High performance current sensing architecture for brushless motors

Abstract

A motor controller for controlling operation of a three-phase permanent magnet synchronous motor, where the three-phase permanent magnet synchronous motor is characterized by three phases A, B, C, and further where the three-phase permanent magnet synchronous motor is driven by adjusting three phase currents iA, iB, and iC for the three phases A, B, C, respectively, the motor controller comprising: a three-phase power source for supplying the three phase currents iA, iB, and iC; a first sensor for sensing a phase current iA; a second sensor for sensing cross-phase currents iB and iC; and a microcontroller for controlling operation of the three-phase power supply to generate three phase currents iA, iB and iC required to operate the three-phase permanent magnet synchronous motor, where the microcontroller reads outputs of the first sensor and the second sensor and adjusts operation of the three-phase power supply to generate the phase currents iA, iB and iC that generate a desired torque in the three-phase permanent magnet synchronous motor.

Description

[0001] Citations to pending prior patent applications

[0002] This patent application:

[0003] (i) claiming the benefit of pending prior U.S. Provisional Patent Application Serial No. 62 / 758,004 filed on November 9, 2018 by Barrett Technology, LLC and Claude F. Valle IV et al. for HIGH PERFORMANCE CURRENT SENSING ARCHITECTURE FOR BRUSHLESS MOTORS (Attorney Docket No. BARRETT-13PROV); and

[0004] (ii) Claiming the benefit of pending prior U.S. provisional patent application serial number 62 / 861,772 filed on June 14, 2019 by Barrett Technologies, LLC and Claude F. Valle IV et al., for HIGH PERFORMANCE CURRENT SENSING ARCHITECTURE FOR BRUSHLESS MOTORS (attorney docket number BARRETT-15PROV).

[0005] The above two (2) patent applications are hereby incorporated herein by reference. Technical Field

[0006] The present invention relates generally to motors, and more particularly to permanent magnet synchronous motors and motor controllers for operating the motors. Background Art

[0007] In order to appreciate the present invention, it is important to understand some key concepts as follows:

[0008] (i) Basic construction and operation of three-phase permanent magnet synchronous motor (PMSM);

[0009] (ii) two of the mathematical building blocks involved: the Clarke transform and the Park transform;

[0010] (iii) Three-phase half-bridge operation: switch states, current paths, diode cycles; and

[0011] (iv) How the pulse width modulation (PWM) pattern moments (excitation and decay) relate to the motor model and sampling window.

[0012] Three-phase permanent magnet synchronous motor (PMSM)

[0013] like Figure 1 As shown, the three-phase permanent magnet synchronous motor 5 typically includes a fixed stator 10 having a plurality of magnetic poles 15 and a rotatable rotor 20 having at least one pair of north poles and south poles (for clarity of illustration, the rotatable rotor 20 is shown in FIG. Figure 1 The rotatable rotor 20 is shown as having only one pair of north and south poles, however it should be appreciated that in practice, the rotatable rotor 20 typically has multiple pairs of north and south poles). The rotatable rotor 20 is movably disposed within the fixed stator 10. When the magnetic poles 15 of the fixed stator 10 are appropriately electrically excited, for example, by the motor controller 25, a rotating magnetic field can be generated inside the fixed stator 10, so that the magnetic poles of the rotatable rotor 20 are sequentially attracted toward the magnetic poles 15 of the fixed stator 10 or repelled away from the magnetic poles 15 of the fixed stator 10, thereby causing the rotatable rotor 20 to rotate within the fixed stator 10. A drive shaft 30 is attached to the rotatable rotor 20 to provide output power from the three-phase permanent magnet synchronous motor 5.

[0014] The three-phase permanent magnet synchronous motor 5 is characterized by three phases A, B, and C, and the motor controller 25 supplies three phase currents i A 、i B 、i C To drive the three phases A, B, and C. The three phase currents i A 、i B 、i C Typically pulses are included, wherein the timing of the pulses is coordinated to cause the rotatable rotor 20 to rotate.

[0015] Clark and Parker

[0016] For a sinusoidally wound permanent magnet synchronous motor (PMSM), each of the three phase current waveforms takes on a sinusoidal shape as the motor rotates (see Figure 2 ). The motor torque is a function of these three phase currents. However, it is easier and more efficient to control a constant current value than to control a set of three sinusoidally varying current values, so the three sensed winding currents are first converted to a 2-phase sinusoidal αβ system using a Clarke transformation (see Figure 3 ), and then use the Park transformation to convert it to a binary dq system (see Figure 4 ), the system eliminates the dependence on the electrical angle θ. The q-axis (orthogonal) current i q It is only responsible for producing motor torque, so it is useful to have this current in a single, easily controllable variable.

[0017] Three-phase half bridge, switch state, current path

[0018] In order to use a single DC bus voltage (Vbus) to vary the current in the three motor phases, Figure 5Six identical power metal oxide semiconductor field effect transistors (MOSFETs) 35 are used in the illustrated three-phase half-bridge amplifier configuration 40. A microcontroller 42 is used to control the operation of the MOSFET gates 35. It will be appreciated that the microcontroller 42 and the three-phase half-bridge amplifier configuration 40 together with appropriate supporting circuitry and logic form the motor controller 25.

[0019] Each MOSFET gate 35 is labeled with the phase it controls (A, B, C) and whether it is the high side (H) or low side (L) of the bridge (i.e. AH, AL, BH, BL, CH, CL). Each motor phase is labeled (A, B, C) where N is the neutral point for a Y-winding motor. The high side MOSFET determines the state of the amplifier in the form of S[ABC]. Each low side MOSFET is manipulated to the opposite state of its associated high side MOSFET. This prevents direct conduction from Vbus to ground, also known as shoot-through.

[0020] By rapidly switching the three bridges (AH / AL, BH / BL, CH / CL) on and off using a calculated timing pattern called pulse width modulation (PWM), the amount of current flowing in each motor phase (A, B, C) can be controlled to achieve the desired torque. For example, the PWM pattern in the table shown in the section entitled "State Description" below consists of a series of 7 states (i.e., S

[000] , S

[100] , S

[110] , S

[111] , S

[110] , S

[100] , and S

[000] ), of which 4 states (i.e., S

[000] , S

[100] , S

[110] , and S

[111] ) are unique.

[0021] See Figures 6 to 9 .

[0022] Status description

[0023]

[0024] The inductance of the motor greatly affects the current flow through the amplifier. This is first apparent in S3. It is logical to assume that current flows into phase B, since phase B is connected to Vbus in this state. But the outflow of current in phase B has already been established during S2, and the current flow cannot change immediately, since it is governed by the following equation:

[0025]

[0026] in:

[0027] ·Δi phase is the change in phase current (A)

[0028] Δt is the time change (s)

[0029] ·L phase is the phase inductance (H)

[0030] ·u phase is the phase voltage (V).

[0031] In addition to inductance, other factors may also affect the current flow through the amplifier and / or affect the performance of the three-phase permanent magnet synchronous motor, such as thermal effects causing changes in coil resistance, thermal effects causing changes in friction within the motor, external loads applied to the motor, etc.

[0032] For these reasons, it is important for the motor controller 25 to continuously sense the current through the three motor stages A, B, C and adjust the three phase currents i A 、i B 、i C , to produce the desired torque in a three-phase synchronous motor.

[0033] Can be Figure 5 The initial state S

[000] before current starts to flow is seen in the context of the three-phase amplifier diagram shown, i.e., Fig.10 The initial state S

[000] (before current starts to flow) is shown in .

[0034] Figures 11 to 16 The current flow in the remaining states of this example can be seen in .

[0035] Various sensor architectures

[0036] As mentioned above, the inductance of the motor greatly affects the current flow through the amplifier. In addition to the inductance, other factors may also affect the current flow through the amplifier and / or affect the performance of the three-phase permanent magnet synchronous motor, such as thermal effects that cause changes in coil resistance, thermal effects that cause changes in friction within the motor, external loads applied to the motor, etc.

[0037] Therefore, it is important for the motor controller 25 to continuously sense the current through the three motor stages A, B, C and adjust the three phase currents i as appropriate. A 、i B 、i C , to produce the desired torque in a three-phase synchronous motor.

[0038] Various schemes have been developed to sense the current flow through the three motor stages A, B, C. The three most common architectures are the so-called "three-sensor" architecture, the so-called "single-sensor" architecture, and the so-called "standard two-sensor (B and C)" architecture.

[0039] Three sensors

[0040] In the three-sensor design, there is a shunt resistor 45 in the current path to ground for each of the three phases. The microcontroller samples each of the three amplifier outputs (e.g., via op amp 50) during the "decay" phase of the PWM mode to get a full picture of the winding current. Fig.17 .

[0041] Additive White Gaussian Noise (AWGN) is present in each sample, but the microcontroller is able to sample both inputs simultaneously, so the noise is not very significant when calculating i β Due to i B -i C The Clarke term cancels out the common mode noise. α AWGN is still included, and this is carried through the Park transform to produce a q-axis noise factor of 1 (times the AWGN amplitude).

[0042] The control system is then applied to the d-axis and q-axis currents. The d-axis and q-axis efforts are then converted back to a sinusoidal alpha-beta system using an inverse Park transform. Finally, the alpha-beta effort is sent to a PWM generator, which determines the three duty cycles required to achieve the control effort. This is a 5-step process after sampling: Clarke, Park, control, inverse Park, and then PWM generation.

[0043] Each sensor (eg, operational amplifier 50) requires two calibration steps to determine its offset voltage and amplifier gain. For three sensors, this results in six calibration steps.

[0044] Single sensor

[0045] The single sensor design minimizes hardware size and cost. Fig.18 .

[0046] However, single-sensor designs cannot match the performance of multi-sensor systems for several reasons:

[0047] (i) Due to the minimum sampling time, the PWM pattern needs to be distorted. This can introduce excess current in some windings, which needs to be corrected by applying a carefully constructed compensation pattern in the subsequent pattern. The fast injection / correction of the phase current leads to undesirable audible noise.

[0048] (ii) Mode distortion causes the winding voltage to not match the natural back EMF voltage of the motor. This results in uneven torque throughout each electrical cycle.

[0049] (iii) Since two consecutive current samples need to be taken, the AWGN cannot be eliminated from either sample. Therefore, the phase reconstruction mathematical method results in a phase with twice the AWGN. After passing this noise through the Clarke and Park transforms, i q The current ends up having an AWGN of 4. This noise can negatively impact the controller's ability to apply constant torque.

[0050] (iv) There is a significant computational overhead involved in choosing which phase to sample, how to stretch the relevant part of the PWM pattern to allow sampling, and how to compensate for those distortions in subsequent PWM patterns.

[0051] Standard dual sensors (B and C)

[0052] Using two current sensors (eg, op amp 50) eliminates many of the problems of a single sensor design. Fig.19 .

[0053] During the decay phase, the phase current can be sampled between each PWM pattern. No pattern distortion is required, so the motor does not generate audible noise.

[0054] Since there is no PWM distortion, the applied winding voltage can be matched to the natural back EMF voltage of the motor. This results in constant torque throughout each electrical cycle.

[0055] The microcontroller can take simultaneous samples from both current sensors. This allows calculation of a clean i β Item, but i α The term contains 2 times the AWGN. This noise is carried to i q current, negatively affecting the controller's ability to apply constant torque.

[0056] It should be noted that if we measure i A and i B , then i C will contain twice the AWGN after reconstruction, and thus i β The term will contain 3 times the AWGN after the Clarke transformation. Therefore, it is best to measure i B and i C .

[0057] Although the third phase current still needs to be reconstructed from the two sampled phases, this design eliminates all computational overhead involved in sample selection, PWM pattern stretching, and pattern compensation.

[0058] In view of the foregoing, a new current sensing architecture is needed that minimizes noise and computational complexity compared to competing designs. Summary of the invention

[0059] To create a high performance micro brushless motor controller, a new current sensing architecture was developed that minimizes noise and computational complexity compared to competing designs. Efforts have been made to implement a dual sensor design, but instead of selecting two of the three motor phases to sample and then reconstructing the third phase current, a differential amplifier (e.g., a differential operational amplifier) ​​of one sensor is used to generate the i of the motor. β Direct measurement of current. This gives a 50% noise reduction at the controller input and allows calculation steps to be skipped in the control loop. See the summary table below:

[0060] Summary table: Comparison of various current sensor architectures

[0061]

[0062] In a preferred form of the present invention, there is provided a motor controller for controlling the operation of a three-phase permanent magnet synchronous motor, wherein the three-phase permanent magnet synchronous motor is characterized by three phases A, B, and C, and further wherein the three-phase permanent magnet synchronous motor is controlled by adjusting three phase currents i for the three phases A, B, and C respectively. A 、i B and i C To drive, the motor controller includes:

[0063] Three-phase power supply, used to supply three phase current i A 、i B and i C ;

[0064] The first sensor is used to sense the phase current i A ;

[0065] The second sensor is used for the cross-phase current i B and i C Performing sensing; and

[0066] A microcontroller for controlling the operation of a three-phase power supply to generate the three phase currents i required to operate a three-phase permanent magnet synchronous motor A 、i B and i C , wherein the microcontroller reads the outputs of the first sensor and the second sensor and adjusts the operation of the three-phase power supply to generate a phase current i that produces a desired torque in the three-phase permanent magnet synchronous motor A 、i B and i C .

[0067] In another form of the present invention, there is provided a method for controlling the operation of a three-phase permanent magnet synchronous motor, wherein the three-phase permanent magnet synchronous motor is characterized by three phases A, B, C, and further wherein the three-phase permanent magnet synchronous motor is controlled by adjusting three phase currents i for the three phases A, B, C respectively. A 、i B and i C To drive, the method includes:

[0068] Supply three phase currents i A 、i B and i C To drive a three-phase permanent magnet synchronous motor;

[0069] Sense phase current i A Parallel cross-phase current i B and i C Performing sensing; and

[0070] Adjust the phase current i A 、i B and i C , to generate the phase current i that produces the desired torque in the three-phase permanent magnet synchronous motor A 、i B and i C . BRIEF DESCRIPTION OF THE DRAWINGS

[0071] These and other objects and features of the present invention will be more fully disclosed or become apparent from the following detailed description of the preferred embodiments of the present invention, which will be discussed in conjunction with the accompanying drawings. Figure 1 wherein like numerals refer to similar parts, and further wherein:

[0072] Figure 1 is a schematic view showing a three-phase permanent magnet synchronous motor;

[0073] Figure 2 is a schematic diagram showing phase currents of a three-phase permanent magnet synchronous motor;

[0074] Figure 3 is a schematic diagram showing Clarke transformation of phase current of a three-phase permanent magnet synchronous motor;

[0075] Figure 4 is a schematic diagram showing Park transformation of phase current of a three-phase permanent magnet synchronous motor;

[0076] Figure 5 is a schematic diagram showing a three-phase half-bridge amplifier that can be used to drive a three-phase permanent magnet synchronous motor;

[0077] Figures 6 to 9is a schematic diagram showing a single nested PWM mode, phase voltage, phase current and α-β current of a three-phase permanent magnet synchronous motor;

[0078] Figures 10 to 16 is a schematic diagram showing current flows in various states of a three-phase half-bridge amplifier driving a three-phase permanent magnet synchronous motor;

[0079] Fig.17 is a schematic diagram showing a three-sensor current sensing architecture;

[0080] Fig.18 is a schematic diagram showing a single sensor current sensing architecture;

[0081] Fig.19 is a schematic diagram showing a dual sensor current sensing architecture;

[0082] Fig. 20 is a schematic diagram showing a novel current sensing architecture of the present invention;

[0083] Fig.21 is a schematic diagram showing how shunt resistors and operational amplifiers may be selected for some sensor architectures; and

[0084] Fig. 22 is a schematic diagram showing how shunt resistors and operational amplifiers may be selected for other sensor architectures. DETAILED DESCRIPTION

[0085] The present invention includes providing and using a novel dual sensor current sensing architecture focusing on alpha and beta currents.

[0086] More specifically, if Fig. 20 As shown, the new method is to place a sensor (e.g., operational amplifier 50) at i A A second sensor (eg, another operational amplifier 50) is applied across phases B and C to monitor the alpha current, and another sensor (eg, another operational amplifier 50) is applied across phases B and C to monitor the beta current.

[0087] The microcontroller 42 of the motor controller 25 reads the output of the sensor on phase A (i.e., the α current sensor) and the sensor across phases B and C (i.e., the β current sensor) and adjusts the operation of the three-phase half-bridge amplifier (i.e., by appropriately controlling the MOSFET gates 35 to produce the desired torque in the three-phase permanent magnet synchronous motor.

[0088] Using this architecture, clean i β , because the op amp 50 sensing across phases B and C is not affected by common mode noise, but now only i α The term contains 1 times the AWGN. This will qThe noise is cut in half (compared to the standard dual sensor approach), allowing the current controller to be adjusted to be more robust. In addition, the op amp 50 sensing across the B and C phases is configured with a gain equal to that of the op amp 50 sensing the A phase. This method eliminates the Clarke transform step from the calculation because the transformed values ​​are read directly from the hardware.

[0089] Offset and gain calculation for α and β values

[0090] For any specific implementation of this design, an op amp 50 must be provided to convert the voltage signal from the shunt resistor 45 into a voltage signal that satisfactorily spans the range of the microcontroller analog-to-digital (ADC) segment, thereby effectively setting the range of currents that may be digitized. For the op amp 50 in the three-sensor, single-sensor, and standard two-sensor designs described above, this is a simple matter of selecting the resistance for the shunt resistor 45 and selecting the non-inverting op amp 50 so that the maximum and minimum desired currents are based on Fig.21 The schematic and formula shown are scaled to the maximum and minimum ADC values, respectively. The formula shows the ADC reading that will be obtained for a given op amp and shunt current, where I R1 is the shunt current, ADC bits is the bit resolution of the ADC, and V CC is the reference voltage of the operational amplifier. From this, acceptable resistors and V CC values ​​to provide the correct range for the application specific motor current and data acquisition system.

[0091] This circuit analysis can also be applied to the α amplifier of the new dual-sensing design (i.e., for sensing i A However, this does not apply to the β amplifier (i.e., the op amp used across i B and i C The operational amplifier 50 that does the sensing. At a high level, the design of the beta amplifier is the same: the offset and gain are controlled so the desired output beta voltage range matches the range of the data acquisition system. However, unlike the single current amplifier, the unweighted differential amplifier cannot set an arbitrary offset via a resistor divider as in the single current design. This is because the input impedance of the two amplifier inputs must be matched to avoid a gain difference between the two input signals (R3 must match R4 and R5 must match R6, see Fig. 22). When this is implemented, the output bias voltage is equal to the input bias voltage because the two resistor dividers are matched. The bias voltages divided by the first, and then multiplied by the second, cancel each other out, and if the first divider ratio is increased so that the bias at 0 is below Vbias (as in the alpha amplifier), the relative gains of B and C are no longer matched. This means that once the resistor ratios are chosen for a given gain, the only remaining way to set the output offset is to change the voltage driven on the top of R5 (perhaps with a dedicated reference voltage). With this added in, the relationship between the ADC value and the input current becomes Fig. 22 The equation shown here only requires R3 and R4 to be the same value, and R5 and R6 to be the same value. Fig. 22 In the case of B is the current flowing through the shunt resistor R2, and i C is the current through R1.

[0092] Modifications of the Preferred Embodiments

[0093] It should be understood that those skilled in the art may make numerous additional changes in the details, materials, steps and arrangements of components that have been described and illustrated herein to explain the essence of the present invention, while remaining within the principles and scope of the present invention.

Claims

1. A motor controller for controlling the operation of a three-phase permanent magnet synchronous motor, wherein: The three-phase permanent magnet synchronous motor is characterized by three phases A, B, and C, and further wherein the three-phase permanent magnet synchronous motor is configured by adjusting the three phase currents i for the three phases A, B, and C respectively. A 、i B and i C To drive, the motor controller includes: Three-phase power supply, used to supply three phase current i A 、i B and i C ; The first sensor is used to sense the phase current i A ; The second sensor is used for the cross-phase current i B and i C Performing sensing; and A microcontroller for controlling the operation of a three-phase power supply to generate the three phase currents i required to operate a three-phase permanent magnet synchronous motor A 、i B and i C , wherein the microcontroller reads the outputs of the first sensor and the second sensor and adjusts the operation of the three-phase power supply to generate a phase current i that produces a desired torque in the three-phase permanent magnet synchronous motor A 、i B and i C .

2. The motor controller according to claim 1, wherein: The first sensor includes an amplifier.

3. The motor controller according to claim 1, wherein: The second sensor includes an amplifier.

4. The motor controller according to claim 1, wherein: The microcontroller causes the three-phase power supply to supply three phase currents i in the form of pulses. A 、i B and i C .

5. The motor controller according to claim 1, wherein: The three-phase power supply includes a three-phase half-bridge amplifier.

6. The motor controller according to claim 5, wherein: The three-phase half-bridge amplifier includes: an A-phase portion including two transistors arranged in series and operated by a microcontroller; a B-phase portion including two transistors arranged in series and operated by the microcontroller; and a C-phase portion including two transistors arranged in series and operated by the microcontroller.

7. The motor controller according to claim 6, wherein: Phase A of the three-phase permanent magnet synchronous motor is connected between two transistors of the A phase part of the three-phase half-bridge amplifier; wherein, phase B of the three-phase permanent magnet synchronous motor is connected between two transistors of the B phase part of the three-phase half-bridge amplifier; and wherein, phase C of the three-phase permanent magnet synchronous motor is connected between two transistors of the C phase part of the three-phase half-bridge amplifier.

8. The motor controller according to claim 7, wherein: The first sensor is connected to the A phase portion of the three phase half bridge amplifier, and wherein the second sensor is connected to the B phase portion of the three phase half bridge amplifier and the C phase portion of the three phase half bridge amplifier.

9. The motor controller according to claim 5, wherein: The three-phase half-bridge amplifier includes: an A-phase portion including two transistors arranged in series and operated by a microcontroller, wherein one transistor of the A-phase portion is a high-side transistor and one transistor of the A-phase portion is a low-side transistor; a B-phase portion including two transistors arranged in series and operated by the microcontroller, wherein one transistor of the B-phase portion is a high-side transistor and one transistor of the B-phase portion is a low-side transistor; and a C-phase portion including two transistors arranged in series and operated by the microcontroller, wherein one transistor of the C-phase portion is a high-side transistor and one transistor of the C-phase portion is a low-side transistor, wherein the A phase of the three-phase permanent magnet synchronous motor is connected to the A phase portion of the three-phase half-bridge amplifier between the high-side transistor and the low-side transistor of the A phase portion of the three-phase half-bridge amplifier; wherein the B phase of the three-phase permanent magnet synchronous motor is connected to the B phase portion of the three-phase half-bridge amplifier between the high-side transistor and the low-side transistor of the B phase portion of the three-phase half-bridge amplifier; and wherein the C phase of the three-phase permanent magnet synchronous motor is connected to the C phase portion of the three-phase half-bridge amplifier between the high-side transistor and the low-side transistor of the C phase portion of the three-phase half-bridge amplifier; And wherein the first sensor is connected to the low side transistor of the A phase portion of the three-phase half-bridge amplifier, and wherein the second sensor is connected to the low side transistor of the B phase portion of the three-phase half-bridge amplifier and the low side transistor of the C phase portion of the three-phase half-bridge amplifier.

10. A method for controlling the operation of a three-phase permanent magnet synchronous motor, wherein: The three-phase permanent magnet synchronous motor is characterized by three phases A, B, and C, and further wherein the three-phase permanent magnet synchronous motor is configured by adjusting the three phase currents i for the three phases A, B, and C respectively. A 、i B and i C To drive, the method includes: Supply three phase currents i A 、i B and i C To drive a three-phase permanent magnet synchronous motor; Sense phase current i A Parallel cross-phase current i B and i C Performing sensing; and Adjust phase current i A 、i B and i C , to generate the phase current i that produces the desired torque in the three-phase permanent magnet synchronous motor A 、i B and i C .

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