Space Vector Pulse Width Modulation for Multiphase Motors

Abstract

The present application relates to space vector pulse width modulation for a multi-phase motor. A technical solution for controlling the operation of a multi-phase motor using a signal generator is described, wherein the signal generator is configured to generate n duty cycle signals of a combined pulse width modulation PWM scheme including a continuous PWM scheme and a discontinuous PWM scheme, wherein n is an integer greater than 3. A mixing coefficient value determines the relative weight of each of the continuous PWM scheme and the discontinuous PWM scheme when forming the combined PWM scheme. A mixing function determines the relative weight of each of the continuous PWM scheme and the discontinuous PWM scheme used to generate the duty cycle signal. The mixing function is calculated in segments based on the difference between the mixing coefficient value and two thresholds. The signal generator uses each duty cycle signal to control the switching of DC power to the corresponding phase of the multi-phase motor.

Description

Technical Field

[0001] The present application relates generally to methods and systems for controlling electric motors, and more particularly to methods and systems for generating a duty cycle signal for controlling an alternating current (AC) motor having n phases, where n is an integer greater than 3. Background Art

[0002] The controller typically controls the AC electric motor by, for example, generating a duty cycle signal for each motor phase using a pulse width modulation (PWM) technique, which is used to provide a phase voltage signal to the motor. For example, an electric motor is typically controlled by a feedback system that includes a current regulator and a modulator that generates a gate drive signal using a sinusoidal PWM scheme and transmits it to a three-phase inverter (DC-AC converter). The inverter provides a voltage signal for each phase of the electric motor. The voltage generated by the inverter depends largely on the inverter control scheme used, and suboptimal techniques may result in undesirable torque ripple and audible noise in high-performance applications such as electric power steering (EPS).

[0003] In safety-critical applications (e.g., safety-critical applications for motors used in EPS systems), redundancy is required. Typically, two or more three-phase motors are used in traditional safety-critical applications to provide the necessary redundancy. Multiphase AC motors (i.e., motors with more than three phases) have great potential to replace the current ubiquitous electric motor drive configurations for providing redundancy in safety-critical applications. Summary of the invention

[0004] According to one or more embodiments, a control system for controlling the operation of a multi-phase motor includes: a signal generator configured to generate n duty cycle signals of a pulse width modulation (PWM) scheme, wherein n is an integer greater than 3. The PWM scheme is a combination of a continuous PWM scheme and a noncontinuous PWM scheme. The combination is based on a mixing coefficient value. The signal generator is configured to use each duty cycle signal to control the switching of DC power to a corresponding phase of the multi-phase motor.

[0005] According to one or more embodiments, a method for controlling a multi-phase motor includes: generating n duty cycle signals by a signal generator using a pulse width modulation (PWM) scheme, wherein n is an integer greater than 3. The PWM scheme is a combination of a continuous PWM scheme and a discontinuous PWM scheme. The combination is based on a mixing coefficient value. The method also includes: switching power to each of the n phases of the multi-phase motor using an associated duty cycle signal in the duty cycle signals.

[0006] These and other advantages and features will become more apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0008] Figure 1 depicts a block diagram of an exemplary embodiment of an electric power steering system according to aspects of the present disclosure;

[0009] Figure 2 depicts a block diagram of a five-phase permanent magnet synchronous motor controller according to aspects of the present disclosure;

[0010] Figure 3 depicts a block diagram of a voltage source inverter for a five-phase permanent magnet synchronous motor according to aspects of the present disclosure;

[0011] Figure 4 A graph depicting five-phase duty cycle waveforms for a discontinuous PWM minimum (DPWMMIN) scheme according to aspects of the present disclosure;

[0012] Figure 5 A graph depicting five-phase duty cycle waveforms of a continuous PWM (CPWM) scheme according to aspects of the present disclosure;

[0013] Figure 6 A graph depicting five-phase duty cycle waveforms for a combination of a continuous PWM scheme and a discontinuous PWM scheme according to aspects of the present disclosure;

[0014] Figure 7 is a graph illustrating an example of a hybrid function for combining a continuous PWM scheme and a discontinuous PWM scheme according to aspects of the present disclosure; and

[0015] Figure 8 A flow chart of a method for five-phase motor control in a steering system according to aspects of the present disclosure is depicted. DETAILED DESCRIPTION

[0016] Reference is now made to the accompanying drawings, in which the present disclosure will be described with reference to specific embodiments, but is not limited thereto, it being understood that the disclosed embodiments are merely illustrative of the present disclosure, which may be implemented in various alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art to use the present disclosure in various ways.

[0017] As used herein, the terms module and submodule refer to one or more processing circuits, such as application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped), and memories that execute one or more software or firmware programs, combinatorial logic circuits, and / or other suitable components that provide the functionality. It is understood that the submodules described below may be combined and / or further divided.

[0018] Now refer to the accompanying drawings, in which the technical solution will be described with reference to specific embodiments, but not limited thereto, Figure 1 is an exemplary embodiment of an electric power steering system (EPS) 40 suitable for implementing the disclosed embodiments. The steering mechanism 36 is a rack and pinion system and includes a toothed rack (not shown) within a housing 50 and a pinion (also not shown) located below a gear housing 52. When the operator input, hereinafter represented as the steering wheel 26 (e.g., hand wheel, etc.), is rotated, the upper steering shaft 29 rotates and the lower steering shaft 51 connected to the upper steering shaft 29 by the universal joint 34 rotates the pinion. The rotation of the pinion moves the rack, which moves the tie rods 38 (only one shown), which in turn moves the steering knuckles 39 (only one shown), which rotates the steerable wheel(s) 44 (only one shown).

[0019] The electric power steering assistance is provided by a control device generally indicated by reference numeral 24 and includes a controller 16 and an electric machine 19, which may be a permanent magnet synchronous motor (PMSM) and is hereinafter referred to as electric machine 19. The controller 16 is powered by a vehicle power supply 10 via line 12. The controller 16 receives a vehicle speed signal 14 representing the vehicle speed from a vehicle speed sensor 17. The steering angle is measured by a position sensor 32, which may be an optical encoding type sensor, a variable resistance type sensor, or any other suitable type of position sensor, and provides a position signal 20 to the controller 16. The motor speed may be measured by a tachometer or any other device and transmitted to the controller 16 as a motor speed signal 21. The motor speed, denoted as ωm, may be measured, calculated, or measured and calculated. For example, the motor speed ωm may be calculated as a change in the motor position θ measured by the position sensor 32 over a specified time interval. For example, the motor speed ωm may be determined as a derivative of the motor position θ according to the equation ωm=Δθ / Δt, where Δt is the sampling time and Δθ is the change in position during the sampling interval. Alternatively, the motor speed may be derived from the motor position as the rate of change of position with respect to time. It will be appreciated that there are many well-known methods to perform the derivative function.

[0020] When the steering wheel 26 is turned, the torque sensor 28 senses the torque applied to the steering wheel 26 by the vehicle operator. The torque sensor 28 may include a torsion bar (not shown) and a variable resistor type sensor (also not shown) that outputs a variable torque signal 18 to the controller 16 that is related to the amount of twist on the torsion bar. Although this is one type of torque sensor, any other suitable torque sensing device used with known signal processing techniques is sufficient. In response to various inputs, the controller sends a command 22 to the electric motor 19, which provides torque assistance to the steering system through the worm 47 and worm gear 48, thereby providing torque assistance for vehicle steering.

[0021] It should be noted that although the disclosed embodiments are described with reference to motor control for electric steering applications, it should be understood that these references are illustrative only and the disclosed embodiments may be applied to any motor control application employing an electric motor, such as steering, valve control, etc. In addition, the references and descriptions herein may be applicable to many forms of parameter sensors, including but not limited to torque, position, and speed, etc. It should also be noted that references to electric machines herein include but are not limited to motors, and for the sake of brevity, only references to motors will be made below, but not limited thereto.

[0022] In the control system 24 as depicted, the controller 16 uses torque, position, speed, etc. to calculate (one or more) instructions for delivering the required output power. The controller 16 is configured to communicate with various systems and sensors of the motor control system. The controller 16 receives signals from each system sensor, quantifies the received information, and responds to it (in this example) to provide (one or more) output command signals, for example, to the motor 19. The controller 16 is configured to develop (develop) corresponding voltages (one or more) from an inverter (not shown), which can optionally be combined with the controller 16 and will be referred to as the controller 16 in this article, so that when the voltage is applied to the motor 19, the required torque or position is generated. In one or more examples, the controller 16 operates as a current regulator in a feedback control mode to generate the instruction 22. Alternatively, in one or more examples, the controller 16 operates in a feedforward control mode to generate the instruction 22. Because these voltages are related to the position and speed of the motor 19 and the required torque, the position and / or speed of the rotor and the torque applied by the operator are determined. The position encoder is connected to the lower steering shaft 51 to detect the angular position θ. The encoder can sense the rotational position based on optical detection, magnetic field changes or other methods. Typical position sensors include potentiometers, resolvers, synchronizers and encoders, etc., and combinations including at least one of the foregoing. The position encoder outputs a position signal 20 indicating the angular position of the lower steering shaft 51 and thus the angular position of the motor 19.

[0023] The desired torque may be determined by one or more torque sensors 28 that transmit a torque signal 18 indicative of the applied torque. One or more exemplary embodiments include such a torque sensor 28 and the torque signal(s) 18 therefrom, which may be responsive to a flexible torsion bar, T-bar, spring, or similar device (not shown) configured to provide a response indicative of the applied torque.

[0024] In one or more examples, the temperature sensor(s) 23 are located at the motor 19. Preferably, the temperature sensor 23 is configured to directly measure the temperature of a sensing portion of the motor 19. The temperature sensor 23 transmits a temperature signal 25 to the controller 16 for processing and compensation as specified herein. Typical temperature sensors include thermocouples, thermistors, and thermostats, among others, and combinations including at least one of the foregoing sensors that, when placed in an appropriate location, can provide a calibrated signal that is proportional to a specific temperature.

[0025] Among other things, the position signal 20, the speed signal 21 and (one or more) torque signals 18 are applied to the controller 16. The controller 16 processes all input signals to generate values ​​corresponding to each signal that produces rotor position values, motor speed values, and torque values ​​that can be used for processing in the algorithms described herein. Measurement signals such as those described above are also typically linearized, compensated, and filtered as needed to enhance the desired characteristics of the acquired signal or eliminate undesirable characteristics of the acquired signal. For example, the signal can be linearized to increase processing speed, or to address the large dynamic range of the signal. In addition, frequency or time-based compensation and filtering can be used to eliminate noise or avoid unwanted spectral characteristics.

[0026] In order to perform the specified functions and required processing, and calculations performed therefor (e.g., identification of motor parameters, (one or more) control algorithms, etc.), the controller 16 may include, but is not limited to (one or more) processors, (one or more) computers, (one or more) DSPs, memories, storage devices, (one or more) registers, timing, (one or more) interrupts, (one or more) communication interfaces and input / output signal interfaces, etc., and combinations including at least one of the foregoing. For example, the controller 16 may include input signal processing and filtering to achieve accurate sampling and conversion or acquisition of such signals from the communication interface. Additional features of the controller 16 and some of the processing therein are discussed in detail later in this document.

[0027] There is a growing need for fault tolerance in safety-critical applications such as EPS systems. Currently, dual-winding three-phase permanent magnet synchronous motors (PMSMs) are used to provide fault tolerance for failures of the electrical actuators used in EPS systems. These motors are often combined with two inverters and / or microcontrollers to provide complete electrical redundancy. However, when half of the system fails, the total assistance that can be provided is reduced to half. By overutilizing the remaining half of the system, the total assistance may only be slightly increased.

[0028] A potential alternative to dual-winding motors is multi-phase synchronous motors (where PMSM falls into the broader category of synchronous motors). These motors consist of n phases, where n is an integer greater than 3, and each phase can be independently controlled. Therefore, in the event of a single-point inverter or motor failure, the overall system performance is much higher than that of an electric drive system based on a dual-winding motor. However, there is little work on controlling power converters used with multi-phase motors, so such motors cannot be easily used in industrial applications. Currently, multi-phase drive systems typically use basic sinusoidal PMW (SPWM) commutation technology with relatively low voltage utilization.

[0029] Figure 2 1 depicts a block diagram of a five-phase PMSM controller 16 according to aspects of the present disclosure. However, the PMSM controller 16 and the motor 19 may have any number n of phases, where n is an integer greater than 3. In other words, the systems and methods of the present disclosure may be used with controllers and / or electric machines (e.g., motors) having 4, 5, 6, 7, 8, 9, etc. phases. The current command module (e.g., current reference calculator 202) converts the torque command T c Converted into current command, which can use d / q current reference I dqc Those current commands are then sent to a current controller module (e.g., current controller 206). Current controller 206 can be a feedback regulator or feed-forward compensator that utilizes the current measurements. The temperature T can be fed into parameter compensator 204 to adjust the PMSM electrical parameters as needed. Current controller 206 then generates d / q voltage commands that are equal to the commanded modulation index m i and phase advance angle δ. In other words, the current controller module generates a modulation index m based on the current command i The duty cycle generator 210 of the power converter switching module 208 modulates the index m i The phase advance angle δ is converted into the equivalent duty cycle d of each phase ph .

[0030] Once the equivalent duty cycle d of each phase is generated ph, the pulse width modulator 212 then generates the on-time t for different switches (eg, FETs) in the phase legs of the power converter (eg, inverter 216). ph The inverter 216 powered by the power source 214 then provides the desired voltage to the motor (eg, PMSM 19), which generates a current I ph and electromagnetic torque T e Then measure the position θ r and current I ph , and feed it back to the position measurement device 220 and the current measurement device 222 of the control system to close the control loop. m Used with the phase current to calculate the d / q measured current I for closed-loop current control dqm A voltage source inverter (VSI) is commonly used as a power converter in PMSM-based electric drives.

[0031] Although the actual motor design and construction are different for three-phase and multi-phase (greater than three-phase) PMSMs, the same vector control principles can be used for all of these motors in a synchronous or d / q reference frame by using an appropriate conversion matrix to convert the phase currents and voltages into equivalent DC quantities in a synchronous frame. The present disclosure focuses on different techniques for commutation of a power converter (e.g., inverter 216) for a multi-phase motor 19. In some example embodiments, the multi-phase motor 19 is a permanent magnet synchronous motor (PMSM). However, the multi-phase motor 19 can be any type of motor or motor / generator having four or more phases. The multi-phase motor 19 can be, for example, an induction motor, a reluctance motor, or a permanent magnet motor.

[0032] Figure 3 An example of an inverter 216 according to aspects of the present disclosure is depicted. Each of the five phases of a multi-phase electric machine 19 (e.g., a PMSM 19) is connected to a corresponding phase leg consisting of two switches. For example, the inverter 216 includes five phase legs 310, 320, 330, 340, 350, each having two switches (e.g., phase leg 310 includes switches 312, 314; phase leg 320 includes switches 322, 324; phase leg 330 includes switches 332, 334; phase leg 340 includes switches 342, 344; phase leg 350 includes switches 352, 354).

[0033] The duty cycle (equivalent to the on-time) of the upper switch and the lower switch (eg, switches 312 and 314 represent the upper switch and the lower switch of phase leg 310, respectively) are denoted as d x and d x', where x = a, b, c, d, e for the five phase legs. The phase to ground voltages are represented by V xg (For example, V of phase leg 310 ag , phase leg 320 V bg etc.) by Figure 2 The duty cycle generator 210 calculates the duty cycle to control these voltages V xg .

[0034] One of the simplest continuous PWM schemes for multi-phase AC motors is the sinusoidal PWM (SPWM) technique. The duty cycle of the SPWM scheme is mathematically expressed as follows:

[0035]

[0036] Among them, m i is the modulation index, θ r is the electrical position, n is the number of phases, and i = 0, 1, ... n-1. The SPWM scheme can produce a sinusoidal voltage with relatively few harmonics. However, one disadvantage of the SPWM scheme is that the maximum AC output voltage is not optimal. For example, there are other PWM schemes that better utilize the DC bus to produce higher phase-to-phase output voltages than provided by using SPWM.

[0037] Other PWM schemes, such as space vector PWM (SVPWM), which may be continuous or discontinuous in nature, may be used to supply AC power to a multi-phase AC motor. The SVPWM scheme has been shown to have a higher DC bus utilization than the SPWM scheme. In other words, the SVPWM scheme may provide a higher phase-to-phase output voltage than that provided using SPWM. This higher phase-to-phase output voltage may extend the torque-speed performance of the multi-phase motor at the same DC voltage.

[0038] The SPWM scheme can be used to obtain a general expression for the duty cycle of the discontinuous PWM minimum (DPWMMIN) technique as shown in the following formula:

[0039]

[0040] The amplitude of the fundamental voltage of DPWMMIN is The amplitude is greater than 1.

[0041] Figure 4 A graph 400 depicts five duty cycle waveforms A, B, C, D, E of a DPWMMIN scheme according to aspects of the present disclosure. Specifically, Figure 4Depicted is a duty cycle waveform for each of the five phases A, B, C, D, E of a multi-phase motor 19 generated using a DPWM minimum (DPWMMIN) technique. The duty cycle waveform of each of the DPWMMIN duty cycle waveforms A, B, C, D, E remains at zero for 1 / n of electrical rotation, where n is the number of phases of the multi-phase motor 19.

[0042] The generalized SVPWM can be obtained from DPWMMIN by the following equation:

[0043]

[0044] Figure 5 A graph 500 depicts five duty cycle waveforms A, B, C, D, E of a continuous PWM (CPWM) scheme according to aspects of the present disclosure. Specifically, Figure 5 Duty cycle waveforms for each of the five phases A, B, C, D, E of the multi-phase motor 19 generated using a continuous SVPWM scheme are depicted.

[0045] The above equation provides a general way to calculate CPWM from DPWMMIN, which can simplify the calculation compared with the traditional method. In addition, by changing the coefficients in the above equation We can get a combined PWM scheme that can generate a PWM waveform mixed from CPWM and DPWMMIN. The combined adaptive PWM (APWM) can be written using the following equation:

[0046] d APWM =d DPWMMIN +α×(1-max(d DPWMMIN ))

[0047] Here, α is the blending coefficient, and its value is 0.0 to 0.5.

[0048] In some embodiments, a sinusoidal PWM scheme may be used in a combined PWM scheme to form a continuous PWM scheme. In some embodiments, a discontinuous PWM minimum (DPWMMIN) scheme may be used to form a non-continuous PWM scheme used in the combined PWM scheme. Alternatively or additionally, a discontinuous PWM minimum with offset (DPWMMINO) scheme may be used to form a non-continuous PWM scheme used in the combined PWM scheme. In some embodiments, two or more different schemes may be used for one or both of the continuous PWM scheme and / or the discontinuous PWM scheme used in the combined PWM scheme.

[0049] Figure 6A graph 600 depicts a five-phase SVPWM duty cycle waveform for each of the five phases A, B, C, D, E of a multi-phase motor 19 generated using a combined APWM scheme that is a mixture of CPWM and DPWMMIN. Specifically, Figure 6 Depicted are duty cycle waveforms for each of the five phases A, B, C, D, E of the multi-phase motor 19 produced using a combined PWM scheme with a mixing coefficient α=0.2.

[0050] Each of the continuous PWM scheme (e.g., SVPWM) and the discontinuous PWM scheme (e.g., DPWMMIN) has its own advantages under certain operating conditions that do not overlap. By changing the value of the mixing coefficient α according to different operating conditions, the combined PWM scheme can have the advantages of both PWMs under its favorable conditions and can switch between the two PWMs continuously and gradually. In order to maximize the advantages of both PWMs, the mixing coefficient α can be constructed as a function. An example is to use the modulation index m i To determine the value of the mixing coefficient α.

[0051] In some embodiments, the value of the mixing coefficient α is a function of the amplitude of the phase current provided to or from the multiphase motor 19. In some embodiments, the value of the mixing coefficient α is a function of the speed of the multiphase motor 19. The speed of the multiphase motor 19 may be a mechanical speed, such as the rotation speed of the output shaft. Alternatively, the speed of the multiphase motor 19 may be an electrical speed, such as the rotation speed of the rotating magnetic field in the stator of the multiphase motor 19. In some embodiments, the value of the mixing coefficient α is a function of the torque of the multiphase motor 19. For example, the mixing coefficient may be a function of the commanded torque or the actual torque generated by the multiphase motor 19.

[0052] In some embodiments, a piecewise function may be used to determine the mixing coefficient α. An example of such a piecewise function is shown below. In the example piecewise function, when the modulation index m i Outside the range defined by a1 and a2, the mixing coefficient α is equal to a constant, and when the modulation index m i In this range, the mixing coefficient α and the modulation index m i Using this piecewise linear function to determine the value of the mixing coefficient α provides a smooth transition from SVPWM to DPWMMIN with only a few additional calculations. An example of this function is as follows:

[0053]

[0054] In some embodiments, a mixing function is used to determine the relative weight of each of the continuous PWM scheme and the discontinuous PWM scheme used to generate the n duty cycle signals. A signal generator (e.g., duty cycle generator 210) may execute the mixing function to generate a mixed PWM scheme to generate the n duty cycle signals. In some embodiments, the mixing function is a piecewise function. Alternatively or additionally, the mixing function may be a continuous function of one or more different variables, such as a modulation index m. i , phase current amplitude I s , the torque of the multi-phase motor 19 and / or the speed of the multi-phase motor 19 .

[0055] Figure 7 is a graph showing an example mixing function for combining continuous and discontinuous PWM schemes according to aspects of the present disclosure. Specifically, Figure 7 A piecewise mixing function using a mixing coefficient α is shown. Curve 700 represents the percentage or weight given to the continuous PWM scheme as a function of the mixing coefficient α, while curve 702 represents the percentage or weight given to the discontinuous PWM scheme as a function of the mixing coefficient α. As shown, the mixing coefficient α is in a relatively low value range, and the continuous PWM scheme (e.g., SVPWM scheme) dominates. The low value range is shown as between zero and a first threshold a1. When the mixing coefficient α is in an intermediate value range between the first threshold a1 and a larger second threshold a2, the continuous PWM scheme is mixed with the discontinuous PWM scheme (e.g., DPWMMIN scheme), so that as the mixing coefficient α increases, the relative weight of the discontinuous PWM scheme increases until the discontinuous PWM scheme dominates with a mixing coefficient α value greater than or equal to the second threshold a2.

[0056] In other words, the example mixing function is calculated based on the difference between the mixing coefficient α and two thresholds a1, a2, wherein the second threshold a2 is greater than the first threshold a1. In some embodiments, based on the value of the mixing coefficient α being less than the first threshold a1, each duty cycle signal is generated via a continuous PWM scheme. In some embodiments, based on the value of the mixing coefficient α being greater than or equal to the second threshold a2, each duty cycle signal is generated via a discontinuous PWM scheme, the second threshold a2 being greater than the first threshold a1. In some embodiments, based on the value of the mixing coefficient α being greater than or equal to the first threshold a1 and less than the second threshold a2, the duty cycle signal is generated via a combination of a continuous PWM scheme and a discontinuous PWM scheme.

[0057] In some embodiments, the mixing function is a function of two or more variables. In one example, the mixing function determines the mixing coefficient α as the modulation index m using the following formula: i and phase current amplitude I s Function:

[0058]

[0059] where λ is an intermediate variable defined by the following equation:

[0060]

[0061] Where b is an adjustable constant and I smax is the maximum current of the motor 19.

[0062] Figure 8 8 shows a flow chart of a method 800 for controlling a multi-phase electric machine (eg, an AC motor) according to aspects of the present disclosure. The method may be used, for example, in Figure 1 The EPS system 40 depicted may be implemented in any other suitable motor or system. Figure 1 and / or 2 component descriptions Figure 4 .

[0063] At block 802, a processing device such as the duty cycle generator 210 generates n duty cycle signals using a pulse width modulation (PWM) scheme, where n is an integer greater than 3. The PWM scheme used may be referred to as a combined PWM scheme, which is a combination of a continuous PWM scheme and a discontinuous PWM scheme, and the combination is based on a mixing coefficient value α. More specifically, the mixing coefficient value α determines the weight or amount of each of the continuous PWM scheme and the discontinuous PWM scheme within the combined PWM scheme and used to generate the duty cycle signals.

[0064] In some embodiments, the continuous PWM scheme used in block 802 is a sinusoidal PWM scheme. In some embodiments, the discontinuous PWM scheme used in block 802 is a discontinuous PWM minimum (DPWMMIN) scheme or a discontinuous PWM minimum with offset (DPWMMINO) scheme.

[0065] At box 804, a power converter such as the inverter 216 switches power to each of the n phases of the multi-phase electric machine 19 using an associated one of the duty cycle signals.

[0066] In some embodiments, the method 800 for controlling the multi-phase motor 19 further includes: receiving a torque command by a current command module (e.g., a current controller 206) and outputting a current command. The method may also include: generating a modulation index value based on the current command. In some embodiments, the method includes: determining the mixing coefficient value α as the modulation index value m i In some embodiments, the value of the mixing coefficient α is equal to the modulation index m iThe value of is multiplied by the scaling constant. In some embodiments, the scaling constant is between 0.5 and 1.0. More specifically, in some embodiments, the scaling constant may be equal to 0.5, so the mixing coefficient α = 0.5 times the modulation index m i .

[0067] In some embodiments, the method 800 further includes determining a relative weight of each of the continuous PWM scheme and the discontinuous PWM scheme using a mixing function based on a difference between the mixing coefficient value and two thresholds.

[0068] In some embodiments, and as Figure 7 As shown, the mixing function is calculated based on the difference between the mixing coefficient α and two thresholds a1 and a2, wherein the second threshold a2 is greater than the first threshold a1. In some embodiments, based on the value of the mixing coefficient α being less than the first threshold a1, each duty cycle signal is generated via a continuous PWM scheme. In some embodiments, based on the value of the mixing coefficient α being greater than or equal to the second threshold a2, each duty cycle signal is generated via a discontinuous PWM scheme, wherein the second threshold a2 is greater than the first threshold a1. In some embodiments, based on the value of the mixing coefficient α being greater than or equal to the first threshold a1 and less than the second threshold a2, the duty cycle signal is generated via a combination of a continuous PWM scheme and a discontinuous PWM scheme.

[0069] In some embodiments, based on the modulation index m i The value of the mixing coefficient α is calculated based on the difference between the value of and the two thresholds a1 and a2. i The value of is less than the first threshold a1, and each duty cycle signal is generated via a continuous PWM scheme. In some embodiments, based on the modulation index m i The value of is greater than or equal to a second threshold a2, each duty cycle signal is generated via a discontinuous PWM scheme, and the second threshold a2 is greater than the first threshold a1. In some embodiments, based on the modulation index m i The value of is greater than or equal to the first threshold a1 and less than the second threshold a2, and the duty cycle signal is generated through a combination of a continuous PWM scheme and a discontinuous PWM scheme.

[0070] In some embodiments, the combination is calculated based on the following relationship: APWM =d DPWMMIN +α×(1-max(d DPWMMIN )), where d APWM is one of the duty cycle signals, d DPWMMIN is the duty cycle calculated based on the discontinuous PWM scheme, max(d DPWMMIN ) is the maximum value of the duty cycle, and α is the mixing coefficient.

[0071] In some embodiments, the multi-phase electric machine 19 is configured to apply assist torque to and / or control a steering system of the vehicle.

[0072] Although the present disclosure has been described in detail in conjunction with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure may be modified to incorporate any number of changes, alterations, substitutions, or equivalent arrangements not heretofore described but commensurate with the scope of the present disclosure. Furthermore, although various embodiments of the present disclosure have been described, it should be understood that aspects of the present disclosure may include only a portion of the described embodiments or a combination of the embodiments. Therefore, the present disclosure should not be considered to be limited by the foregoing description.

Claims

1. A control system for controlling the operation of a multi-phase motor, comprising: a signal generator configured to generate n duty cycle signals of a pulse width modulation (PWM) scheme that is a combination of a continuous PWM scheme and a discontinuous PWM scheme, wherein the combination is based on a mixing coefficient value, the signal generator configured to control switching of DC power to a corresponding phase of a multi-phase motor using each of the duty cycle signals; and Wherein, n is an integer greater than 3; The mixing coefficient value is a function of at least two variables, and the variables include: a modulation index value, a phase current amplitude of the multi-phase motor, a torque of the multi-phase motor, and a speed of the multi-phase motor.

2. The control system according to claim 1, wherein: The continuous PWM scheme is a sinusoidal PWM scheme.

3. The control system according to claim 1, wherein: The discontinuous PWM scheme is one of a discontinuous PWM minimum value DPWMMIN scheme and a discontinuous PWM minimum value DPWMMINO scheme with an offset.

4. The control system according to claim 1, further comprising: a current command module, configured to receive a torque command and output a current command; A current controller module is configured to generate the modulation index value based on the current command.

5. The control system according to claim 1, wherein: The signal generator is configured to determine a relative weight of each of a continuous PWM scheme and a discontinuous PWM scheme using a mixing function to generate the n duty cycle signals; And wherein the mixing function is calculated based on the difference between the mixing coefficient value and two thresholds.

6. The control system according to claim 5, wherein: The duty cycle signal is generated via the continuous PWM scheme based on the mixing coefficient value being less than a first threshold; as well as The duty cycle signal is generated via the discontinuous PWM scheme based on the mixing coefficient value being greater than or equal to a second threshold, and the second threshold is greater than the first threshold.

7. The control system according to claim 5, wherein: The duty cycle signal is generated via a combination of the continuous PWM scheme and the discontinuous PWM scheme based on the mixing coefficient value being greater than or equal to a first threshold and less than a second threshold, the second threshold being greater than the first threshold.

8. The control system according to claim 1, wherein: The combination is calculated based on the following relationship: d APWM =d DPWMMIN +α×(1-max(d DPWMMIN )) Among them, d APWM is one of the duty cycle signals, d DPWMMIN is the duty cycle calculated based on the discontinuous PWM scheme, max(d DPWMMIN ) is the maximum value of the duty cycle, and α is the mixing coefficient value.

9. The control system according to claim 1, wherein: The multi-phase electric machine is configured to perform at least one of: applying assist torque to a steering system of a vehicle, and controlling the steering system.

10. A method for controlling a multi-phase motor, comprising: generating, by a signal generator, n duty cycle signals using a pulse width modulation (PWM) scheme that is a combination of a continuous PWM scheme and a discontinuous PWM scheme, wherein the combination is based on a mixing coefficient value, wherein n is an integer greater than 3; and switching power to each of n phases of a multi-phase electric machine using an associated one of the duty cycle signals; The mixing coefficient value is a function of at least two variables, and the variables include: a modulation index value, a phase current amplitude of the multi-phase motor, a torque of the multi-phase motor, and a speed of the multi-phase motor.

11. The method according to claim 10, wherein: The continuous PWM scheme is a sinusoidal PWM scheme.

12. The method according to claim 10, wherein: The discontinuous PWM scheme is one of a discontinuous PWM minimum value DPWMMIN scheme and a discontinuous PWM minimum value DPWMMINO scheme with an offset.

13. The method according to claim 10, further comprising: The current command module receives the torque command and outputs the current command; The modulation index value is generated based on the current command.

14. The method according to claim 10, further comprising: A relative weight of each of the continuous PWM scheme and the discontinuous PWM scheme is determined using a mixing function based on a difference between the mixing coefficient value and two thresholds.

15. The method according to claim 14, wherein: Each of the duty cycle signals is generated via the continuous PWM scheme based on the mixing coefficient value being less than a first threshold; as well as Wherein, each of the duty cycle signals is generated via the discontinuous PWM scheme based on the mixing coefficient value being greater than or equal to a second threshold, the second threshold being greater than the first threshold.

16. The method according to claim 13, wherein: The duty cycle signal is generated via a combination of the continuous PWM scheme and the discontinuous PWM scheme based on the mixing coefficient value being greater than or equal to a first threshold and less than a second threshold, the second threshold being greater than the first threshold.

17. The method according to claim 10, wherein: The combination is calculated based on the following relationship: d APWM =d DPWMMIN +α×(1-max(d DPWMMIN )) Among them, d APWM is one of the duty cycle signals, d DPWMMIN is the duty cycle calculated based on the discontinuous PWM scheme, max(d DPWMMIN ) is the maximum value of the duty cycle, and α is the mixing coefficient value.

18. The method according to claim 10, wherein: The multi-phase electric machine is configured to perform at least one of: applying assist torque to a steering system of a vehicle, and controlling the steering system.

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