WO2021148308A1

WO2021148308A1 - Power supply control circuits with shunt resistors for synchronous motors

Info

Publication number: WO2021148308A1
Application number: PCT/EP2021/050725
Authority: WO
Inventors: Carlos DOMINGO MÀS
Original assignee: Mahle International Gmbh
Priority date: 2020-01-23
Filing date: 2021-01-14
Publication date: 2021-07-29
Also published as: EP4094355A1; CN114982124A

Abstract

A power supply control circuit (300) for a synchronous motor (130) having three motor phase currents, the power supply control circuit (300) comprising a microcontroller (310) generating a PWM signal having a period (T) and duty cycles T _x, T _y, T _z and T _w, the power supply control circuit (300) characterized in that it comprises a shunt resistor (215) Rshunt used for calculating the DC current consumption (105) I _s.

Description

POWER SUPPLY CONTROL CIRCUITS WITH SHUNT RESISTORS FOR

SYNCHRONOUS MOTORS

DESCRIPTION

The present invention refers to power supply control circuits for synchronous motors having a controller that uses one or more shunt resistors to calculate a DC current consumption of the synchronous motors.

Background of the invention

Synchronous motors as brushless do (BLDC) motors and permanent magnet synchronous motors (PMSM) consist of a permanent magnet which rotates (i.e. the rotor), surrounded by three equally spaced windings, which are fixed (i.e. the stator). Current flow in each winding produces a magnetic field vector, which sums with the fields from the other windings. By controlling currents in the three windings, a magnetic field of arbitrary direction and magnitude can be produced by the stator.

BLDC motors are becoming increasingly popular in sectors such as automotive (particularly electric vehicles (EV)), heating, ventilation, and air conditioning (HVAC), in white goods and industrial goods because it does away with the mechanical brush used in traditional motors. This characteristic makes the BLDC motors more reliable and increases its service life.

Another advantage of a BLDC motor is that it can be made smaller and lighter than a brush type motor with the same power output, making the BLDC motors suitable for applications where space is tight.

The microcontroller of the control circuit of the synchronous motor may be configured to energize the stator coils of the motor at the correct moment bya implementing a control algorithm. Precise timing allows for accurate speed and torque control, as well as ensuring the motor runs at peak efficiency. In this respect, the microcontroller may receive system current values as inputs and signals from position sensors (as e.g. hall sensors that indicate the position of the motor rotor) to implement the control algorithm.

Current values can be measured and used as input for the control algorithm implemented by the microcontroller: Precise motor control performed by the control circuit of the synchronous motor represents a very significant condition for the correct performance of the motor. Whether for electronic power steering, electronic stability control, automatic braking systems, or for the self-driving vehicle, precise motor control may be required to ensure safe and efficient operation. Hence, currents can be measured to collect information primarily on the motor torque as the current measurements can be directly proportional to the motor torque.

Current measurements can also be used to determine the speed at which the motor is turning. Such speed information can be calculated by understanding how the control algorithm affects the current level applied in the synchronous motor. In this respect, the measurement of phase motor currents may be required as an input variable for the control algorithm implemented by the microcontroller. Therefore, the precise measurement of the phase motor currents can improve the motor control solution.

Furthermore, currents can be measured for fault protection: Current measurements may be used to detect when an overcurrent condition occurs allowing the system to take action to prevent a potential damage in the synchronous motor.

In a first example of the prior art, current brushless DC motor control circuits may include 1 to 3 shunt resistors to measure the phase current that can be used as input for the control algorithm implemented by the microcontroller. Some algorithms may require the measurement of the DC current consumption I_s I_S. In order to measure the current I_s, an additional shunt (101, 102) can be included either in the positive battery input (A) or in the battery return (B) (i.e. in the DC link) as shown in figure 1 that represents a conventional power supply control circuit (100) of a BLDC motor. However, the type of shunt resistors (101, 102) imply additional unwanted power consumption and heat dissipation in the system.

Furthermore, the power supply control circuit (100) of figure 1 can comprise a DC source (105), an input AC filter (103), in particular a LC filter, a microcontroller/PWM block (110) that represents a pulse width modulation (PWM) generator that generates a PWM signal to a three-phase inverter (120) and a microcontroller implementing a control algorithm that controls the input current in the synchronous motor (130). The three-phase inverter (120) comprises six switches for high-power switching to feed current to the synchronous motor (130). Hence, the output from the block (110) comprises pulse width modulated (PWM) signals that determine the average voltage and average current applied to the three coils of the BLDC motor having a Ύ” formation as shown in figure 1 in order to control motor speed and motor torque. Furthermore, the synchronous motor (130) may use three hall-effect sensors not shown in the figure to indicate rotor position. The rotor itself uses several pairs of permanent magnets to generate the magnetic flux.

In a second example of the prior art, figure 2 shows the control circuit (200) previously comprising means for calculating a DC current consumption I_S , the means comprises signal processing elements to obtain the DC current consumption I_S of the synchronous motor (130). In this example, the DC current consumption I_S can be used as input for the microcontroller/PWM block (210) as shown in the figure. These signal processing elements comprise an amplifier (405) to amplify the voltage V_shunt and perform an offset correction and a low pass filter (410) to filter the voltage signal V_shunt from the amplifier (405). Hence, an output voltage V₀ is obtained from the low pass filter (410) and the DC current consumption of the BLDC motor is obtained based on said voltage V₀ as shown in figure 2.

Hence, a power supply control circuit for a synchronous motor that uses a procedure for measuring the input DC current consumption I_S other than using shunt resistors in the DC link or extra electronic components (e.g. amplifiers, low pass filters, etc.) and thus, reducing cost and size of electronic board is desired. Description of the invention

The present invention proposes synchronous motor (e.g. BLDC or PMSM motor) power supply control circuit that can measure the DC current consumption of the motor without the requirement of establishing shunt resistors in the DC link of the power supply in contrast to figure 1 and without the requirement of extra electronic components (amplifiers, low pass filters, etc.) in contrast to figure 2 reducing costs and size of the electronics board.

Hence, the power supply control circuit according to the present invention permits to calculate the supply input current, i.e. the DC current consumption I_S of a control circuit of e.g. a three-phase brushless DC (BLDC) motor or of a Permanent Magnet Synchronous Motor (PMSM). This calculation can be entirely done by a code or software running in the microcontroller driving the power inverter of the power supply control circuit.

The present invention proposes an improved software algorithm used in the microcontroller without the need of adding any extra electrical component. The computational resources needed to run the proposed software algorithm are tiny. The accuracy of the DC current consumption I_S calculated with the software algorithm is comparable to that of the hardware solution of figure 2.

The power supply control circuit according to the present invention supports a single-shunt topology, wherein only one shunt resistor as shown in figure 3 is used.

Hence, in a first aspect, in order to measure the DC current consumption of the motor , it is proposed a power supply control circuit for a synchronous motor, e.g. a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”, the power supply control circuit comprising a microcontroller generating a PWM signal having a period T and duty cycles T_x, T_y, T_z and T_w the power supply control circuit comprises a shunt resistor R_shunt used for calculating the DC current consumption I_S, wherein the microcontroller is configured to obtain a first current measure I₁ of the motor across the shunt resistor R_shunt during T, obtain a second current measure I₂ of the motor across the shunt resistor R_shunt during T and obtain Î, the average value of the current across the resistor R_shunt over the period T of the PWM signal:

Finally, the power supply control circuit is configured to perform a low-pass filtering of the average value t to obtain the DC current consumption I_S.

The power supply control circuit according to the present invention also supports a three-shunt topology that comprises three shunt resistors, one per motor phase as shown in figure 9.

Hence, in a second aspect of the present invention, in order to measure the DC current consumption of the motor I_S, it is proposed a power supply control circuit for a synchronous motor, e.g. a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”, the synchronous motor having motor phase currents I_A, I_B , and I_C, the power supply control circuit comprising a microcontroller generating a PWM signal having a period T and duty cycles T_x, T_y, T_z and T_w. The power supply control circuit comprises three shunt resistors R_sh1 , R_Sh2 and R_Sh3 for calculating the DC current consumption I_S I_S. The microcontroller is configured to obtain a phase current measure I_shunt1 of the synchronous motor across the shunt resistor R_sh1 during T = 0 or during T/2, wherein I_shunt1 = I_A, obtain a phase current measure I_{shunt 2} of the synchronous motor across the shunt resistor R_sh2 during T = 0 or during T/2, wherein I_{shunt 2} = I_B , obtain a phase current measure I_shunt3 of the synchronous motor across the shunt resistor R_sh3 during T = 0 or during T/2, wherein I_{shunt 3} = /_C, obtain a first current measure I₁ equal to I_A or I_B or I_C when having the largest duty cycle T_x, T_y, T_z and T_w, obtain a second current measure I₂ equal to —I_A or — I_B or —l_C when having the shortest duty cycle T_x, T_y, T_z and T_w, and calculate t, the average value of the current across the three shunt resistors R_sh1 , R_sh2 and R_sh3 over the period T of the PWM signal:

Finally, perform a low-pass filtering of the average value Î to obtain the DC current consumption I_S I_S. The present invention also supports a two-shunts topology that comprises two shunt resistors as shown in figure 10.

Hence, in a third aspect of the present invention, in order to measure the DC current consumption of the motor I_S , it is proposed a power supply control circuit for a synchronous motor, e.g. a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”, the synchronous motor having motor phase currents I_A, I_B , and /_C, the power supply control circuit comprising a microcontroller generating a PWM signal having a period T and duty cycles T_x, T_y, T_z and T_w, , the power supply control circuit comprises two shunt resistors R_sh1 and R_sh2 used for calculating the DC current consumption I_S based on a phase current signal I_shunt of the synchronous motor.

The microcontroller is configured to obtain a phase current measure I_shunt1 of the motor across the shunt resistor R_sh1 during T = 0 or during T/2, wherein I_shunt1 = I_A, obtain a phase current measure I_{shunt 2} of the motor across the shunt resistor (320) R_sh2 during T = 0 or during T/2, wherein I_{shunt 2} = I_B, obtain a third phase current /_C = I_A - I_B, obtain a first current value I₁ equal to I_A or I_B or /_C when having the largest duty cycle T_x, T_y, T_z and T_w, obtain a second current value I₂ equal to —I_A or I_B or —I_C when having the shortest duty cycle T_x, T_y, T_z and T_w, and calculate Î, the average value of the current across the across the three shunt resistors R_sh1 , R_sh2 over the period T of the PWM signal:

and finally perform a low-pass filtering of the average value I to obtain the DC current consumption I_S.

Brief description of the drawings

For a better understanding the above explanation and for the sole purpose of providing an example, some non-limiting drawings are included that schematically depict a practical embodiment. Figure 1 shows a power supply control circuit using shunt resistors in in the DC link of the power supply to measure the DC current consumption I_S according to the state of the art.

Figure 2 shows a power supply control circuit using shunt resistors for phase current sensing and extra electronic components to measure the DC current consumption (105) I_S according to the state of the art.

Figure 3 shows a power supply control circuit according to the present invention using a shunt resistor for phase current sensing to calculate the DC current consumption (105) I_S.

Figure 4 shows a PWM of the microcontroller.

Figure 5 and 6 show current measurements during a period T.

Figure 7 shows different duty cycles of the PWM signals.

Figure 8 shows a low-pass filtering of the the average value of the current.

Figure 9 shows a power supply control circuit according to the present invention using a three shunt resistors topology.

Figure 10 shows a power supply control circuit according to the present invention using a two-shunt resistors topology.

Description of a preferred embodiment

Single-shunt topology:

Figure 3 shows a power supply control circuit (300) according to the present invention using a shunt resistor (215) to calculate the DC current consumption (105) I_S by the microcontroller. Figure 3 also shows the DC source (105) and the input AC filter (103), in particular a LC filter. The control circuit (300) comprises a microcontroller/PWM generator control block (310) that generates a PWM signal (shown in figure 4) for the power inverter (120) that feeds the synchronous motor (130). The microcontroller/PWM generator block (310) controls current in synchronous motor (130) based on the control algorithm. The microcontroller also implements a routine to calculate the DC current consumption (105) I_S.

Hence, in order to calculate the DC current consumption (105) I_S by the microcontroller, the microcontroller is configured to obtain a first current measure I₁ of the motor (130) across the shunt resistor (215) R_shunt during T and obtain a second current measure /₂ of the motor (130) across the shunt resistor (320) Rshunt during T.

Figure 4 shows the PWM signals (400). The software in the microcontroller (310) drives the synchronous motor (130) by generating a PWM signals (400) for the power inverter (120) as shown in figure 4.

Signals A, B and C are the PWM signals that drive the three half bridges of the power inverter (120) connected to the 3 phases of the motor (130). In this figure, only one period T of the PWM signal is shown. The typical frequency of those signals is 20 kHz, but may range between 8 kHz and 25 kHz, or even a wider range depending on the characteristics of the motor and the application. The duty cycles T_x, T_y, T_z and T_w, of the PWM signal are shown in figure 5 and may vary from period to period T.

Figure 5 shows the PWM signals (400), the duty cycles T_x, T_y, T_z and T_w of the PWM signals (400), the current I_shunt through the shunt resistor (215) R_shunt , the first current measure I₁ of the motor (130) across the shunt resistor (215) R_shunt during T and the second current measure I₂ of the motor (130) across the shunt resistor (215) R_shunt during T. In order to determine the duty cycles of the PWM signals (400), the software of the microcontroller (310) uses the current of the 3 phases of the synchronous motor. In order to measure these currents, the control circuit incorporates one shunt resistor (as shown in figure 3), three shunt resistors (as shown in figure 9) or two shunt resistors (as shown in figure 10).

The voltage drop is proportional to the current:

V_shunt = R_shunt · I_shunt

The voltage drop of the shunt resistor (215) R_shunt is measured twice per period T: once in the area (501) (current I₁) and another time in the area (502) (current /₂). Preferably, the areas (501) and (502) on the left side of the period T are used over areas (501) and (502) on the right. An example of measurement points is displayed with circles in figure 5. Furthermore, the correspondence between the measured currents 4 and 4, and the motor phase currents I_A, I_B , and /_C depends on the duty cycles T_x, T_y, T_z and T_w and on the pattern of the PWM signals (400).

The calculation of the motor phase currents I_A, I_B , and /_C for the example of figure 5 is the following:

I_A = I₁ I_B = I₁ + I₂ l_C = — I₂

After obtaining he measured currents I₁ and I₂, the controller (310) is configured to calculate:

wherein Î is the average value of the across the resistor (215) R_shunt over the period T of the PWM signals (400) which is represented in figure 6.

The period and the duty cycles T_x, T_y, T_z and T_w of the PWM signals are known to the software running in the microcontroller (310). Therefore, it is possible to calculate the activation times T₁ and T₂ of the areas (501) and (502) based on the difference of duty cycles T_x, T_y, T_z and T_w such that:

T₁ = T_x + T_w T₂ = T_y + T_z

And the above equation results in:

Under some circumstances, as shown in figure 7, the PWM signals in the single- shunt topology may be non-symmetrical in some PWM periods. In these periods, the values of T_z and T_wmay be different from T_x and T_y, or even they may be negative values. The plots in figure 7 show the exact representation of the times T_x, T_y, T_z and T_w and the cases when they should be negative.

At this point, the software running in the microcontroller (310) has the average value Î of the current through the shunt resistor (215) at each period of the PWM signal. A low-pass, infinite impulse response (MR), discrete-time filter can be implemented in the software of the microcontroller (310). This filter is applied to the average values of current Î of each PWM period T. The output of this filter is the calculated input current of the power supply (105). A schematic representation of a low-pass filter (800) is shown in figure 8.

The low-pass filter (800) may be an MR filter or any other type of filter, and it may be of any order (1st-order, 2nd-order, etc.). The low-pass filter (800) must be a low-pass filter with 0 dB gain in DC and without resonant peaks. The cut-off frequency of the low-pass filter (800) can be selected depending on the frequency of the PWM signals (400) and the electrical speed range of the motor (130). The cut-off frequency of the low-pass filter (800) may be smaller than those other frequencies. For example, for a PWM signal with frequency of 20 kHz and the electrical speed of the motor between 45 and 370 electrical revolutions per second, the cut-off frequency of the low-pass filter (800) may be set to 15 Hz.

3-shunt topology:

Figure 9 shows the power supply control circuit (300) for the motor (130). The advantages of the configuration of the power supply control circuit (300) are that this configuration can obtain more precise phase currents readings and involve less acoustic noise and less total harmonic distortion (THD). The power supply control circuit (300) comprises the microcontroller/PWM generator control block (310) that generates six PWM signals for the power inverter (120) that feeds the synchronous motor (130). The microcontroller/PWM generator block (310) controls current in the synchronous motor (130) based on a control algorithm. As in the single-shunt topology, the control circuit (300) calculates the DC current consumption I_S based on phase current signals. I_ShuntThe power supply control circuit (300) comprises three shunt resistors R_sh1, R_sh2 and R_sh3 for measuring each phase current.

Hence, the microcontroller (310) is configured to obtain a phase current measure I_shunt1 of the synchronous motor (130) across the shunt resistor (315) R_sh1, obtain a phase current measure I_{shunt 2} of the motor (130) across the shunt resistor (320) R_sh2, and obtain a phase current measure I_shunt3 of the motor (130) across the shunt resistor (325) R_sh3. Contrary to the single-shunt topology, with three shunts the currents of the phases of the motor are sampled at the beginning of the PWM period T as shown in figure 11. In some examples, the sample point with three shunts may be placed in the middle of the PWM period. Hence, three shunts, it is possible to read the currents of the 3 phases of the motor directly: l_A, I_B and l_C. Hence, I_shunt1 = I_A, I_{shunt 2} = I_B and I_shunt3 = /_C. In order to be able to apply the formula used in the single-shunt topology, the values of I₁ and I₂ must be calculated:

The current I₁ must be equal to the current of the phase with the largest duty cycle. For example, in the plot of figure 11 : I₁= I_A

The current I₂ must be equal to the negative of the current of the phase with the shortest duty cycle. For example, in the plot of figure 11 : I₂ = —I_C

The activation times T₁ and T₂ are calculated in the same way as in the single- shunt topology:

Hence, the microcontroller (310) is configured to calculate:

wherein Î is the average value of the current across the three shunt resistors (315, 320, 325) R_sh1 , R_sh2 and R_sh3 over the period T of the PWM signal (400). Finally, a low-pass filtering of the average value Î to obtain the DC current consumption (105) I_S is performed similarly to the single-shunt topology. 2-shunt topology:

Figure 10 shows the power supply control circuit (300) for the motor (130). As in the single-shunt topology, the control circuit (300) calculates the DC current consumption I_S based on phase current signals. I_ShuntThe power supply control circuit (300) comprises two shunt resistors R_sh1 and R_sh2 for measuring each phase current.

Hence, with two shunts, it is possible to read the currents of the two phases of the motor directly, for example I_A and I_B and the other current is calculated in such a way that they add up to zero:

I_C = -I_A - I_B

Contrary to the single-shunt topology, with two shunts the currents of the phases of the motor are sampled at the beginning of the PWM period T as shown in figure 11. In some examples, the sample point with two shunts may be placed in the middle of the PWM period.

In order to be able to apply the formula used in the single-shunt topology, the values of I₁ and I₂ must be calculated:

The current I₁ must be equal to the current of the phase with the largest duty cycle. For example, in the plot of figure 11 : I₁ = I_A

Hence, the microcontroller (310) calculates:

wherein Î is the average value of the current across the two shunt resistors (315, 320) R_Shi and R_sh2 over the period T of the PWM signal (400).

Finally, a low-pass filtering of the average value t to obtain the DC current consumption (105) I_S is performed similarly to the single-shunt topology. Even though reference has been made to a specific embodiment of the invention, it is obvious for a person skilled in the art that the power supply control circuit architectures described herein are susceptible to numerous variations and modifications, and that all the details mentioned can be substituted for other technically equivalent ones without departing from the scope of protection defined by the attached claims.

Claims

i CLAIMS

1. A power supply control circuit (300) for a synchronous motor (130) having motor phase currents I_A, I_B , and /_C, the power supply control circuit (300) comprising a microcontroller (310) generating PWM signals for the phase currents I_A, I_B , and /_C, the PWM signals having a period T and duty cycles T_x, T_y,

T_z and T_w as time fractions wherein the PWM signals are activated or disactivated, the power supply control circuit (300) characterized in that it comprises an input AC filter (103) and a shunt resistor (215) R_shunt used for calculating the DC current consumption (105) I_S, wherein the microcontroller (310) is configured to:

- obtain a first current measure I₁ of the motor (130) across the shunt resistor (215) R_Shunt during T, wherein I₁ is equal to the motor phase current I_A or I_B or /_C having a PWM signal with the largest duty cycle T_x, T_y, T_z and T_w,

- obtain a second current measure I₂ of the motor (130) across the shunt resistor (215) R_Shunt during T, wherein /₂ is equal to the motor phase current —I_A or — I_B or —l_C having a PWM signal with the shortest duty cycle T_x, T_y, T_z and T_w,

- obtain

wherein t is the average value of the across the resistor (215) R_shunt over the period T of the PWM signals; and

-perform a low-pass filtering of the average value Î to obtain the DC current consumption (105) I_S.

2. The power supply control circuit (300) of claim 1, wherein the synchronous motor (130) is a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”.

3. A power supply control circuit (300) for a synchronous motor (130) having motor phase currents I_A, I_B, and /_C, the power supply control circuit (300) comprising a microcontroller (310) generating PWM signals for the motor phase currents I_A, I_B , and /_C, the PWM signals having a period T and duty cycles T_x, T_y, T_z and T_w being time fractions wherein the PWM signals are activated or disactivated, the power supply control circuit (300) characterized in that it comprises an input AC filter (103) and three shunt resistors (315, 320, 325) R_sh1 R_sh2 and R_sh3 for calculating the DC current consumption (105) I_S, wherein the microcontroller (310) is configured to:

- obtain a phase current measure I_shunt1 of the motor (130) across the shunt resistor (315) R_sh1 during T = 0 or during T/2, wherein I_shunt1 = I_A;

- obtain a phase current measure I_{shunt 2} of the motor (130) across the shunt resistor (320) R_sh2 during T = 0 or during T/2, wherein I_{shunt 2} = I_B;

- obtain a phase current measure I_shunt3 of the motor (130) across the shunt resistor (325) R_sh3 during T = 0 or during T/2, wherein I_shunt3 = I_C ;

- obtain a first current measure I₁ equal to I_A or I_B or /_C having a PWM signal with the largest duty cycle T_x, T_y, T_z and T_w;

- obtain a second current measure I₂ equal to —I_A or — I_B or —l_C having a PWM signal with the shortest duty cycle T_x, T_y, T_z and T_w;

- calculate:

wherein Î is the average value of the current across the three shunt resistors (315, 320, 325) R_sh1 R_sh2 and R_sh3 over the period T of the PWM signals; and

-perform a low-pass filtering of the average value t to obtain the DC current consumption (105) I_S.

4. The power supply control circuit (300) of claim 3, wherein the synchronous motor (130) is a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”.

5. A power supply control circuit (300) for a synchronous motor (130) having motor phase currents l_A, I_B, and l_C, the power supply control circuit (300) comprising a microcontroller (310) generating PWM signals for the phase currents I_A, I_B , and /_C, the PWM signals having a period T and duty cycles T_x, T_y, T_z and T_w being time fractions wherein the PWM signals are activated or disactivated, the power supply control circuit (300) characterized in that it comprises an input AC filter (103) and two shunt resistors (315, 320) R_sh1 and R_sh2 used for calculating the DC current consumption (105) I_S based on a phase current signal I_shunt of the motor (130), wherein the microcontroller (310) is configured to:

- obtain a third phase current /_C = - I_A - I_B

- obtain a first current value I₁ equal to I_A or I_B or I_C having a PWM signal with the largest duty cycle T_x, T_y, T_z and T_w;

- obtain a second current value I₂ equal to —I_A or — I_B or —l_C having a PWM signal with the shortest duty cycle T_x, T_y, T_z and T_w;

- calculate:

wherein Î is the average value of the current I_shunt across the resistor (315) R_sh1 over the period T of the PWM signals; and -perform a low-pass filtering of the average value t to obtain the DC current consumption (105) I_S.

6. The power supply control circuit (300) of claim 5, wherein the synchronous motor (130) is a three-phase brushless DC, “BLDC” motor or a permanent magnet synchronous motor, “PMSM”.