient that is negative, and then transitioning the amplitude of the phase current to a second gradient that is positive when the frequency of the phase current reaches a first threshold that determines the transition frequency, and A motor controller IC package including this.

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