CN114236213A - Low-cost current sampling circuit and method - Google Patents
Low-cost current sampling circuit and method Download PDFInfo
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- CN114236213A CN114236213A CN202111356639.XA CN202111356639A CN114236213A CN 114236213 A CN114236213 A CN 114236213A CN 202111356639 A CN202111356639 A CN 202111356639A CN 114236213 A CN114236213 A CN 114236213A
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Abstract
The invention relates to a low-cost current sampling circuit and a method, comprising a first MOS tube, a second MOS tube and a first operational amplifier; the grid electrode of the first MOS tube is connected with an upper bridge driving PWM signal, the grid electrode of the second MOS tube is electrically connected with a lower bridge driving PWM signal, the drain electrode of the first MOS tube and the source electrode of the second MOS tube are simultaneously and electrically connected with a current phase, the source electrode of the first MOS tube is electrically connected with the positive electrode of a power supply, the drain electrode of the second MOS tube is grounded and electrically connected with a zero phase, and the current phase is a U phase or a W phase; the current phase is electrically connected to the positive input end of the first operational amplifier through a differential sampling resistor, the zero phase is electrically connected to the negative input end of the first operational amplifier through another differential sampling resistor, and the operational output end of the first operational amplifier is connected with the first input port of the processor, so that the processor converts the sampling voltage of the first input port to obtain the sampling current of the current phase. The invention obtains the phase current through the voltage drop of the MOS tube in the conducting state so as to achieve the purpose of low cost of the processor.
Description
Technical Field
The invention belongs to the technical field of vehicle control, and particularly relates to a low-cost current sampling circuit and a low-cost current sampling method.
Background
The existing motor control system includes a motor, a driver, a processor, and a current sensor for sampling phase current, and current signals are used to calculate physical quantities such as magnetic field position, flux linkage, torque, and the like, and thus, the current sensor is essential for motor control. At present, a current sensor usually uses a hall current sensor, but the hall current sensor has the defects of high cost and large volume, and is not suitable for application scenes with low cost or small space.
Disclosure of Invention
The invention aims to provide a low-cost current sampling circuit and a low-cost current sampling method, which are used for obtaining phase current through voltage drop of an MOS (metal oxide semiconductor) tube in a conducting state, reducing the production cost and saving the space on the premise of meeting the torque response of a motor, thereby achieving the purpose of reducing the cost of a processor.
In order to solve the technical problem, the invention discloses a low-cost current sampling circuit, which comprises a first MOS tube, a second MOS tube and a first operational amplifier;
the grid electrode of the first MOS tube is connected with an upper bridge driving PWM signal, the grid electrode of the second MOS tube is electrically connected with a lower bridge driving PWM signal, the drain electrode of the first MOS tube and the source electrode of the second MOS tube are simultaneously and electrically connected with a current phase, the source electrode of the first MOS tube is electrically connected with a power supply anode, the drain electrode of the second MOS tube is grounded and electrically connected with a zero phase, and the current phase is a U phase or a W phase;
the current phase is electrically connected to the positive input end of a first operational amplifier through a differential sampling resistor, the zero phase is electrically connected to the negative input end of the first operational amplifier through another differential sampling resistor, and the operational output end of the first operational amplifier is connected with a first input port of a processor, so that the processor converts the sampling voltage of the first input port to obtain the sampling current of the current phase.
Furthermore, each current phase respectively comprises a temperature sampling circuit, and each temperature sampling circuit comprises a temperature sampling resistor, a pull-up resistor, a filter resistor and a filter capacitor;
one end of the temperature sampling resistor is electrically connected with one end of the pull-up resistor and one end of the filter resistor at the same time, the other end of the pull-up resistor is connected with +3.3V voltage, the other end of the filter resistor is electrically connected with one end of the filter capacitor and a second input port of the processor at the same time, and the other end of the temperature sampling resistor and the other end of the filter capacitor are grounded;
and the processor compensates the sampling current according to the real-time temperature of the temperature sampling circuit to obtain the final current.
Further, the circuit also comprises a first capacitor, a first resistor, a second resistor, a third resistor and a second capacitor;
the operational output end of the first operational amplifier is simultaneously and electrically connected with one end of the first capacitor and one end of the first resistor, the other end of the first resistor is simultaneously and electrically connected with one end of the second resistor and one end of the third resistor, the other end of the third resistor is simultaneously and electrically connected with one end of the second capacitor and the first input port of the processor, and the resistance ratio of the first resistor to the second resistor is 1: 2;
the other end of the first capacitor, the other end of the second resistor and the other end of the second capacitor are all grounded.
Further, the intelligent power supply also comprises a protection diode, wherein the positive end of the protection diode is electrically connected with the first input port of the processor, and the negative end of the protection diode is connected with 3.3V voltage.
Further, the circuit also comprises a fourth resistor, a fifth resistor, a third capacitor, a second operational amplifier and a sixth resistor;
one end of the fourth resistor is connected with 5V voltage, the other end of the fourth resistor is simultaneously electrically connected with one end of the fifth resistor, one end of the third capacitor and the positive input end of the second operational amplifier, the negative input end of the second operational amplifier is electrically connected with the operational output end of the second operational amplifier and one end of the sixth resistor, the other end of the sixth resistor is electrically connected with the positive input end of the first operational amplifier, and the resistance values of the fourth resistor and the fifth resistor are equal;
the other end of the fifth resistor and the other end of the third capacitor are both grounded.
In order to solve the technical problem, the invention also discloses a low-cost current sampling method, and the low-cost current sampling circuit comprises the following steps:
s1, when the upper bridge is closed and the lower bridge is opened, phase current flowing on the second MOS tube generates a voltage signal, and the voltage signal is input to the first operational amplifier through the differential sampling resistor to be amplified in proportion to obtain a sampling voltage;
and S2, the processor acquires the sampling voltage, and the sampling current of the current phase is calculated according to the sampling voltage and the resistance value of the on-resistance of the second MOS tube.
Further, the method also comprises the following steps:
and S3, the processor acquires the real-time temperature of the temperature sampling circuit, and the final current is obtained after the sampling current is compensated according to the real-time temperature.
Further, the on-resistance used in calculating the sampling current is a first resistance of the second MOS transistor at a preset first temperature, a real-time resistance of the second MOS transistor at other temperatures and a multiplying factor of the first resistance are used as compensation coefficients of other temperatures, and the compensation coefficients increase with the increase of the real-time temperature;
the step S3 specifically includes: and obtaining a compensation coefficient corresponding to the real-time temperature according to the real-time temperature, and dividing the sampling current by the compensation coefficient to obtain a final current.
Further, the step S3 is specifically:
judging whether the real-time temperatures of the two current-phase temperature sampling circuits are normal or not, if so, compensating the respective sampling currents by using the respective real-time temperatures to obtain the final current corresponding to the current phase, otherwise, judging whether one of the real-time temperatures of the two current-phase temperature sampling circuits is normal or not, and if so, using the normal temperature as the two current-phase real-time temperatures to compensate the respective sampling currents to obtain the final current corresponding to the current phase.
Further, the step S3 is specifically: and if the real-time temperatures of the two temperature sampling circuits of the current phase are abnormal or any one of the real-time temperatures exceeds a temperature alarm value, sending fault prompt information and stopping outputting.
Advantageous effects
A low-cost current sampling circuit and method, can be equivalent to the resistance when the MOS tube is in the conducting state, therefore take the voltage signal of both ends of MOS tube, send to the processor after carrying on the signal proportion amplification processing through the operational amplifier, so that the processor finds the phase current according to sampled voltage and conducting internal resistance of the used MOS tube, namely obtain the phase current through the voltage drop of MOS tube under the conducting state, on the premise of meeting the response of motor torque, have reduced the production cost, has saved the space, thus achieve the purpose of the low cost of the processor.
Drawings
FIG. 1 is a schematic diagram of a low-cost current sampling circuit;
FIG. 2 is a schematic diagram of a temperature sampling circuit;
FIG. 3 is a graph showing the on-resistance characteristics of MOS transistor;
FIGS. 4 and 5 are graphs of on-resistance versus temperature for different MOS transistor types;
fig. 6 and 7 are current sampling waveforms when the MOS transistor is on;
FIG. 8 is a current waveform at the time of current sampling control when the MOS transistor is conducted;
FIG. 9 is a comparison graph of the sampling current after temperature compensation when the MOS transistor is conducted;
FIG. 10 is a schematic flow chart of a low cost current sampling method;
fig. 11 is a schematic flow chart of a low-cost current sampling method.
In the drawings:
c1, a first capacitance; c2, a second capacitor; c3, a third capacitance; c4, a filter capacitor;
d1, protection diode; d2, a diode;
IC5B, a first operational amplifier; IC5A, a second operational amplifier;
IU1, a first input port; IU2, second input port;
m1, a first MOS tube; m2 and a second MOS tube;
n, zero phase;
r1, a first resistor; r2, a second resistor; r3, third resistor; r4, fourth resistor; r5, fifth resistor; r6, sixth resistor; r7, seventh resistor; r8, eighth resistor; r9 and R10, differential sampling resistance; r11, amplification resistor; RT, temperature sampling resistance; r12, pull-up resistor; r13 and a filter resistor;
UL, lower bridge drive PWM signal; UH, upper bridge drive PWM signal.
Detailed Description
The present invention is further described in detail below with reference to examples so that those skilled in the art can practice the invention with reference to the description.
It will be understood that terms such as "having," "including," and "comprising," when used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
Example one
As shown in fig. 1 to 9, in the present embodiment, current sampling is performed using MOSFET on-resistance. The MOSFET has a resistance characteristic in saturation conduction as a multi-sub device, and as can be seen from fig. 3, when VGS is greater than 10V, the MOSFET is in saturation conduction, the drain and the source are constant resistors, and the resistance is small. Different types of MOSFETs have different drain-source on-resistance values.
When the on-state current flows through the MOSFET power switch, due to the existence of the on-state on-resistance, voltage drop can be generated in the on-channel of the MOSFET power switch, and because the on-resistance of the device is basically stable, the voltage drop is in direct proportion to the on-state current, the on-state voltage drop of the MOSFET switch device is detected, and the current flowing through the MOSFET can be calculated, so that the embodiment mode is obtained.
As shown in fig. 1, a low-cost current sampling circuit includes a first MOS transistor M1, a second MOS transistor M2, and a first operational amplifier IC5B, a gate of the first MOS transistor M1 is connected to an upper bridge driving PWM signal UH through a seventh resistor R7, a gate of the second MOS transistor M2 is electrically connected to a lower bridge driving PWM signal UL through an eighth resistor R8, a drain of the first MOS transistor M1 and a source of the second MOS transistor M2 are simultaneously and electrically connected to a current phase, a source of the first MOS transistor M1 is electrically connected to a positive electrode of a power supply, a drain of the second MOS transistor M2 is grounded and electrically connected to a zero phase N, in fig. 1 of this embodiment, the current phase is a U phase, and a sampling circuit of a W phase of the current phase and the U phase are the same circuit structure.
The current phase is electrically connected to the positive input end of the first operational amplifier IC5B through a differential sampling resistor R9 and R10, the zero phase N is electrically connected to the negative input end of the first operational amplifier IC5B through another differential sampling resistor R9 and R10, and the operational output end of the first operational amplifier IC5B is connected to the first input port IU1 of the processor, so that the processor can obtain the sampling current of the current phase through conversion according to the sampling voltage of the first input port IU 1. The negative input end and the operational output end of the first operational amplifier IC5B are also connected with an amplification resistor R11.
Therefore, when the MOS tube can be equivalent to a resistor in a conducting state, voltage signals at two ends of the MOS tube are adopted, and are subjected to signal proportion amplification processing through the operational amplifier and then are sent to the processor, so that the processor obtains phase current according to the sampling voltage and the conducting internal resistance of the used MOS tube, namely the phase current is obtained through voltage drop of the MOS tube in the conducting state.
As shown in fig. 4 and 5, the on-state resistance of the MOSFET is related to the temperature of the MOSFET, and the on-state resistance of the MOSFET needs to be compensated according to the corresponding temperature, so that the on-state resistance is corrected, and the influence of the temperature on the detection precision can be eliminated. Therefore, as shown in fig. 2, each current phase includes a temperature sampling circuit, and the temperature sampling circuit includes a temperature sampling resistor RT, a pull-up resistor R12, a filter resistor R13, and a filter capacitor C4; one end of a temperature sampling resistor RT is electrically connected with one end of a pull-up resistor R12 and one end of a filter resistor R13, the other end of the pull-up resistor R12 is connected with +3.3V voltage, the other end of the filter resistor R13 is electrically connected with one end of a filter capacitor C4 and a second input port IU2 of the processor, the other end of the temperature sampling resistor RT and the other end of the filter capacitor C4 are grounded, therefore, the real-time temperature of the temperature sampling resistor is transmitted to the processor after being filtered by the RC, and the processor compensates sampling current according to the real-time temperature of the temperature sampling circuit to obtain final current.
In this embodiment, the device further includes a first capacitor C1, a first resistor R1, a second resistor R2, a third resistor R3, a second capacitor C2, and a protection diode D1, an operational output end of the first operational amplifier IC5B is electrically connected to one end of the first capacitor C1 and one end of the first resistor R1 at the same time, the other end of the first resistor R1 is electrically connected to one end of the second resistor R2 and one end of the third resistor R3 at the same time, the other end of the third resistor R3 is electrically connected to one end of the second capacitor C2 and the first input port IU1 of the processor at the same time, a ratio of resistance values of the first resistor R1 and the second resistor R2 is 1:2, and the other end of the first capacitor C1, the other end of the second resistor R2, and the other end of the second capacitor C2 are all grounded. The positive terminal of the protection diode D1 is electrically connected with the first input port IU1 of the processor and the negative terminal is connected with 3.3V voltage.
The first capacitor C1 is used as a filter capacitor to filter out interference from an operational amplifier output signal at an operational output end of the first operational amplifier IC5B, the operational amplifier output signal is processed by converting 5V to 3.3V through the first resistor R1 and the second resistor R2, the operational amplifier output signal is further RC filtered through the third resistor R3 and the second capacitor C2 to provide a proper sampling level for the MCU, and the protection diode D1 performs input protection for the first input port IU 1.
In the embodiment, since the internal resistance of the MOS transistor is small, the sampled voltage is low, and the processing of the operational amplifier is not facilitated, the bias voltage 2.5V is introduced. As shown in fig. 1, the circuit further includes a fourth resistor R4, a fifth resistor R5, a third capacitor C3, a second operational amplifier IC5A, and a sixth resistor R6; one end of the fourth resistor R4 is connected with 5V voltage, and the other end is simultaneously electrically connected with one end of the fifth resistor R5, one end of the third capacitor C3, and the positive input end of the second operational amplifier IC5A, the negative input end of the second operational amplifier IC5A is electrically connected with the operational output end thereof and one end of the sixth resistor R6, the other end of the sixth resistor R6 is electrically connected with the positive input end of the first operational amplifier IC5B, and the resistance values of the fourth resistor R4 and the fifth resistor R5 are equal; the other end of the fifth resistor R5 and the other end of the third capacitor C3 are both grounded.
Therefore, the power supply +5V1 is divided into 2.5V by the fourth resistor R4 and the fifth resistor R5, filtered by the third capacitor C3 and then input to the second operational amplifier IC5A, the second operational amplifier IC5A forms a voltage follower input 2.5V, and the voltage follower input is superimposed to the positive input end of the first operational amplifier IC5B by the sixth resistor R6 to provide a bias voltage.
Wherein the power supply +5V1 is connected to the positive input of the first operational amplifier IC5B through a diode D2.
IN this embodiment, the first capacitor C1 and the second capacitor C2 are 101 capacitors, the third capacitor C3 and the filter capacitor C4 are 104 capacitors, and the protection diode D1 is IN 4148W; the first operational amplifier IC5B and the second operational amplifier IC5A are substantially different amplifiers of the same dual operational amplifier.
The resistance of the first resistor R1 is 10K, the resistance of the second resistor R2 is 20K, the resistance of the third resistor R3 is 1K, the resistance of the fourth resistor R4 is 10K, the resistance of the fifth resistor R5 is 10K, the resistance of the sixth resistor R6 is 20K, and the resistances of the seventh resistor R7 and the eighth resistor R8 are 20; the resistance values of the two differential sampling resistors R9 and R10 are both 10K, the resistance value of the amplification resistor R11 is 20K, the resistance value of the pull-up resistor R12 is 20K, and the resistance value of the filter resistor R13 is 1K.
Example two
As shown in fig. 10, a low-cost current sampling method using the low-cost current sampling circuit of the first embodiment includes the following steps:
s1, when the upper bridge is closed and the lower bridge is opened, the phase current flowing on the second MOS tube generates a voltage signal, and the voltage signal is input to the first operational amplifier through the differential sampling resistor for proportional amplification to obtain a sampling voltage;
and S2, the processor obtains the sampling voltage, and the current phase sampling current is obtained through calculation according to the sampling voltage and the resistance value of the on-resistance of the second MOS tube.
The waveforms of the sampling currents are shown in fig. 6 to 8.
And S3, the processor acquires the real-time temperature of the temperature sampling circuit, and the final current is obtained after the sampling current is compensated according to the real-time temperature.
Thus, the final current after compensation and the sample current before compensation are paired as shown in fig. 9.
In this embodiment, the on-resistance used in calculating the sampling current is the first resistance of the second MOS transistor at the preset first temperature, the real-time resistance of the second MOS transistor at other temperatures and the multiplying power of the first resistance are used as compensation coefficients of other temperatures, and the compensation coefficients increase with the increase of the real-time temperature. Step S3 thus specifically includes: and obtaining a compensation coefficient corresponding to the real-time temperature according to the real-time temperature, and dividing the sampled current by the compensation coefficient to obtain a final current.
As shown in fig. 4 and 5, the temperature compensation for different MOS tube type numbers is not the same. For example, the MOS transistors selected as CRSS052N08N and CRSS042N10N are shown in table 1 below.
Temperature compensation for tables 1, CRSS052N08N, and CRSS042N10N
As shown in fig. 11, step S3 specifically includes:
triggering two paths of AD acquisition at each PWM period wave crest, reading out a corresponding current value once in each carrier frequency period, judging whether the real-time temperatures of the two current-phase temperature sampling circuits are normal or not, if so, compensating the respective sampling currents by using the respective real-time temperatures to obtain final currents corresponding to the current phases, otherwise, judging whether the real-time temperatures of the two current-phase temperature sampling circuits are normal or not, and if so, compensating the respective sampling currents by using normal temperatures as the real-time temperatures of the two current phases to obtain the final currents corresponding to the current phases;
and if the real-time temperatures of the two temperature sampling circuits of the current phase are abnormal or any real-time temperature exceeds a temperature alarm value, sending fault prompt information and stopping outputting.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the embodiments shown and described without departing from the generic concept as defined by the claims and their equivalents.
Claims (10)
1. A low-cost current sampling circuit is characterized by comprising a first MOS tube, a second MOS tube and a first operational amplifier;
the grid electrode of the first MOS tube is connected with an upper bridge driving PWM signal, the grid electrode of the second MOS tube is electrically connected with a lower bridge driving PWM signal, the drain electrode of the first MOS tube and the source electrode of the second MOS tube are simultaneously and electrically connected with a current phase, the source electrode of the first MOS tube is electrically connected with a power supply anode, the drain electrode of the second MOS tube is grounded and electrically connected with a zero phase, and the current phase is a U phase or a W phase;
the current phase is electrically connected to the positive input end of a first operational amplifier through a differential sampling resistor, the zero phase is electrically connected to the negative input end of the first operational amplifier through another differential sampling resistor, and the operational output end of the first operational amplifier is connected with a first input port of a processor, so that the processor converts the sampling voltage of the first input port to obtain the sampling current of the current phase.
2. A low cost current sampling circuit according to claim 1, wherein each of said current phases includes a temperature sampling circuit, said temperature sampling circuit including a temperature sampling resistor, a pull-up resistor, a filter resistor and a filter capacitor;
one end of the temperature sampling resistor is electrically connected with one end of the pull-up resistor and one end of the filter resistor at the same time, the other end of the pull-up resistor is connected with +3.3V voltage, the other end of the filter resistor is electrically connected with one end of the filter capacitor and a second input port of the processor at the same time, and the other end of the temperature sampling resistor and the other end of the filter capacitor are grounded;
and the processor compensates the sampling current according to the real-time temperature of the temperature sampling circuit to obtain the final current.
3. The low-cost current sampling circuit according to claim 2, further comprising a first capacitor, a first resistor, a second resistor, a third resistor, and a second capacitor;
the operational output end of the first operational amplifier is simultaneously and electrically connected with one end of the first capacitor and one end of the first resistor, the other end of the first resistor is simultaneously and electrically connected with one end of the second resistor and one end of the third resistor, the other end of the third resistor is simultaneously and electrically connected with one end of the second capacitor and the first input port of the processor, and the resistance ratio of the first resistor to the second resistor is 1: 2;
the other end of the first capacitor, the other end of the second resistor and the other end of the second capacitor are all grounded.
4. A low cost current sampling circuit according to claim 3, further comprising a protection diode having a positive terminal electrically connected to said first input port of said processor and a negative terminal connected to a voltage of 3.3V.
5. The low-cost current sampling circuit according to claim 2, further comprising a fourth resistor, a fifth resistor, a third capacitor, a second operational amplifier and a sixth resistor;
one end of the fourth resistor is connected with 5V voltage, the other end of the fourth resistor is simultaneously electrically connected with one end of the fifth resistor, one end of the third capacitor and the positive input end of the second operational amplifier, the negative input end of the second operational amplifier is electrically connected with the operational output end of the second operational amplifier and one end of the sixth resistor, the other end of the sixth resistor is electrically connected with the positive input end of the first operational amplifier, and the resistance values of the fourth resistor and the fifth resistor are equal;
the other end of the fifth resistor and the other end of the third capacitor are both grounded.
6. A low-cost current sampling method using a low-cost current sampling circuit as claimed in any one of claims 2 to 5, comprising the steps of:
s1, when the upper bridge is closed and the lower bridge is opened, phase current flowing on the second MOS tube generates a voltage signal, and the voltage signal is input to the first operational amplifier through the differential sampling resistor to be amplified in proportion to obtain a sampling voltage;
and S2, the processor acquires the sampling voltage, and the sampling current of the current phase is calculated according to the sampling voltage and the resistance value of the on-resistance of the second MOS tube.
7. A low cost current sampling method as claimed in claim 6, further comprising the steps of:
and S3, the processor acquires the real-time temperature of the temperature sampling circuit, and the final current is obtained after the sampling current is compensated according to the real-time temperature.
8. A low cost current sampling method as claimed in claim 7, wherein: calculating the on-resistance used in the sampling of the current as a first resistance of the second MOS transistor at a preset first temperature, and taking the real-time resistance of the second MOS transistor at other temperatures and the multiplying power of the first resistance as compensation coefficients of other temperatures, wherein the compensation coefficients increase with the increase of the real-time temperature;
the step S3 specifically includes: and obtaining a compensation coefficient corresponding to the real-time temperature according to the real-time temperature, and dividing the sampling current by the compensation coefficient to obtain a final current.
9. The low-cost current sampling method according to claim 7, wherein the step S3 specifically comprises:
judging whether the real-time temperatures of the two current-phase temperature sampling circuits are normal or not, if so, compensating the respective sampling currents by using the respective real-time temperatures to obtain the final current corresponding to the current phase, otherwise, judging whether one of the real-time temperatures of the two current-phase temperature sampling circuits is normal or not, and if so, using the normal temperature as the two current-phase real-time temperatures to compensate the respective sampling currents to obtain the final current corresponding to the current phase.
10. The low-cost current sampling method according to claim 9, wherein the step S3 specifically includes: and if the real-time temperatures of the two temperature sampling circuits of the current phase are abnormal or any one of the real-time temperatures exceeds a temperature alarm value, sending fault prompt information and stopping outputting.
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