System and method for overcoming dead band in switched reluctance motors

Abstract

A work machine (100) includes a frame (110), a traction system (120) supporting the frame (110), a power source (130) mounted on the frame (110), a switched reluctance motor (205), an inverter (220) configured to control power from the power source (130) to the motor (205), and a controller (210). The controller (210) is configured to receive a signal indicative of a desired torque (430) and determine whether the desired torque (430) is between an upper threshold (410) and a lower threshold (420). If the desired torque (430) is between the upper threshold (410) and the lower threshold (420), pulse width modulation is used to produce a PWM regulated torque command (450) and the motor (205) is commanded based on the PWM regulated torque command (450). The PWM regulated torque command (450) is configured to cycle between the upper threshold (410) and the lower threshold (420) to produce the desired torque (430).

Description

Technical Field

[0001] This disclosure relates generally to electric motors and generators, and more specifically to switched reluctance machinery. Background Technology

[0002] Many construction machines, such as tracked tractors and excavators, may include a drivetrain connected to a power source to enable the machine to reposition itself or move between positions. With increasing interest in energy conservation and avoiding fossil fuels, the use of electric motors as a power source is becoming more common. Electric motors convert electrical energy from sources such as batteries into mechanical power to drive the construction machine.

[0003] Switched reluctance motors (SRMs), a type of electric motor, are widely used in various applications, such as the aforementioned construction machinery, due to their robust and sturdy construction. A SRM consists of a rotor and multiple stators. Unlike conventional brushed DC motors, power is delivered to windings in the stator rather than the rotor. This greatly simplifies the mechanical design because power does not need to be delivered to moving parts; however, it complicates the electrical design due to the need for some form of switching system to deliver power to the different windings. Some SRMs have control systems that use sensorless operation, estimating the rotor's position and speed relative to the stator without using direct position sensors. Sensorless operation is important in many applications due to the need for minimal package size, high reliability, and low cost. Accurate determination of the rotor's position at rest or low speed is crucial for the motor's performance and efficiency.

[0004] Such a sensorless control system is described in U.S. Patent No. 10,079,566. However, under low loads, the stator may not have sufficient current to estimate the rotor position, thus failing to produce minimum torque. Therefore, there remains a need for a control system for switched reluctance motors that provides sensorless operation when low torque is required. Summary of the Invention

[0005] According to one aspect of this disclosure, a work machine is disclosed. The work machine includes a frame, a traction system supporting the frame, a power supply mounted on the frame, a switched reluctance motor, an inverter configured to control power from the power supply to the motor, and a controller. The controller is configured to receive a signal indicating a desired torque and determine whether the desired torque is between an upper threshold and a lower threshold. If the desired torque is between the upper and lower thresholds, a pulse width modulation (PWM) torque command is generated, and the motor is commanded based on the PWM-regulated torque command. The PWM-regulated torque command is configured to cycle between the upper and lower thresholds to generate the desired torque.

[0006] According to another aspect of this disclosure, an electric drive system is disclosed. The system includes a switched reluctance motor, an inverter configured to control power from a power source to the motor, and a controller. The controller is configured to receive a signal indicating a desired torque and determine whether the desired torque is between an upper threshold and a lower threshold. If the desired torque is between the upper and lower thresholds, pulse width modulation (PWM) is used to generate a PWM-regulated torque command, and the motor is commanded based on the PWM-regulated torque command. The PWM-regulated torque command is configured to cycle between the upper and lower thresholds to generate the desired torque.

[0007] According to another aspect of this disclosure, a method for overcoming dead zone in a switched reluctance motor is disclosed. The method includes receiving a signal indicating a desired torque and determining whether the desired torque is between an upper threshold and a lower threshold. If the desired torque is between the upper and lower thresholds, pulse width modulation (PWM) is used to generate a torque command regulated by PWM, and the motor is commanded based on the PWM-regulated torque command. The PWM-regulated torque command is configured to cycle between the upper and lower thresholds to generate the desired torque.

[0008] These and other aspects and features of this disclosure will be more readily understood after reading the following detailed description in conjunction with the accompanying drawings. Attached Figure Description

[0009] Figure 1 This is a side view of the operating machinery according to one aspect of this disclosure.

[0010] Figure 2 It is possible under one aspect of this disclosure Figure 1 A block diagram of an electric drive system used on construction machinery.

[0011] Figure 3 This is a cross-sectional view of a switched reluctance motor according to one aspect of this disclosure.

[0012] Figure 4 It is a diagram depicting pulse width modulation according to one aspect of this disclosure.

[0013] Figure 5 It is a torque command chart with pulse width modulation according to one aspect of this disclosure.

[0014] Figure 6 This is a flowchart of a method for overcoming dead zones according to one aspect of this disclosure. Detailed Implementation

[0015] This disclosure relates to a switched reluctance motor control system and its configuration method. The switched reluctance motor control system can be widely applied to any operating machinery utilizing such a system. Referring now to the accompanying drawings and specific details... Figure 1An exemplary work machine 100 including a switched reluctance motor control system is shown. The work machine 100 is shown as a tracked tractor, but may include any type of work machine including a switched reluctance motor and a control system.

[0016] As shown in the figure, the work machinery 100 includes a frame 110, a traction system 120 supporting the frame 110, a power supply 130 supported on the frame 110, and an electric drive system 200 configured to transfer energy from the power supply 130 to the traction system 120. A implement 140, such as, but not limited to, the bucket shown, may be attached to the frame 1110 and may be powered by the electric drive system 220. The work machinery 100 may also include an operator's cab 150. The power supply 130 is configured to supply power to the work machinery 100 and provide operating power for propelling the electric drive system 200. The power supply 130 may be a direct current (DC) power source, an Otto cycle or Diesel cycle engine, etc. The power supply 130 may be operably arranged to receive control signals from an operator controller (not shown) in the operator's cab 150. Additionally, the power supply 130 may be operably arranged to power other systems of the work machinery 100.

[0017] The electric drive system 200 can be operatively arranged with the power supply 130 to selectively propel the work machinery 100 via control signals from an operator in the operator's cab 150. The electric drive system 200 is operatively connected to a traction system 120, which can be movably connected to the work machinery 100 via shafts, drive shafts, transmissions, and / or other components. In some embodiments, the traction system 120 may be configured as a tracked drive system as shown, although a wheel drive system or any other type of drive system configured to engage the ground and propel the work machinery 100 is also possible.

[0018] In some embodiments, the electric drive system 200 may be additionally or alternatively configured to selectively operate the implement 140, which may be movably connected to the work machinery 100 and the electric drive system 200. The illustrated implement 154 is a blade mounted on the work machinery 100 in the form of a tractor loader; however, other embodiments may include any other suitable implement for various tasks, such as, but not limited to, bulldozing, brushing, compaction, mining, slope reduction, hoisting, turning over soil, plowing, etc.

[0019] As mentioned above, Figure 1 This example illustrates a machine tool 100 that can utilize the switched reluctance motor and control system disclosed herein. Other examples are also possible and can be combined with... Figure 1 The descriptions are different.

[0020] like Figure 2As shown, the electric drive system 200 includes a motor 205, a controller 210, an inverter 220, and a current sensor 230. The motor 205 is a switched reluctance (SR) motor, such as... Figure 3 As shown and described in more detail below.

[0021] The controller 210 is configured to receive input from the sensor 230, the operator, and / or other systems of the operating machinery 100. Based on this input, the controller 210 commands the inverter 220 to provide power to the SR motor 205 as needed. This includes start-up commands at startup, switching commands during operation, and other commands required for applications as described herein.

[0022] Inverter 220 is electrically connected to power supply 130 and motor 205. Inverter 220 supplies current to SR motor 205 according to commands from controller 210. In some embodiments, inverter 220 may receive DC current from power supply 130 and may control the phase of the DC current to supply AC current to SR motor 205. Current sensor 230 monitors the current in SR motor 205 and transmits information about the current in each of several phases of SR motor 205 to controller 210.

[0023] An example of the SR motor 205 is in Figure 3 The image is shown in cross-section. The SR motor 205 includes a stator 320 having a plurality of stator teeth 310. The stator teeth 310 are arranged in pairs on opposite sides of the stator. Figure 3 These are labeled A, B, and C. Unlike brushed DC motors, power is transmitted to the stator 310 instead of the rotor 340. This greatly simplifies the mechanical design because it eliminates the need to transmit power to moving parts, but it complicates the electrical design by requiring some kind of switching system to sequentially transmit power to the different stators 310.

[0024] Each stator tooth 310 has a winding (not shown) that allows energization of the stator tooth 310. Each stator tooth 310 can be energized as a different phase. At the center of the stator 320 is a rotor 340 having multiple rotor poles 350 also arranged in pairs. The illustrated example has six stator teeth 310 and four rotor poles 350, but other numbers of stator teeth 310 and rotor poles 350 are also possible.

[0025] The SR motor 205 operates based on the tendency of the rotor 340 to move to a position of minimum magnetic reluctance relative to the stator 320. This position of minimum magnetic reluctance occurs when a pair of rotor poles 350 are aligned with a pair of energized stator teeth 310. This magnetic attraction generates torque that causes the rotor 340 to rotate and move toward the position of minimum magnetic reluctance. As power is transferred to each pair of stator teeth 310 and the rotor 340 moves to align with them, the next stator tooth 310 is sequentially energized to continue the movement of the rotor 340 and maintain angular momentum. This switching mode of energizing and de-energizing the stator teeth 310, along with which phase, complicates the operation of such a motor. The correct operation of the motor 310 depends on the correct timing of the energization of each stator tooth 310. This timing is driven by the angular position of the rotor 340 relative to the stator 320.

[0026] While some SR motors 205 in this field use sensors to detect the position of the rotor poles 350 relative to the stator 320, sensorless operation is important for a variety of applications due to the need for minimal package size, high reliability, and low cost of SR motors. Reliable and accurate position sensing of switched reluctance motors is a key step in developing low-cost, high-performance SR working machine drives.

[0027] One method for estimating the rotor 340 position involves injecting triangular current pulses into one or more idle phases of the stator 310. An observer-based estimation method is then used to estimate the stator current flowing through the idle phases. The controller 310 compares the estimated stator current with the actual stator current received from a current sensor to generate an error signal. The error signal is used to calculate the estimated rotor position and the estimated rotor speed.

[0028] However, this sensorless operation method requires a minimum current to the motor. Under very low torque loads, the required current may be too low for the injection, measurement, and comparison processes to function properly, resulting in a dead zone where the controller cannot determine the rotor's position.

[0029] Therefore, this disclosure proposes to overcome dead time by further configuring the controller to apply pulse width modulation when dead time occurs. This disclosure can also be applied to other dead times in motors, including but not limited to SR generators, SR motors with position sensors, induction motors, permanent magnet motors, and other motors that include motors or generators.

[0030] To overcome the dead zone, the controller must first determine whether the required torque is between an upper threshold 410 and a lower threshold 420 corresponding to the positive and negative torque loads that generate the minimum current required for sensorless operation. In some embodiments, the upper threshold 410 may be 250 N·m and the lower threshold 420 may be -250 N·m, but of course, the specific thresholds depend on the application.

[0031] If the required torque or "desired torque command 430" is not between the thresholds 410 and 420, the controller will normally command the inverter to generate the desired torque.

[0032] On the other hand, if the desired torque command 430 is between thresholds 410 and 420, the controller will apply pulse width modulation (PWM) to generate a PWM-regulated torque command 450. PWM is a method of reducing the average power transmitted by an electrical signal by effectively chopping it into discrete parts. This allows the use of current outside the dead-time limit when the motor generates the desired torque 430.

[0033] like Figure 4 As can be seen, the torque command 450 for PWM regulation can be generated by generating a PWM reference signal 440 and comparing it with the desired torque 430. The PWM reference signal 440 can be a sawtooth wave or a triangular wave and oscillates between an upper threshold 410 and a lower threshold 420. The frequency of the reference signal must be faster than the mechanical response of the SR motor 205, but not fast enough to interfere with position sensing. In some embodiments, the frequency can be 250 Hz, 500 Hz, or any other frequency suitable for a particular application. The same system can use different frequencies under different conditions.

[0034] When the PWM reference signal 440 is less than the desired torque 430, the PWM-regulated torque command 450 is equal to the upper threshold 410. When the PWM reference signal 440 is greater than the desired torque 430, the PWM-regulated torque command 450 is equal to the lower threshold 420. The PWM-regulated torque command 450 generates the same torque as the desired torque 450 from the SR motor.

[0035] As mentioned earlier, the torque command 450 of the PWM regulation is generated only when the desired torque 430 is between the threshold levels. Figure 5 The typical case of the desired torque 430 forming a sine wave is depicted. The PWM-regulated torque command 450 is applied only within a narrow range where the torque is close to 0 N·m.

[0036] Industrial applicability

[0037] This disclosure is generally applicable to many different industries, including but not limited to earthmoving equipment, construction, agriculture, and mining. More specifically, due to the need for minimal package size, high reliability, and low cost in actuators driven by SR (Switch Reluctance Motor) operating systems, the dead-zone-free, sensorless operation disclosed herein is important for a variety of applications. Reliable and accurate position sensing of switched reluctance motors is a key step in developing low-cost, high-performance SR operating system drives. Under very low torque loads, the required current may be too low for this method to function correctly, resulting in a dead zone in which the control system cannot function properly. Therefore, this disclosure proposes a method to avoid sensor dead zones in switched reluctance motors. Figure 6 As shown and discussed in further detail below, this method can be used to correct such dead zones in any SR motor operating without sensors in a variety of work machinery and applications. These may include tracked tractors, excavators, graders, and any other electrically driven work machinery 100 that can utilize the SR motor 205. Furthermore, the same method can be applied to other dead zones in motors, including but not limited to SR generators, SR motors with position sensors, induction motors, permanent magnet motors, and other motors that include motors or generators.

[0038] Now go to Figure 6 Method 600 first requires receiving a signal indicating the desired torque 430, as shown in box 610. Controller 210 may receive signals from other systems of the machine 100 or operator input. Next, controller 210 determines whether the desired torque 430 is between an upper threshold 410 and a lower threshold 420, as shown in box 620. The upper threshold 410 and lower threshold 420 correspond to the dead zone limits for sensorless operation. If the desired torque is not between the upper threshold 410 and lower threshold 420, controller 210 commands SR motor 205 to generate the desired torque normally (box 630).

[0039] On the other hand, if the desired torque 430 is between the upper threshold 410 and the lower threshold 420, the controller uses pulse width modulation to generate a PWM-regulated torque command 450 (box 640), and commands the SR motor 205 based on the PWM-regulated torque command 450, as shown in box 650. The PWM-regulated torque command 450 is configured to cycle between the upper threshold 410 and the lower threshold 420 to generate the desired torque 430.

[0040] The torque command 450 for PWM regulation can be generated by generating a PWM reference signal 440 and comparing it with the desired torque 430. The PWM reference signal 450 can be a sawtooth wave or a triangular wave and oscillates between an upper threshold 410 and a lower threshold 420. The frequency of the reference signal must be faster than the mechanical components can respond to, but not so fast as to interfere with the position sensing system.

[0041] While the foregoing text has described many different embodiments in detail, it should be understood that the legal scope of protection is defined by the wording of the claims set forth at the end of this patent. The detailed descriptions should be interpreted as exemplary only and do not describe every possible embodiment, as describing every possible embodiment would be impractical, if not impossible. Many alternative embodiments can be implemented using current technology or technology developed after the filing date of this patent, and these alternative embodiments still fall within the scope of the claims that define the scope of protection.

Claims

1. A type of operating machinery (100), comprising: Rack (110); A traction system (120) that supports the frame (110); A power supply (130) is installed on the rack (110). Switched reluctance motor (205); An inverter (220) configured to control the power from the power source (130) to the motor (205); and Controller (210), the controller (210) is configured to: Receive a signal indicating the desired torque (430), Determine whether the desired torque (430) is between an upper threshold (410) and a lower threshold (420), wherein, The upper threshold (410) and lower threshold (420) correspond to the positive torque load and negative torque load, respectively, that require the minimum current to generate the sensorless operation of the switched reluctance motor (205). If the desired torque (430) is between the upper threshold (410) and the lower threshold (420), then pulse width modulation is used to generate a PWM-regulated torque command (450), which is configured to cycle between the upper threshold (410) and the lower threshold (420) to generate the desired torque (430). The motor (205) is commanded based on the torque command (450) regulated by the PWM.

2. The working machine (100) according to claim 1, wherein the torque command (450) of the PWM regulation is generated by generating a PWM reference signal (440) and comparing the signal with the desired torque (430).

3. The working machine (100) according to claim 2, wherein the PWM reference signal (440) is a sawtooth wave.

4. The working machine (100) according to claim 1, wherein the desired torque (430) generates a sine wave.

5. A method (600) for overcoming the dead zone in a switched reluctance motor (205), comprising: Receive a signal indicating the desired torque (430); Determine whether the desired torque (430) is between an upper threshold (410) and a lower threshold (420), wherein the upper threshold (410) and the lower threshold (420) correspond to the positive torque load and the negative torque load, respectively, that generate the minimum current required for sensorless operation of the switched reluctance motor (205); If the desired torque (430) is between the upper threshold (410) and the lower threshold (420), then pulse width modulation is used to generate a PWM-regulated torque command (450), which is configured to cycle between the upper threshold (410) and the lower threshold (420) to generate the desired torque (430). as well as The motor (205) is commanded based on the torque command (450) regulated by the PWM.

6. The method (600) according to claim 5, wherein the torque command (450) of the PWM regulation is generated by generating a PWM reference signal (440) and comparing the signal with the desired torque (430).

7. The method (600) according to claim 6, wherein the PWM reference signal (440) is a triangular wave.

8. The method (600) according to claim 5, wherein the desired torque (430) generates a sine wave.

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