Motor phase current sampling method and system

Abstract

The invention discloses a motor phase current acquisition method and system, and the method comprises the steps: obtaining the duty ratio of a drive signal of a motor drive circuit for one bridge arm in the motor drive circuit; if the duty ratio is greater than or equal to a preset threshold value, recording a first voltage sampling signal when a switching tube of a lower bridge arm in the bridge arms is switched on, and determining a motor phase current according to the first voltage sampling signal; and if the duty ratio is smaller than the preset threshold value, recording a second voltage sampling signal when the switching tube of the lower bridge arm in the bridge arms is switched off, and determining the phase current of the motor according to the second voltage sampling signal.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technical field of data acquisition, and particularly to a method and system for sampling motor phase current. Background Art

[0002] In the field of motor drive and control, accurately sampling the motor phase current is crucial for the efficient operation, precise control, and fault diagnosis of the motor. In traditional motor phase current sampling methods, hardware such as Hall current sensors or shunts is used to directly measure the current. Although a certain accuracy can be achieved, there are problems such as high cost, complex installation, and large occupied space; while the estimation method based on software algorithms is easily affected by factors such as motor parameter changes and electromagnetic interference, resulting in large measurement errors.

[0003] With the continuous expansion of motor application scenarios, in fields such as new energy vehicles and industrial automation equipment, higher requirements are put forward for the accuracy, real-time performance, and cost control of motor phase current sampling. Traditional methods have large errors in sampling the phase current under complex working conditions and cannot meet the requirements of high-performance motor control. Summary of the Invention

[0004] The present invention provides a method and system for sampling motor phase current to achieve the purpose of solving at least one defect existing in the prior art.

[0005] In a first aspect, embodiments of the present invention provide a method for sampling motor phase current, including:

[0006] Obtaining the duty cycle of the drive signal of the motor drive circuit for one arm of the motor drive circuit;

[0007] If the duty cycle is greater than or equal to a preset threshold, record the first voltage sampling signal when the switch tube of the lower arm in the arm conducts, and determine the motor phase current according to the first voltage sampling signal;

[0008] If the duty cycle is less than the preset threshold, record the second voltage sampling signal when the switch tube of the lower arm in the arm turns off, and determine the motor phase current according to the second voltage sampling signal.

[0009] Optionally, determining the motor phase current according to the first voltage sampling signal or determining the motor phase current according to the second voltage sampling signal includes using the following formula to determine the motor phase current:

[0010]

[0011] In the formula, I represents the motor phase current, K represents a coefficient, U represents the first voltage sampling signal or the second voltage sampling signal, and Rd represents the on-resistance of the switch tube corresponding to the first voltage sampling signal.

[0012] Optionally, the coefficient includes a temperature correction coefficient, and determining the temperature correction coefficient includes:

[0013] Recording the temperature of the switching tube of the lower arm in the bridge arm, and determining the temperature correction coefficient according to the temperature.

[0014] Optionally, the coefficient includes a current correction coefficient, and determining the current correction coefficient includes:

[0015] Calculating the energized current, and determining the current correction coefficient according to the energized current, where the energized current is determined by the following formula:

[0016]

[0017] In the formula, I0 represents the energized current.

[0018] Optionally, the coefficient includes a current amplification factor, and the current amplification factor is a preset value.

[0019] Optionally, according to the temperature, the on-resistance is determined by using a temperature-internal resistance curve.

[0020] Optionally, the first voltage sampling signal represents the source-drain voltage when the switching tube is conducting.

[0021] Optionally, the second voltage sampling signal represents the voltage of the motor inductor when the switching tube is off.

[0022] In a second aspect, an embodiment of the present invention further provides a motor phase current acquisition system, including a controller configured to execute any one of the motor phase current acquisition methods described in the embodiments of the present invention.

[0023] Optionally, it further includes a voltage sampling circuit for generating a first voltage sampling signal or a second voltage sampling signal.

[0024] Compared with the prior art, the beneficial effect of the present invention is that: the present invention proposes a current sampling method, which flexibly switches the sampling method according to the duty cycle. When the duty cycle is greater than or equal to a preset threshold, the first voltage sampling signal when the lower-arm switching tube is conducting is recorded. At this time, the switching tube has a long conduction time, which can effectively avoid the interference at the moment of conduction and obtain a stable sampling signal, thereby accurately determining the motor phase current. When the duty cycle is less than the preset threshold, the second voltage sampling signal when the switching tube is off is recorded, and by using the characteristic that the current of the motor inductor cannot change suddenly, sampling is performed through the freewheeling circuit, avoiding the problem of inaccurate sampling of the on-resistance of the switching tube due to short time and large interference under a small duty cycle, greatly improving the accuracy of phase current acquisition, and providing reliable data support for precise control and operation state monitoring of the motor. Description of the Drawings

[0025] Figure 1 is the flow chart of the motor phase current acquisition method in the embodiment;

[0026] Figure 2 is the schematic diagram of the full-bridge circuit structure in the embodiment;

[0027] Figure 3 is the schematic diagram of the first sampling circuit structure in the embodiment;

[0028] Figure 4 is the schematic diagram of the second sampling circuit structure in the embodiment;

[0029] Figure 5 is the schematic diagram of the reference power supply structure in the embodiment;

[0030] Figure 6 is the schematic diagram of the temperature sampling circuit structure in the embodiment. Specific Embodiments

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that for the sake of description, only parts related to the present invention rather than all structures are shown in the drawings.

[0032] Embodiment 1

[0033] Figure 1 is the flow chart of the motor phase current acquisition method in the embodiment, refer to Figure 1 , the motor phase current acquisition method includes:

[0034] S101. Obtain the duty cycle of the drive signal of the motor drive circuit.

[0035] In this solution, the motor phase current acquisition method can be used for the phase current acquisition of a DC motor or an AC motor.

[0036] In this solution, the motor is configured with a full-bridge circuit (drive circuit), and for different motors, the power circuit can be configured to implement a rectification function, an inversion function, or a drive function.

[0037] For a DC motor, when the full-bridge circuit is used as the drive circuit, by controlling the on and off combinations of 4 switching devices, the current direction in the armature winding of the motor can be changed to achieve forward and reverse rotation; the PWM technology can be used to adjust the average voltage applied across the motor to achieve speed regulation.

[0038] For an AC motor, when a full-bridge circuit is used as the drive circuit, through technologies such as PWM and SVPWM, the on-off combination control of 6 switching devices can be realized to generate a three-phase alternating voltage, and then the variable-frequency speed regulation of the AC motor can be achieved.

[0039] In this solution, the duty cycle of the drive signal can be obtained in software or hardware.

[0040] For example, when obtaining the duty cycle in software, the controller can be configured to capture the rising edge and falling edge of the drive signal. By calculating the duration of the high level and the cycle time, the duty cycle can be calculated.

[0041] When obtaining the duty cycle of the drive signal in hardware, a comparator can be used to convert the drive signal into a standard square wave signal, and then a counter is used to count the time of the high level and the low level. The duty cycle can be obtained through the ratio of the high-level counting time to the total counting time of one cycle.

[0042] S102. If the duty cycle is greater than or equal to the preset threshold, then record the first voltage sampling signal when the lower switch tube in the bridge arm conducts, and determine the motor phase current according to the first voltage sampling signal.

[0043] S103. If the duty cycle is less than the preset threshold, then record the second voltage sampling signal when the lower switch tube in the bridge arm turns off, and determine the motor phase current according to the second voltage sampling signal.

[0044] Combining steps S102 and S103, for example, spike interference will be generated when the switch tube turns on and off, and the interference has a greater impact on the sampling accuracy at a small duty cycle. According to the characteristic curve of the switch tube and combined with actual tests, it can be determined at what duty cycle the impact of spike interference on sampling is acceptable.

[0045] For example, during actual testing, an actual motor drive and sampling test platform can be built, and a large number of sampling experiments are carried out at different duty cycles to compare the errors between on-sampling and off-sampling. According to the error analysis results, find the duty cycle switching point with the smallest error as the preset threshold.

[0046] For example, in this solution, the numerical range of the preset threshold can be 20% - 50%.

[0047] For example, in this solution, each bridge arm of the drive circuit can correspond to a first voltage sampling signal or a second voltage sampling signal.

[0048] Exemplarily, in this solution, for a leg in the motor drive circuit, when the lower-arm switch is turned on, the current will flow through the motor and the lower-arm switch. To obtain the first voltage sampling signal, a sampling circuit can be set at an appropriate position on the lower arm (such as the node position where the two switches of the upper arm and the lower arm are connected). The sampling circuit can include a signal amplification circuit, a filtering circuit, and an analog-to-digital conversion circuit.

[0049] The signal amplification circuit can include an operational amplifier, which is used to amplify the small signal to a range that can be accurately measured by the ADC (analog-to-digital conversion circuit).

[0050] The filtering circuit can adopt an RC filtering circuit, which is used to filter the noise of the sampling signal to make the sampling signal more stable.

[0051] The analog-to-digital conversion circuit is used to sample the sampling signal at a certain sampling frequency and convert it into a corresponding digital value.

[0052] Exemplarily, in this solution, for a leg in the motor drive circuit, to obtain the second voltage sampling signal, a sampling circuit can be set at an appropriate position on the lower arm, and this sampling circuit can be the same as the sampling circuit used when obtaining the first voltage sampling signal.

[0053] Alternatively, to obtain the second voltage sampling signal, voltage sampling can be performed at one end of the motor or across the freewheeling diode of the switch, and the sampling signal is used as the second voltage sampling signal.

[0054] Exemplarily, in this solution, if the first voltage sampling signal is realized based on a sampling resistor, Ohm's law can be used to obtain the phase current based on the voltage value corresponding to the first voltage sampling signal, the resistance value of the sampling resistor, and a preset coefficient.

[0055] Exemplarily, in this solution, when determining the phase current using the second voltage sampling signal, the equivalent resistance of the freewheeling circuit of this leg (which can be obtained through measurement or calculation) is obtained, and Ohm's law is used to obtain the freewheeling current based on the voltage value corresponding to the second voltage sampling signal, the equivalent resistance, and a preset coefficient. Then, according to the relationship between the freewheeling current and the phase current (usually in the ideal case, the freewheeling current is equal to the phase current), the magnitude of the phase current is determined.

[0056] This embodiment proposes a current sampling method. This method flexibly switches the sampling method according to the duty cycle. When the duty cycle is greater than or equal to the preset threshold, the first voltage sampling signal when the bridge arm switching tube is conducting is recorded. At this time, the switching tube has a long conduction time, which can effectively avoid the interference at the moment of conduction and obtain a stable sampling signal, so as to accurately determine the motor phase current. When the duty cycle is less than the preset threshold, the second voltage sampling signal when the switching tube is turned off is recorded. Utilizing the characteristic that the inductor current of the motor cannot change suddenly, sampling is carried out through the freewheeling circuit, avoiding the problem of inaccurate sampling of the on-resistance of the switching tube caused by short conduction time and large interference under a small duty cycle, greatly improving the accuracy of phase current acquisition, and providing reliable data support for precise control and operation state monitoring of the motor.

[0057] Based on Figure 1 the scheme shown, in an implementable embodiment, determining the motor phase current according to the first voltage sampling signal, or determining the motor phase current according to the second voltage sampling signal includes using the following formula to determine the motor phase current:

[0058]

[0059] In the formula, I represents the motor phase current, K represents a coefficient, U represents the first voltage sampling signal or the second voltage sampling signal, and Rd represents the on-resistance of the switching tube corresponding to the first voltage sampling signal.

[0060] Figure 2 is the schematic diagram of the full-bridge circuit structure in the embodiment, Figure 3 is the schematic diagram of the first sampling circuit structure in the embodiment, Figure 4 is the schematic diagram of the second sampling circuit structure in the embodiment, Figure 5 is the schematic diagram of the reference power supply structure in the embodiment.

[0061] Refer to Figures 2 to 5 , in an implementable embodiment, the full-bridge circuit includes a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a fourth switching tube Q4, an inductor L1, and a capacitor C10. Among them, the first switching tube Q1 and the second switching tube Q2 form the first bridge arm (corresponding to the U phase of the motor), and the third switching tube Q3 and the fourth switching tube Q4 form the second bridge arm (corresponding to the V phase of the motor).

[0062] In this scheme, the DC+ and GND of the full-bridge circuit are connected to the DC power supply. By controlling the conduction and turn-off of the switching tubes Q1~Q4, the voltage polarity and magnitude at both ends of the motor are changed to achieve forward and reverse rotation and speed control of the motor. For example, when Q1 and Q4 are conducting and Q2 and Q3 are turned off, the current flows from DC+ through Q1, L1, Q4 back to GND; switching the conduction combination can change the current direction.

[0063] Exemplarily, in this solution, a first sampling circuit may be provided at M1, and the first sampling circuit includes a first operational amplifier U1_A, a first input of the first operational amplifier U1_A is grounded, and a second input terminal is connected to the U_AI terminal and a reference voltage 1.65V.

[0064] A second sampling circuit may be provided at M2 , and the second sampling circuit includes a second operational amplifier U10 , a first input of the second operational amplifier U10 is grounded, and a second input terminal is connected to the V_AI terminal and a reference voltage 1.65V.

[0065] In this solution, the structure and working principle of the first sampling circuit and the second sampling circuit are basically the same. After M1 and M2 pass through the current limiting resistors (R16 and R17), they are clamped in the forward and reverse directions by diodes (D1 to D4) to prevent the input voltage from being too high or too low to damage the subsequent circuit. When the input voltage is higher than 3V3, D1 and D3 are turned on; when it is lower than GND, D2 and D4 are turned on.

[0066] U1_A and U10 are in-phase proportional amplifier circuits. R2 and R6 are connected to the 1.65V reference voltage, so that the sampling voltages of M1 and M2 are superimposed with the 1.65V reference voltage, so that positive and negative voltages can be collected. For example, when there is a -0.5V voltage at M1, it becomes 1.15V after superposition and enters the amplifier for processing.

[0067] By adjusting the resistance values of R1 (R5) and R3 (R7), the amplification factor can be adjusted. According to the formula of the same-direction proportional amplification circuit, the amplification degree of the input signal can be changed by changing the resistance ratio.

[0068] The amplified signal is filtered by RC (R4, C2; R8, C3) to remove high-frequency noise and output a stable signal to the MCU sampling I / O port.

[0069] Exemplarily, in this scheme, taking the second bridge arm as an example, when the fourth switch tube Q4 is turned on, the conduction path is DC+-Q1-M1-L1-M2-Q4-GND. At this time, the first voltage sampling signal at M2 is obtained through the second sampling circuit. Based on the above formula, the V-phase current of the motor can be determined when the fourth switch tube Q4 is turned on.

[0070] When Q4 is turned off, the motor inductor will generate a voltage in the same direction (same as the current direction) to try to maintain the current because the current cannot change suddenly. At this time, the inductor current forms a freewheeling loop through the diode. When the fourth switch tube Q4 is turned off, the conduction path is M2-Q3 body diode-C10-Q2 body diode-M1.

[0071] The current in the freewheeling circuit decays exponentially, and the formula is I(t) = I0×e^(-t) / τ, where I0 is the current at the moment when the switching tube is turned off, and τ = L / Rtotal (L is the motor inductance, and Rtotal is the total resistance of the freewheeling circuit). Since the time constant τ is much larger than t, it can be considered that the loop current cannot change suddenly in a short time.

[0072] When the fourth switching tube Q4 is turned off, due to the fact that the loop current cannot change suddenly in a short time, the second voltage sampling signal at M1 is obtained through the first sampling circuit. Based on the above formula, the phase current of the V phase of the motor can be determined when the fourth switching tube Q4 is turned off.

[0073] In this solution, the first voltage sampling signal represents the source-drain voltage when the switching tube is conducting.

[0074] In this solution, the first voltage sampling signal represents the source-drain voltage when the switching tube is conducting. By measuring the voltage between the source and the drain when the switching tube is conducting and combining with the on-resistance of the switching tube, the phase current of the motor can be directly calculated.

[0075] In this solution, when the switching tube is conducting, the current will flow from the drain to the source. According to Ohm's law, if the on-resistance of the switching tube and the source-drain voltage (i.e., the first voltage sampling signal) when it is conducting are known, the current flowing through the switching tube can be calculated, and this current is the phase current of the motor.

[0076] In this solution, the second voltage sampling signal represents the voltage of the motor inductance when the switching tube is turned off.

[0077] In this solution, when the switching tube is turned off, the current in the motor inductance cannot change suddenly and will form a freewheeling circuit through the freewheeling diode. At this time, the motor inductance will generate an induced electromotive force, the magnitude of which is proportional to the change rate of the inductance current, and this induced electromotive force is manifested as the voltage across the switching tube, that is, the second voltage sampling signal.

[0078] Exemplarily, in this solution, the coefficient can include one or more correction coefficients. When actually setting, the correction coefficients can be determined according to the influence degree of the characteristics of circuit elements (such as resistors, capacitors, operational amplifiers, etc.) on the voltage sampling signal.

[0079] For example, the gain of the operational amplifier may be affected by factors such as temperature and power supply voltage, thus causing a certain amplification or attenuation effect on the voltage sampling signal. In order to compensate for these errors, adjustment needs to be made through the coefficient K.

[0080] Exemplarily, in this solution, the value of coefficient K is determined through a calibration test. During calibration, a standard current source with a known accuracy is used to inject standard currents of different magnitudes into the motor drive circuit. While injecting the standard currents, the corresponding first voltage sampling signal or second voltage sampling signal is collected, and the value of K under different standard currents is determined respectively.

[0081] Exemplarily, in this solution, the on-resistance Rd of the switching device can be determined according to the data sheet of the switching device. The on-resistance is affected by various factors, such as temperature, gate-source voltage, current magnitude, etc. Therefore, the corresponding correction coefficient can also be determined through a calibration test to compensate for the on-resistance Rd.

[0082] In this solution, the introduction of coefficient K can compensate for various errors in the measurement process. In an actual circuit, due to factors such as the discreteness of component parameters, the influence of the signal conditioning circuit, and measurement errors, the proportional relationship between the voltage sampling signal U and the actual phase current I may change. By experimentally calibrating to determine coefficient K, these errors can be effectively compensated, improving the accuracy of motor phase current measurement.

[0083] Based on any of the foregoing solutions, in an implementable solution, the coefficient includes a temperature correction coefficient. Determining the temperature correction coefficient includes: recording the temperature of the switching device in the lower arm of the bridge arm, and determining the temperature correction coefficient according to the temperature.

[0084] Exemplarily, the switching device can be a MOS transistor. The on-resistance (Rd) of the MOS transistor changes with temperature. The relationship between the temperature of the switching device and the on-resistance of the MOS transistor can be established to obtain the temperature correction coefficient. The temperature correction coefficient can be determined through a calibration test.

[0085] As an implementable manner, in the drive circuit, a temperature sensor (such as a thermistor) can be installed near the MOS transistor to monitor the temperature of the MOS transistor in real time. Build a power supply circuit that can provide stable and different fixed currents to test the drive circuit by applying different magnitudes of currents. Connect a high-precision voltage measurement device to accurately measure the voltage between the D pole and the S pole of the switching device.

[0086] Apply the first fixed current value (for example, 1 A). After the temperature of the drive circuit stabilizes (which can be determined by observing the data of the temperature sensor. When the temperature fluctuates slightly within a certain period of time, it is considered stable), record the temperature value T1 of the MOS transistor at this time. At the same time, use the high-precision voltage measurement device to measure and record the voltage value U1 between the D pole and the S pole of the MOS transistor.

[0087] According to the above steps, sequentially change the fixed current values (such as 2A, 3A, 4A, etc.) applied to the drive circuit, and record the corresponding MOS transistor temperature value Tn and the voltage values Un at the D and S poles of the MOS transistor each time after the temperature stabilizes.

[0088] According to the voltage value Un collected each time and the fixed current value In applied, use Ohm's law Rn = Un / In to calculate the corresponding on-resistance Rn of the MOS transistor each time.

[0089] Taking Tn as the abscissa and the on-resistance Rn of the MOS transistor as the ordinate, plot a scatter diagram. By means of curve fitting (such as the least squares method), find the curve equation that can best fit these scatter points, and establish a relationship model between the module temperature and the MOS on-resistance.

[0090] According to the proportional relationship between the MOS junction temperature and the MOS on-resistance provided by the manufacturer, determine the on-resistance Rstd of the MOS transistor at the standard temperature (such as 25°C). For any measured module temperature T, calculate the corresponding on-resistance R of the MOS transistor at this time according to the established relationship model.

[0091] Calculate the temperature correction coefficient K1 = Rstd / R. In this way, obtain the corresponding temperature correction coefficients K1 at different temperatures, forming a corresponding table or functional relationship of temperature - correction coefficient, so as to quickly obtain the corresponding K1 value according to the measured temperature during actual operation.

[0092] In this solution, in the motor phase current calculation formula I = K×U / Rd, introduce the temperature correction coefficient K1, which can more accurately reflect the actual current value at different temperatures and compensate for the measurement error caused by temperature.

[0093] Figure 6 is a schematic diagram of the temperature sampling circuit structure in the embodiment. Refer to Figure 6 , in an implementable solution, the temperature sampling circuit (for MOS transistor temperature measurement) may include a temperature sampling resistor RT, resistors R19, R20, and a capacitor C9.

[0094] In this solution, the temperature sampling resistor RT is used to sense the temperature change of the MOS transistor and convert it into a change in resistance value. R19 and RT form a voltage - dividing circuit, and the change in its two - end voltage reflects the change in the resistance value of RT, and thus reflects the temperature change. R20 plays a role in current limiting and signal conditioning, limiting the circuit current and protecting RT and the subsequent circuit; it can also cooperate with C9 to filter the voltage signal.

[0095] On the basis of any of the above solutions, in an implementable solution, the coefficient includes a current correction coefficient. Determining the current correction coefficient includes:

[0096] Calculate the energized current, and determine the current correction coefficient according to the energized current. The energized current is determined by the following formula:

[0097]

[0098] In the formula, I0 represents the energized current.

[0099] In this solution, the current correction coefficient is a parameter used to compensate for the current calculation error caused by the change of the on-resistance of the switching tube and other factors. It reflects the proportional relationship between the actual current and the current calculated based on fixed parameters.

[0100] Exemplarily, in this solution, the current-correction coefficient relationship can be established by means of a calibration experiment. A power supply circuit that can provide a fixed current injects different magnitudes of standard currents into the motor drive circuit, and compares different actual currents (which can be measured by a high-precision current sensor, such as a current clamp meter to obtain a relatively accurate actual current value) with the standard current. Record the deviation between the two at different current values and establish the corresponding relationship between the two. Furthermore, the corresponding current correction coefficient can be obtained.

[0101] When the motor is actually running, according to the energized current calculated in real time, obtain the corresponding current correction coefficient from the established relationship. Then apply this correction coefficient to the calculation formula of the motor phase current, so as to obtain a more accurate motor phase current value.

[0102] In this solution, by considering factors such as the change of the switching tube internal resistance with current and using the current correction coefficient to correct the calculated current, the measurement error can be effectively reduced, enabling the measured value of the motor phase current to more accurately reflect the actual operating current, and providing a reliable basis for the precise control and protection of the motor.

[0103] On the basis of any of the foregoing solutions, in an implementable solution, the coefficient includes a current amplification factor, and the current amplification factor is a preset value.

[0104] Reference Figure 3 and Figure 4 , the operational amplifier is used to amplify the sampled signal so that subsequent circuits (such as an analog-to-digital converter) can process it more accurately. The current amplification factor is the key parameter to measure this amplification ability. When designing the circuit, it is necessary to determine the preset value of the current amplification factor according to the actual requirements. If the sampled signal of the motor phase current is weak, a larger current amplification factor is required to improve the detectability of the signal.

[0105] Reference Figure 3 and Figure 4 , in an implementable solution, R1 = R5 = R2 = R6; R3 = R7 = R16 = R17. The current amplification factor can be adjusted by adjusting the resistance values of R1 and R3.

[0106] Based on any of the foregoing solutions, in an implementable solution, according to the temperature, the on-resistance is determined using the temperature-on-resistance curve.

[0107] In this solution, the solution of determining the on-resistance using the temperature-on-resistance curve utilizes the correspondence between the temperature of the MOS transistor and the on-resistance, and finds the corresponding on-resistance from the pre-drawn temperature-on-resistance curve, thereby improving the accuracy of the motor phase current calculation.

[0108] Reference Figures 1 to 6 , based on any of the foregoing solutions, in an implementable solution, the motor phase current is determined according to the following formula:

[0109]

[0110] In the formula, I represents the motor phase current, K1 represents the temperature correction coefficient, K2 represents the current correction coefficient, K3 represents the current amplification factor, U represents the first voltage sampling signal or the second voltage sampling signal, and Rd represents the on-resistance of the switching transistor corresponding to the first voltage sampling signal.

[0111] In this solution, the duty cycle of the drive signal is obtained. If the duty cycle is greater than or equal to the preset threshold, the first voltage sampling signal when the lower switching transistor in the bridge arm conducts is recorded.

[0112] Here, the voltage of the D pole of the MOS transistor to the ground when the switching transistor conducts is measured. Since the switching transistor has an on-resistance, a voltage drop will occur when the current flows through the MOS transistor. By measuring this voltage drop, the current information can be indirectly obtained. The motor phase current is determined according to the first voltage sampling signal. In this case, since the conduction time is relatively long, the sampling when the switching transistor conducts can more accurately reflect the motor phase current situation.

[0113] If the duty cycle is less than the preset threshold, the second voltage sampling signal when the lower switching transistor in the bridge arm turns off is recorded. When the duty cycle is small, the conduction time of the switching transistor is short. When the switching transistor turns off, using the characteristic of the motor inductor, the inductor current cannot change suddenly and will continue to flow through the freewheeling circuit. At this time, the voltage of the motor inductor is collected as the second voltage sampling signal, which can more accurately reflect the motor phase current.

[0114] In this solution, the relationship between the MOS transistor temperature and the MOS on-resistance is obtained through experiments. During the experiment, different fixed currents are applied to the drive, and the actual VDS voltage of the MOS transistor is recorded. The on-resistance of the MOS transistor at different temperatures and currents is calculated according to Ohm's law.

[0115] MOS transistor manufacturers will provide the proportional relationship between the MOS junction temperature and the MOS internal resistance. Based on the relationship between the module temperature and the MOS internal resistance obtained from experiments, and the proportional relationship between the MOS junction temperature and the MOS internal resistance provided by the manufacturer, the temperature correction coefficient K1 corresponding to different temperatures can be determined.

[0116] For example, if the on-resistance of the MOS transistor at the standard temperature is Rstd, and the on-resistance of the MOS transistor corresponding to a certain actual measured temperature T is RT, then the temperature correction coefficient K1 = Rstd / RT.

[0117] In actual products, when a large current is suddenly applied, the MOS junction temperature will rise rapidly. However, due to the limitations of time and space in heat conduction, the temperature sampling cannot quickly and truly reflect the change in the MOS junction temperature, resulting in measurement errors.

[0118] In this solution, the current correction coefficient K2 is determined through experiments. During the experiment, different fixed currents are applied to the drive circuit within a short period of time, and at the same time, the module temperature and the actually measured VDS voltage of the MOS transistor are detected. By comparing the actual measurement results and the theoretical calculation results under different currents, the current correction coefficient K2 corresponding to different currents is determined.

[0119] In this solution, the current amplification factor K3 is a preset value, which is set according to actual requirements and circuit characteristics during the circuit design stage. It is mainly used to amplify the sampled voltage signal for subsequent processing and measurement.

[0120] In this solution, the on-resistance of the MOS transistor is determined according to the corresponding MOS transistor specification sheet and the data provided by the manufacturer.

[0121] In this solution, the obtained temperature correction coefficient K1, current correction coefficient K2, current amplification factor K3, the first voltage sampling signal or the second voltage sampling signal U, and the on-resistance Rd of the switching transistor are substituted into the above formula to calculate the motor phase current.

[0122] In this solution, by adopting different sampling methods at different duty cycles, and introducing the temperature correction coefficient K1 and the current correction coefficient K2, the problems of inaccurate sampling of the MOS internal resistance at small duty cycles and measurement errors caused by temperature and current changes are effectively solved, improving the accuracy and reliability of the motor phase current acquisition, and providing strong support for the precise control of the motor.

[0123] Embodiment 2

[0124] This embodiment proposes a motor phase current acquisition system, including a controller configured to execute any one of the motor phase current acquisition methods described in Embodiment 1. The implementation process and beneficial effects of the method are the same as the corresponding content described in Embodiment 1, and the specific content will not be elaborated here.

[0125] Based on any of the above solutions, in one feasible implementation, the system further includes a voltage sampling circuit, which is used to generate a first voltage sampling signal or a second voltage sampling signal.

[0126] Exemplarily, in this solution, the voltage sampling circuit can be based on Figures 2 to 5 the circuit design shown, the specific content of which is the same as the corresponding content recorded in Embodiment 1, and the specific content will not be elaborated here.

[0127] Based on any of the above solutions, in one feasible implementation, the system further includes a temperature sampling circuit, which is used to measure the temperature of the switching tube.

[0128] Exemplarily, in this solution, the temperature sampling circuit can be based on Figure 6 the circuit design shown, the specific content of which is the same as the corresponding content recorded in Embodiment 1, and the specific content will not be elaborated here.

[0129] Note that the above is only the preferred embodiment of the present invention and the applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here, and various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it can also include more other equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for collecting motor phase current, characterized in that Comprising: Obtaining the duty cycle of the driving signal of the motor driving circuit for one arm of the motor driving circuit; If the duty cycle is greater than or equal to a preset threshold, then recording the first voltage sampling signal when the switch of the lower arm in the arm conducts, and determining the motor phase current according to the first voltage sampling signal; If the duty cycle is less than the preset threshold, then recording the second voltage sampling signal when the switch of the lower arm in the arm turns off, and determining the motor phase current according to the second voltage sampling signal.

2. The method for collecting the motor phase current according to claim 1, wherein, Determining the motor phase current according to the first voltage sampling signal or determining the motor phase current according to the second voltage sampling signal includes determining the motor phase current by using the following formula: In the formula, I represents the motor phase current, K represents a coefficient, U represents the first voltage sampling signal or the second voltage sampling signal, and Rd represents the on-resistance of the switch corresponding to the first voltage sampling signal.

3. The method for collecting motor phase current according to claim 2, wherein The coefficient includes a temperature correction coefficient, and determining the temperature correction coefficient includes: Recording the temperature of the switch of the lower arm in the arm, and determining the temperature correction coefficient according to the temperature.

4. The method for collecting motor phase current according to claim 2, wherein The coefficient includes a current correction coefficient, and determining the current correction coefficient includes: Calculating the energized current, and determining the current correction coefficient according to the energized current, and the energized current is determined by the following formula: In the formula, I0 represents the energized current.

5. The method for collecting motor phase current according to claim 2, characterized in that The coefficient includes a current amplification factor, and the current amplification factor is a preset value.

6. The method for collecting motor phase current according to claim 3, wherein Determining the on-resistance according to the temperature by using a temperature - internal resistance curve.

7. The method for collecting the motor phase current according to claim 1, characterized in that The first voltage sampling signal represents the source-drain voltage when the switch conducts.

8. The method for collecting the motor phase current according to claim 1, characterized in that The second voltage sampling signal represents the voltage of the motor inductor when the switch turns off.

9. A motor phase current acquisition system, characterized in that, Including a controller, the controller is configured to execute the motor phase current acquisition method according to any one of claims 1 to 8.

10. The motor phase current acquisition system according to claim 9, characterized in that, Further including a voltage sampling circuit, the voltage sampling circuit is used to generate the first voltage sampling signal or the second voltage sampling signal.

Images